ABSTRACT Groundwater quality in semi-arid crystalline terrains is increasingly threatened by both anthropogenic activities and geogenic processes. This study evaluates the seasonal and spatial variations of trace elements, including uranium, in groundwater within the Mathur watershed, northeastern Krishnagiri District, Tamil Nadu, India. A total of 46 groundwater samples were collected during the pre- and post-monsoon seasons and analysed for trace metals using atomic absorption spectrophotometry and fluorimetry. Rock samples from the study area were also analysed using XRF and petrographic classification tools (QAPF and TAS diagrams) to determine lithological control on groundwater chemistry. Results reveal that trace metals such as Ni, Cr, Pb, and U exceeded permissible limits in several locations. Seasonal variation indicates dilution from monsoonal recharge, but persistent hotspots reflect ongoing geogenic input. Uranium levels correlate strongly with the presence of quartzrich granitic rocks, suggesting lithology as the primary source. The Drinking Water Quality Index (DWQI) highlights both spatial and seasonal degradation trends, with northern regions consistently showing unsuitability for drinking purposes. This study establishes a robust link between subsurface geology and groundwater contamination and underscores the need for targeted groundwater management strategies in crystalline terrains.
Peethambaran et al. (Mon,) studied this question.