Electrical Resistivity and Physiochemical studies for groundwater contamination at waste dumping site: A case study for I-12 Sector, Islamabad, Pakistan

Abstract

An open dumping site is a major environmental issue that affects water, air, surface water, and ground water. Ground water is a valuable supply of water, yet it's contaminated by leachate, which includes numerous harmful chemical compounds. The purpose of this study was to look into the impacts of leachate on hydrology in the I-12 area of Islamabad. Four vertical electrical resistivity soundings (VES) were recorded using the Schlumberger electrode design, with two VES acquired upstream and two VES acquired downstream of the research region. In addition, five ERT profiles were obtained to explore the impacts of leachate on water. Due to non-availability of borehole data, we compared the vertical sounding and electrical resistivity results to confirm the distribution of leachate in the subsurface. The VES were acquired over the ERT profiles. In ERT profiles the leachate are identifiable based on the encountered resistivity values. For the similar area the VES shows abnormal resistivity curves due to the existence of different contaminant in combination at one place. This simply explains the nature of leachate having variable resistive materials. In the inversion results the contaminated leachate distribution is variable and exists in patches. The maximum depth for the encountered contaminated leachate varies between 38-40 m. The resistivity range for the contaminated leachate ranges between 0-30 Ωm. This resistivity range was assigned based on the test profile, which was acquired in the open field near the dumpsite. Forty-one points were selected for water sampling at different specific distances from the sites in the study area as well as surrounding area to check the extend of contaminated water. Then the samples were examined for seventeen parameters that included electrical conductivity (EC), total dissolved solids (TDS), pH, bicarbonate (HCO3), calcium (Ca), magnesium (Mg), chloride (Cl), sulfate (SO4), hardness, sodium (Na), potassium (K), fluoride (F), and arsenic (As), nitrate (NO3), phosphate (PO4), iron (Fe) and lead (Pb) to investigate the affected ground water quality. The concentration of Arsenic with an average value 34.49 ranges from 7.89– 98.7 and that only 5% of the samples collected had arsenic concentrations within the WHO limit, while 95% of the samples exceeded the limit. The Gibbs plot indicate that the major controlling factor that change the groundwater chemistry is Rock dominance ix and only three samples lie in atmospheric precipitation zone. The health risk assessment is done by Average daily dose (ADD), Hazard quotient (HQ) and Carcinogenic risk (CR). For irrigation purpose Sodium Adsorption Ratio (SAR), Sodium Percentage (Na%), Kelly’s Ratio, Magnesium Adsorption Ratio (MAR) and Salinity Hazard analysis are done, and calculations shows that the groundwater is suitable for the use of irrigation. The water quality index analysis is performed by collecting groundwater samples in the study area. The water quality index analysis shows that 34% of the groundwater samples lie in the excellent class, 36% groundwater samples lie in good water quality class, 20% lie in poor class, 10% in very poor class and no sample lie in worse class. Nearly 95% of the groundwater samples analyzed have Hazard Quotient (HQ) values greater than 1, indicating a potential risk of adverse health effects from exposure to the analyzed substances. Only 5% of the samples have HQ values lower than 1, suggesting that the exposure to the analyzed substances in these samples is unlikely to result in significant health effects.