ASSESSMENT OF GROUNDWATER POTENTIAL USING ISOTOPIC, GEOCHEMICAL AND NUMERICAL MODELING

TECHNIQUES (a case study of Lahore aquifer)

BY

DR. NIAZ AHMADPrincipal Scientist (Geology)

Isotope Application Division

PAKISTAN INSTITUTE OF NUCLEAR SCIENCE AND TECHNOLOGY

OVERVIEW OF THE TALK

• Evolution of Indus River System

• Aquifers and Groundwater

• Recharge and Discharge

• Groundwater Quantity and Quality

• Case Studies: Lahore Aquifer

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

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

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

•

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 10’s, 100’s and even 1000’s 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

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

• 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

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

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

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)

Tools for Investigation

• Isotopes

• Chemical analyses

• Mathematical

• Geophysical (resistivity, seismic etc)

Case Studies: Lahore Aquifer

• IDENTIFICATION OF RECHARGE MECHANISM

Identification of Recharge Mechanism of Lahore Aquifer using 18O Isotope Information

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Frequency histogram of 18O (‰)

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oad

Identification of recharge mechanism in deep groundwater of Lahore aquifer by 18O concentrations in 2006

Rain Recharge

Mixed

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harge

River Rec

harge

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avi

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ay L ine

Model T

own

3D view of 18O concentration of deep groundwater of Lahore in 2006

AN INNOVATIVE FINDING OF A GEOLOGIC FAULT

An innovative finding is reached based on the temperatures in the wellsTemperatures above normal are found in a linear belt in NE-SW directionThe anomalous increase in temperatures is interpreted as the presence of active geologic fault in the Lahore areaDue 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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T em p e ra tu re V aria tio n 0 C

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

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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0 2 k m

M ozang

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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 @ 1m / year

NM ozang

Rav

i Riv

e r

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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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Minimum Water Table Depth

Maximum Water Table Depth

Average Water Table Depth

In 2003, maximum water table depths are at Mozang and Ichhra

i.e, 36 m below surface which was 5 m in 1960

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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ur Road

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Lahore C anal

EC (S/cm at 25 0C)

EC contours of deep groundwater in 2006, Lahore area

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avi

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ay L ineM

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3D view of EC parameter

EC (S/cm at 25 0C)

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Feroze P

ur Road

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Cl (ppm)

Contours of chloride measured in deep groundwater of Lahore aquifer in 2006

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ay L ine

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hore

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3D view of chloride concentration

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water table contoursChloride contours

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)

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

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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Ca Na+K HCO3+CO3 Cl

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Water Types Shallow Deep Sewerage Canal River

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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Water Types Shallow Deep Sewerage Canal River

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)

INNOVATIVE MULTI-RECTANGULAR DIAGRAMS (MRDs) DEVELOPED AT PINSTECH

Classification of water types using innovative Multi-Rectangular Diagram Model

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calcium bicarbonate

magnesium bicarbonate

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sodium chloride

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

Water types differentiated with MRDs and plotted on the sample collection locations in the area

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Calcium BicarbonateMagnesium Bicarbonate

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History of movement of groundwater interpreted with chemical ions I.e. Sodium-calcium relationship in Lahore

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

Location of pumping wells infected by fecal coliform

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coliform count

well No.

GROUNDWATER FLOW AND CONTAMINANT TRANSPORT MODELING

• CASE STUDIES of LAHORE

USE OF MODELING TOOLS IN GROUNDWATER AQUIFERS

• Modeling tools helps for ASSESSMENT & MANAGEMENT OF AQUIFERS

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

• A model is A model is notnot a replica a replica of realityof reality

• Rather, a Rather, a structured structured environmentenvironment for thinking for thinking through a problemthrough a problem

WHY MODELS ?

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

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

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

FLOW MODELS

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

aquifers

TRANSPORT MODELS

• Are used to assess the contaminant transport behavior in groundwater regime leaked from

• Landfill sites

• radioactive repositories

• other sources

Advection-Dispersion

Equation solved by MT3D

Dij C - (vi C ) + q

s Cs - [C + b S] = R C

xi

xj x

i t

Dispersion Advection Sink/Source Reactions Retardation

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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C o u n to u rs o f w a te r lev e l o b se rv a tio n s in N o v . 1 9 8 9

FLOW MODEL OF LAHORE AQUIFER

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

Map of Lahore on UTM Coordinates

Aquifer layers constructed from bore hole lithologic logs

Cross-sectional view of model layers in Visual Modflow

Plan view of the model area showing:

River boundaries

Constant Head Boundary(NE)

General Head Boundary(NW)

Inactive Cells

Grid Mesh

Pumping Wells in the Visual Modflow

BRBD Can

al

Ravi River

Lahore Canal

Steady State calculation before pumping

Groundwater Flow Conditions

1960 - beginning of pumping1910 - Pre-pumping

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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C o u n to u rs o f w a te r lev e l o b se rv a tio n s in N o v . 1 9 8 9

Calculated Water Table Contours in 1998

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M ozang

W ater tab le contours above m ean sea level (m eters) in N ov. 1998

3D view of transient flow model

Depression cone is visible

Water is crossing underneath the River Ravi and Lahore Canal

Predicted water table contours in 2018 by Visual Modflow

DELINEATION OF WELL HEAD PROTECTION ZONE

Transient transport simulation:

Particles introduced at one of the waste disposal site are captured by the screens of pumping wells

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

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.

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

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.

•

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.

THANKS