Geophysical geochemical studies and groundwater modelling in south Chennai coastal aquifer

Abstract

Groundwater in coastal aquifers is susceptible to contamination by newlineseawater intrusion Chennai is the fourth largest metropolitan city and one of newlinethe highest populated cities in India The city utilizes groundwater sources newlineespecially from coastal aquifers in the north and south of the city The usage newlineof groundwater has increased to meet the domestic agriculture and industrial newlineneeds The overpumping of groundwater leads to seawater intrusion and newlineresults in deterioration of groundwater quality Hence research was carried newlineout in the south Chennai coastal aquifer to delineate the zone of extension of newlineseawater influence to arrive at groundwater quality zonation to understand newlinethe status of aquifer with present level of pumping and to predict the behavior newlineof the aquifer with respect to the groundwater level under different hydrologic newlinestresses newlineThe study area 35 km located at the south of Chennai city is newlinebounded by contaminated water on all the sides The annual average rainfall newlinebased on the rainfall data collected over the past 10 years is 1066 mm newlineGeologically the study area has two distinct formations crystalline newlineCharnockite rocks of Archean age and Quaternaryrecent sediments The newlinecrystalline charnockite rock is overlined by Quaternary recent sediments The newlineQuaternaryrecent sediments weathered and fractured crystalline charnockite newlinefunction as an unconfined aquifer system The groundwater head follows the newlinetopography and flows towards the east and west from the central part of the newlinearea newlineInitially the secondary data like longterm rainfall data newlinegroundwater level data of wells and borehole logs was collected The primary newlinedata collection was begun with the geoelectrical survey May 2008 May newline2009 and groundwater monitoring of wells Groundwater monitoring was newlinecarried out once in three months from August 2008 to May 2010 newlineGroundwater level electrical conductivity EC hydrogen ion activity pH newlinesalinity and temperature were measured insitu Major ions such as Ca Mg newlineNa K HCO CO SO Cl and minor ions like Br F NO and NO were newlineanalysed in the laborato