Hydrogeochemical Evaluation of Groundwater Quality for Drinking and Irrigation in a Granite Mining Region of Chikkaballapur District, Karnataka, India

Abstract

This study investigates the hydrogeochemical characteristics and suitability of water resources for human consumption and agricultural irrigation in the granite mining area of Chikkaballapur District, Karnataka. A total of thirty-five water samples were collected during the pre-monsoon season and analyzed for eleven critical physicochemical parameters. The drinking water Quality Index (DWQI) was calculated using the weighted arithmetic method (Brown et al., 1970), and irrigation suitability was evaluated through seven standard indices, including Sodium Adsorption Ratio (SAR), Residual Sodium Carbonate (RSC), and Permeability Index (PI) (Richards, 1954). The results reveal a significant regional water quality crisis driven by geogenic mineral weathering and anthropogenic mining impacts. The DWQI values ranged from 18.51 to 162.34, with Arror mines identified as the only source of "Excellent" quality water. Approximately 48.6% of the sampled locations (including Chinnepalli mines, Kanishhyhalli, and Mittemari mines) were classified as "Poor Water" (DWQI > 100), rendering them unsuitable for direct ingestion. Fluoride enrichment (up to 1.91 mg/l) and high Total Hardness (up to 669 mg/l) were the primary factors contributing to this degradation, with Fluoride alone accounting for 77.5% of the total index influence. While the irrigation indices indicate the water is generally safe for agricultural use, 40% of the samples fall into the high-salinity (C3S1) category, requiring careful soil management. This study concludes that immediate interventions, specifically community-scale defluoridation and strict regulation of mining waste, are required to mitigate severe public health risks, such as dental and skeletal fluorosis, in the mining-impacted communities of Chikkaballapur.