Characterization of an aquifer in Roorkee, India using the spatially constrained inversion of in-loop TEM data
The study area is a sewage farm in Saliyar in the state of Uttarakhand, India, which is irrigated using untreated sewage from the nearby city of Roorkee. Previous studies showed that due to sewage irrigation the first unconfined aquifer at a depth of 5–15 m is contaminated. The aim of this study is to characterize the deeper aquifers to a depth of 100 m, underlying the first unconfined aquifer. Therefore 46 in-loop TEM measurements were carried out in the farming area and an uncontaminated reference site with a transmitter loop of 50 x 50 m² and receiver loops of 20 x 20 m² and 5 x 5 m². To benefit from the geologically expected one-dimensional subsurface we applied the spatially constrained inversion technique on the data resulting in a geologically reasonable model and allowing the identification of a conducting layer of 28 Ωm as the second aquifer. The resolution of model parameters was computed using singular value decomposition. The low resistivity of the underlying aquifer, however, is not locally restricted to the sewage farm but is also visible in the reference area; it is therefore unlikely caused by irrigation with untreated sewage.