Geoelectrical mapping of aquifer contamination: a case study from Roorkee, India

摘要

The impact of untreated sewage disposal and sewage irrigation practice around Roorkee, Uttarakhand, India, on groundwater contamination is studied using surface geoelectrical techniques. Electrical resistivity tomography (ERT) and transient electromagnetic (TEM) soundings data were recorded in and around a sewage-irrigated area in Saliyar and Khanjarpur and a remote site where groundwater contamination due to sewage was not expected. The sewage is mainly composed of domestic and municipal waste. Lithology data was used for correlating the resistivity values, which were derived from 2D inversion of resistivity and 1D Occam inversion of TEM data, with the subsurface formation. These two methods were used jointly to increase the reliability of the results in mapping of groundwater contamination. It was thus observed that the sewage pollutants, infiltrated through the soil, reach the shallow unconfined aquifer in and around the polluted area, up to a limited distance from the existent waste disposal sites. The present study suggests that the groundwater present in the shallow unconfined aquifer (<10 m depth) close to waste disposal sites is contaminated. It was noticed that the decrease in the resistivity of a shallow unconfined aquifer is up to 50% in comparison with that of the shallow unconfined aquifer at a remote site located about 20 km north-west of the disposal sites. The extent of the polluted aquifer zone was delineated by comparing its resistivity with that of the same aquifer at a point away from the disposal sites. Thus, the extent of groundwater pollution and relative direction of its flow were also determined qualitatively.