Interpretation of groundwater quality applying simple statistical tools in Penna-Chitravati River Basins, Anantapur district, Southern India.

The major ion study of groundwater in parts of Penna-Chitravati river basins attains significance due to its varied hydrogeological settings and different irrigation pattern. The groundwater samples collected in pre and post monsoon seasons covering an area of 2200 km² representing aquifers in granite, sedimentary and alluvium were analysed for Ca²⁺, Mg²⁺, Na⁺, K⁺, CO₃⁻, HCO₃⁻, Cl⁻, SO₄^2-, NO₃⁻, and F⁻ ions. The graphical interpretation, statistical analysis and co-relationship between different ionic constituents were attempted to understand the various hydrochemical factors that were controlling the water quality. Basic statistical tools were applied to study the seasonal and temporal variations patterns in aquatic chemistry of the area. The studies indicate that standard deviation is high for EC, TH, Na⁺ and Cl⁻ reflecting wide dispersion from mean within the samples of different categories. The covariance shows considerable seasonal and temporal variation among some of the analysed parameters. The correlation matrix for each season and formation also indicates interdependence between K⁺, SO₄⁻², NO₃⁻ and Cl⁻ for which r-value ranges from 0.54 to 0.97. The close association between NO₃⁺-SO₄⁻²-K⁻ and Na⁺-Cl⁻ pairs suggests influence of fertilizers and local sewerage contamination in groundwater. The t test agrees with the null hypothesis that the seasonal effect on ground water was negligible whereas geological formations of an aquifer play an important role in determining the chemical characteristics of the groundwater. The TDS estimation by three different methods and their comparison show that regression model can be applied for fine tuning the TDS calculations.