Evaluation of groundwater quality for domestic and irrigation purposes in a coastal alluvial aquifer using multivariate statistics and entropy water quality index approach: a case study from West Godavari Delta, Andhra Pradesh (India)

The present study investigates the groundwater quality for domestic and irrigation purposes in a coastal aquifer in the West Godavari delta region based on geochemical evaluation, integrated multivariate statistical analysis and entropy water quality index (EWQI). The study area is underlain by the Quaternary sediments with unconsolidated to semi consolidated sand, silt and clay formation. In the study, the significant hydrochemical facies of groundwater observed were Na-Mg-Cl-HCO₃⁻, Na-Cl-HCO₃⁻ and Mg-Na-Cl-HCO₃⁻. The results revealed that the area occupies high salinity groundwater controlled mainly by evaporation and also by rock weathering-solubilization to some extent. The concentrations of major cations and anions decreased in the order: Na⁺ > K⁺ > Mg²⁺ > Ca²⁺ = Cl⁻ > HCO₃⁻ > SO₄²⁻ > NO₃⁻. The chemical constituents of the samples TA (85%), TDS (100%), TH (83%), Mg²⁺ (91%), Cl⁻(81%) and SO₄² (12%) exceeded the limits, making them unfit for drinking. Based on EWQI (53.3–143.4), nearly 70% of groundwater samples were of poor to very poor quality for drinking, which required treatment, and the remaining 30% of samples were unsuitable for domestic purposes. Some samples of the irrigation suitability parameters (Na%, SAR, RSC, PI, CAI, KR and CCR) exhibit moderate to good categories, which can be used for irrigation with proper management. The multivariate statistical analysis was performed to understand the relationships among the chemical constituents present in groundwater. TDS is highly correlated with EC, TH, Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃⁻ and Cl⁻. Principal component analysis (PCA) applied to the datasets showed that the first three PCs accounted for 65% of total variance cumulatively 94.5% for a total of 7 PCs. The PCA results indicate that the variation of groundwater quality is possibly attributed to various anthropogenic and geogenic factors, rock–water interactions and ion exchange processes in groundwater. The uncontrolled drawl of subsurface waters and aqua forming at an advanced rate when compared with recharge has led to this coastal aquifer being in a critical stage.