Figure 5. Mean resistivity contour map in the depth ranges of 0 to 5 m, 5 to 10 m, 40 to 50 m, 80 to 100 m, and 130 to 150 m showing the extent of saline zones. distinguish between two formations having similar resistivity, but the ambiguity is minimized when resistivity sounding interpretations are constrained by seismic refraction results. Such a combined geophysical survey and data integration can be used as a subsurface mapping tool for delineating the various geological formations, aquifer zones, and zones of saline water. Resistivity profiling coupled with resistivity sounding, periodic chemical analysis of ground water samples, and data integration was found to be a highly effective method for determining the fresh water areas and the saline watercontaminated zones, as well as the mode and cause of saline water intrusion. Such integrated research also evolved a new concept of minimum resistivity of a subsurface formation in an area below which ground water contained in it is brackish/saline and unsuitable for drinking. 676 K. Choudhury, D.K. Saha GROUND WATER 42, no. 5: 671–677 Such data integration was successfully applied in a coastal region in India to identify one narrow saline water zone/channel, which caused high TDS and high chloride in the ground water. Further, the integrated study delineated subsurface saline-contaminated zones close to a sea water canal and potable ground water zones at different depth levels. Acknowledgments The authors gratefully acknowledge the help rendered by the Chemical Division of Central Headquarters of Geological Survey of India in the analysis of ground water samples. Thanks are due to N.R. Biswas for drafting the figures. The authors express their deep gratitude to Mary P. Anderson, E Zia Hosseinipour, and the associate editor for reviewing this paper andoffering valuable suggestions.
Figure 6. Chemical analysis of ground water samples during premonsoon and postmonsoon periods; ρ is the resistivity of water samples. Editor’s Note: The use of brand names in peer-reviewed papers is for identification purposes only and does not constitute endorsement by the authors, their employers, or the National Ground Water Association. References Albouy, Y., P. Andrieux, G. Rakotondrasoa, M. Ritz, M. Descloitres, J.L. Join, and E. Rasolomanana. 2001. Mapping coastal aquifers by joint inversion of DC and TEM soundings—Three cases histories. Ground Water 39, no. 1: 87–97. Choudhury, K., D.K. Saha, and D.C. Ghosh. 2000. Urban geophysical studies on the ground water environment in parts of Gangetic delta. Journal of the Geological Society of India 55, no. 3: 257–267. Frohlich, R.K., D.W. Urish, J. Fuller, and M. Reilly. 1994. Use of geoelectrical method in ground water pollution surveys in a coastal environment. Journal of Applied Geophysics 32, no. 2: 139–154. Ginsberg, A., and A. Levanton. 1976. Determination of saltwater interface by electrical resistivity sounding. Hydrological Science Bulletin 21, no. 6: 561–568. Goswami, A.B., and B. Bose. 1981. Water Resources of West Bengal. Calcutta, India: Jadavpur University Publication, School ofWater Resources Engineering. Kalimas, A., and M. Gregorauskas.2002. Ground water abstraction and contamination in Lithuania as geoindicators of environmental change. Environmental Geology 42, no. 7: 767–772. Klimentov, P.P. 1983. General Hydrogeology. Moscow: Mir Publishers. Niyogi, D, and A. Chakraborty. 1966. Applied geomorphology along Digha beach, W. Bengal. In Proceedings of the Geomorphological Seminar, University of Sagar, India, 28–32. Nowroozi, A.A., B.H. Stephen, and P.Henderson. 1999. Saltwater intrusion into the fresh water aquifer in the eastern shore of Virginia: A reconnaissance electrical resistivity survey. Journal of Applied Geophysics 42, no. 1: 1–22. Orellana, E., and H.M. Mooney. 1966. Water Table and Curves for Vertical Electrical Sounding Over Layered Structures. Madrid, Spain: Interetencia. Shalivahan. 2000. Non-linear inversion of electrical and magnetotelluric data using very fast simulated annealing. Ph.D. thesis, Department of Applied Geophysics, Indian School of Mines, Dhanbad, India. Singhal, B.B.S. 1963. Occurrence and geochemistry of ground water in the coastal region of Midnapur, West Bengal, India. Economic Geology 58, no. 4: 419–433. Todd, D.K. 1959. Ground Water Hydrology. New York: John Wiley & Sons. Yechieli, Y. 2000. Fresh-saline ground water interface in the western Dead Sea area. Ground Water 38, no. 4: 615–623. K. Choudhury, D.K. Saha GROUND WATER 42, no. 5: 671–677 677