NWRB Iloilo GMP

GROUNDWATER MANAGEMENT PLAN December 2013
Development of Groundwater Management Plan for Highly Urbanized Water Constraint Cities
(Pilot Area: Iloilo City and Surrounding Areas of Oton, Pavia and Leganes)
TABLE OF CONTENTS
Executive Summary ..........................................................................................................................ES-1

1. Introduction...................................................................................................................................... 1
1.1 Background ............................................................................................................................. 1
1.2 Purpose ................................................................................................................................... 1
1.3 Limitations ............................................................................................................................... 3
1.4 The Report .............................................................................................................................. 3
2. The Study Area ............................................................................................................................... 4
2.1 Physical Characteristics .......................................................................................................... 4
2.1.1 Location and Accessibility ............................................................................................... 4
2.1.2 Topography and Drainage .............................................................................................. 4
2.1.3 Land Area and Political Subdivisions .............................................................................. 4
2.1.4 Existing Land Use ........................................................................................................... 5
2.1.5 Meteorology..................................................................................................................... 7
2.1.5.1 Rainfall ........................................................................................................................ 7
2.1.5.2 Temperature ................................................................................................................ 7
2.1.5.3 Relative Humidity ........................................................................................................ 8
2.1.6 Geology ........................................................................................................................... 8
2.1.6.1 Regional Geology ........................................................................................................ 8
2.1.6.2 Local Geology ............................................................................................................. 8
2.1.7 Hydrogeology ................................................................................................................10
2.1.7.1 Hydrogeological Units and Characteristics ...............................................................10
2.1.7.2 Groundwater Level ....................................................................................................10
2.1.7.3 Groundwater Quality .................................................................................................12
2.1.8 Natural Hazards ............................................................................................................12
2.2 Socio-Economic Environment ...............................................................................................14
2.3 Legal Framework ..................................................................................................................15
3. Groundwater Utilization and Management Issues ........................................................................16
3.1 Groundwater Withdrawal .......................................................................................................16
3.2 Challenges in Groundwater Management ............................................................................16
3.3 Impact of Climate Change on the Hydrogeologic Condition of the Iloilo Basin ....................17
4. Groundwater Flow Model ..............................................................................................................19
4.1 Types and Use of Groundwater Models ...............................................................................19
4.2 Model Design ........................................................................................................................19
4.2.1 Concept Development ...................................................................................................20
4.2.2 Selection of Computer Code .........................................................................................20
4.2.3 Definition of Model Geometry........................................................................................20
4.2.4 Input of Model Parameters ............................................................................................21
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4.2.5 Definition of Boundary Conditions .................................................................................21

4.2.6 Definition of Initial Distribution of Hydraulic Head .........................................................22
4.2.7 Definition of the Stresses Acting Upon the System ......................................................22
4.2.8 Calibration and Sensitivity Analysis ..............................................................................22
4.2.9 Verification of Model Validity .........................................................................................22
5. The Groundwater Flow Modeling for Iloilo Basin ..........................................................................24
5.1 Model Design ........................................................................................................................24
5.1.1 Concept Development ...................................................................................................24
5.1.2 Computer Code .............................................................................................................24
5.1.3 Model Geometry ............................................................................................................24
5.1.4 Model Parameters .........................................................................................................24
5.1.5 Boundary Conditions .....................................................................................................27
5.1.6 Initial Distribution of Hydraulic Heads ...........................................................................27
5.1.7 Stress Applied to Water System ...................................................................................27
5.2 Modeling Results ...................................................................................................................27
5.3 Implication of Modeling Results on the Hydrogeologic Condition at the Lower Basin ..........44
6. Groundwater Management Plan ...................................................................................................45
6.1 Groundwater Basin Management Strategy ...........................................................................45
6.2 General Principles in the Wise Use of Groundwater.............................................................45
6.3 Specific Action Plans .............................................................................................................46
6.4 Rainwater Harvesting ............................................................................................................46
6.5 Conjunctive Use of Surface and Ground Water ....................................................................51
6.6 Increase Storage of Shallow Aquifers ...................................................................................51
6.7 Monitoring System ................................................................................................................51
6.8 Modification of Groundwater Model ......................................................................................52
6.9 Climate Change Mitigation ....................................................................................................52
6.10 Enabling Environment ...........................................................................................................53
6.11 Institutional Arrangement ......................................................................................................53
References ............................................................................................................................................56
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LIST OF TABLES
Table 2.1: Land Area ............................................................................................................................... 5

Table 2.2: Iloilo Climatological Normals (1971 to 2000) ......................................................................... 7
Table 2.3: Climatological Extremes ........................................................................................................ 7
Table 2.4: Static Water Level MIWD Wells ........................................................................................... 10
Table 2.5: Income Class and Population .............................................................................................. 14
Table 5.1: Simulated Hydraulic Head Around MIWD Well Field with Additional Wells......................... 27
Table 6.1: Summary Matrix Control, Groundwater Management Action Plan, Iloilo City and
Surrounding Areas .............................................................................................................. 47
Table 6.2: Proposed Groundwater Monitoring Wells ............................................................................ 55
LIST OF FIGURES
Figure 1.1: The Study Area .................................................................................................................... 2

Figure 2.1: Existing Land Use ................................................................................................................ 6
Figure 2.2: General Geology of the Study Area and Vicinity ................................................................. 9
Figure 2.3: Piezometric Map of Deep Aquifer ....................................................................................... 11
Figure 2.4: Landslide and Flood Hazard Map of the Study Area .......................................................... 13
Figure 2.5: Seismicity Map of Panay (Magnitude ≥5, 1903 – 31 July 2013) ........................................ 14
Figure 3.1: Production of MIWD Wells .................................................................................................. 16
Figure 5.1: Geologic Cross Sections .................................................................................................... 25
Figure 5.2: Model Grid Design .............................................................................................................. 26
Figure 5.3: Specific Capacity vs Transmissivity Graph ......................................................................... 28
Figure 5.4: Iso-Transmissivity Map ....................................................................................................... 29
Figure 5.5: Generalized Piezometric Surface Map ............................................................................... 30
Figure 5.6: Steady State Head .............................................................................................................. 31
Figure 5.7A: Simulated Head Year 1, Q=20lps ..................................................................................... 32
Figure 5.7B: Simulated Head Year 10, Q=20lps ................................................................................... 33
Figure 5.7C: Simulated Head Year 20, Q=20lps .................................................................................. 34
Figure 5.7D: Simulated Head Year 1, Q=25lps .................................................................................... 35
Figure 5.7E: Simulated Head Year 10, Q=25lps ................................................................................... 36
Figure 5.7F: Simulated Head Year 20, Q=25lps ................................................................................... 37
Figure 5.8A: Simulated Head with Additional Wells Year 1, Q=20lps .................................................. 38
Figure 5.8B: Simulated Head with Additional Wells Year 10, Q=20lps ................................................ 39
Figure 5.8C: Simulated Head with Additional Wells Year 20, Q=20lps ................................................ 40
Figure 5.8D: Simulated Head with Additional Wells Year 1, Q=25lps .................................................. 41
Figure 5.8E: Simulated Head with Additional Wells Year 10, Q=25lps ................................................ 42
Figure 5.8F: Simulated Head with Additional Wells Year 20, Q=25lps ................................................. 43
Figure 6.1: Proposed Groundwater Monitoring Well Network .............................................................. 54
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ANNEXES
Annex 1: Summary of Water Quality Analysis
Annex 2: Well Data Summary
Annex 3: Technical Specifications for the Construction of Groundwater Monitoring Well
Annex 4: Preliminary Design of Monitoring Wells
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Executive Summary
1. Introduction
Iloilo City and it’s environs have been identified as one of the highly urbanized water
constraint area by the National Water Resources Board (NWRB) (Water Resources
Management Master Plan, 1998, JICA). The NWRB earmarks the preparation of a
Groundwater Management Plan for Iloilo City and its surrounding areas, as a strategy in
groundwater utilization, allocation, protection and conservation.
The study area covers the catchments or watersheds of the Jaro River System and the Iloilo-
Batiano River System where urbanization is concentrated. Approximately, the study area
has a total land coverage of 602 square kilometers (km2).
At present, groundwater in the study area is mainly utilized for domestic purposes. The
Metro Iloilo Water District (MIWD) is the principal groundwater user in the locality. Also,
considerable number of households has own groundwater point sources, majority utilizing
shallow aquifers. Other major users are those in the business of water delivery and food
industries such as bottling and ice plant.
The Plan is the first of a kind in the area and a starting point in the development of long-term
strategies to manage the finite groundwater resources.
2. The Study Area
Iloilo City is the provincial capital of Iloilo Province, which occupies the southern and
northeastern portions of the Panay Island in Region VI (Western Visayas). It is situated on
the southern part of the Province. The City is highly urbanized and serves as the regional center
Region IV as well as the center of Iloilo-Guimaras Metropolitan Area.
The study area has generally flat terrain on the southeast and mountainous on the
northwest, where the two main river systems originate. About 50% of the study area has flat
to nearly flat ground. Ground elevation at the northwestern part reaches 1200m above
mean seal level (mamsl).
The Jaro River and the Iloilo-Batiano River are the two main natural waterways that drain
into the Iloilo Strait. Jaro River has two major tributaries, Tigum and Aganan Rivers. The
downstream portion of Jaro River is nearly flat resulting to its floodwaters flowing into the
Iloilo-Batiano River when the river bank overflows.
The study area covers 13 political subdivisions, namely; Iloilo City, Pavia, Oton, Leganes,
San Miguel, Sta. Barbara, Cabatuan, Alimodian, Maasin, Janiuay, Leon, San Remigio and
Valderama. It has total land area of 602km2. It covers most areas of Iloilo City, Pavia,
Maasin and San Miguel. The study area also extends over significant area of Oton,
Alimodian, Leganes, Cabatuan and Sta. Barbara.
Iloilo City has more than 70% of its total land area classified as residential, commercial and
industrial. Pavia is identified as the Regional Agro-Industrial Center for Western Visayas with
220 identified manufacturing establishments, which include the Coca Cola Bottling Philippines.
Oton, San Miguel, Santa Barbara and Cabatuan are basically are agricultural towns. Overall,
the Jaro and Iloilo-Batiano River Systems watersheds are mainly agricultural.
Climate in the Province falls under Type I based on Modified Corona’s Classification, which
is characterized by pronounced wet and dry seasons. Average annual rainfall in Iloilo is
about 2,194mm. Rainy period is usually between the months of June and October. The
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wettest month is normally observed in August. The mean annual temperature in the area is
about 27.8°C, while relative humidity ranges from 73 to 84% and averages 81%.
Iloilo City and the rest of the study area are situated in a sedimentary basin referred to as
“Iloilo Basin” that rests on a volcanic basement. The basin is largely made up of sediments
of Late Miocene to Recent ages. Recent Alluvium is predominant in the southern part and
makes up about 50% of the study area covering the entire Iloilo City, Oton, Leganes and
Pavia and portions of Sta. Barbara and San Miguel, Cabatuan, Maasin and Alimodian.
Older sediments make up the upland area.
Groundwater in Iloilo City and surroundings is mainly derived from the Recent Alluvium and
the Late Pleistocene Cabatuan Formation. These are the main hydrogeologic units in the
study area. Based on the available data, there are two main aquifers in the alluvial plain of
Iloilo Basin. The shallow aquifer extends between 5 to 35m. The deeper aquifer occurs
from 50 to 110m. Clayey and silty materials serve as aquiclude between the two aquifers.
Yields of existing MIWD wells in the alluvium range from 4 to 14liters/second (lps). Static
groundwater level in the shallow aquifer varies from 4 to 20m below ground level (mbgl),
while in deep aquifers ranges from 16 to 54mbgl. In terms of water quality, the usual
problem is color and high total dissolved solids, particularly near the coast.
The study area, being the growth center in the Province of Iloilo, is vulnerable to various
geologic and climate-related hazards. Nearly 55% of the study area is considered highly
susceptible to flooding. Flood occurrences were largely attributed to climate, extreme
precipitation by monsoon and typhoons. Likewise, coastal areas are prone to storm surge.
The upland area is considered susceptible to mass movements or landslides. About 32% of
the study area has moderate to high susceptibility to precipitation-triggered landslide. Since
Iloilo is located in the Philippine Mobile Belt, the study area is likewise prone to earthquakes
and related hazards (ground shaking, liquefaction, tsunami and landslide).
The city and municipalities in the study area are classified as1st to 4th class with agriculture
as the main source of income. Major land-based produces are rice, corn, banana, coconut,
mango and sugarcane. Other agricultural outputs are fish and fisheries products and
livestocks.
Being the most urbanized in the study area, Iloilo City has the highest population. It
registered a total population of nearly 500,000 in year 2010, which is more than 5 times the
population of the other municipalities. Estimated population within the project area is close
to 600,000.
The development and management of the groundwater resources of Iloilo City and the entire
country are governed by several laws, rules and regulations and policies. These laws and
policies provide the legal, economic, political and administrative authority of various
institutions including national government agencies, local government units (LGUs), water
service providers (WSPs) and the private sector. The Water Code of the Philippines of
1976, the Creation of a National Water Resources Council [now National Water Resources
Board] of 1974, the Clean Water Act of 2004 and the Ecological Solid Waste Management of
2000 are among the related legal framework for the groundwater management plan (GMP)
of Iloilo City and its environs.
3. Groundwater Utilization and Management Issues
Groundwater in the study area is mainly utilized for domestic purposes. MIWD, households
and handful of industries are the primary local users of groundwater. The MIWD is presently
extracting 8,300m3/day, which is about 21% of its daily water production. Majority of the
water supplied to its customers is derived from Tigum River in Maasin. Of the total MIWD
groundwater extraction, 7,700m3/day or 93% is from the deep aquifers. Only 600m3/day or
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7% of MIWD production is taken from shallow aquifers. Other deep aquifer users are
residential subdivisions. Households, water delivery and industries largely derive
groundwater from shallow aquifers.
Production of MIWD water wells has generally declined over the past years. This could be
attributed to reduction of specific capacity resulting from encrustation of well intake
(screened/slotted) sections or well interference.
At present, groundwater in the study area is not much given importance as compared to
surface waters. In fact, there are already existing river management councils or boards that
oversee the development and management of watersheds including a regular surface water
quality monitoring program.
The primary challenge in the study area lies on sustainable groundwater management where
implementation of existing regulations and guidelines on groundwater management is strictly
enforced, specifically on monitoring of groundwater level, abstraction rate and quality, as
well as the operation and maintenance of groundwater infrastructure. However, this activity
is constrained by the lack of a groundwater resource assessments using science based
methodology to support the implementation.
Specifically, these are:
 Weak implementation of existing strategies and policies on groundwater
management such as the rules and regulations spelled out in the Water Code;
 Outdated and incomplete hydrogeological databasing, specifically on aquifer
parameters and groundwater information system;
 Unregulated utilization of groundwater, particularly for domestic (households),
commercial water delivery and industrial uses;
 Intrusion of seawater as observed in the coastal areas of Iloilo City, Leganes and
Oton;
 Absence of regular monitoring of groundwater withdrawal, water level and quality;
 Lack of enabling environment, such as local legislation adopting the Water Code of
the Philippines and Clean Water Act to support groundwater management;
 Poor assessment, planning and management of groundwater resources;
 Lack of technologies to enhance storage capacity of groundwater reservoirs;
 Inadequate personnel capacity and resources to fulfill the mandatory groundwater
resource management function;
 Lack of a communication plan focusing on promoting “best practices” on groundwater
use and management; and
 Absence of harmonization of an integrated water resources management approach
and climate change adaptation to groundwater resource planning for sustainable
infrastructure (climate proofing).
Recent issue affecting water supply as a whole is climate change. While ground water
exists mainly in the subsurface, climate change affects the groundwater system indirectly
through its effect on surface water resources and the watershed areas. Extremes climatic
events have great effects on groundwater systems as these reduce groundwater recharge.
Likewise, baseflow of the rivers will decrease and may eventually dry up during extended
drought periods as groundwater feeds the streams.
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4. Groundwater Flow Model
Groundwater modeling has become part of many projects dealing with groundwater
exploitation and management. Available computer software facilitates modeling of
groundwater flow and quality. But there are limitations that should be understood such as:
 The models rely on various assumptions regarding the real natural system being
modeled;
 Hydrogeologic parameters used in the models are in most cases only an
approximation of their actual field distribution and cannot be determined with
absolute certainty; and
 Current field data will certainly improve the reliability and validity of the model.
A model simulates the spatial and temporal properties of an aquifer system in either physical
(real) or mathematical (abstract) way. Currently, finite difference models are in more
common use because they are easier to design and understand and require much less
mathematical expertise. The modular three-dimensional groundwater flow model known as
MODFLOW is the most popular choice for groundwater modeling.
The groundwater flow modeling is accomplished through the following processes:
 Concept Development
The most important part of the modeling activity is to develop a modeling concept. It
requires a thorough understanding of the hydrogeology, hydrology and the dynamics
of groundwater flow in the area of interest.
 Selection of Computer Code
The computer should be able to effectively simulate the concept and the purpose of
the modeling. The code traditionally used is MODFLOW, which utilizes a numerical
solution for the equation governing groundwater flow through porous media.
 Definition of Model Geometry
To define the size and shape of the model requires the identification of the model
boundaries and the selection of the rectilinear model grid. The model boundaries
can be either physical (real boundaries such as geology and hydrologic features) or
hydraulic (artificial boundaries which are derived from groundwater flow nets). The
actual model design starts with the laying out of grid to form blocks called cells, which
center or node has assigned hydraulic properties assumed uniform over the extent of
the cell. Consistent with local hydrogeology, model layers are defined. MODFLOW
recognizes and solves for different types of layers, confined aquifer conditions and
unconfined aquifer conditions.
 Input of Model Parameters
The model parameters are divided into three groups, namely: a) time, b) space
(layer top and bottom), and c) hydrogeologic characteristics such as hydraulic
conductivity, transmissivity and storage parameters.
 Definition of Boundary Conditions
A boundary condition can be defined as a constraint put on the active model grid to
characterize the interaction between the active simulation grid domain and the
surrounding environment. There are generally three types of boundary conditions;
specified head, specified flow, and head-dependent flow. The no-flow boundary
condition is a special case of the specified flow boundary condition.
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 Definition of Initial Distribution of Hydraulic Head

Initial conditions specify the values of the hydraulic head for each active and
constant-head cells in the model. The iterative model calculations require that initial
hydraulic head should be higher than the elevation of the cell bottom. For transient
conditions the initial hydraulic head should approximate the head distribution
obtained from field data. For steady state conditions, only the hydraulic head in
constant-head cells must be the actual values.
 Definition of the Stresses Acting Upon the System
Aquifer stress refers to any recharge to or withdrawal from the aquifer system. The
MODFLOW can simulates both extraction and recharge wells. Although it assumes
full aquifer penetration, it can also be used for partially penetrating wells. It is a good
tool for modeling lateral flow into and out of the layer.
 Calibration and Sensitivity Analysis
Model calibration can be defined as the process of producing agreement between
model simulated water levels and aquifer discharge, and field measured water levels
and aquifer discharge through the adjustment of hydrogeologic parameters.The
calibration involves numerous single and multiple changes of model parameters. In
most cases, the quality of the calibration depends on the amount and reliability of the
available field data. The field data should also be assessed for consistency,
homogeneity and measurement error.
 Verification of Model Validity
A model is verified “if its accuracy and predictive capability have been proven to lie
within acceptable limits of error by test independent of the calibration data”.
Verification is performed for an additional field data set in either steady state or
transient simulation.
5. The Groundwater Flow Modeling for Iloilo Basin
Based on several geologic cross sections created using the driller’s logs of the boreholes,
confined or artesian aquifers underlie and dominate the study area. Also, there are shallow
wells (depth < 10 meters) drawing water from water table or unconfined aquifers. On this
premise, a two-layer model was created.
Visual MODFLOW Flex, which is a finite-difference flow model program, was selected as the
computer code for this undertaking. The model program uses a modular structure wherein
similar program functions are grouped together, and specific computational and hydrologic
options are constructed. The division of the program into modules permits the user to
examine specific hydrologic features of the model independently. The input and output
systems of the computer program are also designed to permit maximum flexibility.
Since the available data is few and concentrated mainly in the southern part of the basin, it
was decided that a custom or deformed grid would best represent the model. The model is
oriented in the northwest direction nearly parallel to the orientation of the rivers within the
study basin.
Static water level measurements available span a few decades and only a few were taken
within the last year. Only the most recent data were utilized as previous conditions no longer
exist such as the free-flowing wells in San Miguel. To estimate the transmisssivity (T) of the
aquifer, the specific capacity values (discharge divided by the drawdown) were plotted on
semi-logarithmic paper against the calculated transmissivity values from pumping tests. The
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T values were obtained from the graph were then plotted on the working map and contoured
to create an iso-transmissivity map.
From the piezometric surface map, flow lines were drawn to create orthogonal flow net. No
flow boundaries at the perimeter were set up along flow or streamlines, while a constant
head boundary marked the northwestern edge of the modeled area. No head changes are
expected in the Alimodian area.
The initial distribution of hydraulic head represents steady state condition for the
groundwater model. Simulation of pumping stresses was made using the existing MIWD
wells with pumping rates ranging from 13 to 25lps.
Upon application of the pumping stresses mentioned above, the changes in the hydraulic
head were made to simulate the wells pumping at the rate of 20lps for durations of 1 year,
10 years and 20 years. Again the rate was increased to 25lps for the same pumping time.
The modeling results indicate that after prolonged pumping at rates exceeding 20 L/s, the
water levels in the MIWD well field will not be significantly lowered. In actual case, the pump
and the well are rested for a few hours daily, which in effect allows water level to recover.
Considering further that the current discharge rates of the MIWD wells are very much less
than 25lps, the change in hydraulic head in the MIWD well field would also be smaller.
Further, since MIWD existing wells are at least 6 km away from the shoreline and the drop in
hydraulic head at the current pumping rates and even for pumping durations greater than 10
years will not reach mean sea level, induced salt water intrusion into the inland aquifers is
less likely.
6. Groundwater Management Plan
The Groundwater Management Plan is intended to be a roadmap and planning tool that
builds directly on the groundwater basin assessment (including the result of the flow
modeling) and addressing identified groundwater resources challenges. It also includes a
timetable for implementation of the measures/interventions. The Plan adopts a practical and
simpler but no less viable groundwater management plan by adhering to the general
principles in the wise use of groundwater, as described below.
This Plan is divided into 3 phases, Immediate (2015 to 2016) following the timeline of the
Philippine Development Plan (2011-2016), Short-term (2017 to 2022) and Long-term (2013
to 2028). The first 2 years (Immediate phase) are dedicated to reinforcing the existing
implementation activities, the next 5 years (Short-term phase) are for strengthening and
provision of support mechanisms, and another 5 years (Long-term) are for increased
knowledge and use of groundwater along with capacity and awareness to ensure
sustainable management tailored to local needs.
To realize all the above proposals for the management of groundwater in Iloilo, it is
necessary to put in place enabling policy environment. Cooperation among the LGUs is
needed to implement the proposed management plan. These can be made through
legislations.
There are two water quality management areas that cover the study area, the Tigum-Aganan
Watershed and Iloilo-Batiano River System Water Quality Management Areas (WQMAs).
These were officially designated through DENR Administrative Orders (DAO) Nos. 2006-18
and 2009-11, respectively. The DAO also created the governing boards for the above
WQMAs. These governing bodies can also oversee the management of the groundwater as
the boards are represented by stakeholders from different sectors. This is a scaling up
scheme of the WQMA’s, which at present covers only surface waters.
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Summary Matrix Control, Groundwater Management Action Plan, Iloilo City and Surrounding Areas
Problems: Weak implementation of existing strategies and policies on groundwater management such as the rules and regulations spelled out in the Water Code
Outdated and incomplete hydrogeological and hydrological databasing
Unregulated utilization of groundwater, particularly for domestic (households), commercial water delivery and industrial uses
Intrusion of seawater as observed in the coastal areas of Iloilo City, Leganes and Oton
Absence of regular monitoring of groundwater withdrawal, water level and quality
Lack of enabling environment, such as local legislation adopting the Water Code of the Philippines and Clean Water Act to support groundwater management
Inadequate effective assessment, planning and management of groundwater resources
Lack of technologies to enhance storage capacity of reservoirs
Inadequate personnel, capacity and resources to fulfil the mandatory groundwater resource management functions
Lack of a communication plan focussing on promoting “best practices” on groundwater use and management
Absence of harmonization of an integrated water resources management approach and climate change adaptation to groundwater resource planning for sustainable infrastructure (climate
proofing)
Time Frame: Immediate: 2015 – 2016
Measures Actions Sub-actions Outputs Timeline
Implementation of recommendations
- Continued implementation of the rules
and regulations of the Water Code and
drawn from the monitoring and
evaluation reports and strict
other national laws on conservation and - Increased compliance to the rules
protection of groundwater resource and regulations of the Water Code,
compliance/adherence of the rules and
1) Strengthen enforcement of existing laws, - Revision of monitoring programs specifically the permitting system
regulations of the Water Code
policies, guidelines and appropriate considering previous experiences - Updated data on records on the
implementing rules and regulations relevant compliance of the Water Code
Generation and validation of most recent 2015-onwards
to groundwater management, specifically Data collection on existing groundwater including updated information on
information of wells
the Water Code infrastructures existing groundwater infrastructures
Conduct of quarterly monitoring and
updating reports including non-compliant
Monitoring and updating of information users/owners, issues/violations resolved
(for compliance monitoring)
2) Updating of groundwater and surface water - Maintain a comprehensive database Generation of quarterly reports including Database with updated information
database to be filled-up with the required on the hydrogeology and hydrology of performance of existing wells filled in 2015-onwards
information in the form the Iloilo basin
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- Complete inventory of existing wells
and selective field tests to determine
the aquifer characteristics
- Complete inventory of surface waters
to include information on discharges
- Wise efficient use of groundwater for

irrigation
3) Regulated extraction of groundwater to Promote efficient use of groundwater Database on groundwater withdrawal
protect and conserve the resources of the specifically for irrigation where 75% of - Urban water supplies well-maintained -do-
study area the water is used for agriculture with minimal losses
- Land use priorities are established to
ensure protection of water quality
Time Frame. Short-term: 2017 – 2022 2/

1) Address salt water intrusion problem in the - Regulated use of groundwater along Studies for various options
coastal areas of Iloilo City, Leganes and coastlines - Control through issuance of permits to recommended
Oton 1/ - Recommendations of appropriate construct wells in the area 2017-2022
technology and siting considerations - Identification of appropriate
for problem areas technologies that will be recommended
- Conduct of monitoring and regulating

the extraction of groundwater to
cover withdrawal, water level and
2) Regular monitoring of groundwater quality Database on groundwater withdrawal,
Generation of quarterly monitoring reports 2017-onwards
withdrawal, water level and quality 1/ - Establish monitoring station network water level and quality
for groundwater levels and water
quality of surface and groundwater
- NWRB to provide advisory services to City/Municipal Ordinances adopting the

3) Creating an enabling environment through Assistance provided to the LGUs in
the working committee formed at the Water Code of the Philippines, Clean
LGUs, such as local legislation adopting the drafting local legislations so that LGUs
local level to take charge of coordinating Water Act and Ecological Solid Waste 2017-2022
Water Code of the Philippines and Clean Water shall endeavor to formulate regulatory activities related to groundwater
Act to support groundwater management policies Management Act to support groundwater
management
management
- If necessary, attend Sangguniang
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sessions during presentation of the
ordinances for approval of the
Sangguniang Bayan or Panlalawigan
Time Frame. Long-term: 2023 – 2028 1/
- Monitoring of groundwater withdrawal,

water level and quality (can be
Establishment and control of protection integrated to self-monitoring report,
zone around groundwater abstraction (SMR) to Environmental Management
1) Effective assessment planning and Policies on the establishment and control
points especially the MIWD well fields to Bureau) 2023-2024
management of groundwater resources of protection zone
control over-exploitation and
groundwater pollution - Updating of the groundwater flow model
- Delineated areas where groundwater
level significantly declining
Verfify the following:
- Presence of adequate permeability,
thickness, and lateral extent to satisfy
the desired performance criteria
- for the artificial recharge facility
Guidelines on Artificial Recharge to
2) Development of guidelines on groundwater - no geochemical reactions would occur Groundwater to include planning,
management such the artificial recharge Study viability of artificial recharge that adversely impact aquifer water 2023
techniques and design, and monitoring,
strategy quality mechanism
- availability to provide the required
additional groundwater recharge
- construction, operation and
maintenance of the artificial recharge
project are technically feasible
- Implementation of capacity building
milestones
Conduct of workshops, trainings and
3) Enhance technical capacity of personnel to - Implement practical, in-service seminars covering topics on regulatory
fulfill the mandatory groundwater training courses on permitting Seminars, Workshops and Trainings 2023-onwards
compliance, technology, and monitoring
management function process, groundwater monitoring ,
etc. for staff
4) Prepare and implement a communication - Compilation of “best practices” and - Conduct of NWRB-LGU workshops on
and awareness plan promoting groundwater developing guidelines on policies/strategies (permit requirements, Documentation of workshops, -do-
management utilizing “best practices” of groundwater management abstraction regulations, pollution, etc) to consultations and the corresponding
ES -9

actual implementation as opportunity to - Conduct of information, education improve enforcement of existing rules IEC materials used
enhance awareness and communication campaigns and and regulations
consultation forum among - Conduct of stakeholder’s forum, i.e.,
stakeholders users dialogues to disseminate
information on enforcement, encourage
voluntary compliance of regulations,
and adopting ”best practices” to
promote conservation and protection of
the groundwater resources
IWRM, environmental protection and

5) Harmonization of IWRM approach and Incorporation of the IWRM and climate
climate change adaptation to groundwater
climate change considered in enhancing
change adaptation issues and concerns in
- Projects implemented to mitigate
the integrity of water resources and the impacts of a changing climate -do-
resource planning and design for the design to be adopted as well as on the
provisions of sustainable infrastructure - Watershed areas preserved r
sustainable infrastructure (climate proofing) options to be considered for implementation
during the planning and design stage.
Notes: 1/ = Depending on available resources including manpower, NWRB can start the implementation of these activities early on
ES -10
1. Introduction
1.1 Background
Iloilo City and it’s environs have been identified as one of the highly urbanized water
constraint area by the National Water Resources Board (NWRB) (Water Resources
Management Master Plan, 1998, JICA). In this regard, the NWRB earmarks the
establishment of systematic management strategies, specifically for allocation and protection
of the aquifers. One of these strategies is the preparation of a Groundwater Management
Plan for Iloilo City and its surrounding areas, which will serve as a guide in groundwater
utilization, protection and conservation. Specifically, the plan is envisaged to help the
stakeholders meet the following objectives:
 Prepare and enhance the existing quality of the study area’s groundwater;
 Preclude surface or groundwater exports that would reduce the long-term supply
groundwater;
 Coordinate groundwater management efforts between regional and local water
users;
 Maintain local management of groundwater resources;
 Implement a groundwater monitoring program to provide an “early warning” system
to future problems;
 Stabilize groundwater levels in order to minimize pumping costs and energy use and
provide groundwater reserves for use during drought periods;
 Maximize the use of surface water, including available flood water, for beneficial use;
and
 Participate in local and regional efforts to effectively manage available water supplies
to protect the stakeholders.
The study area covers the catchments or watersheds of the Jaro River System and the Iloilo-
Batiano River System. It encompasses wholly or parts of the administrative areas of Iloilo
City, Oton, Pavia, Leganes, San Miguel, Sta. Barbara, Cabatuan, Alimodian and Maasin
(Figure 1.1). Small portions of Janiuay, Leon, San Remigio and Valderama are also
included in the study area. Approximately, the study area has a total land coverage of
60,190 hectares (has) or 602 square kilometers (km2).
At present, groundwater in the study area is mainly utilized for domestic purposes. The
Metro Iloilo Water District (MIWD) is the principal groundwater user in the locality.
Groundwater production of MIWD averages about 8,000m3/day or 21% of its total output/1.
Also, considerable number of households has own groundwater point sources, majority
utilizing shallow aquifers. Other major users are those in the business of water delivery and
food industries such as bottling and ice plant.
1.2 Purpose
This groundwater management plan is aimed at improving and protecting the groundwater of
Iloilo City and the surrounding municipalities. The plan is the first of a kind in the locality and
a starting point in the development of long-term strategies to manage the finite groundwater
resources.
1
Based on MIWD 2011 and 2012 production data
1
It is hoped that this Plan be implemented by the concerned local government units (LGUs)
through integration and/or harmonization with the local (provincial and city/municipal) land
use and development plans as well as local policies. This proposed Plan should be regularly
updated to adapt to current conditions.
1.3 Limitations
The assessment made was based on limited hydrogeological and groundwater data. Aquifer
hydraulic parameters are available for the boreholes of the MIWD only. Also, except MIWD
boreholes, water level measurements do not reflect the current condition as records are
several years ago. It should be noted that groundwater assessment requires spatial and
temporal data and information. Thus, the groundwater flow modeling covers only the lower
half of the study area, where MIWD boreholes are concentrated.
This is the same challenge experienced during the preparation of Metro Iloilo Water District
Water Resources Master Plan (1995-2030) financed by the Swedish International
Development Agency (SIDA) in 1996.
1.4 The Report
This report presents the proposed groundwater management plan for Iloilo City and its
surroundings. It discusses the existing conditions in the study area, with focus on the
groundwater, the future rate of groundwater withdrawal, the result of the groundwater flow
simulation as a management tool, and the proposed groundwater management plan.
3
2. The Study Area
2.1 Physical Characteristics
2.1.1 Location and Accessibility
Iloilo City is the provincial capital of Iloilo Province. The Province occupies the southern and
northeastern portions of the Panay Island in central Philippines. It is divided into 2 cities and
42 municipalities. Iloilo Province is the third-largest province in Region VI, the Western
Visayas Region. Iloilo is bordered by the Capiz Province and the Jintotolo Channel to the
north, the Visayan Sea to the east, the Antique Province to the west, and the Panay Gulf and
Iloilo Strait to the south. Just off Iloilo's southeast coast is the island-province of Guimaras.
Iloilo City is situated on the southern part of the Province. The City is between geographic
coordinates 10° 41’ to 10° 48’ north latitude and 122° 31’ to 122° 37’ east longitude. It is bounded
to the north by the Municipality of Pavia, to the northeast by the Municipality of Leganes, to the
west by the Municipality of Oton, and the Iloilo Strait to its eastern and southern coastline. The
City is highly urbanized. It serves as the regional center Region IV as well as the center of Iloilo-
Guimaras Metropolitan Area.
The City can be reached from Manila by plane or sea travel. Regular air and sea transports
are available. For air travel, all the leading airlines have two or more flight daily to and from
Manila, Cebu City and Davao through the Iloilo International Airport in the Municipality of
Cabatuan (about 19km northwest from the City). By sea, Iloilo City is about 20 hours travel
from Manila. Large sea vessels serve direct Manila-Iloilo route and vice versa five times a
week through Fort San Pedro in the City Proper. The City is accessible by land to the other
municipalities within the study area. There are regular and readily available buses, jeepneys
and taxies plying to and from the adjoining municipalities.
2.1.2 Topography and Drainage
The study area has generally flat terrain on the southeast and mountainous on the
northwest, where the two main river systems originate. About 50% of the study area has flat
to nearly flat ground. Iloilo City, Pavia, Leganes, Oton, San Miguel and Sta. Barbara are
within this geomorphic unit. Cabatuan has extensive nearly flat profile with rolling hilly
portions. Alimodian and Maasin are rolling to mountainous. Ground elevation at the
northwestern part reaches 1200m above mean seal level (mamsl).
The Jaro River and the Iloilo-Batiano River are the two main natural waterways in the study
area. Both river systems drain into the Iloilo Strait. Jaro River has two major tributaries,
Tigum and Aganan Rivers. The downstream portion of Jaro River is nearly flat resulting to
its floodwaters flowing into the Iloilo-Batiano River when the river bank overflows.
2.1.3 Land Area and Political Subdivisions
The study area encompasses the catchment area of the Jaro River and Iloilo-Batiano River
Systems. The Jaro River system includes the Tigum and Aganan Rivers. These two rivers
were designated as water quality management area (WQMA), the Tigum-Aganan Watershed
WQMA. Iloilo-Batiano River is a small river system covering the urbanized districts of Iloilo
City and surrounding municipalities. Iloilo-Batiano River System is also a designated WQMA
through DENR Administrative Order (DAO) No. 11 Series of 2009.
4
The study area covers 13 political subdivisions, namely; Iloilo City, Pavia, Oton, Leganes,
San Miguel, Sta. Barbara, Cabatuan, Alimodian, Maasim, Janiuay, Leon, San Remigio and
Valderama. It has total land area of 602km2. It covers most areas of Iloilo City, Pavia,
Maasin and San Miguel. The study area also extends over significant area of Oton,
Alimodian, Leganes, Cabatuan and Sta. Barbara. Table 2.1 presents the coverage area in
each political district.
Table 2.1: Land Area

Total
Administrative City/Municipal Study Area % Coverage of % Coverage of
2 2/
Area Land Area (km ) City/Municipality the Study Area
2 1/
(km )
Iloilo City 78.34 78.34 100 13
Leganes 32.20 21.23 66 4
Oton 86.44 66.16 77 11
Pavia 27.15 27.15 100 5
San Miguel 31.97 29.74 93 5
Sta. Barbara 131.96 48.93 37 8
Cabatuan 112.90 71.67 63 12
Maasin 128.59 128.13 100 21
Alimodian 144.82 99.47 69 17
3/
Other 570.85 31.05 5 5
Total - 601.90 - 100
1/- from NSO
2/ - based on GIS
3/ - Janiuay, Leon, San Remigio and Valderama
2.1.4 Existing Land Use

Of the geopolitical units covered, Iloilo City is the most highly urbanized. Of its total land
area, almost 60% is residential zone. About 12% is utilized for commercial and industrial
purposes. Only 4% is used for cultivation and another 4% for fishery.
Pavia is identified as the Regional Agro-Industrial Center for Western Visayas in the late
1990s. There are 220 identified establishments operating in the municipality, 38 of which
are into manufacturing. These manufacturing establishments include producers of animal
feeds, milled rice, farm machineries, noodles, industrial and medical gasses, banana chips,
beverages and foams. The Coca Cola Bottling Philippines is the biggest manufacturing
plant in the Pavia.
Oton is classified as a 2nd class municipality. It is primarily an agricultural district with rice as
major crop produce. About 54km2 of its land is planted with rice. Mango also contributes
significantly to agricultural output of the Municipality with more than 20.00km2 of land
planted.
San Miguel is basically an agricultural town with rice as the principal produce. About 17km2
of the land area is cultivated for rice.
Santa Barbara is also an agricultural area. About 85% of its land area is primarily devoted to
farming. The built-up areas cover approximately 9% of the total municipal land area. Also
included in this category are the areas utilized for commercial, institutional and parks and
open space. Its agro-industrial land is only about 1% of the total land area.
Cabatuan hosts the New Iloilo International Airport. It is mainly agricultural with about 8,251
has of agricultural land, covering 70% of its total land area. Maasin (128.59km2) and
Alimodian (144.82km2) are also agricultural municipalities.
Overall, the Jaro and Iloilo-Batiano River Systems watersheds are mainly used for
agricultural purposes (Figure 2.1).
5
2.1.5 Meteorology
Climate in the Province falls under Type I based on Modified Corona’s Classification, which
is characterized by pronounced wet and dry seasons. Below is a brief description of the
meteorology of the study area.
2.1.5.1 Rainfall
Average annual rainfall in Iloilo is about 2,194mm, while recorded extreme rainfall is about
320mm as measured in July 2004. This is based on Iloilo City Synoptic Station as provided
in the table below. Rainy period is usually between the months of June and October. Within
this period, the amount of rainfall reaches 74% of annual precipitation. The wettest month is
normally observed in August.
Table 2.2: Iloilo Climatological Normals (1971 to 2000)

o
No. of Temperature ( C) Relative Wind
Rainfall
Month Rainy Humidity Speed
(mm) Min. Max. Mean Direction
Days (%) (mps)
January 39.9 9 22.6 30.5 26.5 81 NNE 4
February 30.4 6 22.8 31.2 27.0 79 NNE 4
March 41.2 5 23.4 32.4 27.9 75 NNE 4
April 70.1 6 24.5 33.8 29.1 73 NNE 4
May 113.5 10 24.9 33.7 29.3 77 SW 3
June 308.1 19 24.5 32.0 28.2 82 SW 3
July 347.6 20 24.3 31.1 27.7 84 SW 3
August 388.8 19 24.4 31.0 27.7 84 SW 3
September 296.3 19 24.2 31.2 27.7 84 SW 3
October 283.2 19 24.1 31.6 27.9 84 NNE 3
November 171.9 14 24.0 31.4 27.7 84 NNE 3
December 103.9 12 23.2 30.8 27.0 83 NNE 4
Annual 2,194.4 158 23.9 31.7 27.8 81 NNE 3
Source: PAGASA Iloilo Synoptic Station, Iloilo City
Table 2.3: Climatological Extremes

Greatest Daily
Temperature (oC) Highest Wind (mps)
Month Rainfall (mm)
Depth Date High Date Low Date Speed Direction Date
January 118.6 01-03-31 34.7 01-28-90 16.5 01-23-76 21 NNE 01-05-52
February 79.5 02-16-25 35.4 02-19-27 16.7 02-04-76 24 NNE 02-17-62
March 214.6 03-01-96 39.0 03-04-73 18.6 03-03-68 22 NNE 03-20-65
April 104.6 04-28-94 37.5 04-25-98 20.0 04-08-76 25 NNE 04-25-71
May 223.8 05-21-22 37.8 05-26-87 20.2 05-19-77 22 SW 05-27-97
June 179.9 06-14-90 37.5 06-05-91 21.0 06-28-97 26 SW 06-25-92
July 319.8 07-29-94 35.2 07-10-36 19.5 07-31-75 25 SW 07-28-82
August 222.3 08-08-29 34.8 08-11-39 20.0 08-01-75 25 SW 08-01-86
September 154.7 09-04-62 37.8 09-16-75 19.8 09-05-75 20 SW 09-03-91
October 225.0 10-28-95 35.4 10-03-76 19.2 10-18-75 36 NNE 10-28-95
November 255.6 11-05-84 34.8 11-01-30 19.4 11-22-75 45 NNE 11-24-68
December 172.2 12-21-33 34.5 12-19-98 18.3 12-03-04 34 NNE 12-10-51
Annual 319.8 07-29-04 39.0 03-04-73 16.5 01-23-76 45 N 01-23-76
Period of
1903-2002 1903-2002 1949-2002
Record
Source: PAGASA Iloilo Synoptic Station, Iloilo City
2.1.5.2 Temperature
The mean annual temperature in the area is about 27.8°C. The maximum annual is 31.7°C,
while the minimum is 23.9°C. The hottest month is May with mean temperature of 29.3°C.
On the other hand, the coolest month is normally experienced in January with mean
temperature of 26.5 °C.
7
2.1.5.3 Relative Humidity

Relative humidity (the amount of atmospheric moisture present relative to the amount that
would be present if the air were saturated expressed as percentage) in the project area
ranges from 73 to 84% and averages 81%. High relative humidity occurs during the period
of relatively high precipitation.
2.1.6 Geology
2.1.6.1 Regional Geology
Iloilo City and the rest of the study area are situated in the southeastern part of the Panay
Island. The island is partly within in the so-called North Palawan Block and the Philippine
Mobile Belt. The North Palawan Block is aseismic (free from earthquakes). The mobile belt
is an active region in terms of seismic and volcanic processes. These processes are results
of tectonic plate subduction, collision and faulting. The island is product of collision of
several Tertiary volcanic arcs with the North Palawan Block.
The western Panay, which includes the Antique Range, is a thrusted oceanic mass over the
Cuyo shelf (part of the North Palawan Block – a fragment of the Eurasian continental
margin). The eastern Panay is a sedimentary basin and is referred to as “Iloilo Basin”.
The Iloilo Basin rests on a volcanic basement. This basement is exposed east and west of
this north-south-trending basin. On its eastern edge, the Iloilo Basin rests on the diorite
intruded volcanic and sedimentary suites. On the western edge is along the Antique Range.
The basin ends in the Municipality of Dumalog, southeastern Panay.
The study area is part of the Iloilo Basin. Its northwestern section rests on the Antique
Range and the southeastern part ends at the Guimaras Strait.
2.1.6.2 Local Geology
The study area is largely made up of sediments of Late Miocene to Recent ages (Figure
2.2). Quaternary alluvium is predominant in the southern part and makes up about 50% of
the study area. It covers the entire Iloilo City, Oton, Leganes and Pavia. The alluvium also
comprises great portions of Sta. Barbara and San Miguel, small sections of Cabatuan,
Maasin and Alimodian. Borehole logs of existing wells show that the alluvial deposit extend
up to 110m. The alluvial deposits are loose and unconsolidated clay, silt, sand, gravel and
mixtures of these detrital materials.
The Late Pleistocene (N3+Q1) Cabatuan Formation, as the name implies, is predominant in
the Municipality of Cabatuan. It is also partly underlain Sta. Barbara, San Miguel and
Maasin. This formation covers about 10% of the study area. It underlies the alluvial deposit
in the lowland portion of the study area. The Cabatuan Formation has nearly horizontal
bedding of mudstone, sandstone and siltstone. It is divided into 3 members, the Balic
Mudstone (basal member with interbedded fine-grained sandstone), Maraget Sandstone
(middle member that is made up of loosely consolidated, porous, light and permeable
sandstone at the upper section and siltstone at the base) and Sta. Barbara Member (the
upper unit composed of massively bedded coarse-grained and silty sandstone and siltstone
with minor claystone). The Cabatuan Formation has thickness of more than 390m/2.
2
Lexicon of Philippine Stratigraphy, Rolando Peña, 2008
8
The upstream portion of the study area is made up of older detrital sedimentary rocks (N2 and
N1). These include the Late Pliocene Ulian Formation (primarily claystone and/or mudstone with
minor sandstone, siltstone and limestone), Late Miocene to Early Pliocene Iday Formation
(conglomerate, sandstone and claystone), Late Miocene Tarao Formation (basically sandstone
and mudstone with minor conglomerate, marl, and limestone) and Early to Middle Miocene
Singit Formation (made up of sandstone, shale, conglomerate and clastic limestone). Of these
rock units, the most predominant are the Singit Formation and the Tarao Formation.
2.1.7 Hydrogeology
2.1.7.1 Hydrogeological Units and Characteristics
Groundwater in Iloilo City and surroundings is mainly derived from the Recent Alluvium and
the Late Pleistocene Cabatuan Formation. These are the main hydrogeologic units in the
study area. Much of the boreholes in the alluvium are between the Jaro River and the Iloilo-
Batiano River. All the accounted existing boreholes are in the alluvium. Very few of the
deep wells penetrate the Cabatuan Formation. Well No. 12 of MIWD is the only recorded
borehole that penetrates into the Cabatuan Formation. Some household boreholes are
probably drilled in to this formation and other rock units, particularly in Maasin, Alimodian
and other municipalities upstream of the Tigum-Aganan catchment.
Based on the available data, there are two main aquifers in the alluvial plain of Iloilo Basin. The
shallow aquifer extends between 5 to 35m. Clayey and silty materials intervene with the aquifer.
The deeper aquifer occurs from 50 to 110m. Thick clayey horizon separates the two aquifers.
Yields of existing MIWD wells, which are in the alluvium range from 4 to 14liters/second (lps).
Further, the transmissivity values (measures the ability or the amount of water a groundwater
reservoir can transmit, which is valid for non-turbulent flow) of aquifers in the alluvial deposits
ranges from 3.5 to 10.3 x 10-3m2/sec/3. This indicates moderate to good yield to boreholes.
2.1.7.2 Groundwater Level
Based on the data provided by MIWD, static groundwater level in the shallow aquifer varies
from 4 to 20m below ground level (mbgl). Measured static water level in deep aquifer
ranges from 16 to 54mbgl. Figure 2.3 provides piezometric map of the deep aquifer based
on the data provided by MIWD from its 2013 measurements.
Previous report/4 indicates declining water level from 1987 to 1996 in 6 MIWD wells located in
the alluvial plain. This declining water level continues to present as revealed by 2013 sounding
of static water level of MIWD wells (Table 2.4), particularly for the old wells.
Table 2.4: Static Water Level MIWD Wells
Well ID Well Depth (m) 1983 1989 2006 2009 2012 2013
1 136 4.90 - 49.67 49.40 51.90 51.00
2 200 4.84 - - 29.00 37.70 36.20
3-A 91 18.46 - 52.90 49.28 55.0 54.00
7 150 - - 46.40 46.45 49.70 48.30
8 150 - - 30.59 18.59 23.90 23.00
9 101 - 8.85 42.20 17.55 37.20 40.90
10 92 - - 32.70 29.90 19.5 19.10
11 100 - - 29.35 29.34 28.2 24.10
12 98 - - 9.77 14.00 18.50 16.60
14 45 - - - 6.00 6.00 19.60
15 41.75 - - - - 9.30 9.00
Source: NWRB and MIWD
3
Water Resources Master Plan, Metro Iloilo Water District, LWUA-UNDP-SWECO, 1997
4
Ibid
10
2.1.7.3 Groundwater Quality
Water samples had been collected from numerous wells in Metro Iloilo and tested using field
chemical test kits. The results, however, were not used in the study because upon
examination of well data, the samples were taken from very shallow wells with an average
depth of 6 meters. Thus, these water samples would represent mainly the chemical
properties of meteoric water rather than the natural groundwater in the area.
Instead, the water quality from MIWD Wells Nos. 9 and 10 were utilized. The water samples
were collected in January 2012 and February 2013. Platinum Research Laboratory and SGS
performed the tests and the results are summarized in Annex 1. SGS tested the well waters for
selected parameters mostly metal contents, while Platinum conducted additional tests for
electrical conductivity, alkalinity, acidity, hardness, calcium, magnesium and benzene.
The results from both laboratories showed the absence of potentially toxic or hazardous elements
such as arsenic, cadmium and lead. With the exception of a few parameters, the natural
groundwater quality passes the Philippine National Standard for Drinking Water (PNSDW).
Aside from being more alkaline (pH=8.09), the water from Well No. 9 also recorded a slightly
elevated value for chloride content, although still within acceptable limit. The total dissolved solids
content exceeded the standard limit of 500mg/L. The high chloride is remarkable because this
well is situated farther inland than Well No. 10 whose average chloride content is only 41mg/L
compared to the average chloride content of 201mg/L for Well No. 9. This well may have reached
the zone of mixing between fresh and the saline connate water. Reducing the pump rate may help
lower the chloride content at Well No. 9.
The excessive hardness of the water from Well No. 10, together with a pH of 8.09 may increase
the incrusting tendencies and cause scaling of pipes. The hard water obviously affects bathing
and laundry use.
2.1.8 Natural Hazards
The study area, being the growth center in the Province of Iloilo, is vulnerable to various natural
hazards, geologic and climate-related. With climate change, the intensity and frequency of the
natural hazards increases. As can be observed in the recent disasters experienced in the
country, water supply, sanitation and hygiene of the citizenry are greatly affected.
The most frequent natural hazard that brought havoc in the study area is flooding. Nearly
55% of the study area is considered highly susceptible to flooding (based on the Mines and
Geosciences Bureau (MGB) Map Sheets 3552 IV Pototan and 3552 III Iloilo City) as
depicted in Figure 2.4. Flood occurrences were largely attributed to climate, extreme
precipitation by monsoon and typhoons. Likewise, coastal areas are prone to storm surge.
The upland area is considered susceptible to mass movements or landslides. Based also on
the published MGB hazard maps, about 32% of the study area has moderate to high
susceptibility to landslide. Heavy and prolonged precipitation also triggers landslides.
The Province of Iloilo is located in the Philippine Mobile Belt where earthquake is frequent as
earlier mentioned. Figure 2.5 presents the location of epicenters of ground tremors of
Magnitude 5 and above. The nearest earthquake generators in the study area are the West
Panay Fault and Negros Trench and Negros Fault. Attendant hazards to ground shaking in
the study area are liquefaction, tsunami and landslide. The lowland areas covered with
alluvial or loose deposits and where groundwater occurs at shallow depth are susceptible to
liquefaction. These include Iloilo City, Pavia, Oton and Leganes.
12
Figure 2.5: Seismicity Map of Panay (Magnitude ≥5, 1903 – 31 July 2013)
2.2 Socio-Economic Environment
The city and municipalities in the study area are classified as1st to 4th class as provided in
Table 2.5. Fourth class municipalities are those with income of PhP25M or more, but less
than PhP35M. Agriculture is the main source of income in the study area. Major land-based
produces are rice, corn, banana, coconut, mango and sugarcane. Other agricultural outputs
are fish and fisheries products and livestocks. Commercial and industrial activities are active
in Iloilo City, Pavia and San Miguel. Leading commercial banks are present in the City.
Global and leading food industries such as Coca Cola, Pepsi and Swift are operating locally.
Since Iloilo City is the most urbanized area, it has the highest population among the
city/municipalities within the Jaro and Iloilo-Batiano River Basins. As shown in Table 2.5,
the city registered a total population of nearly 500,000 in year 2010, which is 5.14 times the
population of Oton, the next most populated municipality. Sta. Barbara is third and followed
by Cabatuan, both with population of almost 55,000. The other municipalities have
population ranging from 25,000 to 48,000.
Table 2.5: Income Class and Population
City/ Income Population City/ Income Population
Municipality Class (2010) Municipality Class (2010)
st nd
Iloilo City 1 424,619 Sta. Barbara 2 55,472
th nd
Leganes 4 29,438 Cabatuan 2 54,950
st
Oton 1 82,572 Maasin - 35,069
nd
Pavia 2 43,614 Leon - 47,522
th rd
San Miguel 4 25,013 Alimodian 3 47,248
Source: www.nscb.gov.ph
14
Basic and secondary schools are available in every municipality. For tertiary education,
Iloilo City has 42 schools, of which 5 are universities.
Health services in Iloilo City and in other municipalities are readily available. Almost every
barangay has health station. For more intensive medical attention, Iloilo City has 20
registered hospitals.
In terms of infrastructures, Iloilo City has several ports for passenger and cargo vessels.
Cabatuan is host to the New Iloilo International Airport. Iloilo City can be accessed from and to
the different municipalities by all weathered roads. Mobile communication is accessible in all the
municipalities, while land-based is available in Iloilo City and the immediate municipalities.
2.3 Legal Framework
The development and management of the groundwater resources of the country are
governed by several laws, rules and regulations and policies. These laws and policies
provide the legal, economic, political and administrative authority of various institutions
including national government agencies, local government units (LGUs), water service
providers (WSPs) and the private sector.
 Water Code of the Philippines of 1976 (Presidential Decree [PD] 1067) defining the
policies relating to appropriation, development, exploitation and conservation of water
resources owned by the State and mandating defining the policies relating to
appropriation, development, exploitation and conservation of water resources owned
by the State and mandating the National Water Resources Council, the precursor of
the National Water Resources Board (NWRB) to be primarily responsible for the
implementation of the Water Code including the granting of permits and imposition of
penalties for administrative violations.
 Creation of a National Water Resources Council [now National Water Resources Board] of
1974 (PD 424) as the government coordinating and regulating agency for all water
resources management development activities; tasked with the formulation and
development of policies on water utilization and appropriation, the control and supervision
of water utilities and franchises, and the regulation and rationalization of water rates.
 Clean Water Act of 2004 (Republic Act [RA] 9275) mandating the State to pursue a policy
of economic growth in a manner consistent with the protection, preservation and revival of
the quality of our fresh, brackish and marine waters using sustainable development frame
work. Under this law, each LGUs are also provided with powers and functions to: (a)
monitor water quality, (b) comply with the Water Quality Management Action Plan; (c) take
active participation in all efforts concerning water quality protection and rehabilitation; and
(d) coordinate with other government agencies and civil society and the concerned sectors
in the implementation of measures to prevent and control water pollution.
 Ecological Solid Waste Management of 2000 (RA 9003) ensures that quality of
surface and groundwater from leachate contamination.
 Water Rules and Regulations on Groundwater Development and Conservation. The
following are the rules and regulations, among others:
a. Permits to Dig or Drill Boreholes and to Construct Wells. Except for domestic use
that needs to be only registered, no person shall drill any well for the extraction of
groundwater or make any alteration to any existing well without securing a permit
from the Board.
b. Drilling of deep wells for the extraction of groundwater shall conform with
requirements on the design and construction, siting such as possibility of salt water
intrusion, land subsidence and mining of groundwater; and spacing requirements.
15
the operation and maintenance of groundwater infrastructure. However, this activity is

constrained by the lack of a groundwater resource assessments using science based
methodology to support the implementation.
Specifically, these are:
 Weak implementation of existing strategies, and policies on groundwater
management such as the rules and regulations spelled out in the Water Code;
 Outdated and incomplete hydrogeological databasing, specifically on aquifer
parameters and groundwater information system;
 Unregulated utilization of groundwater, particularly for domestic (households),
commercial water delivery and industrial uses;
 Intrusion of seawater as observed in the coastal areas of Iloilo City, Leganes and
Oton;
 Absence of regular monitoring of groundwater withdrawal, water level and quality;
 Lack of enabling environment, such as local legislation adopting the Water Code of
the Philippines and Clean Water Act to support groundwater management;
 Inadequate effective assessment, planning and management of groundwater
resources;
 Lack of technologies to enhance storage capacity of groundwater reservoirs;
 Inadequate personnel capacity and resources to fulfill the mandatory groundwater
resource management function;
 Lack of a communication plan focusing on promoting “best practices” on groundwater
use and management; and
 Absence of harmonization of an integrated water resources management approach
and climate change adaptation to groundwater resource planning for sustainable
infrastructure (climate proofing).
3.3 Impact of Climate Change on the Hydrogeologic Condition of the Iloilo Basin
Climate change is manifested by global warming and more specifically, extended drought
and extremely intense rainfall. While ground water exists mainly in the subsurface, climate
change affects the groundwater system indirectly through its effect on surface water
resources and the watershed areas.
Of the three adverse events, the most threatening to the groundwater system is the
extremely intense rainfall and unusually strong winds. Tornadoes and strong winds can
topple trees and create havoc in the watershed areas, which are often recharge areas as
well. If these events occur, flash floods can lead to an accelerated erosion of the topsoil in
the watershed. Such erosion removes the soil cover that absorbs the rainfall and feed the
aquifers. If the forest cover is also lost, very little barrier will prevent further soil erosion.
Consequently, the groundwater recharge will be reduced.
Massive runoff and flash floods do not leave enough time for the rainwater to infiltrate into
the ground. Most of the water will discharge to the sea. These floods also bring with them
enormous amount of debris and soil particles that effectively denude the soil cover in the
watershed. Heavy siltation in the lower elevations will create an almost impermeable soil
cover that does not readily permit water to infiltrate into the ground.
17
When the soil cover thins out, only a little amount of water can be stored in it. Since it is this
water that often feeds streams, the baseflow of the rivers will likewise be reduced. Some
streams may eventually dry up during extended drought periods.
Higher surface temperature can induce enhanced evaporation losses. Soils will dry up and
will result in a higher demand for irrigation water and most probably greater groundwater
withdrawal. Surface water reservoirs may at this time also lose a significant amount of
stored water to evaporation.
18
4. Groundwater Flow Model
Groundwater modeling has become a major part of many projects dealing with groundwater
exploitation and management. Although many computer software are now available, it is
essential that for any groundwater model to be used properly, its limitations should be
understood.
These limitations include the accuracy of the computations by the software and the
hardware. Furthermore, the following facts apply to any computer modeling:
 The models rely on various assumptions regarding the real natural system being
modeled;
 Hydrogeologic parameters used in the models are in most cases only an
approximation of their actual field distribution and cannot be determined with
absolute certainty; and
 Current field data will certainly improve the reliability and validity of the model.
From these elements, it is obvious that a model will only be reliable and useful as its
developer and the data that he worked on. The limitations must always be a major
consideration so that the model can be used meaningfully.
4.1 Types and Use of Groundwater Models
A model simulates the aerial and temporal properties of a system in either physical (real) or
mathematical (abstract) way. In the 1970's, groundwater systems were simulated by
comparing groundwater flow to other physical processes such as the flow of electrical
current through conductors. They were analog models.
Deterministic mathematical models use mathematical equations to describe the elements of
ground water flow. They evolved into either the simple analytical model or the numeric
model, the latter being more in use today.
Numeric models describes the entire flow field of interest at the same time, providing
solutions for as many data points as specified by the user. The flow field is subdivided into
small cells and the basic groundwater flow equation is solved for each cell considering the
water input and output. The algebraic equations are solved through an iterative process,
thus the name numeric model. Numeric models are divided into two groups, namely, the
finite element and the finite difference models. Currently, finite difference models are in
more common use because they are easier to design and understand and require much less
mathematical expertise.
Groundwater models can be used for three general purposes:
 To predict or forecast expected natural or artificial changes in the system.
 To describe the system in order to analyze various assumptions about its nature and
dynamics.
 To generate a hypothetical system that will be used to study the principles of ground
water flow.
4.2 Model Design
Designing a groundwater flow model involves the following activities:
19
4.2.1 Concept Development
The most important part of the modeling activity is to develop a modeling concept. It
requires a thorough understanding of the hydrogeology, hydrology and the dynamics of
groundwater flow in the area of interest. This knowledge is represented by a computerized
database and simplified hydrogeologic maps and cross sections that can be used in the
model design. The hydrogeologic map should show the water level contours and the
general direction of groundwater flow.
4.2.2 Selection of Computer Code
The computer should be able to effectively simulate the concept and the purpose of the
modeling. Since finite difference models are easier to program, require less data and more
user-friendly for data input, the modular three-dimensional ground-water flow model better
known as MODFLOW is often the most popular choice for this type of modeling.
MODFLOW utilizes a numerical solution for the equation governing groundwater flow
through porous media.
Since its original release, various new packages and its compiled versions for various
computer platforms and PC configurations are already available. Several integrated, user-
friendly pre- and post-processing software packages for MODFLOW that provide easy data
input and the modeling results can be shown in the form of contour maps and graphs.
4.2.3 Definition of Model Geometry
To define the size and shape of the model requires the identification of the model boundaries
and the selection of the model grid.
The model boundaries can be either of two types: the physical or real boundaries and the
hydraulic or artificial boundaries.
The physical boundaries includes well-defined geologic and hydrologic features the strongly
influence the pattern of groundwater flow. Examples are impermeable contact between two
geologic units or a fault. Real physical boundaries are preferable as external model
boundaries unless they are not possible because of scale limitation. If so, the hydraulic
boundaries need to be defined.
Hydraulic boundaries are artificial boundaries that a model designer chooses. They are
derived from groundwater flow nets. They can be no-flow boundaries represented by
selected flow lines or boundaries with known hydraulic head represented by equipotential
lines or water level contour lines. These boundaries are not the most desirable because
their location can change in time. However, if they should be located far from the area of
interest so that they cannot influence the future flow pattern created by the projected
activities such as pumping.
The actual model design starts with the laying out of the grid. In MODFLOW, the grid is
formed by two sets of parallel lines that are orthogonal. The blocks are called cells; the
center of the cell is the node where the model assigns the hydraulic head. It is assumed that
the hydrogeologic properties are uniform over the extent of the cell as represented by the
node. MODFLOW uses this block-centered grid.
The grid can be uniform where all the cells have the same dimension or custom where cell
site varies. A uniform grid is preferred when available data on aquifer characteristics are
evenly distributed over the model area. Or the entire field is equally important to achieve the
objectives of the modeler.
20
The custom grid is often used when little or no data is available in certain parts of the model.
Generally, a custom grid can greatly reduce computational time by decreasing the model
size. The areas of interest are discretized into smaller cells which give them more weight
and make the model with greater accuracy while the distant portions of the flow fields are
described with fewer and larger cells thus reducing the size of the model.
In designing the grid size, modelers follow a rule of thumb. The size of a cell in all three
dimensions (row, column, layer) cannot be more than 1.5 times larger or smaller than the
size of the adjacent cell.
In truly isotropic aquifers, the grid orientation is not critical. However, when the hydraulic
conductivity varies widely, the grid should be oriented to minimize the number of inactive
cells.
MODFLOW recognizes and solves for different types of layers. It can simulate confined
aquifer conditions where the transmissivity of each cell remains constant for the entire
simulation run. A second layer type is used for unconfined aquifer conditions and is usually
valid only for the uppermost layer.
Another layer type is used when the aquifer alternates between confined and unconfined. It
is assumed that minimal desaturation will occur during the simulation period.
4.2.4 Input of Model Parameters
The model parameters are divided into three groups, namely: a) time, b) space (layer top
and bottom), and c) hydrogeologic characteristics such as hydraulic conductivity,
transmissivity and storage parameters.
When modeling transient (time-dependent) conditions, time parameters are specified
beforehand. They include time unit, the length and number of time periods and the number
of time steps. During any one time (stress) period, all model parameters associated with the
boundary conditions and various stresses remain constant. Using more time periods allows
changes in the parameters. More time steps increases the accuracy of the iterative
computations.
The elevation of the layer top and bottom is required if the user wants the program to
calculate aquifer transmissivity and vertical leakage. MODFLOW reads the top and bottom
elevations for the unconfined-confined layer type. Hydraulic conductivity is needed only
when modeling unconfined aquifers. MODFLOW calculates the transmissivity by multiplying
the hydraulic conductivity with the saturated thickness. In all other cases or layer types, the
transmissivity and storage coefficient is specified by the user.
The most relevant modeling parameter is the hydraulic conductivity. It is desirable to use
realistic values derived in the field through pumping tests. A modeler can create meaningful
modeling results if he can vary hydraulic conductivity to closely resemble the actual field
data. It is commonly assumed that the vertical hydraulic conductivity is at least one
magnitude lower than the horizontal hydraulic conductivity for most stratified sedimentary
rocks.
Storage coefficient for confined aquifers and specific yield for unconfined layers is required
for transient simulations only.
4.2.5 Definition of Boundary Conditions
Although MODFLOW assumes a no-flow boundary or a boundary with the flow set to zero
around the perimeter of the grid. If the modeler's intention is assign one or more model
edges with some other boundary type, this must be done by assigning boundary conditions
to the last cells along the grid edge.
21
4.2.6 Definition of Initial Distribution of Hydraulic Head
Initial conditions specify the values of the hydraulic head for each active and constant-head
cells in the model. The iterative model calculations require that initial hydraulic head should
be higher than the elevation of the cell bottom. For transient conditions the initial hydraulic
head should approximate the head distribution obtained from field data. For steady state
conditions, only the hydraulic head in constant-head cells must be the actual values.
Once the model is calibrated, the resulting distribution of hydraulic heads will then be the
new set of hydraulic heads for the prediction phase. This can be performed several times
during the calibration in order to reduce the calculation time.
4.2.7 Definition of the Stresses Acting Upon the System
Aquifer stress refers to any recharge to or withdrawal from the aquifer system. MODFLOW
addresses these stresses through several packages such as, the Drain Package, the River
Package, General Head Boundary Package and the Well Package. Particularly relevant to
the current project is the Well Package. It simulates both extraction and recharge wells.
Although it assumes full aquifer penetration, it can also be used for partially penetrating
wells. It is a good tool for modeling lateral flow into and out of the layer.
4.2.8 Calibration and Sensitivity Analysis
Assuming that all the model parameters are correctly assigned to each cell, the user must
choose the “solver” packages, specify the calculation parameters and select which model
results will be saved. The most common criterion for the solvers is the head change and
the maximum allowable iterations. The iteration process stops when the maximum absolute
value of hydraulic head change is less than or equal to the head change criterion.
To determine which parameters are more sensitive to changes with regard to the final model
result, calibration should be performed. Calibration is the process of finding a set of
boundary conditions, stresses and hydrogeologic parameters which produces the result that
most closely matches the field measurements of hydraulic heads and flows. The calibration
involves numerous single and multiple changes of model parameters. In most cases, the
quality of the calibration depends on the amount and reliability of the available field data.
The field data should also be assessed for consistency, homogeneity and measurement
error.
Calibration can either be manual or automated. However, the manual calibration is always
recommended. By changing parameter values and analyzing the corresponding effects, the
modeler develops a better feeling for the model and the assumptions on which the design is
based. During manual calibration, boundary conditions, parameter values and stresses are
adjusted for each consecutive model run until the calculated heads match the pre-set
calibration targets. At this time, the user should work more closely with parameters that are
determined with less accuracy or assumed and change only slightly those that are more
certain.
The automated method of calibration has not gained much ground because it involves
substantial knowledge of statistics. The package PEST is probably the most appropriate
calibration method available in the MODFLOWFLEX program, if coupled with manual input
from the user.
4.2.9 Verification of Model Validity
A model is verified “if its accuracy and predictive capability have been proven to lie within
acceptable limits of error by test independent of the calibration data”. Verification is
22
performed for an additional field data set in either steady state or transient simulation. If the
calibrated model parameters such as boundary conditions, stresses and distribution of
hydrogeologic characteristics are correct, this additional field data set should be closely
matched by the model for the new boundary condition and stresses.
23
5. The Groundwater Flow Modeling for Iloilo Basin
5.1 Model Design
5.1.1 Concept Development
After creating several geologic cross sections (Figures 5.1) using the driller’s logs of the
boreholes, it was evident that confined or artesian aquifers underlie and dominate the study
area. The observation was further enforced by the drop in the water level of previously free-
flowing wells In San Miguel. It appears further that only the truly shallow wells (depth < 10
meters) draw water from water table or unconfined wells. Please note that the water level in
wells invariably stand at a level higher than the top of well intake structure.
On this basis, a two-layer model was created. The model features the generally clay layer at
the surface and the confined aquifer at the bottom.
5.1.2 Computer Code
MODFLOW Flex which is a finite-difference flow model program was selected as the
computer code for this undertaking. It was originally developed by Michael G. McDonald
and Arlen W. Harbaugh of the United States Geological Survey (USGS) in 1988. The model
program uses a modular structure wherein similar program functions are grouped together,
and specific computational and hydrologic options are constructed.
The division of the program into modules permits the user to examine specific hydrologic
features of the model independently. This also facilitates the development of additional
capabilities because new packages can be added to the program without modifying the
existing packages. The input and output systems of the computer program are also
designed to permit maximum flexibility.
Groundwater flow within the aquifer is simulated using block-centered finite-difference
approach. Layers can be simulated as confined, unconfined or a combination of confined
and unconfined. Flow related to external stresses, such as wells, areal recharge,
evapotranspiration, drains and streams can also be simulated.
5.1.3 Model Geometry
Since the available data is few and concentrated mainly in the southern part of the basin, it
was decided that a custom or deformed grid would best represent the model. The model
(Figure 5.2) is oriented in the northwest direction nearly parallel to the orientation of the
rivers within the study basin.
5.1.4 Model Parameters
Static water level measurements shown in the Well Data Summary (Annex 2) span a few
decades and only a few were taken within the last year. Only the most recent data were
utilized. The recorded water levels from previously free-flowing wells in San Miguel were
ignored because these wells no longer exist.
Monitoring reports from the Coca Cola plant in Pavia indicate fluctuations in the static water
levels in the range of less than 3.0 meters.
24
To estimate the transmissivity (T) of the aquifer, the specific capacity values (discharge
divided by the drawdown) were plotted on semi-logarithmic paper against the calculated
transmissivity values from pumping tests. The T values were obtained from the graph
(Figure 5.3). These T values were then plotted on the working map and contoured to create
an iso-transmissivity map (Figure 5.4).
5.1.5 Boundary Conditions
From the piezometric surface map (Figure 5.5), flow lines were drawn to create orthogonal
flow net. No flow boundaries at the perimeter were set up along flow or streamlines, while a
constant head boundary marked the northwestern edge of the modeled area. No head
changes are expected in the Alimodian area.
5.1.6 Initial Distribution of Hydraulic Heads
The initial distribution of hydraulic head is shown in Figure 5.6. This map represents steady
state condition for the groundwater model.
5.1.7 Stress Applied to Water System
Simulation of pumping stresses was made using the existing MIWD wells. The applied
pumping rates range from 13 to 25lps.
5.2 Modeling Results
Upon application of the pumping stresses mentioned above, the simulated changes in the
hydraulic head are presented in Figures 5.7A to 5.7F. The first three figures (Figures 5.7A to
5.7C) present how the hydraulic head will vary when the wells are pumped at the rate of
20lps for pumping durations of 1 year, 10 years and 20 years. The simulated hydraulic head
are shown in Figures 5.7D to 5.7F when the pumping rate is increased to 25lps.
Another set of diagrams (Figures 5.8A to 5.8B) was prepared to show the simulated change
in hydraulic head for a scenario with additional wells pumped at 20 and 25 L/s for durations
of 1, 10 and 20 years. To create reference points for the changes that may occur at different
pumping times, three points were selected around the proposed well field. The simulated
changes in the hydraulic heads as compared to steady state conditions at these points are
tabulated in Table 5.1.
Table 5.1: Simulated Hydraulic Head Around MIWD Well Field with Additional Wells
Pumping Rate Duration Simulated Hydraulic Head (mamsl)
of Wells (L/s) (years) A B C
1 0.19 0.16 0.23
20 10 0.65 0.74 1.24
20 0.69 0.91 1.48
1 0.21 0.17 0.24
25 10 0.75 0.75 1.34
20 0.85 1.02 1.67
Notes: Point A is 3 km north of EW-2
Point B is 3 km east of EW-6
Point C is 3 km southeast of EW-4
The modeling results indicate that after prolonged pumping at rates exceeding 20 L/s, the
water levels in the MIWD well field will not be significantly lowered.
27
5.3 Implication of Modeling Results on the Hydrogeologic Condition at the Lower

Basin
It must be emphasized at this point that uninterrupted pumping is not practiced in reality.
Seldom does 24-hour pumping occur. In most cases, the pump and the well are rested for a
few hours daily. In effect, then the water level is allowed to recover. Thus, the stipulated
pumping duration in the simulation would likely be greater. A pumping duration of 1 year can
mean about 1.5 years in actuality.
Given these results and considering further that the current discharge rates of the MIWD
wells are very much less than 25lps, the change in hydraulic head in the MIWD well field
would also be smaller.
With respect to the possibility of drawing sea water into the aquifers being tapped by MIWD,
the existing wells are at least 6 km away from the shoreline. At this distance, the drop in
hydraulic head at the current pumping rates and even for pumping durations greater than 10
years will not reach mean sea level. In other words, the operation of the MIWD wells will not
induce salt water intrusion into the inland aquifers.
44
6. Groundwater Management Plan
6.1 Groundwater Basin Management Strategy
The Groundwater Management Plan is intended to be a roadmap and planning tool that
builds directly on the groundwater basin assessment and addressing identified challenges.
This involves: 1) the protection of natural recharge and use of artificial recharge; 2) planned
variation in amount and location of pumping over time; 3) use of groundwater storage
conjunctively with surface water from local and imported sources; and 4) protection and
planned maintenance of groundwater quality (California State Department of Water
Resources). The Plan will identify groundwater management problems and formulate
feasible management measures/interventions and actions to these problems. It will also
include a timetable for implementation of the measures/interventions.
This Plan is divided into 3 phases, Immediate (2015 to 2016) following the timeline of the
Philippine Development Plan (2011-2016), Short-term (2017 to 2022) and Long-term (2013
to 2028). The first 2 years (Immediate phase) are dedicated to reinforcing the existing
implementation activities, the next 5 years (Short-term phase) are for strengthening and
provision of support mechanisms, and another 5 years (Long-term) are for increased
knowledge and use of groundwater along with capacity and awareness to ensure
sustainable management tailored to local needs.
Prior to developing strategies, the problems/challenges identified (refer to sub-section 3.2)
and the results of the modeling were used with the end view of improving groundwater
management through focus interventions or actions to address these challenges of the area.
The Plan adopts a practical and simpler but no less viable groundwater management plan by
adhering to the general principles in the wise use of groundwater, as described below (Table
6.1).
6.2 General Principles in the Wise Use of Groundwater
The principles advocate action plans that do not need highly sophisticated management
techniques or costly facilities.
 Development of technologies that will enhance the storage capacity of groundwater
reservoirs.
 Maximize the safe yield over the long term.
 Perennial overdrafts of groundwater supplies should not be tolerated.
 Resource augmentation or artificial recharge.
 Conservation and reallocation of resources
 Protection of groundwater quality.
 Minimize the adverse effect of man's activities on groundwater quality.
Prevent excessive use of groundwater in coastline as it permits salt water
intrusion.
 Adopt engineering intervention to prevent wastes or leachates from
contaminating the ground water.
 Utilization of groundwater resources for their most valuable or highest use to society.
This means that all activities must be directed to:
 Use drinking water wisely, not to pollute it;
 Establish an integrated water resources management based on water as an
integral part of the ecosystem and as a limited natural resource that must be
protected in quantity and quality;
45
 Increase the availability of water resources;

 Integrate the management and operation of water supply, sanitation and solid
waste disposal to minimize adverse environmental impact on water;
 Avoid inconsistency and contradiction between different areas of
governmental and regulatory actions concerning environmental protection;
 Collaborate and exchange knowledge and experience on local and regional
levels; and
 Improve education and training of personnel to ensure proper operation and
maintenance of water supply facilities and management.
6.3 Specific Action Plans
Specific action plans should ensure that:

 groundwater used for irrigation should be used wisely and efficiently;
 urban water supply systems should be well-maintained, metered and with minimal
line losses;
 price of water should correlate with the cost of supplying water;
 conservation of groundwater resources should be a continuing commitment, not only
during drought periods.
 water demand management, such as reuse and recycling of wastewater; and
 land use priorities are established to ensure the protection of water quality.
Some examples of action plans that relate to the development of sustainable water supply
and environmental protection follows:
 monitoring station networks for water quality of surface and ground water;
 awareness campaign and public education for water resource protection;
 use of marginal-quality water and treated sewage for agriculture and non-drinking
purposes;
 creation and efficient control of protection zones for surface and ground water;
 prevent potential pollution by artificial recharge; and
 promotion of schemes for rational water use.
6.4 Rainwater Harvesting
In order to reduce the demand on piped water, rainwater harvesting can be employed by
residential units as well as commercial establishments. Parking lots of malls may be used to
collect storm runoff that can recharge the shallow aquifers. Storm drains can be devised
such that the runoff is given time to infiltrate into the ground rather than discharge to rivers or
the sea.
In Seoul, South Korea, the city government has passed an ordinance that requires new
buildings to construct three-chambered cisterns to collect rainwater. The water will be
released only after the rain stops. In this manner, flooding during rains can be minimized.
However, some of the collected rainwater may also be utilized for non-potable uses, such as
watering plants or flushing toilets.
46
Table 6.1: Summary Matrix Control, Groundwater Management Action Plan, Iloilo City and Surrounding Areas
Problems: Weak implementation of existing strategies and policies on groundwater management such as the rules and regulations spelled out in the Water Code
Outdated and incomplete hydrogeological and hydrological databasing
Unregulated utilization of groundwater, particularly for domestic (households), commercial water delivery and industrial uses
Intrusion of seawater as observed in the coastal areas of Iloilo City, Leganes and Oton
Absence of regular monitoring of groundwater withdrawal, water level and quality
Lack of enabling environment, such as local legislation adopting the Water Code of the Philippines and Clean Water Act to support groundwater management
Inadequate effective assessment, planning and management of groundwater resources
Lack of technologies to enhance storage capacity of reservoirs
Inadequate personnel, capacity and resources to fulfil the mandatory groundwater resource management functions
Lack of a communication plan focussing on promoting “best practices” on groundwater use and management
Absence of harmonization of an integrated water resources management approach and climate change adaptation to groundwater resource planning for sustainable infrastructure (climate
proofing)
Time Frame: Immediate: 2015 – 2016
Implementation of recommendations
- Continued implementation of the rules
and regulations of the Water Code and
drawn from the monitoring and
evaluation reports and strict
other national laws on conservation and - Increased compliance to the rules
protection of groundwater resource and regulations of the Water Code,
compliance/adherence of the rules and
1) Strengthen enforcement of existing laws, - Revision of monitoring programs specifically the permitting system
regulations of the Water Code
policies, guidelines and appropriate considering previous experiences - Updated data on records on the
implementing rules and regulations relevant compliance of the Water Code
Generation and validation of most recent 2015-onwards
to groundwater management, specifically Data collection on existing groundwater including updated information on
information of wells
the Water Code infrastructures existing groundwater infrastructures
Conduct of quarterly monitoring and
updating reports including non-compliant
Monitoring and updating of information users/owners, issues/violations resolved
(for compliance monitoring)
47
- Maintain a comprehensive database

on the hydrogeology and hydrology of
the Iloilo basin
2) Updating of groundwater and surface water - Complete inventory of existing wells Generation of quarterly reports including Database with updated information
database to be filled-up with the required and selective field tests to determine performance of existing wells filled in 2015-onwards
information in the form the aquifer characteristics
- Complete inventory of surface waters
to include information on discharges
- Wise efficient use of groundwater for

irrigation
3) Regulated extraction of groundwater to Promote efficient use of groundwater Database on groundwater withdrawal
protect and conserve the resources of the specifically for irrigation where 75% of - Urban water supplies well-maintained -do-
study area the water is used for agriculture with minimal losses
- Land use priorities are established to
ensure protection of water quality
Time Frame. Short-term: 2017 – 2022 2/

- Regulated use of groundwater along Studies for various options
1) Address salt water intrusion problem in the
coastlines - Control through issuance of permits to recommended
- Recommendations of appropriate construct wells in the area 2017-2022
coastal areas of Iloilo City, Leganes and
Oton 1/ technology and siting considerations - Identification of appropriate
for problem areas technologies that will be recommended
- Conduct of monitoring and regulating

the extraction of groundwater to
cover withdrawal, water level and
2) Regular monitoring of groundwater quality Database on groundwater withdrawal,
Generation of quarterly monitoring reports 2017-onwards
withdrawal, water level and quality 1/ - Establish monitoring station network water level and quality
for groundwater levels and water
quality of surface and groundwater
48
- NWRB to provide advisory services to

the working committee formed at the City/Municipal Ordinances adopting the
3) Creating an enabling environment through Assistance provided to the LGUs in local level to take charge of coordinating Water Code of the Philippines, Clean
LGUs, such as local legislation adopting the drafting local legislations so that LGUs activities related to groundwater
Water Act and Ecological Solid Waste 2017-2022
Water Code of the Philippines and Clean shall endeavor to formulate regulatory management
Water Act to support groundwater Management Act to support groundwater
management
policies - If necessary, attend Sangguniang
management
sessions during presentation of the
ordinances for approval of the
Sangguniang Bayan or Panlalawigan
Time Frame. Long-term: 2023 – 2028 1/

- Monitoring of groundwater withdrawal,
water level and quality (can be
Establishment and control of protection integrated to self-monitoring report,
zone around groundwater abstraction (SMR) to Environmental Management
1) Effective assessment planning and Policies on the establishment and control
points especially the MIWD well fields to Bureau) 2023-2024
management of groundwater resources of protection zone
control over-exploitation and
groundwater pollution - Updating of the groundwater flow model
- Delineated areas where groundwater
level significantly declining
Verify the following:
- Presence of adequate permeability,
thickness, and lateral extent to satisfy
the desired performance criteria
- for the artificial recharge facility
Guidelines on Artificial Recharge to
2) Development of guidelines on groundwater - no geochemical reactions would occur Groundwater to include planning,
management such the artificial recharge Study viability of artificial recharge that adversely impact aquifer water 2023
techniques and design, and monitoring,
strategy quality mechanism
- availability to provide the required
additional groundwater recharge
- construction, operation and
maintenance of the artificial recharge
project are technically feasible
3) Enhance technical capacity of personnel to Conduct of workshops, trainings and
fulfill the mandatory groundwater - Implementation of capacity building seminars covering topics on regulatory
Seminars, Workshops and Trainings 2023-onwards
49

management function milestones compliance, technology, and monitoring
- Implement practical, in-service
training courses on permitting
process, groundwater monitoring ,
etc. for staff
- Conduct of NWRB-LGU workshops on

policies/strategies (permit requirements,
abstraction regulations, pollution, etc) to
- Compilation of “best practices” and improve enforcement of existing rules
4) Prepare and implement a communication developing guidelines on and regulations
and awareness plan promoting groundwater groundwater management - Conduct of stakeholder’s forum, i.e., Documentation of workshops,
management utilizing “best practices” of - Conduct of information, education users dialogues to disseminate consultations and the corresponding -do-
actual implementation as opportunity to and communication campaigns and information on enforcement, encourage IEC materials used
enhance awareness consultation forum among voluntary compliance of regulations,
stakeholders and adopting ”best practices” to
promote conservation and protection of
the groundwater resources
IWRM, environmental protection and

5) Harmonization of IWRM approach and Incorporation of the IWRM and climate
climate change adaptation to groundwater
climate change considered in enhancing
change adaptation issues and concerns in
- Projects implemented to mitigate
the integrity of water resources and the impacts of a changing climate -do-
resource planning and design for the design to be adopted as well as on the
provisions of sustainable infrastructure - Watershed areas preserved r
sustainable infrastructure (climate proofing) options to be considered for implementation
during the planning and design stage.
Notes: 1/ = Depending on available resources including manpower, NWRB can start the implementation of these activities early on.
50
Bangladesh has also introduced a new regulation that requires new houses with a roof area
of more 200 sq. m. to provide for rainwater collection facilities. The collected rainwater will
be used to recharge the groundwater system and so prevent salt water intrusion in coastal
areas.
If suitable areas can be acquired or be made available near the coastline, artificial recharge
through rainwater harvesting can help build a water barrier that could prevent further
incursion of sea water inland. Studies on how where these courses of action will be
implemented should be considered.
6.5 Conjunctive Use of Surface and Ground Water
Since the amount of the groundwater that MIWD supplies to its customers consists only of
about 20% of its total water supply, it should consider reducing further the groundwater
abstraction during rainy months and only to supplement the surface water during peak
hours. MIWD may have to increase the amount of the surface water supply by expanding
the water treatment facilities. The surface water supply will then be utilized to the maximum
while the groundwater system will be allowed to recover.
6.6 Increase Storage of Shallow Aquifers
Shallow wells that are readily recharged during the rainy season may be used widely during
the dry season. Lowering the water level in the shallow aquifers creates a greater storage in
the subsurface that can accept more rainwater infiltration during the rainy periods.
6.7 Monitoring System
Effective groundwater management requires a regular monitoring system at least twice a

year – at the onset of the rainy season and again at the end of the rainy season. The
management of groundwater resources using computer simulation also requires accurate
groundwater levels and quality.
A database system that processes meteorological and hydrological data, well inventory,
groundwater level, water quality and well performance must be maintained to supplement
the data obtained from monitoring system and other agencies like the NWRB, LWUA and
water districts.
Well sites have been selected for groundwater monitoring (water level and quality). The
proposed groundwater monitoring well network encompasses areas where heavy
exploitation is currently occurring. But areas at the fringes, which are relatively less
exploited, are also considered to determine extent or progression of water level decline and
water quality deterioration.
Six (6) sites were selected for monitoring well installation (Figure 6.1). These sites provide
wide distribution of wells across the study area and based on hydrogeological (physical and
chemical) conditions. The sites more or less follow the general flow of surface and
groundwater. .
Final well locations will ultimately depend on landowner permission, and availability of fund.
The monitoring points should be as close as possible to the recommended sites.
For areas near the coast, it is proposed that the existing boreholes of the Panay Power can
be utilized. Hence, no investment is necessary. Collaboration of the power generation firm
should be sought by NWRB. Initial talk to the company was positive and NWRB just need to
make follow up and finalize agreement.
51
Table 6.2 provides few details of the proposed groundwater monitoring well locations, while
Annex 3 and Annex 4 present the technical specifications for the construction and
preliminary designs, respectively, of the groundwater monitoring wells.
6.8 Modification of Groundwater Model
Groundwater simulation models that may be generated at present should be improved in the
future. Additional information about the hydrogeology of Iloilo basin, the groundwater extraction,
more accurate aquifer parameters and updated water levels will certainly be useful in preparing
a more representative groundwater model. It will then be used or effectively as a predictive
management tool.
In the execution of the management plan, several constraints have been identified that may
affect the effectiveness of the specific action plans, namely:
 The lack or shortage of trained and experienced hydrogeologists in the region may
result in higher unnecessary costs for developing water supplies or protecting water
quality. They are needed to support or strengthen the organizations that shall
implement the groundwater management plan.
 The complexity of most groundwater environment prevents easy or cheap solutions
to groundwater quality and supply problems.
 Increased demands of groundwater supplies forces a shift in how groundwater is
used. Prioritizing water demand may cause economic dislocation if not done
properly.
It should be reminded that in the past, activities administered by committees sometimes do not
materialize because of the parochial attitude of some members of the committee. They should
realize that the implementation of the groundwater management plant is a collective and
cooperative effort. Information, data and ideas that may be useful in the implementation of the
management plan should be shared among all the members. The committee can then finally
make informed decisions that will meaningful to the task at hand.
There is the imperative need to upgrade and update the groundwater database. The present
effort to develop a groundwater management plan based on the modeling of the hydrogeologic
conditions in Iloilo had been hampered to a large extent by the use of secondary data available
at the NWRB. The data is generally outdated and sometimes unreliable. There had been no
effort to verify or validate the information that was submitted by well owners to the NWRB.
Since the NWRB files are often several years old, the preparation of a groundwater model for a
particular area should be preceded by a thorough well inventory and selective field tests to
determine the aquifer properties. Slug tests may be cheap and simple and can provide some
quantitative values that may be useful in the modeling.
6.9 Climate Change Mitigation
First and foremost, the watershed areas must be preserved at all costs and at all times. Aside
from the disastrous effect of climate change, destructive human activities in the watershed areas
should be curbed if not totally abolished.
Siltation dams may be constructed along the slopes of watershed areas to minimize soil erosion.
Deep-rooted trees and such weeds as vetiver may be planted to hold the soil cover. They can
withstand typhoons and are effective erosion control measures.
The water storage in shallow unconfined aquifers are the first to show the effects of climate
change. Small handpumps will often break suction when the water level drops. However, these
aquifers are also the first to recover at the onset of the rainy season. If such cyclic events
52
repeatedly occur, the pumps may have to be replaced with reciprocating (jack) pumps that can
operate at deeper levels.
The shallow ground water may also be utilized to the maximum before the rainy season by
deliberately lowering the water table. A greater storage will result. It can be readily replenished
during the rainy season. This scheme can be applied to rice lands.
6.10 Enabling Environment
To realize all the above proposals for the management of groundwater in Iloilo, it is necessary to
put in place enabling policy environment. Cooperation among the LGUs is needed to implement
the proposed management plan. These can be made through legislations.
6.11 Institutional Arrangement
Participatory groundwater management is encouraged. The plan is envisioned to be

implemented by a “task force” to be composed of representatives of the local government units
(LGUs), national government agencies in the region, water districts and other responsible
stakeholders. The representative of the NWRB will sit in as adviser to the group. The task force
will formulate policies and coordinate the action plans related to the main groundwater
management plan.
There are two water quality management areas that cover the study area, the Tigum-Aganan
Watershed and Iloilo-Batiano River System Water Quality Management Areas (WQMAs).
These were officially designated through DENR Administrative Orders (DAO) Nos. 2006-18 and
2009-11, respectively. The DAO also created the governing boards for the above WQMAs.
These governing bodies can also oversee the management of the groundwater as the boards
are represented by stakeholders from different sectors. This is a scaling up scheme of the
WQMA’s, which at present covers only surface waters.
The organization that shall be formed to implement the groundwater management plan should
maintain a comprehensive database on the hydrogeology and hydrology of the Iloilo basin. The
data must include the location and depth of the wells, well construction details, water levels and
well yield and water quality.
53
Table 6.2: Proposed Groundwater Monitoring Wells

Well Geopolitical Geographic Coordinate
Geology Land Use Remarks
ID Location Northing Easting
Highly exploited area, close to Calajunan Dump Site and Pavia
Cabolo-an, Residential and industrial zone, for monitoring advance of groundwater level
MW 1 122° 28’ 51.8” 10° 44’ 30.0” Recent Alluvium
Oton industrial decline and domestic/industrial pollution, and ambient water
quality
For monitoring domestic and industrial pollution, for monitoring
Residential and
MW 2 Pavia 122° 32’ 32.27” 10° 47’ 45.64” Recent Alluvium advance of groundwater level decline and domestic/industrial
industrial
pollution, and ambient water quality
Recent
Less exploited and less anthropogenic activities, for monitoring
MW 3 Cabatuan 122° 29 4.53” 10° 52’ 37.80” Alluvium/Cabatuan Agricultural
agricultural pollution and ambient water quality
Formation
Recent
Less exploited and less anthropogenic activities, for monitoring
MW 4 Alimodian 122° 26 14.98” 10° 47’ 12.67” Alluvium/Cabatuan Agricultural
agricultural pollution and ambient water quality
Formation
MW 5 Oton 122° 30 41.51” 10° 42’ 26.44” Recent Alluvium Residential for monitoring sea water progression and ambient water quality
Recent Alluvium/
Residential and For monitoring domestic, agricultural pollutants and ambient water
MW 6 San Miguel 122° 29’ 02.40” 10° 48’ 28.80” Cabatuan
Agricultural quality
Formation
55
GROUNDWATER MANAGEMENT PLAN
References
Water Quality Status Report 2010; Governing Board, Iloilo-Batiano River System Water
Quality Management Area, Region VI.
Water Resources Master Plan, Metro Iloilo Water District, LWUA-UNDP-SWECO, 1997
Lexicon of Philippine Stratigraphy, Rolando Peña, 2008
Philippine National Standards for Drinking Water 2007, Department of Health Administrative
Order No. 12 Series of 2007
www.philgis.org; Regional, Provincial, City/Municipal and Barangay Boundaries and Land

Contours
Shuttle Radar Topographic Mission (SRTM); NASA; Digital Elevation Model (DEM); 2007
www.openstreetmap.org; Roads; 2012
56
Annex 1: Summary of Water Quality Analysis
Well No. 9 Well No. 10 PNSDW

Date Sampled 01-02-12 02-06-13 01-02-12 02-06-13
Parameters * ** * **
Physical Analysis
Turbidity (TCU) 3 0.65 1 0.68 5
Color (CU) 23 25 5 5 5
Electrical Conductivity (μs/cm) - 1,125 - 649
Chemical Analysis
pH 8.03 8.09 7.59 7.53 6.5-8.5
Alkalinity (mg/L as CaCO3) - 306 - 306
Acidity (mg/L as CaCO3) - 9 - 9
Hardness (mg/L as CaCO3) - 206 - 414 300
Total Dissolved Solids (mg/L) 844 615 518 347 500
Calcium (mg/L) - 83 - 77
Magnesium (mg/L) - 15 - 56
Carbonate (mg/L) - 0 - 0
Bicarbonate (mg/L) - 373 - 373
Chloride (mg/L) 205.5 196 48.1 34 250
Nitrate (mg/L) <0.1 2.0 <0.1 1.1 50
Sulfate (mg/L) 9.5 5.3 5.2 3.5 250
Benzene (mg/L) - Nil - Nil
Metal Analysis
Iron (mg/L) <0.05 Nil <0.05 0.07 1.00
Manganese (mg/L) <0.05 0.01 <0.05 0.02 0.40
Cadmium (mg/L) <0.01 Nil <0.01 Nil 0.003
Lead (mg/L) <0.05 Nil <0.05 Nil 0.01
Arsenic (mg/L) <0.01 Nil <0.01 Nil 0.05
* Tests performed by SGS
** Tests performed by Platinum Research Laboratory
Annex 2: Well Data Summary
Annex 3: Technical Specifications for the Construction of Groundwater
Monitoring Well
1. Mobilization and Demobilization
This includes mobilization of drilling machine, personnel and materials, and set the equipment
up to the well site. It also involves site clearing, temporary access (if necessary) and setting
up of camp for the drilling crew.
Demobilization includes removal of the base camp, cleaning the site and moving the drilling
unit and all other equipment, materials and personnel from the drill site to the place of origin.
2. Personnel, Drilling Equipment and Safety Equipment
The Contractor shall provide capable and experienced personnel and suitable rotary drilling
machine, drilling bits and appurtenances to perform the work.
The Contractor shall take all reasonable precautions to prevent any death or injury to
persons. These shall include but not be limited to fencing of the work sites, providing workers
with necessary safety apparels such as helmets, hard-toed boots, eye-protector, ear plugs
and gloves, ensuring that all plant, tools and equipment are in safe condition, and implement
safety policies in and out of working place.
The Contractor shall ensure that his workmen have access to first aid equipment, protective
clothing and helmets to the reasonable satisfaction of the workmen and approved by the
Consultant.
The Employer (NWRB) shall not be liable for any damages or compensation as a result of
accident or injury to any workers employed by the Contractor or any sub-Contractor unless
such accidents or injury is caused by an act or default of the Employer or of nominated
representatives of the Employer.
The Contractor shall comply with local authority regulations applicable to the use and storage
of diesel, petrol, paraffin fuel and lubricating oil used at the work site or stored at the base
camp, and shall ensure that adequate precautions are taken against fire and environmental
contamination.
Before the order to commence any works, the contractor shall submit an Environmental
Management Plan (EMP) for the project. The plan shall spell out how the contractor should
maintain the environment at original state as specified in the EMP. It shall include, to the
extent practicable and reasonable, all steps to be taken by the Contractor to protect the
environment in accordance with the current provisions of national environmental regulations.
Notwithstanding the contractor obligation under the above clause, the Contractor shall
implement all measures necessary to restore the sites to acceptable guidelines and abide by
environmental performance indicators specified under the EMP to measure progress towards
achieving objectives during drilling or upon completion of any works. These measures shall
include but not limited to the following:
(a) Minimize the effect of dust on the surrounding environment resulting from drilling, and
other related works to ensure safety, health and the protection of workers and
communities living downwind of drilling site.
(b) Ensure that noise levels emanating from drilling equipment, vehicles and noisy
borehole construction activities are kept at a minimum for the safety, health and
protection of workers and communities within the vicinity of drill site.
(c) Ensure that existing water flow regimes in rivers, streams and other natural or
irrigation channels is maintained and/or re-established where they are disrupted due
to drilling works being carried out.
(d) Prevent bitumen, oils, lubricants and wastewater used/produced during the execution
of works from entering into rivers, streams, irrigation channels and other natural water
bodies/reservoirs and also ensure that stagnant water in uncovered borrow pits is
treated in the best way to avoid creating possible breeding grounds for mosquitoes.
(e) Prevent and minimize the impacts of drill cuttings and building of temporary
construction camps and access roads on the biophysical environment including
protected areas and arable lands; local communities and their settlements. In as
much as possible restore/rehabilitate all sites to acceptable standards.
(f) Upon discovery of ancient heritage, relics or anything that might or believed to be of
archeological or historical importance during the execution of works report such
findings to National Museum in fulfillment of the measures aimed at protecting such
historical or archaeological resources.
(h) Implement drill cutting control measures in order to avoid surface run off and prevents
siltation etc.
(h) Ensure that garbage, sanitation and drinking water facilities are provided in drilling
worker’s camp.
(i) Ensure that in as much as possible, local materials are utilized to avoid importation of
foreign material and long distance transportation.
(j) Ensure public safety and meet traffic safety requirements for the operation of work to
avoid accidents.
The contractor shall indicate the period within which it shall maintain status on site after
completion of the works to ensure significant perturbations arising from such works have been
taken into account.
3. Drilling of Borehole
A suitable rotary rig capable of drilling boreholes with the following schedules:
Well 1: Diameter – 150 mm

Depth: L = 100m, 1 hole
Well 2: Diameter – 150 mm

Depth: L = 45 m, 1 hole
4. Drill Cutting Sampling and Logging
During drilling, sample from drill cuttings shall be collected at one (1) lm interval or at every
change of rock type or colour material. The samples shall be logged by a geologist and the
record kept on a daily log sheet. The record should indicate:
(a) Lithology;
(b) Degree of consolidation or hardness; and
(c) If unconsolidated, nature of grounder material, i.e., subjective description of grain

size, degree of rounding, clay content, color.
The samples shall be prepared in polythene bags and accurately labelled with the name of
borehole, date and depth of sampling.
Also, accurate records of penetration rate per meter shall be maintained and included on the
daily log sheet. Other pertinent drilling data shall be recorded such as mud viscosity and
return water/water loss.
5. Geophysical Logging
Prior to monitoring well construction, geophysical borehole logging shall be carried out. The
electrical resistivity and self-potential (SP) shall be made for the two (2) boreholes.
6. Final Drilling Depth and Design
The Site Engineer has the responsibility for determining the final drilling depth, being aided by
indications provided by the geophysical survey and the analysis of the drill cuttings on site.
The boreholes shall be designed by NWRB or its Consultant. The design of borehole is site
specific and the Contractor shall be required to follow the design procedure and process
outlined by the NWRB. Each borehole shall be constructed by the Contractor as per the
design and all linings installed plumb and true to line such that all equipment to be used for
groundwater monitoring can be easily installed.
7. Casing and Screen (Slotted Casing) Installation
The boreholes shall be lined completely with high impact-resistant unplasticized Polyvinyl
Chloride (uPVC) casings and screens specifically manufactured for boreholes. The uPVC
shall have uniform colour and shall not have been directly exposed to the sun for long periods
or damaged in any form. All borehole lining materials shall be subject for inspection prior and
after delivery to the site.
The following are the tentative casing and screen schedule:
Material : uPVC Pipe

Inner Diameter: 75 mm
Blank Casing:
Well 1: L= 64 m
Well 2: L= 27 m
Screen (Slotted Casing) length:
Well 1: L= 36 m
Well 2: L= 18 m
Plain Casing
The casings shall be uPVC of new stock and have an inner diameter of 75mm (3ins.) and a
wall thickness of 7.5mm.
Screen
All screens shall be plant and machine slotted uPVC of new stock. The inner diameter and
wall thickness shall be the same as for the plain casing. The screen shall have a slot size of
0.5mm to 1mm depending on the aquifer material. The open area of the screens shall be at
least 10% of the surface area of the pipe.
Joints
All casings and screens shall have screwed flush joints. The threads must be sturdy, either
curved or angular with no eccentricity, to allow for easy handling.
Centralizers
Centralizers of suitable size (certified by the Site Engineer) shall be fitted to both casings and
screens at 12m intervals.
8. Filter Pack/Formation Stabilizer
The boreholes shall be gravel-packed as per design with clean, well rounded quartz gravel of
1-2mm grading. The gravel shall be placed within the annulus using approved method and
the level measured accurately before placing of the bentonite seal. Other material to be used
as gravel pack should be approved by the Site Engineer.
Filter pack seal shall be placed to prevent infiltration of grout slurry into the filter pack. The
filter pack seal consists of one (1) meter thick fine-grained sand cushion placed in the annulus
above the filter pack.
9. Bentonite Seal
The annulus between the borehole and casing from top of the gravel pack to the bottom of the
cement grout seal shall be filled bentonite pellets or slurry. No drill cutting or imported clay
material shall be used for this purpose.
For dry bentonite sealing, to reduce the potential for bridging, use chips or pellets that are
less than one-fifth the diameter of the borehole or the width of the annular space into which
they are being placed.
For bentonite slurry, use granular sodium bentonite containing no additives, mixed according
to the manufacturer's directions, to a minimum mud weight of at least 9.5 pounds per gallon,
and containing at least 15 to 20 percent solids. Use mixing methods which prevent the slurry
from being excessively lumpy.
10. Well Development
The Contractor shall develop the well as will effectively clean the walls of casings and screens
and extract from the water bearing formation the maximum practical quantity of sand, drilling
mud, mud cake and other fine sediments as may, during the life of the well, be drawn through
the screen when the well is pumped under maximum conditions of drawdown to a sand-free
condition.
Development of completed boreholes shall be carried out initially by surging with compressed
air and air-lifting. If the development is not complete, that is free from sand and clay, after 6
hours, further development will be carried out by horizontal jetting with suitable jetting tools
and air-lift pumping for at most 6 hours.
11. Aquifer Testing
Each borehole shall be tested for a minimum of 24 hours of after completion of development,
to determine aquifer characteristics. The constant discharge at a suitable rate approved by
the Site Engineer shall be carried out after the borehole has been rested for at least 12 hours
after well development.
Water levels in the pumped borehole shall be measured as follows:
- Every one minute for the first 10 minute of pumping;
- Every two minutes for the next 20 minutes of pumping;
- Every 5 minutes for the next 40 minutes of pumping;
- Every 10mins for the next 60mins of pumping;
- Every 20mins for the next 120mins of pumping; and
- Every 1 hour thereafter for the rest of the pumping period.
Recovery Test shall be carried out immediately on cessation of the of the constant discharge
test. The Contractor shall commence measuring the water level recovery in the pumped
borehole according to the same schedule as for the constant discharge test.
The actual time each reading is taken should be recorded.
12. Water Quality Analysis
A sample of water from each borehole shall be taken at the end of the constant rate test for
both physico-chemical and bacteriological analyses. The physico-chemical and
bacteriological analysis shall determine the following parameters:
Physical
Color, odor , electrical conductivity (EC)and total dissolved solids (TDS).
Chemical
pH, hardness, alkalinity, calcium (Ca), magnesium (Mg), sodium (Na), potassium (K),
bicarbonate (HCO3), sulphate (SO3), chloride (Cl), iron (Fe), manganese (Mn), nitrate (NO3),
nitrite (NO2), ammonium (NH4), , carbonate (CO3), dissolved oxygen, hydrogen sulfide (H2S),
+6
chromium hexavalent (Cr ), mercury (Hg) total, lead (Pb), arsenic (As), antimony (Sb),
cadmium (Cd), copper (Cu), zinc (Zn), aluminium (Al), selenium (Se), benezene, phenols, and
pesticides.
Bacteriologial
Total coliform, fecal coli, heterotropic plate count
13. Well Completion
The Contractor shall disinfect the borehole before borehole capping. Disinfection must be
carried out using calcium hypochlorite in powder or in tablet form. During the disinfection
process it must be ensured that the concentration of available chlorine in the well and filter
pack is at least 50 mg/l.
The borehole linings shall be completed 0.6 to 1.0m above ground surface and be protected
by steel casing and well head cap with a heavy duty lock anchored at concrete base.
The Contractor shall install a concrete base or pad of dimension 1m x 1m x 0.3m thick around
the monitoring well as specified.
The concrete used for the pad shall be prepared using normal portland cement with a mixture
of coarse and fine aggregate. The concrete shall meet the following specifications:
Fine aggregate: 0.15mm to 9.5mm

Coarse aggregate: 2.4mm to 40.0mm
Minimum cement content: 320kg/cubic meter
Compressive strength at 28 days: 25N/mm2
The concrete shall have a ratio of 1:2:4
Water used for mixing concrete and for curing shall be clean, and free from injurious amounts
of oil, acid, alkali, organic matter or other deleterious substance. It shall be equal to potable
water in physical and chemical properties.
14. Reporting
The report shall include 3 copies each of the following:
a. Daily drilling log showing all operations of the drilling and development machines,
materials used, personnel, casing measurement, etc. as employed;
b. The geological log giving the depth and logging record of all formations intercepted and
penetration rates;
c. A record of the assembly of casing, screen and centralizer as constructed;
d. Record of the filter pack, filter pack seal, bentonite seal and cement grout;
e. Records of all development work including static water level, pumping water levels,
methods and materials used, duration of each operation, personnel working hours.
f. All pumping records including a full description and duration of all operations.
g. Demobilization and Site Clean-up – The site shall be cleaned and restored to its
original condition prior to full demobilization.
BILL OF QUANTITIES
CONSTRUCTION OF TWO (2) MONITORING WELLS
Item Unit Total

Item Qty Unit
No. Price Cost
1 Mobilization of equipment and field personnel incl.

1 ls
site preparation & setting-up of equipment
2. Well site to well site mobilization 1 ls
Drilling of 150mm dia. borehole from ground level
to specified depth, as follows:
3 145 m
Well 1: 100 m
Well 2: 45 m
4 Electric Logging 2 units
Furnish and install 75mm dia. uPVC Blank Casing
5 Well 1: 64 m 91 m
Well 2: 27 m
Furnish and Install 75mm dia. uPVC Screen
6 Well 1: 36 m 54 m
Well 2: 18 m
Furnish and Install 3-5mm dia. well-rounded
graded gravel pack inside annular space between
7 75mm dia. casing and 150mm dia. borehole. 95 m
Well 1: 60 m
Well 2: 35 m
Well development by high pressure water jetting
8 and air-lifting and treatment with polyphosphate 2 units
solution for 2 wells.
Furnish and Install Bentonite Seal (with 1m fine
sand at the bottom) inside annular space between
9 75mm dia. casing and 150mm dia. borehole. 35 m
Well 1: 30 m
Well 2: 5 m
Furnish and Install Cement Grout
10 Well 1: 15 m 20 m
Well 2: 5 m
11 Furnish and Install casing centralizer and bottom 1 ls
cap for 2 wells.
12 Constant discharge test (if possible) 24 hrs
Well completion including installation of 1m stick-
13 up pipe, well head cap with lock and concrete 1 LS
pump base for 2 wells.
14 Submission of Report (3 hard copies and 1
electronic copy) including the electric log, lithology,
well design (location of well screens), water quality 1 ls
analysis and record of all works accomplished in 2
Monitoring Wells
15 Demobilization and site clean-up 1 ls

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GROUNDWATER MANAGEMENT PLAN December 2013

Executive Summary ..........................................................................................................................ES-1

4.2.5 Definition of Boundary Conditions .................................................................................21

Table 2.1: Land Area ............................................................................................................................... 5

Figure 1.1: The Study Area .................................................................................................................... 2

2. The Study Area

3. Groundwater Utilization and Management Issues

4. Groundwater Flow Model

 Definition of Initial Distribution of Hydraulic Head

5. The Groundwater Flow Modeling for Iloilo Basin

6. Groundwater Management Plan

Time Frame: Immediate: 2015 – 2016

Measures Actions Sub-actions Outputs Timeline

Measures Actions Sub-actions Outputs Timeline

- Wise efficient use of groundwater for

Time Frame. Short-term: 2017 – 2022 2/

Measures Actions Sub-actions Outputs Timeline

- Conduct of monitoring and regulating

- NWRB to provide advisory services to City/Municipal Ordinances adopting the

Measures Actions Sub-actions Outputs Timeline

Time Frame. Long-term: 2023 – 2028 1/

Measures Actions Sub-actions Outputs Timeline

- Monitoring of groundwater withdrawal,

Measures Actions Sub-actions Outputs Timeline

IWRM, environmental protection and

1.4 The Report

2. The Study Area

2.1 Physical Characteristics

2.1.1 Location and Accessibility

2.1.2 Topography and Drainage

2.1.3 Land Area and Political Subdivisions

Table 2.1: Land Area

2.1.4 Existing Land Use

Table 2.2: Iloilo Climatological Normals (1971 to 2000)

Table 2.3: Climatological Extremes

2.1.5.3 Relative Humidity

2.1.6.1 Regional Geology

2.1.6.2 Local Geology

2.1.7.1 Hydrogeological Units and Characteristics

2.1.7.2 Groundwater Level

2.1.7.3 Groundwater Quality

2.1.8 Natural Hazards

2.2 Socio-Economic Environment

2.3 Legal Framework

the operation and maintenance of groundwater infrastructure. However, this activity is

4. Groundwater Flow Model

4.1 Types and Use of Groundwater Models

4.2 Model Design

Designing a groundwater flow model involves the following activities:

4.2.1 Concept Development

4.2.2 Selection of Computer Code

4.2.3 Definition of Model Geometry

4.2.4 Input of Model Parameters

4.2.5 Definition of Boundary Conditions

4.2.6 Definition of Initial Distribution of Hydraulic Head

4.2.7 Definition of the Stresses Acting Upon the System

4.2.8 Calibration and Sensitivity Analysis

4.2.9 Verification of Model Validity