Imaging of groundwater contamination using 3D joint inversion of electrical resistivity tomography and radio magnetotelluric data: A case study from Northern India

Abstract

The impact of untreated sewage irrigation and waste disposal practices on groundwater is investigated by 3D joint inversion of radio magnetotelluric and electrical resistivity tomography data. In this case study, electrical resistivity tomography and radio magnetotelluric field measurements were carried out on several profiles near a waste disposal site which was irrigated with untreated sewage water for agriculture purpose. In addition, radio magnetotelluric and electrical resistivity tomography measurements were carried out, far away from the waste site, to derive the uncontaminated geology. The data were analysed earlier using 2D inversion techniques. However, for the 2D inversion of the electrical resistivity tomography and radio magnetotelluric data, assumptions about the strike direction are required. As no clear strike direction is evident for the contamination, we considered the problem as 3D and interpreted the present data set using the 3D inversion algorithm ‘AP3DMT‐DC’. The inverted 3D resistivity model shows an unconfined aquifer of low resistivity which is overlain by an unsaturated slightly resistive near surface formation. With increasing distance from the waste sites, an increase in the resistivity of the shallow unconfined aquifer is observed. Furthest away from the waste site undisturbed geology is expected. We derived consistent and meaningful 3D resistivity models. The uncontaminated reference site indicates an increased resistivity for the aquifer layer. A synthetic 3D study was carried out to demonstrate and validate algorithm performance as well as convergence capabilities. The study demonstrates that the two methods, electrical resistivity tomography and radio magnetotelluric, complement each other. Besides, a better resolved inverted model is obtained through a 3D joint inversion, in comparison to individual 2D and 3D inversions.

Tracking contaminant transport using time-lapse geophysics: A review on applications of electrical methods

“…Recently, electrical resistivity and radio magnetotelluric methods were used to map the waste disposal site which was irrigated with untreated sewage water for agriculture purpose [22]. Surinaidu et al [82] used a multidisciplinary approach including ERT, satellite-based land surface temperature observations, continuous Soil Electrical Conductivity and Volumetric Soil Moisture, to identify contaminated perennial groundwater seepage source locations in the highly industrial watershed in Hyderabad city.…”

Two‐dimensional joint inversion of electromagnetic soundings at low induction numbers and direct current resistivity

“…In contrast, the DCR data are collected by a multi‐electrodes system along a line. The current is injected directly into the earth, and the potential difference is measured on the surface (Devi et al., 2020).…”

Electrical resistivity tomography monitoring of two managed aquifer recharge ponds in the alluvial aquifer of the Llobregat River (Barcelona, Spain)

“…Reliance on geophysical responses to changes in soil moisture content, gauged through changes in electrical resistivity or dielectric constant, is the key factor that enables non-invasive techniques to be used to monitor the vadose zone in time-lapse mode (repeated measurements over time). The widespread use of multi-electrode systems for electrical resistivity tomography (ERT) was a step forward in monitoring, for example, the infiltration of rain into the soil (Benderitter and Schott, 1999), because the use of this technique in different configurations and at different depths of the NSZ can be done at a lower cost (Mitchell, 2010) and can provide high resolution images of hydrogeological structures (Perdomo et al, 2018;Ikard and Pease, 2019;Devi et al, 2020).…”