GEOPHYSICAL INVESTIGATION AND GROUNDWATER QUALITY ASSESSMENT AROUND AN MSW SITE

Abstract

The study focuses on geophysical investigation using vertical electrical soundings along with chemical analysis of groundwater resources around the MSW dumpsite of Roorkee at Saliyar, Uttarakhand. At this site five VES were conducted first using Schlumberger array configuration to characterize the subsurface lithology and the underlying aquifer properties. From the apparent resistivity data obtained in field experiments, an estimate of the true resistivity was obtained along with the underlying formation using IPI2Win software. It was found that there is an unconfined shallow aquifer starting at depths of around 6-7 m bgl. during the post monsoon season of the area. A contaminant plume probably due to the MSW leachate was found in between 7-30 m bgl at locations of VES stations II and III, which are close to the dumpsite. The secondary geophysical parameters, Dar Zarrouk, were obtained to find the aquifer properties such as longitudinal conductance, transverse resistance, and coefficient of anisotropy. The soil resistivity of unsaturated zone was also taken into consideration to judge the protective capacity of the aquifer against the MSW originated pollution. Groundwater samples were also collected from the nearby handpumps and tube wells to analyze their quality parameters. Parameters like pH, EC and TDS were measured in-situ using the multi-parameter probe and their detailed analysis was performed in the laboratories of IIT Roorkee. Total hardness (TH) and sulfate concentrations were found higher in a few samples above the BIS and WHO allowable limits, while nitrate concentration was above the permissible limit. The hydrochemical facies of the samples were studied in detail using the Piper and Durov diagrams. Further, correlation plots were obtained between the major ions/cations and the easily measurable in-situ parameters (pH, TDS, EC). Relevant water quality indices, like groundwater quality index (GWQI), sodium adsorption ratio (SAR), residual sodium bicarbonate (RSC), soluble sodium percentage (SSP), magnesium hazard (MH), Kelly’s ratio (KR), permeability index (PI) and potential salinity (PS) were then calculated to assess the status of groundwater in the study area. The GWQI showed high correlation with nitrate concentration showing nitrate dominance in the groundwater of the area. The other irrigation indices (SAR, RSC, SSP, MH, KR, %Na, PI, and PS) were also studied to analyze the groundwater suitability used for irrigation purposes. Concentrations of the heavy metals were found above permissible limits for Cr, Mn, Ni, Fe, Pb, Al, Cd in majority of the samples. The computed range of heavy metal indices; heavy metal pollution index (HP), heavy metal evaluation index (HEI) and degree of contamination (Cd) were used to see the cumulative impact of the heavy metals.