Cumulative Probability and Water Quality Index (WQI) for Finding Drinking Water Suitability in a Tannery Belt (Southern India)

Groundwater quality is continuously getting polluted due to the increasing human activities and the rapid growth of urbanization in and around a tannery belt of Southern India, where around 80 functioning tanneries are discharging untreated effluents into open land and channels. Detecting and evaluating the effects of industrial and human activities are keys to finding the hydrochemical backgrounds and drinking water suitability. Thus, this paper deals with the cumulative probability distribution of analytical hydrochemical data, which was adopted to estimate the backgrounds on groundwater quality as well as quantify its abnormality. Results show two types of threshold values. The first threshold values of TDS, Ca²⁺, Mg²⁺, Na⁺ and K⁺ ions are estimated at about 906, 182, 60, 160 and 5 mg/l, respectively, whereas 191, 280, 109 and  12 mg/l for Cl⁻, \({{\text{HCO}}_{3}}^{ - }\), \({{\text{SO}}_{4}}^{2 - }\) and \({{\text{NO}}_{3}}^{ - }\) ions. They directly indicate the background levels of these ions. The second threshold values indicate the strong influence areas, mainly distributed in and around the tannery clusters. Furthermore, Water Quality Index (WQI) shows that there is no excellent groundwater type but about 59% of the samples are of poor quality for drinking water use.