Major ion, trace metal and environmental isotope characterization of groundwater in selected parts of Uddanam coastal region, Andhra Pradesh, India

This paper elaborates the hydrochemical and environmental isotope (delta H-2 and delta O-18) inferences obtained from Uddanam region, Andhra Pradesh, India. Groundwater samples collected during pre-monsoon (June 2019) showed that the quality is fresh (EC < 1539 mu S/cm) and contaminants like fluoride (<1.6 mg/L) and nitrate (<49 mg/L) are present within permissible limits. The composite water quality indices for drinking (DWQI: 14.1-92.5) and irrigation (IWQI: 2.8-20.2) are found to be satisfactory. The major water types are found to be Ca-Na-HCO3, Na-Ca-HCO3, Na-Mg-HCO3-Cl, Ca-Mg-HCO3-Cl and Na-HCO3. Three geochemical pathways are found signifying evaporite dissolution, contribution of silicate mineral weathering and base-exchange process, which is supported by estimated chloro-alkaline indices (CAI-1: -4.3 to -0.2, CAI-2: -1.03 to -0.08). Trace metal data clearly suggest that groundwater is free from any metal pollution. Dissolved silica (SiO2) levels range from 34 to 131 mg/L and do not show any particular spatial trend. Isotope data infer that groundwater is recharged by rainwater after undergoing evaporation (delta O-18: -6.0 parts per thousand), which matches with that of the combined isotope signature (delta O-18: -5.5 parts per thousand) of SW and NE monsoon rainfall.delta O-18-TDS correlations and hydrochemical facies evolution (HFE) diagram do not infer any seawater intrusion into these coastal aquifers.