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BY DR. NIAZ AHMAD Principal Scientist (Geology) Isotope Application Division

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  1. 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

  2. OVERVIEW OF THE TALK • Evolution of Indus River System • Aquifers and Groundwater • Recharge and Discharge • Groundwater Quantity and Quality • Case Studies: Lahore Aquifer

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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)

  11. Tools for Investigation • Isotopes • Chemical analyses • Mathematical • Geophysical (resistivity, seismic etc)

  12. Case Studies: Lahore Aquifer • IDENTIFICATION OF RECHARGE MECHANISM

  13. Identification of Recharge Mechanism of Lahore Aquifer using 18O Isotope Information  D (‰) Frequency histogram of 18O (‰) 18O (‰)

  14. Identification of recharge mechanism in deep groundwater of Lahore aquifer by 18O concentrations in 2006 River Recharge Mixed Recharge Rain Recharge

  15. 3D view of 18O concentration of deep groundwater of Lahore in 2006

  16. 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

  17. 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

  18. 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

  19. 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

  20. In 1998, Water table further lowered to 185 m from 191m in 1989 i.e. lowered 6 m further in 9 years

  21. In 2003, maximum water table depths are at Mozang and Ichhra i.e, 36 m below surface which was 5 m in 1960

  22. 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.

  23. EC (S/cm at 25 0C) EC contours of deep groundwater in 2006, Lahore area

  24. EC (S/cm at 25 0C) 3D view of EC parameter

  25. Cl (ppm) Contours of chloride measured in deep groundwater of Lahore aquifer in 2006

  26. 3D view of chloride concentration

  27. water table contours Chloride contours

  28. 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)

  29. 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

  30. 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

  31. A TRILINEAR GEOCHEMICAL MODEL REPRESENTING DIFFERENT GROUNDWATER TYPES IN THE LAHORE AREA. THE METHODOLOGY OF THE TRILINEAR MODEL WAS DEVELOPED BY PIPER (1944)

  32. 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)

  33. INNOVATIVE MULTI-RECTANGULAR DIAGRAMS (MRDs) DEVELOPED AT PINSTECH

  34. Classification of water types using innovative Multi-Rectangular Diagram Model

  35. 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

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

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

  38. 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

  39. Location of pumping wells infected by fecal coliform

  40. GROUNDWATER FLOW AND CONTAMINANT TRANSPORT MODELING • CASE STUDIES of LAHORE

  41. USE OF MODELING TOOLS IN GROUNDWATER AQUIFERS • Modeling tools helps for ASSESSMENT & MANAGEMENTOF AQUIFERS

  42. 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

  43. A model is not a replica of reality • Rather, a structured environmentfor thinking through a problem

  44. WHY MODELS ? Groundwater Hydrologists are often called upon to predict the behavior of groundwater systems by answering questions like:

  45. 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

  46. 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

  47. FLOW MODELS Are used to estimate the spatial and temporal variation of quantity of water in the aquifers

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

  49. Advection-Dispersion Equation solved by MT3D Dij C-  (vi C ) + qsCs- [C +bS] = RC xixjxit Dispersion Advection Sink/Source Reactions Retardation