Hydrogeochemical characterisation and appraisal of groundwater suitability for domestic and irrigational purposes in a semi-arid region, Karnataka state, India

Abstract

Hydrogeochemical investigations have been carried out in a semi-arid region of Aland taluk of Karnataka State, India. The analysis has been done to examine the quality of groundwater for drinking, domestic and irrigational purposes. In this concern, thirty-two groundwater samples were collected in pre-monsoon (April 2016) and post-monsoon season (November 2016), from the different location within the study area. These samples have been further analysed for different ions such as CO32−, HCO3−, NO3−, Ca2+, Mg2+, Na+, K+ Fe2+, SO42−, Clˉ and F− to evaluate the hydrochemical behaviour with SSP (sodium soluble percentage), SAR (sodium absorption ratio), % Na (percentage sodium), RSC (residual sodium carbonate), KR (Kelly’s ratio), PI (permeability index) and MH (magnesium hazards). These positive and negative ions have been further correlated with the maximum annual rainfall within the study area to find out the variations between these ions for the precipitation. Suitability of groundwater for drinking purposes around the catchment was not suitable except in a few places. Irrigational suitability of groundwater showed that the water is within the limit for irrigation except in a few locations. Wilcox diagram depicts that 90% of the pre-monsoon samples and 65% of the post-monsoon samples fell into excellent to good category zone. US salinity diagram explains that 71% of pre-monsoon samples belong to medium-salinity-hazard to low-sodium-content zones, whereas 50% of post-monsoon samples fall into high-salinity-hazard to low-sodium-content zone. Gibbs’s plot showed that the water–rock processes control the geochemistry of the Aland region in both monsoon seasons. Chadha’s diagram depicts that 56.25% of the groundwater samples fall under the subfield of Ca2+–Mg2+–Cl− water type with permanent hardness during pre-monsoon season, whereas 50% of groundwater samples falls under the subfield of Ca2+–Mg2+–HCO3− water type with temporary hardness during post-monsoon season.