<p>The geochemical impacts of monsoon cycles and human activities on trace element concentrations represent a critical gap in environmental knowledge for specific regional watersheds. While seasonal influences on groundwater quality are generally understood, the quantitative differentiation between natural and anthropogenic sources remains under-explored in the Mathur watershed, Tamil Nadu, India. This study aims to provide the first detailed analysis to distinguish between geogenic and human-induced metal contamination in this region. We analyzed groundwater and soil samples to establish a comprehensive baseline for eight key trace elements: Iron (Fe), Nickel (Ni), Cobalt (Co), Copper (Cu), Lead (Pb), Zinc (Zn), Manganese (Mn), and Chromium (Cr). A robust statistical framework, including the Geo-accumulation Index (Igeo) and factor analysis, was employed to identify contaminant sources. Our findings challenge the simple assumption of monsoonal dilution, revealing that seasonal recharge simultaneously mobilizes specific contaminants. Significantly elevated levels of Cr, Zn, and Ni were identified and statistically linked to industrial and agricultural activities. Conversely, other elements were determined to be of geogenic origin. The integration of statistical modelling and hydrogeological data serves as a replicable model for source identification in complex settings. This research provides actionable insights for environmental management, offering a critical case study for watersheds facing the dual pressures of industrial development and climate change.</p>