Hydrogeochemical investigation of groundwater quality in the hard rock terrain of South India using Geographic Information System (GIS) and groundwater quality index (GWQI) techniques

A total of 194 groundwater samples were collected from hard rock terrain of Medak, a fast urbanizing region of Telangana State, South India to assess the groundwater quality using Geographic Information System (GIS) and groundwater quality index (GWQI) techniques. Groundwater samples were analyzed for pH, electrical conductivity (EC), total dissolved solids (TDS), total hardness (TH), calcium (Ca2+), magnesium (Mg2+), sodium (Na+), potassium (K+), bicarbonate (HCO3-), chloride (Cl-), sulfate (SO42-), nitrate (NO3-) and fluoride (F-). The minimum and maximum values of pH (6.6-8.79), electrical conductivity (168-3170 mu S/cm), total hardness (50-1550 mg/L), bicarbonate (18-527 mg/L), sulfate (21-328 mg/L), calcium (10-164 mg/L), magnesium (2.4-680 mg/L), sodium (14-145 mg/L) and potassium (1-24 mg/L) were recorded in the hard rock terrain of Medak region. About 32% and 22% of groundwater samples exceeded the maximum desirable limit of Cl- and SO42- for drinking purposes as prescribed by the World Health Organization (WHO) standards. The total dissolved solids classification divulges that the 182 groundwater locations are within the enviable for drinking uses. The analytical data reveals that the nitrate concentrations vary from 4 to 440 mg/L, with a mean of 73 mg/L. It is noted that the maximum value (440 mg/L) is one of the highest value found in Medak district, and 50% of the total samples show nitrate concentrations exceeding the maximum permissible limit recommended by WHO. The high fluoride concentration (>1.5 mg/L) in about 57% of the groundwater samples are beyond the recommended limit of drinking purposes. Spatial distribution of high fluoride concentration is noticed in the eastern and also some parts of the western region, while high nitrate concentration is shown in north and southern agricultural regions of the study area. The chemical relationships in Piper diagram identified Ca2+-Mg2+-Cl-, Ca2+-Na+-HCO3- and Ca2+-HCO3- are all most predominant water types, while Gibbs diagrams revealed that groundwater of the study region are mainly controlled by rock weathering dominance and partially evaporation dominance. The GWQI indicates that 37.11% and 57.21% of groundwater samples are excellent and good in water quality for drinking uses, respectively. Geologically, 80% of the study area consists of granites and gneiss, and 20% with basalts and laterites. Eventually, groundwater quality in the Medak region is fettered by geogenic and anthropogenic activities, therefore, people are advised to maintain a groundwater management strategy to protect further sustainability.