Factors determining the hydrogeochemical processes occurring in shallow groundwater of coastal alluvial aquifer, India

A hydrochemical study on the coastal aquifers were collected initiated to determine the factors affecting the groundwater chemistry in South India. 48 groundwater samples from bore wells during post monsoon period. The samples were measured for in situ parameters and major ions following the standard procedures. The analyzed results were further interpreted using geochemical plots, ionic ratios, water quality indices, geochemical modeling and statistics. pH values in the groundwater ranged from 6.6 to 8.0 and alkaline in nature. The average value of EC was 7155 mu S/cm and higher values were mostly distributed along the coastal region of the study area. From the Piper plot, hydrochemical evolution path was identified, from Ca-HCO3 (recharge waters) to mixed Ca-Mg-Cl (reverse ion exchange waters) through Ca-Cl types (leachate waters), indicating the reverse ion exchange and seawater intrusion. Saturation index reflected that Calcite was oversaturated due to availability of Ca and HCO3 ions. Factor analysis further improved the understanding of the major controlling hydrochemical processes for groundwater chemistry. The hydrochemistry of the coastal aquifer was affected by several factors such as dissolution, water-rock interaction, reverse ion exchange, seawater intrusion, and influence of minor agricultural. The water quality assessment showed that the concentration of most of the parameters exceeded the standards limit, and considered as unsuitable for drinking purposes. But they are inferred to be suitable for agricultural purposes according to SAR, Na%, RSC and PI.