ASSESSMENT OF GROUNDWATER POTENTIAL USING ISOTOPIC, GEOCHEMICAL AND NUMERICAL MODELING TECHNIQUES (a case study of Lahore aquifer)

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ASSESSMENT OF GROUNDWATER POTENTIAL USING
ISOTOPIC, GEOCHEMICAL AND NUMERICAL MODELING
TECHNIQUES (a case study of Lahore aquifer)
BY DR. NIAZ AHMAD Principal Scientist
(Geology) Isotope Application Division PAKISTAN
INSTITUTE OF NUCLEAR SCIENCE AND TECHNOLOGY
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OVERVIEW OF THE TALK

• Evolution of Indus River System
• Aquifers and Groundwater
• Recharge and Discharge
• Groundwater Quantity and Quality
• Case Studies Lahore Aquifer

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EVOLUTION OF INDUS RIVER SYSTEM

• As the Himalayas gained their maximum height, the
  present watershed system of Indus, Brahma-Putra
  and Ganges emerged and attained the present
  geographical position
• The course of the rivers Indus, Brahma-Putra,
  Ganges and their tributaries is constantly
  changing, as the slope of the land is changing
  due to tectonic stresses
• The Himalayas are still rising but due to
  erosion, they have attained a steady height
• The river systems are responsible for the
  development of thick pile of sediments (2 KM
  thick) to the south from Himalayan foothills to
  the Arabian Sea Delta
• The alluvial sediments constitute aquifers which
  store huge amount of fresh water which is termed
  as groundwater

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IMPORTANT FEATURES OF GROUNDWATER

• Upper part of Lithosphere (approximately 1 KM)
  supports fresh groundwater aquifers
• To the depth of approximately 800 meters below
  the water table, about 4 million cubic
  kilometers of water is present (Singh, 1992)
• In the upper 800 meters of the continental crust,
  the groundwater volume is 3000 times greater
  than that of all the rivers at any one time and
  about 20 times greater than the combined volume
  of water in all the rivers and lakes together.
• Surface water bodies (Rivers Lakes) respond
  rapidly to rain events but
• Groundwater has a much longer natural
  accumulation and discharge time

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Total Amount of Groundwater Available in Pakistan

• Fresh groundwater is present along the rivers
  about 10 km to each side to the depth of 1 km
• Total amount of fresh groundwater is about 25000
  km3

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IMPORTANT FEATURES OF GROUNDWATER

• Groundwater is buffered against short-term
  weather and climate processes
• The huge reserves of fresh groundwater are not
  being renewed wholly every year when compared to
  exploitation rate by pumping
• Large scale tapping of aquifers is virtually
  equivalent to a process of non-renewable mining
  for water
• It moves through the geological materials at a
  slower rate and residence times in the 10s,
  100s and even 1000s of years are not uncommon
  (Freeze and Cherry, 1979)
• Because of its long residence time in aquifers,
  groundwater is highly vulnerable for pollution
  and overexploitation by pumping
• overexploitation leads to salinization
• Knowledge of the recharge rate is essential for
  managing the sustainable extraction of potable
  water

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Composition of Aquifers

• The Indus Basin alluvium consists of alternating
  layers of clay, silt, sand and gravels deposited
  by meandering rivers in different proportions
• The source materials originate from the erosion
  of rising Himalayan rocks
• Groundwater quantity in an aquifer depends on the
  transmission and storage properties of that
  aquifer
• Chemistry of the rocks plays vital role in the
  evolution of groundwater quality

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Composition of Aquifers---------cont

• The aquifers are constantly recharging from the
  watershed areas and the resulting groundwater is
  flowing towards the sea
• In the way groundwater is interacting with the
  surrounding rocks and dissolving the chemical
  content
• Due to its high dielectric constant, water is the
  excellent solvent
• With dissolving salts its hunger for dissolving
  more salts increases, its salinity increases with
  time
• Due to mixing of fresh water in the way,
  groundwater maintains its quality
• Due to global warming if the precipitation
  patterns change and the drought periods extend,
  the groundwater quality will also be affected as
  a result of less fresh water recharge

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EXPLOITATION OF GROUNDWATER

• With the dawn of scientific era and development
  in petroleum industry, it is now possible to
  drill a well even more than 1 kilometer depth
• Since 1960, a large number of tube wells were
  installed to extract groundwater for agriculture
  and drinking purposes
• Recharge is an important component of
  groundwater, if recharge and discharge do not
  match overexploitation starts
• Over-exploitation gives way to problems of
  pollution, salinization, increased cost of water
  extraction and resource depletion

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Important Diagnostics of GroundwaterBefore
Exploitation

• Identification of recharge mechanism
• Surface water/ Groundwater interaction
• Transmission/storage properties of aquifers
• Residence time of water within the aquifer
• Water quality (physical, chemical biological)

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Tools for Investigation

• Isotopes
• Chemical analyses
• Mathematical
• Geophysical (resistivity, seismic etc)

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Case Studies Lahore Aquifer

• IDENTIFICATION OF RECHARGE MECHANISM

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Identification of Recharge Mechanism of Lahore
Aquifer using 18O Isotope Information
? D ()
Frequency histogram of ?18O ()
?18O ()
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Identification of recharge mechanism in deep
groundwater of Lahore aquifer by ?18O
concentrations in 2006
River Recharge
Mixed Recharge
Rain Recharge
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3D view of ?18O concentration of deep
groundwater of Lahore in 2006
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AN INNOVATIVE FINDING OF A GEOLOGIC FAULT

• An innovative finding is reached based on the
  temperatures in the wells
• Temperatures above normal are found in a linear
  belt in NE-SW direction
• The anomalous increase in temperatures is
  interpreted as the presence of active geologic
  fault in the Lahore area
• Due to sliding of the fault, frictional heat is
  generated, which is increasing the temperatures
  of the groundwater in contact with the fault area

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Water Supply from Lahore Aquifer

• Whole supply to the public and industry is from
  groundwater reservoir
• About 400 tube wells (each 2.5cusecs) are in
  operation under the jurisdiction of WASA, LDA
  -About three fourth of WASA is extracted by
  private stakeholders
• Total abstraction is about 800 million gallons
  per day
• We can say a canal of the size of Lahore Canal is
  operating from the aquifer to the surface
• Water table is lowering at the rate of 2.5 feet
  per year
• Aquifer capacity is depleting every year
• A large depression cone is producing surrounding
  the Mozang area
• As a result more saline water is intruding the
  aquifer from the south

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Water Table Conditions of Lahore Aquifer
In 1960 before pumping, water table was at 210 m
above mean sea level, about 5 to 6 meter below
surface
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In 1989, a depression cone is visible at Mozang
area as a result of pumping, Water table lowered
to 191 m from 210 m amsl, i.e. Water table
lowered 19 m from 1960 _at_ 1m / year
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In 1998, Water table further lowered to 185 m
from 191m in 1989 i.e. lowered 6 m further in 9
years
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In 2003, maximum water table depths are at Mozang
and Ichhra i.e, 36 m below surface which was 5 m
in 1960
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Salinization Problem of Lahore Aquifer

• EC and Cl can be used to determine the salinity
  condition of Lahore aquifer
• Chloride is more reliable as it is considered a
  conservative anion due to its less participation
  in chemical reactions
• Spatio-temporal measurements of chloride could
  be reasonably used to determine the increase of
  salinity in an area
• Once the water enters the geologic formations,
  its salinity goes on increasing with the passage
  of time. It changes from fresh water to brackish
  water and then to brine. Salinity of water could
  only be decreased by mixing of fresh water in the
  way.

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EC (?S/cm at 25 0C)
EC contours of deep groundwater in 2006, Lahore
area
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EC (?S/cm at 25 0C)
3D view of EC parameter
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Cl (ppm)
Contours of chloride measured in deep groundwater
of Lahore aquifer in 2006
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3D view of chloride concentration
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water table contours
Chloride contours
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Reasons of Salinization

• Lahore has a large network of unlined sewerage
  drains
• Water is leaking from these drains to shallow
  aquifer
• Salinity of shallow aquifer is increasing
• A large depression cone has developed in the
  Mozang area
• As the aquifer is unconfined, Shallow saline
  groundwater is making its way to the deep aquifer
  , where it is mixing with the deep relatively
  fresh groundwater
• As a result, the salinity of deep aquifer is
  increasing in the central city area (Mozang,
  Ichhra, Gawal Mandi, Assembly Hall)

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Water Types of Lahore Aquifer

• Major chemical ions dissolved in groundwater are
  Ca, Mg, Na, K, CO3, HCO3, SO4 and Cl
• Concentrations of these ions should be determined
  before use at homes, industry and agriculture
• There are different graphical methods for
  classification of groundwater types in an area

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HYDROCHEMICAL EVIDENCE OF LAHORE AQUIFER

• About 175 samples were collected from Shallow and
  Deep aquifer, Canals, Drains and River Ravi
• EC, pH and Temperature were measured in the field
• Major Cations (Na, K, Ca, Mg) and Anions
  (carbonates, bicarbonates, sulfate, chloride)
  were analyzed in the laboratory
• For interpretation cations and anions were lumped
  into three variables respectively
• Their milli-equivalent/L percentages were
  calculated

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A TRILINEAR GEOCHEMICAL MODEL REPRESENTING
DIFFERENT GROUNDWATER TYPES IN THE LAHORE AREA.
THE METHODOLOGY OF THE TRILINEAR MODEL WAS
DEVELOPED BY PIPER (1944)
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A DUROV GEOCHEMICAL MODEL REPRESENTING DIFFERENT
GROUNDWATER TYPES IN THE LAHORE AREA. THE
METHODOLOGY OF THE MODEL WAS DEVELOPED BY A
RUSSIAN SCIENTIST DUROV (1948)
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INNOVATIVE MULTI-RECTANGULAR DIAGRAMS (MRDs)
DEVELOPED AT PINSTECH
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Classification of water types using innovative
Multi-Rectangular Diagram Model
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• Important benefit of MRDs classification of
  groundwater are
• Groundwater types are clearly singled out, which
  is not possible by previous diagrams
• It also helps to mark the zones with different
  groundwater quality by plotting a representative
  symbol on the location from where the sample is
  collected.
• i.e, Hydro-chemical facies maps can be prepared

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Water types differentiated with MRDs and plotted
on the sample collection locations in the area
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History of movement of groundwater interpreted
with chemical ions I.e. Sodium-calcium
relationship in Lahore
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Sewerage Contamination of Lahore Aquifer

• Groundwater from all the sampled wells (111) was
  tested for Coliform bacteria to observe the
  sewerage contamination
• It appears in 15 wells
• Five wells were tested in Shahdara Area, coliform
  appeared in all these wells
• Water seepage from sewerage drains is polluting
  the deep good quality groundwater
• On the other hand, Sewerage water from all the
  city is disposed of to the river Ravi without any
  treatment. As the river Ravi is recharging the
  underground aquifer, sewerage water is also
  seeping to the deep aquifer thereby polluting it

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Location of pumping wells infected by fecal
coliform
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GROUNDWATER FLOW AND CONTAMINANT TRANSPORT
MODELING

• CASE STUDIES of LAHORE

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USE OF MODELING TOOLS IN GROUNDWATER AQUIFERS

• Modeling tools helps for ASSESSMENT MANAGEMENT
  OF AQUIFERS

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WHAT IS A MODEL

• A model is any device that represents an
  approximation of a field situation
• Physical models (sand tanks simulate
  groundwater flow directly)
• Mathematical models simulate groundwater flow
  indirectly by means of a governing equation
  thought to represent the physical processes that
  occur in the system

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• A model is not a replica of reality
• Rather, a structured environment for thinking
  through a problem

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WHY MODELS ?

• Groundwater Hydrologists are often called upon
  to predict the behavior of groundwater systems by
  answering questions like

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WHY MODELS ?

• What changes can be expected in groundwater
  levels in the aquifer beneath Lahore in the year
  2020
• How will a change in stream stage (River Ravi)
  affect the water table in an adjacent alluvial
  aquifer

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WHY MODELS ?

• What is the capture area for a well field that
  furnishes municipal water supplies to the city
• What is the most likely pathway of contaminants
  if the toxic materials enter the groundwater
  environment

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FLOW MODELS

• Are used to estimate the spatial and temporal
  variation of quantity of water in the aquifers

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TRANSPORT MODELS

• Are used to assess the contaminant transport
  behavior in groundwater regime leaked from
• Landfill sites
• radioactive repositories
• other sources

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Advection-Dispersion Equation solved by MT3D

• ? ?Dij ?C ? - ? (vi C ) qs Cs - ? C
  ?b S R ? ?C ?
• ?xi ?xj ?xi
  ? ?
  ? t
• Dispersion Advection
  Sink/Source Reactions Retardation

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Aquifer Main Features

• 400 m thick Quaternary Alluvial Deposits (Sands
  with clay lenses)
• High K 26 to 158 m/d
• Sy 0.07 - 0.25
• Recharge Rates 40 - 100 mm/yr
• Irrigation canals and influent river Ravi
• Over-pumping in Lahore

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FLOW MODEL OF LAHORE AQUIFER

• A Model was developed, which is digital
  equivalent to actual Lahore aquifer

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Map of Lahore on UTM Coordinates
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Aquifer layers constructed from bore hole
lithologic logs
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Cross-sectional view of model layers in Visual
Modflow
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Plan view of the model area showing River
boundaries Constant Head Boundary(NE) General
Head Boundary(NW) Inactive Cells Grid Mesh
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Pumping Wells in the Visual Modflow
Ravi River
Lahore Canal
BRBD Canal
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Steady State calculation before pumping
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Groundwater Flow Conditions
1960 - beginning of pumping
1910 - Pre-pumping
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Contours of calculated heads with steady state
model in 1989. Model also shows two depression
cones as shown in observed head contours. These
heads were used as initial heads in transient
simulations
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Calculated Water Table Contours in 1998
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3D view of transient flow model Depression cone
is visible Water is crossing underneath the River
Ravi and Lahore Canal
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Predicted water table contours in 2018 by Visual
Modflow
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DELINEATION OF WELL HEAD PROTECTION ZONE
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Transient transport simulation Particles
introduced at one of the waste disposal site are
captured by the screens of pumping wells
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CONCLUSIONS

• Water table of Lahore aquifer is lowering down at
  a rate of about 3 feet per year
• A depression in the water table has produced
• Generally, deep aquifer ( 200 m) has less
  salinity as compared to shallow aquifer ( 50 m).
  Sewerage drains are adding salinity to shallow
  aquifer. Deep aquifer is getting saline in the
  areas where water table has maximum depth. This
  salinity increase is due to mixing of more saline
  shallow water with deeper fresh water under the
  action of high hydraulic gradient.
• Groundwater of Lahore Aquifer consists of
  calcium bicarbonate, magnesium bicarbonate and
  sodium bicarbonate types

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CONCLUSIONS------continued

• chloride is found Dominant underneath the central
  city area (Assembly Hall, Mozang, Nisbat Road
  etc.) in both shallow (motor pumps/hand pumps)
  and deep (WASA wells) aquifer. This is the area
  where highest decline in water table exists as a
  result of pumping.
• There are strong indications that waters of
  shallow and deep aquifer are mixing together in
  the area of dominance of chloride. If the
  leachates from industrial waste enters into
  shallow aquifer, then there is strong chance that
  the deeper fresh aquifer will get polluted also.
  Pumping from this central area needs a great care.

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CONCLUSIONS------continued

• There are strong indications that waters of
  shallow and deep aquifer are mixing together in
  the area of dominance of chloride. If the
  leachates from industrial waste enters into
  shallow aquifer, then there is strong probability
  that the deeper fresh aquifer will get polluted
  also. Pumping from this central area needs a
  great care.
• Biological quality in some areas is not good as
  Sewerage contamination is detected in some areas
• It is obvious from these findings that Aquifer is
  vulnerable for pollution more in the central city
  area

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Recommendations

• Formulation of a rational water supply policy is
  needed through which Lahore aquifer should be
  managed by coordination of all the stake holders
  including Government of Punjab, WASA Lahore,
  Cantonment Boards, private societies,
  industrialists and public.
• During modeling exercise, it has been observed
  that wells are not placed at optimized distances.
  At least well to well distance should be kept 1.5
  kilometer. If the wells are installed shorter
  than this distance, their depression cones will
  overlap with the result of increased lowering in
  water table.
• In the depression cone area some of the wells
  must be shutdown observing the well to well
  distance as proposed above.
• New wells should be installed near BRBD Canal and
  installing wells within the city should be
  discouraged.

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Recommendations ---cont

• Quality of sewerage water should be improved in
  treatment plants before disposing it of in the
  river Ravi.
• There is a strong need to install a peizometer
  network to gather data on water table
  fluctuation. At present this data is acquired
  directly from the pumping wells. It is not
  representative hydraulic head data, as the
  pumping wells induce perturbation in the system.
  An automatic telemetric system is suggested.
• Periodic monitoring of chemical and biological
  quality of water is suggested.
• Supervision of Total Quality Management (TQM) is
  recommended through national scientific
  organizations such as PINSTECH, PCRWR, PCSIR, EPA
  etc., other than WASA Lahore and Cantonment
  Boards.

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• THANKS