Factors controlling the salinity in groundwater in parts of Guntur district, Andhra Pradesh, India

Abstract

Groundwater chemistry has been studied to examine the associated hydrogeochemical processes operating for the development of salinity in the groundwater in parts of Guntur district, Andhra Pradesh, India. The study area is underlain by charnockites and granitic gneisses associated with schists of the Precambrian Eastern Ghats. Groundwater is the main resource for irrigation besides drinking. Chemical parameters, pH, EC, TDS, Ca²⁺, Mg²⁺, Na⁺, K⁺, ${\text{CO}}^{{{\text{2}} - }}_{{\text{3}}}$, ${\text{HCO}}^{ - }_{{\text{3}}}$, Cl⁻, ${\text{SO}}^{{{\text{2}} - }}_{{\text{4}}}$, ${\text{NO}}^{ - }_{{\text{3}}}$, F⁻ and SiO₂, are taken into account. Groundwater is of brackish type. Na⁺−Cl⁻ facies dominates the groundwater. Examination of compositional relations and mineral saturation states shows that the ion exchange of Ca²⁺ for adsorbed Na⁺, evapotranspiration, dissolution of soil salts, dissolution of NaCl and CaSO₄, and precipitation of CaCO₃ are the dominant hydrogeochemical processes associated with the groundwater composition in the area. Evapotranspiration causes accumulation of salts in the soil/weathered zone. These salts reach the water table by leaching through infiltrating recharge water. A positive relation between depth to water table and TDS with season supports this inference. The effects of human activities, such as intensive and long-term irrigation, irrigation-return-flow, application of unlimited agricultural fertilizers and recycling of saline groundwater, act to further increase the salinity in the groundwater. Therefore, the groundwater quality increases towards the flow path, while the post-monsoon groundwater shows higher concentrations of TDS, Na⁺, Mg²⁺, Cl⁻, ${\text{SO}}^{{{\text{2}} - }}_{{\text{4}}}$, ${\text{NO}}^{ - }_{{\text{3}}}$, F⁻ and SiO₂ ions. The study could help to understand the hydrogeochemical characteristics of the aquifer system for taking effective management measures to mitigate the inferior groundwater quality for sustainable development.