Assessment of hydrogeochemical processes in the aquifers of Coimbatore city, India with special reference to nickel contamination

Abstract

Rapid industrialization of the city of Coimbatore in the recent past has imposed stress on groundwater resources, resulting in quantity depletion and quality deterioration. The present study aimed at evaluating the groundwater quality of Coimbatore city, India. Qualitative analysis of 17 groundwater samples were made during the post monsoon and pre-monsoon in 2015. As groundwater forms a dominant source for irrigation and domestic pur poses, an evaluation of its suitability for these purposes were assessed. Classic geochemical methods have been coupled with geospatial approaches to arrive at the geochemical processes controlling the hydrochemistry of groundwater. The study reveals that the high concentration of Nickel and Total Dissolved Solids in the groundwater is caused due to the contamination from textile mill effluent, which is discharged into the Noyyal river and ultimately join the water table. The influence of this contamination is reflected in the geochemical processes, wherein the contaminated area exhibits different water type at different seasons; Ca-type water was converted to Na-type or mixed Na, Ca-type during the transition from post-monsoon to pre-monsoon. Majority of the samples are influenced by rock-water interaction and the dominance of the processes followed the order ion exchange > weathering > reverse ion exchange. The major driving force for ion exchange between Ca2þ in rock and Naþ in water was the abundance of Naþ in the percolating water, which is contributed by textile effluent. Among the weathering process, carbonate weathering dominated silicate weathering due to the presence of limestone deposit and red calcareous soil. The quantification of saturation index suggests that carbonate minerals are super saturated in the groundwater in the following order: dolomite > calcite > aragonite, while other minerals including fluorite, halite and gypsum were unsaturated.