Assessing Aquifer Vulnerability Using GIS-Based DRASTIC Model Coupling with Hydrochemical Parameters in Hard Rock Area from Southern India

Abstract

In this article, aquifer vulnerability has been assessed by incorporating the major geological and hydrogeological factors that affect and control the groundwater contamination using GIS-based DRASTIC model. This work demonstrates the potential of GIS to derive a vulnerability map by overlying various spatially referenced digital data layers (i.e., depth to water, net recharge, aquifer media, soil media, topography, impact of vadose zone, and hydraulic conductivity) that portray cumulative aquifer sensitivity ratings across a tannery belt affected by the untreated 80 functional tannery effluents and located in a hard rock area (granitic terrain) in Southern India. It provides a relative indication of aquifer vulnerability to contamination. It has been also cross-verified with the association of selective hydrochemical parameters such as total dissolved solids (TDS), Cl⁻, ${\text{HCO}}_{3}^{ - }$, ${\text{SO}}_{4}^{2 - }$, and Cl⁻/${\text{HCO}}_{3}^{ - }$ molar ratios. The results have recognized four aquifer vulnerability zones based on DRASTIC vulnerability index (DVI), which ranged from 39 to 132. It has been deduced that approximately 18, 25, 34, and 23% of the area lies in negligible, low, medium, and high vulnerability zones, respectively. It shows that about 43% of the study area is under negligible and low vulnerable area where TDS varies from 650 to 1,796 mg/l and Cl⁻ varies from 106 to 148 mg/l. It occupies in the southern and northern most parts, whereas about 57% area in central part is moderately and highly contaminated due to the disposal of tannery industries and is more prone to aquifer vulnerability, where the high ranges of TDS (2,304–39,100 mg/l), Na⁺ (239–6046 mg/l), and Cl⁻ (532–13,652 mg/l) values are well correlated with the observed high vulnerable zones. The Cl⁻/${\text{HCO}}_{3}^{ - }$ molar ratios (=1.4–106.8) of the high vulnerable zone obviously indicate deterioration of the aquifer contamination due to the tannery effluents. It is realized that GIS is an effective platform for aquifer vulnerability mapping with reliable accuracy, and hence, the study is more useful for environmental planning and predictive groundwater management in granitic terrain.