Chemistry and quality of groundwater in a coastal region of Andhra Pradesh, India

Abstract

The chemistry of groundwater in the coastal region between Chirala and Ongole of Andhra Pradesh, India shows pollution to varying extent. The relative contribution of ions in six zones divided based on TDS indicates unsuitability of groundwater here for drinking, irrigation and industrial use. The water is brackish except in first zone and further alkaline. TDS is less than 1,000 mg/L in first zone, while it is more in other zones. This classification of groundwater into zones is also investigated by hydrogeochemical facies, genetic classification, mechanisms of groundwater chemistry and geochemical signatures. Hydrogeochemical facies of Na+>Mg2+>Ca2+: {text{HCO}}_{3}^{ - } > Cl− > SO _{4}^{2 - } is observed from zone I, while that of Na+>Mg2+>Ca2+:Cl− > HCO _{3}^{ - } > SO _{4}^{2 - } from second to sixth zones. The genetic classification of groundwater in first and second zones is HCO _{3}^{ - } type and supported by good drainage conditions, while zones III to VI belong to Cl− category evident from poor drainage scenario. The location of six zones on mechanisms of groundwater chemistry supports sluggish drainage conditions of second to six zones, while predominate rock-water interaction in first zone. The geochemical signatures (HCO _{3}^{ - } :Cl− > 1 and Na+:Cl− < 1) also endorse the pollution. The quantities of chemical species (Mg2+, Na+, K+, HCO _{3}^{ - } , Cl ^{ - } , SO _{4}^{2 - } , NO _{3}^{ - } and F ^{ - } ) and TDS in all zones are far greater than the stipulated limits for drinking. The United States Salinity Laboratory plots discriminated the suitability of groundwater in second to sixth zones for irrigation after only special soil treatment. Higher concentrations of TDS, HCO _{3}^{ - } , Cl− and SO _{4}^{2 - } in all zones render it unsuitable for industry too. This information is crucial for public and civic authorities for taking up strategic management plan for preventing further deterioration of hydrogeochemical environmental conditions of this part of the coastal region.