Characterizing spatial variability of groundwater quality indices using GIS for Palar Basin

ABSTRACT Ensuring the availability of high-quality water is a critical challenge. This study evaluates groundwater quality in the Palar basin, Tamil Nadu, India, during 1973, 1983, 1993, 2003, 2013, and 2022, focusing on pre- and post-monsoon seasons. Key irrigation indices – sodium absorption ratio (SAR), residual sodium carbonate (RSC), sodium percentage (Na%), permeability index (PI), magnesium hazard (MH), Kelly's ratio (KR), and potential salinity (PS) – were assessed using parameters such as calcium (Ca), magnesium (Mg), chlorine (Cl), potassium (K), and sulfate (SO4). pH, electrical conductivity (EC), SAR, Na%, RSC, MH, and water quality index (WQI) showed significant spatial and temporal variability. EC ranged from 250 to >3,000 μS/cm, with industrial hotspots like Ranipet exhibiting high levels. SAR was mostly ‘excellent’ (0–10) but exceeded 18 in 1993, indicating irrigation unsuitability. Na% values >60% degraded soil permeability, while RSC and MH exceeded thresholds near industrial zones, impairing soil and irrigation quality. WQI classified most samples as ‘none’ to ‘slight,’ but hotspots >450 posed consumption risks. Seasonal variations showed post-monsoon runoff effects, increasing Na and SO4. GIS mapping and statistical analyses highlighted contamination hotspots. Mitigation requires stricter regulations, improved wastewater treatment, groundwater recharge, and sustainable agriculture to ensure long-term water quality.