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Unexpected mistreatment of groundwater from coastal aquifers may possibly cause salt water intrusion in coastal aquifers. Coastal areas are mostly overpopulated with productive agricultural lands and expanded irrigated farming actions. Field and modeling studies were started to consider the special effects of possible seawater intrusion into the coastal aquifers. Groundwater levels were measured at 61 locations in Nagapattinam and Karaikal coastal region, identified flow direction pointing toward the coast with no major change in groundwater table. Groundwater samples were collected and analyzed for major ionic parameters, represented higher concentration of conductivity, total dissolved solids, sodium and chloride along the coastal parts of the study area. A computer package for the simulation of dimensional variable density groundwater flow, SEAWAT, has been used to model the seawater intrusion in the coastal aquifers of the study area. The model was stimulated to predict the amount of seawater incursion in the study area for a period of 50 years. The simulation results signify saline water intrusion mainly due to up coning of saline water owing to over drafting of groundwater.

ABSTACTThe absence of perennial river, semi arid climatic condition and growing neediness of water increased the usage of groundwater. In the area proposed for the study, all the water necessities are fulfilled with groundwater. Hydrochemistry of groundwater is influenced by geogenic and anthropogenic sources. Hence to assess the chemical characteristics of groundwater in the study area, a total of 74 groundwater samples were collected and analyzed for physical parameters such as pH, conductivity and Total Dissolved Solids along with major cations and anions using standard procedures. The dominant cations and anions were, Na ˃ Ca ˃ Mg ˃ K and HCO ˃Cl> NO3 ˃ F ˃ PO4 ˃SO4 respectively. Hydro chemical facies demarcated were NaCl , CaNaHCO3 , CaHCO3 and CaMgCl. The facies suggests ionic exchange, dissolution, silicate weathering and anthropogenic sources are responsible for the variation in groundwater chemistry of the study area. The silicate group minerals show over equilibrium conditions sulphate and halide group minerals indicate under saturation condition. The saturation values trend increases along the flow path. Identified hydro geochemical process were verified and quantified using hydro geochemical inverse mass-balance modeling (net geochemical reactions along a flow path,PHREEQC,WATQ4F).

Understanding the geochemical evolution of groundwater is an essential part of the performance assessment and safety analysis of the geological system. Geochemical modeling techniques using PHREEQCI will aid in demarcating the main factors and mechanisms controlling the chemistry of groundwater. An attempt has been made in hard rock terrain of Chinnar basin, Dharmapuri district of Tamilnadu, India to interpret the processes and factors controlling hydrogeochemistry of groundwater. The area is made up of rock units belonging to Charnockite and Granitic Gneiss. Groundwater chemistry has been attempted based on laboratory observations of major cations like Na + , K + , Ca 2+ and Mg 2+ and anions like Cl -, HCO 3 -, NO 3 -, F -, SO 4 2-and PO 4 3-. Piper diagram reveals higher bicarbonate, calcium and magnesium along the recharge zones and tend to decrease along the flow path and vice versa for ions like sodium, potassium and chloride. Two flow paths based on piper and saturation index were identified for two major lithounits. The granitic terrain shows precipitation of calcium and sulfate minerals and dissolution of silicate minerals. The charnockite terrain shows precipitation of silicates and dissolution of calcium and sulfate minerals. From initial to final solution slight variation in calcium and sulfate stability were identified but drastic change with reference to silicate minerals stability due to effective dissolution of silicate minerals from the litho units of the study area.

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