Heavy metal contamination, major ion chemistry and appraisal of the groundwater status in coastal aquifer, Kalpakkam, Tamil Nadu, India

Abstract

A total of 228 groundwater samples were collected at a depth of 10–30 feet below ground level (bgl) during one year period from nineteen wells around Kalpakkam, Tamil Nadu, India which is known for nuclear installations. The studied aquifer mainly constitutes of sand and weathered charnockite with thickness varying from 3 to 12m and is of unconfined nature. Physical parameters, major ions, and heavy metals level were compared with guideline values and water quality index. The order of dominance of cations and anions were; Na+>Ca+2>Mg+2>K+ and HCO3−>Cl−>NO3−>SO4−2>PO4−3>Br−>F−. Four major water types (Ca-HCO3, Na-Cl, mixed Ca-Na-HCO3 and mixed Ca-Mg-Cl) were observed. Alkali metals (Na++K+) exceeded the alkaline earth (Ca+2+Mg+2) and weak acid (HCO3−) exceeded the strong acid (Cl−+SO4−). The order of heavy metals was Zn>Fe>Mn>Ni>Cu. Bureau of Indian Standards compliance of total dissolved solids (26–27%), total alkalinity (35–44%), total hardness (24–27%) and nitrate (41–43%) indicated that most of the samples exceeded the acceptable limit for drinking water. High nitrate level with an average of 104.5mg/l (82% samples exceeded BIS limit) was observed in the central part of the study area (between Kalpakkam township and nuclear site) and ascribed to the influence of domestic sewage and septic tank effluents. Observed low fluoride values in this study (avg. 0.1mg/l) contradicted the earlier report of high level of fluoride from this location. Based on the Canadian Council of Ministers of the Environment Water Quality Index (CCME WQI), the water quality was classified as marginal to excellent class with a majority falling under fair category. Except for 4–5 wells which were categorized as marginal, the water quality in other wells was suitable for drinking. The studied wells formed spatial distinct groups based on the water quality ranking. The present study provides a comprehensive status of groundwater quality in terms of its suitability for human consumption.