Physico-chemical characteristics of borewell waters of Bellary taluk, Karnataka, India

Abstract

The study area was undertaken in the serial hillocks mining area of Bellary taluk located in the Bellary district, Karnataka. The important geological formations in this area were Archean granites (pink to grey), schists/phyllites and peninsular gneiss. The assessment of water quality for its suitability for agricultural and domestic purposes was carried out. The results of chemical analysis for the major ions of 40 water samples, collected from the study area of Bellary taluk, have been evaluated. The quality analysis was performed through the estimation of calcium, magnesium, sodium, potassium, iron, zinc, manganese, carbonate, bicarbonate, sulphate, chloride, fluoride, nitrate, total alkalinity, total dissolved solids, turbidity, pH, electrical conductance and total hardness. Based on the analysis, certain parameters like sodium adsorption ratio, percent sodium and magnesium ratio were calculated. The bicarbonates (68 to 630 mg/L) and total alkalinity (241 to 429 mg/L) were medium and this may be due to the presence of crystalline schists and granitic gneiss in the study area. Based on the Piper trilinear diagram, it is confirmed that the dug wells were characterized by high amount of calcium and magnesium in the mining areas. In the study area 70% of the water samples fall under mainly C2S 1, C3S1 and C3S2, which were suitable for irrigation of most crops as per USSL. The remaining 30% samples falling in C3S3, C4S2, C4S3 and C4S4 were not suitable for irrigation. From SAR classification, 75% of the water samples contained carbonate hardness and only 25% contained non carbonate hardness. The presence of E.coli in only seven dug wells indicated potential and dangerous faecal contamination, which require immediate attention. Fluoride was most dominant ion responsible for contamination of the groundwater. Seven water samples of the study area were prone to excess fluoride concentration (>1.2 mg/L) and not suitable for drinking purpose. These studies indicate that the water quality of 70% of the dug wells is suitable for both domestic and irrigation purposes, where as in the 30% of the water samples, one or the other chemical constituent was found beyond WHO permissible limits. The study indicates the need for periodic monitoring of groundwater in the study area.