deeper groundwater flow and chemistry in the arsenic affected western bengal basin, west bengal PDF
Preview deeper groundwater flow and chemistry in the arsenic affected western bengal basin, west bengal
UUnniivveerrssiittyy ooff KKeennttuucckkyy UUKKnnoowwlleeddggee University of Kentucky Doctoral Dissertations Graduate School 2006 DDEEEEPPEERR GGRROOUUNNDDWWAATTEERR FFLLOOWW AANNDD CCHHEEMMIISSTTRRYY IINN TTHHEE AARRSSEENNIICC AAFFFFEECCTTEEDD WWEESSTTEERRNN BBEENNGGAALL BBAASSIINN,, WWEESSTT BBEENNGGAALL,, IINNDDIIAA Abhijit Mukherjee University of Kentucky, [email protected] RRiigghhtt cclliicckk ttoo ooppeenn aa ffeeeeddbbaacckk ffoorrmm iinn aa nneeww ttaabb ttoo lleett uuss kknnooww hhooww tthhiiss ddooccuummeenntt bbeenneefifittss yyoouu.. RReeccoommmmeennddeedd CCiittaattiioonn Mukherjee, Abhijit, "DEEPER GROUNDWATER FLOW AND CHEMISTRY IN THE ARSENIC AFFECTED WESTERN BENGAL BASIN, WEST BENGAL, INDIA" (2006). University of Kentucky Doctoral Dissertations. 368. https://uknowledge.uky.edu/gradschool_diss/368 This Dissertation is brought to you for free and open access by the Graduate School at UKnowledge. It has been accepted for inclusion in University of Kentucky Doctoral Dissertations by an authorized administrator of UKnowledge. For more information, please contact [email protected]. ABSTRACT OF DISSERTATION Abhijit Mukherjee The Graduate School University of Kentucky 2006 i DEEPER GROUNDWATER FLOW AND CHEMISTRY IN THE ARSENIC AFFECTED WESTERN BENGAL BASIN, WEST BENGAL, INDIA ______________________________________________________ ABSTRACT OF DISSERTATION ______________________________________________________ A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the College of Arts and Sciences at the University of Kentucky By Abhijit Mukherjee Lexington, Kentucky Director: Dr. Alan E. Fryar, Associate Professor of Earth and Environmental Sciences Lexington, Kentucky 2006 Copyright © Abhijit Mukherjee 2006 ii ABSTRACT OF DISSERTATION DEEPER GROUNDWATER FLOW AND CHEMISTRY IN THE ARSENIC AFFECTED WESTERN BENGAL BASIN, WEST BENGAL, INDIA A regional-scale hydrogeologic study was conducted in a ~21,000-km2 area of West Bengal (Murshidabad, Nadia, North and South 24 Parganas districts), India, with severe, natural arsenic contamination of shallow groundwater jeopardizing ~13.5 million inhabitants. The study evaluated the suitability of deeper water as an alternate drinking water source. A hydrostratigraphic model (resolution: 1000 m × 1000 m × 2 m, ≤ 300 m below MSL) indicates a continuous, semi-confined sand aquifer (main aquifer) underlain by a thick clay aquitard. The aquifer deepens toward the east and south. In the south, there are several deeper, laterally connected, confined aquifers. Based on observed hydrostratigraphy, eight seasonal groundwater models (resolution: 1000 m × 1000 m × 15 m) were developed with presence of pumping (2001), absence of pumping (pre-1970s) and projected irrigational pumping (2011 and 2021). Simulations indicate topographically controlled, seasonally variable regional groundwater flow, which has been severely distorted by pumping. Samples of deep groundwater, river water and rainwater were collected for major and minor solutes, dissolved gases and stable isotopes. A δ18O-δ2H bivariate plot of groundwater falls subparallel to the constructed local meteoric water line (δ2H = 7.24 δ18O + 7.73), suggesting a predominance of meteoric recharge (from monsoonal rainfall of present-day composition) with some evaporation. A trend of δ18O depletion of groundwater was observed northward and westward from the Bay of Bengal, indicating a continental effect. Major solutes indicate the presence of hydrochemically distinct water bodies in the main and deeper isolated aquifers. Spatial trends of major and redox-sensitive solutes and geochemical modeling indicate that carbonate dissolution, silicate weathering, and cation exchange along with seawater and connate- water mixing control the major-ion chemistry. The suboxic main aquifer water exhibits partial redox equilibrium, with the possibility of oxidation in micro-scale environments. The redox processes are depth-dependent and hydrostratigraphically variable. Deeper water was found unsafe with elevated (≥10 μg/L) As in ~60% of samples. The presence of As is related to coupled Fe-S redox cycles. Deeper water is probably polluted by groundwater flow though interconnected aquifers with reduced sediments. Deep irrigational pumping has potentially attracted shallower, polluted water to greater depths. iii KEYWORDS: Arsenic Contamination, Hydrostratigraphy, Groundwater Flow Modeling, Hydrogeochemistry, West Bengal, India Abhijit Mukherjee 3 July 2006 iv DEEPER GROUNDWATER FLOW AND CHEMISTRY IN THE ARSENIC AFFECTED WESTERN BENGAL BASIN, WEST BENGAL, INDIA By Abhijit Mukherjee Alan E. Fryar Director of Dissertation Susan M. Rimmer Director of Graduate Studies 3 July 2006 i RULES FOR THE USE OF DISSERTATION Unpublished dissertations submitted for the Doctor’s degree and deposited in the University of Kentucky Library are as a rule open for inspection, but are to be used only with due regard to the rights of the authors. Bibliographical references may be noted, but quotations or summaries of parts may be published only with the permission of the author, and with the usual scholarly acknowledgements. Extensive copying or publication of the thesis in whole or in part also requires the consent of the Dean of the Graduate School of the University of Kentucky. ii DISSERTATION Abhijit Mukherjee The Graduate School University of Kentucky 2006 iii DEEPER GROUNDWATER FLOW AND CHEMISTRY IN THE ARSENIC AFFECTED WESTERN BENGAL BASIN, WEST BENGAL, INDIA _______________________________________________________ DISSERTATION _______________________________________________________ A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the College of Arts and Sciences at the University of Kentucky By Abhijit Mukherjee Lexington, Kentucky Director: Dr. Alan E. Fryar, Associate Professor of Earth and Environmental Sciences Lexington, Kentucky 2006 Copyright © Abhijit Mukherjee 2006 iv This dissertation is dedicated to my parents Kajali and Barindra Lal Mukherjee, my loving wife Abira, and my friend, philosopher, and guide Dr. Alan E. Fryar, without whose inspiration this work would not have been possible. v
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