Hydrogeochemical Evolution and Drinking Water Suitability Assessment of Groundwater in Semi-Arid Basaltic Terrain of Akkalkot Taluka, Maharashtra, India

Abstract

Groundwater is the principal source of drinking and irrigation water in the semi-arid Deccan basaltic terrain of Akkalkot taluka, Solapur district, Maharashtra. This study assesses the hydrogeochemical evolution, the geochemical processes governing groundwater composition, and the drinking-water suitability of the resource using 5,352 groundwater samples drawn from handpumps, dug wells and borewells over eight hydrological years (2016–17 to 2023–24). The water is neutral to slightly alkaline (mean pH 7.5) and predominantly hard to very hard (93% exceed 150 mg L⁻¹ as CaCO₃). Electrical conductivity (mean 1,532 µS cm⁻¹) and total dissolved solids (mean 989 mg L⁻¹) indicate moderate mineralization. Piper and Chadha diagrams reveal a mixed facies assemblage dominated by Ca–Mg–HCO₃ recharge water (33%) that evolves towards Na–HCO₃ and Na–Cl types. Gibbs plots, Na⁺/Cl⁻ ratios (>1 in 74% of samples) and negative chloro-alkaline indices (74%) identify silicate (plagioclase) weathering and cation exchange as the dominant controls, modified by evapoconcentration. Elevated nitrate (exceeding the 45 mg L⁻¹ limit in 29% of samples) reflects anthropogenic loading from both agricultural fertilizers and sanitation sources. The weighted-arithmetic water quality index rated 78% of samples as excellent–good; hardness, salinity and nitrate are the chief constraints on potability.