Significance of pCO2 values in determining carbonate chemistry in groundwater of Pondicherry region, India

The partial pressure of Carbon-Di-oxide plays a significant role in the water chemistry. It reflects thegeochemical process and relates to the saturation index (SI) of the Carbonate minerals. A total number of 98 samples were collected from layered sequential aquifers like Alluvium, Upper Cuddalore sandstone, Lower Cuddalore Sandstone and Cretaceous formations, during Pre-Monsoonand Post-Monsoon seasons. Chemical parameters of groundwater such as pH, EC, TDS, Na+, K+, Ca2+, Mg2+, Cl–, HCO–3 , SO2–4 , PO3–4 and H4SiO4 were determined. The study shows that an increase in the log pCO2 values during water-rock interaction which influences the processof mineral dissolution. Saturation index of the carbonate minerals like Calcite, Aragonite, Dolomite and Magnesite were derived and compared with the log pCO2 values. In both the seasons the decreasing log pCO2 increases the saturation index of most of the carbonate minerals studied. The saturation index of almost all carbonate minerals during both the seasons showed negative correlationirrespective of the formation. Log pCO2 also develops a negative correlation with pH in groundwater of the study area