A Product of the Groundwater Resources Program Prepared in

Cooperation with the National Cave and Karst Research Institute

U.S. Geological Survey Karst Interest Group

Proceedings, Carlsbad, New Mexico,
April 29 – May 2, 2014

Scientific Investigations Report 2014-5035

U.S. Department of the Interior

U.S. Geological Survey
A Product of the Groundwater Resources Program Prepared in
Cooperation with the National Cave and Karst Research Institute

U.S. Geological Survey Karst Interest Group

Proceedings, Carlsbad, New Mexico,
April 29 – May 2, 2014

Edited by Eve L. Kuniansky and Lawrence E. Spangler

Scientific Investigations Report 2014-5035

U.S. Department of the Interior

U.S. Geological Survey
i
U.S. Department of the Interior
SALLY JEWELL, Secretary
U.S. Geological Survey
Suzette Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2014

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Suggested citation:
Kuniansky, E.L., and Spangler, L.E., 2014, U.S. Geological Survey Karst Interest Group Proceedings, Carlsbad, New
Mexico, April 29–May 2, 2014: U.S. Geological Survey Scientific Investigations Report 2014-5035, 155 p.,
http://dx.doi.org/10.3133/sir20145035.

ISSN 2328-0328 (online)

ISSN 2328-031X (print)

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Although this report is in the public domain, permission must be secured from the individual
copyright owners to reproduce any copyrighted material contained within this report.

ii
Contents

INTRODUCTION AND ACKNOWLEDGMENTS ........................................................................ 1

AGENDA U.S. GEOLOGICAL SURVEY KARST INTEREST GROUP WORKSHOP ................. 3
KEYNOTE.................................................................................................................................. 7
Speleotrek: The Cutting Edges of Karst into the 21st Century ..................................................... 7
PROGRAMS AND KARST AQUIFERS .....................................................................................19
A Preview of “Karst in the United States of America: A Digital Map Compilation and Database”
.................................................................................................................................................19
Groundwater Availability of the Floridan Aquifer System ...........................................................28
Assessing Potential Impacts from a Proposed Phosphate Mine on Ashley Spring, a Unique
Karst Public Water Supply in the Uinta Mountains, Uintah County, Utah ...................................30
TRACERS.................................................................................................................................39
Groundwater Tracing in Arid Karst Aquifers: Concepts and Considerations ..............................39
Challenges to a Karst Dye-Tracing Investigation in an Urban Brownfields Area, Springfield,
Missouri ....................................................................................................................................44
SPELEOGENESIS, GEOLOGIC FRAMEWORK, GEOPHYSICS, AND GEOLOGIC HAZARDS
.................................................................................................................................................54
The Role of Spongework in the Speleogenesis of Hypogenic Caves in the Guadalupe
Mountains, New Mexico ............................................................................................................54
Geologic Framework, Structure, and Hydrogeologic Characteristics of the Knippa Gap Area in
Eastern Uvalde and Western Medina Counties, Texas .............................................................65
A Hypothesis for Carbonate Island Karst Aquifer Evolution from Analysis of Field Observations
in Northern Guam, Mariana Islands...........................................................................................66
Using Borehole and Surface Geophysics to Develop a Conceptual Model of Hydrostratigraphic
Layers, Pecos County Region, Texas, 2012 .............................................................................67
Perils of a Dissolving State—Florida .........................................................................................68
MODELING KARST AQUIFERS ...............................................................................................69
Taking the Mystery Out of Mathematical Model Applications to Karst Aquifers—A Primer ........69
Refined Hydrostratigraphic Framework and Model of the Edwards Aquifer, Texas ...................82
Simulation of Groundwater Flow in the Edwards-Trinity and Related Aquifers in the Pecos
County Region, Texas...............................................................................................................83
Automatic Methods of Groundwater Flow Model Construction of the Ozark Plateaus Aquifer
System ......................................................................................................................................85
CHEMICAL FATE AND TRANSPORT ......................................................................................86
Transport of Salt, Trace Metals, and Organic Chemicals from Parking Lot and Road Surfaces
into Mammoth Cave ..................................................................................................................86

iii
CAFOs on Karst—Meaningful Data Collection to Adequately Define Environmental Risk, with a
Specific Application from the Southern Ozarks of Northern Arkansas .......................................87
An Initial Investigation of Hydrogeology and Water Quality of Big Creek in the Buffalo River
Watershed near a Major Concentrated Animal Feeding Operation............................................97
A Method to Investigate Karst Groundwater Flow in Nash Draw, Eddy County, New Mexico, to
Delineate Potential Impacts of Potash Industry Discharge and Runoff ......................................98
Use of A Dual Continuum Model to Describe Solute Transport in Karst ..................................108
GEOCHEMISTRY ...................................................................................................................109
Geochemical Evidence for Denitrification in the Epikarst at the Savoy Experimental Watershed,
Northwest Arkansas ................................................................................................................109
Geochemistry of Paleokarst Aquifers of the Knox Group in Tennessee and Kentucky ............121
Integration of Geochemical and Isotopic Data to Assess Sources of Discharge at a Major Spring
in the Edwards Aquifer, South-Central Texas ..........................................................................125
MICROBIAL ECOLOGY AND KARST ECOSYSTEMS ...........................................................126
Linking Climate Change and Karst Hydrology to Evaluate Species Vulnerability: The Edwards
and Madison Aquifers .............................................................................................................126
Response of Cave-Stream Bacteria to Sub-Lethal Concentrations of Antibiotics ....................127
Role of Surface Water Dissolved Organic Carbon in the Survival, Growth, and Transport of
Escherichia coli in a Deep Limestone Aquifer in South Florida ................................................129
Cave Bacteria and Crystal Formation in the Laboratory ..........................................................133
Non-Target Bacterial Response to White-Nose Syndrome Treatment: Quaternary Ammonia
Compounds and Linear Alkylbenzene Sulfonate .....................................................................134
THURSDAY, MAY 1, 2014, FIELD TRIP GUIDE.....................................................................135
Evaporite Karst of the Lower Pecos Valley, New Mexico ........................................................135

iv
INTRODUCTION AND ACKNOWLEDGMENTS
Karst aquifer systems are present throughout parts of the United States and some of its territories, and
have developed in carbonate rocks (primarily limestone and dolomite) that span an interval of time
encompassing more than 550 million years. The depositional environments, diagenetic processes, post-
depositional tectonic events, and geochemical weathering processes that form karst aquifers are varied
and complex, and involve biological, chemical, and physical changes. These factors, combined with the
diverse climatic regimes under which karst development in these rocks has taken place, result in the
unique dual- or triple-porosity nature of karst aquifers. These complex hydrogeologic systems typically
represent challenging and unique conditions to scientists attempting to study groundwater flow and
contaminant transport in these terrains.
The dissolution of carbonate rocks and the subsequent development of distinct and beautiful
landscapes, caverns, and springs has resulted in the most exceptional karst areas of the United States
being designated as national or state parks; commercial caverns and known privately owned caves
number in the tens of thousands. Both public and private properties provide access for scientists to study
the flow of groundwater in situ. Likewise, the range and complexity of landforms and groundwater flow
systems associated with karst terrains are enormous, perhaps more than for any other aquifer type. Karst
aquifers and landscapes that form in tropical areas, such as the cockpit karst along the north coast of
Puerto Rico, differ greatly from karst landforms in more arid climates, such as the Edwards Plateau in
west-central Texas or the Guadalupe Mountains near Carlsbad, New Mexico, where hypogenic processes
have played a major role in speleogenesis. Many of these public and private lands also contain unique
flora and fauna associated with these karst hydrogeologic systems. As a result, numerous federal, state,
and local agencies have a strong interest in the study of karst terrains.
Many of the major springs and aquifers in the United States have developed in carbonate rocks, such
as the Floridan aquifer system in Florida and parts of Alabama, Georgia, and South Carolina; the Ozark
Plateaus aquifer system in parts of Arkansas, Kansas, Missouri, and Oklahoma; and the Edwards-Trinity
aquifer system in west-central Texas. These aquifers, and the springs that discharge from them, serve as
major water-supply sources and as unique ecological habitats. Competition for the water resources of
karst aquifers is common, and urban development and the lack of attenuation of contaminants in karst
areas can impact the ecosystem and water quality of these aquifers.
The concept for developing a platform for interaction among scientists within the U.S. Geological
Survey (USGS) working on karst-related studies evolved from the November 1999 National Ground-
Water Meeting of the USGS. As a result, the Karst Interest Group (KIG) was formed in 2000. The KIG is
a loose-knit, grass-roots organization of USGS and non-USGS scientists and researchers devoted to
fostering better communication among scientists working on, or interested in, karst science. The primary
mission of the KIG is to encourage and support interdisciplinary collaboration and technology transfer
among scientists working in karst areas. Additionally, the KIG encourages collaborative studies between
the different mission areas of the USGS as well as other federal and state agencies, and with researchers
from academia and institutes. The KIG also encourages younger scientists by participation of students in
the poster and oral sessions.
To accomplish its mission, the KIG has organized a series of workshops that are held near nationally
important karst areas. To date (2014) six KIG workshops, including the workshop documented in this
report, have been held. The workshops typically include oral and poster sessions on selected karst-related
topics and research, as well as field trips to local karst features. Proceedings of the workshops are
published by the USGS and are available online at http://water.usgs.gov/ogw/karst/kig.

1
 The first KIG workshop was held in St. Petersburg, Florida, February 13–16, 2001, in the vicinity of
the large springs and other karst features of the Floridan aquifer system. The second KIG workshop was
held August 20–22, 2002, in Shepherdstown, West Virginia, in proximity to the carbonate aquifers of the
northern Shenandoah Valley and highlighted an invited presentation on karst literature by the late Barry
F. Beck of P.E. LaMoreaux and Associates. The third KIG workshop was held September 12–15, 2005, in
Rapid City, South Dakota, nearby to karst features in evaporites and limestones of the Madison Group in
the Black Hills of South Dakota, including Wind Cave National Park and Jewel Cave National
Monument. The workshop also included a featured presentation by Thomas Casadevall, Central Region
Director, USGS, on the status of earth science at the USGS and evening trips to Jewel Cave led by Mike
Wiles, National Park Service (NPS) and Wind Cave led by Rod Horrocks, NPS. The fourth KIG
workshop was held May 27–29, 2008, and hosted by the Hoffman Environmental Research Institute and
Center for Cave and Karst Studies at Western Kentucky University in Bowling Green, Kentucky, near
Mammoth Cave National Park and karst features of the Chester Upland and Pennyroyal Plateau. The
workshop featured a late-night field trip into Mammoth Cave with Rickard Toomey and Rick Olsen, NPS.
The fifth workshop was held April 26–29, 2011, and was a joint meeting of the USGS KIG and
University of Arkansas HydroDays, hosted by the Department of Geosciences at the University of
Arkansas in Fayetteville. The workshop featured an outstanding field trip to the unique karst terrain along
the Buffalo National River of the southern Ozarks and a keynote presentation on paleokarst in the United
States by Art and Peggy Palmer.
This sixth and current 2014 KIG workshop is hosted by the National Cave and Karst Research
Institute (NCKRI) in Carlsbad, New Mexico, with Director of NCKRI, George Veni, serving as co-chair
of the workshop with Eve Kuniansky, USGS. The session planning committee for this sixth workshop
includes Van Brahana, USGS retired and University of Arkansas Professor Emeritus; Tom Byl, USGS
and Tennessee State University; Zelda Bailey, former Director of NCKRI and retired Director, National
Institute of Standards and Technology, Boulder Laboratory, Colorado; Patrick Tucci, USGS retired; and
Mike Bradley, Allan Clark, Geoff Delin, Daniel Doctor, James Kaufmann, Eve Kuniansky, Randy
Orndorff, Larry Spangler, and Dave Weary of the USGS. The karst hydrology field trip on Thursday will
be led by Lewis Land (NCKRI karst hydrologist) and the optional Friday field trip on the geology of
Carlsbad Caverns National Park will be led by George Veni. The keynote speaker is Dr. Penelope Boston,
Director of Cave and Karst Studies at New Mexico Tech, Socorro, and Academic Director at NCKRI,
who will address the future of karst research. Additionally, there is a featured presentation “Irish karst and
its management,” by Caoimhe Hickey, The Geological Survey of Ireland, preceding a panel discussion on
“Collaboration During Times of Limited Resources.”
The extended abstracts of USGS authors were peer reviewed and approved for publication by the U.S.
Geological Survey. Articles submitted by university researchers and other federal and state agencies did
not go through the formal USGS peer review and approval process, and therefore may not adhere to our
editorial standards or stratigraphic nomenclature and is not research conducted or data collected by the
USGS. However, all articles had at a minimum of two peer reviews, and all articles were edited for
consistency of appearance in the published Proceedings. The use of trade, firm or product names in any
article is for descriptive purposes only and does not imply endorsement by the U.S. Government. The
USGS, Office of Groundwater, provides technical support for the Karst Interest Group website and public
availability of the Proceedings from these workshops, and the USGS Groundwater Resources Program
funds the publication costs. Finally, the cover illustration is the work of Ann Tihansky, USGS, used since
the first KIG workshop in 2000.
Eve L. Kuniansky
USGS Karst Interest Group Coordinator

2
AGENDA U.S. GEOLOGICAL SURVEY KARST INTEREST GROUP WORKSHOP
April 29–May 2, 2014 Carlsbad, New Mexico
Hosted by the National Cave and Karst Research Institute
TUESDAY, APRIL 29
Registration
Start at 8:00 am-- All day – pick up name tags and Proceedings
Welcome and Introductions
8:20 – 8:40 Eve Kuniansky, U.S. Geological Survey, Karst Interest Group Coordinator and
George Veni, Director of National Cave and Karst Research Institute

Programs and Karst Aquifers (Randall Orndorff, moderator)

8:40 – 9:00 A preview of “Karst in the United States of America: A digital map compilation
and database” by David Weary and Dan Doctor
9:00 – 9:20 Groundwater availability of the Floridan aquifer system by Andrew O’Reilly and
Eve Kuniansky (presenter)
9:20 – 9:40 An overview of the Ashley Spring groundwater system - a unique public water-
supply karst spring in northeastern Utah, and potential impacts from a proposed
phosphate mine by Lawrence Spangler
9:40 – 10:20 BREAK
KEYNOTE (Zelda Chapman Bailey, moderator)
10:20 – 10:40 Speleotrek: Cutting edge karst into the 21st century by Penelope Boston, Director
of Cave and Karst Studies, New Mexico Tech and Academic Director, National
Cave and Karst Research Institute
Tracers (Zelda Chapman Bailey, moderator)
10:40 – 11:00 Groundwater tracing in arid karst aquifers: Concepts and considerations by
George Veni
11:00 – 11:20 Challenges to a karst dye-tracing investigation in an urban Brownfields area by
Douglas Gouzie, Kevin Mickus, and Micah Mayle
11:20 – 1:20 LUNCH ON YOUR OWN
Modeling Karst Aquifers (J. Van Brahana, moderator)
1:20 – 1:40 Taking the mystery out of mathematical model applications to karst aquifers—A
primer by Eve Kuniansky
1:40 – 2:00 Refined hydrostratigraphic framework and model of the Edwards aquifer, Texas
by Beth Fratesi, Ron Green, Ronald McGinnis, Hakan Basagaoglu, Leslie
Gergen, Jim Winterle, Marques Miller, and Paul Bertetti
2:00 – 2:20 Simulation of groundwater flow in the Edwards-Trinity aquifer in the Pecos
County region, Texas by Brian Clark, Jonathan Bumgarner, and Natalie Houston
2:20 – 3:00 BREAK

3
Chemical Fate and Transport (Michael Bradley, moderator)
3:00 – 3:20 Transport of salt, trace metals, and organic chemicals from parking lot and road
surfaces into Mammoth Cave by David Solomon, Irucka Embry, Bobby Carson,
Roger Painter, Lonnie Sharpe, Rick Toomey, and Tom Byl (presenter)
3:20 – 3:40 CAFOs on karst—Meaningful data collection to adequately define environmental
risk, with a specific application from the southern Ozarks of northern Arkansas
by Van Brahana, Joe Nix, Carol Bitting, Chuck Bitting, Ray Quick, John
Murdoch, Amie West, Sarah Robertson, Grant Scarsdale, and Vanya North
3:40 – 4:00 A method to investigate karst groundwater flow in Nash Draw, Eddy County,
New Mexico, to delineate potential impacts of potash industry discharge and
runoff by Jim Goodbar and Andrea Goodbar
4:00 – 6:00 Poster Session at National Cave and Karst Research Institute

WEDNESDAY, APRIL 30
Geochemistry, Fate and Transport, Microbial Ecology and Karst Ecosystems (Patrick Tucci,
moderator)
8:20 – 8:40 Geochemical evidence for denitrification in the epikarst at the Savoy
Experimental Watershed, northwest Arkansas by Jozef Laincz and Phillip D.
Hays
8:40 – 9:00 Geochemistry in paleokarst aquifers of the Knox Group in Tennessee and
Kentucky by Michael Bradley and Marty Parris
9:00 – 9:20 Linking climate change and karst hydrology to evaluate species vulnerability:
The Edwards and Madison aquifers by Barbara Mahler, Andrew Long, John
Stamm, Mary Poteet, and Amy Symstad
9:20 – 9:40 Response of cave–stream bacteria to sub-lethal concentrations of antibiotics by
Tom Byl, Petra Byl, and Rickard Toomey
9:40 – 10:20 BREAK
Modeling Karst Aquifers (David Weary, moderator)
10:20 – 10:40 Automatic methods of groundwater flow model construction of the Ozark
Plateaus aquifer system by Brian Clark and Joseph Richards
10:40 – 11:00 A hypothesis for carbonate island karst aquifer evolution from analysis of field
observations in northern Guam, Mariana Islands by John Jenson, Danko
Taboroŝi, Kolja Rotzoll, John Mylroie, and Stephen Gingerich (presenter)
Speleogenesis (David Weary, moderator)
11:00 – 11:20 The role of spongework in the speleogenesis of hypogenic caves in the
Guadalupe Mountains, New Mexico by Mark Joop
11:20 – 1:20 LUNCH ON YOUR OWN
Featured Presentation
1:20 – 1:40 Irish karst and its management by Caoimhe Hickey, The Geological Survey of
Ireland

4
PANEL DISCUSSION: Collaboration During Times of Limited Resources (Eve Kuniansky,
moderator)
1:40 – 3:00 U.S. Department of the Interior panelists:
James Goodbar, Bureau of Land Management,
Randy Orndorff, U.S. Geological Survey, and
Dale Pate, National Park Service
University Perspective:
Doug Gouzie, Missouri State University
Institute Perspective:
George Veni, National Cave and Karst Research Institute
Other Federal Agency with Stewardship Responsibilities:
Johanna Kovarik, U.S. Department of Agriculture-Forest Service

3:00 – 3:40 BREAK

Karst Interest Group Business
3:40 – 4:00 Discuss proposals for location of next KIG workshop in 2017
4:00 – 4:20 Thursday Field Trip overview and logistics by Lewis Land
THURSDAY, MAY 1
7:45AM – 5:30PM Field Trip Day 1—Evaporite karst of the Lower Pecos Valley, New Mexico
by Lewis Land
FRIDAY, MAY 2
7:45AM – 5:30PM Field Trip Day 2—Geology tour of Carlsbad Cavern by George Veni

POSTERS
Geologic Framework, Geophysics, and Geologic Hazards
Geologic framework, structure, and hydrogeologic characteristics of the Knippa Gap area in eastern
Uvalde and western Medina Counties, Texas by Allan K. Clark (presenter), Diana E. Pedraza,
and Robert R. Morris
Three-dimensional model of the hydrostratigraphy and structure in and around the Camp Stanley storage
facility, northern Bexar County, Texas by Michael P. Pantea and Allan K. Clark (presenter)
Using borehole and surface geophysics to develop a conceptual model of hydrostratigraphic layers, Pecos
County region, Texas, 2012 by Jonathan V. Thomas, Johnathan R. Bumgarner, Gregory P.
Stanton, Andrew P. Teeple, and Jason D. Payne
Perils of a dissolving State—Florida by Clint Kromhout
Geochemistry, Fate and Transport, Microbial Ecology, and Karst Ecosystems
Role of surface-water dissolved organic carbon in the survival, growth, and transport of Escherichia coli
in a deep limestone aquifer in south Florida by Ronald W. Harvey, Jen Underwood, John Lisle,
David W. Metge, and George Aiken
Integration of geochemical and isotopic data to assess sources of discharge at a major spring in the
Edwards aquifer, south-central Texas by MaryLynn Musgrove and Cassi L. Crow
Cave bacteria and crystal formation in the laboratory by Petra Byl, Aaron Covey, Jessica Oster, Tasneem
Siddiquee, and Tom Byl (presenter)

5
Non-target bacterial response to white-nose syndrome treatment: Quaternary ammonia and linear alkyl
sulfonate compounds by JeTara Brown, Zheer Ahmed, and Tom Byl (presenter)
Flowable fill for subsurface cavity remediation by Chase Kicker (Carlsbad High School, accepted at New
Mexico Tech for fall, 2014)
Chemical Transport and Contamination in Karst
Use of a dual continuum model to describe solute transport in karst by Justin Harris, Roger Painter,
Lonnie Sharpe and Tom Byl (presenter)
An initial investigation of hydrogeology and water quality of Big Creek in the Buffalo River watershed
near a major concentrated animal feeding operation By Victor L. Roland II, Phillip Hays, Van
Brahana, and Erik Pollock
Demonstration
The National Karst Map by David Weary

6
 KEYNOTE
Speleotrek: The Cutting Edges of Karst into the 21st Century
By Penelope J. Boston1,2
1
New Mexico Tech, 801 Leroy Place, Socorro, NM 87801
2
National Cave and Karst Research Institute (NCKRI), 1400-1 Cascades Ave., Carlsbad, NM 88222

Abstract
Exploration and study of Earth’s subsurface has been the delight of some but a blank slate to many
within the mainstream geoscience and biology communities until perhaps the past several decades.
Especially in the United States, many aspects of cave and karst studies have been marginalized but this
picture is now changing. Increasing awareness of karstic processes include the classic areas of cave
origins and development (speleogenesis) and karst geohydrology, but now include such fields as
geomicrobiological influences on karst, the role of karst and cave environments in biogeochemical
cycling, and caves as repositories of several types of important climate proxy data. A dawning
appreciation of the subsurface habitat connection with surface habitats is upon us, especially with regard
to material and energy transfers. Even apparent examples of karstic phenomena beyond Earth have begun
to seep into the larger scientific landscape. Such contemplation can provide a new basis for comparative
studies enabling us to test our ideas in more than one planetary context. Finally, new technology and
methodologies emerging now will help to advance karstic studies into the future and bring karst science
into the mainstream of the 21st century science portfolio. Implications of karst in matters of human
welfare, and opportunities for applications of new arenas of research are numerous. Concerns range from
geohazards associated with karst and special issues unique to karst aquifer management, to the potential
for unique compounds of pharmaceutical and industrial uses derived from subsurface sources. The 21st
century is shaping up to be a productive time for karst understanding and utilization.
KARST IN THE BROAD CONTEXT speleology, research also benefits from
The existing body of work on karst and interdisciplinary synthesis. Some cutting edge
related topics is an important source of research fits within the geoscience framework
understanding of fundamental processes, not and some is clearly biological in nature. Often
only in relation to the particulars of dissolvable these broad disciplines overlap, and all research
landforms, but also in the greater context of the approaches will be enhanced by new
Earth sciences writ broadly. Shallow crustal and technologies that can allow us to better detect,
surficial processes involving aqueous access, and study caves and the karstic terrains
dissolution, consequences for hydrological that house them. Furthermore, any ways in
drainage, modification of the landforms which karst studies can fruitfully interact with
overlying and underlying soluble rock facies, other scientific research areas will enhance both
and the properties of caves as environments for the broader picture and in turn feed back into
microbial and macroscopic biota are already further invigorating karst science itself.
acknowledged arenas of speleology. In a highly CUTTING-EDGE SCIENCE DIRECTIONS
interdisciplinary 2007 workshop organized by
Although numerous questions remain to be
the Karst Waters Institute (KWI), a number of
answered and understood in detail, many aspects
major research directions for the future of karst
of classical karst science are relatively mature
were identified (Martin and White, 2008).
fields, with suites of major fundamental
However, since that assessment was completed
principles currently understood and
there are a handful of developments of particular
implementable in field, laboratory, and modeling
note that are newly emerging or are undergoing
efforts (Palmer 2007; Ford and Williams, 2007).
major development and these constitute the topic
However, several aspects of karst studies that
of this paper. By its very nature, speleology is a
have been little explored are now gaining
place-based, highly interdisciplinary field.
attention and are discussed below.
Where karst geohydrology overlaps with

7
More Than Just CaCO3! scientifically important examples occur in many
The classic conception of karst dates from as other parts of the world.
far back as the mid-17th century (Larsen, 2003) Also associated with many evaporite rocks
and was described originally for the Dinaric are halite (NaCl) deposits. Such salt deposits
carbonate karst of Slovenia and surrounding may house caves and related karst drainage
areas. Jovan Cvijić, the famous Serbian scientist features. Seminal work by a relatively small
and polymath of the late 19th century, also made number of investigators (e.g. Frumkin, 1994;
seminal contributions to the early concepts of Bosak and others, 1999) has enabled
carbonate karst, publishing a major work on the understanding of the basic behaviors of such
subject in 1895. This early work firmly planted systems but much remains to be done to extend
the notion of karst in carbonate lithology. understanding. Halite karst is uncommon but
Arguments have raged in the past over widely distributed, occurring in Iran, Israel,
whether the term karst should be reserved only Algeria, Chile, Romania, Spain, Syria,
for terrains in calcium carbonate rock types (see Tadjikistan, and Tunisia (Chabert and Courbon,
Monroe (1970) for a typical version of such a 1997).
definition of karst.) Perhaps most modern Even more exotic karstic processes occur in
thinkers on the subject have broadened the scope quartzite, most notably in massifs in South
of karst to encompass any geomorphic terrain America (Gibbs and Barron, 1993; Piccini,
type that relies on dissolution of soluble rock as 1995). Wray (1997) has argued convincingly
its primary driving mechanism (e.g. Ford, 1980). that caves in South American quartzite massifs
Surface and subsurface characteristics typically qualify as true dissolutional karst. Further, he
associated with many karst terrains can be points to a number of other quartzite karst
helpfully diagnostic in assessing the karst status occurrences in Chad and Australia. Quartzite
of a particular area but should not be required as karst is one instance among a growing number
definitive because of the great complexity of of cases that implicates biological processes in
features that can be considered as karst. The the alteration, modification, or even inception of
trend to broaden the lithologies under the karst a karstic phenomenon. In this case,
umbrella is very handy because there are a microbiologically enhanced silica dissolution
number of compelling examples in a variety of and mobilization appears to be significant in the
rock types around the world! development of karst in siliceous materials like
Gypsum and other evaporite minerals are an quartzite (e.g. Chalcraft and Pye, 1984; Zhou
important additional type of dissolvable rock and others, 2011).
with wide global distribution of resulting Further comparative study of soluble rock
landforms and caves. Many speleologists processes can be extremely fruitful, allowing us
already refer to these lithologies as karst (see to explore along a gradient from extremely
Klimchouk and others (1996) for a review of the soluble and needing only the presence of water
state of the art at that time.) Powerful (halite and gypsum), to the classical pH-
comparisons of gypsum karst with carbonate dependent karst in limestone, dolomite, and
karst can yield a refined partitioning of the marble, to extremely refractory siliceous rock
relative roles of physical and chemical processes like quartzite that requires the presence of
that govern solubility of bedrock in the natural significant microbial (and perhaps plant)
environment. For example, the major influence chemical mobilization.
of pH that we see in carbonate karst is irrelevant
Caves as Key Interface Systems in the
to gypsum dissolution, and of course, the Critical Zone
intrinsically high solubility of calcium sulfate is
itself a critical factor in the origin and The Critical Zone (CZ), that part of the
development of gypsum karst. Truly enormous Earth that houses the interactions of the
and spectacular examples of gypsum caves and atmosphere, hydrosphere, biosphere, and near
karstification exist in western Ukraine and surface lithosphere, was invented as a defined
Moldova (e.g. Andrejchuk, 1996; Klimchouk phrase over a decade ago in a largely ecological
and Andrejchuk, 2002). Smaller scale but context (National Research Council, 2001). The
8
intent was to capture the essence of the thin subterranean animals that inhabit caves and
outer envelope of our planet within which all life cavities within limestone aquifers and other
resides, and where we conduct the vast majority types of caves, it is in the realm of microbiology
of our human activities. Caves are discrete that many new research directions are
systems uniquely positioned to capture these particularly coming to the fore.
dynamic interactions that collectively describe
The awareness of microbial interactions
the Critical Zone. Indeed, caves may represent
with rocks and minerals has developed from the
the single best example of the terrestrial Critical
surface down, with an important early attempt to
Zone in miniature since they contain some
classify organisms on the basis of how they were
combination of atmosphere, fluid, rock, often
positioned within, over, or under rocks (Golubic
sediment, a huge array of microorganisms, and
and others, 1981). Since that seminal attempt,
often macroscopic animal life.
our grasp of the degree to which Earth’s
There are several key properties of caves terrestrial and marine crust is thoroughly
that come together to enable us to take a systems infested with tiny life forms has greatly
approach to cave study and place it within the expanded. We now know that there is a vast
Critical Zone context: 1) all three common global subsurface rock fracture habitat that
phases of matter come together in caves, 2) houses countless strains of microorganisms, and
caves are separated from the surface by that aquifers, caves, and even volcanic terrains,
significant boundary conditions, and 3) they are and the immense ocean floor with a mix of
partly open systems vis a vis energy and young and very aged rocks are part of the rock
materials, but over short timescales they can act fracture wilderness (Boston and others, 2001,
as discrete closed systems! 2009a; Cowan and others, 2003; Frederickson
and Balkwill, 2006; Gihring, 2006; Lin and
Ideally, subsurface cavities as Critical Zone
others, 2006; Northup and Lavoie, 2001).
examples can capture the attention of non-karst
Clearly caves and karst systems are vital and
scientists as well as speleologists to further the
important parts of this hidden microbial
understanding of interfaces between the various
wilderness because they can provide us windows
compartments of the Earth system both in caves
into that terra incognita.
and as applicable to the wider surface
environment. A recent major assessment of In our research team’s experience in caves,
Critical Zone science and applications in we see unique features of subsurface microbial
response to various global environmental communities that often include extremely high
challenges set forth a broad plan for research biodiversity and a large degree of habitat
and applications and did mention karst in partitioning at a very fine spatial scale on the
connection with hydrogeology. However, the order of centimeters to meters (Boston and
paper did not mention caves a single time in the others, 2009b). In contrast, those working in the
course of a rather lengthy document, in spite of deep subsurface may be seeing a much reduced
the unique nature of karst habitats (Banwart and biodiversity, perhaps even as little as a single
others, 2013). More work on the part of the karst species (Chivian and others, 2008)! The pace of
community is necessary to sensitize the broad growth can be very slow in the typically energy-
scientific community to the importance of karst limited subsurface (Kieft and Phelps, 1997;
systems on Earth and their properties Boston and others, 2009b) and opportunities for
specifically in the Critical Zone context. transport around such systems can be severely
Caves in the Era of Geomicrobiology limited by lithologic and hydrologic barriers.

A major new research thrust over the past 20 Coupled with the growing understanding of
years or so has been subsurface the vertical extent of the rock fracture habitat,
geomicrobiology studied at depths ranging from the awareness of the role of organisms in
shallow caves and lava tubes to extremely deep precipitation of minerals has been occurring at
mines and deep within the ocean floors. While the same time (e.g. Banfield and Nealson, 1997;
there is still much to be learned about the Newman and Banfield, 2002). This has been a
unusual and often unique species of critical development in interpreting how many
subterranean microbes make their living
9
chemolithotrophically, that is, by transforming and Unterman, 1993; Rawlings and others,
inorganic materials like minerals into energy 2007).
rather than relying for energy on utilization of
Importantly for purposes of human use,
organic compounds derived from the above-
many subsurface microbes produce a wealth of
ground biosphere. Oxidation of metal-containing
unusual chemical compounds of potential use to
minerals is a very common energy-acquisition
the pharmaceutical, industrial, and remediation
mechanism, and the proximity to the waste
communities, thus providing a major new
products of those transformations make
application for speleology (Poulson and others,
subterranean microbes inclined to auto-fossilize
1986). Much of the work that has been done on
as they are growing, thus providing a
these compounds has not yet been published in
mechanism for exquisite preservation of
the open literature for a variety of reasons, one
biotextures and even microbial body fossils (e.g.
of which is the uncertain legal framework under
Boston and others, 2001, 2009b; Curry and
which potentially commercially important
others, 2009; Melim and others, 2001, 2009).
compounds coming from organisms within the
Additionally, the ubiquity of biofilms that the
purview of a national land management agency
organisms make for protection and manipulation
should be handled (e.g. Northup and others,
of the chemistry of their environments, also
Boston and others, and Mallory and others,
contributes to the production and preservation of
unpublished data).
distinctive biosignatures including biomineral
textures. Battin and colleagues (2007) have Besides the microorganisms that we can
exhorted us to view biofilms as miniature understand well enough to at least study, an
landscapes and those who study these materials extraordinary biological morphology has come
are well–acquainted with the clear parallels to to our research group’s attention that we are still
the larger scale landscapes we see in nature. at a loss to explain after 15 years of finding
variants of this morphology in a variety of caves
Very small cell sizes (100-500 nm diameter)
around the world in all lithologies (Melim and
and very slow growth rates are common in
others, 2008; Northup, Boston, and Spilde,
subsurface microbial communities and
unpublished data). Very tiny hexagonal mesh
presumably are an adaptation to stringently
tubes, ~0.5 µm in diameter and up to several
limited energy sources to be found there (Kieft,
2000, 2002). Energy limitation is also coupled tens of µm in length appear draped across the
with the absence of grazing by animals or micro-landscape in scanning electron
protists in many of the deeper systems that micrographs. They display a host of
allows organisms to prosper without having to mineralogical characteristics indicating that they
“outgrow” the rate at which they are being are covered by compounds in their environment.
consumed by other organisms (Boston and We do not know who or what these structures
others, 2009b). are; we have so far not succeeded in growing
them, and the long dance cards of DNA strains
A further outgrowth of the work of a number that we obtain cannot be matched up to a single
of investigators is beginning to point to the role morphology seen only in electron micrographs.
of microorganisms in low temperature Are they some sort of cellular skeletons? Are
hydrothermal ores (e.g. Southam and Saunders, they microstructures belonging to a higher life
2005), and particularly copper (Enders and form? Are they organisms in their own right?
others, 2006), and gold (Karthikeyan and So far we are stumped.
Beveridge, 2002; Lengke and Southam, 2006;
Southam and others, 2009). Carbonate systems However tantalizing it is to study the
that host emplacement of such ores as a result of peculiar and exotic as with our reticulated
a granitic intrusion are known as skarn deposits filaments described above, Northup and Lavoie
(Einaudi and Burt, 1982). The potential for use (2001) have pointed out that, “Caves should be
of organisms from these environments is great used as experimental study systems for
and could be used for biomining, geomicrobiology, not because they are strange,
bioremediation, and biobeneficiation (Shannon but because they are simple and often locally
abundant, allowing for replicate studies….”

10
This is an important observation which means Earth’s geological history and are still doing that
that we do not necessarily need to seek out the today.
most extreme and extraordinary caves or Climate Proxies in Caves
bizarre-appearing life forms in order to study the
geomicrobiology. All caves can offer important Several decades ago, calcite in caves was
insights into bio-diversity, functional diversity, identified as important material for investigating
critical metabolic pathways, and metabolic climate records, particularly during non-glacial
products that may be of use for human concerns. times (e.g. Gascoyne, 1992; Bar-Matthews and
others, 1996). Of the many potential data types
Subsurface Biodiversity as a that calcite speleothems may supply, stable
Hydrological Proxy
isotope ratios have gained ascendency and are
Patterns of microbial and functional gene being used extensively to reconstruct ancient
biodiversity are on the threshold of emerging climates (Ghosh and Brand, 2003). As those
from phylogenetic studies of well samples, authors point out in the paleoclimate context,
borehole cuttings, natural caves, active and “Atmospheric CO2 provides a link between
abandoned mines, deep ocean drilling cores, and biological, physical and anthropogenic processes
from beneath glaciers and ice fields. As the in ecosystems.” As we well know, CO2 is an
databases swell with entries at an ever greater intrinsic part of karst mechanisms and thus, the
pace due to continuous improvements in the use of speleothem stable isotopes as one of the
technology and lower analytical cost per sample, climate proxy data sets has become very popular
it is now possible to suggest that the emerging (Fairchild, 2006). In concert with stable isotopic
patterns may provide useful proxies for fractionation, recent work (Woodhead and
hydrological connectivity in fractured aquifers others, 2010) has extended the radiometric
that are difficult to measure directly. I have dating timeline back to ancient speleothems in
expressed this as karst-controlled biogeography paleokarst systems as far back as the Permian,
of subsurface life (Boston, 2002). The essence of which makes such studies even more useful.
the idea is that organisms move very slowly Speleothem climate study using stable isotopes
through a connected fracture system in the is thus, a tremendously exciting and promising
subsurface. Transport mechanisms include fluid field of research. However, what has not yet
flow, which can be extremely slow, and active been addressed is the potential for microbial
motion by organisms with independent motility, interference in these signals. Microorganisms
also typically slow. The patterns of propagation are not known to alter the fractionation of
of organisms through the subsurface and their oxygen, so the O16/O18 ratio used to indicate
relationships to one another will eventually be evaporation and indirectly temperature is
able to provide insights into connectivity in probably safe from microbial effects. However,
subsurface systems that may be difficult to infer carbon is highly fractionated between C13 and
by direct physical evidence. C12 isotopes on the basis of photoautotrophy or
Besides the inherently slow nature of the chemolithotrophy, both of which slightly favor
two transport mechanisms mentioned above, the lighter isotope and can be used to define
there are a number of other roadblocks to carbon sources and sinks (see Ghosh and Brand,
microbial movement through a karst system, 2003, for a nice explanation of these
ranging from geological barriers like complicated interactions.) Organic carbon
impermeable facies, to microbiologically- received from above-ground, coupled with
induced blockage of porosity and permeability chemolithotrophic carbon fixation by
by biofilms and biominerals that the organisms microorganisms in-cave, complicated further by
may produce. The biofilm lifestyle is ubiquitous reports of direct excavation of solid carbonate by
in nature and its antiquity dates to some of the microorganisms (Garcia-Pichel and others,
earliest evidences of life on Earth, some 3.25 2010), means that the straightforward
billion years ago (Hall-Stoodley and others, interpretation of carbon in the climate context is
2004). Thus, organisms may well have been not always possible and certainly presents
influencing porosity and permeability of rock caveats to be considered.
masses in the crust for the vast majority of
11
 Caves and rock shelters have been identified others, 2007; Cushing, 2012) to hypothetical
as excellent sediment traps in the archaeological exotic true karst in radically different planetary
context (Colcutt, 1979) and this also applies to settings (Boston, 2004; Grin and others, 1998,
their role as sediment traps in general. Further, 1999). Within this context, we include water ice
vegetation indicators in sediments are often well "bedrock", liquid methane rain, and derived
preserved in caves. Primarily, pollen has been organic surface “soil” on Titan (Mitchell and
studied in this context although not exploited as Malaska, 2011; Malaska and others, 2011). The
much as it can be (McGarry and Caseldine, epistemological power of comparative planetary
2004) but plant biominerals (known as studies can now be extended into speleology.
phytoliths) and diatoms (photosynthetic algae Can we take what we believe we understand
with silica tests) are equally promising and often about karstic processes on Earth and validly
the most abundant botanical remains recovered translate that to another planetary body and vice
from cave sites. For several good examples of versa? Such a rigorous test bed could play an
combining these data types see Martínez and important role in providing new perspectives
others (2013) and Trombold and Israde- and potentially new insights.
Alcantara (2005). The use of phytoliths in
In order to handle the concept of karstic
climate reconstruction has now been applied to
phenomena on other planetary bodies, a new
very recent climate and vegetation change of
conceptual framework is needed. A number of
only several hundred years in the past (Morris
speleologists have devised schemes for karst or
and others, 2009).
cave classification that are of great utility for
The partitioning of trace elements in Earth applications (e.g. Cams, 1989; Dreybrodt,
speleothems as indicators of ancient conditions 1988; Ford and Williams, 1989; Self and
has also been explored, although to a far lesser Mullan, 1996). However, most may not fit some
degree than the other proxy data sets. This of the more unusual processes that we can
includes laboratory simulations of uptake of anticipate seeing on other bodies. Table 1 shows
trace elements as well as field observations of an ongoing attempt to reduce the complexity of
natural systems (Huang and others, 2001a, b; karst and cave processes that may be seen on
Treble and others, 2005; Johnson and others, other planets to basic physical and chemical
2006, Day and Henderson, 2004). There is processes (modified from Boston, 2004). As a
additional potential for applying this approach to work in progress, this is hardly definitive but a
cave climate records. start in attempting to rethink the issues involved
in radically different gravitational environments.
Broadly viewed, all of the proxy indicators
of climate discussed above can be combined CUTTING-EDGE TECHNOLOGIES
fruitfully in cave studies (Couchard, 2008). For New non-invasive or less invasive
an excellent example of vegetation bioindicators methodologies can reveal the subsurface in new
combined with isotopic data, see Scott (2002). In ways or allow us to directly explore them using
the future, studies which attempt to cross- robotic proxies. Application of well known
correlate all possible climate data sets contained techniques to the cave environment is one
within caves could be immensely valuable in important direction and exemplified by the
helping us to unravel Earth’s past climates in development of a prototype mass spectrometer
non-marine and low- to mid-latitude for in-situ analysis of cave atmospheres working
environments. toward a better understanding of the gases that
Extraterrestrial Karst? make up cave air (Patrick and others, 2012).
Other well known instruments could also be
The tantalizing prospect of extraterrestrial
tailored for the rigorous challenges of using high
caves ranges from lava tubes, pit crater shafts,
precision instrumentation in a dirty and difficult
and other collapse features first speculated about
environment. However, entirely new approaches
and then observed on the Moon (Oberbeck and
to karst research are being tried and discussed
others, 1969; Greeley, 1971; Sakimoto and
below.
others, 1997; Haruyama and others, 2009), and
Mars (Wyrick and others, 2004; Cushing and

12
Thermographic Mapping surface of a bizarre mixture of organic
Mapping relative degrees of heat to show compounds awash with alkane lakes and rain
contrasts potentially indicating subsurface possibly produce structures like caves and
cavities has been shown to be feasible in karstic terrain familiar to us on Earth and other
ground-based infrared camera trials on Earth rocky terrestrial bodies? A plausibility argument
conducted in New Mexico, West Virginia, can be made and tested using orbital radar
Missouri, Greece, and the Atacama Desert, imaging data and modeling.
Chile, and balloon-borne trials conducted in the Even more futuristically, muon imaging may
Mojave Desert, CA (Thompson and Marvin, provide ultra-deep penetration (~1 km). The
2006). Modeling efforts have been mounted to technique, which relies on the production of
study the Martian thermal environment to muons by collision of galactic cosmic rays with
determine suitability of this method in the much the atmosphere has already been tested for
colder temperatures of Mars with lower volcanology, archeology, and national security
temperature contrast between inside and outside applications, and has recently been suggested for
cavities (Wynne and others, 2008). Applicability imaging the interior of small solar system bodies
to ultra low-temperature bodies with minimal like asteroids or comets (Prettyman, 2013). A
thermal contrast remains to be demonstrated: preliminary (Phase I) study has been funded by
Titan, which has a very dense atmosphere, or NASA to explore the possibilities. While the
Enceladus and Europa, both of which have muon production rate is slow, meaning long
virtually no atmospheres. signal collection times of days to weeks, caves
Imaging are usually not moving targets and so may be
perfect for such a leisurely approach!
Miyamoto and colleagues (2005) have been
developing a ground penetrating radar (GPR) Robotics for Cave Access
system with shielded antennas and stepped- Successful robotic access to caves, rock
frequency capability (50-500 MHz) that will shelters, and other rugged and unpredictable
enable both significant penetration depth (>10 surface terrain is essential to allow exploration
m) and high spatial resolution (< 1 m) at the of other planets and even for some extreme
same time. They field tested the instrument in a Earth sites. Concepts like hopping, self-
lava tube (Koumoriana, Aokigahara lava flow, deploying microbots with high energy-density
Japan), and is also applicable to karst as well. power and polymer “muscle” actuated motion
Recently a team from the NASA Jet for subsurface sensing and telemetering
Propulsion Laboratory analyzed interferometric networks have been suggested and developed to
synthetic aperture radar (InSAR) imagery of the an early stage (Dubowsky and others, 2004).
area around a giant sinkhole that opened up in Unique clinging and climbing mechanisms also
Bayou Corne, LA, in 2011 (Jones and Blom, are being developed (Parness, 2010). A field
2014). Uninhabited Airborne Vehicle Synthetic demonstration with Jet Propulsion Laboratory
Aperture Radar (UAVSAR) is mounted on a C- colleagues during 2014 tested gravity-
20A jet. The InSAR instrument can measure tiny independent inverted clinging robots in lava
deformations in a planet’s surface, and very caves in New Mexico and California and will
small horizontal surface irregularities have now continue into mid-2016 to investigate methods
been shown to precede the development of a of advanced mobility.
sinkhole far in advance of its collapse, SUMMARY
potentially providing a predictive capability for
In summary, speleology is a place-based
Earth applications and possibly a detection
field of tremendous depth that has often been
method for other planets.
marginalized from mainstream science,
Radar imaging of gigantic frigid Titan, especially in the United States. Over a decade
orbiting Saturn, suggests both cryovolcanism ago, I wrote of the then-new National Cave and
(e.g. Wall and others, 2009) and subsurface Karst Research Institute (NCKRI) and its
structures (Burr and others, 2009). Can aspirations for the future (Boston, 2003). Five
processes on a body of water-ice bedrock and a years later, at the 2008 Karst Interest Group
13
meeting, I attempted to further expand on our most to the future of the field and applications.
grasp of how we can be useful to the karst The past decade has seen emergence of a suite of
community and the directions to follow in research directions that map an exciting future in
accomplishing our mission. It is now time to karst studies as we go into the next century of
reassess and possibly to reposition ourselves to science and exploration. NCKRI stands ready to
proactively advocate for the cutting edge areas assist in the development of this future.
of research and application that will matter the

Table 1. Fundamental physical and chemical process classification of caves including karst, karst-like processes, and
non-karst mechanisms for karst formation. Revised and updated from Boston, 2004.

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18
 PROGRAMS AND KARST AQUIFERS

A Preview of “Karst in the United States of America: A Digital Map

Compilation and Database”
By David J. Weary and Daniel H. Doctor
U.S. Geological Survey, 12201 Sunrise Valley Drive, MS926A, Reston, VA 20192

Abstract
A series of new digital maps delineating areas of known and potential karst and pseudokarst
development in the United States, including Puerto Rico and the U.S. Virgin Islands, have been compiled
and are being released as a U.S. Geological Survey Open-File Report (OFR). These maps show areas
underlain by soluble rocks with potential for karst development as well as volcanic rocks, sedimentary
deposits, and permafrost with potential for pseudokarst development. Data indicate that all 50 States
contain areas with potential for karst development. About 18 percent of the area of the United States is
underlain by karst or soluble rocks that have the potential for karst development. The mapped areas of
soluble rocks, containing significant amounts of carbonate or evaporite minerals, are primarily based on
their distribution shown on state geologic maps. Areas underlain by soluble rocks are further classified by
general climate setting, induration, and exposure. Areas with potential for volcanic pseudokarst are those
chiefly underlain by basaltic extrusive rocks no older than Miocene in age. Potential pseudokarstic
features in unconsolidated sedimentary rocks include piping caves. Areas with potential for development
of thermokarst subsidence features in Alaska contain permafrost mantled by various thicknesses of
sediment. The OFR includes a GIS database with links from the map unit polygons to online geologic
unit descriptions. This paper is an interim product, and a formal publication and print edition, with
revisions and additions, is planned for the near future.
INTRODUCTION conditions, and time. Because very sparse karst
A new digital national karst map will be features evident at the land surface can indicate
published as an Open-File Report (OFR) (Weary important groundwater flow processes in the
and Doctor, in press). The OFR contains subsurface, we have included all areas
extensive discussion and detailed descriptions of containing soluble bedrock types as potentially
the processes used to compile and classify the hosting karst features.
karst data that it contains. In addition, the maps Pseudokarst (Halliday, 2007) discussed in
included in the OFR are both more complex and the OFR includes areas with features analogous
of higher resolution than the figures shown in to karst that arise from processes other than rock
this paper. solution. Potential pseudokarst includes areas
Because the development of karst is underlain by geologic materials susceptible to
primarily dependent on the presence of soluble formation of voids produced in lava flows and
rocks, the delineation of karst was based on by erosion of fine-grained sediments by piping
compiling areas of soluble rocks from geologic (stoping), and melting of permafrost. Examples
maps (e.g. Williams and Ford, 2006). We include lava tubes in Miocene and younger
compiled regions of known and potential karst in volcanic flow rocks (primarily basalts), piping
the United States using the latest, most detailed features within unconsolidated sediments in
published digital geologic map information. semiarid to arid regions, as well as areas of
While this approach is representative of karst piping in sediments affected by intermittently or
potential, a complex interaction of many factors progressively thawing permafrost in Alaska.
determines the formation, localization, and Pseudokarst in permafrost areas is also known as
intensity of karst development. These factors thermokarst (Sweeting, 1973). Large karst-like
include the rock type, structural setting, climate, integrated groundwater flow systems that
sedimentary cover, vegetation, local hydrologic resurge at large springs occur in some areas of
19
layered volcanic rocks in the western United and Analysis (NSA) Project (available at
States. Examples include the Columbia Plateau http://mrdata.usgs.gov/geology/state/, accessed
aquifer system in Oregon and Washington, and 02/10/2014). Use of the USGS digital geologic
the Snake River Plain aquifer system in Idaho. data provided a consistent data structure within
which a derivative database of areas with
Five thematic maps in the report include 1)
potential for karst could be constructed. Edits,
karst and potential karst areas of relatively
deletions, and additions to this database were
soluble rocks (e.g. limestone, dolomite, gypsum,
made based on 1) comparison to other published
anhydrite, halite, etc.) exposed at the surface or
karst maps (principally Davies and others, 1984;
buried at depths up to 300 feet in the contiguous
Veni, 2000), 2) comments and contributions by
United States, 2) karst and potential karst areas
other cave and karst researchers having local
of relatively soluble rocks (e.g. limestone and
knowledge of particular areas, and assisted by
dolomite) in Alaska, Hawaii, Puerto Rico, and
the comprehensive compilation in Palmer and
the U.S. Virgin Islands, 3) areas underlain by
Palmer (2009), and 3) the personal knowledge of
evaporite rocks at varying depths up to 7,000
the authors. Further characterization of the karst
feet, 4) areas with potential for pseudokarst in
areas was also accomplished via overlay
the contiguous United States, and 5) areas with
analyses with other data including distribution of
potential for pseudokarst in Alaska and Hawaii.
glacially-derived sediments (Soller and others,
The extent of outcrop of soluble rocks 2012), permanently frozen ground (Brown and
provides a good first-approximation of the others, 2002), and Level III Ecoregions (U.S.
distribution of karst and potential karst areas, Environmental Protection Agency, 2013).
particularly in parts of the United States with a MAPS
humid climate. Criteria for further refinement of
the karst map units includes 1) climate of The maps shown in figures 1-5 were
regions based on annual precipitation and Level generated from GIS data derived from various
III ecoregion designation, 2) degree of burial original geologic map sets that ranged from
and nature of the overlying sediments, and 3) 1:24,000 to 1:500,000 scale. The graphic files
degree of consolidation of the lithostratigraphic provided in the OFR are designed for display at
unit. 1:6,000,000 scale for the contiguous United
States and Alaska, and 1:3,000,000 scale for
The geographic information system (GIS) Hawaii, Puerto Rico, and the U.S. Virgin
data that accompany the OFR represent karst Islands. They will print at these scales at 100
areas as spatially registered polygons containing percent resolution. The geographic data for all of
multiple attributes that allow the user to perform these maps is in Albers projection using the
selection and analysis on the data. Certain North American Horizontal Datum of 1983.
attributes also allow linking back to the original
lithostratigraphic unit descriptions and ecoregion Map of Karst in Soluble Rocks in the
descriptions. Contiguous United States

DATA SOURCES The distribution of karst and potential karst

areas of soluble rocks in the contiguous United
Most of the spatial data compiled in this States is shown on figure 1. Because of space
project originated as lithologic map units on limitations, this is a greatly simplified version of
geologic maps produced by various state the map that will be available in the OFR.
geological surveys. Versions of the original
source maps are available for purchase or Distribution of mature surface karst areas in
download from the respective state geological the contiguous United States is primarily
surveys. Much of the digital map data was dependent on the presence of soluble rocks at or
compiled from a series of integrated geologic near the land surface and where the mean annual
map databases for the United States produced by precipitation above approximately 30 inches
the United States Geological Survey (USGS) (in.) (76 centimeters (cm)). In the humid parts of
Mineral Resources Program, National Surveys the United States, most karst features such as
caves and sinkholes (dolines) occur in carbonate
20
(limestone and dolomite) rocks; evaporite rocks sandstone in Minnesota with documented
are rarely found at or near the surface in these solution karst is also shown (Shade, 2002).
areas. Most of the eastern United States and the Other areas of anomalous solution, in what are
Pacific coastal zone are considered to be humid. normally considered insoluble rocks, may exist
Local areas of the Rocky Mountains and the elsewhere in the United States and are yet to be
Sierra Nevada are also classified as humid documented.
regions in this paper because of higher
For figures 1 and 3, the boundaries between
precipitation totals mostly due to orogenic
dry and humid regions were delineated by
effects. All areas of Alaska, Hawaii, Puerto Rico
comparing the average annual precipitation map
and the Virgin Islands are considered humid at
for the years 1961-1990 with descriptions of
the resolution of this study. In the semi-arid and
North American Level III Ecoregions (Daley
arid regions of the western United States less
and Taylor, 2000; U.S. Environmental
soluble carbonate rocks are more resistant to
Protection Agency, 2013). These boundaries are
erosion while the more soluble evaporite rocks
coincident with the Level III Ecoregion
that can exist at or near the surface in those
boundaries and they approximate the 30 in. (76
environments, exhibit the most prominent karst
cm) per year annual average precipitation
features. Karst features created by hypogenic
isohyet (Daley and Taylor, 2000). These
processes tend to be better preserved in arid and
boundaries, although shown as hard lines on
semi-arid areas as these features are less likely
figures 1 and 3, are actually diffuse and
to be modified by epigenic processes in drier
approximate. The principal boundary separating
climates (Palmer, 2000; Auler and Smart, 2003).
the eastern from the western areas of the United
Potential karst areas shown on figure 1 are States also approximates the southern part of the
grouped by areas of humid climate and areas of annual average precipitation isohyet used by
dry (semi-arid to arid) climates. In addition to Epstein and Johnson (2003). There is some
carbonate and evaporite rocks, an area of quartz divergence of the humid and dry region

Figure 1. Simplified map of the distribution of karst and potential karst areas of soluble rocks, as well as arid, semi-arid, and
humid climate regions. Thick white line indicates approximate maximum southern extent of Pleistocene ice.
21
boundaries from the principal 30-inch • Calcareous sediments at or near the
precipitation line at both north and south land surface
latitudes, as the effective regional humidity is
also a function of the regional evapotrans- • Unconsolidated calcareous
piration rate, which itself is affected by sediments buried beneath <300 feet
temperature. of insoluble sediments

Effects of late Cenozoic glaciations have a • Evaporite rocks exposed at or near

profound influence on the development and the land surface
preservation of karst features in the northern and • Evaporite rocks buried beneath <50
eastern parts of the contiguous United States. feet of glacially-derived insoluble
The line of demarcation approximating the sediments
greatest extent of the last glaciation is shown on
figure 1, and the thickness of glacially-derived • Evaporite rocks buried beneath >50
sediments overlying areas of soluble rocks is feet of glacially-derived insoluble
also integrated into the classification of map sediments
units in the OFR. The glacial data are derived • Quartz sandstone buried beneath
from Soller and others (2012). <50 feet of glacially-derived
Karst Map Units insoluble sediments
Space limitations preclude a detailed • Quartz sandstone buried beneath
description of the 11 map units shown on the >50 feet of glacially-derived
OFR map (not shown separately on figure 1 in insoluble sediments
this paper). Map units occurring in either a Map of Karst in Soluble Rocks in Alaska,
humid or arid climate regime include Hawaii, Puerto Rico, and the U.S. Virgin
Islands
• Carbonate rocks at or near the land
surface The distribution of potentially karstic areas
of soluble rocks in Alaska, Hawaii, Puerto Rico,
• Carbonate rocks buried beneath
and the U.S. Virgin Islands is shown on figure 2.
<300 feet of insoluble sediments All of these areas have relatively humid
• Carbonate rocks buried beneath <50 climates, so evaporite rocks rarely occur at or
feet of glacially-derived insoluble near the surface. Areas of carbonate rocks
sediments occurring at or near the surface are shown as a
single map unit on figure 2.
• Carbonate rocks buried beneath >50
feet of glacially-derived insoluble
sediments

22
Figure 2. Simplified map of karst and potential karst areas of soluble rocks in A, Alaska; B, Hawaii; and C, Puerto Rico and the
U.S. Virgin Islands.
Map of Areas Extensively Underlain by Map of Pseudokarst Areas in the
Evaporite Rocks at Depths up to 7,000 Contiguous United States
Feet Below the Surface
Two different pseudokarst units are
In addition to areas of outcropping and near- portrayed on the map of the contiguous United
surface evaporite rocks, figure 3 shows the States (fig. 4). The first unit represents areas of
extent of subsurface evaporite basins and the poorly consolidated sedimentary rock units
greater extent of commonly occurring evaporite known, at least locally, to contain piping
rocks in the subsurface. The evaporite basins features (tubes, caves, and subsidence features).
contain soluble rocks buried to depths of up to Most of the areas of piping potential are
about 7,000 feet, but generally much less. commonly characterized by fine-grained
Because of the physical properties and very high sedimentary rocks. These units are known to
solubility of evaporite rocks, human activities contain pseudokarst features; however, areas
such as fluid injection or leaking well casings with potential for such features are probably
can induce large solution voids. Collapses of more widespread. The second unit represents
these voids are known to propagate up to the areas of volcanic rock that may contain lava
surface from depths of more than 1,000 feet. tubes (vulcanokarst) and/or layered volcanic
rocks with integrated fast groundwater flow
systems.

23
Figure 3. Simplified map of areas underlain by evaporite rocks at depths up to 7,000 feet. Arid regions receive less than about 30
inches of annual precipitation.
Map of Pseudokarst Areas in Alaska and The cold climate of Alaska results in
Hawaii extensive regions of permafrost, or permanently
Because of the relatively recent and ongoing frozen ground (Brown and others, 2002) (fig.
volcanism in both Alaska and Hawaii, they 5A). As the climate warms and these areas
contain widespread, relatively young (Miocene experience melting, landforms and hydrologic
age or younger) lava flow deposits that contain conditions that are analogous to karst terrains,
lava tubes and other pseudokarst features (fig. such as sinkholes and sinking streams result.
5A, B). Lava tubes form most readily and Because this phenomenon is related to melting
extensively in low-viscosity lava flows, of ice rather than solution of bedrock, these
generally of basaltic composition. Lava tube permafrost features are considered a category of
caves are relatively short-lived geologic features pseudokarst (Halliday, 2007) and termed
as they are 1) either filled by succeeding thermokarst (Sweeting, 1973, p. 308).
eruptive lavas, or 2) as near surface features they The OFR describes several classes of
are susceptible to erosion and collapse of the thermokarst terrain, on the basis of ice quality
overlying rocks. Lava tubes are generally not and overlying sediment thickness.
found in rocks older than Miocene age, and this
age was used as a cutoff for selecting volcanic
flow units for this map.

24
Figure 4. Areas of known pseudokarst features in the contiguous United States.

SPATIAL STATISTICS drilling is not included in these statistics. These

Simple spatial statistics were used to calculate values underestimate the area of the United
the percentage area of the United States that is States underlain by karst aquifers, a major
underlain by the areas of karst and pseudokarst source of potable water for the nation. About 2
defined in the OFR. These statistics are percent of the United States is underlain by
exclusive of Puerto Rico and the U.S. Virgin sedimentary rocks prone to pseudokarst features
Islands. The results are shown on figure 6. In developed primarily by piping. Almost 4 percent
summary, about 25 percent of the United States of the country, and entirely restricted to Alaska,
is underlain by rocks or sediments, as previously is underlain by sediments and permafrost prone
described, with a potential for karst or to development of thermokarst. Lastly, about 1.5
pseudokarst features. About 18 percent of the percent of the total area of the United States,
United States is underlain by soluble rocks, of which includes areas in the western part of the
which 16 percent consists of carbonate rocks and contiguous United States, Alaska, and Hawaii,
the remaining 2 percent are evaporite rocks. The are underlain by volcanic rocks with potential
area of the nation underlain by basins where for lava tubes.
evaporite rocks may be encountered by deep

25
Figure 5. Simplified map of areas that may contain lava tubes or thermokarst pseudokarst features, A, Alaska; and B, Hawaii.

Figure 6. Chart showing proportion of the area of the 50 United States underlain by potentially karstic and pseudokarstic rocks.

26
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states: Mineral Resources Program, U.S.
Daley, C., and Taylor, G., 2000, United States
Geological Survey, Reston, VA., accessed
average annual precipitation, 1961-1990: Spatial
02/010/2014, at
Climate Analysis Service, Oregon State
http://mrdata.usgs.gov/geology/state/
University, accessed 5/22/2013 at
http://www.prism.oregonstate.edu/pub/prism/map Veni, G., 2000, Revising the karst map of the United
s/Precipitation/Total/U.S./us.gif States: Journal of Cave and Karst Studies, v. 64,
p. 45-50.
Davies, W.E., Simpson, J.H., Ohlmacher, G.C., Kirk,
W.S., and Newton, E.G., 1984, Engineering Weary, D.J., and Doctor, D.H., in press, Karst in the
aspects of karst: U.S. Geological Survey, United States of America: A digital map
National Atlas of the United States of America, compilation and database: U.S. Geological
scale 1:7,500,000. Survey Open-File Report.
Epstein, J.B., and Johnson, K.S., 2003, The need for Williams, P.W., and Ford, D.C., 2006, Global
a national evaporite-karst map, in Johnson, K.S., distribution of carbonate rocks: Zeitschrift für
and Neal, J.T., eds., Evaporite karst and Geomorphologie, Supplement, v. 147, p. 1-2.
engineering/environmental problems in the
United States: Oklahoma Geological Survey
Circular 109, p. 21-30.
Halliday, W.R., 2007, Pseudokarst in the 21st
century: Journal of Cave and Karst Studies, v.
69, no. 1, p. 103–113.
Palmer, A.N., 2000, Hydrogeologic control of cave
patterns, in Klimchouk, A.B., and others, eds.,
Speleogenesis—evolution of karst aquifers:
National Speleological Society, Huntsville,
Alabama, p. 77-90.
Palmer, A.N., and Palmer, M.V., eds., 2009, Caves
and karst of the USA: National Speleological
Society, Huntsville, Alabama, 446 p.
Shade, B.L., 2002, The genesis and hydrology of a
sandstone karst in Pine County, Minnesota:
Minneapolis, University of Minnesota, M.S.
thesis, 131 p., 8 tables.
Soller, D.R., Packard, P.H., and Garrity, C.P., 2012,
Database for U.S. Geological Survey Map I-1970
-- Map showing the thickness and character of
Quaternary sediments in the glaciated United
States east of the Rocky Mountains: U.S.
Geological Survey Data Series 656, available at
http://pubs.usgs.gov/ds/656/.
27
Groundwater Availability of the Floridan Aquifer System
By Andrew M. O’Reilly1 and Eve L. Kuniansky2
1
U.S. Geological Survey, Florida Water Science Center, 12703 Research Parkway, Orlando, FL 32826
2
U.S. Geological Survey, Water Mission Area, 1770 Corporate Drive, Suite 500, Norcross, GA 30093

Abstract
The Floridan aquifer system is one of the most productive aquifers in the world and extends
throughout 100,000 square miles of the southeastern United States in Florida and parts of Georgia,
Alabama, South Carolina, and Mississippi. The Floridan aquifer system has been used since the late
1800s and currently is the primary source of water for almost 10 million people (in 2000) in parts of
Florida, Georgia, Alabama, and South Carolina. Water from the Floridan aquifer system is used for
public, domestic, and industrial water supply, and almost 50 percent of withdrawals are used for
irrigation. Where water in the Floridan aquifer system is not potable, shallower aquifers generally are
used for water supply, most notably the Biscayne aquifer, which is the sole source of fresh groundwater in
southeast Florida.
The U.S. Geological Survey (USGS) Groundwater Resources Program
(http://water.usgs.gov/ogw/gwrp/) is assessing groundwater availability in areas of critical importance
across the Nation. The objectives of the current study on the Floridan aquifer system are to quantify
current groundwater resources, evaluate possible groundwater resource changes over time, and provide
tools to better understand aquifer system responses to future human and environmental stresses. This
regional study of the Floridan aquifer system will provide numerous benefits, including an updated
hydrogeologic framework incorporating new data available since the USGS Regional Aquifer-System
Analysis study completed in the 1980s, regional and subregional water budgets, and a modern, system-
wide groundwater flow model that can be used to assess the effects of human and environmental stresses
on the aquifer system. Further information on the approach and current products of the study are available
at http://fl.water.usgs.gov/FASWAM/.
The Floridan aquifer system is a sequence of carbonate rocks more than 3,000 feet (ft) thick in
southern Florida, thinning to less than 200 ft at the northern extent in southern Alabama, southeast
Georgia, and southern South Carolina where it grades into clastic coastal plain sediments. A thick
sequence of sand, silt, and clay confine the Floridan aquifer system over much of its extent; in these areas
recharge to the aquifer system generally is less than 1 inch per year (in/yr). Where the Floridan aquifer
system is thinly confined (less than 100 ft thick), karst terrain is common, leading to semiconfined to
unconfined conditions and recharge rates generally ranging from 10 to 25 in/yr. The karst geologic
characteristics contribute to specific aquifer vulnerabilities, including groundwater/surface-water linkage
and saline-water encroachment in some areas.

28
 Stresses on the Floridan aquifer system include land-use change and associated groundwater
withdrawals, climate change, and sea-level rise; the effects of these stresses may be magnified by the
vulnerabilities of the aquifer system in certain areas. For example, increased irrigation of crops in the
Dougherty Plain (southwest Georgia, southeast Alabama, and adjacent areas of northern Florida) have led
to streamflow and water-level decreases in the ecologically sensitive Apalachicola-Chattahoochee-Flint
River Basin. Reduction or cessation of flow at some springs, sinkhole collapse and lake drainage, and
reduced lake and wetland levels have occurred in central and northern Florida since the 1950s while total
groundwater withdrawals from the Floridan aquifer system increased nearly fourfold. In central Florida,
developed land area has increased 160 percent, and cropland/pasture has decreased 40 percent from 1977
to 2006. Such land-use changes may influence the partitioning of rainfall into evapotranspiration, runoff,
and infiltration, thus affecting short-term and long-term groundwater levels and flows. Also, changing
land-use practices have led to degraded water quality, particularly elevated nitrate concentrations in
groundwater (wells) and springs. Saline water encroachment has occurred in localized coastal areas of
South Carolina, Georgia, and northeast Florida, where groundwater movement is largely controlled by
geologic features, such as paleochannels, fractures, solution-enlarged joints, or paleocollapse structures.
Climate change and sea-level rise may affect the future quantity of available groundwater in the
Floridan aquifer system. Water budget analysis indicates the system is largely meteorologically driven.
Water demands are likewise substantially influenced by weather owing to the prevalence of groundwater
withdrawals for irrigation. Predevelopment conditions consisted of 53 in/yr of rainfall, 37 in/yr of
evapotranspiration, 16 in/yr of runoff, and less than 0.5 in/yr of offshore discharge. In 2000, groundwater
withdrawals totaled nearly 4 billion gallons or 0.9 in/yr, representing 2 and 6 percent of predevelopment
evapotranspiration and runoff, respectively. Therefore, the Floridan aquifer system likely will be sensitive
to future weather extremes and climate change, while sea-level rise may affect coastward hydraulic
gradients. Even though total groundwater withdrawals are a relatively small component of the water
budget, these withdrawals may be sufficient to reduce the frequency at which the system is “filled and
reset,” thus causing long-term declines in water levels and flows in certain areas.

29
Assessing Potential Impacts from a Proposed Phosphate Mine on
Ashley Spring, a Unique Karst Public Water Supply in the Uinta
Mountains, Uintah County, Utah
By Lawrence E. Spangler
U.S. Geological Survey, 2329 Orton Circle, Salt Lake City, Utah 84119

Abstract
Ashley Spring is one of the largest springs in Utah, with a reported discharge that ranges from about
15 cubic feet per second (ft3/s) at low flow (base flow) to at least 80 ft3/s during the snowmelt runoff
period in May and June. The spring rises from the Weber Sandstone alongside the channel of Ashley
Creek in the bottom of Ashley Gorge near its outlet along the southeast flank of the Uinta Mountains.
Water from the spring is a public supply for the nearby city of Vernal and residents in several rural
communities in Ashley Valley, as well as for irrigation. In 2010, an estimated 3,800 acre-feet or about 3.4
million gallons per day were withdrawn from the spring for municipal use.
Previous studies of the hydrology of Ashley Spring and adjacent springs have shown a complex
groundwater flow system along the southeast flank of the Uinta Mountains. Dye-tracer tests carried out
primarily in the late 1960s and late 1970s indicate that most of the flow discharging from Ashley Spring
originates from the Dry Fork watershed more than 10 miles to the west and also from a losing reach in
Ashley Creek about 7 miles upstream of the spring. Water losses in the Dry Fork and Ashley Creek
drainages occur through glacial and alluvial deposits that overlie the Madison Limestone. Fractures in the
Weber Sandstone, which overlies the Madison Limestone, allow upward movement of water back to the
surface at Ashley and other springs.
Proposed mining of the Park City Formation near Ashley Spring has raised concerns among county
leaders and local citizens that mining may impact the quality and discharge of the spring water. Possible
impacts of the mining operation on the hydrologic system include effects on the water quality of the
spring by downward movement of water from the Park City Formation through the Weber Sandstone with
constituents related to mining activities, such as phosphate and selected trace elements; possible effects
on the water quality of the Madison Limestone aquifer, from which the spring discharges; and the effects
of blasting on the groundwater flow system. This study expands upon previous studies and is conducting
additional investigations to improve our understanding of the recharge (contributing) area for Ashley
Spring, and the relation between groundwater movement in the Madison Limestone aquifer and the
overlying Weber Sandstone, to evaluate the potential impacts of the proposed phosphate mine on the
groundwater system.
INTRODUCTION Although previous studies have documented the
Proposed mining of the Park City general boundaries of the Ashley Spring
(Phosphoria) Formation near Ashley Spring, groundwater system to the west and northwest,
about 12 miles north of Vernal, Utah, has raised additional studies are needed to further identify
concerns among county leaders and local sources of water to the spring and better define
citizens of the effects that the mining may have groundwater basin boundaries between Ashley
on the quality and discharge of the spring water. and adjacent groundwater basins, particularly
Groundwater travel times of only a few days the Brush Creek Spring basin to the northeast.
have been documented through the Madison An understanding of the directions and rates of
Limestone aquifer that supplies water to the groundwater flow in this area would allow a
spring (Maxwell and others, 1971), but better assessment of the potential for the
relatively little data are available with respect to proposed mining operation to affect the
groundwater movement in the overlying units in groundwater system supplying Ashley Spring.
this area, particularly the Weber Sandstone. Further, Uintah County is in the process of
30
updating the groundwater source-protection area conglomeratic, quartzitic sandstones and
for Ashley Spring, and this study will provide interbedded shales of the billion-year old Uinta
additional information to help fulfill the Mountain Group (Stokes, 1988). Late Paleozoic-
recommendations outlined in the source- and Mesozoic-age rocks unconformably overlie
protection management plan for the spring. the Uinta Mountain Group along the flanks of
the uplift and generally dip away from the core
To address these concerns, the U.S.
in all directions. Rocks along the southeast flank
Geological Survey in cooperation with Uintah
of the uplift, including the Ashley Creek-Brush
County, is conducting a 3-year study that began
Creek area, generally dip about 10 to 20 degrees
in the spring of 2013, to evaluate the
to the south-southeast, except in areas of faults
vulnerability of the Ashley Spring groundwater
and folds, where they can be considerably
flow system and the potential effects of the
steeper (Kinney, 1955).
proposed phosphate mining operation on the
spring. The objectives of this study are to 1) Superimposed on the larger Uinta Mountain
refine the contributing area of the groundwater Anticline are regional faults and fractures that
flow system for Ashley Spring and to understand generally trend from west to east, and from
its relation/connection to adjacent basins and northwest to southeast (Maxwell and others,
downgradient areas along the southeast flank of 1971). The South Flank fault between Dry Fork
the Uinta Mountains, 2) evaluate groundwater and Ashley Creek trends generally north 70
movement in the Madison Limestone aquifer degrees east and forms a boundary between the
and overlying geologic units in the vicinity of quartzitic rocks of the higher Uintas and
the spring, particularly the Weber Sandstone, overlying Paleozoic rocks (Sprinkel, 2006).
and the potential for downward movement of Water flowing off the quartzitic rocks and onto
water from the Park City Formation through the carbonate rocks typically loses to the subsurface
Weber Sandstone, and 3) assess the potential for within a short distance of this boundary (fig. 1).
blasting and other mining activities to affect the The Deep Creek fault zone between Mosby Sink
groundwater system that supplies water to and Dry Fork (not shown on figure 1) consists of
Ashley Spring. This paper provides an overview a series of parallel faults that trend generally
of the hydrogeology along the southeast flank of northwest at about 60 degrees (Maxwell and
the Uinta Mountains in the vicinity of Ashley others, 1971). North-northwest trending
Spring and discusses the multi-phased approach fractures are also present throughout the area,
that will be used to fulfill the objectives outlined often associated with localized anticlinal
above. structures, such as those present in both the
GEOLOGY AND KARST DEVELOPMENT Ashley Creek and Big Brush Creek drainages.
The trend of many of the major surface
The Uinta Mountains (Uintas) are part of the drainages in the southeastern part of the Uintas,
Middle Rocky Mountains physiographic as well as the location of large springs such as
province and are an east-west trending anticlinal Ashley and Brush Creek, have been influenced
structure. The range was initiated in the early by regional fault and fracture systems (Maxwell
Tertiary Period (Paleocene) and intermittently and others, 1971).
uplifted into the Miocene (Untermann and
Untermann, 1969). Rocks making up the Uintas The principal carbonate and cave-forming
are Precambrian to Tertiary in age, with a units in the Uinta Mountains are Mississippian
distinct absence of Ordovician- and Silurian-age in age and include the Madison and Deseret
rocks; outcrops of Devonian-age rocks are found Limestones, and the Humbug Formation
only on the western edge of the mountain range. (Sprinkel, 2006). In the study area, the Madison
Unlike most other mountain ranges that have Limestone is the predominant unit. These
cores of igneous and metamorphic rocks, the formations typically consist of light to dark gray,
core of the Uintas is composed of reddish

31
Figure 1. Location of major springs along the southeast flank of the Uinta Mountains near Vernal, Utah, results of dye tracing,
and location of proposed phosphate mine.

thin- to thick-bedded, cherty (siliceous), and Sandstone in the vicinity of Ashley Spring is the
locally brecciated, dolomitic limestones. Permian-age Park City Formation. The
Average thickness of the Mississippian-age formation is quite variable in lithology and
limestones is about 900 to 1,200 feet. The consists of light gray to brown sandy dolostone
overlying Pennsylvanian-age Weber Sandstone interbedded with reddish-orange siltstone and
is a very prominent rock unit in the eastern dark gray phosphatic shale (basal 20 feet)
Uintas, forming many of the canyon walls in the (Haddox and others, 2010). Thickness of the
major drainages, such as in Ashley Gorge and Park City Formation ranges from 50 to 145 feet.
Big Brush Gorge (fig. 2). The formation ranges
Karst features are sporadically developed in
from about 1,000 to 1,275 feet in thickness in
the eastern Uintas, largely because of the limited
the study area and consists of predominantly
exposure of carbonate rocks. Losing or sinking
massive, tan to white cross-bedded sandstone
streams can be found in many drainages,
with minor amounts of sandy limestone (Haddox
particularly where surface streams originating on
and others, 2010). Many of the large springs in
the quartzitic core of the mountains at higher
the region, including Ashley and Brush Creek,
elevations cross the band of limestones that
discharge upward through fractures in the Weber
flank the core, a transition zone roughly defined
Sandstone (fig. 3). Overlying the Weber
32
Figure 2. Outcrop of the Weber Sandstone in Big Brush Figure 3. Near-vertical northwest-trending fractures in the
Gorge. Fractures in the sandstone allow water to discharge Weber Sandstone. Fractures such as these likely serve as
at the surface at Brush Creek Spring, located in the bottom pathways for upward movement of water from the Madison
of the canyon at lower right. Limestone to the surface at Ashley Spring.

by the South Flank fault (fig. 1). Both Big Brush

Creek and Little Brush Creek Caves were
formed by entrenchment of surface streams
flowing off the insoluble core of the Uintas onto
the soluble limestones, which has resulted in the
development of blind valleys at the entrances of
both caves (fig. 1). Streamsinks or “sinks” also
have formed in the drainages of Dry Fork and its
tributaries, and in the upper reaches of Ashley
Creek (fig. 4), where they are capable of
swallowing the entire streamflow except during
periods of snowmelt runoff and possibly during
locally intense rainfall events. In the Dry Fork
drainage, glacial moraines appear to have
Figure 4. Ashley Creek Sink. All flow in streambed,
impounded or otherwise influenced the location estimated to be at least 10 ft3/s, abruptly sinks through
and development of the streamsinks (Godfrey, boulders into the underlying Madison Limestone, which
1985). The largest springs in the southeastern then conducts water along solution-enlarged fractures and
part of the Uintas also discharge within or along (or) down dip along bedding planes to Ashley Spring, 7
the principal drainages. On the basis of average miles to the south.
discharge, Ashley and Brush Creek Springs are
elevations where it discharges at large springs
considered second magnitude springs (10 to 100
along the major drainages. Because the aquifer
cubic feet per second [ft3/s]) (Meinzer, 1927).
is generally confined (under artesian pressure)
HYDROLOGY near the springs, groundwater movement is
typically upward from the Madison Limestone
Groundwater movement along the southeast aquifer along fractures and faults in the
flank of the Uintas is generally to the south and overlying Pennsylvanian-age rocks, particularly
southeast, following the geologic structure. the Weber Sandstone. White (1979) calculated
Direction of movement is influenced in large the depth to the top of the Madison Limestone in
part by structural dip of the rocks, regional the vicinity of Ashley and Brush Creek Springs
fractures and faults, and localized breccia zones. to be as much as 2,000 feet by extrapolating the
Water generally moves down dip or along faults structural dip of the rocks. On the basis of dye-
in the Mississippian-age limestones to lower tracer tests carried out in the mid-1940s and
mid-1950s, and in the late 1960s and 1970s
33
(table 1), at least five major groundwater basins
have been delineated along the southeast flank
of the Uintas. A brief summary of the hydrology
of four of these basins is as follows.
Ashley Spring
Ashley Spring rises from boulder alluvium
on the east side of Ashley Creek in the bottom of
Ashley Gorge near its outlet. The main spring is
covered and partly diverted to two water
treatment plants for drinking-water and other
public-supply uses in the city of Vernal as well
as several smaller communities in the region.
Water not diverted for public supply is Figure 5. Overflow from Ashley Spring. Water not
discharged from the springhouse and rejoins diverted for public supply is discharged from springhouse
Ashley Creek downstream (fig. 5). Several other back into Ashley Creek.
springs discharge directly from bedrock outlets
on the west side of the channel, and
subsequently flow into Ashley Creek (fig. 6).
Water discharging from the west side of the
channel is not used for public supply but is
withdrawn from the channel farther downstream
for use in irrigation. Total discharge of all
springflow is reported to range from about 15
cubic feet per second (ft3/s) at base flow to about
80 ft3/s following snowmelt runoff (Mundorff,
1971). Historic dye tracing (Maxwell and others,
1971) indicates that a large part of the flow
discharging from Ashley Spring originates from
the Dry Fork Canyon watershed, which also
supplies water to Dry Fork Springs (see next
Figure 6. Ashley Spring discharges from the west and east
section) (table 1). During periods when Dry sides of Ashley Creek (foreground). Flow from the west
Fork Springs do not flow, all flow from the sinks side (shown here) discharges from at least four major and
in the Main Fork of Dry Fork is assumed to several smaller outlets.
discharge at Ashley Spring. Water losing in Dry
Fork and its tributaries appears to move through Dry Fork Springs
glacial and alluvial deposits into the underlying
Madison Limestone aquifer to Ashley Spring Dry Fork Springs rise in the bed of Dry Fork
where fractures in the overlying Weber about 2 miles upstream of the community of Dry
Sandstone allow upward movement of water Fork (fig. 1). The springs discharge from the
back to the surface. These fractures are probably Weber Sandstone upward through alluvium at
related to an anticlinal structure in this area, several locations in the channel. Discharge of
which has likely influenced the discharge point the springs normally is zero, but during
of the spring. Part of the flow path to Ashley snowmelt runoff is estimated to be as much as
Spring from Dry Fork may be along segments of 80 ft3/s (Mundorff, 1971). Estimates of flow
the Deep Creek fault zone. Results of dye from current meter measurements indicate that
tracing have also shown that an additional springflow generally begins once surface flow in
source of water to Ashley Spring originates from the three principal tributaries of Dry Fork
a losing reach in Ashley Creek about 7 miles upstream of the springs exceeds about 40 ft3/s
upstream of the spring (Godfrey, 1985). (Maxwell and others, 1971). Because water from

34
Table 1. Results of dye-tracer tests for selected karst springs in the southeastern Uinta Mountains.

[BOR, Bureau of Reclamation; SCS, Soil Conservation Service; USGS, U.S. Geological Survey; USFS, U.S. Forest Service]

Linear
Date of Agency Travel
Input site Altitude Altitude Relief dis- 1
test conduct- Output(s) site(s) time
(feet) (feet) (feet) tance
ing test (days)
(miles)

6/1968 BOR, SCS Little Brush 8,100 Brush Creek at 6,120 1,980 5.6 2.2
Creek at cave phosphate mine
8/1967 BOR, SCS Big Brush Creek 8,180 Brush Creek at 6,120 2,060 5.9 2.6
above cave phosphate mine
2/1956 USGS Mosby Sink 9,160 Deep Creek Spring 7,160 2,000 6.4 14
mid- BOR Dry Fork Sinks 8,080 Dry Fork Springs 6,860 1,220 6.7 No
1940s? data
8/1967 BOR, SCS Dry Fork Sinks2 8,080 Ashley Spring 6,260 1,820 10.5 2.8
(Merkeley Park)
10/1967 BOR, SCS Main Dry Fork3 8,080 Ashley Spring 6,260 1,820 10.5 3.3
(Blanchett Park) (Merkeley Park)
4
8,080 Deep Creek Spring 7,160 920 6 20
5/1979 USFS Dry Fork Sinks 8,080 Brush Creek Spring5 6,120 1,960 15.8 14
8/1978 USFS Ashley Creek 7,800 Ashley Spring 6,260 1,540 7.0 9
(Red Pine) Brush Creek Spring 6,120 1,680 8.1 9
1
Groundwater travel time based on first appearance of dye, whether detected in water samples or on activated charcoal.
2
Dye was injected into Main Fork, North Fork, and Brownie Canyon simultaneously. Calculations based on Main Fork Sinks.
3
Dye was injected upstream of Main Fork Sinks and initially traveled on surface for 8.3 miles (17 hours) before losing at sinks.
4
Distance uncertain; losing reach between Mosby Sink and Dry (Main) Fork Sinks.
5
Tracer test conducted during high-flow conditions.
Discharge of the spring is reported to range from
Dry Fork Sinks and its tributaries also 3 to 15 ft3/s, with higher flows during snowmelt
discharges at Ashley Spring, Dry Fork Springs runoff (Mundorff, 1971). Results of dye tracing
may represent a high-level or overflow point indicate that water diverted into Mosby Sink,
within the Ashley Spring groundwater flow located along a tributary to the Main Fork of the
system. Detailed studies by Maxwell and others Dry Fork drainage, resurges at Deep Creek
(1971) indicate that water losing from Dry Fork Spring 6 miles southeast of the sink (fig. 1).
and its tributaries, between 5 and 7 miles Actual travel time of groundwater from Mosby
upstream of the springs, flows through conduits Sink to Deep Creek Spring was about 14 days
in the underlying Madison Limestone aquifer (table 1). Because water discharging from the
and thence upward along fractures in the spring is confined, however, an increase in
overlying rocks to discharge at the surface, springflow was observed in only 3 hours, in
rather than through the fluvioglacial channel response to a pressure wave generated by the
deposits (sub-channel flow) to the springs. The diverted water. Some of the base flow of Deep
flow system feeding Dry Fork Springs is likely Creek Spring also appears to originate directly
developed along segments of the Deep Creek from the Main Fork of Dry Fork (fig.1).
fault zone (Maxwell and others, 1971, fig. 2). Groundwater flow from Mosby Sink and Dry
Fork to Deep Creek Spring is probably along
Deep Creek Spring northwest-trending faults that are associated
with the Deep Creek fault zone. These faults
Deep Creek Spring rises along a hillside also serve as pathways for upward movement of
from the base of the Triassic-age Moenkopi water from the underlying Madison aquifer.
Formation on the upthrown side of a northwest-
trending fault (Maxwell and others, 1971).
35
Brush Creek Spring Fluorescent dye tracing will be used to
establish hydrologic connections between
Brush Creek Spring rises in the bottom of focused points of recharge (surface-water inputs)
Big Brush Gorge near its outlet. The spring and Ashley Spring, particularly in areas where
discharges from the lower part of the Weber data are sparse with regard to groundwater
Sandstone where localized fracturing along the movement, and also will be used to determine
axis of an anticline has permitted upward better estimates of groundwater travel time. If
movement of water from the underlying possible, tracer tests also will be used to refine
Madison Limestone aquifer back to the surface. the boundary between groundwater movement to
Groundwater movement to Brush Creek Spring Ashley and Brush Creek Springs. A dye-tracer
is likely down the structural dip of the Madison study was carried out in September 2013 to
Limestone to the spring. Estimated discharge of verify a previous tracer test that was done
Brush Creek Spring ranges from 3 to about 200 indicating a hydrologic connection between
ft3/s (Mundorff, 1971), making this one of the Ashley Creek Sink and Ashley and Brush Creek
largest springs in Utah. Results of dye tracing Springs (fig. 1, table 1). Results of this test are
during the summers of 1967 (Big Brush Creek) currently being evaluated.
and 1968 (Little Brush Creek) indicate that
much of the water discharging from the spring Ten water samples were collected from
originates from both of these creeks via Big and selected springs and wells in bedrock aquifers in
Little Brush Creek Caves (fig. 1, table 1). These the study area in 2013 and analyzed for major
dye tests confirmed previous indications of this ions, nutrients, and a suite of trace elements that
relation when reservoir releases upstream of are often associated with phosphate mining in
Little Brush Creek Cave resulted in substantial other areas. These include aluminum, barium,
increases in the discharge of Brush Creek Spring strontium, arsenic, selenium, uranium, cadmium,
(Maxwell and others, 1971). Dye travel time chromium, lead, copper, nickel, and zinc. Water
from Big Brush Creek at the Red Cloud Loop samples also will be collected from Ashley
Road above the entrance to Big Brush Creek Spring during base flow, moderate flow, and
Cave, to Highway 191 where it crosses over spring (peak) runoff, and analyzed for major
Brush Creek, about 3.5 miles downstream from ions and trace elements to establish baseline
the spring, was about 63 hours. Dye travel time conditions for the natural system prior to
from Little Brush Creek Cave to Brush Creek at potential mining. Nitrate, orthophosphate, and
Highway 191 was about 52 hours. Although the phosphorus samples will be analyzed to
majority of flow from Brush Creek Spring determine background (native) concentrations
appears to originate from the Brush Creek for comparison with natural concentrations of
drainage basin, additional dye tracing also has these constituents in the Park City Formation,
indicated apparent hydrologic connections the lower part from which phosphate ore would
between Dry Fork Sinks (at high flow) and be mined. Historic chemical data for Ashley
Brush Creek Spring, and Ashley Creek Sink and Spring will be examined to evaluate trends or
Brush Creek Spring (Godfrey, 1985) (fig. 1). variations in water quality over time. In addition,
water-quality data will be compiled and water
DISCUSSION samples collected from other springs and wells
in the Weber Sandstone, Park City Formation,
During the 3-year study beginning in April and other potential water-bearing units in the
2013, a multi-phased approach will be used to vicinity of Ashley Spring and analyzed for the
further our understanding of the hydrology of same suite of constituents to characterize
Ashley Spring and the hydrology of overlying groundwater in these formations. The chemistry
geologic units in the vicinity of the spring. The of groundwater from these units will then be
approach includes dye tracing, water sample compared to the water chemistry of the Madison
collection and analysis, discharge measure- Limestone aquifer. Samples for selected isotope
ments, water-level measurements, and analysis analyses may be collected to further assist in
of seismic data. determining source areas for water discharging
36
from Ashley Spring (deuterium/oxygen-18) and that can be used in conjunction with the
for possible dating of the groundwater in the upstream gage to determine only the flow from
Madison Limestone, Weber Sandstone, and Ashley Spring, in addition to withdrawals for
other aquifers in the study area (tritium/helium, public supply. A continuous record of discharge
sulfur-35, and chlorofluorocarbons). from the spring over the study period will also
establish a baseline to which future changes in
Preliminary data indicate that dissolved- flow from natural and human-induced activities
solids concentrations in water from Ashley and can be compared.
Brush Creek Springs (Madison Limestone
aquifer) during base-flow conditions is low (less Water levels in all bedrock aquifers in the
than 150 milligrams per liter [mg/L]) compared vicinity of Ashley Spring will be measured
to water from the overlying Weber Sandstone during the spring and fall to assess the
and other bedrock units in the area, which tends magnitude of water-level changes and for
to be noticeably higher (greater than 200 mg/L). evaluating hydraulic-head relations between the
The source waters for these springs, which aquifers. In particular, water-level data will be
originate on the quartzitic core of the mountain collected from wells completed in the Weber
range, can be very low in dissolved solids (less Sandstone aquifer and compared to water levels
than 50 mg/L). Concentrations of trace elements in the underlying Madison Limestone aquifer to
and nutrients from these springs were also very determine hydraulic-head relations (differences
low during base-flow conditions and below state in water levels) between the units. These data
drinking-water standards. In addition, would help to assess the potential for vertical
continuous (1- and 2-hour intervals) movement of water between the formations,
measurements of temperature and specific especially in the confined portions of the
conductance have been made at Ashley and aquifers. An evaluation of the potential for
Brush Creek Springs since April and November downward movement of water from the Park
2013, respectively, to document changes in these City Formation into and through the Weber
parameters with changes in discharge and to Sandstone, and thus, the ability for selected
further assess groundwater travel times to the constituents from phosphate mining to move
springs in response to precipitation events. downward into the discharge zone of the spring
Between May 2013 and March 2014, specific within the Weber Sandstone or the underlying
conductance and temperature of water from Madison Limestone also will be done. As part of
Ashley Spring was quite variable, and ranged this assessment, data on fracture trends and
from 94 microSiemens per centimeter (µS/cm) fracture density will be compiled for the Weber
at 25 oC to 168 µS/cm, while temperature ranged Sandstone to evaluate potential pathways along
from about 6.8 to 8.7 oC. which downward moving groundwater could
occur.
Discharge measurements of Ashley Spring
will be used to evaluate response of the Finally, water-quality and hydrologic data
groundwater system to surface events such as from the adjacent Brush Creek Spring basin will
snowmelt runoff and rainfall and to help with be compiled for comparison to that from the
determining the potential size of the drainage Ashley Spring basin. The geologic and
basin needed to supply the discharge of the hydrologic setting of Brush Creek Spring is very
spring. Because of the numerous outlets and similar to that of Ashley Spring, and the location
diversions for Ashley Spring, an accurate of Brush Creek Spring in proximity to the
discharge measurement of the spring had not Simplot phosphate mining operation about 6
been determined previously. Therefore, a miles northeast of Ashley Spring (fig. 1), could
streamflow gage was installed for the study on provide a useful comparison (analog) with
Ashley Creek upstream of Ashley Spring and its regard to the hydrologic relation between the
outlets on the west side of the channel. Madison Limestone and the overlying Weber
Downstream of the outflow from Ashley Spring, Sandstone in this area. This relation could also
a long-term streamflow gage records discharge allow a better assessment of the potential for
37
downward movement of water from the Park Sprinkel, D.A., 2006, Interim geologic map of the
City Formation through the Weber Sandstone Dutch John 30’ x 60’ quadrangle, Daggett and
and thus, the potential for the proposed mine to Uintah Counties, Utah, Moffat County, Colorado,
affect water quality in the area near Ashley and Sweetwater County, Wyoming: Utah
Geological Survey Open-File Report 491 DM, 3
Spring. In addition, to evaluate the potential
pl.
effects of blasting on the hydrologic system
supplying Ashley Spring, records from Stokes, W.L., 1988, Geology of Utah: Utah Museum
seismograph stations located near the Simplot of Natural History Occasional Paper No. 6, 307 p.
phosphate mine along with blasting records from White, W.B., 1979, Karst landforms in the Wasatch
the mine, will be compared to discharge records and Uinta Mountains, Utah, in Alpine karst
and continuous water-quality data for Brush symposium: National Speleological Society
Creek Spring. Identifying changes or Bulletin, v. 41, no. 3, p. 80-88.
fluctuations in these parameters with mine- Untermann, G.E., and Untermann, B.R., 1969,
related activities could then be used to evaluate Geology of the Uinta Mountain area, Utah–
the potential for mining-induced disturbances at Colorado, in Lindsay, J.B., ed., Geologic
the proposed mine site to affect the hydrologic guidebook of the Uinta Mountains–Utah’s
system within the Madison Limestone or the maverick range: Intermountain Association of
fracture network within the Weber Sandstone at Geologists and Utah Geological Society 16th
Ashley Spring. Annual Field Conference, p. 79-86.

REFERENCES

Godfrey, A.E., 1985, Karst hydrology of the south

slope of the Uinta Mountains, Utah, in Picard,
M.D., ed., Geology and energy resources, Uinta
Basin of Utah: Utah Geological Association
Publication 12, p. 277–293.
Haddox, D.A., Kowallis, B.J., and Sprinkel, D.A.,
2010, Geologic map of the Steinaker Reservoir
quadrangle, Uintah County, Utah: Utah
Geological Survey Miscellaneous Publication 10-
3, 2 pl.
Kinney, D.M., 1955, Geology of the Uinta River–
Brush Creek area, Duchesne and Uintah Counties,
Utah: U.S. Geological Survey Bulletin 1007, 185
p., 6 pl.
Maxwell, J.D., Bridges, B.L., Barker, D.A., and
Moore, L.G., 1971, Hydrogeology of the eastern
portion of the south slopes of the Uinta
Mountains, Utah: Utah Department of Natural
Resources Information Bulletin 21, 54 p.
Meinzer, O.E., 1927, Large springs in the United
States: U.S. Geological Survey Water-Supply
Paper 557, 94 p.
Mundorff, J.C., 1971, Nonthermal springs of Utah:
Utah Geological and Mineralogical Survey,
Water-Resources Bulletin 16, 70 p.

38
 TRACERS

Groundwater Tracing in Arid Karst Aquifers: Concepts and

Considerations
By George Veni
National Cave and Karst Research Institute, 400-1 Cascades Avenue, Carlsbad, New Mexico 88220

Abstract
Few groundwater tracing studies have been conducted in karst aquifers located in arid landscapes.
This paper conceptually evaluates the effects of arid conditions on the injection and detection of tracers,
and the interpretation of the results. Tracer injection is primarily challenged by the absence of a constant
source of flowing water to flush the tracer into and through the aquifer. Artificial recharge is often
needed, with the amounts best determined by examining typical conduit volume, flow, and morphological
conditions of caves in the area. The tracer mass should be calculated based not only on the volume of
discharge from the target spring or well, but also on the volume of discharge in the conduit into which the
tracer is injected. Tracer detection is challenged mostly by the paucity of monitoring sites and factors that
may compromise tracer detection, such as alluviation of springs and adsorption/filtration of the tracer, and
the potentially very slow flow velocities in these aquifers. Interpretation of the results is challenged by
distinguishing hydrologic behavior resulting from low hydraulic gradients/velocities, and ponded and
perched conditions, from inherently different conditions in arid karst such as poorly developed vadose
permeability and sedimentation within the conduit system.
INTRODUCTION provide ample opportunity to test the methods
By the time the Karst Interest Group holds and concepts presented below.
its 2014 workshop at the Headquarters of the CONSIDERATIONS FOR TRACER
National Cave and Karst Research Institute INJECTION
(NCKRI), construction should be underway or Tracer studies were developed in humid
soon-to-begin on NCKRI’s lab. Adjoining, but climates where many streams sink perennially
distinctly separate from the lab, will be a room into karst landscapes. Pouring some substance
specially designed to store dyes for groundwater into the water as it disappeared underground was
tracing. While those of us at NCKRI look an intuitive and easy action to find where the
forward to starting a tracer program to study a flow reappeared, especially when many springs
variety of karst aquifers, our location in were also present.
Carlsbad, New Mexico, also opens another
research opportunity. In arid karst, springs are few and perennial
sinking streams are rare to non-existent. The
Few tracer studies have been conducted in absence of a constant source of water that is
arid karst regions. This raises some important assured to carry the tracer to the water table and
questions that this paper conceptually discusses through the aquifer significantly complicates
as three major categories: consideration for tracing efforts. Two main factors must be
tracer injection and detection, and the considered when injecting tracers in such
implications on hydrological interpretation of regions: tracer mass and water volume.
the results. This paper does not distinguish
between fluorescent dyes, which are most Worthington and Smart (2003) examined the
commonly used in karst groundwater tracing, results of 185 dye-tracing tests in carbonate
and other tracers, although dye traces are often aquifers. They derived the following empirical
used as examples. NCKRI plans on conducting regression equations for calculating the mass of
tracer studies in all climatic settings, but its dye needed and the peak recovery
home base in an arid karst landscape will concentrations:

39
 m = 0.73 (tQc)0.97 (eq. 1) based on relatively few data points and thus,
have lower precision compared to maps and
models of aquifers where data and monitoring
m = 19 (LQc)0.95 (eq. 2) locations are abundant.
The second major factor for tracer injections
where: in arid conditions is water volume, both for
injection and within the aquifer. Without a
m is the mass of dye injected, in grams, constant source of water flowing into the aquifer
t is the time elapsed between injection and from the surface, two methods are available to
peak recovery in seconds, deliver the tracer to the water table. The first is
Q is the output discharge, in cubic meters to place the tracer into the recharge feature and
per second (m3/s), wait for rain. While such a strategy can be
effective for qualitative tracing, quantitative
c is the peak recovery dye concentration for tracing is impossible and even accurate
optimum detection, in grams per cubic meter groundwater velocities cannot be assured if
(g/m3), and multiple storms occur before the tracer is
L is the distance in meters between injection detected.
and recovery points. The second water delivery method involves
Equation 1 is used where t is known, such as artificially injecting water into a recharge feature
from previous tracer tests, and Equation 2 is or well. If the injection site is near a spigot or
used when a particular flow route is traced for fire hydrant, a constant source of water can flush
the first time. the tracer until it is detected. If no constant water
Numerous subsequent studies have shown source is available nearby, water tankers can be
these equations work effectively, but they were used to flush the tracer if the terrain allows. For
not derived from data primarily collected in arid either method to be effective, the morphology
karst aquifers and have been rarely tested in and hydrology of caves in the area should be
such conditions. Inherent in the equations is the evaluated to estimate the likely volume of water
fact that groundwater conduits in karst aquifers necessary to wash the tracer into the aquifer.
are parts of tributary systems and tracers will be That volume should be at least tripled,
diluted by inflows from other conduits. depending on the level of confidence in the
However, in arid karst aquifers, Q needs to be estimate and the depth to the water table.
considered as a percentage of the volume of Additionally, a minimum of two estimated
flow in the conduit where the tracer was injected volumes should be injected as a pre-flush, to
(Qin). If Q = Qin, or is similar in volume, there is saturate the pores in cave sediments and
little or no dilution of the tracer. This may result maximize the speed and volume of tracer
in the discoloration of water supplies and higher transmission to the aquifer. These methods have
costs in materials for no additional benefit. proven effective in karst aquifers in semi-arid
While this problem is conceptually easy to state, climates (e.g., Johnson and others, 2010).
in many cases Qin will not be observable and The volume of water within the aquifer must
may need to be estimated based on tracing also be considered when injecting a tracer—not
experience in the aquifer and from other data, total groundwater storage but the volume within
which often may not exist. the flow path being traced. In karst aquifers,
Human population in a region generally tracers are not dispersed throughout a substantial
correlates to the amount of precipitation. While section of the aquifer, but through the far more
there are concentrated population centers in arid limited volume of the conduits between the
climates, regional populations are usually sparse injection site and where the tracer is likely to
and so too are groundwater data and monitoring discharge. The most effective means of
wells and springs. Consequently, water table evaluating that volume is by studying the
maps and aquifer models, if even available, are aquifer’s springs.
40
 White (1988), for example, describes how evaporates or sinks into the stream channel. The
aquifer and conduit storage may be determined easy availability of aerial photos through Google
from spring hydrographs. In the most simplistic Earth now makes it simpler to find such
sense, a non-flowing spring indicates that a locations for monitoring.
tracer will not be detected until groundwater
Where individual springs cannot be
levels rise and springflow resumes; artificial
identified, tracer detectors can be placed at
recharge is unlikely to result in spring discharge
regular intervals along flowing streams. If no
in most cases. If springflow is seasonal or
tracer is recovered, repeating the trace by
episodic, springflow should be monitored and
injecting a greater tracer mass may be warranted
aquifer behavior quantified prior to conducting a
if the springs emerge below thick alluvial
tracer test to better plan the study and predict the
deposits that could adsorb or otherwise filter the
likely tracer dilution (for calculating the tracer
tracer.
mass for injection) and time until tracer
detection. Without such monitoring, there is a The discrete conduit flow paths in karst
much greater chance that the tracer will be aquifers often make it impractical to trace to
missed by not waiting long enough to detect it. wells, but in arid karst aquifers where few
springs are available for monitoring, wells
CONSIDERATIONS FOR TRACER
DETECTION should be considered important parts of the
tracer detection program whenever possible. If
Too often tracer novices have concluded that all wells within the likely flow paths cannot be
a trace “didn’t work” when in fact they didn’t monitored, wells with indications of intersecting
look in the right place for the tracer and/or didn’t groundwater conduits should be selected (e.g.,
wait long enough for the tracer to arrive. These bit drops, rapid changes in water levels, turbid
factors are especially problematic in arid karst flows, large volume discharge, etc.). By
aquifers. intersecting high-permeability conduits, these
Tracing in humid climates often poses the wells monitor groundwater that has converged
challenge of selecting which, of an abundance of from broader areas, increasing the likelihood of
springs, are most important to monitor within tracer detection.
the time, cost, and logistical constraints of the Perhaps the greatest challenge and
study. The challenge in arid climates is finding uncertainty in tracing arid karst groundwater is
any spring to monitor. Not only are springs determining how long to wait for a tracer to
fewer due to less water, be it by natural causes appear. Tracing experience in the area is helpful
or exacerbated by groundwater pumping, but the but there is probably more variability in arid
dry climate promotes sedimentation of stream karst than in humid karst to offer reliable
channels where springs are most likely to occur. predictability. Hydrograph and other directly
Alluviated springs are common, but with related hydrogeologic data should be collected
comparatively little hydraulic head, fewer and interpreted in advance whenever possible to
distinctly identifiable springs form in thick estimate the probable time frame of tracer
alluvium. Many provide underflow through arrival. It is important that such estimates be
sediments beneath valley floors, which may based on karstic, not Darcian flow conditions.
emerge as surface flow kilometers from the As indicated previously, conduit storage is an
buried spring outlets. The flow of many other important consideration but so are antecedent
springs never rises in ways that can be conditions, lag time between recharge events
connected to the individual springs, and the and spring response, and the degree of spring
presence of some is only vaguely reflected by response to variable precipitation rates and
areas of more lush vegetation in the dry volumes.
landscape.
Some arid springs are poorly known and
unidentified in hydrogeologic surveys because
they flow short distances before the water
41
IMPLICATIONS FOR HYDROLOGICAL would be less aggressive in dissolving the
INTERPRETATION bedrock, which could potentially be overcome
Once a tracer has been detected at a well or with sufficient time, but it is not currently
spring, what does it mean about the hydrology of suggested by maps and observations of most arid
the aquifer? In general, groundwater velocities climate caves beyond typical storage and flow
are slower in arid climates due to less hydraulic from fractures and bedding planes that surround
head, but is that the sole consideration? cave passages.
Jim Nepstad and Paul Burger (personal Alternatively, sediment deposition in low-
communication, 2014) respectively conducted gradient conditions could create other
tracer tests from above Wind Cave, South restrictions to groundwater flow. Travel times
Dakota, in 1993-1996, and Carlsbad Cavern, could be reduced and, as with alluviated surface
New Mexico, in 2005. Mean rainfall in those streams, large volumes of saturated sediment
areas is 44 and 33 cm/year, respectively. Both could adsorb or filter tracers to reduce their
traces exhibited mostly slow and variable detectability.
groundwater velocities and long storage times. Perched and pooled groundwater in conduits
Dye appeared in Wind Cave in as little as 1 day is potentially more common in arid versus
to as long as 5 years. Dye in Carlsbad Cavern humid karst, which will affect tracer detection.
first appeared in 21-40 days and persisted for at Intermittent appearance of a tracer may reflect
least 1.5 years. These slow velocities, at least intermittent flushing of a tracer out of a pool or
when compared to many karst aquifers, is at perched zone by multiple recharge events. It
least partly the result of poor saturation of could also result from a single recharge event
vadose zone fractures. However, other factors converging at and flushing the tracer from the
must also be considered. pool or perched zone at different times. Residual
Both Wind Cave and Carlsbad Cavern are tracer that is trapped within a pool or in perched
hypogenic caves formed independently of groundwater may reappear during subsequent
immediately overlying recharge features. While trace studies and result in misleading data and
overprinting of vadose, epigenic morphologies faulty conclusions if its source is not correctly
occurs in many hypogene caves (for examples, recognized.
see Klimchouk, 2007), the semi-arid climate at Where groundwater is shallow, roots from
these caves has minimized their development. trees occasionally extend into conduits and
Hypogene factors aside, are arid karst aquifers withdraw water. Groundwater is not subject to
recharged at a quantifiably lower rate due to less evaporation, but potentially substantial
water and carbon dioxide (from less vegetation) transpirational losses may occur. Calculations of
available to enhance vadose permeability? conduit groundwater storage from tracer and
Additional future tracer studies may help answer hydrograph data may show exceptional
this question. variability and inaccuracy as a result of such
Goodbar (2009) also reported apparently losses.
slow groundwater velocities in the Carlsbad area Anthropogenic factors must also be
but within the phreatic zone. Do phreatic considered in arid regions, more so than in
conditions in arid climates fundamentally affect humid climates. Groundwater mining
aquifer hydrology? Surface streams in arid (unsustainable groundwater withdrawals) is
regions form anastamosed and braided patterns. more common in arid regions where pumping
Related patterns occur in bedrock conduits of water wells have a proportionally greater impact
caves due to flooding, where groundwater is on aquifer hydrology. As a result, the influence
injected into bedding planes and fractures, where of wells on groundwater movement should
it is stored and dissolves a multitude of conduits increasingly be considered in planning tracer
until the floodwaters drain away. Could similar tests at potential major detection sites and in
patterns significantly form in caves by low- interpreting the time, direction, and volume of
gradient to ponded water? The water chemistry flow.
42
CONCLUSIONS
Tracer studies in arid karst aquifers pose a
variety of challenges and uncertainties not found
in humid climates. This paper presents some of
these factors, which are present throughout all
aspects of a tracer study: injection, detection,
and interpretation. Presently, relatively few
tracer investigations have occurred in arid karst
areas, but future research will refine the
observations of this paper, answer its questions,
and probably provide hydrogeological insights
not currently considered.
REFERENCES
Goodbar, J.R., 2009, Dye tracing oil and gas drilling
fluid migration through karst terrain: A pilot
study to determine potential impacts to critical
groundwater supplies in southeast New Mexico,
USA, in White, W.B., ed.: Proceedings of the 15th
International Congress of Speleology, p. 1507-
1510.
Johnson, Steve, Schindel, Geary, and Veni, George,
2010, Tracing groundwater flowpaths in the
Edwards aquifer recharge zone, Panther Springs
Creek Basin, northern Bexar County, Texas:
Edwards Aquifer Authority Report No. 10-01:
112.
Klimchouk, Alexander, 2007, Hypogene
speleogenesis: Hydrogeological and morphogenetic
perspective: National Cave and Karst Research
Institute Special Paper No. 1, 106 p.
White, W.B., 1988, Geomorphology and hydrology of
karst terrains: New York, Oxford University Press,
464 p.
Worthington, S.R.H., and Smart, C.C., 2003,
Empirical determination of tracer mass for sink to
spring tests in karst, in Beck, B.F., ed., Sinkholes
and the engineering and environmental impacts of
karst, Proceedings of the ninth multidisciplinary
conference: American Society of Civil Engineers,
Geotechnical Special Publication, No. 122, p.
287-295.

43
Challenges to a Karst Dye-Tracing Investigation in an Urban
Brownfields Area, Springfield, Missouri
By Douglas R. Gouzie1, Kevin L. Mickus1, and Micah V. Mayle1
1
Department of Geography, Geology, and Planning, Missouri State University, 901 S. National Ave.,
Springfield, MO 65897

Abstract
Urban karst areas seldom lend themselves well to traditional karst investigation methods such as dye
tracing. Often the impetus for an urban karst investigation is the detection of chemicals at a specific
location, such as a spring, leading landowners or regulators to seek for the source area feeding that spring.
If historic dye traces have not been done or recorded and disseminated in an accessible database, new
studies may be hampered by limited access to obvious surficial karst features such as sinkholes and
springs, many of which may have been covered over with engineering projects. Dye tracing may also be
impacted by urban stormwater management, which may direct excess water into tracing routes and thus
interfere with estimates of appropriate dye-injection amounts. Other tools more recently added to the karst
toolbox, such as shallow geophysics, may also be hampered by urban infrastructure, such as electrical
interference from utility lines.
A recent investigation to determine the source of water to a hydrocarbon-contaminated spring
uncovered during Brownfields remediation activities at an urban karst site in Springfield, Missouri,
encountered numerous practical problems. A combination of dye-tracing and shallow geophysical
methods was used to determine possible subsurface flow paths contributing flow to the spring. Urban
issues posed challenges for the project, including high-discharge stormflows related to urban pavement
runoff, limited dye input locations due to urban cover and past landscape alteration, timeline pressures of
a remedial project, and contaminant interference with dye detection. The issues encountered and efforts to
address those issues and arrive at a successful end result of the karst investigation are presented.
INTRODUCTION hydrocarbon contamination to a spring
Traditional karst investigations often involve discovered during remediation of an urban
the study of water movement in a region Brownfields site.
underlain by carbonate rocks. Such studies may Site Background
include drainage basin delineation, specific
The study site is an urban Brownfields
recharge/discharge areas, groundwater flow
project in the city of Springfield, Missouri.
paths and velocities, or similar issues (Luhmann
Springfield is located in the Ozarks Plateaus
and others, 2012). Often these studies have no
physiographic region. The study area consists of
specific timetable and only follow the workload
an east-west-trending valley containing a
of the investigators and the climate conditions at
channelized urban stream, Jordan Creek. Jordan
the site (Brahana, 2011). Investigations in urban
Creek flows roughly east to west for
karst areas tend to have similar strategies,
approximately 4 miles through the central
although there are some notable differences. For
business district of Springfield before emptying
example, in urban areas, surface karst features
into Wilsons Creek, a major stream running
such as sinkholes, may have been covered over
southward along the western edge of the city.
by buildings or infrastructure. Equally troubling,
disruption to the routines of local citizens may The study area, shown in figure 1, was
impose shortened timelines for investigations primarily occupied for many years by the
than are typically experienced in regional Springfield railway station and multiple railyard
studies. In addition, issues such as industrial sidings, freight docks, and rail maintenance
pollution tend to be more common in urban facilities. In the mid 20th century, the main
areas. This report discusses an investigation railyard operations moved farther north toward
attempting to determine the source of the edge of the city, and the site area reverted to
44
mostly abandoned or under-used buildings and The geologic setting of Springfield is
rail sidings. The Brownfields Program is a dominated by nearly flat-lying carbonate rocks
means by which the U.S. Environmental with dips of 0 to 2 degrees. The surficial unit
Protection Agency (EPA) can accelerate the across the entire project area is the
typical superfund remedial process in order to Mississippian-age Burlington-Keokuk
facilitate urban renewal and development. Limestone, which is in excess of 200-feet thick
Geologic Setting in most of the Springfield area. The Burlington
and a few thinner underlying carbonate units
Springfield has a four-season climate with (Pierson, Elsey, and Reeds Spring Formations)
warm, humid summers and winter temperatures compose the Springfield Plateau aquifer.
cold enough for snow. Average annual Underlying these units, the Northview
precipitation is 45 inches spread across the year Formation is a shaly unit that acts as a leaky
(Springfield Business Development Corp, 2013). confining layer overlying the Ozark aquifer
(Imes and Emmett, 1994). The Ozark aquifer
includes greater than 1,000 feet of Ordovician-
age dolostones and limestones.

Figure 1. Brownfields study site and area features within Springfield city limits. Point BS is Brewery Spring, point DS is Diesel
Spring, point VS is Vich Spring, and point WC is a monitoring location on Wilsons Creek. Letters A through E are sinkhole
locations discussed in the text. The shaded area is the outline of figure 2, the study site. The dashed lines are potential fracture
trends. Springfield’s downtown square is at Boonville Avenue and College Street.

45
 Both the Springfield Plateau and Ozark was a confining bed within the Burlington
aquifers exhibit numerous features and flow Limestone and allowed a rise pool spring to
patterns consistent with karst conduit flow. form. As this rise pool flowed, globules of
Recent studies in the area surrounding discolored and odoriferous hydrocarbon
Springfield have indicated that much of the contamination issued regularly from within the
shallow groundwater flow system is controlled pool at intervals spaced from a few seconds to a
by hydraulically conductive vertical joints and few minutes apart. These globules dispersed as
relatively horizontal conduits congruent with an oily sheen on the surface of the spring water
bedding planes (Gouzie and others, 2010; as it flowed approximately 200 feet down the
Berglund and Gouzie, 2012; Berglund and tributary reach and into Jordan Creek. Also of
others, 2012). note was that the previously existing Diesel
Site History Spring located offsite, on the south bank of
Jordan Creek and approximately 125 feet
The city of Springfield was founded in the upstream, had been experiencing the same
1830s along the banks of Jordan Creek and near intermittent hydrocarbon contamination. A few
a spring on the Fulbright homestead. By the start days after the onsite spring was uncovered by
of the 20th century, the central business portion the backhoe, Diesel Spring ceased flowing and
of Springfield extended from about 0.75 mile was not observed to flow during the remainder
south of Jordan Creek to1 mile north of Jordan of the project. For the purpose of this report, the
Creek. The original railway station was located new onsite spring will be called Brewery Spring.
on or near the old Fulbright homestead. As
Springfield grew, the growing railway moved After discovering Brewery Spring, the city
toward the northern edge of the city (near the and its contractors sought someone with
town of North Springfield), merging the two, expertise to conduct a dye trace to determine the
and the original downtown railyard became source of the spring water and the likely location
essentially unused. Recent investigations of the hydrocarbon contamination source.
indicate that roughly 75percent of the site study Geophysical studies were proposed by the
area was contaminated by industrial and railyard authors to aid in focusing the dye-trace
operations prior to the railroad transferring the investigation.
property to the city (City of Springfield, 2013). Sub-Contractor Status
A spring located on the south bank of Jordan
The authors were selected as sub-contractors
Creek discharged hydrocarbons, earning the
to the city’s primary remedial contractor for this
local nickname of “Diesel Spring” owing to the
portion of the Brownfields project. That decision
strong hydrocarbon odors common at the site.
relegated dye tracing and geophysical tasks to a
Subsequently, the city of Springfield began a
secondary status compared to other site activities
Brownfields project to investigate and remediate
and timelines already established for site
the site area as part of an urban development
investigation and remediation. It also allowed
project to create a greenway park corridor
access to the otherwise closed site, which was
running along Jordan Creek through the urban
permitted through agreements already negotiated
core of Springfield.
by the remedial contractor.
PROJECT ACTIVITIES
Field Reconnaissance
Project activities at the Brownfields site
Field reconnaissance was conducted during
included a preliminary investigation,
the first calendar quarter of 2013. In addition to
contaminated soil removal, revegetation, and a
meeting the primary remedial contractor and
number of other remedial actions by the city and
going over their site procedures, a brief
its Brownfields Program contractors. During
reconnaissance of the prospective geophysical
these efforts, some of the soil-removal activities
study area was conducted and the timing of
uncovered a spring buried beneath the bed of a
geophysical fieldwork was planned. Following
(usually) dry drainage tributary to Jordan Creek.
these initial activities, topographic maps were
Backhoe activities breached what apparently
reviewed and a cursory driving assessment was
46
conducted of areas north and south of the site to As can be seen on figure 2, the most
investigate the suitability of local sinkholes for promising trend for fractures running through
the dye injection. Suitability was defined as 1) the new onsite spring appeared to be along an
property access, and 2) documented stream azimuth trending between about 320 and 340
losses or a clear indication that water could degrees. This trend also correlated well with the
disappear underground if conditions were wet. trend between the old (now dry) contaminated
Site Geophysical Study Diesel Spring offsite on the south bank of Jordan
Creek and a line projected from that spring
After site reconnaissance was completed, it through the new onsite Brewery Spring, a line
was determined that direct current (DC) that would trend at an azimuth of approximately
electrical resistivity profiles would likely offer 305 degrees.
the most useful results and that electromagnetic
Dye-Tracing Study
(EM) surveying would also be used in order to
offer a more robust interpretation than one As is usually the case with any dye-tracing
method alone would offer. The resistivity and study, the initial tasks were to identify potential
EM surveys were conducted in the second tracer-injection locations and, in the case of
calendar quarter of 2013 and a geophysical unknown conditions, to identify all potential
report was prepared in early May 2013. Results dye-resurgence locations surrounding the
and interpreted fracture or joint orientations injection point.
from the resistivity data are shown in figure 2. Dye-Injection Point Locations
Using the geophysical report, a meeting was Using both topographic maps and driving
held with the primary remedial contractor to tours of the area (and walking possible sites
discuss the results and implications for dye where property access allowed), five potential
tracing and the selection of appropriate sites were considered, and these sites were
sinkholes for dye injection. identified by letters A through E on figure 1.

Figure 2. Electrical conductivity map of the Brownfields site as determined from the electromagnetic survey. White lines
indicate the possible location of fractures determined from electrical resistivity profiles. Numbers 1 and 2 represent high
conductivity regions on the electromagnetic profiles. Dark blue areas represent areas of site debris. Small rows of circles are the
locations of the resistivity lines (each circle represents an electrode location.) This figure is the shaded area in figure 1 with north
oriented toward top of page.
47
 A. small sink in field north of Calhoun
Street (private property),
B. small sink in unused residential lot on
northeast end of Scott Street,

C. sink used as city stormwater drain on

northwest corner of West Avenue and
Calhoun Street,
D. small sink immediately west of Kansas
and Nichols Streets, and
Figure 3. Dye-injection site at West Avenue and Calhoun
E. sink mapped at west end of railyard Street.
north of Division Street.
2) BS-The new onsite Brewery Spring (the
Possible sinkholes south of the site were also anticipated resurgent location for the dye),
evaluated, but no apparent sinkholes near any of
the projected azimuths were identified from 3) VS-An unnamed drainage northeast of the
topographic maps to the south of the site, dye-injection point (this drainage was the
probably due to the more developed or approximate location of “Vich Spring”
urbanized grading south of College Street. where historical dye traces from north of the
Based on preliminary reconnaissance, the Division Street railyard had been detected),
lack of any discernible physical openings
4) WC-A wet portion of the north branch of
(swallow holes or sinkhole depressions with
Wilsons Creek to the west of the injection
open “throats”) removed two of the sites (B and
point, and
D) from further consideration. The inability to
gain access to the Division Street railyard 5) Rader Spring, on the banks of Wilsons
eliminated the sink at location E from Creek several miles south of site WC (a
consideration. Of the two remaining sites, the “catch all” location in the southwestern part
corner of West Avenue and Calhoun Street of the metropolitan area).
(location C) was selected as the preferred dye-
injection location based on closest linear This array of monitoring points was
distance to the Brownfields site and also based designed to cover streams north, west, and south
on its current use as a stormwater drainage of the site, in addition to the onsite Brewery
structure for the city of Springfield’s stormwater Spring, and one upstream Jordan Creek site
drainage system. A photograph of this site and designed to detect any dye resurging east of the
the stormwater inlet structure, a slotted pipe site. Charcoal packets (which adsorb the dye)
made of welded steel approximately 3 feet in were placed at each of these locations and an
diameter and surrounded by coarse gravel, is automated water sampler (Hach 900) was also
shown in figure 3. utilized at the Brewery Spring site. All
Dye-Monitoring Point Locations monitoring sites were sampled either with
charcoal packets or grab sample bottles (or both)
Five monitoring locations were selected for for analysis of the natural background
the dye trace. These monitoring locations were: fluorescence prior to selection of a dye for the
1) Jordan Creek on the West Meadows site, trace. Based upon the background sample
upstream (east) of the confluence with the analyses, no interferences were found within the
Brewery Spring tributary, spectral wavelengths associated with Rhodamine
WT dye (RWT), and it was selected for the test.

48
Dye-Trace Injection Details—Problems was expected to serve as a backup for any
and Challenges issues, such as the autosampler failure.
Based partly on contractor schedules, it was The charcoal packets for the first 2 weeks
decided to inject the RWT as promptly as onsite displayed significant interference with the
possible. Groundwater tracers in Missouri are detection (or more likely the sorption) of RWT.
regulated so that only those trained in proper use Although background interference samples were
of photochemical dyes should be injecting collected prior to the traces, the project timeline
suitable amounts of dye into the state’s waters. was met by evaluating potential interference
The regulatory program also requires pre- with grab-sample bottles of water from the
notification of the Missouri Department of monitoring locations rather than waiting for
Natural Resources before injecting any dye to charcoal packets to be retrieved from the field,
prevent interference with any existing dye traces dried, and processed. No interference was
already underway. These steps delayed the first observed with detection of RWT in any of the
trace until after a rainfall event on Monday, May background grab samples.
20. Based on weather forecasts of no other
rainfall for that week, arrangements were made When the charcoal packets were analyzed, it
to use city water from a nearby fire hydrant for appeared that the organic contamination at the
the actual dye injection. On Thursday, May 23, site either preferentially adsorbed to the charcoal
starting at approximately 2:30 pm, approxi- or otherwise had such a strong signal when
mately 500 gallons of city water were flushed eluted from the charcoal as to significantly
into the stormwater inlet, followed by 2 gallons obscure any RWT signal. Given the nature of the
of RWT dye (Koch Industries, 20% solution). hydrocarbon contamination (almost certainly
This was followed by approximately another hydrophobic based on the globules and oily
400 additional gallons of city water to continue sheen onsite), it is reasonable to believe that the
flushing the dye into the stormwater structure, contamination preferentially sorbed on the
and into the shallow aquifer. charcoal and limited the sorption of the
hydrophilic RWT on the charcoal. An example
Based on past experience in the region and fluorometric scan of the analysis of a charcoal
map distance from the stormwater injection site sample with detectable RWT is shown in
to the Brewery Spring, an estimated dye figure 4.
(groundwater) travel time of approximately 30-
36 hours was expected. Therefore, the 60
automated sampler was programmed to collect a
sample every hour for the first 24 hours, 50

beginning at 6 pm Thursday, May 23; the unit 40

was refilled with clean bottles and reset at 24-
30
hour intervals after that.
20
Unfortunately, the unit experienced a
malfunction (battery, timer, or programming 10

issue) at the beginning of the second 24-hour 0

interval (i.e., the first 24 hourly samples were 450 500 550 600
Nanometers
collected, then the unit failed to collect samples
for hours 27–42 after dye injection before the
malfunction was discovered.) An identical Figure 4. Fluorometric synchronous scan of sample
(substitute) Hach unit with an alternate battery charcoal packet elutant from Brewery Spring, showing a
was placed onsite approximately 44 hours after notable RWT peak at about 545 nm of excitation, and a
dye injection, and the second unit operated much stronger but unknown peak around 440 nm
excitation. The Y-axis of the figure is in fluorescence
properly for the following week. The onsite intensity units recorded by the fluorometer.
charcoal packet placed next to Brewery Spring

49
 Due to the autosampler malfunction, the hours after injection, at no point in time did
Brewery Spring charcoal packet was changed on elutant from any charcoal packet at any
the morning of May 24, as scheduled, and then monitoring location show a positive detection
again late in the day on May 25, to cover the for RWT.
specific period of autosampler malfunction.
After the first major storm event and
As shown in figure 4, it appears the charcoal replacement of the failed autosampler with a
sample from the Brewery Spring site collected functional unit, plans were made to re-introduce
on May 25 does show the presence of RWT. more of the same RWT dye into the same
However, the amount of fluorescence is well sinkhole. Although a second injection of the
below the threshold used in our lab of at least same dye would add a level of uncertainty to the
three times the fluorescence value of a pre-trace actual travel time (as it would not be possible to
background sample in order to declare the prove which injection was being detected), it
sample a positive dye recovery. After was more expedient than the delay which would
discovering this interference, the charcoal packet have ensued in using a second dye such as
monitoring location for Brewery Spring was fluorescein (an alternate dye would have
moved approximately 100 feet downstream on required additional approval of the Missouri
Jordan Creek (to the underpass of Fort Avenue) Department of Natural Resources.) This
in an attempt to allow site contaminants to dilute expedient use of RWT for the second trace
or disperse more before encountering the attempt was deemed acceptable because the
charcoal, and thus allowing the RWT dye to primary purpose of the project (for the
have a greater chance of sorbing on the charcoal. Brownfields site work) was to identify a
connection between a sinkhole and the Brewery
Because dye concentration and duration did
Spring.
not match our lab requirements of a positive
trace during the first 48 hours, the autosampler This second dye injection was planned to
was re-stocked with clean bottles and coincide with an anticipated storm event in mid-
programmed to continue sampling on a regular June. On the morning of June 15, 2 gallons of
basis. The charcoal packets were also removed RWT were injected into the same West and
and replaced on a weekly schedule. Calhoun Streets stormwater sinkhole (location
C) on the leading edge of a storm hydrograph,
On May 30, approximately 1 week after
during the first 30 minutes of storm runoff.
sampling began, an intense storm event
After injecting the dye, the authors travelled to
(approximately 2 inches of rain in less than 4
the onsite Brewery Spring to check the
hours) occurred in the Springfield area, causing
autosampler unit. Upon arrival at the site, a
a significant flooding event in the onsite north-
visual discharge estimate of approximately 35 to
south tributary where Brewery Spring is located.
40 cubic feet per second (ft3/s) was made. The
The flooding during this event was so extensive
approximate discharge was calculated by
that the autosampler, secured about 5 feet above
multiplying the average of width times depth
normal spring stage, was apparently floated
times velocity, with velocity determined by
downstream and overtopped by flood water.
measuring the time it took a floating object on
The chain securing the autosampler in place
the water surface to move downstream a known
apparently caused the unit to be submerged in
distance. Because previous estimates of
enough water to flood and short-out the main
discharge from Brewery Spring typically had
circuit board. As a result, no spring water
been in the range of 3 to 6 ft3/s or less using the
samples were collected from May 30–June 14.
same visual estimation method, it appears that
However, throughout this time period, charcoal
the urban runoff from the rain event of June 15
packets were maintained at all locations
may have diluted the dye recovery to a point
(including Brewery Spring) and continued to be
where once again it would be undetectable.
changed and analyzed on a regular basis. With
the exception of the one possible interference- After the June 15 injection, monitoring was
masked detection noted above during the first 48 continued with both the autosampler and
50
charcoal packets and in the surrounding area, Flashy urban runoff poses the challenge of
although the West Bypass charcoal packet site diluting a normal injection amount to become so
went dry approximately June 21, which dilute as to no longer be detectable. The easiest
indicated no dye could resurge along that way to overcome this challenge is to find a
segment of stream. Monitoring was continuedfor losing stream rather than an existing storm
8 weeks after the initial dye injection on July 17, drainage structure, which may lead to
at which time the primary remedial contractor groundwater but where the current groundwater
for the site chose to cease all further tracing connection cannot be observed or determined.
activities. Using the criteria of the Missouri A recently located segment of losing stream
State University Cave and Karst Lab, no dye northeast of the Brewery Spring site shows
was ever definitively detected from either promise for a future dye-tracing attempt.
injection. Plans were made for another trace at a Contract Limitations on Study Timeline
future time during wetter weather; however, the
contractor’s work plan and site access ended As noted, this work was performed under a
before any additional traces were attempted. sub-contract to the city’s primary remedial
activity contractor for the site. Because the
DISCUSSION OF CHALLENGES Brownfields Program is intended to accelerate
Below is a brief summary of the challenges redevelopment of urban lands, the project
encountered beyond the normal issues found in already was on a strict timeline before the
dye tracing and field work. Also offered are authors were contacted for involvement.
some possible causes or major contributing
The applied approach of determining the
factors to the challenges and possible ways to
source area for a springfed stream created a
mitigate the issues.
challenge because typical tracing approaches
Urban Stormwater Issues using a point of known, ongoing flow into the
One key issue was the unseasonal weather subsurface were hampered by the desire to keep
combined with the flow regimes of urban the tracer test moving forward on the established
stormwater runoff. As noted above in the dye- timeline. Adding the seasonal nature of study
tracing section, both attempts at a successful activities (pre-leafout being preferred for
trace were hampered by unusual and unexpected geophysics activities and post-freezing, wet-
rainfall runoff. The first dye-injection event was season weather preferred for dye tracing) to the
impacted by a small but intense rainstorm already existing schedule posed challenges for a
which, based on water levels at the Brewery successful completion.
Spring, probably generated stormwater runoff at The ability to perform site geophysical
the site that was at least 10 times greater than studies quickly after study approval by the
typical baseflow at the site. Visual discharge primary remedial contractor was a positive item
estimates shortly after the second dye injection – all parties were pleased to see activity onsite
suggested that runoff in the site tributary soon after approval of the proposed workplan,
containing Brewery Spring was in the range of and the ability to perform the geophysical
40 ft3/s. The stage associated with this discharge surveys during winter plant dormancy was
was below the elevation of the onsite fortunate. However, the additional insight
autosampler, so water levels high enough to offered by the geophysics and the time
float and flood the autosampler would need to consumed by geophysical tasks did add
have been in excess of 40 ft3/s. Such large increased pressure to the timeline and success of
variations in flow were particularly challenging the dye trace. The desire to establish a successful
in determining amounts of dye to inject. dye trace led the authors to offer to conduct
Groundwater tracers in Missouri are another trace after the project had officially
regulated, therefore, it is expected that registered ended.
dye-tracing professionals will limit the amount Although such a tracer test is still planned,
of dye injected to an amount that would not be the added challenges of negotiating site access
expected to discolor any waters of the state.
51
after the primary remedial activity contract has Given the reasonable prediction of a
ended have delayed any new dye-trace attempts. groundwater feature trending at azimuth 305
Although site access was relatively easy under degrees (based on the Diesel Spring going dry
the umbrella of a site contractor, reaching an soon after the onsite Brewery Spring was
agreement on liability that satisfies the city’s uncovered), a reasonable interpretation of the
normal contract for property access and which is geophysics data indicates linear features
acceptable to the university (as a state agency trending in azimuths ranging from 320 to 340
limited in liability waivers to which it can agree) degrees and in general agreement with the 305-
requires time-consuming negotiations between degree azimuth trend. However, none of the
attorneys with more pressing legal issues on discovered sinkhole features were actually in the
their schedules. geophysics-predicted range. The closest sinkhole
Contaminant Interference with Dye discovered during the initial study, the urban
stormwater drain at West and Calhoun Streets, is
Discovered during the first dye injection, the roughly on a 305-degree azimuth from the site,
hydrocarbon contamination that prompted the but there has not yet been a successful dye trace
investigation may also have interfered with from this location. A newly discovered sinking
detection of the dye by preventing sorption of stream segment that shows great promise is
the dye on the activated charcoal in the packets. actually slightly northeast of the site and is in the
Although fluorescence in the narrow wavelength upper reaches of the stormwater channel
range of RWT was detectable using a modern tributary running onto the site.
scanning spectrofluorometer, the intensity and
recurrence was not enough to meet the Missouri Given the location of the newly discovered
State University Cave and Karst Lab criteria for sinking stream segment, it seems worth
a definitive detection. It appears that moving the revisiting the geophysical data and considering
Brewery Spring charcoal detector packet slightly the other low-resistivity features (marked as
downstream from the contamination source may areas 1 and 2 on figure 2). It is possible that
have adequately overcome the challenge of these features represent contamination that may
contaminant interference, but this remains to be be closer to a trend between the sinking stream
tested. The use of larger amounts of dye is also segment and Brewery Spring. It also is possible
planned for future efforts, as the existing that Jordan Creek itself is losing flow
contamination of the site makes the issue of underground on the eastern edge of the
discoloration of the water less offensive during downtown area, and that the lost flow is
the remedial project. Local residents are already resurfacing at Brewery Spring after picking up
offended by the strong hydrocarbon odors and some contamination in the east-west-trending
the oily sheen, so a brief period of slightly tinted alluvial fill in the Jordan Creek valley.
water would likely be tolerated in order to Understanding that the historical Jordan Creek
achieve a definitive trace and move the remedial meandered across the east-west-trending valley
efforts forward. through downtown, but is now channelized on
the southern margin of the valley due to urban
Geophysics – Guidance or Misguidance? development, may open up new interpretations
Perhaps the most puzzling challenge of site geophysics related to groundwater (and
encountered is the utility of using geophysical contaminant) movement. Hopefully a successful
data in guiding or shaping the dye-tracing dye trace conducted in the near future will offer
efforts. Although geophysics as used on the site more data for a combined geophysical –
have become very useful in other parts of the hydrogeologic interpretation.
metropolitan Springfield area (Berglund and CONCLUSIONS
others, 2012; Gerson and others, 2012), it is
unclear whether the geophysics contributed to a Based on the challenges encountered, much
better understanding of the site subsurface or if was learned about modifying a traditional dye-
it led investigators down a “primrose path.” tracing research project into an applied site

52
investigation and remedial effort under the U.S. REFERENCES
EPA Brownfields Program. Berglund, J., and Gouzie, D., 2012, Conceptualizing
Lessons learned for future studies include flow interaction and conduit geometry in near-
the following: surface karst using a quantitative dye tracing
method: Geological Society of America
• Be flexible in using the entire karst toolset to Abstracts with Programs, v. 44, no. 5, p. 20.
adapt to schedule pressures of commercial Berglund, J., Mickus, K., and Gouzie, D., 2012,
contracts and timelines. Being able to use Studying urban karst features using near-surface
additional methods such as geophysics geophysics in Springfield, Missouri: Geological
during weather conditions not conducive to Society of America Abstracts with Programs, v.
dye tracing was helpful to the overall 44, no. 5, p. 27.
success of the project. Brahana, V., 2011, Ten relevant karst hydrogeologic
• Remember that the site is already insights gained from 15 years of in situ field
studies at the Savoy Experimental Watershed, in
contaminated and undesirable side effects of
Kuniansky, E., ed., U.S. Geological Survey Karst
the current tasks may be more tolerated than Interest Group Proceedings, Fayetteville, AR,
they would be at undisturbed research sites. April 26-29, 2011: U.S. Geological Survey
The hydrocarbon contamination driving this Scientific Investigations Report 2011-5031, p.
project may have interfered with the 132–141.
sorption of dye at the part-per-billion levels
City of Springfield, Missouri, 2013, Jordan Valley
typically used in modern tracing, whereas West Meadows Project Fact Sheet, accessed at
higher levels up to a few hundred parts-per- www.springfieldmo.gov/brownfields
billion for brief periods might have been
tolerated as the cost of moving site Gerson, L., Mickus, K., and Gouzie, D., 2012, An
remediation forward. urban karst geophysical study in Springfield,
Missouri: Geological Society of America
• Maintain the fundamental principles of the Abstracts with Programs, v. 44, no. 7, p. 78.
simplest research approach. Staying true to Gouzie, D., Dodd, R., and White, D., 2010, Dye
traditional dye tracing under “normal” tracing studies in southwestern Missouri, USA:
conditions of existing streamflow losing to Indication of stratigraphic flow control in the
the subsurface and re-surfacing at a spring Burlington Limestone: Hydrogeology Journal, v.
would have led to increased searching to 18, no. 4, p. 1043–1052.
locate losing stream segments in the urban Imes, J.L., and Emmett, L.F., 1994, Geohydrology of
area, or more searching for city employees the Ozark Plateaus aquifer system in parts of
familiar with past use, now covered, of the Missouri, Arkansas, Oklahoma, and Kansas: U.S.
natural karst drainage features incorporated Geological Survey Professional Paper 1414-D,
into the city’s stormwater system. 127 p.
Knowledge gained after the unsuccessful Luhmann, A., Covington, M., Alexander, S., Chai, S.,
traces were reported has provided at least Schwartz, B., Groten, J., and Alexander, E., Jr.,
two additional potential dye-injection 2012, Comparing conservative and
locations that are anticipated to yield more nonconservative tracers in karst and using them to
successful traces in the near future. estimate flow path geometry: Journal of
Hydrology, v. 448-449, p. 201–211.
Overall, the interaction with remedial and
urban managers was a satisfying experience and Springfield Business Development Corporation,
one that is encouraged for all researchers. 2013, Springfield area Chamber of Commerce
However, those used to research projects website, Live in Springfield, Climate in
Springfield, accessible at
designed and conducted with few, or no, http://www.liveinspringfieldmo.com/live/climate
external pressures or timelines, should be
prepared for the challenges involved in applied
urban studies in karst areas.

53
SPELEOGENESIS, GEOLOGIC FRAMEWORK, GEOPHYSICS, AND GEOLOGIC HAZARDS

The Role of Spongework in the Speleogenesis of Hypogenic Caves in

the Guadalupe Mountains, New Mexico
By Mark Joop
New Mexico State University, Carlsbad, New Mexico 88220

Abstract
Recent studies of the few active sulfuric acid caves in the world have shed some light on the
interpretation of relic sulfuric acid caves in the Guadalupe Mountains, New Mexico. The Guadalupe
caves share most of the common features, including spongework morphology. The spongework clearly
predates the hypogenic speleogenesis in the Guadalupe caves and provided the cavernous porosity needed
to form the sulfuric acid subaerially. The generation of sulfuric acid requires an abundant supply of sulfur
and oxygen. It is argued that the hydrogen sulfide came from microbial reduction of the abundant sulfate
in the brine water, and that the oxygen came from the atmosphere in the spongework above the water
table. A modern analog of how sulfuric acid is produced in caves may be found in concrete wastewater
pipes and tanks.
INTRODUCTION dissolution in a massive, essentially
Spongework has been recognized in the homogeneous limestone” (USEPA, 2002).
caves of the Guadalupe Mountains as far back as Earlier definitions focused on the morphology of
1949, when Bretz wrote, “Carlsbad’s spongework, and did not include its genesis.
magnificent display of spongework is to be seen Palmer (1991) defined spongework as
from the highest to the lowest levels of the “interconnected solution cavities of varied size
cave,” and “the spongework of the [Left Hand] in a seemingly random three-dimensional pattern
Tunnel is unsurpassed in any cave that the writer like the pores of a sponge.” White (1988) had
has ever seen” (Bretz, 1949). It is clear from earlier defined spongework as “interconnected,
Bretz’s statements that he had seen spongework nontubular solution cavities of varied size and
in caves in other areas (e.g., Meramec Cave in irregular geometry arranged in an apparently
Missouri and Wind Cave in South Dakota). In random, three-dimensional pattern,” but added
fact, Bretz studied over 100 caves in 50 states, that it “appears in caves formed in young,
including Carlsbad Cavern, and coined the term porous, and poorly jointed limestones.” Both
“spongework” for the cave morphology Palmer (1975, 2005, 2007) and White (1988)
discussed here (Bretz, 1942). Thus, while the categorize spongework as a feature of maze
spongework in Carlsbad Cavern was not cited as caves. While there are some divergent
the type locality (White, 1988), it is definitely an hypotheses on the genesis of spongework, most
excellent example of the relation between speleologists agree with Bretz that spongework
spongework and hypogene speleogenesis. is produced in the phreatic zone under slow,
diffuse, hydraulic conditions (Klimchouk, and
The purpose of this paper is to re-examine others, 2000). This is indicated by the smooth,
the spongework in Carlsbad Cavern and Spider rounded, irregular speleogens such as cupolas,
Cave, as type localities in the Guadalupe holes, pendants and bridges, the lack of scallops
Mountains, in light of more recent work, to and channels, and the irregular floors and
determine its role in the speleogenesis of these ceilings. Bretz deduced that spongework is “the
caves. solutional work of water without definite
DEFINITION OF SPONGEWORK current, without surface gradient, without air
above it.”
Spongework is defined in the Lexicon of
Cave and Karst Terminology as “Randomly Modern investigations of spongework caves
shaped cavities created by undirected phreatic not associated with hypogenic speleogenesis
54
have determined that this morphology formed by lateral development is not far from the fracture
corrosion at the fresh/salt water mixing zone of unless there are intersecting or parallel fractures,
coastal aquifers; such caves are now called and is characterized by small interconnected
flank-margin caves (Mylroie and Carew, 1990). pockets that dead-end. Even the trunk passages
The mixing can be explained by the hydraulic come to a dead-end, though the fracture usually
action of tides, penetrating into the bedrock as continues. In Spider Cave, the spongework
far as the hydraulic conductivity of fractures, developed along a bedding plane contact
joints, and bedding planes allow, which would between a sandstone member of the Yates
increase with time as porosity and transmissivity Formation and the underlying dolomite. The
increased due to corrosion. Constant mixing is natural floors of the spongework are not flat
essential to maintain aggressiveness, which is unless they have been filled in and leveled with
initially most active close to the coastline. The secondary clay or sediment deposits (e.g., Big
mixed water is corrosive to limestone because it Room, Kings Palace/Lower Cave), which
is undersaturated with respect to calcite represent water table stands. Most of the
(Plummer, 1975; Bogli, 1980). Spongework spongework in Carlsbad Cavern is located at the
caves are found in a wide variety of carbonate Big Room level – the northeast ends (the Zoo,
lithologies (Klimchouk and others, 2000), the Underground Lunchroom and all along Left
though primary porosity is believed to be Hand Tunnel), and the Boneyard (above Lower
important (Palmer, 2005, 2007). The large Cave spongework); at the Lower Cave level –
chambers of flank-margin caves appear to be the northeast side; and at the Main Corridor
due to the coalescing of cupolas and holes, often level – the north side (the New Section).
leaving remnants of the rock in between as
pendants protruding from the ceiling, walls, and
floor (Mylroie and Carew, 1990). Spongework is
not a common cave morphology (White, 1988),
yet with so many relic and active spongework
caves associated with emergent limestone in
contact with seawater, perhaps the flank-margin
environment, as opposed to being a special case
(Klimchouk, 2000), is the common, or at least
primary, geologic setting required to produce
spongework caves. In other words, it is not
mixing corrosion alone which best explains most
occurrences of this phreatic morphology
Figure 1. Typical spongework in Carlsbad Cavern.
(Palmer, 2005), but this type of dissolution in
combination with the low-velocity, turbulent, In addition to pendants, rock bridges are
swirling, back and forth flow pattern associated another common speleogen found throughout
with tidal action. the spongework, where the bedrock between
NATURE OF SPONGEWORK IN holes is left suspended, with air space on all
CARLSBAD CAVERNS NATIONAL PARK sides of the bridge (fig. 2). Some of these rock
bridges are only a couple of centimeters in
The spongework in Carlsbad Cavern is diameter at the thinnest spot. Typical of
variable in size, from walking passages to small spongework in this and other caves, primary
holes that only a finger can pass through. This flow features such as scallops are absent
cave morphology is found around the perimeter (Klimchouk, and others, 2000).
and in between the large chambers (fig. 1). A
nearly vertical fracture is typically observed in The vertical extent of the spongework in
the center of the ceiling of the “trunk” passages, Carlsbad Cavern is from the bottom of the lower
indicating that the spongework developed along sandstone unit in the Triplet Member of the
this secondary porosity, and spread laterally on Yates Formation, as can be seen in the Main
both sides of the fracture (fig. 2). Usually, the Corridor and in the route to Hall of the White
55
Giant, to at least the floor of Lower Cave in the with no Triassic- or Jurassic-age deposits in the
Capitan Reef. Spider Cave formed at the same Delaware Basin, this date made sense. But is the
upper limit. This 5-meter thick sandstone unit end of the Permian the first emergence of the
may have been a groundwater confining layer. reef complex? Most early workers agreed that
The vertical extent represents about 207 meters. the Delaware Basin was first tilted eastward at
the end of the Permian, but there is strong
evidence that this tilting occurred earlier (Hill,
1996).
The spongework developed along pre-
existing, near vertical fractures, the major ones
being the same two sets on which most of the
caves in the Guadalupe Mountains developed:
one set parallel to the reef escarpment, and one
set almost perpendicular to the reef escarpment.
Strong evidence indicates that the earliest of
these fractures are syndepositional with the reef,
and Capitanian in age (Hunt and others, 2002;
Kosa and others, 2006). Basin and Range
extensional stress most likely reactivated these
pre-existing fractures. When this evidence is
coupled with the fact that the Ochoan-age
evaporite deposits in the basin are wedge-
shaped, thickening to the east, unlike the
underlying Delaware Mountain Group, it seems
reasonable to deduce that some eastward tilting
of the Delaware Basin occurred at the end of the
Guadalupian (Hill, 1996). Saller (1996)
concluded that the reef complex had tilted 10º
basinward after deposition due to compaction-
Figure 2. Fracture in the ceiling, with spongework on both induced differential subsidence (the backreef
sides. Note the rock bridge spanning across the fracture, as
well as the one in the upper left corner of the picture.
deposits thicken toward the reef margin). Hunt
and others (2002) refined this tilt to a 2º
GEOLOGIC TIMING OF SPONGEWORK depositional dip of the Yates Formation with an
Because the spongework occurs around the additional 6-8º syndepositional tilting due to
perimeter and in between the large chambers of subsidence, which was believed to be
Carlsbad Cavern, Hill (1996, 2006) recognized responsible for the progradation of the Capitan
that it pre-dates the sulfuric acid hypogene shelf. However, during and/or after the
speleogenesis that occurred during the Miocene. deposition of the Tansill Formation, an
The spongework represents the first stage of additional 4-6º basinward tilt occurred (Hunt
dissolution in the Guadalupe Mountains. Hill and others 2002), which perhaps was due to
suggested that the timing of the spongework tilting of the basin itself. Because the evaporites
started no later than after the Permian and are the result of the Delaware Basin being cut
extended through the Mesozoic into the early off from the ocean to the west, then perhaps this
Cenozoic, when the Delaware Basin was cutoff was due to eastward tilting of the basin, as
emerging (Hill, 1996). A date of early Jurassic opposed to a drop in sea level.
(188 ± 7 ma) was provided by a speculative Hill (1996) summarizes evidence supporting
40K/40Ar date for montmorillonite clay found a strong case that the Castile sea did not cover
in the spongework. Hill recognized that the reef the reef or forereef on the western side of the
complex had to be emergent for a freshwater Delaware Basin, from the Guadalupe Mountains
lens to be present to create spongework, and to the Apache Mountains, indicating that it was
56
emergent during Castile time, and perhaps even As discussed above, the spongework in
during Salado time. If this is the case, then the Guadalupe caves clearly pre-dates the sulfuric-
freshwater lens required to create the mixing acid dissolution phase by at least 240 million
corrosion that produced the spongework was years (the caves are believed to be 2-12 million
present as early as the Capitanian/Ochoan years old, as determined by 40Ar/39Ar dating of
boundary (260 ma). Kirkland and others (2000) alunite, a potassium-clay mineral that can only
agree that the basin was closed off from the form in acidic environments; Polyak and others,
ocean during deposition of the 260,000 laterally 1998). Therefore, the age of the spongework, its
correlative, varved lamina of the Castile existence along the perimeter and in between the
evaporites due to the western reef complex being large chambers having developed along the
emergent. They show that the parent brine water same fracture sets as the large chambers and
of the Castile evaporites was predominantly passages, and that spongework remnants such as
marine, and that the source of the marine water pendants and cupolas are seen in the bedrock of
kept pace with evaporation, such that desiccation the large chambers, all suggest that the large
never occurred. They conclude that the brine chambers could be the result of enlargement of
water entered the basin by seepage through the pre-existing spongework by sulfuric acid. The
Capitan Formation, and the brine water level fact that most active sulfuric acid caves have
remained close to sea level. spongework morphology has led some writers to
ROLE OF SPONGEWORK IN HYPOGENE think the relation is causal (e.g., Palmer, 2007).
SPELEOGENESIS There are several reasons to believe otherwise:
1) sulfuric acid is very corrosive, so there is no
That sulfuric acid hypogene speleogenesis reason to believe that it would dissolve
was involved in the formation of the large limestone preferentially, creating sculpted
chambers and passages that make the Guadalupe interconnecting holes as opposed to uniform
caves world famous is well accepted and dissolution, 2) it would be hard to explain how
supported today (Palmer, 2006). However, how so many rock bridges remain, when they can be
this process works is still being studied. A recent attacked from all sides, 3) the gypsum rinds
comparison of active sulfidic karst systems in conform uniformly to the morphology of the
the world (Hose and Macalady, 2006) has found spongework (fig. 3), as opposed to producing it,
some common features: 1) thermal groundwater and the rinds are not found in the interior of the
rich in sulfate, 2) sulfate-reducing and sulfur- peripheral spongework, where they would be
oxidizing chemoautotrophic bacteria, 3) the expected to survive, and 4) this morphology is
release of sulfides from the aquifer into the produced phreatically, which would require the
atmosphere of pre-existing caves/cavities, 4) the sulfuric acid to be created subaqueously, which
subaerial formation of sulfuric acid in the is not observed in active sulfuric acid caves.
condensate on the walls, 5) gypsum rinds on the
walls from limestone replacement, 6) massive
gypsum floor deposits from stoped rinds, and 7)
spongework cave morphology. The sulfuric acid
production in the Guadalupe Mountains ceased
long ago, which makes these caves relict. Even
in Lechuguilla Cave, which intersects the
groundwater table 488 meters below the surface,
there is no sulfuric acid in the water or in the
cave. Therefore, if the present is the key to the
past, then observations made at active sulfuric
acid caves would indeed aid in our under-
standing of the speleogenesis of Guadalupe
caves. Figure 3. Gypsum rind on spongework. Note how the rind
conforms to the shape of the spongework, even inside the
hole.

57
 The relation between spongework and the basin where the petroleum deposits exist, to
sulfuric acid appears to be related to the question the water table within the shelf.
of whether sulfuric acid forms subaqueously or
Hydrogen sulfide, which is only slightly
subaerially, or both. Sulfuric acid in active caves
soluble, reacts with water to form hydronium
is formed subaerially within the condensate on
and HS: H2S + H2O → H3O + HS. At the pH
the walls. However, do the active sulfuric acid
range of seawater (7.5-8.4), most available H2S
caves represent a late stage of development that
dissociates to HS (pK1 = 7 in pure water at
is different from the initial stage, or are the
25ºC), and this occurs at lower pH with
observed processes consistent throughout the
increasing salinity and temperature; HS is stable
speleogenesis of these caves? This question is
(pK2 = 17 at 25ºC). Therefore, H2S would have
best answered by determining whether sulfuric
dissociated in the saline groundwater before it
acid can be formed subaqueously.
could reach meteoric water, especially if the
Hill never included spongework as one of water was above 25ºC.
the controlling factors in cave development. This
Why would the meteoric water come to have
was because she believed that the hypogenic
such high levels of dissolved oxygen, which is
caves cut across the previous stage, and because
usually low in mountainous areas due to a lack
she believed the sulfuric acid was in solution
of soil (Palmer and Palmer, 2000)? This could
below the top of the water table, where hydrogen
only occur if the water was aerated as it traveled
sulfide (H2S) gas rising through the brine water
down epigenic conduits, which are not observed
encountered oxygenated meteoric water and
in Guadalupe caves, or there were air-filled
reacted with dissolved oxygen. But a review of
cavities above the water table.
the abiotic origin of sulfuric acid outside of
caves and in the manufacturing process revealed The abiotic oxidation of H2S is very slow
that in each case, the acid forms in the due to the lack of dissolved oxygen in
atmosphere, not subaqueously. Sulfuric acid in groundwater and to kinetic constraints (Luther
its anhydrous form does not occur in nature and others, 2011), but when it occurs in
because the hydration reaction is freshwater, it produces sulfur according to the
thermodynamically favorable (Ka1 = 2.4 x 106), equations: 2H2S(aq) + O2(aq) → 2H2O + 2S, or
and so it has a strong affinity for water. Sulfuric H2S(aq) + O2(aq) → H2O2 + S, not sulfuric acid.
acid is even used as a desiccant because of this Biotic oxidation enhances the rate by three or
property. The reaction is highly exothermic, and more orders of magnitude, but the outcome is
produces hydronium and sulfate according to the the same. This reaction most likely explains the
equations: H2SO4 + H2O → H3O + HSO4, and occurrence of elemental sulfur found in sulfuric
HSO4 reacts with water to form H3O + SO4 (Ka2 acid caves (e.g., Cueva de Villa Luz; Hose and
= 1.2 x 10-2). Therefore, sulfuric acid would not Pisarowicz, 1999). If the source of H2S is the
form in a medium that strongly forces it to petroleum deposits in the basin, why has the
dissociate. sulfuric acid process ceased, as there is still
plenty of oil, and the Delaware Mountain Group
Hill’s concept of H2S gas, produced by
formations still contain “sulfur water”?
sulfate-reducing bacteria (SRB) thriving on the
petroleum hydrocarbons that migrated up dip All abiotic occurrences of sulfuric acid (acid
when the Delaware Basin tilted eastward during rain) do not start with H2S, but with oxidized
the Miocene uplift, bubbles up through brine sulfur, usually sulfur dioxide (SO2), which is
water and reacts with dissolved oxygen in oxidized in air (producing sulfur trioxide, SO3)
oxygenated meteoric water below the water in the presence of water vapor to form sulfuric
table, is problematic on many accounts. The H2S acid. Sulfuric acid is the world’s most important
would not degas at pressures greater than a industrial chemical, and the manufacturing
meter or two below the water table (Palmer and process also starts with SO2, which is obtained
Palmer, 2000), so a transport mechanism would by either burning sulfur, or as an alternative,
be required to move aqueous H2S from deep in incinerating H2S gas (2H2S + 3O2 → 2H2O +
2SO2). In other words, the production of SO2 by
58
the oxidation of H2S cannot occur abiotically in SRB. However, isotopically light δ34S values
water, nor is it going to occur in air (heat of appear to be common in active sulfuric acid
formation = -1,036 kilo Joules per mole caves that are not near petroleum reservoirs
[kJ/mol]; compare to S + O2 → SO2 = -297 (Hose and others, 2000; Galdenzi and Maruoka,
kJ/mol). The chemical equation that Hill used, 2003). Another common feature of sulfuric acid
H2S + 2O2 → H+ + HSO4 → 2H+ + SO4, while caves is thermal, sulfate-rich, saline water. The
thermodynamically feasible (ΔG = -760.88 main sulfur compound in seawater is sulfate; it
kJ/mole for the first product), does not occur is the third most abundant component of
abiotically in water because of the kinetic seawater by weight. H2S is a negligible
constraints of three molecules of low concen- dissolved-gas component (outside of microbial
trations due to low solubilities coming together action) because it quickly dissociates. The
at the same place at the same time to react. But isotopically light δ34S values can be explained
can this reaction occur biotically in air? by the fractionation due to SRB thriving in the
thermal water near the aerobic/ anaerobic
Gypsum rinds are a common feature of
interface (water table). Perhaps the source of the
active sulfuric acid caves, including Carlsbad
high H2S content in the water of active sulfuric
Cavern and other Guadalupe caves, and they are
acid caves is due to sulfate reduction by SRB in
best explained by subaerial replacement of
the caves, rather than a possible source
limestone by sulfuric acid in the condensate
upgradient of the caves. The biofilms in the
(Hose and Pisarowicz, 1999). In fact, this
streams in the Frasassi cave system were found
subaerial process is believed to account for the
to include predominantly gamma- and delta-
greatest volume of carbonate dissolution in
proteobacteria (Macalady and others, 2006).
Guadalupe caves and in the Frasassi caves in
Italy (Palmer and Palmer, 2012, and Galdenzi A SULFURIC ACID SPELEOGENESIS
and Maruoka, 2003, respectively). The domed MODEL FOR GUADALUPE CAVES
cross-sectional shape of Carlsbad Cavern, with The following model is based on studies of
its flat floors representing the water table, previous workers (Kirkland, 1982; Palmer and
suggests that this cave formed subaerially Palmer, 2000; Hose and others, 2000; Palmer,
(Palmer and Palmer, 2012). For sulfuric acid to 2006; Hose and Macalady, 2006), combined
be generated at the water table, as what appears with the author’s own observations in the 4.5
to be the case for the Guadalupe caves, a years working at Carlsbad Caverns National
constant supply of sulfur and oxygen is required, Park.
as both are consumed with the dissolution of
limestone. If sulfuric acid is formed subaerially, The cave morphology of typical flank-
then subterranean, humid air space directly margin caves includes a large chamber with
above the water table, large enough for spongework along the perimeter, the chamber
condensation to occur and have air flow (oxygen being the result of the holes coalescing in an
has to be replenished), is required. The pre- area of more aggressive dissolution. The
existing spongework would have provided such spongework extends inland into the limestone
an environment, and would have provided the via fractures or other secondary porosity. The
necessary supply of oxygen, especially if the spongework is the result of mixing corrosion at
spongework had small connections (fractures) to the freshwater lens/seawater boundary, and near
the outside. But what was the source of sulfur to the coastline where the freshwater lens is
create the sulfuric acid? thinnest and the tidal action is more aggressive
(Mylroie and Carew, 1990). This scenario is
The reason that Hill turned to H2S as the easily superimposed onto the geologic setting of
source of sulfur is because the δ34S isotopic the Guadalupe Mountains, an emergent reef
values for the cave gypsum and sulfur are complex due to the closure of the Delaware Sea
isotopically light (mean = -16.8 permil for 22 260 ma. Basinward tilting of the reef complex
samples), which she could only ascribe to the by syndepositional subsidence caused tensional
fractionation that occurs by reduction of sulfate fractures to develop parallel to the reef
in the evaporites in contact with petroleum by escarpment, as well as a nearly perpendicular
59
conjugate set. These fractures, along with the potentiometric surface was at that level, but the
vuggy porosity of the Capitan Reef massive, breakdown floor at the southwest end of the Big
provided the avenues for both the infiltration of Room is covering the connection. Devil’s Den
meteoric water and the horizontal penetration of may have been a thermal spring when the Main
seawater. At the fresh/salt water boundary, Corridor was enlarging, with the current bottom
mixing corrosion occurred initially along these of the pit, where a gypsum block and rinds
fractures, especially at intersections, but spread remain, being the potentiometric surface.
laterally as the fractures were enlarged,
SRB, most likely thermophiles (40-70ºC
producing spongework caves at sea level. The
temperature range, with 50ºC optimum), were
vertical extent of the spongework indicates that
thriving near the air/water interface in this
either sea level dropped 207 meters after the
warm, anaerobic, sulfate-rich brine water, with
Capitanian, or the western side of the basin was
the densest colonies (biofilms and mats) at the
being tilted. Many of the caves in the Guadalupe
spring orifices. The sulfate reduction produced
Mountains occur near the escarpment, the late
H2S, most of which was released as a gas to the
Permian coastline (Palmer and Palmer, 2000,
air-filled spongework above the water table.
fig. 2). Once the mixing zone intersected the
Some of the H2S dissolved in the brine water
backreef formations, spongework also began to
could have oxidized abiotically to SO3 (as well
develop along bedding planes (e.g., Spider
as to sulfur; Zhang and Millero, 1993), which
Cave).
then hydrated in the humid atmosphere to create
During Miocene Basin and Range tensional sulfuric acid vapor that would eventually
faulting, three western sections of the buried reef condense on the cooler walls and ceilings, but
ring were in the path of the north-northwest- could travel away from the spring. The H2S gas
trending uplift. The section now known as the would have adsorbed onto the film of condensed
Guadalupe Mountains broke perpendicular to the and/or seeped water on the walls, where abiotic
reef at the Border Fault and was thrust upward at and biotic oxidation occurs using the oxygen in
the fault about 1,500 meters from its late the cave atmosphere; this oxidation produces
Permian position, analogous to pulling on a tire elemental sulfur. The sulfur is further oxidized
buried in the sand, where the tire was cut in two. by aerobic sulfur-oxidizing bacteria (SOB), such
The uplift was episodic, as evidenced by the flat as Acidithiobacillus sp., to form sulfuric acid
cave floors at different levels, which represent (Hose and others, 2000). The sulfur folia on the
long stands of the water table. This period was walls of sulfuric acid caves may be a remnant of
accompanied by rifting, flood basalts, igneous this process.
intrusions, and heating of the crust to over 50ºC
Sulfuric acid generation would not have
(Barker and Pawlewicz, 1987). This paleo-
extended far from a thermal spring, due to the
geothermal gradient would have heated the
water becoming cooler with distance–not a
groundwater as well, producing thermal
conducive environment for mesophilic or
convection upwelling. In Carlsbad Cavern, this
thermophilic bacteria. The sulfuric acid caused
upwelling may have occurred as a thermal
the outer layer of limestone to be replaced with
spring at the Bottomless Pit, which is currently
gypsum as a rind. This replacement could only
18 meters deeper than Lower Cave (the lowest
penetrate into the limestone a limited depth,
water table stand within the cave), the floor of
usually 5-15 centimeters, due to the rind acting
which is very sandy, with stoped breakdown
as a barrier. The rinds allowed the H2S gas and
blocks. Another possible thermal spring may
acid vapor to travel farther down passage in the
have occurred at Lake of the Clouds (63 meters
direction of air flow. The ceiling height in the
deeper). The potentiometric surface for both
Big Room, which decreases from about 60
springs was at the level of the Big Room floor at
meters at the southwest end to about 6 meters at
the time this chamber was enlarging. Bottomless
the northeast end, indicates that the acid was
Pit, which is on the same fracture as the large
generated at the southwest end, and that the air
chambers of Lower Cave, was most likely the
flow was toward the Main Corridor at the
spring that also fed Lower Cave when the
northeast end. Once the cave system opened to
60
the atmosphere by breaching the surface, H2S, SRB thrive in the anaerobic, sulfate-rich water
which is heavier than air, would rise higher in as a biofilm that coats the wall of the submerged
the cave due to barometric convection and portion of the pipe. The produced H2S that
thermal gradients. This breach must have volatilizes into the humid air space diffuses into
already occurred by the time the water table was the condensate on the pipe wall. SOB thriving in
at the level of the Big Room, as the rillenkarren that water oxidize the H2S through a series of
on the limestone breakdown blocks of Appetite steps via sulfur to produce sulfuric acid. Abiotic
Hill (in the borehole passage between the Main oxidation also occurs, but the reaction is slow
Corridor and the Big Room) indicates that and proceeds via thiosulfate (S2O3) (Okabe and
sulfuric acid condensate was still dripping at the others, 2005). The acid corrodes the pipe wall,
point of ascension after the collapse. Original most intensely at the crown (where drips
spongework is extant in the areas peripheral to accumulate) and just above the water line, by
the main path of air flow, as evidenced by the converting the calcium carbonate in the concrete
absence of gypsum rinds in the interior of the into gypsum rinds. The gypsum is usually
spongework. dissolved away by high wastewater flow,
leaving pitted walls of reduced thickness.
The weight of a rind would cause it to peel
Unreacted acid runs down the pipe wall,
off of inclined surfaces. As each rind fell off the
producing rills.
walls and ceiling, a new layer of limestone
became exposed to the acid, and the process When this scenario is compared to an active
would repeat itself, enlarging the spongework sulfuric acid cave like Cueva de Villa Luz, the
into the huge chambers we see today. The similarities seem to outweigh the differences. In
spongework provided greater surface area and both scenarios, sulfuric acid is generated
less rock to dissolve. The height of the chambers subaerially and biotically by oxidizing elemental
and passages appears to have been controlled by sulfur.
both the vertical extent of the spongework (it CONCLUSIONS
does not continue above the ceilings) and the
horizontal distance from the acid source. Above Not all the caves in the Guadalupe
the Bottomless Pit spring orifice, the ceiling was Mountains were formed by spongework
under constant acid attack and a dome was enlargement, especially for those caves that
created (Liberty Dome). Subsequent stoping developed above and beyond the reaches of tidal
increased the ceiling height where closely mixing, where no mixing corrosion occurred.
spaced vertical fractures occurred (e.g., south- Based on a comparison of Carlsbad Cavern with
west end of the Big Room and Appetite Hill). active sulfuric acid caves, it appears that the
geologic setting must include three features for
The fallen rinds dissolved in the water, sulfuric acid hypogene speleogenesis to occur:
causing the water table to become saturated in
gypsum, which eventually precipitated out as a 1) Pre-existing cavernous porosity
blanket that covered the floor wall-to-wall as (sufficient air space for condensation and air
much as 10 meters thick (Hill, 1996). Much of flow) in the carbonate rock to allow sulfuric acid
this gypsum blanket is now gone due to to form above the water table as a vapor and
dissolution by dripping meteoric water, and left within condensate. In the Guadalupe Mountains,
the cave system as the water table lowered. and perhaps in many sulfuric acid caves, this
pre-existing porosity appears to have been
There is a very close, modern analog to this spongework, not phreatic conduits.
model of sulfuric acid speleogenesis, which has
been studied since the mid-1940s (Parker, 1951), 2) Subterranean springs of sulfate-rich
decades before the concept was applied to caves. groundwater (seawater or brine water) to allow
It is called biogenic sulfide corrosion, and SRB to flourish near the top of the water table
occurs in concrete sanitary wastewater pipes and and produce H2S as a byproduct.
tanks (USEPA, 1992). When the wastewater 3) A geothermal heat source to heat the
flow is sluggish and there is air space above it, groundwater to cause upwelling, creating an
61
environment where meso- and/or thermophilic sulfuric acid caves, spongework is believed to be
SRB can thrive, and a thermal gradient between the result of phreatic mixing corrosion at the
the groundwater and the walls above the water freshwater/seawater interface of a coastal
table to promote condensation and an aquifer. The speleogens that are the product of
environment for SOB to thrive. sulfuric acid dissolution include walls that are
pitted and have upward-pointing scallops from
A geologic setting where all three features
convective air currents. The absence of these
combine to produce sulfuric acid caves is
speleogens and gypsum rinds in the peripheral
relatively rare, but includes proximity to a sea or
spongework indicates that it was outside the
a former sea basin with evaporites. This would
reaches of sulfuric acid dissolution and is
explain the common combination of
original. Both chemistry and modern analogs
spongework and sulfate-rich groundwater. The
indicate that sulfuric acid is not generated
relation between petroleum reservoirs and
subaqueously. Therefore, the pre-existing
sulfuric acid caves is a shared geologic setting–
spongework provided the necessary air space
basins. However, the relation ends there. That
above the water table for sulfuric acid to form
minor quantities of oil can migrate up from the
subaerially, mostly by SOB. Without the pre-
basin via fractures and seep into sulfuric acid
existing spongework, sulfuric acid would never
caves on the edge of the platform is not
have formed. Sulfuric acid forms abiotically
surprising, but it is not a forgone conclusion that
from sulfur oxides, so the sulfuric acid equation
the petroleum is the source of the H2S. That H2S
commonly used, H2S + 2O2 → H2SO4, is
is being produced by SRB in connection with
actually shorthand for a two to four step process
high petroleum deposits in the Delaware Basin
of oxidation, which is greatly enhanced by SOB.
is not doubted. However, petroleum-derived
The process of sulfuric acid enlargement of pre-
H2S(aq) in the brine water would remain
existing porosity (spongework) only lasted as
undissociated under lithostatic pressure,
long as the high heat flow from the Basin and
allowing it to oxidize abiotically to sulfur upon
Range crustal thinning and igneous intrusions
mixing with meteoric water, as is found in the
(about 20-0 ma), which provided a warm, saline
Ochoan evaporites (Davis and Kirkland, 1970),
water environment for thermophilic SRB to
or dissociate as it approaches the water table.
thrive in and produce abundant H2S. Perhaps an
Only when H2S is produced near the water table
active sulfuric acid cave like Cueva de Villa Luz
can it be expected to enter air-filled cavities as a
is more of a modern analog to the relic caves of
gas.
the Guadalupe Mountains than initially
An excellent example of how a sulfuric acid perceived, the only significant difference being
cave can transition from active to relic by the that Guadalupe caves were not resurgent caves.
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Palmer, A.N., 2005, Passage growth and
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Palmer, A.N., 2006, Support for a sulfuric acid origin
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Speleogenesis: Evolution of karst aquifers: Cave Books, 454 p.
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Provencio, P., 1998, Age and origin of Carlsbad
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1705-1718.

64
Geologic Framework, Structure, and Hydrogeologic Characteristics of
the Knippa Gap Area in Eastern Uvalde and Western Medina Counties,
Texas
By Allan K. Clark, Diana E. Pedraza, and Robert R. Morris
U.S. Geological Survey, 5563 De Zavala Rd., San Antonio, TX, 78249

Abstract
The Edwards aquifer is the primary source of potable water for the San Antonio area in south-central
Texas. The Knippa Gap area was postulated to channel or restrict flow in the Edwards aquifer in eastern
Uvalde County, and its existence was based on a series of numerical simulations of groundwater flow in
the aquifer. To better understand the function of the area known as the Knippa Gap as it pertains to its
geology and structure, the geologic framework, structure, and hydrogeologic characteristics of the area
were evaluated by the U.S. Geological Survey in cooperation with the U.S. Army Corps of Engineers Fort
Worth District. The principal structural feature in the San Antonio area is the Balcones Fault Zone, which
is the result of Miocene-age faulting. Groundwater flow paths in the Edwards aquifer are influenced by
faulting and geologic structure. Some faults act as barriers to groundwater flow where the aquifer is offset
by 50 percent or more and result in flow moving parallel to the fault. The effectiveness of a fault as a
barrier to flow changes as the amount of fault displacement changes.
The structurally complex area of the Balcones Fault Zone contains relay ramps, which form in
extensional fault systems to allow for deformation changes along the fault block. In Medina County, the
faulting of the Balcones Fault Zone has produced a relay ramp that dips to the southwest from the
Edwards aquifer recharge zone and extends westward and below land surface from Seco Creek. In the
northern part of the county, groundwater moves downgradient (downdip) to the southwest along this relay
ramp towards a structural low (trough). In Uvalde County, groundwater also moves downdip from a
structural high known as the Uvalde Salient towards a structural low (trough) to the northeast. These two
opposing structural dips result in a subsurface structural low locally referred to as the Knippa Gap. This
trough is located in eastern Uvalde County beneath the towns of Knippa and Sabinal. By using data that
were compiled and collected for this study and previous studies, a revised map was constructed depicting
the geologic framework, structure, and hydrogeologic characteristics of the Knippa Gap area in eastern
Uvalde and western Medina Counties, Texas. The map also shows the interpreted structural dip directions
and interpreted location of the structural low in the area known as the Knippa Gap.
REFERENCE
Clark, A.K., Pedraza, D.E., and Morris, R.R., 2013, Geologic framework, structure, and hydrogeologic
characteristics of the Knippa Gap area in eastern Uvalde and western Medina Counties, Texas: U.S. Geological
Survey Scientific Investigations Report 2013–5149, 35 p., 1 pl., http://pubs.usgs.gov/sir/2013/5149/.

65
A Hypothesis for Carbonate Island Karst Aquifer Evolution from
Analysis of Field Observations in Northern Guam, Mariana Islands
By John W. Jenson1, Danko Taboroši1, Kolja Rotzoll2, John E. Mylroie3, and Stephen B.
Gingerich4
1
Water & Environmental Research Institute of the Western Pacific, University of Guam, Mangilao, GU
96923
2
Water Resources Research Center, University of Hawaii, Honolulu, HI 96822
3
Department of Geosciences, Mississippi State University, Mississippi State, MS 39762
4
Pacific Islands Water Science Center, U.S. Geological Survey, Honolulu, HI 96813

Abstract
Field studies of coastal discharge and aquifer properties on northern Guam, an uplifted eogenetic
karst plateau, suggest carbonate island karst aquifers undergo profound reorganization of porosity and
permeability and develop complex but predictable patterns of hydraulic conductivity, internal transport,
and coastal discharge. Discharge features along the coast can be classified into four geomorphic
categories: beach seeps and springs, reef seeps and springs, fracture springs, and cave springs. The styles
and distribution of discharge among these four categories suggest that in aquifers composed of uplifted
geologically young limestone, matrix, fracture, and conduit porosity each play significant but varying
roles. Analyses of tidal attenuation in wells across the plateau indicate that hydraulic conductivity near the
periphery is two orders of magnitude lower than in the interior: 20-800 meters/day, compared to 2,000-
90,000 meters/day. We propose a conceptual framework that relates the four categories of coastal
discharge to the evolution and reorganization of porosities in the aquifer, and offer a hypothesis for the
general distribution of hydraulic conductivity on uplifted carbonate island aquifers, in particular the
juxtaposition of high conductivity in the interior against lower conductivity on the periphery: (1)
dissolutional enhancement of horizontal hydraulic conductivity in the interior, (2) concurrent reduction of
local hydraulic conductivity in the cliffs and steeply inclined rocks on the periphery by case hardening
and perhaps other karst processes that promote occlusion of primary porosity on and inland of the
rampart, and (3) development of the stronger influence of higher conductivity regional-scale features in
the interior relative to the periphery. Complexity is further increased by glacioeustasy and tectonic
fluctuations that moved the freshwater lens vertically through the bedrock column and forced
reorganization of porosities within horizontal planes at different levels.
REFERENCES
Gingerich, S.B., 2013, The effects of withdrawals and drought on groundwater availability in the northern Guam
Lens aquifer, Guam: U.S. Geological Survey Scientific Investigations Report 2013–5216, 76 p.,
http://dx.doi.org/10.3133/sir20135216.
Rotzoll, Kolja, Gingerich, S.B., Jenson, J.W., and El-Kadi, A.I., 2013, Estimating hydraulic properties from tidal
attenuation in the northern Guam Lens aquifer, territory of Guam, USA: Hydrogeology Journal, v. 21, p. 643–
654, DOI 10.1007/s10040-012-0949-9.

66
Using Borehole and Surface Geophysics to Develop a Conceptual
Model of Hydrostratigraphic Layers, Pecos County Region, Texas,
2012
By Jonathan V. Thomas, Johnathan R. Bumgarner, Gregory P. Stanton, Andrew P.
Teeple, and Jason D. Payne
U.S. Geological Survey, 2775 Altamesa Blvd., Fort Worth, TX 76133

Abstract
Future groundwater availability is a concern in the Pecos County region of west Texas, where the
Edwards-Trinity aquifer is an important water resource. The U.S. Geological Survey (USGS), in
cooperation with the Middle Pecos Groundwater Conservation District, Pecos County, City of Fort
Stockton, Brewster County, and Pecos County Water Control and Improvement District No. 1, developed
a conceptual model of the Edwards-Trinity aquifer as part of a multi-phase study of the Pecos County
region. Interpreting the hydrostratigraphic layer contacts from historic and newly collected borehole
geophysical logs, surface geophysical soundings, and geologic data was a major part of model
development. Approximately 200 borehole geophysical logs and 300 well reports, along with 4 time-
domain electromagnetic soundings, and 13 audio-magnetotelluric soundings were correlated to determine
tops and bases of the aquifer (hydrostratigraphic) layers. Data collected by the USGS during 2009-11 and
historical data from 1930-2011 collected by various state and local agencies were used in the model.
Previous studies in this region indicate that groundwater flow is largely controlled by collapse structures
and associated faulting. Multiple north-south and east-west geologic sections were constructed from
hydrostratigraphic surface grids across the Pecos County region to analyze fault zones and local structural
features. Updated grids were created to reflect the fault displacement associated with fault zones, in many
cases showing units juxtaposed across the fault zone. The resulting hydrostratigraphic grids were used
along with geochemistry and hydraulic-property data to develop the conceptual model, which aids in
understanding the hydrogeologic framework, geochemistry, and groundwater-flow system. This
information will be used to construct a groundwater flow model of the region. Additional information on
this study can be found online at http://pubs.usgs.gov/sir/2012/5124/pdf/SIR12-5124.pdf.

67
Perils of a Dissolving State—Florida
By Clint Kromhout
Florida Geological Survey, Department of Environmental Protection, 903 West Tennessee Street,
Tallahassee, Florida 32304

Abstract
Florida is no stranger to tropical storms or sinkholes, and for many who live in the state their primary
worry is focused on the state’s annual hurricane season. Sinkholes, however, have become a storm of
their own in recent years. In June 2012, Tropical Storm Debby dropped record amounts of rain upon
Florida during a time of extended drought, which triggered hundreds of sinkholes that resulted in property
damage across a wide swath of the state. Several subsequent well-publicized sinkhole events in Florida,
combined with pervasive insurance industry financial troubles, have brought these natural karst features
to main stage. The Florida Division of Emergency Management (DEM), a first responder to many of
these sinkhole incidents, sought a science-based solution to assessing regional sinkhole vulnerability. In
September 2013, the DEM’s Mitigation Section contracted with the Florida Geological Survey to produce
a statewide map depicting relative vulnerability to sinkhole formation.

68
 MODELING KARST AQUIFERS

Taking the Mystery Out of Mathematical Model Applications to Karst

Aquifers—A Primer
By Eve L. Kuniansky
U.S. Geological Survey, 1770 Corporate Drive, Suite 500, Norcross, GA 30093

Abstract
Advances in mathematical model applications toward the understanding of the complex flow,
characterization, and water-supply management issues for karst aquifers have occurred in recent years.
Different types of mathematical models can be applied successfully if appropriate information is available
and the problems are adequately identified. The mathematical approaches discussed in this paper are
divided into three major categories: 1) distributed parameter models, 2) lumped parameter models, and 3)
fitting models. The modeling approaches are described conceptually with examples (but without
equations) to help non-mathematicians understand the applications.
INTRODUCTION differential equations, which are solved
numerically. This first category of mathematical
Understanding the nature of karst aquifers,
models is used to simulate flow in a karst aquifer
including their management and protection,
as inferred from hydrogeologic investigations of
poses unique challenges. Advances have been
all types. The second category, lumped
made in the development (codes developed in
parameter models, is based on mathematical
late 1970s through 90s) and use of mathematical
methods that combine a physically based
model applications (late 1980s to present) to
equation (ordinary differential equation) with
improve the understanding of dual flow
control theory or operations research techniques
processes as well as characterization and
(Hillier and Lieberman, 1967; Takahashi and
management of karst aquifers.
others, 1972; U.S. Department of Agriculture,
Several different types of mathematical 1973). This second category has some physical
models can be applied to problems in complex basis, but generally lumps the karst aquifer into
dual or triple porosity karst aquifers. Depending large basins and is not meant to simulate details
on the types of data available and the problems of the flow system. This type of model also is
that are identified, different mathematical incapable of distinguishing between different
techniques can be applied appropriately. The system compartments and different flow
naming of the types of mathematical models that processes. Many of the hydrogeochemical
have been applied has become somewhat mixing models used for estimating the average
confusing because terminology has not been age of water (binary mixing, piston flow,
used consistently among all authors. This paper exponential, and dispersion) fall into this
groups the different mathematical approaches category (Maloszewski, 2000; Katz, 2004). The
into three major categories: 1) distributed third category, fitting models, refers to
parameter models, 2) lumped parameter models, mathematical methods that involve either
and 3) fitting models. The three categories were statistical regression, fitting shape functions,
chosen based on the general mathematical statistical transfer functions, or use of pattern
methods applied in the calculations. The recognition functions, such as artificial neural
modeling approaches are described conceptually networks to recreate observations (Long and
with examples (but without equations) to help Putnam, 2002, 2007; Hu and others, 2007).
non-mathematicians understand the applications. There is some overlap in the mathematical
The first category, distributed parameter or methods employed in the categories of lumped
deterministic numerical models, includes models parameter models and fitting models, because
derived for physical processes defined by partial both categories involve mathematical techniques
69
that come from the fields of control theory continuum porous equivalent model with a
(sometimes called operations research) or linear discrete one-dimensional pipe network. The last
systems theory (U.S. Department of Agriculture, two examples are the discrete single-fracture set
1973). (DSFS) and the discrete multiple fracture set
(DMFS) models, which may involve the
DISTRIBUTED PARAMETER MODELS
stochastic generation of fracture networks;
Distributed parameter models, also called however, the networks once generated are
deterministic numerical models, are frequently simulated with equations for pipe or fracture
applied to karst aquifer systems (Teutsch and flow. Each approach has advantages and
Sauter, 1998; Scanlon and others, 2003). disadvantages, described below (fig. 1).
Distributed parameter models are process
Single Continuum or Porous Equivalent
oriented: equation(s) are derived that include the
Models
important physical process (es) that result in a
partial differential equation(s) that can be solved A single continuum porous equivalent
numerically. In general, the physical processes approach using the groundwater flow equation
involved in the flow of water through an aquifer based on laminar flow is the simplest to apply.
are simplified in order to develop an equation Generally, this approach has been applied for
that can be solved by a numerical method, such regional flow problems because the investigation
as finite element or finite difference. Because scale is much greater than the scale of the
distributed parameter models require dividing heterogeneities (conduits), and for water-
(discretizing) the system into smaller volumes, resources investigations in which the models can
such as finite-difference cells or finite elements, be calibrated to flow and head information and
representation of the karst aquifer is greatly only water budgets are desired (Kuniansky and
simplified, but the physical parameters, such as Holligan, 1994; Davis, 1996; Teutsch and
storage, hydraulic conductivity, or transmissivity Sauter, 1998; Kuniansky and others, 2001;
are distributed spatially and allowed to vary in Svensson, 2001; Scanlon and others, 2003;
each cell or element. Davis and Katz, 2007; Davis and others, 2010).
In general, this approach can simulate transient
Several types of deterministic models have
springflow for monthly or annual averages, but
been applied to karst aquifers (fig. 1). The
may not reproduce detailed storm event
simplest method is called the single continuum
hydrographs as well as other model types as a
porous equivalent, potential flow,
result of the onset of turbulence during storms
(Hill and others, 2010; Kuniansky and others,
2011; Gallegos and others, 2013; Saller and
others, 2013). However, simulations of
advective transport using a single continuum
model are frequently performed and are able to
match geochemical age estimates and tracer-test
times of travel when using a porosity of less than
5 percent (Knochenmus and Robinson, 1996;
Figure 1. Approaches to karst modeling with deterministic
Kuniansky and others, 2001; Renken and others,
numerical models and some stochastic methods for 2005; Davis and others, 2010). The flow in these
developing fracture networks, where the networks are studies was mainly determined by the model cell
simulated with flow equations for pipes or fractures (from hydraulic conductivity and total model layer
Teutsch and Sauter, 1998). thickness. In some cases where conduit locations
heterogeneous continuum, distributed parameter, are known, the finite-difference cells with
or smeared conduit approach. Another method is conduits are assigned much greater hydraulic-
called the dual continuum porous equivalent conductivity values than surrounding cells and
approach (DCPE), which links two flow regimes have been successful in reproducing transient
at each cell or element with an exchange term. spring discharge and matching tracer tests in part
The hybrid model (HM) couples a single of the Floridan aquifer system (Davis and others,
70
2010). A similar attempt was not successful Dual Continuum or Porous Equivalent
within the Edwards aquifer system (Lindgren Models
and others, 2009).
Dual continuum models link two single
Both finite difference and finite element continuum models via a hydraulic head-
methods have been widely applied. Finite dependent flux term between each model cell.
element methods allow for greater variation in One continuum has high hydraulic conductivity
element size, and streams, wells, and springs can and low storage, representing conduits, and the
be more accurately located. Finite elements other continuum has low hydraulic conductivity
readily accommodate sites where geologic and high storage, representing the primary
structure results in preferential directions of porosity of the rock matrix. The main advantage
dissolution that can create anisotropy varying in of the dual continuum approach is that the
direction over the aquifer domain (Kuniansky detailed geometry of the conduits is not required
and Lowther, 1993). However, developing (Teutsch, 1993; Sauter, 1993; Lang, 1995), and
model datasets for a finite-element model is dual continuum models have been applied
more complex than a block-centered finite- successfully when the geometry of conduits is
difference scheme, and a graphic-user interface not known (Teutsch and Sauter, 1991; Teutsch,
(GUI) is essential. As computer speeds have 1993; Sauter, 1993; Teutsch and Sauter, 1998;
increased, so has the simulation speed of larger Painter and others, 2007). Dual continuum
finite-difference model grids with smaller grid models can simulate rapid variations in
spacing. Additionally, packages such as the discharge and head change following recharge
horizontal flow barrier package for MODFLOW events and can accommodate the variable
(Hsieh and Freckleton, 1993) have been used to contributions of conduit and rock matrix flow
help incorporate geologic structure that reflects with time. The data demand of the model is
anisotropy rather than direct incorporation of relatively modest and the parameterization effort
anisotropy into the flow equation (Lindgren and is manageable for general field studies. The dual
others, 2004). The new code for MODFLOW continuum model, however, is not always
that allows unstructured grids has many of the capable of simulating transport processes on a
advantages of finite elements, but also requires a small scale (Mohrlok, 1996).
sophisticated GUI (Panday and others, 2013).
Hybrid Models
Most single-continuum applications A hybrid model is the coupling of a single
described above involve simulating laminar continuum model with a discrete conduit or pipe
flow. The most commonly used computer code network model (Kiraly, 1998; Teutsch and
is MODFLOW Sauter, 1998). The approach allows the
(http://water.usgs.gov/ogw/modflow/). However, integration of detailed information about the
turbulent flow for large-pore aquifers, where conduits in areas where the geometry of the
flow becomes turbulent at low Reynolds conduits may be known, thus providing a more
numbers, has been incorporated as an option into physically representative model. They are
MODFLOW-2005, called the conduit flow considered hybrid models because they link a
process mode 2 (MODFLOW-CFP mode 2; single continuum model for groundwater flow in
Shoemaker and others, 2008; Kuniansky and 3 dimensions with a 1-dimensional pipe network
others, 2008). Reimann and others (2011a) model. The two models exchange water via
derived a general form for incorporation of hydraulic head-dependent flux terms and iterate
turbulence into MODFLOW-CFP mode 2, calculations between the two models until both
which can simulate turbulence for porous media converge, similar to the dual continuum model.
or conduits, employing a single continuum
approach. The 2008 distribution of the conduit flow
process (CFP) for MODFLOW-2005 (Harbaugh,
2005; Shoemaker and others, 2008) takes the
hybrid modeling approach developed in the
Conduit Aquifer Void Evolution (CAVE) code
71
(Clemens and others, 1996; Bauer and others, Discrete Single and Multiple Fracture
2003; Liedl and others, 2003) from a research Network Models
code to a tool that can be used by a wider group
The discrete fracture approach has been
of practitioners. The main advantage of this
proposed for problems where transient solute-
modeling approach is that it allows simulation of
transport responses are desired for a system
the high transport velocities observed in karst
dominated by conduits (Adams and Parkin,
systems, while continuing to represent the
2002). Knowledge of the fracture network
presence of a lower hydraulic conductivity
geometry, however, is required for this model.
matrix, representing the storage component of
Generally, there are limited data for mapping the
the karst aquifer. Limitations of this approach
fracture network(s); therefore, stochastic
are the lack of geometric data for the conduit
methods are often used to generate the single- or
system (i.e., effective properties have to be
multiple-fracture network for deterministic
assumed). The first release of CFP has
numerical simulations of flow. The
limitations in that the pipe network is intended
disadvantages of discrete multiple fracture
for full pipes (flow controlled by difference in
networks are the requirements of detailed
pressure gradient - no free surface) and does not
knowledge of a fracture network at multiple
account for free surface flow (open channel
scales and the application of computationally
flow-flow is under atmospheric pressure and
intensive codes that have long computer
flow is dominated by gravity.)
simulation time and memory requirements
Several models originally intended for (Lang, 1995). Application of this approach to
surface-water systems have been applied to karst field scale problems is not common, and no
aquifers. The Storm Water Management Model examples can be provided.
(SWMM) (Metcalf and Eddy Inc., 1971),
Application of Deterministic Numerical
designed for simulation of sewer systems, was
Models – Example Comparisons of
applied by Peterson and Wicks (2006) to
Single Continuum and Hybrid Models
simulate conduits, but no interchange with the
rock matrix was simulated. The MODBRANCH The karst drainage system of the Wakulla
code (Swain and Wexler, 1996) was modified Springs-Leon Sinks, Florida, submerged conduit
for simulation of karst systems by Zhang and system is moderately well characterized as a
Lerner (2000). MODBRANCH was originally result of pioneering work accomplished over the
developed by coupling a 1-dimensional free- past 20 years by cave divers of the Global
surface open channel flow model with the top Underwater Explorers as part of their Woodville
layer of a 3-dimensional groundwater flow Karst Plain Project (WKPP). The Woodville
model for simulation of groundwater/surface- karst plain containing the Wakulla Springs-Leon
water interactions. Reimann and others (2011b) Sinks system covers an area of 450 mi2. Wakulla
developed the ModBraC version of a hybrid Springs is one of the largest first magnitude
model that couples the single continuum model springs in Florida with an average flow of
with a pipe network model capable of simulating approximately 400 ft3/s and issues from a large
storage in the conduit system, including full opening forming the headwaters of the Wakulla
flowing pipes as well as cave streams in the River at Edward Ball Wakulla Springs State
conduits. An accurate representation of conduit Park, Florida.
storage is essential in order to be able to The WKPP maps served as the basis for
simulate the lag time between discharge changes three model approaches used for simulation of
and the transport signal (for example, the groundwater-conduit system: (1) single
temperature or conductivity) after recharge continuum laminar flow only (equivalent porous
events. media approach documented in Davis and
others, 2010), (2) a hybrid model that consists of
a single continuum model coupled to a 1-
dimensional pipe-flow network capable of both
turbulent and laminar flow (Gallegos and others,
72
2013), which is an evaluation of the CFP mode l Model approach 1, the subregional model of
(Shoemaker and others, 2008), and (3) simulated Davis and others (2010), was a single continuum
turbulence within the model layer with large transient simulation from January 1, 1966, when
hydraulic-conductivity values assigned to cells spray field (irrigation using treated wastewater
with conduits using the single continuum model as part of municipal wastewater treatment
(Davis and others, 2010; Kuniansky and others, processing) operations began, through 2018,
2011), which is an application of CFP mode 2 when effects of system upgrades will occur. The
(Shoemaker and others, 2008, with modification stress periods were mostly annual. Calibration
to mode 2 documented in Reimann and others, data for water levels and spring discharge were
2011a). Large hydraulic-conductivity values available for November 1991, and May to early
were assigned to cells that represent mapped June 2006. Additional hydrologic information
conduits (fig. 2) in approaches 1 and 3. For the was provided by tracer tests conducted in 2006
hybrid model, the single continuum model of and 2007 by Hazlett-Kincaid, Inc. (listed in
Davis and others (2010) was modified by Davis and others, 2010). The hybrid model
removing the large hydraulic-conductivity cells (approach 2) was calibrated to steady-state
and replacing them with a pipe network using conditions for the same calibration datasets as in
MODFLOW-CFP mode 1 (Shoemaker and approach 1 (Gallegos and others, 2013). The
others, 2008) and recalibrated to a steady-state third approach, single continuum with
average condition (Gallegos and others, 2013). turbulence turned on for layer 2, yielded almost
identical heads and flows as in Davis and others
(2010) for the original monthly to annual
average transient simulation. All three model
approaches simulated observed average spring
discharge at Wakulla and Spring Creek Springs
within 10 percent, and head residuals were
within the calibration criteria of plus or minus 5
feet. Thus, for average spring discharge and
tracer test time of travel, the models produce
similar results and all are considered acceptable
calibrations (Davis and others, 2010; Kuniansky
and others, 2011; Gallegos and others, 2013).
To observe differences between the single
continuum and hybrid model approaches, a
transient period with daily spring-flow
observations and a storm event (rising and
falling springflow, no recalibration) was
simulated (Kuniansky and others, 2011;
Gallegos and others, 2013). For the 52-day
storm event, which was simulated with daily
time steps, none of the models simulated the
observed peak discharge accurately (within 10
percent of observed) (fig. 3). The shape of the
Figure 2. Simulated hydraulic conductivity in model layer storm hydrograph for Wakulla Springs is best
2 with large hydraulic conductivity located at mapped matched by the single continuum with
submerged conduits (modified from Davis and others,
2010, fig. 27). turbulence (approach 3, labeled CFP mode 2 in
Reimann and others (2011a), fig. 3), and the
The field applications of MODFLOW-2005 peak discharge at about day 15 is matched
(Harbaugh, 2005) and the CFP (Shoemaker and within 10 percent; however, neither approach 1
others, 2008) examined spring discharge under (labeled MODFLOW, fig. 3) nor approach 2
various time discretization and flow conditions. (labeled CFP mode 1 hybrid, fig. 3) matched
73
peak discharge within 30 percent. If the total watershed in the Madison aquifer in South
volumes of measured and simulated discharge Dakota and found that although the hybrid
for the 52-day period at Wakulla Springs are model matched observation well heads better,
compared, approach 1 matched observed within both models simulated spring discharge
23 percent, approach 2 within 16 percent and accurately. The Wakulla Springs example
approach 3 within 0.01 percent of total volume indicates that, for simulation of average
of discharge under the 52-day hydrograph. conditions, none of the three model approaches
Model 1 overestimated and model 2 is distinctly better (hybrid model calibrated with
underestimated peak discharge at Wakulla steady-state). For the simulation of a transient
Springs. The computation time required by the 52-day storm hydrograph, the single continuum
hybrid model approach 2 (over 72 hours on a with turbulence model (approach 3) matched
personal computer) was more than 100 times peak spring discharge within 10 percent at
longer than the time required for the single Wakulla Springs, and the hybrid model
continuum approaches 1 and 3. This test using (approach 2) matched the total volume of
hybrid models is perhaps the largest ever springflow. Improved calibration with parameter
undertaken, with more than 1,000 pipes and estimation techniques was not possible for the
nodes simulated. The hybrid approach requires hybrid model approach as a result of the long
that two models are iteratively solved until both simulation time. Thus, it is unclear if the extra
converge for each 1-day stress period, resulting effort required to use a hybrid model, both in
in very slow convergence. The greater than 72- data preparation and computation time, is
hour simulation time precludes using parameter justified for large submerged conduit networks
estimation to improve model fit for the hybrid (over 100 pipes and nodes in Kuniansky and
model and thus, no attempt was made to others, 2011). The change in temporal
recalibrate all three models to both annual or discretization appeared to result in the need for
monthly average and the daily storm recalibration of the models for storm events if
hydrographs (Kuniansky and others, 2011). the desired accuracy between the model
simulation and observed data was 10 percent or
less. However, as computer speeds increase, it
likely will be feasible to fully calibrate the
hybrid models using parameter estimation,
resulting in more physically realistic models. An
additional test of model capabilities could be
comparison of residence times of rapid (event)
flow components or slow flow matrix
components, derived from use of geochemical
mixing models with hydrograph separation
techniques given time series datasets of
chemistry and flow information. Unfortunately,
no such data were available at the time of
publication.
Figure 3. Simulated and observed springflow at Wakulla
Springs (modified from Gallegos and others, 2013). LUMPED PARAMETER MODELS
A recent study (Hill and others, 2010), The control theory approach has been
comparing the hybrid model approach with the successfully applied to simulate karst aquifers
single continuum model approach for two other using mathematical methods for solving sets of
spring systems in Florida concluded that the ordinary differential equations, as for example,
hybrid model more closely simulated observed filling and mixing of water in a tank or a
transient spring discharge. Another recent study network of tanks. Coefficients (or lumped
(Saller and others, 2013) converted a single parameters) for each tank are developed by
continuum model to a hybrid model for a calibrating a system of equations (Wanakule and
Anaya, 1993; Barret and Charbeneau, 1997).
74
Data preparation for lumped parameter models recharge estimates. Additionally, the monthly
is simpler than that used in deterministic pumpage by county was reapportioned to each
numerical models, and computational times are watershed (Wanakule and Anaya, 1993). These
faster. However, detailed representation of the values were then matched to monthly
aquifer is not possible using this approach. groundwater levels in each basin and to the
Groundwater withdrawals and recharge are historical spring discharge at Comal and San
summed together for each tank, which represents Marcos Springs by calibrating storage and
a geographic area (or spring basin), rather than transmissivity parameters for each tank. The
being placed at actual locations. In addition, filtering methods for the disaggregation of
withdrawals and recharge may be used as input recharge fall into category 3 (fitting models),
to simulate spring discharge. This method may which includes time series techniques.
be adequate for providing gross estimates of the Wanakule and Anaya (1993) were successful in
effects of hypothetical pumpage and recharge refining estimates of monthly recharge and
rates on spring discharge as well as for pumpage for each basin and simulating the
providing better estimates of recharge given spring discharge at Comal and San Marcos
natural discharge and pumpage. Mathematical Springs (fig. 4c) along with water levels in each
filters can be applied to some of the input data, basin (not shown herein, refer to Wanakule and
such as development of filters to distribute the Anaya, 1993).
annual basin recharge to each month, to gain a
Schulman and others (1995) developed
better fit of observed versus simulated spring
equations for stochastically generating recharge
discharge (Dreiss, 1982; Wanakule and Anaya,
for the watershed basins (generated recharge has
1993).
the same statistical properties as the historical
Application of Lumped Parameter data--recharge estimates available since 1934.)
Models Endangered species at the springs are at issue,
and the courts have required minimum
The lumped parameter modeling method is
discharges to be maintained at both springs.
demonstrated in a simulation of springflow at
Groundwater use frequently is restricted during
Comal and San Marcos Springs, Texas. The
the summer months even as the population
model input and calibration data were based on
continues to grow. Thus, water-resources
annual estimates of recharge and pumpage in
planners recognize that water may need to be
nine surface-water basins and an index water
imported to maintain discharge at the springs.
level in each basin of the Edwards aquifer
Because of its computational speed and
(Wanakule and Anaya, 1993). The lumped
simplicity, the calibrated lumped parameter
parameter mathematical relation was developed
model of Wanakule and Anaya (1993),
much like a statistical regression model where
combined with the generated recharge scenarios,
recharge and pumpage in each lumped
were used in an attempt to screen water-supply
parameter block (conceptually, these are nine
options for the Edwards aquifer (Watkins and
interconnected tanks as described above) were
McKinney, 1999).
treated as input to a set of linked tanks that
transport water to the major springs. The
mathematical description of each tank was
formulated with an ordinary differential
equation. Figure 4 shows the Edwards aquifer
and catchment area and how the tanks are
arranged. Surface runoff from the catchment
area infiltrates the Edwards aquifer across its
outcrop area. Wanakule and Anaya (1993) used
the recharge and pumpage data as inputs to the
system. They developed filters to disaggregate
the annual estimates of recharge into monthly
estimates using streamgage data and annual
75
 recently been applied to karst aquifers (Neuman
and de Marsily, 1976; Dreiss, 1982; Wicks and
Hoke, 2000). To some extent, these are
considered “black box” methods because
detailed knowledge about the physical system
(locations of conduits, transmissivity, or storage
properties) is not required. These methods have
advantages and disadvantages that are similar to
the lumped parameter models. In fact, statistical
models are similar to the lumped parameter
approach described earlier, except that they lack
any physically-based differential equation to
describe the physical aquifer. Instead, complex
mathematical functions sometimes based on
statistical or probability distributions are used as
transfer functions, with time offsets and shape
terms used to take an input(s) and create an
output (response) that mimics the desired output
(response) signal. Another fitting model would
be the application of artificial neural networks, a
form of pattern recognition, to karst aquifers (Hu
and others, 2007; Trichakis and others, 2009). A
physical understanding of how the karst aquifer
system works is required to select an appropriate
input, such as recharge and pumpage that is
physically related to the output, such as
springflow or water level.
Simple regression analysis has been used to
Figure 4. A) Map of the Edwards aquifer and its recharge predict spring discharge from the water level of
area, B) Schematic diagram of the lumped parameter a nearby well by developing a linear regression
model, and C) Comparison of observed and simulated
equation using historical data. This technique
spring discharge (modified from Wanakule and Anaya,
1993). has also been used for tidally affected springs by
developing a multiple linear regression using
FITTING MODELS both water levels at a nearby well and stage data
Fitting or statistical models have long been to estimate spring discharge (Wanakule, 1988;
used in the field of hydrology. For this Knochenmus and Yobbi, 2001). Development of
discussion, statistical models involve the the regressions requires numerous discharge
matching of field data to either a statistical measurements over the full range of conditions
distribution or the development of a single- or anticipated, but does not involve time-series
multiple-linear regression equation. analysis.
Additionally, the broad category includes other More complex auto-correlation analysis has
forms of linear systems modeling in which the been used with time-series data to predict
karst aquifer is treated as a filter, and complex springflow from precipitation data (Eisenlohr
mathematical functions (linear kernels) are used and others, 1997). Time-series analysis has also
to process inputs like recharge and pumpage to been used with isotope data to estimate travel
generate an output of springflow. The simplest times and the diffuse versus conduit flow nature
application of linear systems in hydrology has of karst aquifers as demonstrated with the
been in rainfall-runoff models that employ what following case study.
is called the unit hydrograph method (Sherman,
1932). These and similar techniques have
76
 The advantage of fitting models is that they
are easy to apply and to calibrate. The
disadvantage is that these models are specific to
the respective catchment, and model results are
highly uncertain if prediction simulations require
input or output variables that exceed those of the
historic calibration period.
Application of Fitting Model
Stable-isotope samples were collected at
about 6-week intervals over a 6-year period at a
streamflow-loss zone that recharges the karstic
Madison aquifer in South Dakota and at a
nearby well located close to or within a main A) Location of the study area.
groundwater flow path (fig. 5a) (Long and
Putnam, 2002, 2007). Time-series analysis of the
isotope data indicates that the well responds
rapidly to recharge from a sinking stream during
wet periods. The hydraulic connection between
the stream’s loss zone and the well primarily
results from flow along conduits. During dry
periods when streamflow is low, isotopic values
in the well samples primarily were influenced by
aquifer-matrix water that has been in storage for
many months or years.
Data were analyzed by correlation and B) δ18O data and streamflow recharge to the Madison
aquifer from Spring Creek for 1996 through 2001. The
linear-systems analysis for a 34-month period of curved line through the δ18O data points was interpolated
high recharge. Figure 5b shows the original data by a cubic spline. The A sections indicate periods of near-
that were used to develop the model. Figure 5c maximum recharge, whereas B sections indicate periods of
shows the final model and the log-normal lower recharge. The streamflow recharge has a maximum
distribution used as the transfer function for estimated rate of 21 ft3/s (Hortness and Driscoll, 1998).
estimating the oxygen-18 isotope value in the
spring discharge from the streamflow
concentration as the input data.
The stable-isotope and water-level datasets
correlate most closely when the data from the
losing stream reach and the well are lagged 22
days, which may approximate the travel time
from the loss zone to the well. Linear-systems
analysis results in an estimated travel time to the
well of about 15 days and a system memory of 2
to 3 years, resulting from diffuse matrix flow.
C) Results of linear-systems analysis including the
Based on these analyses, the conduit-flow computed δ18O data for the sampled well and the transfer
velocity was estimated at 380 to 800 feet/day function used in the analysis. The curved line through the
(120 to 240 meters/day). A log-normal δ18O data points was interpolated by a cubic spline.
distribution approximates the distribution of Figure 5. Statistical regression model of stable isotope
travel times of a plume for conduit flow. values for springs in the Madison Limestone aquifer. A)
Location of study area, B) Isotope and streamflow data, and
C) Linear-systems analysis model (from Long and Putnam,
2002).

77
CONCLUSIONS Davis, J.H., Katz, B.G., and Griffin, D.W., 2010,
Nitrate-N movement in groundwater from the
The mathematical methods for simulation of land application of treated municipal wastewater
karst aquifers are well developed. All of the and other sources in the Wakulla Springs
methods require an understanding of each karst springshed, Leon and Wakulla Counties, Florida,
aquifer and its unique hydrogeologic setting. 1966-2018: U.S. Geological Survey Scientific
Investigations Report 2010-5099, 90 p.
The main difficulty in application of the
methods relates to the difficulty of mapping the Dreiss, S.J., 1982, Linear kernels for karst aquifers:
conduit networks, or having high-quality Water Resources Research, v. 18, no. 4, p. 865–
datasets to calibrate the models. Advances in 876.
geophysics, tracer testing, geochemistry, cave Eisenlohr, Laurent, Kiraly, Laszlo, Bouzelboudjen,
exploration, streamflow measurement, and Mahmoud, and Rossier, Yvan, 1997, Numerical
recharge estimation will further improve simulation as a tool for checking the
application of the mathematical models. interpretation of karst spring hydrographs: Journal
of Hydrology, v. 193: p. 306-315.
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81
Refined Hydrostratigraphic Framework and Model of the Edwards
Aquifer, Texas
By S. Beth Fratesi1, Ronald T. Green1, Ronald M. McGinnis1, Hakan Basagaoglu1,
Leslie Gergen1, Jim Winterle2, Marques Miller1, and F. Paul Bertetti1
1
Southwest Research Institute®, 6220 Culebra, San Antonio, Texas 78238 (www.swri.edu)
2
Edwards Aquifer Authority, 900 E. Quincy, San Antonio, Texas 78215 (www.edwardsaquifer.org)

Abstract
A refined conceptual and numerical groundwater flow model is being developed for the karstic
Edwards aquifer in central Texas. Improved understanding of the Edwards aquifer, its extent, boundary
conditions, recharge, and internal hydraulics warrants development of this new conceptualization and
model. The refined conceptualization is predicated on an enhanced hydrostratigraphic framework model.
The framework has as many as nine separate units, although not all units are pervasive across the model
domain. Over 100 faults are explicitly incorporated into the model. The framework was developed to be
consistent with hydraulic characteristics of the Edwards aquifer to facilitate calibration of a new
numerical model. The ensuing hydrostratigraphic framework and numerical model have resulted in
significant refinements to the existing Edwards aquifer geologic framework and groundwater flow model.
These refinements provide enhanced opportunity to replicate and predict the hydraulic response of the
aquifer.

82
Simulation of Groundwater Flow in the Edwards-Trinity and Related
Aquifers in the Pecos County Region, Texas
By Brian R. Clark1, Johnathan R. Bumgarner2, Natalie R. Houston3, and Adam L.Foster3
1
U.S. Geological Survey, 700 W. Research Blvd., Fayetteville, AR, 72701
2
U.S. Geological Survey, 5563 De Zavala Rd., San Antonio, TX, 78249
3
U.S. Geological Survey, 1505 Ferguson Ln., Austin, TX, 78754

Abstract
The Edwards-Trinity aquifer is a vital groundwater resource for agricultural, industrial, and public
supply uses in the Pecos County region of western Texas. The U.S. Geological Survey completed a
comprehensive, integrated analysis of available hydrogeologic data to develop a numerical groundwater-
flow model of the Edwards-Trinity and related aquifers in the study area in parts of Brewster, Jeff Davis,
Pecos, and Reeves Counties. The active model area covers about 3,400 square miles of the Pecos County
region of Texas west of the Pecos River, and its boundaries were defined to include the saturated areas of
the Edwards-Trinity aquifer. The model is a five-layer representation of the Pecos Valley, Edwards-
Trinity, Dockum, and Rustler aquifers. The Pecos Valley aquifer is referred to as the alluvial layer, and
the Edwards-Trinity aquifer is divided into layers representing the Edwards part of the Edwards-Trinity
aquifer and the Trinity part of the Edwards-Trinity aquifer, respectively. The calibration period of the
simulation extends from 1940 to 2010. Simulated hydraulic heads generally were in good agreement with
observed values; 1,833 out of 2,929 (63 percent) of the simulated values were within 25 feet of the
observed value. The average root mean square error value of hydraulic head for the Edwards-Trinity
aquifer was 33.61 feet, which was approximately 4 percent of the average total observed change in
groundwater-level altitude (groundwater level). Simulated springflow representing Comanche Springs
indicates a similar pattern as compared to the observed springflow. Independent geochemical modeling
corroborates results of simulated groundwater flow that indicates groundwater in the Edwards-Trinity
aquifer in the Leon-Belding and Fort Stockton areas is a mixture of recharge from the Barilla and Davis
Mountains and groundwater that has upwelled from the Rustler aquifer.
The model was used to simulate groundwater-level altitudes resulting from prolonged pumping to
evaluate sustainability of current and projected water-use demands. Each of three scenarios utilized a
continuation of the calibrated model. Scenario 1 extended recent (2008) irrigation and nonirrigation
pumping values for a 30-year period from 2010 to 2040. The results of scenario 1 indicate widespread
declines in groundwater levels ranging from 5.0 to 15.0 feet. Projected groundwater-level declines in and
around the Leon-Belding area and the Fort Stockton area are almost nonexistent apart from a small area
of decline in the southwestern part of the Leon-Belding area. Scenario 2 evaluated the effects of extended
recent (2008) pumping rates as assigned in scenario 1, with year-round permitted values in the Belding
area. Results of scenario 2 reflect the modification of year-round pumping in the Belding area through
increased declines in groundwater levels (maximum decline of approximately 27.3 feet). The extent of the
projected groundwater-level decline in the Leon-Belding area expanded from that of scenario 1 to include
much of the central and southern part of the irrigation area. Scenario 3 evaluated the effects of periodic
increases in pumping rates over the 30-year extended period. Results of scenario 3 are similar to the
results of scenario 2 in terms of the areas of groundwater-level decline. The maximum projected
groundwater-level decline increased to approximately 32.7 feet in the Leon-Belding area and the extent of
the decline is larger areally than that of scenario 2, joining with an existing area of decline to the north.
The localized nature of the projected groundwater-level declines is a reflection of the highly fractured
nature of the Edwards-Trinity aquifer. Additionally, the finding that simulated springflow is highly
contingent on the transient nature of the underlying hydraulic heads indicates the importance of
adequately understanding and characterizing the entire groundwater system.

83
REFERENCES
Bumgarner, J.R., Stanton, G.P., Teeple, A.P., Thomas, J.V., Houston, N.A., Payne, J.D., and Musgrove, Marylynn,
2012, A conceptual model of the hydrogeologic framework, geochemistry, and groundwater-flow system of
the Edwards-Trinity and related aquifers in the Pecos County region, Texas: U.S. Geological Survey Scientific
Investigations Report 2012-5124 (revised July 10, 2012), 74 p., available at http://pubs.usgs.gov/ds/678/.

Clark, B.R., Bumgarner, J.R., Houston, N.A., and Foster, A.L., 2014, Simulation of groundwater flow in the
Edwards-Trinity and related aquifers in the Pecos County region, Texas: U.S. Geological Survey Scientific
Investigations Report 2013-5228, 56 p., available at http://pubs.usgs.gov/sir/2013/5228/.

Pearson, D.K., Bumgarner, J.R., Houston, N.A., Stanton, G.P., Teeple, A.P. and Thomas, J.V., 2012, Data collection
and compilation for a geodatabase of groundwater, surface-water, water-quality, geophysical, and geologic
data, Pecos County region, Texas, 1930–2011: U.S. Geological Survey Data Series 678, 67 p., available at
http://pubs.usgs.gov/ds/678/.

Thomas, J.V., Stanton, G.P., Bumgarner, J.B., Pearson, D.K., Teeple, A.P., Houston, N.A., Payne, J.P., and
Musgrove, MaryLynn, 2012, A conceptual model of the hydrogeologic framework, geochemistry, and
groundwater-flow system of the Edwards-Trinity and related aquifers in the Pecos County region, Texas: U.S.
Geological Survey Fact Sheet 2013-3024, 6 p., available at http://pubs.usgs.gov/fs/2013/3024/.

84
Automatic Methods of Groundwater Flow Model Construction of the
Ozark Plateaus Aquifer System
By Brian R. Clark1 and Joseph M. Richards2
1
U.S. Geological Survey, 700 West Research Blvd., Fayetteville, AR 72701
2
U.S. Geological Survey, 1400 Independence, Rolla, MO 65401

Abstract
As computational speeds increase, highly parameterized groundwater flow models are becoming
more common. A typical model may include thousands or tens of thousands of parameters representing
components of hydraulic properties, recharge, boundary conditions, and stresses. Often these parameters
are estimated or include measured values that include a certain degree of error. The sensitivity of
simulation results to the accuracy of these parameters or to variability in these parameters is evaluated by
comparing changes in parameter values to the resultant effect on simulated water levels and flows. The
scale of horizontal and vertical discretization used to develop the model grid may introduce structural
noise into the simulation, however, and changes in grid dimensions can directly affect calibrated
parameters. Despite this recognized dependence of model parameters on the underlying grid, grid
dimensions typically are developed early in the model construction process and are based on a quick
computation of potentially active cells with some regard to the resolution of existing data and the purpose
of the simulation. The grid dimensions are then held constant throughout the modeling process. Using
automated scripting methods to dynamically rediscretize a model grid allows the grid dimensions to
become parameters that also can be evaluated by using sensitivity analysis to optimize the cell sizes and
layering, and minimize the structural noise.
The challenge of including grid dimensions as a parameter of the model is that the model grid is the
basis of all model inputs (layer, row, and column is the typical method to reference the location of all
features in a model), and changes to the dimensions of the grid affect how all simulated features are
represented. Therefore, the automated scripting methods must be capable of intersecting each feature
within the model grid and creating appropriate model files. The Python® scripting language provides
robust methods to interface with database structures, text-based files, and spatial data files. Initial tests of
the scripts applied to information about the Ozark Plateaus aquifer system indicate potential in evaluating
the sensitivity of grid dimensions to groundwater-level altitude. The scripts are used to create the grid
(with associated layer elevations), split layers if desired, assign hydraulic parameter zones, create
observation files, and create preliminary river and drain files. Post-processing scripts are included as final
steps in the process. These scripts calculate residual statistics and produce plots for comparison to other
simulations using various grid dimensions.
REFERENCE
U.S. Geological Survey, 2014, Ozark Plateaus groundwater availability study, accessed February 20, 2014, at
http://ar.water.usgs.gov/ozarks/.

85
 CHEMICAL FATE AND TRANSPORT

Transport of Salt, Trace Metals, and Organic Chemicals from Parking

Lot and Road Surfaces into Mammoth Cave
By David Solomon1, Irucka Embry2*, Bobby Carson3, Larry Johnson3, Roger Painter1,
Lonnie Sharpe1, Rickard Toomey, III3, and Thomas D. Byl1,2
1
Tennessee State University, College of Engineering, 3500 John A Merritt Blvd., Nashville, TN 37209
2
U.S. Geological Survey, 640 Grassmere Park, Suite 100, Nashville, TN 37209 (*contract employee)
3
Mammoth Cave International Center for Science and Learning, Science & Resource Management,
Mammoth Cave National Park, KY 42259

Abstract
Mammoth Cave National Park in south-central Kentucky is the world’s longest known cave system
and is host to many unique and threatened species including the Kentucky cave shrimp. The National
Park Service operates Mammoth Cave National Park to educate tourists while still protecting the unique
and fragile ecosystem in the cave. The Park in partnership with Tennessee State University and the U.S.
Geological Survey has established a monitoring system to characterize selected chemicals transported
from parking lots and dissolved salt from winter-treated roads. The project was initiated, in part, because
of the high volume of traffic into and through the Park, and because the Park has begun phasing in the
application of brine and rock salt to melt ice on primary roads through the Park. The scope of this
investigation included six surface monitoring stations and two cave streams for the winter road-runoff
study, and seven surface drains and six cave sites for the parking lot segment of the project. Chemical
analysis of road runoff included grab samples between and during storms, and continuous measurement
of specific conductance as a surrogate measure of salt concentration. Chemical analysis of parking lot
runoff included quaternary ammonia compounds, anionic surfactants, nitrate, ammonia, zinc, and copper.
The road-runoff monitoring sites were selected based on their location with respect to primary roads
targeted for salt treatment, traffic volume, drainage qualities, and drainage to critical cave shrimp habitat.
This project began in 2011 prior to any road treatments in the Park, and continued through the winter of
2013. Specific conductance meters and autosamplers were used to monitor the runoff waters. There were
three brining events in January 2013. The specific conductance of road runoff during the January 2013
storms ranged from 50 to 400 microSiemens per centimeter (µS/cm) at 25 degrees Celsius. Specific
conductance of road storm runoff during winter storms with no brine or salt applications ranged from 50
to 300 µS/cm. Analysis of the specific conductance pattern on the surface and in the corresponding cave
found that it took from 0.5 to 3 hours for road runoff to reach the mid-level of the cave.
The parking lot sampling sites were associated with storm filters. First-flush storm samplers and
random grab samples were collected from 2011-2014. Concentrations of quaternary ammonia compounds
ranged from below detection (<0.1 milligrams per liter (mg/L)) to a high of 22 mg/L in storm runoff from
an RV waste transfer station. Quaternary ammonia compound concentrations in Annette’s Dome (in the
cave below the RV waste transfer station) exceeded 0.5 mg/L two times in the summer of 2012 (5.4 and
2.5 mg/L). Copper and zinc concentrations were less than 1 mg/L in all monitored events. Nitrate (as N)
and ammonia concentrations spiked as high as 29 and 22 mg/L, respectively, in parking lot runoff from
areas frequented by grazing deer. The concentration of ammonia in most surface runoff was less than 1
mg/L, and nitrate (as N) rarely exceeded 5 mg/L. Concentrations of ammonia and nitrate in the cave were
generally less than half the surface concentrations. The anionic surfactant concentrations in the surface
runoff samples were generally less than 10 micrograms per liter (µg/L) with an occasional spike as high
as 100 µg/L in runoff draining the biosecurity mats. Trace concentrations (<5 µg/L) of anionic surfactants
were detected at all the cave sampling sites and probably represent natural surfactants. The results of the
investigation indicate that concentrations are diluted as water moves from the land surface into the cave.

86
CAFOs on Karst—Meaningful Data Collection to Adequately Define
Environmental Risk, with a Specific Application from the Southern
Ozarks of Northern Arkansas
By Van Brahana1, Joe Nix2, Carol Bitting3, Chuck Bitting4, Ray Quick5, John Murdoch6,
Victor Roland7, Amie West7, Sarah Robertson8, Grant Scarsdale9, and Vanya North5
1
Department of Geosciences, 20 Ozark Hall, University of Arkansas, Fayetteville, AR 72701
2
Ouachita Baptist University Water Lab, Arkadelphia, AR 71988
3
HC 73, Box 182 A, Marble Falls, AR 72648
4
National Park Service, Harrison, AR, 72601
5
Department of Geosciences, 216 Ozark Hall, University of Arkansas, Fayetteville, AR 72701
6
11908 Elk Ridge Rd., Wesley, AR 72773
7
Program of Environmental Dynamics, 216 Ozark Hall, University of Arkansas, Fayetteville, AR 72701
8
243 South Gregg Ave., Fayetteville, AR 72701
9
303 Oxford, Harrison, AR 72601

Abstract
Karst typically contains a noticeably larger percentage of groundwater in its hydrologic budget than
insoluble lithologies. Because subsurface flow is not directly observable, flow quantity, flow direction,
flow velocity, water quality, groundwater basin delineation, and hydrologic variation with changing water
levels are key components essential to characterizing the hydrogeology and assessing contaminant risk in
karst aquifers. Concentrated animal feeding operations (CAFOs) are but one of the many sources of
contamination that have been documented in karst, and owing to the large concentration of animal wastes
generated by these factory farms and their potential for allowing pollution to enter nearby waters, these
nonpoint sources require thorough and careful study prior to permitting by state and federal
environmental agencies. Environmental impact statements and preconstruction studies are essential to
preserve the environmental and ecological integrity of karst basins. Remediation is typically much more
expensive and commonly requires more time to mitigate the damage.
The state environmental protection agency (Arkansas Department of Environmental Quality [ADEQ])
approved the construction of a 6,500-head swine CAFO in accordance with existing regulations on karst
terrain in the area of Big Creek basin in Newton County, Arkansas. The CAFO lies less than 10
kilometers from the confluence of Big Creek with the Buffalo National River, a National Park Service
facility that is the main drain from this karst drainage basin. The Buffalo National River is one of the few
free-flowing rivers remaining in the contiguous 48 states, hosting various recreational activities, including
canoeing, fishing, and swimming, in addition to ecosystems for a large number of unique aquatic and
endangered bat species. This CAFO was permitted under a General Permit which did not require
appropriate investigations, including a hydrogeologic study, a karst study, and an evaluation of
groundwater/surface water interaction. Newton County is characterized by karst hydrogeology, containing
more known caves than any other county in Arkansas. Operation of the CAFO has been the subject of
much debate and has pitted the landowners and small family farms against big-agriculture factory
farming. This paper describes the resulting pro bono research that was undertaken to fill in essential data
originally missing (hydrogeology, karst inventory, dye tracing, water quality), and the continuing effort to
educate the local landowners about a resource that moves unseen beneath the ground. It has strong
technical components, but more importantly, has a direct relevance to the human impacts of our science
on environmental justice and policy.

87
INTRODUCTION
Karst regions typically are considered to be
vulnerable with respect to various anthropogenic
land-use activities, owing to the intimate
association of surface and groundwater.
Inasmuch as the soluble rocks of the karst
landscape can be dissolved to create large, rapid-
flow zones that compete successfully with
surface streams, groundwater and subsurface
flow represent a much larger component of the
hydrologic budget in karst regions than in areas
where non-soluble rocks predominate. Karst
areas typically are distinguished by being unique,
but some general approaches can be applied to Figure 1. General area of major physiographic regions of
characterize the hydrology of the area. These the Ozark Plateaus, including the Buffalo National River and
approaches include an evaluation of the degree of the Ozark National Scenic Riverways, two unique and
Extraordinary Resource Waters that are part of the National
karstification, the hydrologic attributes of the
Park Service. The karst area discussed in this study is
groundwater flow system, the baseline water restricted to the Springfield Plateau in the area of the Buffalo
quality, the time-of-travel through the karst flow National River. Figure from Adamski and others (1995).
system, and the general flux moving through the
system. The nature of potential contaminants and From a hydrogeologic standpoint, much of this
their total mass and range of concentrations are objective is a reiteration of commonly well-
critical to understanding the potential known sampling requirements in karst (Quinlan,
environmental risk. Using these approaches, it is 1989; Alexander, 1989). The second objective is
possible to represent a minimum level of to provide an abbreviated case study from the
hydrogeologic characterization to assess southern Ozarks in northern Arkansas, in the
environmental risk in a karst area. Well- drainage basin of the Buffalo National River (fig.
established, fast-flow systems with structural 1), which shows that implementation of
deformation likely will demand more complete meaningful environmental impact studies for
study, but lacking the aforementioned minima, potentially risky industrial activities on karstlands
the cost of remediating contamination is typically is fraught with politics and emotion. The third
increased many fold. objective is to propose a scientifically-sound,
thorough, fair approach for the ultimate
CAFOs are but one of many industrial achievement of environmental justice for the
activities that pose a threat to the environmental greatest number of stakeholders.
integrity of a karst basin. The typically large
number of animals (from hundreds to more than a MINIMAL STUDY REQUIREMENTS FOR
hundred thousand animals—most commonly INDUSTRIAL ACTIVITIES PROPOSED ON
cattle, pigs, chickens and turkeys) generate KARSTLANDS
wastes in solid, liquid, and gaseous phases. Our Based on the seminal work of Quinlan
focus in this paper is limited to nitrate and total (1989), we have modified his original assessment
phosphorus, major dissolved constituents, of required study components to include what we
organics, sediment, and pathogens. believe are minimum questions that should be
The objectives of this paper are threefold. answered prior to siting CAFOs on karst.
The first is to describe minimal requirements for 1. Compile, study and interpret topographic,
siting any facility on karst. soils, and geologic maps, and all related
previous hydrogeologic studies of the
area. Fully document this in a list of
selected references.

88
 2. Conduct a complete karst inventory, quality of the Buffalo River, which is classified
including input, flow through, and as an Extraordinary Resource Water. The
discharge features accurately plotted on resulting furor brought deeply held emotions to
topographic and geologic maps of the surface. Unfortunately, space constraints for
appropriate scale. this paper limit discussion to only key elements
of the controversy, but the interested reader is
3. Determine groundwater-flow directions,
directed to the following websites, each of which
flow type, velocities, and water budgets,
and estimate groundwater basin offers disparate views of the facts. These sources
boundaries using the principle of represent web pages of some of the major
normalized base flow (Brahana, 1997). participants, and additional information can be
acquired from pointers on each webpage, or web
4. Characterize the baseline water quality of searches using examples such as the Buffalo
the shallow karst aquifer and overlying National River, Big Creek Hog Farm, or Newton
and underlying aquifers to assess County, Arkansas Hog Farm, to name a few.
interaquifer transfer of flow and Some specific connections with those involved
contaminants, including dissolved major and shown in parentheses are:
constituents, original contaminants and
their breakdown products from the http://www.arfb.com/ (Arkansas Farm
industrial operation, and in the case of Bureau);
CAFOs, key nutrients, pathogens, http://www.adeq.state.ar.us/ (ADEQ);
sediments, and other unique water-
quality indicator parameters. http://www.cfra.org/news/140127/corporate-
farming-notes-industrial-hog-operation-divides-
5. Conduct dye-tracing studies concurrently community (Center for Rural Affairs);
with items 3 and 4, using study results to
answer questions raised in item 2. http://www.npca.org/news/media-
center/press-releases/2013/groups-go-to-court-to-
6. Integrate items 1 through 5 into a report protect (National Parks Conservation
that synthesizes groundwater hydrologic Association);
characteristics in the karst aquifer,
proposes a defensible conceptual model, http://www.ozarksociety.net/2013/03/conserv
and accurately assesses the background ation-issue-hog-farm-near-big-creek/ (Ozark
water quality prior to the permitting of Society);
the industrial operation. Insofar as the http://buffaloriveralliance.org/Default.aspx?p
complexity of the karst is not well ageId=1547312 (Buffalo River Alliance);
understood by disciplines outside
geology, this study should be conducted http://www.npca.org/news/media-
only by a registered professional center/press-releases/2013/groups-go-to-court-to-
geologist. protect.html.

CASE STUDY OF THE INDUSTRIAL HOG It should be noted that these sources reflect
CAFO ON THE KARST OF BIG CREEK the bias of each support group, and that
BASIN, NEWTON COUNTY, ARKANSAS misrepresentations or inaccuracies may be
present on non-peer-reviewed web pages. These
The approval by the Arkansas Department of are provided to assist the reader and to show how
Environmental Quality (ADEQ) of a 6,500-head distinctly different interpretations are possible
swine facility on Big Creek less than 10 from the same data set. The difference lies in the
kilometers upstream from the Buffalo National filters, the fears, the politics, and the emotional
River (fig. 2) was approved on August 3, 2012. reactions of each stakeholder.
This approval came as a surprise to almost all
stakeholders in the region, not the least of whom
was the National Park Service (NPS), the agency
responsible for maintaining the environmental
89
Selected Components of the Permitting gaining and losing reaches where it crosses the
Process Boone Formation, and during low flow there are
entire reaches that are completely dry
As previously mentioned, the permit for the
downstream of flowing reaches.
CAFO was granted by ADEQ according to
existing regulations, which did not include a
through characterization of the site. The geology,
hydrology, and unique karst terrain were not
adequately considered. Additionally, no
predevelopment characterization was made to
evaluate the true effects of the CAFO on the
watershed.
Site Geology, Hydrogeology, Karst, and
Hydrology
Big Creek is one of the two largest tributaries Figure 2. Aerial view of 6,500-head industrial hog CAFO,
to the Buffalo National River, encompassing including waste lagoons. The facility is sited on the Boone
about 8 percent of the total drainage of the entire Formation, a karst aquifer less than 10 km upstream from the
Buffalo River watershed. Physiographically, confluence of Big Creek with the Buffalo National River.
tributaries head in uplands of the Boston
Mountains Plateau (fig. 1) on terrigenous
sediments of Pennsylvanian age and flow
generally toward the north with relatively steep
gradients. The stratigraphic units of concern are
within the Boone Formation (Braden and
Ausbrooks, 2003), an impure limestone that
contains as much as 70 percent chert, much of
which was thought to have formed through
geochemical alteration of volcanic ash from
atmospheric deposition from the island arcs south
of the Ouachita Orogeny, approximately 150
kilometers south of study area. The upper and
lower units of the Boone Formation have much
less chert (typically less than 5 percent) than the
middle part of the Boone. Structurally, the Boone
is near-horizontal; owing to the high
concentration of brittle chert, it has been
subjected to extensional faulting and jointing.
The upper and lower parts of the Boone
Formation host significant caves (fig. 4) in the
region (Mott and others, 2000). Intervening
layers of limestone are karstified by smaller
dissolution features (fig. 5), with the chert acting
as confining units above and below.
The geologic unit underlying the CAFO is
the Boone Formation, and all formations in Big
Creek basin are shown in figure 3. Approxi-
mately 50 meters of the middle Boone
Figure 3. Stratigraphic column of most of Big Creek basin
limestone/chert lithology is exposed in a cliff face
in the vicinity of the CAFO, from the Mt. Judea 7.5-minute
about 2 kilometers downstream from the CAFO quadrangle (Braden and Ausbrooks, 2003).
(fig. 6). Big Creek is characterized by both
90
 Big Creek and its major tributary, Left Fork, The existence of well-developed karst near a
flow in alluviated valleys composed of NPS facility designated as an Extraordinary
nonindurated sediments, primarily chert and Resource Water, increases vulnerability to
terrigenous rock fragments from younger, anthropogenic sources of contaminants that can
topographically higher formations (fig. 3). The move through the hydrologic cycle with little
alluvium in these valleys varies in thickness from attenuation of contaminants. The concentrated
a feather-edge to about 8 meters. Outcrops of the wastes of the CAFO and the calculated allowable
Boone Formation are common in the streambed. leakage through the clay of the lagoon liner (fig.
Springs are common along the entire reach of Big 7) and the waste-spreading fields (fig. 8) are
Creek, ranging from relatively small discharges perceived as being a risk, not only to the ecology
in the tens of liters per minute range to large and environmental integrity of Big Creek, but to
discharges of tens of liters per second. These the Buffalo National River, with the extensive
larger discharges resurge from relatively pure direct contact of its waters with the many tourists
limestone lithologies (Mott and others, 2000). who canoe and swim there. The lack of any
geologic, hydrogeologic, or karst studies do not
allay fears related to assessing the overall risk
this CAFO poses.

Figure 4. Newton County, where Big Creek occurs, has the

largest number of recorded caves of all counties in the state.
Most of these, such as this cave just north of Big Creek basin
on the Buffalo River, are concentrated in the upper and
lower parts of the Boone and St. Joe Formations, which
include more pure limestone. Photo by Carol Bitting.

Figure 6. Erosional bluff face showing approximately 50 m

of interbedded limestone and chert in the middle part of the
Boone Formation near the confluence of Big Creek with its
major tributary, Left Fork. The differential weathering
Figure 5. Karst dissolution features in limestone interbedded suggests that this landscape reflects the solubility of the
with chert from the middle Boone Formation. The chert acts limestone facies. Photo courtesy of John Murdoch.
as an insoluble confining unit for the karst. The scale of
these voids typically ranges from 2 to more than 5 cm.

91
 In response to the lack of appropriate
hydrogeologic and karst studies of the basin
associated with the CAFO, a diverse group of
volunteers (the authors) proposed a pro bono
investigation of several unstudied elements that
would minimally describe 1) the karst inventory
in Big Creek basin, and its relation to the
geology; 2) the baseline groundwater quality,
including an assessment of expected capability of
the soil/regolith/bedrock flow system to
accommodate additional wastes; and 3) the
general flow directions, rates of flow, quantities
of flow, and water budgets based on dye tracing.
The interpretation of these field data are expected
to be shared with all stakeholders in a report.
Geologic, hydrologic, and karst inventories
which were outlined earlier under minimal study
requirements were conducted. These were
accomplished by an intensive map and previously
published reports study, intensive field work to
identify gaining and losing reaches, caves,
springs, sinkholes and visible karst landforms,
low-level aerial surveillance, and canvassing of
the local farmers and landowners. Figure 8. Fields permitted for spreading hog waste along
Big Creek by the CAFO (white color) granted by ADEQ.
Strict baseline water-quality (pre-CAFO) Most of the permitted fields are on alluvium and regolith that
sampling was not possible, but the slow startup of directly overlie the Boone Formation at thicknesses ranging
the CAFO in the summer of 2013 allowed from a feather edge to about 8 m. The proximity to Mt.
Judea school (magenta color) to the spreading fields is
sampling approximately 40 wells, springs, and shown in the upper right-hand corner of the figure.

streams for field parameters, major dissolved

constituents, nutrients, and pathogens prior to the
major CAFO activity. Nutrients and pathogens
were analyzed by the Arkansas Water Quality
Lab on the campus of the University of Arkansas
owing to the short holding-time requirements,
and dissolved major and selected trace
constituents were analyzed by the Water Quality
Lab of Ouachita Baptist University in
Arkadelphia.
The dye-tracing study has yet to be
undertaken, because permission to inject non-
toxic fluorescent dyes was just granted in mid-
Figure 7. The clay liner shown here is the sole confining
entity separating the hog waste in the lagoons from the March 2014.
underlying Boone Formation. This photo, taken after
construction of the liner, indicates that it has numerous chert
fragments up to fist size within the clay, and dessication
cracks, and that erosion rills have eroded some of the
thickness. These features reduce its ability to confine. The
liner was required to be 30 cm thick, but the owners of the
CAFO increased that to 45 cm. Photo courtesy of Tony
Morris (ADEQ).
92
 spraying waste on fields adds additional contaminants
lagoon with 45-cm “liner”
that drain downward into the underlying karst

land surface
Big Creek

West
permeable voids created by secondary dissolution in karstified limestone of the East
Boone Formation transmit hog waste and related contaminants to Big Creek

Figure 9. Conceptual model showing surface and groundwater interaction in a cross-sectional view in the area of Big Creek near
the hog CAFO. Red arrows identify potential karst flow pathways that were not characterized or previously studied.

Preliminary Results zones of limestone dissolution between chert

layers are. The large number of caves in the basin
Description of the geology and karst of Big
(fig. 10) provides additional support for large
Creek basin in the area of the CAFO support the
discharge, rapid-flow systems with turbulent flow
observation that the Boone Formation is a
that have the ability to transport not only
mantled karst with numerous springs and a high
conservative solutes, but nutrients, sediment, and
degree of surface and groundwater interaction.
pathogens. At this time, the shallow karst aquifer
Sinkholes are typically not common in the middle
is dominated by bicarbonate water type,
part of the Boone, but springs and secondary

Figure 10. Locations of selected reference points, sampling sites, spreading fields permitted for the CAFO, caves, and springs in
Big Creek and contiguous basins. Spreading fields are yellow, springs are blue, caves are green, surface-water sampling sites are
red, major roads are in white, forested regions are dark green, and cemeteries are brown. Locations are from GPS measurements
plotted on Google Earth.

93
dissolved solids generally less than 400 SELECTED REFERENCES
milligrams per liter (mg/L), groundwater Adamski, J.C., Petersen, J.C., Freiwald, D.A., and
temperatures consistent with shallow karst flow Davis, J.V., 1995, Environmental and hydrologic
(summer temperatures in the 16-19 oC range, setting of the Ozark Plateaus study unit,
winter temperatures in the 12 to 14 oC range), Arkansas, Kansas, Missouri, and Oklahoma:
nutrients elevated above background levels (e.g. U.S. Geological Survey Water-Resources
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8. Above all else, base decisions and insights gained from 15 years of in situ field
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point sources in karst terrane: Arkansas Water
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Fayetteville, 59 p. 1998, Resuspension of viable sediment-bound
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96
An Initial Investigation of Hydrogeology and Water Quality of Big
Creek in the Buffalo River Watershed near a Major Concentrated
Animal Feeding Operation
By Victor L. Roland II1, Tyler Wright1, J. Van Brahana1, and Phil D. Hays1,2
1
University of Arkansas, Department of Geosciences, Ozark Hall 216, Fayetteville, AR 72701
2
U.S. Geological Survey, Arkansas Water Science Center, 401 Hardin Rd., Little Rock, AR 72211

Abstract
A swine concentrated animal feeding operation (CAFO) in Newton County, Arkansas near the
Buffalo River was approved, permitted, and constructed in 2012. The CAFO is adjacent to Big Creek,
which is a major tributary of the Buffalo River. The region has a mature karst landscape, which provides
rapid recharge to groundwater. Groundwater and surface-water interaction within the Big Creek
watershed is extensive, raising concerns over potential contamination of surface water or groundwater.
Contamination pathways associated with CAFOs include leakage and lagoon overflow, preferential flow
paths through the soil, and nutrient-rich runoff from manure application fields. Contaminants of concern
are nutrients, pathogens, sediment, and trace metals. The objective of this project was to provide
preliminary data on water-quality conditions in the Big Creek basin associated with the CAFO drainage
area. Water samples were collected from Big Creek, natural springs, and private wells during base-flow
conditions in July and August 2013. Sampling was conducted before initial application of CAFO waste
effluent to fields in the watershed designated for manure application. Analyses of dissolved solutes
indicated calcium-bicarbonate as the predominant water type in the study area. Calcium-bicarbonate-type
water is indicative of dissolution of Boone Formation limestone, which crops out in the study area.
Biological data show Escherichia coli and total coliform concentrations ranged from <1.0–980 Most
Probable Number counts per 100 milliliters (MPN/100mL) and from <1.0–241,900 MPN/100mL,
respectively. The wide range of Escherichia coli and total coliform concentrations may result from small-
scale CAFOs, wildlife, and anthropogenic sources in the water; however, more data are necessary to
elucidate sources of bacteria in groundwater and surface water. Nutrient concentrations varied spatially
with no discernible trend; however, phosphorus and nitrate concentrations were elevated in groundwater
samples relative to surface-water samples. Preliminary data from this study show the variability in
chemical and biological water quality in the study area, and provide background information necessary
for future assessments of potential changes in water quality in the Big Creek watershed as the CAFO
becomes fully operational.

97
A Method to Investigate Karst Groundwater Flow in Nash Draw, Eddy
County, New Mexico, to Delineate Potential Impacts of Potash
Industry Discharge and Runoff
By James Goodbar1, and Andrea Goodbar2
1
Bureau of Land Management, 620 E. Greene St., Carlsbad, NM 88220
2
Central New Mexico Community College, 3027 Derrick Rd., Carlsbad, NM 88220

Abstract
Nash Draw is a karst valley approximately 15 miles east of Carlsbad, New Mexico. It is the site of
several potash mines – one has been operating since the early 1930s. During that time a significant
amount of refining brine waste has been disposed of into the valley. The geology and hydrology of Nash
Draw have been studied extensively in relation to the potash industry, the Gnome Project, and the Waste
Isolation Pilot Plant. All studies agree that the karst nature of Nash Draw plays an important role in the
overall hydrology of the area. Specific studies suggest that the brine effluent of the potash industry may
be causing dramatic changes in the ecosystem associated with the draw. To date, there have been no
quantitative (or qualitative) studies to delineate specific flow paths in this complex hydrologic system. A
quantitative water-tracing study may supply a critical piece of information in understanding the
complexities and flow paths of the karst groundwater system in Nash Draw. It would also provide useful
information for environmental assessments and impact statements necessary in making responsible
resource management decisions related to the potash industry and the Nash Draw ecosystem.
SETTING AND BACKGROUND mining fluids have been intermittently
discharged into the karst valley as a result of
Nash Draw is a karst subsidence valley in
dike breaches and/or releases of brine fluids to
southeastern New Mexico that is 4 to 6 miles
avoid catastrophic dike failure. Sinkholes have
wide, 22 to 23 miles long, and covering about
formed in the bottom of tailings ponds draining
128 square miles (fig. 1). The average depth
the brine tailings into the subsurface. Large
ranges from 100 to 200 feet. It generally runs
sinkholes have developed in salt tailings piles,
from the north-northeast to the south-southwest,
suggesting a direct release of at least some of the
and is bound on the north by the Maroon Cliffs,
waste directly to the subsurface conduits with
on the west by Quahada Ridge, on the east by
eventual discharge at downstream locations.
Livingston Ridge, and on the south by the Pecos
Several of the natural playas on the south end of
River. More than 100 collapsed sinks and cave
Nash Draw have progressively become more
entrances have been documented in the bottom
and more salty over the decades. This has
of the valley. Dissolution takes place primarily
resulted in some of the playas becoming
in the Rustler and the Salado Formations of
unsuitable for certain species of plants and
Permian age. At Nash Draw, the Rustler consists
wildlife that previously inhabited them.
of interbedded sulfates, dolomites, and
mudstones while the Salado is primarily halite Previous Studies
with minor sulfate beds. At the lower end of
Geologic and hydrologic studies conducted
Nash Draw are a series of seven shallow lakes or
in Nash Draw over the decades have attempted
playas. The presumed base level of the Nash
to accurately describe the geology and
Draw hydrologic system is the Pecos River due
characterize groundwater flow. Most of the
to the increased salt content in the Pecos River
studies acknowledge that the solution activity
below Nash Draw at Malaga Bend (fig. 1).
and associated collapse, subsidence, and
Potash mining has been operating along the fracturing have increased the permeability of the
flanks of Nash Draw since the early 1930s overlying rock members and increased the
(Brokaw and others, 1972). Tailings ponds were hydrologic communication between formations.
established in the margins of the draw and The earliest of these works by Willis T. Lee
98
(1925) describes “erosion by solution and fill.” paper on the geology and hydrology of Nash
After the discovery of potash in the area, Draw. This study identified the brine aquifer at
Robinson and Lang (1938) published an early the top of the Salado running down the

Figure 1. Nash Draw boundary and potentiometric surface at the top of the brine aquifer.

99
length of Nash Draw to the Pecos River. karst features during a study along the
Hendrickson and Jones (1952) also noted that realignment of Highway 128 where it crosses
the brine aquifer moves under the Salt Lake and Nash Draw, concluding that karst processes are
discharges into the Pecos River near Malaga still active in that area. Powers and others (2006)
Bend. A landmark report was written by James brought many of these studies together in their
Vine on behalf of the Atomic Energy paper on Nash Draw evaporite karst features and
Commission to study the surface geology of processes. They also suggest that brine water of
Nash Draw in preparation for the Gnome Laguna Grande may be infiltrating sediments in
Project, the detonation of a nuclear device for a low divide known as Scoggin Flat. Powers and
peaceful purposes (Vine, 1962). His report was others (2006) also cite the lack of quantifiable
one of the first comprehensive works on the data in being able to differentiate springflows
geology of Nash Draw and included the first into the lagunas and calculate storage capacities
detailed geologic map of Nash Draw. He in the karst hydrologic system.
describes Nash Draw and the lakes on the south
All authors agree that karst processes are at
end as having no external surface drainages or
work in Nash Draw and acknowledge that the
outlets. Brokaw and others (1972) reported
underground transport of water and subsequent
comprehensively on the geology and hydrology
solution and collapse of the evaporite
of the Carlsbad potash area as background for
formations, with attendant erosion, is
siting a repository for nuclear waste.
responsible for the development of the karst
Geohydrology Associates (1978) was contracted
valley. The extent of influence that karst conduit
by the Bureau of Land Management (BLM) to
flow has on the system and the potential impacts
specifically study the effects of potash industry
to the downstream ecosystems are still not
brine disposal on the limited quantities of fresh
understood.
water in the area. They were asked to address
three questions: 1) is fresh water in the Carlsbad This is an abbreviated account of geological
potash area in danger of contamination from and hydrological studies of Nash Draw. A few
expanded potash mining activities, 2) is the additional background references include
brackishness of the Pecos River below Malaga Bachman and Johnson (1973), Hale and others
Bend due to mining activity, and 3) is the (1954), Cooper and Glansman (1971), and
amount of leakage from brine-disposal ponds Mercer (1983). Numerous more detailed articles
significant compared to the volumes of naturally and documents have been produced for Project
occurring brine? This study was followed up by Gnome, the Waste Isolation Pilot Plant (WIPP),
a second study by the same company and industrial interests in the area.
(Geohydrology Associates, 1979) to address Climate
other objectives: 1) establish the depth and
configuration of the water table in the potash The area has an arid to semiarid climate.
area, 2) measure aquifer parameters in the The average rainfall is between 25 and 35
potash area, 3) refine the hydrologic parameters centimeters (9-12 inches) per year. The average
used in water-budget studies in order to establish monthly maximum temperatures in July range
more accurate inflow-outflow relations at from 34.5 to 36.5 oC (94 to 98 oF) with average
various plant sites, and 4) evaluate the suitability monthly minimums of -2 to -1 oC (28 to 31 oF)
of several natural salt lakes as brine-disposal in December and January. Average annual
sites. Geohydrology Associates (1979, p. 86) potential evaporation rates far exceed average
concluded that leakage from the Salt Lake “may annual precipitation. Evaporation rates approach
discharge into the Pecos River” and that 13,400 cubic meters per hectare (4.4 acre-feet
groundwater quality and levels have been per year) in the brine ponds of this area,
affected by potash-refinery waste disposal. resulting in a large moisture deficit. Lesser
Bachman (1981, 1987) postulates that Nash evaporation rates can be attributed to spoil piles,
Draw has taken its present form as a result of the mud flats, bare soil, and plant transpiration
coalescing of collapse sinkholes. Powers and (Geohydrology and Associates, 1978, p. 60).
Owsley (2003) identified numerous cave and
100
GEOHYDROLOGY
The Nash Draw area contains Permian-age
evaporites of the Rustler and Salado Formations.
In this area, the Rustler is primarily made up of
interbedded sulfates, dolomites, and
mudstone/siltstones while the Salado is
composed of 75 percent halite (fig. 2). A
potentiometric surface map on top of the brine
aquifer (fig. 1) was developed by Geohydrology
Associates (1979), but it contains uncertainties
inherent in all such maps regarding specific flow
paths in karst terrain such as Nash Draw.
Within the Rustler Formation from the top
units to the bottom (fig. 2), the members are the
Forty-niner, the Magenta Dolomite, the
Tamarisk, the Culebra Dolomite, and the Los
Medaños, an interbedded unit of sandstone,
siltstone, and sulfate.
The Forty-niner is 12-19 meters (40-65 feet)
thick and is composed primarily of sulfate with
lesser amounts of mudstone. Where exposed the
Forty-niner also contains well developed cave
systems that, at times, reach the Magenta
(Goodbar, 2013).
The Magenta is 6-9 meters (20-30 feet) Figure 2. Basic stratigraphic units in Nash Draw (modified
thick, composed of dolomite and sulfate, and can from Powers and others, 2006). Each of the
mudstone/siltstone units has halite or halitic facies
be identified in outcrop by its color, weathering equivalents east of Nash Draw.
to a pink to pale-red. The dolomite is alternately
laminated with yellowish-green anhydrite or
gypsum. The Magenta is water-bearing in the The Culebra is a microcrystalline gray
Nash Draw area, with generally very low dolomite approximately 9 meters (30 feet) thick,
production. containing numerous small spherical cavities
The Tamarisk in Nash Draw is 35 meters and having high porosity (Vines, 1963, p. 13-
(115 feet) thick and largely composed of sulfate 18). The Culebra also contains the lower aquifer
(gypsum in Nash Draw) that can be coarsely of the Rustler.
crystalline where exposed at the surface; these Below the Culebra Dolomite is the Los
sulfate beds are laterally continuous downdip to Medaños Member (Powers and Holt, 1999). It is
the east out of Nash Draw where they are composed of mainly siltstone and mudstone, but
anhydrite. The Tamarisk also contains caves and also includes sulfate beds as well as halitic to
swallets in the floor of Nash Draw where water halite intervals to the east of Nash Draw.
can be channeled into subsurface conduits (fig.
3) or sink slowly into them where sinkholes are
covered by soil layers (fig. 4). The two sulfate
beds of the Tamarisk (A-2 and A-3, fig. 2) are
separated by a mudstone unit (M-3) in Nash
Draw and nearby surrounding areas.

101
 WATER TRACING
The purpose of conducting a water tracing
project in Nash Draw would be to determine 1)
where water goes once it enters the subsurface,
2) what the water budget is for the hydraulic
system when factoring in the potash mining
discharge rates, 3) the extent conduit flow
contributes to the overall groundwater flow in
Nash Draw, and (4) the residence times and flow
rates within the system. The concerns prompting
such a study are the same as those identified in
the 1970s; do salts from potash operations enter
the natural lakes and depressions in Nash Draw
and the Pecos River in sufficient quantities to
create undesirable impacts to the ecosystem?
Conventional hydrologic and hydrogeologic
methods of groundwater modeling often do not
provide accurate results when applied to karst.
Karst-specific methods are needed to more
accurately characterize flow and transport in
conduit networks (International Association of
Hydrogeologists, 2013).

Figure 3. Cave entrances in the bottom of Nash Draw

create point sources for aquifer recharge.

The Salado Formation is composed of thick

beds of halite and thinner beds of sulfate
(commonly anhydrite with lesser amounts of
polyhalite). At Nash Draw, the upper section
consists of variably consolidated clay and
reddish-gray to brown silt with varying amounts
of gypsum that may be brecciated. This layer is
thought to be the insoluble residue left over from
the solution of halite in the upper part of the Figure 4. Alluviated sinkholes provide slow infiltration of
Salado. It is through this breccia, resting on top runoff into the subsurface.
of undissolved Salado halite, that the brine Groundwater tracing has long provided the
aquifer flows (Vine, 1963, p.7-8). detailed point-to-point connection information in
The two primary aquifers in Nash Draw are complex hydrologic systems where the exact
the brine aquifer in the solution breccia at the nature of interactions between the hydrologic
top of the Salado and the Culebra Dolomite. and geologic settings is difficult to determine.
Other upper members of the Rustler, such as the This is particularly the case in karst terrains. A
Magenta and Forty-Niner, may also contribute to groundwater trace would provide a more
the overall water input and can be considered as empirical and definitive study needed to identify
hydrologically connected over parts of Nash point-to-point connections in the Nash Draw
Draw due to extensive dissolution and karst groundwater system. This will help
associated collapse, subsidence, and fracturing managers better understand the dynamics and
(Brokaw and others, 1972, p. 54). interactions of that complex system and the
potential impacts to a properly functioning

102
ecosystem. Figure 5 shows a generalized cross connections between input sources and
section of Nash Draw and the relation between monitoring points. Qualitative methods may also
geologic members and the hydrologic system. be used to estimate flow rates. They are not
designed to determine how much of the tracer
It is widely held that in order to obtain the
material is escaping past the monitoring
most useful information, it is much more
locations and into other parts of the hydrologic
effective to conduct a quantitative trace than a
system. Using a quantitative tracing method can
qualitative trace. Field (2002) showed that
give a better idea of how significant an amount
quantitative tracing studies provide detailed
of tracer is moving into unmonitored locations.
information about flow dynamics. This is done
Quantitative tracer studies can also provide
by developing a tracer budget and plotting the
better data about mean residence time, flow
amount of tracer injected with the amount of
rates, and dispersion. This information allows
tracer recovered over time while factoring in
for better analysis and evaluation of the
groundwater discharge. This is referred to as a
hydrologic system’s divergence, convergence,
breakthrough curve. The use of qualitative
dilution, and storage properties.
tracing methods is good to establish positive

Figure 5. Generalized cross section of Nash Draw showing geologic and hydrologic relations (From Geohydrology Associates,
1979). There are no current “fresh water springs” along the margins of Nash Draw at the Magenta outcrops.

The first phase of the project would begin in There are several factors to consider when
the lower reaches of Nash Draw at its terminus initiating a water-tracing project. These include
near the Pecos River and include the Mosaic 1) using the appropriate tracer for the
potash mine tailings piles/discharge points. The environment, 2) using a sufficient amount of
second phase would move up Nash Draw to its tracer, 3) how the tracer will be introduced into
northern reaches and include the Intrepid potash the hydrologic system, 4) sampling techniques
mine tailings piles/discharge points (fig. 6). and locations, and 5) the analysis and
interpretation of the data.
103
 The first of these factors is using the The next factor is how the tracer will be
appropriate tracer for the environment at hand, introduced into the hydrologic system. In karst
as some tracers may not perform well or give the terrains, entry points may be natural sinkholes,
desired results due to specific water chemistry, swallets, cave entrances, or other surface
geologic conditions, and other variables. features such as lakes or other man-made
impoundments. Input point sources may also
Another factor is using a sufficient amount
occur from collapse of closed depressions into
of tracer to ensure that the trace will be
conduits below.
successful, which requires understanding the
potential water quantities in the aquifer and the
potential for loss of the tracer.

Figure 6. Proposed dye traces and boundaries: Phase 1 and Phase 2 showing cave and karst features.

104
 This can be a relatively common occurrence and dual-advection dispersion equations may
in the natural world but may be exacerbated provide for a more accurate interpretation (Field,
when closed depressions are used for solid or 2012). Together the collective data will provide
fluid storage. Tracers can be introduced in liquid a much more detailed picture of the hydrologic
form or as a solid (powder). In areas where system.
rainfall is low and water flow is limited, tracers
APPLIED SCIENCE AND ADAPTIVE
may need to be flushed into the system using
MANAGEMENT
large water tankers, although this may be
impractical in some situations. Once a water trace has been conducted and
the data analyzed and interpreted it should
A forth factor is that of selecting the
provide a much clearer understanding of the
appropriate techniques and locations, which
hydrologic system from which to make resource
become a critical part of tracer project design.
management decisions. Options and alternatives
Sampling locations should be selected carefully.
for proposed actions involving mine operations
Multiple background samples should be can be analyzed from a knowledge-based
taken prior to the introduction of any tracer into standpoint and potential outcomes can be more
the system. Background concentrations can accurately predicted. Through a better
adversely affect tracer analysis if not recognized understanding of this complex hydrologic
and taken into account. There are a large number system the BLM in conjunction with the potash
of both naturally occurring and man-made industry can develop better mitigation and
materials and substances that can affect accurate monitoring plans and reach a finer balance
tracer analysis. Due to this, it becomes critically between resource use and resource protection.
important to be able to subtract those With a clearer picture of the groundwater flow
background concentrations from subsequent system in Nash Draw, adaptive management
samples to obtain more accurate tracer results strategies can be generated to react to
(Field, 2011). This ensures there is no cross undesirable events and changes in mine
contamination from other sources that may give operations. Knowing the point-to-point flow
false data. The method(s) of sampling are also paths and probable impacts downgradient should
critical to the success of a tracer test. The use of help guide management decisions and avoid
continuous autosamplers, activated carbon future adverse impacts to the environment. In
receptors or intermittent grab samples makes a the long term, higher quality water flowing
difference in the quality of data gathered and the through the system will provide better water
reliability of the test. quality and habitat for the collective ecosystems.
A final and critical point is having proper The BLM Carlsbad Field Office maintains
analysis and interpretation of the data. A poor or and manages geographic information system
inadequate analysis can taint the results of the (GIS) data used within the land management
test and cause the trace to lose credibility. agency. Data generated through the course of an
Choosing a laboratory that maintains high investigation such as this could be maintained
standards and reliability can make the difference and managed for ease of retrieval for further
between a successful trace or not (Aley, 2002). analysis. It could be combined with existing
A proper analysis requires both experience in spatial data as well as analytical data such as
interpreting tracer tests and modeling land use, well pumping and recharge,
breakthrough curves. Multiple peaks on evapotranspiration, surface-water flow, stream
breakthrough curves may indicate multiple flow networks, digital elevation models (DEMs) and
channels or conduits that have been partially geology. This will allow the BLM to create new
constricted, forcing flow to diverge into groundwater models and information for
auxiliary channels. It could also mean that there environmental assessments.
were some areas in which the flow was held in
Resource management issues could be
detention pools or in waterfall plunge pools. In
addressed using 3-D hydrogeological models,
such cases the use of a multi-dispersion model
groundwater level and quality spatial
105
information products that show the area of The use of GIS as a method of tracking and
critical interest, and animations that show analyzing data would provide a long-term rapid
groundwater changes and movement through retrieval system for the data. It could also be
time. used as a groundwater modeling tool for future
studies and in developing future adaptive
SUMMARY
management strategies.
Nash Draw is a karst valley approximately
ACKNOWLEDGMENTS
15 miles east of Carlsbad, New Mexico. It is
formed in the Rustler Formation of Permian age The authors thank Dr. Malcolm Field and
as a result of dissolution and collapse of Dr. Dennis Powers for their constructive reviews
dolomite and sulfate beds within the formation. and comments, which greatly improved the
There are two aquifers within the system. One manuscript. The authors also thank Shiva Achet,
aquifer is in the Culebra Dolomite and the other David Herrell, and Ruben Rodriguez for their
is a brine aquifer at the base of the Rustler and in reviews, comments, and GIS assistance.
the top of the Salado Formations. Nash Draw
The views expressed in this paper are solely
has been the site of several potash mines since
those of the authors and do not necessarily
the 1930s. Three tailings piles and brine ponds
reflect the views or policies of the BLM.
are located along the edges of Nash Draw. Brine
pond leakage has been an acknowledged REFERENCES
occurrence since the industry began their Aley, Thomas, 2002, Groundwater tracing handbook:
disposal operations. There have been multiple Ozark Underground Laboratory, Protem,
events over the decades where brine ponds have Missouri, USA, 44 p.
breached and sinkholes have opened up in
Bachman, G.O., 1981, Geology of Nash Draw, Eddy
tailings piles and brine ponds, diverting their
County, New Mexico: U.S. Geological Survey
contents into subsurface conduits. The natural Open-File Report 81-31, 10 p., 4 pl.
playas at the lower end of Nash Draw have been
getting more and more salty. Species of plants Bachman, G.O., 1987, Karst in evaporites in
and wildlife can no longer survive the salt southeastern New Mexico: Sandia National
Laboratories, SAND84-7178, p. 38-41.
concentrations. There have been no conclusive
studies to determine where water or potash Bachman, G.O., and Johnson, R.B., 1973, Stability of
industry discharge goes once it enters the karst salt in the Permian Salt Basin of Kansas,
conduit system. There is speculation that fluids Oklahoma, Texas, and New Mexico: U.S.
entering the aquifer may go into the natural Geological Survey Open-File Report 73-14,
62 p.
playas and the Pecos River.
Brokaw, A.L., Jones, C.L., Cooley, M.E., and Hays,
A primary method of determining W.H., 1972, Geology and hydrology of the
subsurface connections and transport rates, Carlsbad potash area, Eddy and Lea Counties,
particularly in karst areas, is through the use of New Mexico: U.S. Geological Survey Open-File
water-tracing techniques. The use of water Report 72-49, 86 p.
tracers has been used very successfully for
Cooper, J.B., and Glanzman, V.M., 1971,
decades and has proven to give reliable results.
Geohydrology of project Gnome site, Eddy
The most efficient way to gather sufficient data County, New Mexico: U.S. Geological Survey
to answer the critical questions needed to make Professional Paper 712-A, 24 p.
informed management decisions regarding
future discharge and retention of potash Field, M.S., 2002, The QTRACER2 program for
tracer-breakthrough curve analysis for tracer
industrial discharge would be to conduct a
tests in karst aquifers and other hydrologic
quantitative water trace rather than a qualitative systems: U.S. Environmental Protection Agency
trace. This would provide the BLM with the /600/R-02/001, 179 p.
information needed to make decisions and
develop best management practices based on the Field, M.S., 2011, Application of robust statistical
methods to background tracer data characterized
best available science and verifiable results.
106
 by outliers and left-censored data: Water Powers, D.W., and Holt, R.M., 1999, The Los
Research, v. 45, p. 3107-3118. Medanos Member of the Permian Rustler
Formation: New Mexico Geology, v. 21, no. 4,
Field, M.S., and Feike, J.L, 2012, Solute transport in
p. 97-103.
solution conduits exhibiting multi-peaked
breakthrough curves: Journal of Hydrology, v. Powers, D.W., and Owsley, D., 2003, Field survey of
440-441, p. 26-35. evaporite karst along New Mexico Highway 128
realignment routes, in Johnson, K.S., and Neal,
Geohydrology Associates, 1978, Ground-water study
J.T., eds, Evaporite karst and
related to proposed expansion of potash mining
engineering/environmental problems in the
near Carlsbad, New Mexico: Bureau of Land
United States: Oklahoma Geological Survey
Management, Contract YA-512-CT7-217, p. 1-2.
Circular 109, p. 233-240.
Geohydrology Associates, 1979, Water-resources
Robinson, T.W., and Lang, W.B., 1938, Geology and
study of the Carlsbad potash area, New Mexico:
ground-water conditions of the Pecos River
Bureau of Land Management, Contract YA-512-
Valley in the vicinity of Laguna Grande de Sal,
CT8-195, 86 p.
New Mexico: New Mexico State Engineer 12th
Goodbar, J.R., 2013, Solution mining and the and 13th Biennial Report, 89 p.
protection of karst groundwater supplies in
Vine, J.D., 1963, Surface geology of the Nash Draw
Burton Flats, southeast New Mexico, USA, in
quadrangle, Eddy County, New Mexico, in
Land, L., ed., Proceedings of the 20th National
Contributions to general geology: U.S.
Cave and Karst Management Symposium, p. 13-
Geological Survey Bulletin 1141-B, 46 p.
17.
Hale, W.E., Hughes, L.S., and Cox, E.R., 1954,
Possible improvement of quality of water of the
Pecos River by diversion of brine at Malaga
Bend, Eddy County, New Mexico: Pecos River
Commission, 43 p., 8 pl.
Hendrickson, G.E., and Jones, R.S., 1952, Geology
and ground-water resources of Eddy County,
New Mexico: New Mexico Bureau of Mines and
Mineral Resources Ground-Water Report 3,
73 p.
International Association of Hydrogeologists, 2013,
available online at
http://karst.iah.org/karst_hydrogeology.html
Lee, W.T., 1925, Erosion by solution and fill, in
Contributions to the geology of the United
States: U.S. Geological Survey Bulletin 760-C,
107 p.
Mercer, J.W., 1983, Geology of the proposed waste
isolation pilot plant site, Los Medanos area,
southeastern New Mexico: U.S. Geological
Survey Water-Resources Investigations Report
83-4016, 121 p.
Powers, D.W., Beauheim, R.L., Holt, R.M., and
Hughes, D.L., 2006, Evaporite karst features and
processes at Nash Draw, Eddy County, New
Mexico, in Land, L., Lueth, V., Raatz, W.,
Boston, P., and Love, D., eds., Caves and karst
of southeastern New Mexico: New Mexico
Geological Society Fifty-seventh Annual Field
Conference, p. 253-264.

107
Use of A Dual Continuum Model to Describe Solute Transport in Karst
By Roger Painter, Justin Harris, and Lonnie Sharpe
Tennessee State University, College of Engineering, 3500 John A Merritt Blvd., Nashville, TN 37209

Abstract
The advection dispersion equation (ADE) as applied to pipe flow often successfully models solute
transport along major karst features. This approach has had success when flow within these features is
predominantly along conduits. However, the slower solute transport associated with flow in the diffuse
continuum may explain the tendency of tracer response concentration data to have a long upper tail
compared to the diminishing tail predicted by the ADE. The hydraulic response of karst to a rain event
also reflects the dual continuum for karst flow. The high permeability of the conduit network allows for a
subsequent quick response at the spring to a rain event. A slow recession to pre-rain event springflow is
often related to water being released from storage in the fractured media or epikarst. It is in this context
that the case is made for a dual continuum transport model for karst. In existing double continuum models
the matrix and the conduit network are each represented by a continuum, and the exchange of water
between the two continua is governed by lumped exchange parameters. This paper presents a dual
continuum model for karst, which is based on the finite element solution of the rigorous model in terms of
the Navier-Stokes and continuity equations describing conduit flow, the Forchheimer-corrected Brinkman
equations describing the diffuse phase flow, and finally, the transient ADE describing solute
concentration. In the model, the two adjacent continua share a common boundary. Due to the extreme
differences in the flow regimes near the common boundary, the boundary conditions are characterized by
very steep gradients. Furthermore, the hydraulic characteristics are independent of the concentration of
the diluted contaminant. To facilitate validation of the computational approach, a laboratory-scale analog
model was constructed consisting of an open channel submerged in a porous media. The analog model
allows the conduit cross section and the hydraulic conductivity of the porous media to be varied as
parameters. The computer code, COMSOL 4.4 Forchheimer Flow Module, was modified to provide the
steady state solution for the system (COMSOL user’s manual, 2014), and the transient flow model with
solute transport was developed using the FlexPDE 6.0 finite element solver (FlexPDE 6 user’s manual,
2014).
REFERENCES
COMSOL user’s manual, 2014, Introduction to COMSOL multiphysics: COMSOL Inc., Burlington, MA, USA, 158
p., website accessed on 3/12/2014, also available at
http://www.comsol.com/shared/downloads/IntroductionToCOMSOLMultiphysics.pdf

FlexPDE user’s manual, 2014, FlexPDE 6, version 6.35, Spokane Valley, WA, website accessed on 3/12/2014, also
available at http://www.pdesolutions.com/download/flexpde635.pdf

108
 GEOCHEMISTRY

Geochemical Evidence for Denitrification in the Epikarst at the Savoy

Experimental Watershed, Northwest Arkansas
By Jozef Laincz1 and Phil D. Hays2,3
1
Environmental Dynamics, 216 Ozark Hall, University of Arkansas, Fayetteville, AR 72701
2
University of Arkansas, Department of Geosciences, Ozark Hall 216, Fayetteville, AR 72701
3
U.S. Geological Survey, Arkansas Water Science Center, 401 Hardin Rd, Little Rock, AR 72211

Abstract
Karst aquifers are highly vulnerable to agricultural nitrate (NO3-) contamination due thin soils and
rapid conduit flow characteristic of karst geology. Many karst regions contain epikarst, an upper
weathered layer of carbonate bedrock, which could support a higher degree of denitrification, as a result
of physical properties that are distinctly different from the underlying karst. This study aimed to identify
denitrification and characterize controls on denitrification in a well-delineated epikarst system in
northwest Arkansas. Water samples were collected at an interceptor trench and at epikarst springs
downgradient from the trench after four storm events in the spring 2011 and analyzed for NO3-
concentration, NO3- delta-nitrogen-15 (δ15N; ratio of nitrogen-15 (15N):nitrogen14 (14N) isotopes) and
delta-oxygen-18 (δ18O; ratio of oxygen-18 (18O):oxygen-16 (16O) isotopes), dissolved organic/inorganic
carbon ratio (DOC/DIC) concentration and delta-carbon-13 (δ13C; ratio of carbon-13 (13C):carbon-12
(12C) isotopes), and dissolved gas concentration of nitrogen and oxygen (N2, O2 respectively).
Denitrification was indicated by an average NO3- decrease of approximately fifty percent along the
trench-spring flowpaths. For flowpaths upgradient from the trench, denitrification was indicated by
simultaneous isotopic enrichment in NO3- with 15N and 18O and by the trend of increasing DIC
concentration with decreasing δ13C of DIC detected in the trench samples. The occurrence of
denitrification in the system was corroborated by dissolved N2 measurements which showed
supersaturation of up to one hundred-six percent in all except for three samples. Consistent with
environmental requirements of denitrifiers, N2 saturation negatively correlated with O2 saturation and
positively correlated with DOC concentration at the springs, with the latter suggesting a limiting role of
DOC on denitrification in the epikarst. The results also suggest that hydrology (epikarst saturation) plays
an important indirect role in controlling denitrification: more saturated conditions likely deliver more
DOC substrate and more restrict O2 diffusion into the epikarst, thus helping to create an anoxic
environment suitable for denitrification. In conclusion, this study successfully identified denitrification
and several of its controls in the studied epikarst system, and its findings can serve as a foundation for
future, quantitative studies.
INTRODUCTION conduit network with little microbial
remediation and high rates of dispersion offer
High nitrate (NO3-) concentrations in water
little protection of aquifers from contamination
pose a risk to human health (Tenovuo, 1986) as
originating at the surface. A case in point is the
well as the health of aquatic ecosystems
area under study, the karst region of northwest
(Goolsby and Battaglin, 2001; Rabalais and
Arkansas, where intense animal production and
others, 1996). The problem of groundwater NO3-
excess nutrient generation have been linked to
contamination is most often associated with
elevated NO3- concentrations in local springs
agricultural activity, and one type of landscape
and wells (Adamski, 1997; Davis, Brahana, and
especially vulnerable to such contamination is
Johnston, 2000; Laubhan, 2007; Steele and
karst (Boyer and Pasquarell, 1996; Power and
McCalister, 1990). Protection of these systems is
Schepers, 1989). Here, the typically thin or
paramount as karst aquifers are important
missing soil cover, direct point-recharge via
sources of drinking water; as much as one
sinkholes, and rapid, concentrated flow in the
quarter of the world's population obtains its
109
drinking water from karst aquifers (Ford and number of studies on this topic have
Williams, 2007). characterized karst systems where the epikarst
was present (Einsiedl, 2005; Lee and Krothe,
Many karst systems are mantled by a layer
2001; Panno, Hackley, Hwang, and Kelly,
known as regolith or epikarst, generally defined
2001), but none focused solely on the epikarst
as the dissolutionally weathered, typically 3-15
itself.
m thick, upper portion of the carbonate bedrock
(Ford and Williams, 2007). The U.S. karst map The purpose of our investigation was to add
(Veni and others, 2001) identifies more than to the knowledge of the biogeochemical
50% of U.S. karst as being buried, i.e, covered functioning of the epikarst and, more
by the epikarst. specifically, to identify denitrification and its
spatial and temporal variation as well as any
Epikarst hydrology is distinctly different
controlling factors in an epikarst system with
from that in the underlying bedrock and could
well-delineated hydrology. Study methods relied
be conducive to significant microbial activity
on a complex geochemical characterization
including denitrification, which is the most
involving measuring concentration and stable
important NO3- attenuation process removing
isotopes of all of the key reactants and products
NO3- from watersheds in the form of gaseous
of the denitrification reaction, including nitrate,
nitrogen. For example, as porosity and
dissolved organic and inorganic carbon, and
permeability diminish with depth, the epikarst
dissolved dinitrogen. The application of
has a tendency to detain and delay recharge
dissolved dinitrogen measurements to detect
(Aquilina, Ladouche, and Dörfliger, 2006;
denitrification in an epikarst system is somewhat
Bakalowicz, 1995; Einsiedl, 2005), which
novel. While commonly applied to aquatic and
translates into increase in residence time, an
marine systems, the technique rarely has been
important factor facilitating denitrification
employed in unsaturated terrestrial systems due
(Green and others, 2009; Seitzinger and others,
to challenges posed by high N2 background and
2006). The decrease in permeability also induces
its rapid exchange with air (Groffman and
lateral flow (Klimchouk, 2004) which acts to
others, 2006), and there appears to be no study
route the flow away from vertical shafts and
that has employed it specifically in the epikarst.
conduits leading to the phreatic zone in the
deeper bedrock. Studies have documented that Site Description
the epikarst is a chemically reactive zone
The study site is located at the Savoy
changing the chemistry of recharging water with
Experimental Watershed (SEW) near the town
respect to Cl-, Br-, oxygen-18 and deuterium
of Savoy in northwest Arkansas. The landscape
(Aquilina and others, 2006) as well as
of SEW is characterized by steep-sided valleys
attenuating organic dye and phosphate tracers
cut into a highly dissected plateau formed on
(Sinreich and Flynn, 2011).
impure, chert-rich limestone. Land use is
At the same time, epikarst discharge has dictated by the topography, with the steep side
been found to constitute as much as 55% of the slopes and narrow ridge tops in hardwood forest
total discharge volume of springs or small and the broader ridge tops and valley bottoms in
catchments (Lee and Krothe, 2001). Therefore, permanent pasture characteristic of the Illinois
the quality of waters discharging out of karst River Watershed. Geologically, the SEW
watersheds likely is dictated to a great degree by represents the regolith-mantled karst setting of
biogeochemical processes taking place in the the Ozark Highlands, and is a geologic setting
epikarst, which emphasizes the importance of typical of approximately 15% of the eastern
understanding of biogeochemical functioning of U.S., where karstified carbonate bedrock is
the epikarst. overlain by a variable thickness of erosional
residuum (regolith or epikarst) composed mainly
While various aspects of epikarst hydrology
of clay and rock fragments of silicic carbonate.
have been well established, the understanding of
The epikarst at the site is from 1 to 4 m thick.
its biogeochemical functioning, including the
The soil at the top consists of up to 60% of rock
processes of nitrate attenuation, is lacking. A
110
fragments, which become more abundant and of 5 tons per acre across the pasture area of
also progressively turn into more continuous and about 80 x 150 m upgradient from the trench in
less weathered rock ledges with depth. A March 2011 to simulate common NO3- loading
detailed pedologic characterization of the site practices in Arkansas and also to increase NO3-
can be found in Sauer and Logsdon (2002) and a signal.
structural description of the epikarst based on
Samples were collected following each of
subsurface geophysics in Ernenwein and
four consecutive storm events from May 2011
Kvamme (2004).
until July 2011 in conditions of increased
METHODOLOGY saturation and flow. Water samples were
collected from the trench and all of the springs
Denitrification was studied in a section of
for each storm event. Samples were collected
the epikarst in Basin 1 of the SEW. Samples
into appropriate containers for each type of
were collected at two stages of the hydrologic
chemical and isotopic analysis, and filtered and
gradient of the epikarst section: an interceptor
preserved in accordance with guidelines from
trench located on a sloping (15%) ridge-top
the analyzing lab. For anion (NO3-, Cl-) and
pasture and five epikarst springs (J1-J5) located
NO3- stable isotope (δ15N and δ18O) analyses,
on the side slope from 29 to 137 m
samples were collected without filtration or
downgradient from the trench (fig. 1). The
preservation. For DOC/DIC concentration and
trench is about 1.5 m deep, excavated down to 13
C stable isotope analysis, samples were filtered
relatively unweathered carbonate bedrock, and
on-site (0.7 µm Whatman GF/F filters in a
fitted with a French drain. The trench serves to
Millipore 47-mm syringe filter assembly), and
intercept waters representative of epikarst
samples for DOC-13C isotopic analysis were
throughflow. The springs are natural, terminal
acidified with 85% H3PO4. For dissolved-gas
discharge points of the epikarst flowpaths and
analyses, samples were collected via a portable
thus provide samples representing the final
sampler (Masterflex E/S, Cole-Parmer, Vernon
geochemical signature of waters leaving the
Hills, IL) directly from the point of emergence
epikarst. The springs were fitted with V-notch
of water from the ground to minimize contact
weirs for accurate discharge measurement. The
with air. The pump outflow tubing was inserted
hydrologic connections between the trench and
each of the springs had previously been to the bottom of a sample vial, with 234 µl of
established by dye tracing (Laincz, 2007). Prior 50% ZnCl2 preservative solution (1.2% final
to sampling, chicken litter was applied at a rate conc., v/v) pre-dosed in each vial (18 ml Kimax

Figure 1. Conceptual model of the epikarst illustrating the lateral flow and sampling points along the flowpath. (Not to scale)

111
test tube with a ground glass stopper), and water to a Finnigan Delta+ XL isotope ratio mass
was pumped at a slow rate to prevent bubble spectrometer (Finnigan-MAT, San Jose, CA)
formation before the vial was stoppered, sealed (St-Jean, 2003). The DIC and DOC
with Parafilm, and carefully checked to ascertain measurements had an error margin of ±0.03 and
that no air bubbles were present. Samples were ±0.13‰, respectively. Dissolved O2 and N2
placed on ice and transported into laboratory, analyses were performed in the Scott
where they were stored in the dark at 4°C until Biogeochemistry Lab at the University of
analysis. During sample collection, several field Arkansas Department of Crop, Soil and
and environmental parameters were measured Environmental Sciences using a membrane inlet
including pH, electrical conductivity, mass spectrometry (MIMS) setup consisting of a
temperature, dissolved oxygen (DO), and Pfeiffer Prisma mass spectrometer and a Bay
barometric pressure. Instruments DGA membrane inlet S-25-75. The
MIMS setup and analysis are described in detail
Chemical Analyses
in Kana and others (1994) and Grantz and others
Chemical analysis of samples for major (2012), respectively. The precision of the MIMS
anions and cations was conducted at the analysis was ±0.3%.
Arkansas Department of Environmental Quality
RESULTS
Water Quality Lab using ion chromatography
(U.S. Environmental Protection Agency (EPA) Nitrate Concentration and δ15N and δ18O
method 300.0) and inductively coupled plasma-
Nitrate concentrations ranged from 1.5 to
atomic emission spectrometry (EPA method
7.6 mg/L, with an average of approximately 3
200.7), respectively. Stable isotopes of NO3-
mg/L. These concentrations are similar to those
(δ15N and δ18O) were analyzed at the University
reported for the watershed by other authors
of Arkansas Stable Isotope Lab using the
(Sauer and others, 2008; Winston, 2006). The
denitrifier method (Casciotti, Sigman, Hastings,
NO3- concentration did not seem to have been
Bohlke, and Hilkert, 2002; Sigman and others,
significantly affected by the application of
2001) involving the use of genetically modified
chicken litter two months prior to the test. The
denitrifier to quantitatively convert sample NO3-
average NO3- concentrations of the trench and
to N2O, with adaptations described in Winston
spring water samples were 4.7 and 2.6 mg/L,
(2006). The analysis was performed using a
respectively. The NO3--δ18O values ranged
GasBench II system with a CO2 trap made of
between 1.3 and 4.6‰. The trench average was
stainless steel and organics and a water trap
higher than the springs average (5.2 and 3.7‰,
consisting of isopropanol-dry ice slush,
respectively). The NO3--δ15N values varied
connected to a continuous flow isotope ratio
between 2.5 and 5.8‰. The trench samples
mass spectrometer (XP, ThermoFinnigan,
averaged approximately 2‰ while water from
Bremen, Germany). The method precision for
the springs averaged 3.6‰. The measured NO3--
δ15N and δ18O was ±0.46 and ±0.49‰,
δ15N and -δ18O values are consistent with NO3-
respectively. The results are expressed in the
originating from soil organic matter and animal
text below in δ notation defined as δ X (‰) =
waste (i.e., manure, chicken litter) (Kendall and
(Rs/Rst – 1) * 1000, where X is 15N, 18O, or 13C,
McDonnell, 1998). The indicated origin is
and R is the 15N/14N, 18O/16O, 13C/12C ratios of
accurate as soil and animal waste were in fact
the sample (s) and reference standard (st),
the primary potential sources of NO3- at the site.
respectively. The reference standards were Air
for δ15N, Vienna Standard Mean Ocean Water DIC, DOC Concentration, and δ13C
(VSMOW) for δ18O, and Vienna Pee Dee DIC varied from 7.2 to 35.5 mg/L-C, with
belemnite (VPDB) for 13C. DOC and DIC an average of 25.5 mg/L-C. The average DIC
concentration and stable isotope (13C) concentrations of the trench and spring samples
composition were analyzed at the Colorado were 28.6 mg/L-C and 10.1 mg/L-C,
Plateau Stable Isotope Lab, Flagstaff, AZ, using respectively. Isotope analyses showed the DIC
an O.I. Analytical Model 1010 TOC analyzer δ13C values ranging between -13 and -21‰. The
(OI Analytical, College Station, TX) interfaced
112
springs averaged at approximately -15‰ while dilution and denitrification (Clark and Fritz,
the trench average was lower (-19‰). DOC 1997). Dilution did not appear to be the cause
concentration varied between 0.3 and 4.8 mg/L- since chloride concentration between these two
C. DOC concentration in the springs averaged points of the flowpath did not decrease.
0.8 mg/L-C, which is typical for groundwater, Consequently, the likely process responsible for
while the trench average was higher, at 3.9 the NO3- depletion was denitrification.
mg/L-C, possibly as a result of being situated
Denitrification causes an isotopic
closer to the organics-rich soil zone than the
enrichment in both 15N and 18O of the remnant
springs. DOC δ13C values were within a
NO3-, with the 15N enrichment approximately
relatively narrow range of about -25 to -27‰.
twice that of 18O (Bottcher, Strebel, Voerkelius,
This is an expected range that accurately
and Schmidt, 1990; Mariotti, Landreau, and
pinpoints the origin of this DOC in the local
Simon, 1988). This phenomenon shows on a
vegetation dominated by C-3 plants.
δ15N vs. δ18O plot as a line with a positive slope
Dissolved N2 and O2 of 0.5. While all of the samples do not produce
such trend, the trench samples δ15N and δ18O
Dissolved N2 concentration ranged from
exhibit a strongly positive correlation with a
15.1 to 17.2 mg/L. The concentration data varied
slope of 0.6 (fig. 2). This is an indication of
in both time and space. Spatially, on average, the
denitrification in the upper compartment of the
highest concentration was in J2 (103 mg/L)
epikarst drained by the trench. Further down the
while the lowest was in J5 samples (100.8
flowpath, the spring samples do not show any
mg/L). Temporally, samples collected on April
definite δ15N-δ18O relation. Denitrification might
28 had the highest average concentration (104.2
be occurring on the flow path to the springs as
mg/L) while the lowest average concentration
well, but the remnant NO3- may mix with NO3-
was found in the only sample of April 15 (99.4
from extraneous sources (e.g. decomposition of
mg/L). N2 saturation levels calculated from
organic matter) concealing the isotopic signature
N2:Ar ratios and Ar concentrations ranged from
of denitrification.
99.4 to 105.6%, with an average of 102.2%. All
but three samples were supersaturated with
respect to N2, i.e., their N2 content exceeded the
equilibrium-with-air concentration or 100%
saturation. DO concentration ranged from 4.9 to
8.2 mg/L and averaged 6.5 mg/L. On average,
the highest DO concentration was in the trench
(7.9 mg/L), the lowest in J2 (5.1 mg/L).
Temporally, the variation in DO was small, with
the highest value at 7.1 mg/L on 4/15 (only one
sample from J3) and the lowest average at 6.2
mg/L on 4/28. Calculated O2 saturation ranged
between 46.9 and 90.5% and averaged 65.9%.
The trends of temporal and spatial averages were
similar to those for DO concentration.
Figure 2. Isotopic composition of nitrate in trench samples
DISCUSSION (squares) and spring samples (triangles).
Nitrate Concentration and δ15N and δ18O DIC Concentration and δ13C
The NO3- concentration data show a pattern The denitrification reaction also is known to
of decreasing concentration between the trench increase DIC concentration (Aravena and
and the springs. The concentration of the former Robertson, 1998) as well as to impart 13C
was on average two times higher than of the depletion to the DIC through the addition of 13C-
latter. The processes that in subsurface situations depleted organic carbon participating in the
can cause decreases in NO3- concentration are reaction (Fritz, Cherry, Weyer, and Sklash,
113
1976). The spring samples indeed had were supersaturated with respect to N2. This
significantly higher DIC compared to the trench supersaturation is most probably the footprint of
samples, with the average concentration in the denitrification because virtually no other process
springs about 3 times that in the trench. This could feasibly occur in this system that would
DIC, however, was not depleted in 13C relative cause dissolved N2 to increase beyond saturation
to the trench values. A likely reason is addition levels. The only other possible process would be
of DIC via carbonate dissolution along the the incorporation of excess air, i.e., the
flowpath. If the only DIC source was dissolution of air bubbles entrapped in capillary-
denitrification, DIC in the samples would have a sized pore spaces by downward migrating
δ13C in the range of its source organic matter waters. This mechanism, however, is only
(Aravena and Robertson, 1998). In this case, the feasible at sufficient depth and hydrostatic
δ13C of dissolved organic matter of all samples pressure below the water table, with about 10 m
ranged 25-27‰. However, if the aquifer is a depth required for complete dissolution of the air
carbonate aquifer, dissolution of carbonate bubbles (Heaton and Vogel, 1981). The thin
minerals (δ13C ~ 0‰) will buffer the input of the (generally <2 m) and transiently saturated
depleted 13C generated by denitrification. epikarst does not offer conditions for the
Mixing equal amounts of organic (δ13C = -26‰) occurrence of this process. Denitrification as the
and inorganic (δ13C = 0‰) carbon would cause of N2 supersaturation is corroborated by
generate DIC with a δ13C value of -13‰. A multiple lines of evidence already presented –
calculation using a binary mixing equation NO3- and DIC concentrations as well as the
shows that DIC with the same δ13C value as the corresponding isotopic data. Hence,
average for the springs (-15‰) would be denitrification is the most plausible cause of N2
produced by mixing of about 42% of inorganic supersaturation.
and 58% of organic carbon. Thus, denitrification
may have been occurring along the trench-to-
spring flowpaths and is responsible for the NO3-
depletion observed at the springs, but the
expected DIC δ13C response was masked by DIC
from calcite dissolution.
Applying the same approach as with NO3-
isotopes and separately analyzing for trends in
the spring samples and the trench samples, a
positive relation was noted between DIC and
δ13C in the trench samples, indicating
denitrification occurring in the upper epikarst
compartment drained by the trench (fig. 3). This
is consistent with the NO3- δ15N and δ18O data,
which also indicated denitrification in the trench Figure 3. Relationship between DIC concentration and
samples. The spring samples, however, δ13C in trench samples (squares) and spring samples
exhibited a weakly positive trend for DIC vs. (triangles).
δ13C, which does not support an interpretation of We have not found any other denitrification
denitrification; however, as shown by the above studies that determined N2 supersaturation in the
mixing calculation, mixing in the epikarst may epikarst or in other groundwater systems, which
have occurred and could be masking the effect precluded comparison of the data with similar
of denitrification on the DIC and δ13C studies. However, a few studies, which
composition of the samples. determined N2 supersaturation linked to
Dissolved N2 and O2 denitrification in deep sea waters, report values
in the range between 101% and 108%
The most significant observation that can be (Quinones-Rivera and others, 2007; Rönner and
made from the data is that 18 out of 21 samples
114
Sörensson, 1985). This range is similar to the denitrification occurring along the J2-J5
values obtained in our study. flowpaths of the epikarst. Dissolved O2, or lack
thereof, appears to play a role in enabling this
Most denitrifiers are facultative anaerobes
denitrification.
and, consequently, denitrification requires
anoxic or very low oxygen conditions – The effect of O2 saturation on denitrification
generally below 0.2 mg/L (Tiedje, 1988). The suggested by the data invites the question as to
measured O2 concentration, however, was in the exactly what mechanism could enable the
range of 4.7-8.2 mg/L and therefore, any further drawdown of O2 concentration, creating
denitrification activity in the epikarst would anaerobic conditions within the microsites.
have to be restricted to anoxic While, in general, dissolved O2 is consumed by
mircroenvironments such as those described by aerobic or anaerobic microbial activity and
Sexstone and others (1985) or Koba and others geochemical reactions, the key mechanism
(1997). Such microsites could exist in the enabling the development of anoxic conditions
studied epikarst, indeed; pockets of grayish in the microsites could be the blocking of access
colors indicative of reducing conditions were of O2 by waterlogging. The phenomenon of
observed in abundance throughout the epikarst waterlogging causing an increase in
profile during excavation works at the site. denitrification and consequently loss of soil
nitrogen by restricting oxygen diffusion to the
Concentration of O2 within these microsites
soil is widely known among agronomists and
would probably be affected by O2 concentration
soil scientists. Under certain conditions, even a
in the surrounding matrix; the lower the latter,
small percentage increase in soil saturation can
the lower the former. As a result, granted that all
initiate denitrification by sealing off a sufficient
other requirements for denitrification are met,
soil volume from diffusion of atmospheric O2
one could expect to see that the less O2 is in the
(Craswell, 1978). Similarly, according to Sylvia
system as a whole, the more denitrification will
and others (1999), rates of denitrification are
occur in these microsites. This phenomenon
would then manifest itself as a negative
correlation between the measured N2 and O2
saturation levels. While such correlation is found
to be only negligible for the entire dataset,
correlation is relatively strong when the highest
O2 saturation sites – the trench and J1 site – are
excluded from the analysis (fig. 4). The
exclusion seems justified since the relatively
high O2 content of waters from these two sites
could well be due to the distinct physical
hydrologic character of these flowpaths as
opposed to being a reflection of some intrinsic
biogeochemical process affecting the O2 content Figure 4. Relationship between dissolved oxygen and
in the epikarst (i.e. aerobic or anaerobic nitrogen saturation in J2-J5 spring samples (samples from
respiration consuming O2 along the other J1 and trench are excluded).
flowpaths). This is especially true for the trench generally greatest in wet soils where more than
waters which could be oxygenated in the final, 80% of pore space is saturated and respiratory
pipe segment of the installed collector (French activity is reasonably high. The data in this study
drain) of this flowpath. The J1 flowpath, as provide some evidence for the occurrence of this
suggested by discharge and specific conductance mechanism in the epikarst. Assuming the
(this study data) as well as DOC bioavailability average discharge for a sampling event to be a
(Winston, 2006), is dominated by focused flow, measure of epikarst saturation, the highest
a more turbulent type of flow characterized by epikarst saturation event (4/28) had the lowest
increased potential for oxygenation. Thus, a average O2 saturation (and the highest average
combined analysis of N2 and O2 data indicates
115
N2 saturation), the lowest epikarst saturation denitrifiers also depends on quality or
event (4/15) had the highest O2 saturation (and bioavailability of this DOC. While this
the lowest N2 saturation), and the two parameter was not assessed, the positive relation
intermediate epikarst saturation events had between DOC and N2 saturation suggests that
proportionally inverse intermediate O2 saturation this DOC was sufficiently labile for denitrifiers.
(and intermediate N2 saturation) (fig. 5). When
The relation thus indicates that carbon
the analysis is conducted for the sites
availability has a limiting effect on
individually instead of averaging the sites for
denitrification in the epikarst, and two reasons
each event, the trend of increasing discharge
may explain why this perhaps should be the case
with decreasing O2 saturation is present for all
in the epikarst even more than in other
sites except for the trench. This inconsistency
environments: Firstly, in general, in
again could be caused by aeration effects of the
environments that are not completely anaerobic
collector elevating the O2 content of trench
such as the epikarst, denitrifiers have to compete
waters, particularly at higher discharge rates.
for carbon with obligately aerobic heterotrophs,
The evidence overall thus indicates that physical
which make up the bulk of the microbial
hydrology of the epikarst can control
biomass in these environments (Sylvia and
geochemistry, specifically, O2 concentration and
others, 1999). Secondly, organic carbon in the
subsequently denitrification. The analysis,
system is already a limited resource due to the
however, relies on only four events and uses
discharge to assess water saturation. The trend
therefore should be confirmed with an analysis
involving more measurements and perhaps some
more direct method of measuring water
saturation (e.g., the electrical resistivity method).
DOC
One of the reactants of denitrification is
organic carbon, which the microbes use as an
electron donor. Denitrifying activity has been
found to be related to organic carbon contents in
a wide range of environments, including
sediments (Van Kessel, 1978), soils (Bremner
and Shaw, 1958; Burford and Bremner, 1975),
riparian zones (Vidon and Hill, 2005), shallow
aquifers (Starr and Gillham, 1993) as well as
oxic surface waters and porewaters (Sobczak
and Findlay, 2002). The data from this study
suggest this to also be the case in the epikarst;
for the spring samples, N2 saturation, which can
be taken as a proxy measure of denitrification, is
positively correlated with DOC concentration
(fig. 6). This correlation does not hold when the
trench samples are included in the analysis due
to their abnormally high DOC levels, on average
about 5 times higher than those in the springs.
These are suspected to be caused by
contamination of carbon compounds leaching
from surface-derived organic detritus
accumulated in the French drain gravel pack and
Figure 5. Average discharge (Q), O2 saturation, and N2
pipe. The trench samples, therefore, were saturation for four sampling events (error bars represent
excluded. In addition, the utilization of DOC by mean +/- 1 SD).
116
fact that karst groundwater systems do not have Additional geochemical indicators, including
significant autotrophic sources of organic carbon relations between nitrate δ15N and δ18O as well
(Susan Ziegler, personal comm.). as DIC concentration and DIC δ13C, did not
corroborate this evidence, although it is possible
The correlation also shows data points
that the positive signature of denitrification had
clustered according to event date, with the
been masked – in the case of NO3- isotopic
higher discharge events having higher N2
composition by mixing in of extraneous NO3-
saturation and DOC concentration (fig. 6). This
and in the case of DIC δ13C by dissolution of
indicates that hydrology (epikarst saturation) not
calcite.
only impacts O2 concentrations and
subsequently denitrification in the epikarst as Denitrification was also detected in the
noted before, but epikarst saturation also seems epikarst upgradient from the trench. The
to exert control on denitrification by controlling evidence includes the trend of simultaneous
DOC availability. Higher discharge events likely enrichment in nitrate 15N and 18O and another
mobilize and deliver more DOC than lower trend of increasing depletion in 13C of DIC as
discharge events. The greater supply of DOC DIC concentration in the trench samples
then likely translates into a greater increased. The trench waters also had higher
denitrification potential during storm events. concentration of DOC relative to the epikarst
This dynamic makes the epikarst different from springs, being closer to the soil zone DOC
surface systems where storm-flow events are source, which would give the former a greater
typically thought of as events where more potential for denitrification.
refractory carbon is delivered (Susan Ziegler,
The most significant finding of this study is
personal comm.). The lack of significant
the dissolved N2 supersaturation detected in all
autotrophic sources of carbon means that the
except for three samples, strongly signaling
epikarst system depends upon the pulse of
denitrification in the epikarst. Negative
carbon from storm events.
correlation between N2 and O2 saturation
suggested that the magnitude of denitrification is
controlled by oxygenation levels of the epikarst
5/29 waters. Oxygen concentration, in turn, seemed to
have been affected by the wetness or saturation
Av. Q = 20.3 l/min 4/28 level of the epikarst as suggested by negative
Av. Q = 13.4 l/min correlation between discharge and O2 saturation.
Thus, as is the case in soils, hydrology
(waterlogging) appears to be an important
5/4
control on denitrification in the epikarst.
Av. Q = 19.3 l/min
Further, N2 saturation was positively
correlated with DOC concentration indicating a
limiting role of carbon in denitrification in this
system. Such a situation would be expected
Figure 6. Relationship between DOC concentration and N2 given the lack of autotrophic sources in karst
saturation of spring samples (trench samples are excluded). and the dominant presence of obligately aerobic
Circles enclose datapoint clusters which correspond with heterotrophs which compete with denitrifiers for
sampling dates with varying hydrologic conditions carbon. As with the O2 content, hydrologic
(saturation) as indicated by average discharge (avg. Q). conditions also appear to affect DOC: higher
CONCLUSIONS discharge events tended to have higher DOC
concentrations. The greater storm pulses likely
The occurrence of denitrification along the are able to mobilize and deliver more C which
flowpaths between the trench and the epikarst then drives denitrification activity.
springs was indicated by the general trend of
NO3- depletion, which in the absence of dilution The suite of geochemical parameters
could only be caused by denitrification. measured for this study indicates denitrification
117
occurring in this epikarst system. While the Bakalowicz, M., 1995, La zone d’infiltration des
experimental approach did not allow for aquifères karstiques. Méthodes d’étude: Structure
quantitative evaluation of denitrification or its et fonctionnement: Hydrogéologie, v. 4, p. 3-21.
controlling variables, it succeeded in identifying Bottcher, J., Strebel, O., Voerkelius, S., and Schmidt,
their occurrence, which is a valuable H.L., 1990, Using isotope fractionation of nitrate-
contribution to understanding the nitrogen and nitrate-oxygen for evaluation of
biogeochemical functioning of the epikarst. microbial denitrification in a sandy aquifer:
These findings also reaffirm the concept that Journal of Hydrology, v. 114, no. 3-4, p. 413-424.
within karst systems characterized by limited Boyer, D.G., and Pasquarell, G.C., 1996, Agricultural
soil development and lack of bioremediation land use effects on nitrate concentrations in a
capacity, the epikarst is a potentially important mature karst aquifer: Journal of the American
zone of attenuation of leaching nitrate. The Water Resources Association, v. 32, no. 3, p. 565-
findings serve as a foundation for future, more 573.
quantitative investigations of these epikarst Bremner, J., and Shaw, K., 1958, Denitrification in
phenomena and of their response to specific soil. II. Factors affecting denitrification: The
nutrient management practices so that they may Journal of Agricultural Science, v. 51, no. 01, p.
be optimized to reflect the ecological limitations 40-52.
of vulnerable karst landscapes. Burford, J., and Bremner, J., 1975, Relationships
ACKNOWLEDGMENTS between the denitrification capacities of soils and
total, water-soluble and readily decomposable soil
The authors would like to thank Dr. Van organic matter: Soil Biology and Biochemistry, v.
Brahana of the University of Arkansas and Mr. 7, no. 6, p. 389-394.
Tim Kresse of the U.S. Geological Survey for Casciotti, K.L., Sigman, D.M., Hastings, G.M.,
their helpful reviews. Dr. Thad Scott of the Bohlke, J.K., and Hilkert, A., 2002, Measurement
University of Arkansas shared his expertise and of the oxygen isotopic composition of nitrate in
equipment for dissolved gas analysis. Mr. Roger seawater and freshwater using the denitrifier
Miller of the Arkansas Department of method: Analytical Chemistry, v. 74, no. 19, p.
Environmental Quality assisted with water 4905-4912.
chemistry analysis. Finally, this research was Clark, I.D., and Fritz, P., 1997, Environmental
made possible in large part by funding from the isotopes in hydrogeology: Boca Raton, Florida,
U.S. Department of Agriculture, National CRC Press LLC, 328 p.
Resources Conservation Service – National
Craswell, E., 1978, Some factors influencing
Water Management Center and the Arkansas denitrification and nitrogen immobilization in a
Water Resources Center. clay soil: Soil Biology and Biochemistry, v. 10,
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Geochemistry of Paleokarst Aquifers of the Knox Group in Tennessee
and Kentucky
By Michael Bradley1, and Thomas (Marty) Parris2
1
U.S. Geological Survey, Tennessee Water Science Center, 640 Grassmere Park, Nashville, TN 37211
2
Kentucky Geological Survey, 228 Mining and Mineral Resources Building, Lexington, KY 40506

Abstract
Water-quality samples were collected from deep carbonate formations in the Cambrian- and
Ordovician-age Knox Group in the central areas of Kentucky and Tennessee as part of an evaluation of
the formations for carbon sequestration (Kentucky) and the geohydrology of the paleokarst aquifers
(Tennessee). Geochemical data from the deep carbonate formations have been used to evaluate the
chemical evolution of the groundwater, residence time, and the degree of confinement. The geochemical
data indicate differences in groundwater evolution in the different structural settings including the
Nashville Dome, Cincinnati Arch, and Illinois Basin (fig. 1).

Figure 1. Major geologic structures and locations of selected wells in the Knox Group, Hancock and Scott Counties, Kentucky,
and Hickman, Perry, and Wayne Counties, Tennessee.

Geologic units being tested include formations equivalent to the Mascot Dolomite of the upper Knox
Group, the Chepultepec Dolomite of the middle Knox Group, and the Copper Ridge Dolomite of the
lower Knox Group. The unconformity at the upper contact of the Knox Group is a major stratigraphic
break between the lower-middle Ordovician Knox Group and the overlying middle Ordovician
carbonates. Paleokarst features present in the Knox Group include secondary porosity and permeability,
121
and collapse breccia (fig. 2). Water-quality data from about 900 samples from aquifers in Precambrian- to
Pennsylvanian-age geologic units in Kentucky and about 600 samples from aquifers in Cambrian- to
Pennsylvanian-age geologic units in Tennessee indicate that groundwater from the Mascot Dolomite of
the Knox Group has lower dissolved-solids concentrations than would be expected based on data trends in
other aquifers.

Water-quality and geochemical data from recently sampled Knox Group wells along the western side
of the Cincinnati Arch in Tennessee and Kentucky indicate a mixing of formation and meteoric waters.
Groundwater samples from a well in the Illinois Basin in Kentucky has high dissolved-solids and chloride
concentrations that are indicative of possible connate water and long residence time rock-water
interaction in the formation. Groundwater from three recently sampled wells in Middle Tennessee, west
of the Cincinnati Arch, has relatively low dissolved-solids and chloride concentrations and indicates the
presence of relatively young meteoric water in the formation. The stable-isotope (δ18O and δH) values for
groundwater from wells in the Nashville Dome and Jessamine Dome are close to the meteoric water line,
suggesting the presence and possible mixing with meteoric water (fig. 3). The stable-isotope values for
groundwater from a well in Hancock County, plot along an isotopic trend line for the Illinois Basin,
indicating rock-water interaction.

____________________________________________________________
Depth below
Location land surface δ18O δ2H
(feet) (permil) (permil)
Illinois Basin
Hancock Co., KY 3,500 – 5,000 -5.1 to -5.5 -40.0 to -41.5

Cincinnati Arch – Jessamine Dome

Scott Co., KY 1,800 – 2,100 -7.3 to -8.1 -41 to -57

Cincinnati Arch – Nashville Dome

Hickman Co., TN 1,450 – 3,069 -6.26 to -6.35 -35.6 to -36.0
Wayne Co., TN 1,200 – 1,221 -5.26 to -5.9 -28.2 to -35
Perry Co., TN 4,727 – 4,960 -6.09 -35.53

Chlorine-36 isotope analysis for water from two wells indicate substantially younger water in the
Knox Group in Hickman County, Tennessee (Nashville Dome) than in water from a well in Hancock
County, Kentucky (Illinois Basin), which is much older water (>1.5 million years).

The occurrence of lower dissolved solids in water at depth in the Knox Group in Middle Tennessee is
indicative of a permeable unit that has some connection with meteoric water. The indicated mixing of
formation and meteoric waters and the potential connection with groundwater from shallower aquifers has
implications regarding possible carbon sequestration in these formations. Potential recharge and
movement of younger, relatively fresh water into and through the Mascot Dolomite indicates the potential
for carbon dioxide leakage updip, or possible leakage through fractures in the overlying formations.

122
 Core interval, in feet below Kelly bushing of drill rig
(18.5 feet above land surface)

2,091–2,092 2,117–2,118 3,130–3,131

Photographs from E.I. DuPont, 1992

Figure 2. Core photographs from E.I. duPont GHS no. 1 well, Humphreys County, Tennessee, showing paleokarst features with
collapse breccia, calcite mineralization, and secondary porosity in the Mascot Dolomite, Knox Group.

Nashville Dome
Hickman, Perry, Meteoric Water Line
and Wayne Co.,
TN Illinois Basin
Jessamine
Dome Hancock Co.,
KY

Scott Co., KY

Figure 3. Relation between stable isotope ratios for hydrogen (δ2H) and oxygen (δ18O), in permil (0/00), for groundwater from
wells in the Knox Group, Kentucky and Tennessee.

123
REFERENCES

Bradley, Michael W., 2001, Geochemistry of the Upper Knox aquifer in Tennessee, in Kuniansky, E.L. (ed.), U.S.
Geological Survey Karst Interest Group Proceedings, St. Petersburg, Florida, February 2001: U.S. Geological
Survey Water-Resources Investigations Report 01-4011, 211 p.
Bradley, Michael W., and Parris, Thomas, 2012, Geochemistry of deep aquifers in Tennessee and implications for
carbon sequestration: Tennessee Section-American Water Resources Association, Proceedings of the 22nd
Tennessee Water Resources Symposium, April 2012, Burns, Tennessee, p. 1C-2.
Brahana, J.V., and Bradley, M.W., 1985, Delineation and description of the regional aquifers of Tennessee: The
Knox aquifer in central and west Tennessee: U.S. Geological Survey Water-Resources Investigations Report
83-4012, 32 p.
Clark, I.D., and Fritz, P., 1997, Environmental isotopes in hydrogeology: Boca Raton, Florida, CRC Press, 328 p.
E.I. DuPont, 1992, Geohydrological survey well, Johnsonville plant, Book 2 of 2, Mascot Dolomite #3: E.I. duPont
de Nemours, Inc., New Johnsonville, Tennessee.
Ford, Derek, and Williams, Paul, 2007, Karst hydrology and geomorphology: West Sussex, England, John Wiley
and Sons, Ltd., 562 p.
Gragg, Michael, and Perfect, Ed, 2011, Rock core sample porosity testing for the Knox Group–Stones River Group
carbon dioxide storage assessment unit in Tennessee: Department of Earth and Planetary Sciences, University
of Tennessee–Knoxville, Report to the Tennessee Division of Geology, 18 p.
James, N.P., and Choquette, P.W., eds., 1988, Paleokarst: Berlin-Heidelberg, Springer-Verlag, 416 p.
Kipp, James A., 1997, Fresh-water aquifer in the Knox Group (Cambrian–Ordovician) of central Kentucky:
Kentucky Geological Survey Report of Investigations 12, Series XL, 15 p.
Parris, Thomas, and Bradley, Michael W., 2012, Fluid evolution in Cambrian-Ordovician Knox Group reservoirs:
Kentucky Water Resources Research Institute, Kentucky Water Resources Annual Symposium, March 19,
2012, Lexington, Kentucky, p. 55-56.
Tennessee Division of Geology, 2011, Regional east-west and north-south cross sections across Tennessee from the
eastern escarpment of the Cumberland Plateau province to the Mississippi Embayment: Tennessee Division of
Geology, prepared for the U.S. Geological Survey National Geologic CO2 Sequestration Assessment, 1 pl.
U.S. Department of Energy, 2013, NATCARB-National carbon sequestration database and geographic information
system: U.S. Department of Energy, accessed February 21, 2014, at
http://www.netl.doe.gov/research/coal/carbon-storage/carbon-storage-natcarb

124
Integration of Geochemical and Isotopic Data to Assess Sources of
Discharge at a Major Spring in the Edwards Aquifer, South-Central
Texas
By MaryLynn Musgrove1 and Cassi L. Crow2
1
U.S. Geological Survey, 1505 Ferguson Ln., Austin, TX 78754
2
U.S. Geological Survey, 5563 DeZavala Rd., Ste. 290, San Antonio, TX 78249

Abstract
The Edwards aquifer in south-central Texas is a productive and important water resource. Several
large springs issuing from the aquifer are major discharge points, popular locations for recreational
activities, and habitat for threatened and endangered species. Discharge amounts from Comal and San
Marcos Springs, the first and second largest spring complexes in Texas, are used as thresholds in
groundwater management strategies. It is generally understood that Comal Springs is predominantly
supplied by regional groundwater flow paths; however, the hydrologic connection of San Marcos Springs
with the regional flow system is less understood. During November 2008–December 2010, the U.S.
Geological Survey conducted a hydrologic and geochemical investigation of San Marcos Springs to
define and characterize its sources of discharge. During the study, hydrologic conditions transitioned from
exceptional drought to wetter than normal, which provided the opportunity to investigate the
hydrogeology of San Marcos Springs under a wide range of hydrologic conditions. Water samples were
collected from streams, groundwater wells, and springs at and near San Marcos Springs, including
periodic sampling (every 3 to 7 weeks) and sampling in response to storms. Additionally, selected
physicochemical properties were measured continuously at several orifices of San Marcos Springs. The
integration of geochemical and isotopic data with geochemical modeling allowed for distinguishing and
quantifying sources of discharge at San Marcos Springs. Results indicate that discharge at San Marcos
Springs was dominated by regional recharge sources and flow paths, and that the contribution from local
streams was relatively minor. Different orifices of San Marcos Springs responded differently to changes
in hydrologic conditions. Some orifices are influenced by mixing with a component of saline
groundwater, likely from the downdip Edwards aquifer saline zone. Results of this study are useful for
resource management strategies and for understanding geochemical and hydrologic processes that affect
the Edwards aquifer.

125
 MICROBIAL ECOLOGY AND KARST ECOSYSTEMS

Linking Climate Change and Karst Hydrology to Evaluate Species

Vulnerability: The Edwards and Madison Aquifers
By Barbara J. Mahler1, Andrew J. Long2, John F. Stamm2, Mary F. Poteet3, and Amy J.
Symstad4
1
U.S. Geological Survey, 1505 Ferguson Ln., Austin, TX 78751
2
U.S. Geological Survey, 1608 Mountain View Rd., Rapid City, SD 57702
3
University of Texas at Austin, 1 University Station G2500, C0930, Austin, TX 78712
4 th
U.S. Geological Survey, Northern Prairie Wildlife Research Center, 8711 37 Street SE, Jamestown, ND
58401

Abstract
Karst aquifers present an extreme case of flow along structurally variable pathways, making them
highly dynamic systems and therefore likely to respond rapidly to climate change. In turn, many
biological communities and ecosystems associated with karst are sensitive to hydrologic changes. We
explored how three sites in the Edwards aquifer (Texas) and two sites in the Madison aquifer (South
Dakota) might respond to projected climate change from 2011 to 2050. Ecosystems associated with these
karst aquifers support federally listed endangered and threatened species and state-listed species of
concern, including amphibians, birds, insects, and plants. The vulnerability of selected species associated
with projected climate change was assessed.
The Advanced Research Weather and Research Forecasting (WRF) model was used to simulate
projected climate at a 36-kilometer grid spacing for three weather stations near the study sites, using
boundary and initial conditions from the Community Climate System Model (CCSM3), a global climate
model, and an A2 emissions scenario. Daily temperature and precipitation projections from the WRF
model were used as input for the hydrologic Rainfall-Response Aquifer and Watershed Flow
(RRAWFLOW) model and the Climate Change Vulnerability Index (CCVI) model. RRAWFLOW is a
lumped-parameter model that simulates hydrologic response at a single site, combining the responses of
quick and slow flow that commonly characterize karst aquifers. The CCVI model uses historical and
projected climate and hydrologic metrics to determine the vulnerability of selected species on the basis of
species exposure to climate change, sensitivity to factors associated with climate change, and capacity to
adapt to climate change.
An upward trend in temperature was projected for 2011 to 2050 at all three weather stations; there
was a trend (downward) in annual precipitation only for the weather station in Texas. A downward trend
in mean annual springflow or groundwater level was projected for all of the Edwards aquifer sites, but
there was no significant trend for the Madison aquifer sites. Of 16 Edwards aquifer species evaluated
(four amphibians, six arthropods, one fish, one mollusk, and four plants), 12 were scored as highly or
moderately vulnerable under the projected climate change scenario. In contrast, all of the eight Madison
aquifer species evaluated (two mammals, one bird, one mollusk, and four plants) were scored as
moderately vulnerable, stable, or intermediate between the two. The inclusion of hydrologic projections in
the vulnerability assessment was essential for interpreting the effects of climate change on aquatic species
of conservation concern, such as endemic salamanders. The linkage of climate, hydrologic, and
vulnerability models provided a bridge to project the effects of global climate change on local karst
aquifer and stream systems, and selected species.

126
Response of Cave-Stream Bacteria to Sub-Lethal Concentrations of
Antibiotics
By Thomas D. Byl1, Petra K. Byl1*, Shannon Trimboli2, and Rickard Toomey, III2
1
U.S. Geological Survey, 640 Grassmere Park, Suite 100, Nashville, TN 37209 (*Volunteer for Science)
2
Mammoth Cave International Center for Science and Learning, Science & Resource Management,
Mammoth Cave National Park, KY 42259

Abstract
Mammoth Cave National Park (MACA) in central Kentucky, is a world renowned karst system that
attracts over 500,000 tourists per year. The high volume of tourists contributes to incidental surface
releases of soaps and disinfectants at the waste-transfer station for recreational vehicles and the
biosecurity mats used to reduce the spread of Pseudogymnoascus destructans (formerly known as
Geomyces destructans, the fungus that causes white nose syndrome (WNS) in bats) spores on footwear.
Multi-antibiotic resistant (MAR) bacteria were reported in high numbers around the waste-transfer station
and WNS disinfection stations. Additionally, some disinfectant was observed in the cave streams after a
storm. The potential problems identified by these observations led to a study by the U.S. Geological
Survey (USGS), in partnership with MACA and Tennessee State University, to determine substrate
utilization patterns and antibiotic resistance of microbial communities associated with cave streams at
different levels of passages in the historic section of Mammoth Cave.
The cave streams within MACA were targeted because they represent a hydrologic connection
between land surface and the cave system. Storm water runoff carries suspended and dissolved
constituents from the surface or near surface into the cave. The suspended and dissolved constituents can
either be toxic, immaterial, or serve as food for microbes and other organisms that live in the subsurface
streams. However, very little is known about the microbial community in cave streams, the food
preference, or the response to anti-microbial compounds by the cave-stream bacteria. Water samples were
collected at one surface and seven cave sites in the summer of 2012 through the fall of 2013. The surface
sampling was limited to storm events due to lack of flow between storms. The cave-stream sampling sites
had continuous flow and were sampled during and between storms. The sampling sites were located on
different vertical levels of the cave system: three sites in the upper mid-level passages, two in the lower
mid-level passages, and two in the deeper levels of the cave.

127
 Bacterial sensitivity to antibiotics was quantified using agar plates with 10-percent trypticase soy agar
(10-percent TSA) augmented with 0.00, 0.01, 0.1, 1.0, and 10.0 milligrams per liter (mg/L) antibiotic
(erythromycin, kanamycin, gentamicin, tetracycline, linear alkylbenzene sulfonates, or quaternary
ammonia compounds). Bacteria resistant to antibiotic existed in all levels of the cave. However, the
number of colony forming units (cfu) on the 10-percent TSA plates generally decreased as the antibiotic
dosage increased. One exception to this pattern was erythromycin, which significantly (p < 0.05)
increased the number of bacteria colonies in agar supplemented with 0.1 and 1.0 mg/L erythromycin in
samples collected from Lee’s Cistern, Shaler’s Brook, and Charlotte’s Dome within the historic section of
Mammoth Cave. Biolog Ecolog™ (Ecolog) plates with 31 different substrates were used to evaluate
community substrate utilization patterns. The waters used to inoculate the Ecolog plates were
standardized by turbidity to reduce disparity between inoculum bacteria concentrations. This
standardization was confirmed with plate counts. Bacterial community samples collected deeper in the
cave tended to use fewer substrates than those collected from or near the surface. Bacterial communities
from the lower passages had a lower average well color development with the exception of Charon’s
Cascade, located on the lowest level of the cave. It is possible that bacteria from Charon’s Cascade did
not conform to the pattern because the lowest level of the cave floods with backwater from the Green
River on occasion. The results of the investigation suggest that microbial communities have different
antibiotic resistance and substrate utilization patterns associated with different locations in the cave
stream.

128
Role of Surface Water Dissolved Organic Carbon in the Survival,
Growth, and Transport of Escherichia coli in a Deep Limestone
Aquifer in South Florida
By Ronald W. Harvey1, Jen Underwood1, John Lisle2, David W. Metge1, and
George Aiken1
1
U.S. Geological Survey, National Research Program, 3215 Marine St., Suite E-127, Boulder, CO 80303
2
U.S. Geological Survey, 600 4th Street-South, St. Petersburg, FL 33701

Abstract
Much is unknown about survival and activities of bacteria within deep aquifers hydrologically
isolated from surface-water intrusion. Groundwater about 15,000-20,000 years old was collected from
317-482 meters below land surface in the subtropical (22 oC) Floridan aquifer in southeast Florida.
Dissolved organic carbon (DOC), often a major control of heterotrophic activity in shallow aquifers, had
a low concentration (1.1 milligrams per liter). Its low specific ultraviolet (UV) absorbance (2.2) and high
fluorescence index (1.8) indicated only modest aromaticity and a likely microbial (versus terrestrial)
origin. Surface properties and growth of Escherichia coli (E. coli) K12 were both affected by the presence
of the hydrophobic organic acid (HPOA) fraction of DOC in surface waters to be used in regional aquifer
storage and recovery (ASR). Collectively, the effect of surface water DOC on the growth and surface
properties of E. coli K12 is predicted to alter its fate in the Floridan aquifer.
INTRODUCTION DOC and Survival
A concern regarding deep-well injection of Unfortunately, most studies of bacterial
wastewater and planned expansion for aquifer survival in subsurface environments involve
storage and recovery (ASR) in south Florida is very limited set(s) of conditions. Transport of
the effect of highly reactive dissolved organic bacteria from surface waters through a vadose
carbon (DOC) on aquifer microbiology, zone into an underlying aquifer necessitates
particularly as it affects survival and transport of survival in several environments that have very
pathogenic and indicator bacteria. Plans for ASR different conditions. Consequently, survival over
involve a seasonal injection of about 6 billion the entire transport pathway is exceedingly
liters per day of surface water into the upper difficult to predict.
Floridan aquifer. Organic-rich (17 milligrams
Even when conditions favor rapid die-off of
per liter [mg/L] DOC) Lake Okeechobee (1,714
the bulk population of pathogens, some sub-
km2) is likely to be an important source of
populations can persist for long periods. Many
surface water for injection into the Floridan
bacterial pathogens and indicators, including
aquifer (Wedderburn and others, 2013). There
Escherichia coli (E. coli) and Pseudomonas
are many factors that affect the survival of
aeruginosa, are able to enhance their survival in
bacterial pathogens and indicators in
low-carbon environments by entering a pseudo-
groundwater, including levels of nutrients,
dormant state, termed “viable but nonculturable”
temperature, ionic strength/salinity, redox
(VBNC) (Oliver, 2010). The VBNC state, which
conditions, presence/absence of biofilms,
can be classified as a persistent phenotype, is an
environmental microbial diversity and ecology,
adaptation to survival under variable
physicochemical characteristics of the solid
environmental conditions (Rotem and others,
phase, and the character and concentration of
2010) and can be triggered by environmental
DOC. In very old, carbon-limited groundwater
factors, such as lack of labile DOC. Cook and
such as that present in the Floridan aquifer,
Bolster (2007) demonstrated that E. coli in
levels and lability of the DOC can be important
groundwater transitioned into a VBNC state
controls of growth, survival, and transport for
characterized by changes in morphology and a
non-native bacteria that are introduced during
reduced rate of respiration in response to
the ASR process.
129
starvation. Most studies involving environment of non-indigenous bacterial
environmental survival of bacterial pathogens pathogens is sometimes referred to as
use culture-based methods, which underestimate “regrowth” (Zaleski and others, 2005), as it is
survival of bacterial pathogens that transition suspected to occur if the optimal growth
into and out of the VBNC state. However, Lisle conditions are met.
(2014) has shown that for the Floridan aquifer,
We examined the effect of Lake
die-off of coliform bacteria can be considerably
Okeechobee DOC upon the surface properties,
more rapid than previously believed.
growth, and survival of E. coli K12. Although E.
The activities of indigenous subsurface coli is generally considered incapable of
microorganisms, which depend, in part, on the growing outside a mammalian host (Avery and
levels and character of the DOC, can enhance or others, 2008), it may be able to grow in tropical
inhibit the survival of bacterial pathogens and and temperate soils (Ishii and Sadowsky, 2008).
indicators. For example, biofilm formation has In this study, Lake Okeechobee DOC
been shown to favor pathogen survival under (hydrophobic organic acid [HPOA] fraction, 20
both typical environmental conditions and under mg/L), caused growth of E. coli K12 relative to
active disinfection (Murphy and others, 2006). unamended artificial lake water (ALW) devoid
Conversely, competition for limited DOC is of DOC (fig. 1). This suggests that DOC
known to inhibit pathogen survival (Crane and introduced during ASR could affect survival of
Moore, 1986). Bacteriophages are abundant and bacterial indicators and, possibly, certain
ubiquitous in nature (Kimura and others, 2008) bacterial pathogens.
and can impact host bacterial populations by
lysis of cells and by altering the host phenotype
via genetic alterations (Dröge and others, 1999).
107
It is likely that coliphages play an antagonistic
viable cells/mL

role in the survival of coliform bacteria in many 106

aquifers, although the roles of protozoa in the
survival of bacterial pathogens in the subsurface
are not well understood. However, it is known 105
that the diverse communities of nanoflagellates
in aquifers (Novarino and others, 1997) can be a
significant sink for bacteria being advected from 104 ALW
HPOA (20 mg/L)
the surface environment (Kinner and others, HPOA (40 mg/L)

1997; Kinner and others, 1998). The role of 103

predation appears to increase where there are
substantive inputs of labile DOC (Kinner and 0 2 4 6 8 20 30 40 50 60
others, 2002), because the protozoan community Days
is stimulated by the resulting bacterial growth. Figure 1. Growth of Escherichia coli K12 in the absence of
DOC and Growth DOC (ALW) and in the presence of 20 mg/L and 40 mg/L
of the more aromatic hydrophobic organic acid (HPOA)
The ability of bacterial pathogens to grow in fraction of the DOC. The study was conducted using a
the environment has been a topic of considerable laboratory microcosm with artificial lake water (ALW).
Shaded section indicates period of observed bacterial
debate. The degree of growth depends upon the growth.
environmental conditions and the specific
pathogen of interest. Some bacterial pathogens, DOC and Transport
such as Campylobacter jejuni are typical
inhabitants of some subsurface environments The effect of surface-water derived DOC,
and are expected to proliferate in-situ under both natural organic matter (NOM) and organic
conditions that are most favorable, i.e., optimal contaminants, on transport of bacteria through
nutrients, substrates, temperature, and lack of the aquifers subject to ASR or deep-well
competition and predation. Growth in the wastewater injection has important public health

130
and environmental implications. Elevated levels surface characteristics of E. coli K12 that affect
of labile DOC can affect the surface its propensity for attachment: hydrophobicity
characteristics of bacterial pathogens and, and surface charge (table 1). The presence of
consequently, their transport behavior in the surface-water derived DOC had a substantive
aquifer. The ability of humic material to enhance effect on the net surface charge of E. coli K12,
advective bacterial transport through aquifer decreasing the zeta potential about 4-fold from
material has been well documented (Foppen and -88 to -22 millivolts. The decrease in the surface
others, 2008). However, to assess the role of charge in the presence of Lake Okeechobee
DOC in bacterial transport at the field scale, it is HPOA would have the effect of making E. coli
useful to consider also the contributions of K12 more likely to attach to aquifer surfaces
contaminant organic compounds that may also characterized by net negative charge. This is due
be present in surface waters and can affect to a decreased electrostatic repulsion between
bacterial attachment behavior at “trace” levels the cell surface and the solid phase. However,
(Harvey and others, 2010). Although the the decreased surface charge would make E. coli
majority of studies examining the roles of DOC K12 less likely to attach to aquifer surfaces
on subsurface microbial transport indicate characterized by patches of net positive charge
decreased attachment and increased transport, in the form of aluminum and iron oxides. The
some organics have the opposite effect decreased hydrophobicity of E. coli K12 in the
(Marshall and others, 2000). Undoubtedly, the presence of HPOA from 26 to 18 percent should
extent to which DOC facilitates or inhibits enhance transport in the aquifer by decreasing
bacterial transport is dependent upon a complex the propensity for partitioning to the solid phase.
suite of interactions involving the nature of the Results of bacterial attachment in the presence
DOC, physicochemical conditions, aqueous of aquifer material and Lake Okeechobee DOC
chemistry, and the surface characteristics of the were inconclusive. Clearly, the role of surface
bacteria and solid phase. Consequently, use of water DOC upon transport of indicator bacteria
model organic compounds bacterial transport in the Floridan aquifer is complex and worthy of
studies involving ASR or deep-well injection further study. However, our findings suggest
can lead to misleading results compared to the that the effect of surface water DOC on the fate
use of DOC isolated directly from the source and transport of non-native bacteria that are
water. introduced inadvertently during ASR should not
be ignored.
We examined the role of the HPOA fraction
of Lake Okeechobee DOC upon two important

Table 1. Effect of Lake Okeechobee dissolved organic carbon on Escherichia coli K12 surface properties.
____________________________________________________________________________________________
Dissolved Organic Carbon (DOC) Hydrophobicity Surface charge
1 2
( MATH test) ( zeta potential)

3
Hydrophobic Organic Acid (HPOA) fraction 18.0 ± 2.3 percent -22.0 ± 2.6 millivolts

No DOC 26.1 ± 4.9 percent -88.5 ± 2.0 millivolts

1
Microbial adhesion to hydrocarbon test.
2
Measured at ionic strength of 0.01 M (moles per liter).
3
Concentration of 40 mg/L (milligrams per liter).

131
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Kwiatkowski, P., Nevulis, R., Goodwin, C.R.,
Kimura, M., Jia, Z.J., Nakayama, N., and Asakawa, Cunningham, K.J., Renken, R.A., and Reese,
S., 2008, Ecology of viruses in soils: Past, present R.S., 2013, What is aquifer storage & recovery?
and future perspectives: Soil Science & Plant http://sofia.usgs.gov/sfrsf/rooms/hydrology/ASR/
Nutrition, v. 54, p. 1-32.
Zaleski, K.J., Josephson, K.L., Gerba, C.P., and
Kinner, N.E., Harvey, R.W., Blakeslee, K., Pepper, I.L., 2005, Potential regrowth and
Novarino, G., and Meeker, L.D., 1998, Size- recolonization of salmonellae and indicators in
selective predation on groundwater bacteria by biosolids and biosolid-amended soil: Applied and
nanoflagellates in an organic-contaminated Environmental Microbiology, v. 71, p. 3701-
aquifer: Applied and Environmental 3708.
Microbiology, v. 64, p. 618-625.
Kinner, N.E., Harvey, R.W., and Kazmierkiewicz-
Tabaka, M., 1997, Effect of flagellates on free-
living bacterial abundance in an organically
contaminated aquifer: FEMS Microbiology
Reviews, v. 20, p. 249-259.

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Cave Bacteria and Crystal Formation in the Laboratory
By Petra K. Byl1*, Aaron Covey2, Jessica Oster2, Tasneem Siddiquee3, and
Thomas D. Byl1,3
1
U.S. Geological Survey, 640 Grassmere Park, Suite 100, Nashville, TN 37209 (*Volunteer for Science)
2
Earth & Environmental Sciences, Vanderbilt University, Nashville, TN 37240
3
Tennessee State University, 3500 John A Merritt Blvd., Nashville, TN 37209

Abstract
Speleothems (secondary cave mineral deposits) are used as recorders of past climate change, but little
is known about the role microbes may play in biocrystallization as well as modifying trace element
microclimate records. This study serves to explore microbe-mineral interactions through analyzing
bacteria endemic to Blue Spring Cave, Tennessee and Mammoth Cave, Kentucky. Microorganisms were
swabbed from active stalagmite growth in Blue Spring and Mammoth Cave, and later suspended in a
liquid culture media, or streaked onto the same agar media in aerobic conditions under constant
temperature. The media were an amalgam of chitin-mineral salts media (0.04 percent chitin) and
traditional actinomycete isolation media with 0.1 percent ammonia acetate. Bacterial exposure to the
ammonia and phosphate salts, both present in the media, caused the biologically mediated precipitation of
orthorhombic white crystals as evidenced by the lack of precipitates in the sterile control media. The
crystals were identified through x-ray diffraction, energy dispersive spectroscopy, and scanning electron
microscopy, and were determined to be struvite (NH4MgPO4 *6H2O) as well as calcite (CaCO3). The
calcite rhombs were about 10 µm in length and appeared to form clusters within the biofilm, while the
struvite orthorhombic crystals averaged 250 µm in length and did not appear in conglomerates. In cave
settings, struvite is naturally found in areas of high bat guano concentration, and calcite deposits over
time form the speleothems that paleoclimatologists study. The results indicate that the microorganisms
from active stalagmites have the potential, in the presence of ammonia and phosphate, to affect the
precipitation and mineral composition of speleothems.

133
Non-Target Bacterial Response to White-Nose Syndrome Treatment:
Quaternary Ammonia Compounds and Linear Alkylbenzene Sulfonate
By JeTara Brown1, Zheer Ahmed2*, and Thomas D. Byl1,2
1
Tennessee State University, 3500 John A Merritt Blvd., Nashville, TN 37209
2
U.S. Geological Survey, 640 Grassmere Park, Suite 100, Nashville, TN 37209 (*Volunteer for Science)

Abstract
White-Nose Syndrome (WNS) is decimating the North American bat population in many caves east
of the Mississippi River. Tour caves, such as those in Mammoth Cave National Park in Kentucky, are
trying to prevent the spread of this disease by requiring all visitors coming out of the caves to disinfect
their footwear. From April 2011 through early 2013, everyone who entered the cave at Mammoth Cave
National Park on a walking tour was required to walk across biosecurity mats soaked with the chemical
disinfectant quaternary ammonia compounds (QAC). The National Park Service switched from a QAC-
based product in 2013 to a laundry detergent containing the anionic surfactant linear alkylbenzene
sulfonate (LAS). LAS has been shown to inhibit growth of the fungus that causes WNS at regular
strength concentrations. Both chemicals (QAC and LAS) can have a detrimental effect on other
organisms besides WNS fungal spores. The U.S. Geological Survey (USGS) Tennessee Water Science
Center in partnership with Mammoth Cave National Park and Tennessee State University conducted a
study to determine the effect of QAC and LAS on non-target bacteria.
The heavily used biosecurity mats were soon colonized by non-target bacteria that had adapted to the
chemicals and could use the QAC or LAS as a food source. The QAC-resistant bacteria had multiple
antibiotic resistance (MAR) to clinical concentrations of erythromycin, gentamicin, ampicillin,
tetracycline, and kanamycin. The QAC-resistant bacteria were generally Gram-negative and rod shaped.
Twelve liquid microcosms were established using 250 milliliters of raw liquid from the two times full-
strength QAC-soaked mats. Half the microcosms had sterile marbles added to increase the surface area
2.6 times compared to the other microcosms. The microcosms were placed on a rotary shaker at 75 rpm
and maintained at 25 oC. The microcosms with higher surface area for biofilm development had a QAC
half-life of 11 days. The microcosms with less surface area had a QAC half-life of 37 days. After
switching to LAS, the bacteria collected from the biosecurity mats were again susceptible to antibiotics,
with some minor resistance to gentamicin and kanamycin. The predominant LAS-associated bacteria
were Gram-negative and cocci shaped.
The bacteria grew on agar plates containing only LAS, indicating they readily consumed the anionic
surfactant as a food source. The LAS-soaked mats also produced an unpleasant odor during the warm
summer months. Additional tests focused on ways to rid the mats of these nuisance bacteria. Clean
sponges were inoculated by placing them under the LAS-soaked mats for 4 hours during busy tour hours,
and then exposing these sponges to different cleaning scenarios. Waters extracted from the sponges were
then tested for culturable bacteria using 10-percent trypticase soy agar media. A 20-minute exposure to
bleach at one-tenth the recommended laundry strength at 25 oC eliminated the bacteria. Hydrogen
peroxide at 0.3 percent was also effective after a 45-minute exposure. Soaking the sponges in water with
no chemicals at 50 oC for 45 minutes also eliminated all bacteria growth. Full strength ammonia cleaners
at 25 oC did not significantly reduce the number of colonies. The results of these studies help us
understand several of the unintentional risks of using chemicals to disinfect WNS spores on footwear, and
ways to reduce some of the detrimental side effects.

134
 THURSDAY, MAY 1, 2014, FIELD TRIP GUIDE

Evaporite Karst of the Lower Pecos Valley, New Mexico

By Lewis Land
New Mexico Bureau of Geology and Mineral Resources, 801 Leroy Pl, Socorro, New Mexico 87801
and
National Cave and Karst Research Institute, 400-1 Cascades Avenue, Carlsbad, New Mexico 88220

Overview of Mirror Lake, Bottomless Lakes State Park, Chaves Co., New Mexico; view to south. Photo
courtesy of Lewis Land, National Cave and Karst Research Institute.

135
Figure 1. Map of field trip route. Figure 2. Stratigraphy of the lower Pecos
region, southeastern New Mexico.

Figure 3. Stratigraphic profile showing facies relationships of Permian strata in the lower Pecos Valley.

136
Text is based in part on road logs in Land and Love (2006). Distances are given in miles for
consistency with United States odometers.

Vehicles assemble at NCKRI headquarters, 400-1 Cascades Ave., Carlsbad, NM. Proceed to
intersection of Cascades Ave. and Park Dr. Zero odometers and turn left onto Park Dr.

0.3 miles: Potash mines locomotive on left; Lake Carlsbad, an impounded section of the Pecos
River, on right. Continue north through traffic circle on Riverside Dr.

0.6 miles: Bear left and continue on Riverside Dr.

1.2 miles: Crossing Canal St., bridge to right crosses Pecos River. Continue straight on
Riverside Drive, one of the more prosperous neighborhoods in Carlsbad. Homes on the right side
of the street have back yards facing the Pecos River.

2.4 miles: Turn left onto Landsun Drive.

2.6 miles: Turn right onto Westridge Road.

3.0 miles: Stop 1: Carlsbad Spring to right

Carlsbad spring is one of several springs that discharge into this reach of the Pecos River.
Carlsbad spring used to discharge over 7,500 liters/min (~2000 gal/min), but its flow has been
substantially reduced over the years due to pumping from the Capitan Reef aquifer, the principal
source of drinking water for the City of Carlsbad. Additional discharge from the spring is derived
from leakage from Lake Avalon and the Carlsbad Irrigation District’s South Canal, and from
irrigation return flow (Cox, 1967).
Carlsbad flume is visible at 12:00, ~200 m upstream from the spring. This large large
concrete aqueduct crosses the Pecos and transports water of the Pecos River from Lakes Brantley
and Avalon through the CID South Canal (thus, according to Ripley’s Believe It or Not, “the
river that crosses itself”). This concrete structure was built in 1903 to replace the original
wooden flume that was destroyed by floods.

Return to vehicles and continue west on Westridge Rd, passing under flume.

3.2 miles: Stop sign. Turn left onto Callaway Dr.

3.4 miles: Traffic light. Turn right onto US 285.

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4.1 miles: Roadcut to left is an exposure of the shallow marine, outer shelf facies of the Tansill
Formation on the northeast flank of Tracy Dome, dipping ~10° east toward the Pecos River.
Dolomites of the grapestone-grainstone facies belt indicate deposition in the subtidal
environment of a backreef lagoon.
Pecos River to right. Between Brantley Dam and Carlsbad Springs the Pecos River is a
losing stream, in the process recharging near-backreef units of the Capitan Reef aquifer (Cox,
1967).

8.7 miles: NM 524 to left leads to Happy Valley. Continue straight on US 285. The hill on the
left is a ridge surrounding a circular depression ~1.5 km in diameter, interpreted by Motts (1962)
as a young solution-collapse feature. Tansill dolomites on the flanks dip steeply toward the
center of this crater-like structure, which is floored by gypsum of the Yates and Tansill
Formations. Non-tectonic folds caused by subsurface dissolution and subsidence are widespread
in this portion of the Pecos Valley. A well drilled to a depth of 336 m in the center of the
depression bottomed in Seven Rivers dolomites (Kelley, 1971b).

9.9 miles: The feature superficially resembling a cinder cone on the skyline at 9:00 is Round
Mountain, the largest of the so-called Three Twins, residual knolls formed in evaporites and
redbeds of the Yates Formation and capped by more resistant Tansill dolomite. Such residual
hills and ridges are common features in the carbonate-to-evaporite transitional facies belt of the
Artesia Group.

10.0 miles: Roadcuts over the next mile expose interbedded gypsum, dolomite and redbeds of
the Yates Formation, representing the carbonate-to-evaporite and redbed facies change within the
Yates. Note small folds in the roadcuts, part of an arcuate fold belt called the Waterhole
anticlinorium (Kelley, 1971a) that wraps around the west and north sides of the Carlsbad area.

12.1 miles: Cross Rocky Arroyo, a dry tributary of the Pecos River. Ridge at 10:00 is the Seven
Rivers Hills, a southeast dipping cuesta of the Seven Rivers Formation.

12.9 miles: Turn right onto CR 30/Capitan Reef Road to Brantley Lake State Park. Brantley
Dam to left. Driving over partially cemented terrace gravels of the Pecos River.

15.2 miles: Spillway of Brantley Dam at 9:00. Well-developed Holocene coppice dunes on both
sides of road. Prominent bluffs on opposite bank of Pecos River at 1:00 are formed in Quaternary
cemented terrace gravels, rotated as much as 40° due to solution-subsidence in underlying
evaporites, redbeds and dolomites of Yates transitional facies.

138
15.4 miles: Cross Pecos River on bridge south of Brantley Dam.

17.5 miles: Road to left leads to Brantley Lake State Park and Visitors Center. Continue
straight on CR 30.

17.7 miles: Cuesta to right is formed in redbeds and gypsum capped by dolomite of the Yates
Formation.

18.7 miles: Cross railroad tracks. Yates gypsum exposed in railroad bed on both sides of road.
McMillan Escarpment at 10:00. Dolomitic facies of Yates is exposed in railroad cuts ~800 m SE.

19.2 miles: T-junction with Lake Road (CR 34). Turn left onto Lake Road.

19.5 miles: Stop sign at intersection with Netherlin Road. Continue straight.

20.1 miles: Seven Rivers dolomite capping cuesta at 3:00.

20.2 miles: McMillan Dam at 12:00. Brantley Lake at 9:30. Seven Rivers Hills on horizon
(Seven Rivers dolomite capping redbeds and gypsum).

20.3 miles: Stop 2: McMillan Dam and old Lake McMillan Lake Bed.
Park on shoulder. Breached dam straight ahead. Note man-made dike along east margin
of lake, at base of McMillan Escarpment (Figure 4). The following discussion is based largely on
Cox (1967), who investigated geohydrologic conditions beneath McMillan Dam and downstream
as far as Carlsbad Springs.
Lake McMillan is located within the evaporite facies belt of the Seven Rivers Formation.
The lake was an artificial impoundment that formerly stored water for the Carlsbad Irrigation
District. McMillan Dam was constructed in 1893, and the reservoir almost immediately began
experiencing leakage problems through sinkholes formed in the lake bed, particularly along the
eastern margin of the lake. Water flowed through karst conduits in the Seven Rivers gypsum and
returned to the Pecos River through discharge from Major Johnson Springs, ~5.6 km
downstream at the present site of Brantley Reservoir. East and southeast of the facies change, the
less soluble dolomite facies of the Seven Rivers retards any significant formation of solution
channels. In 1908-09 a dike was constructed along the southeast shore of the lake, near the base
of the McMillan Escarpment, in an attempt to isolate the areas of worst sinkhole formation. The
dike was extended in 1953-54 along most of the eastern shore to prevent water from reaching
exposed sinkholes during periods of high lake level. Occasionally breaks would occur in the
dikes causing lake water to inundate the sinkholes. At these times whirlpools were reported in
the lake, indicating that sediment cover over sinkholes in the lake bed had been disturbed. High
139
rates of leakage would occur for short periods of time until the dikes were repaired and sediment
cover on the floor of the lake restored.

Figure 4. Mass wasting processes indicated by gypsum fissures formed in the face of the McMillan
Escarpment. Note man-made dike at base of escarpment.

Storage capacity of Lake McMillan steadily decreased after the dam was constructed
because of deposition of suspended sediment, particularly during flood events, and by the early
1940’s less than half of its original storage capacity remained. The possibility of dredging was
considered but soon discarded when it was realized that removal of the accumulated sediment
would considerably increase leakage through karst fissures in the gypsum bedrock underlying the
lake. Fortunately, loss of storage capacity decreased by the mid-40’s because a stand of salt
cedar, an invasive species, became established in bottom lands upstream from Lake McMillan,
acting as a baffle for much of the suspended sediment carried by the Pecos River.
Consideration for construction of a new dam began as early as 1905. The U.S. Bureau of
Reclamation began construction of Brantley Dam in 1984, and in 1991 McMillan Dam was
breached and Lake McMillan allowed to drain into Brantley Lake. Based on recommendations
by Cox (1967), the new reservoir is located mostly within the dolomitic facies belt of the Seven
Rivers Formation.
Features to note near the old damsite include small-scale non-tectonic folds, expressed as
undulations in the Seven Rivers dolomite, almost certainly the result of subsurface dissolution of
evaporites. Larger-scale folds exposed in the walls of the Pecos River channel on the other side
of the dam probably have a similar origin.

Return to vehicles and proceed to Stop 3. Zero odometer, turn around and proceed southeast on
Lake Road.

0.8 miles: Intersection with Netherlin Road (CR236). Turn left. High clearance vehicles only
from this point on. Other vehicles park on shoulder.
140
1.4 miles: Slow down, turn left on two-track just before cattle guard. All remaining vehicles
should have high clearance from here to stop 3. Follow fence line.

1.7 miles: Turn left away from fence line. Watch for deep ruts in two-track.

2.3 miles: Two track reaches ridge crest. Lake bed of old Lake McMillan below. Northeast end
of Brantley Dam at 7:00.

2.4 miles: Small sinkhole to right. Vehicles should be careful of footing.

2.5 miles: Stop 3: Crest of McMillan Escarpment.

The McMillan Escarpment is a cuesta formed in gypsum and redbeds of the Seven Rivers
Formation, capped by more resistant Seven Rivers dolomites. The carbonate-to-evaporite and
redbeds facies change can be readily observed in a vertical sense during a partial descent down
the face of the escarpment. Also present are large gypsum fissures and slump blocks, indicating
continued mass wasting and evolution of the eastern margin of the lower Pecos Valley by
undercutting of the gypsum escarpment (Figure 5). Small gypsum caves and sinkholes occur at
the base of the cliff. These karst features began causing serious leakage shortly after construction
of the reservoir. Attempts to isolate the worst areas of sinkhole formation by construction of a
dike along the eastern shore of the lake were only partially successful.

Figure 5. Mass-wasting processes indicated by large gypsum fissures formed in face of McMillan
Escarpment.
Watch your footing on unstable slopes. After stop, return to Netherlin Road.
Zero odometers and turn right onto Netherlin Road.

0.5 miles: Junction of Netherlin and Lake Roads. Turn left onto Lake Road.

141
0.8 miles: Junction with CR 30. Turn right and return to US 285.

7.1 miles: Junction of CR 30 with US 285. CR 30 is known as the Capitan Reef Road on the east
side of the highway. The road continues across the highway toward the village of Queen in the
high Guadalupes and is known as the Queen Highway. The Queen Highway is one of the earliest
roads built by the Civilian Conservation Corps (CCC) in New Mexico. It connects US 285 with
the Queen, El Paso Gap, and Dog Canyon areas of the western Guadalupe Mountains.
Prepare to turn right onto Highway 285. Re-zero odometers as you turn onto highway.

0.0: Turn right and proceed north on US 285.

0.3 miles: mile post (MP), MP 46.

1.0 miles: Seven Rivers Hills at 10:00. Brantley Dam at 3:00.

2.7 miles: Yates dolomite at top of roadcut on left probably overlies siltstone and gypsum
covered by dolomite riprap.

3.0 miles: Brantley Lake road and boat ramp to right.

3.8 miles: Crest of Seven Rivers Hills. Brecciated redbeds and gypsum of the Seven Rivers
evaporite facies are exposed in roadcuts to left and right. The McMillan Escarpment can be seen
as a low cuesta east of the Pecos River at roughly 3:00. The north-south-trending Seven Rivers
gypsum and dolomite outcrop belt, which forms the McMillan Escarpment, swings southwest at
this point and crosses the Pecos River, due to a northeast-trending, southeast-dipping monocline.
The same outcrop belt forms the cuesta of the Seven Rivers Hills, which are capped by more
resistant dolomites of the Azotea Tongue of the Seven Rivers Formation (Kelley, 1971b). The
Seven Rivers Hills are (somewhat arbitrarily) regarded as the southern boundary of the Roswell
Artesian Basin.

3.9 miles: Descending into alluvial lowlands formed by a confluence of the Seven Rivers
tributaries of the Pecos River. For the past several million years, the Pecos has been migrating
progressively eastward due to uplift of the Sacramento Mountains to the west combined with
dissolution of gypsum bedrock to the east. Floodplain deposits of the Pecos River form a shallow
water-table aquifer in the Roswell Artesian Basin.

5.3 miles: MP 51. About 1 km to the west the New Mexico Interstate Stream Commission has
drilled several augmentation wells to pump water from the deep Artesian Aquifer and pipe it
directly into the Pecos River. These augmentation wells form part of a consensus plan between
142
the Carlsbad Irrigation District (CID) and the Pecos Valley Artesian Conservancy District
(PVACD) to help meet our interstate compact obligation to share water resources in the Pecos
with the state of Texas.

5.9 miles: Crossing South Seven Rivers Arroyo. Pecan orchard to right. Pecans are an important
cash crop in the largely agricultural economy of the Artesian Basin.

6.7 miles: Gravels capped with soil in roadcuts are Seven Rivers terrace deposits.

9.6 miles: MP 55. Junction with CR 31 to Lakewood to right. Residents of Lakewood were
evacuated due to flooding during extreme monsoonal rains last fall, 2013. Several sinkholes
formed in the aftermath of the flooding, one damaging a small structure in the Lakewood RV
park. Continue straight.

10.4 miles: Crossing North Seven Rivers Arroyo. Route continues north on broad, east-sloping
plain.

12.2 miles: Partially-cemented Quaternary gravel terrace deposits in roadcut to right.

12.6 miles: MP 58. Crossing Fourmile Draw.

14.1 miles: BP pipeline crosses under road. In 2003 several shallow fissures were discovered by
a BP aerial survey in the vicinity of the pipeline (Figure 6). The fissures are probably associated
with subsurface dissolution and subsidence in the Seven Rivers gypsum, which underlies the
alluvial valley fill in this area. Depth of some of the fissures exceeds 1 m (Figure 7).

143
Figure 6. Fissure crossing pipeline access road south of Artesia, developed in alluvium overlying Seven
Rivers evaporites.

Figure 7. Close-up of earth fissure near pipeline south of Artesia. Consultant for scale. (consultant is ~2
m long).

144
14.4 miles: For the next several miles the route crosses a relatively nondescript terrain composed
of pediment gravels, caliche soil and alluvial deposits of the ancestral Pecos River. The principal
features to notice are the dense concentration of pump jacks and other oil and gas infrastructure
on both sides of the highway. The first oil discovery in southeastern New Mexico was made in
this area in 1924. The field trip route passes through a portion of the giant Empire Abo Field,
which produces oil and gas from Permian strata of the Abo reef complex, Yates and Grayburg
Formations of the Artesia Group, the San Andres limestone, Wolfcamp carbonates, as well as
upper Pennsylvanian carbonates and lower Pennsylvanian clastic reservoirs in the Morrow and
Atoka Formations. These multiple pay zones overlie the Artesia-Vacuum Arch, an east-west
trending structural nose that extends to the east for ~120 km into Lea Co., New Mexico (Kelley,
1971a). The Arch is almost completely covered by post-Permian beds; its principal surface
manifestation is the high concentration of oil wells. Since 1960 >200 million barrels of oil have
been produced from the Empire Abo field (Christiansen, 1989).

16.1 miles: The Slipper Gentlemen’s club on the right, one of only two adult entertainment
facilities in the lower Pecos Valley.

17.2 miles: Crossing the Rio Peñasco. The Peñasco is a perennial stream in the Sacramento
Mountains to the west, but becomes a losing stream when it flows across the Pecos Slope west of
Artesia, in the process recharging the underlying San Andres Artesian Aquifer.

18.2 miles: Junction with CR 65 to left. Continue straight. Sprinkler irrigation systems become
increasingly common from this point north, as we drive farther into the Artesian Basin. Note the
repeating image of three transformers on a utility pole and a mound of earth, indicating the
presence of a nearby water well and pump and a pond for surface storage.

19.8 miles: Atoka Grocery on left. The village of Atoka grew along the ATSF railroad and is
host to the Eddy County Arena. Note pecan orchards along both sides of the road.

21.8 miles: MP 67. Historic marker, showing the route of Castaño de Sosa’s 1590-91 expedition
up the Pecos River.

22.0 miles: Halliburton service company yard to right.

22.5 miles: Entering southern Artesia. The town acquired its name in 1903 because of the
abundant resources of artesian groundwater that were discovered in the area around the turn of
the 20th century, making the region an agricultural oasis. Principal crops include alfalfa,
sorghum, chiles, and pecans. In recent years dairy farming has become increasingly important to
the agricultural economy of the lower Pecos Valley.

145
 Artesia lies near the southern end of the Roswell Artesian Basin, from which
groundwater is withdrawn from the karstic San Andres limestone aquifer to support irrigated
agriculture. The Seven Rivers Formation in its redbed-evaporite facies serves as a leaky
confining unit for the San Andres aquifer. Although water levels in the Artesian aquifer have
declined substantially since development began in the early 1900s, some wells northwest of
Artesia still display strong artesian flow.

24.1 miles: Main Street Artesia, and junction with Highway 82. Continue straight and proceed
north through town. Navajo Refinery to right. In addition to irrigated agriculture, Artesia is also a
local center for oil and gas activity. Yates Petroleum corporate headquarters is located 3 blocks
to the west. The Wellhead Brewpub, owned by one of the Yates family and one of only two
brewpubs in the lower Pecos Valley, is across the street from Yates’ offices.

24.4 miles: Crossing Eagle Draw, an east-flowing tributary of the Pecos River.

26.6 miles: Artesia adult video store to left. Bear right onto Highway 2 and continue north.

29.8 miles: MP 3. Low hills at 2:30 on east side of valley are formed in redbeds of Seven Rivers
Formation.

32.1 miles: Bridge over Cottonwood Creek. This drainage is controlled by large levees on both
sides of the channel for several km.

32.8 miles: Chavez County line. At this point the route crosses the NNE-trending subsurface KM
fault. The KM fault parallels the Pecos Buckles, a series of surface faults that extend across the
Pecos Slope to the west. Like the Buckles, the KM fault is thought to combine right-lateral
motion with normal vertical displacement, and may be of Laramide age (Kelley, 1971a). The
hydraulic gradient in the Artesian Aquifer increases abruptly just west of the KM fault,
indicating that it acts as a partial barrier to down-gradient groundwater flow. Water levels are
several tens of meters deeper in the Artesian Aquifer on the southeast side of the fault.

34.0 miles: Crossing Walnut Creek.

35.1 miles: Entering outskirts of Lake Arthur, one of several small agricultural communities of
the lower Pecos Valley between Roswell and Artesia. In 1977, a Lake Arthur resident discovered
an image of Jesus Christ on a flour tortilla she was preparing for her husband. By 1979, the
Shrine of the Holy Tortilla had been visited by over 35,000 of the faithful. Images of Christ on a
tortilla were later reported in Phoenix, AZ and Hidalgo, TX, but the Lake Arthur holy tortilla
may be the first documented sighting in recent history.

146
36.1 miles: Lake Arthur cemetery to left. Sierra Blanca, composed of igneous intrusives and
volcanics, on western horizon at 9:00. Capitan Mountains batholith at 10:00.

39.6 miles: El Gomez bar on left.

43.4 miles: Entering Hagerman, home of the Hagerman Bobcats. Unlike most communities in
the Artesian Basin, Hagerman farmers derive most of their irrigation water from the Hagerman
Canal west of town, rather than from the Artesian Aquifer, and secondarily from wells in the
shallow alluvial aquifer. The Hagerman canal originally transported water south from the Rio
Hondo east of Roswell. Because of intensive pumping from the Artesian Aquifer, all of the
tributaries of the Pecos River, including the Rio Hondo, have been dry for many decades, except
during brief flood events. For this reason, most of the “surface water” in the Hagerman canal is
actually groundwater pumped into the canal from wells. Pumping from the shallow aquifer has
resulted in a significant cone of depression in agricultural areas west of town.

45.0 miles: Historic bridge to right over the Rio Felix, another of the now dry tributaries of the
Pecos River.

45.3 miles: Red bluffs east of Pecos River at 2:30 are formed in Seven Rivers redbeds and
gypsum.

49.7 miles: Entering village of Dexter, home of the Dexter Demons. As the Pecos Slope
descends to the east toward the river, the potentiometric surface approaches ground level. Water
levels in wells near the river are only a meter or two deep, and many wells near Dexter still
display strong artesian flow during winter months when irrigation is minimal.

50.3 miles: Turn right and cross railroad tracks onto First St./Shawnee Road East (NM 190).

51.1 miles: Lake Van, an artificially flooded sinkhole, is visible between houses to the right,
south of Shawnee Road. Lake Van is one of at least nine lakes or seasonal lakes here.

51.6 miles: Dexter Fish Hatchery entrance to right. The Dexter National Fish Hatchery and
Technology Center was established in 1931 to meet the demand for warm water game fish; its
main focus was to supply local waterways with sport fish via rearing at the Center. After the
Endangered Species Act was established in 1973 the hatchery mission was transformed from a
facility that raised fish for recreational purposes to a facility that would house and protect
endangered fish species. The Center is the only federal facility in the nation dedicated to holding,
culturing and studying fishes facing extinction.

147
51.8 miles: Route descends low terrace of Pecos River. Agricultural activity quickly diminishes
east of Dexter because of deteriorating water quality east of the freshwater-saltwater interface in
the Artesian Aquifer. Groundwater near the Pecos River has a TDS content in some areas as high
as 7,000 mg/l.

52.4 miles: Sharp bend to left onto Wichita Road.

52.7 miles: Zuber Lake Farm and artesian well to right. Rock-walled mound in front of house is
an intermittently-flowing spring.

53.2 miles: Crossing Pecos River. Note banks 3 – 4 m high with natural levee sloping to the east.
The banks are lined with Catclaw and Salt Cedar (Tamerisk), an invasive species. Water in this
reach of the Pecos River is quite brackish, with TDS >2,000 ppm. Lakes along the river are a
combination of oxbows and sinkholes.

53.5 miles: Sharp left turn to north.

54.9 miles: Bear right, staying on paved road, and begin

ascending Seven Rivers escarpment. For the next five miles the
route crosses extensive exposures of Seven Rivers gypsum and
mudstone.

56.4 miles: Sacramento Mountains on western horizon; Sierra

Blanca on skyline at 8:30. Capitan Mountains batholith at 9:30.
City of Roswell across valley at 9:00. Reddish-brown ridge on
far horizon to east is part of the outcrop belt of Triassic Santa
Rosa Sandstone.

60.9 miles: Road veers left and descends into valley. Dimmitt
Lake to right, a large sinkhole lake on private land. Lea Lake, the
largest of the cenotes of Bottomless Lakes State Park, at 11:30.

61.3 miles: Stop sign. Turn left toward Bottomless Lakes State
Park.
Figure 8. Digital orthophoto image of Bottomless Lakes State Park,
showing flooded cenotes. All lakes visible in this image are formed in
gypsum and redbeds within the Seven Rivers Escarpment, a geologic
setting similar to that observed at Lake McMillan.

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61.5 miles: Cross Lea Lake overflow canal; turn right into Lea Lake parking lot.

61.6 miles: Stop 4: Lea Lake sinkhole, Bottomless Lakes State Park. Bus parks in parking
lot. Field trip participants assemble by lake shore.

Lea Lake sinkhole is the only lake in Bottomless Lakes State Park where swimming is
permitted. Because of the clarity of the water, the lake is popular with local scuba divers.
Bottomless Lakes is New Mexico’s first state park, established in 1933. The sinkhole lakes are
formed in gypsum and mudstone of the Seven Rivers Formation, and are some of the larger and
more impressive examples of the many sinkholes and other karst features that line the lower
Pecos Valley (Figure 8).
The Bottomless Lakes sinkholes may more properly be described as cenotes because of
their deep, steep-walled morphology, similar to the cenotes formed in limestone bedrock on the
Yucatan Peninsula in Mexico (Caran, 1988). The cenotes of the lower Pecos Valley are unusual
in that they occur in a semi-arid setting, where annual evaporation rates may exceed mean annual
precipitation by a factor of 7 or more. The lower Pecos region is also unique in that it is one of
the few areas in the world where sinkholes are actively forming in a region of groundwater
discharge rather than recharge (Salvati and Sasowsky, 2002).
These sinkholes, and the many others that occur in the lower Pecos Valley, are the
product of subsurface dissolution of gypsum by upward leakage of groundwater from the karstic
San Andres limestone, which comprises most of the artesian aquifer in the Roswell Artesian
Basin (Figure 9) (Martinez et al., 1998). The lakes are fed by submerged springs discharging
from the artesian aquifer, and thus represent the down gradient end of the regional hydrologic
system in the Artesian Basin. Discharge from the springs has caused subsurface dissolution of
evaporites within the Seven Rivers Formation, localized subsidence, and upward propagation of
collapse

149
Figure 9. West-east hydrostratigraphic section of the artesian aquifer system in the vicinity of Bottomless
Lakes State Park. Recharge occurs by direct infiltration from precipitation, and by runoff from
intermittent losing streams that flow eastward across the Pecos Slope west of Roswell. Groundwater
flows east and south, down gradient from the recharge area, then upward through leaky confining beds
into the alluvial aquifer, and ultimately into the Pecos River.

chimneys, which ultimately formed the cenotes (Land, 2003). Spring sapping at the base of the
Seven Rivers escarpment has also resulted in oversteepening of the eastern walls of the sinks,
causing occasional rockslides and other mass-wasting events, an indication of the fundamental
role that gypsum karst processes have played in shaping the morphology of the lower Pecos
Valley.
The gentle (~1°) eastward regional dip of the area is locally reversed along the
escarpment, where strata of the Seven Rivers Formation dip abruptly southwest by as much as
40°. This local dip reversal, best viewed in the walls of Mirror Lake, is probably the result of
subsurface dissolution of gypsum in the vicinity of the sinkholes and consequent slumping of
overlying beds (James Quinlan 1, unpublished report, 1967).
Bottomless Lakes occurs on the saline side of the fresh water/saline water transition in
the Roswell Artesian Basin (Figure 9), thus water in all the lakes is brackish, with Total
Dissolved Solids (TDS) content ranging from ~6000 to 38,000 mg/L. In spite of the high mineral
content, some of the lakes are periodically stocked with fish.

1
The late James F. Quinlan very precisely summarized the geology and hydrology of Bottomless Lakes
State Park in the text and graphics of an unpublished Christmas card he circulated among friends in 1967.
150
 The Roswell Artesian Basin is one of the most intensively farmed areas in New Mexico,
deriving virtually all of its irrigation water from groundwater stored in the artesian and alluvial
aquifers. Since the inception of irrigated agriculture in the Artesian Basin more than a century
ago, most of the discharge from the artesian aquifer has been from wells, although substantial
natural discharge still occurs through fractures and solution channels in the overlying confining
beds (Welder, 1983). Groundwater from the artesian aquifer discharges into the many springs
and sinkhole lakes that line the Pecos River, and is manifest in the development of extensive
wetlands above and below Roswell. These wetlands are visible along the river immediately west
of Bottomless Lakes, and to the north at Bitter Lake National Wildlife Refuge (Land and
Newton, 2008).

Figure 10. Rockslide in

Seven Rivers Escarpment,
eastern shore of Lea Lake
cenote.

In the early history

of settlement in this area,
most of the cenotes at
Bottomless Lakes
overflowed into wetlands
along the eastern shore of
the Pecos River, but the
progressive decline in
hydraulic head in the
artesian aquifer (up to 70 m in some areas) caused lake levels to fall, so that now only Lea Lake
overflows. In 1975, a catastrophic rockslide occurred on the steep eastern wall of Lea Lake
(Figure 10), and the resulting lake surge caused significant damage to a pavilion on the opposite
shore. No measurements of lake discharge are available prior to 1976 (probably because there
was no discharge overflow before that date). However, the rockslide appears to have been
associated with an increase in spring discharge and the opening of new spring outlets in the lake
bed, as indicated by a significant post-rockslide increase in flow from the lake and the flooding
of adjacent grazing lands with several million gallons per day of saline and alkaline water. A
culvert was installed to convey the increased flow into wetlands west of the park, but the lake
continued to flood an adjacent parking lot and camping area during the winter. In 2002, the park
completed construction of a more efficient drainage canal to capture all of the discharge,
resulting in a substantial increase in the measured flow volume from the lake. As discharge
continued to increase, a second drain was installed in 2005. On January 14, 2006, the New
Mexico Interstate Stream Commission measured a combined discharge of 576.2 liters/s (20.35
cfs) from both drains.
The increased flow from Lea Lake, amounting to roughly 18 million m3/yr (~14,600
acre-ft/yr), has caused an expansion of wetlands to the west, which are now hydraulically
connected to the Pecos River, and a net gain in streamflow downstream from the park, an
interesting phenomenon in a semi-arid region that is currently experiencing an extended drought.

151
Field trip participants return to vehicles and proceed to Stop 6. Zero odometer at visitor pay
station, exit parking lot and turn left onto loop road.

0.4 miles: Begin ascent of Seven Rivers Escarpment. Dimmit Lake to right.

1.0 miles: Turn left into scenic overlook parking lot.

Stop 5: Lea Lake scenic overlook.

We are standing on the Seven Rivers Escarpment, in a geologic setting very similar to
that at the McMillan Escarpment farther south. As at Stop 2, large fissures are formed in the
Seven Rivers gypsum along the upper edge of the escarpment, and large rockslides can be
observed where they have fallen into the lake, showing the continued morphologic evolution of
the lake margin by mass wasting. The principal difference between this location and Lake
McMillan is the presence of active discharge of artesian groundwater at the base of the Seven
Rivers Escarpment, enhancing mass wasting processes. At least half a dozen springs discharge
from the lakebed in ~8 m water depth at the base of the escarpment, suggesting that spring
sapping may have played a role in initiating the 1975 rockslide.

Field trip participants return to vehicles and proceed to Stop 6. Exit parking lot and turn left
onto loop road.

3.7 miles: Lazy Lagoon at base of escarpment to left. During winter months, when water levels
are high due to low levels of irrigation from the Artesian Aquifer, Lazy Lagoon appears to be a
single body of water. It is in fact three sinkholes formed in an abandoned channel of the Pecos
River, the southernmost of which is over 25 m deep. The Lazy Lagoon sinkholes contain the
most saline water in the park, with TDS exceeding 37,000 mg/l, greater than the salinity of
seawater.

3.9 miles: Bear left, and begin descent of Seven Rivers Escarpment. Over the next mile the
route passes large gypsum slump blocks detached from the escarpment.

5.0 miles: Lazy Lagoon sinkholes to right.

5.9 miles: Dry sinkholes in escarpment to left.

6.2 miles: Turn left into Bottomless Lakes visitors center parking lot.
152
Stop 6: Cottonwood Lake cenote, Mirror Lake, and Bottomless Lakes visitors center.
Cottonwood Lake is a small cenote containing water that in the past has been fresh
enough to support fish, although too brackish for them to reproduce. Note rockslide on the far
wall of the sink. The visitors center contains excellent exhibits, including air photo images and a
3-D model of all the sinkholes in the park.

Figure 11. Mirror Lake, view to south.

A trail along the escarpment continues south for ~300 m, crossing a dry sinkhole and
terminating at Mirror Lake, a compound lake consisting of two cenotes that have grown together
(Figure 11, and cover photo). A climb to the top of the escarpment reveals large gypsum fissures
and small tectonic caves formed in the upper margin of the sinkholes. Excellent examples of
gypsum karren are exposed in bluffs along the north margin of Mirror lake. Note the pronounced
west dip exposed in the walls of the Mirror Lake cenote. Regional dip is about 1º to the east. This
local dip reversal is probably the result of subsurface dissolution of gypsum along the
escarpment.
Field trip participants return to vehicles. Zero odometer, exit visitors center parking lot, and
turn left onto loop road.

2.0 miles: Pass Lea Lake entrance and turn right onto Wichita Road, following same route back
to Carlsbad.

153
10.8 miles: Turn right onto Shawnee Road.

13.0 miles: In Dexter, turn left onto Highway 2 and continue south toward Hagerman.

36.4 miles: Turn left onto Highway 285, drive straight through Artesia.

58.9 miles: Begin crossing Seven Rivers Hills; Brantley Reservoir to left.

72.0 miles: Entering city of Carlsbad; Tracy Dome/C-Hill to right. US-285 becomes W. Pierce
St.

74.6 miles: Bear right onto South Canal St.

75.1 miles: Turn left onto Church St.

75.6 miles: Turn right onto Park Dr. and return to NCKRI headquarters.

Figure 12. Pump jack in sinkhole, Dagger Draw oil field, Eddy Co., New Mexico.
154
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Christiansen P.W., 1989, The story of oil in New Mexico: New Mexico Bureau of Mines and Mineral Resources
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