CI/ASCE 38-02: Standard Guideline For The Collection and Depiction of Existing Subsurface Utility Data
CI/ASCE 38-02: Standard Guideline For The Collection and Depiction of Existing Subsurface Utility Data
CI/ASCE 38-02: Standard Guideline For The Collection and Depiction of Existing Subsurface Utility Data
for the
Collection and Depiction
of
Existing Subsurface Utility Data
CI/ASCE 38-02
Contents
1.0 INTRODUCTION
2.0 SCOPE
3.0 DEFINITIONS
4.0 ENGINEER AND OWNER COLLECTION AND DEPICTION TASKS
4.1 Engineer
4.2 Project Owner
5.0 UTILITY QUALITY LEVEL ATTRIBUTES
5.1 Quality Level D
5.2 Quality Level C
5.3 Quality Level B
5.4 Quality Level A
6.0 DELIVERABLES FORMATTING
6.1 General
6.2 Basic Deliverable
6.3 Quality Level Attributes
6.4 Utility Depiction Legend
6.5 Examples of Mapping Deliverables
7.0 RELATIVE COSTS AND BENEFITS OF QUALITY LEVELS
1.0 INTRODUCTION
The nation’s infrastructure continues to grow as a result of population growth and other factors. New
technologies are proliferating, such as fiberoptics, which are replacing copper communication cables. In
addition, the deterioration and replacement of existing structures have expanded activities dealing with the
utility infrastructure. The effort to clean up the environment has necessitated considerable excavation in
areas of high-density infrastructure development. Available right-of-way is becoming limited, especially in
urban and suburban areas. The “footprint” of new construction, repair, or remediation often conflicts with
existing infrastructure. When this existing infrastructure is hidden from view (e.g., buried), it is often
discovered in the construction phase of a project. During this phase, the costs of conflict resolution and the
potential for catastrophic damages are highest.
Existing subsurface utilities and their related structures constitute a significant portion of this infrastructure.
They create risks on projects. Inaccurate, incomplete, and/or out-of-date information on the existence and
location of existing subsurface utilities reduces the engineers’, owners’, and contractors’ abilities to make
informed decisions and to support risk management decisions regarding the project’s impact on existing
utilities.
A convergence of new equipment and data-processing technologies now allows for the cost-effective
collection, depiction, and management of existing utility information. These technologies encompass
surface geophysics, surveying techniques, computer-aided design and drafting and geographic information
systems, and minimally intrusive excavation techniques. This convergence of technologies and systematic
use of the data derived from these technologies is known as subsurface utility engineering (SUE).
Organizations such as the U.S. Department of Transportation, the National Transportation Safety Board, the
U.S. Department of Energy, Associated General Contractors of America, Inc., universities, and utility
companies are endorsing the use of SUE.
The engineer’s job in collecting and depicting utility information is complicated by the relatively limited
control over utility owners’ record data. The utility owner is typically under no obligation to the engineer to
provide information. The engineer is therefore often unable to obtain available and pertinent utility
information.
Utility owners are obligated under statute in most states to mark the location of their known active facilities
on the ground surface just before construction. This is often too late for design purposes or for contractor
bidding purposes. A very few states have laws that encourage utility owners to mark facilities at the time of
design; however, utility owners are under no legal requirement to do so. Some utility owners may desire to
mark their facilities for the engineer.
For reliable information during design and construction, the engineer, owner, and constructor should be
certain that utilities, active, abandoned, or unknown, are identified; that the utilities are marked correctly;
that the numbers of actual utility pipes or cables under the ground are known or represented by multiple
marks; that the width of facilities is correct; and that the depths of utilities are known. Reliable information
has historically not always been provided by utility owners.
Engineers may have received, made, or obtained a mixture of evidence of the existence, character, and
location of utilities. Evidence may vary widely as to its credibility. Application of this guideline and the
establishment of a credible nomenclature system will permit affixing attributes to utility information that
denote the quality of that utility information. Problems with existing utilities are routinely handled through
change orders, extra work orders, insurance payouts, and contingency pricing. When problems create
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significant costs, the finger of blame is pointed everywhere, including at the engineer who has affixed his or
her stamp to the plans, regardless of disclaimers. All involved in the design and construction process will
benefit from better information for the management of risk.
2.0 SCOPE
The scope of this document is a consensus standard for defining the quality of utility location and the
attribute information that is placed on plans. The standard guideline addresses issues such as (a) how utility
information can be obtained, (b) what technologies are available to obtain that information, and (c) how that
information can be conveyed to the information users.
The intent of this standard guideline is to present a system of classifying the quality of data associated with
existing subsurface utilities. Such a classification will allow the project owner, engineer, constructor, and
utility owner to develop strategies to reduce risk by improving the reliability of information on existing
subsurface utilities in a defined manner. This document, as a reference or as part of a specification, will
assist engineers, project and utility owners, and constructors in understanding the classification of the
quality of utility data .
3.0 DEFINITIONS
Locating The process of exposing and recording the precise vertical and
horizontal location of a utility.
Minimally intrusive
excavation method A method of excavation that minimizes the potential for damage to the
structure being uncovered. Factors such as utility material and
condition may influence specific techniques. Typical techniques for
utility exposures include air-entrainment/vacuum-extraction systems,
water-jet/vacuum-extraction systems, and careful hand tool usage.
One-call notification center An entity that administers a system through which a person can notify
utility owners and operators of proposed excavations. Typically, the
one-call center notifies member utility owners that they may send
records to the designer or designate and mark on the ground surface
the existing indications of some or all of the utilities that may be
present.
Subsurface utility engineer A person who by education and experience is qualified to practice
subsurface utility engineering.
Surface geophysical method Any of a number of methods designed to utilize and interpret ambient
or applied energy fields for the purpose of identifying properties of,
and structure within, the earth. Such methods typically include
variants of electromagnetic, magnetic, elastic wave, gravitational, and
chemical energies.
Survey datum The points of reference used by the project owner and engineer to
define a specific geographic location in three-dimensional space.
Test hole The excavation made to determine, measure, and record the presence
of a utility structure.
Utility accommodation policy A policy for accommodating utility facilities on the project. This
policy includes, but is not limited to, establishing the horizontal and
vertical location requirements and clearances for the various types of
utilities; referencing applicable provisions of government or industry
codes required by law or regulation; providing standards,
specifications, detailed procedures, criteria, and methods of
installation; providing requirements for the preservation and
restoration of project facilities; setting forth limitations on the utility's
activities within the project area; and establishing measures necessary
to protect traffic, workers, and the general public during and after the
installation of utility facilities.
Utility quality level A Precise horizontal and vertical location of utilities obtained by the
actual exposure (or verification of previously exposed and surveyed
utilities) and subsequent measurement of subsurface utilities, usually
at a specific point. Minimally intrusive excavation equipment is
typically used to minimize the potential for utility damage. A precise
horizontal and vertical location, as well as other utility attributes, is
shown on plan documents. Accuracy is typically set to 15-mm vertical
and to applicable horizontal survey and mapping accuracy as defined
or expected by the project owner.
Utility quality level B Information obtained through the application of appropriate surface
geophysical methods to determine the existence and approximate
horizontal position of subsurface utilities. Quality level B data should
be reproducible by surface geophysics at any point of their depiction.
This information is surveyed to applicable tolerances defined by the
project and reduced onto plan documents.
Utility quality level C Information obtained by surveying and plotting visible above-ground
utility features and by using professional judgment in correlating this
information to quality level D information.
Utility quality level D Information derived from existing records or oral recollections.
Utility relocation policy A policy (typically of the project owner or utility owner) for the
relocation of utility facilities required by the project. This policy
includes, but is not limited to, establishing provisions for
compensating utility owners; for removing and reinstalling utility
facilities; for acquiring or permitting necessary rights-of-way at the
new location; for moving, rearranging, or changing the type of existing
facilities; and for taking necessary protective measures.
Utility search The search for a specific or unknown utility or utilities using a level of
effort in accordance with the specified quality level, within a defined
area.
Utility trace The process of using surface geophysical methods to image and track
a particular utility.
The list of tasks or work elements below is a guideline to the development of the scope of work and contract
between the owner and engineer.
4.1 Engineer
The engineer should:
4.1.1 Advise the project owner regarding potential effects that the project may have on
existing subsurface utilities.
4.1.2 Inform the project owner regarding utility quality levels and reliability of data for
each quality level. Such information may include a discussion of costs and benefits
associated with obtaining quality levels.
4.1.3 Recommend a scope for utility investigations dependent on project needs. This may
include a list of the types of utilities for detection and depiction and the desired utility
data quality level. It may include certain systems to be investigated and depicted at a
lower quality level. It may include geographic sections of the project to have utilities
investigated and depicted at various quality levels.
4.1.5 Discuss the sequence of acquiring appropriate quality level data throughout the
planning and design process. This is dependent on project design elements, design
timetables, the type of project, the criticality of utility service, and so forth.
4.1.6 Prepare a utility composite drawing or file with appropriate supporting documents, in
accordance with owner specification, that clearly identifies utilities at their desired
quality levels at the appropriate time within project development. The deliverable
may contain utilities depicted at quality levels A, B, C, and/or D.
4.1.8 Review plans as design develops to analyze the effects of design changes to current
utility information.
4.1.9 Recommend areas or particular utility systems for a “quality level” upgrade after
review. Such an upgrade may be to quality level C, B, or A.
4.1.10 Follow applicable one-call statutes or other applicable laws. Most of these
regulations limit engineers to a notification requirement. Other action is typically the
responsibility of the utility owner.
4.1.11 Place a note on the plans explaining the different utility “quality levels.”
4.1.12 Affix an engineer’s stamp on the plans that depict existing subsurface utility data at
the indicated quality levels.
4.2.1 Specify the scope of work and the formatting of deliverables for the engineer. The
engineer should review and discuss the scope of work and the specified deliverable
formats with the owner.
4.2.2 Render assistance when necessary in persuading utility owners to allow engineers
access to pertinent records and facilities. Such persuasion may include landowner
involvement and a willingness to accommodate existing utilities with minimal
relocations. Discussions and decisions on these topics should be communicated to
the engineer. The engineer may render assistance to the owner in these tasks.
4.2.3 Review the definitions of quality levels with the designer, constructor, and other
users. The project owner may wish to have the engineer prepare a written summary
to accompany the plans or may attend pre-bid or post-bid meetings. The engineer
should attend pre-bid and pre-construction meetings, should also be involved in the
pre-selection of contractors, and should be retained to perform plan review
4.2.4 Notify the engineer within a reasonable time frame of any suspected deficiencies in
the utility depictions at the specified quality level discovered during construction.
4.2.5 Furnish utility information to the utility owners for their consideration during utility
marking for construction (one-call statutes).
5.1.1 Conduct utility records research to assist in identifying utility owners that may have
facilities on or be affected by the project. Sources of information may include, but are
not limited to (project- and scope-dependent):
Utility section of the state Department of Transportation or other public
agency
One-call notification center
Public Service Commission or similar organization
County Clerk’s office
Landowner
Internet or computer database search
Visual site inspection
Utility owners
5.1.2 Collect applicable utility owner records. Applicable records may include:
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Previous construction plans in area
Conduit maps
Direct-buried cable records
Distribution maps
Transmission maps
Service record cards
“As-builts” and record drawings
Field notes
County, city, utility owner or other geographic information system databases
Circuit diagrams
Oral histories
5.1.4 Develop utility composite drawing or equivalent. The engineer should also make
professional judgments regarding the validity and location of topographic features on
records versus current topographic features (when available) and conflicting
references of utilities. And the engineer should indicate quality levels; utility type
and/or ownership; date of depiction; accuracy of depicted appurtenances (quality
level C vs. quality level D); end points of any utility data; active, abandoned, or out-
of-service status; size; condition; number of jointly buried cables; and encasement.
5.2.1 Perform tasks as described for quality level D. Quality level C and D tasks do not
necessarily need to be performed in any prescriptive order.
5.2.2 Identify surface features on the topographic plan and ground surface that are surface
appurtenances of existing subsurface utilities.
5.2.3 Survey such features if the features have not already surveyed by a registered
professional. If previously surveyed, check survey accuracy and completeness for
applicability with the existing project.
5.2.4 Correlate applicable utility records to these surveyed features, taking into account the
geometries and indications on the records of these surface features.
5.2.5 Determine when records and features do not agree and resolve discrepancies. This
may be accomplished by depiction of a utility line at quality level D, effectively
bypassing or disregarding (but still depicting) a surveyed structure of unknown
origin. Additional resolution may result from consultation with utility owners.
5.3.2 Select an appropriate suite of surface geophysical methods (see the Appendix for
discussions of methods, relative merits, and relative costs) to search for utilities
within the project limits or to perform a utility trace for a particular utility system.
5.3.3 Apply appropriate surface geophysics to search for utilities within the project limits,
or trace a particular utility system if the scope of investigation is limited.
5.3.4 Interpret the surface geophysics. Depending on the methods, this may be performed
in the field or in the office.
5.3.5 Mark the indications of utilities on the ground surface for subsequent survey. Local
utility owners, agencies, and/or one-call statutes may dictate, or suggest, the
markings’ colors, sizes, and/or other labeling. Care should be taken to differentiate
markings placed on the ground for design purposes from those placed on the ground
for damage prevention purposes. (Note: If a particular surface geophysical method
allows for field data collection or storage for future computer downloading and
evaluation, if a utility search technique that allows for comprehensive area coverage
is used, and if a survey grid or line is laid out that allows for future correlations of
surface geophysical data to points depicted on a map, then ground markings may be
unnecessary.)
5.3.6 Survey all markings that indicate the presence of a subsurface utility. This survey
should be to the accuracies and precision dictated by the project’s survey control.
5.3.7 Depict all designated utilities. These utility depictions may follow the general
guideline as presented in Section 6.0. Depiction is usually accomplished via
computer-aided design and drafting or manual plotting methods onto plan sheets, into
geographic information systems databases, or onto other appropriate documents.
Quality level B data should be reproducible by surface geophysics at any point of
their depiction.
5.3.8 Correlate the designated utilities’ depictions with utility records and/or surveyed
appurtenances to identify utilities that may exist but were not able to be designated.
5.3.9 Resolve differences between designated utilities and utility records and surveyed
appurtenances. This may take the form of additional surface geophysical searches or
depiction of designated or nondesignated utilities at a lower quality level. It may take
the form of an upgrade at appropriate points to quality level A information.
Situations require judgment that a designated utility and a utility of record are
actually identical, even if not interpreted as geographically coincident.
5.3.10 Recommend to the project owner additional measures to resolve differences if they
still exist. Such recommendations may include additional or different surface
geophysical methods, exploratory excavation, or an upgrade to quality level A data.
5.4.1 Perform tasks as described for quality level B at the appropriate project location.
Quality level B, C, and D tasks do not necessarily need to be performed in any
prescriptive order.
5.4.2 Select an appropriate method of gathering data that will achieve the accuracies and
precision required by the project. These accuracies are currently typically set to 15-
mm vertical and to applicable horizontal survey and mapping accuracy as defined by
the project owner. Exposure and survey of the utility at each specific location where
quality level A data are obtained are currently necessary.
5.4.3 Excavate test holes exposing the utility to be measured in such a manner that protects
the integrity of the utility to be measured. Exposure is typically performed via
minimally intrusive excavation. In some cases, data gathering during utility
construction may eliminate the need for excavation of the utility, as it is already
exposed.
5.4.4 Comply with applicable utility damage prevention laws, permits, and specifications,
and coordinate with utility and other inspectors, as required.
5.4.5 Determine (a) the horizontal and vertical location of the top and/or bottom of the
utility referenced to the project survey datum; (b) the elevation of the existing grade
over the utility at a test hole referenced to the project survey datum; (c) the outside
diameter of the utility and configuration of non-encased, multiconduit systems; (d)
the utility structure material composition, when reasonably ascertainable; (e) the
benchmarks and/or project survey datum used to determine elevations; ( f) the paving
thickness and type, where applicable; (g) the general soil type and site conditions; and
(h) such other pertinent information as is reasonably ascertainable from each test hole
site.
5.4.6 Resolve differences between depicted quality level A data and other quality levels.
This may take the form of additional surface geophysical searches or a depiction of
adjacent or nearby data points at a lower quality level. It may require that utilities
already depicted at quality level B, C, or D should be re-depicted to coincide with the
more accurate quality level A data. It may take the form of additional upgrades at
appropriate points to quality level A information.
6.1 General
It is not the intent of this section to prescribe the format of deliverables. Many owners have
individual computer-aided design and drafting (CADD) requirements and other
specifications that must be adhered to by the engineer. Rather, it is the intent of this section
to communicate some broad guidelines and illustrate specific examples that have been
effective on past projects.
Attributes such as size; material type; age; condition; ownership; in-service, out-of-service,
active, or abandoned status; and number of conduits and direct buried cables are examples of
attributes that may have been depicted traditionally. The basic difference between traditional
depictions of utilities and utilities depicted as a result of this standard guideline is that a
6.3.3 Labeling
This is also one of the main methods to date of differentiating quality levels D, C, B,
and A. Labeling can differentiate quality levels; utility type and/or ownership; date
of depiction; accuracy of surveyed appurtenances (quality level C vs. quality level
D); end points of any utility data; active, abandoned, or out-of-service status; size;
condition; number of jointly buried cables; and encasement.
6.3.5 Color
Color is frequently used to indicate utility type. It must usually be used in
conjunction with other methods because of a loss of distinguishing characteristic data
with blue-lining or noncolor copying.
In most cases, a separate utility legend and/or section within the project notes is desirable to
clearly indicate the methods of quality level differentiation and other utility attributes. See
Figure 6-1.
Most mapping deliverables consist of a combination of line code and style (Section 6.3.2),
labeling (Section 6.3.7), symbol embedding (Section 6.3.4), and color (Section 6.3.5).
Figures 6-2 through 6-4 show actual work products already in use. These examples are in
no way intended to be exclusive.
Figure 6-2. An example of line code, labeling, symbol embedding, and notes.
A paper by Stevens (1993) states that the total savings on a typical project using
quality level B and A data may range from 10% to 15% (compared with costs from a
project using quality level C and D data). The approximate cost savings as a
percentage of project costs are as follows:
Administrative (1/10 of 20%) 2.00%
Engineering (1/20 of 10%) 0.50%
Utility relocation (1/2 of 10%) 5.00%
Construction (1/20 of 45%) 2.25%
Cost Overruns (1/3 of 15%) 5.00%
7.2 Costs
Cost data vary greatly as a factor of climate, soil, project specifics, geography, and so forth.
Providers and project owners have used the following rules of thumb for transportation
projects:
(a) The costs of obtaining quality level B throughout a project and quality level A in
sufficient locations to identify important utility conflicts are about 1% of a typical
highway design and construction budget.
(b) The costs of obtaining quality level B throughout a project and quality level A in
sufficient locations to identify important utility conflicts are about 10% of a typical
highway design budget.
(c) The costs of obtaining quality level B throughout a project and quality level A in
sufficient locations to identify important utility conflicts are greater on urban projects
than on rural projects.
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