Hydrochemical analysis of salinization for a tannery belt in Southern India

This paper deals with hydrochemical analysis of groundwater salinization due to untreated effluents from 80 functioning tanneries forming a tannery belt in Southern India. A total of 29 groundwater samples were collected and analyzed. Results show that total dissolved solids (TDS), chloride (Cl(-)), and sodium (Na(+)) significantly deteriorated groundwater quality. Concentrations of analyzed hydrochemical constituents were wide ranging, suggesting that hydrochemistry was controlled by several intermixing processes, such as saline water mixing, anthropogenic contamination, and water-rock interaction. Therefore, cumulative probability distributions of selected groundwater were analyzed and accordingly, waters were classified into three types, i.e., (1) type-I waters (28%): water-rock interaction; (2) type-II waters (17%): saline water mixing; and (3) type-III waters (55%): significant anthropogenic pollution. An index, called 'saline water mixing index' (SWMI), was also developed based on the concentration of Na(+), Mg(2+), Cl(-), and SO(4)(2-) originating from the untreated tannery effluents and entering into groundwater for evaluating the relative degree of salinization. Most waters affected by the effluents had SWMI values >2.5 and 1.0 based on the 1st and 2nd threshold values, respectively. Further, correlation matrix of different chemical constituents with TDS showed that a correlation coefficient of 0.99 was observed between TDS and Cl(-), Na(+), and Mg(2+) and 0.98, 0.97, 0.85, and 0.83, between TDS and, respectively, SO(4)(2-), Ca(2+), K(+), and NO(3)(-). It was found that the quality of groundwater around the tannery cluster deteriorated mainly due to the extensive use of salts. (C) 2011 Elsevier B.V. All rights reserved.