Hydrochemical Evolution of Groundwater in the Phreatic Aquifers of Chhattisgarh

The phreatic aquifers form the most important repository of groundwater in Chhattisgarh state, India. Based on 323 representative water samples of the phreatic aquifers, the present study is conducted to trace the materials and processes controllig groundwater chemistry. Groundwater is mostly low in dissolved constituents. Bicarbonate type is the dominant type of water irrespective of the rock type. Sulphate and Chloride type waters are restricted to small patches δD and δ¹⁸O characteristics of groundwater samples suggest that recharge to the phreatic aquifer system is rapid with little or no evaporative enrichment of the meteoric water.

Electrical conductivities and chloride concentrations, when plotted against the distance from water divide, do not show any trend. Dissolution of bicarbonate by CO₂ charged meteoric water is the principal process controlling bicarbonate content in groundwater. Dissolution of gypsum from the gypsiferous formations (Maniyari shale and Raigarh Formation) produces sulphate type water in parts of Durg, Janjgir Champa, Bilaspur and Raigarh districts. Chloride concentration in groundwater is low Ca/Mg carbonates in sedimentanes. Ca-feldspars and ferromagnesian minerals in the crystallines are the major sources of Ca and Mg in groundwater. Cation exchange process in the sedimentaries, and albite weathering in the crystallines were found to be important processes controlling concentration of Na in groundwater.