Hydrogeochemical Assessment of Groundwater Suitability for Drinking and Irrigation in the Limestone Terrain of Southern Kaladgi Sub-Basin (Pre-Monsoon), Karnataka, India

Abstract

Water, the most essential natural resource for life and the environment, is becoming scarce due to increasing demand, making conservation through reduced wastage, recycling, reuse, and artificial recharge crucial.This study evaluates the suitability of pre-monsoon groundwater in the Limestone Terrain of Southern Kaladgi Sub-Basin of Bagalkote district, Karnataka, for drinking and irrigation purposes. The region is predominantly underlain by sandstone, limestone, dolomite, and granite formations. A total of 44 groundwater samples were collected and analyzed to determine their physicochemical characteristics. The Drinking Water Quality Index (DWQI) was calculated using the Weighted Arithmetic WQI method based on the permissible limits specified inthe Indian Standard (IS 10500:2012). The analysis showed that the water at all sampled locations (44 out of 44) is currently suitable for drinking, with 38 villages classified as Excellent (DWQI< 50) and 6 as Good (50 < DWQI< 100). Hydrogeochemically, the water is characterised by the Ca – HCO3facies which is characteristic of systems dominated by the dissolution of carbonate and dolomitic rocks. The system is considered geochemically immature. For irrigation suitability, indices like the Sodium Adsorption Ratio (SAR) and Magnesium Hazard Ratio (MHR) were calculated. While the majority of samples show a low sodium hazard, the sample from Kalabandakeri was a consistent outlier, classified as a severe sodium hazard (SAR of 9.77) Crucially, the Magnesium Hazard Ratio (MHR) indicated a significant magnesium hazard, classifying 34 out of 44 samples (approximately 77.3%) as unsuitable for irrigation based on this index This highlights that while the water is safe for consumption, its long-term use for irrigation is constrained by a pervasive Magnesium Hazard.