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.

中文翻译：

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使用 ERT 和 RMT 数据的 3D 联合反演对地下水污染进行成像：来自印度北部的案例研究

摘要 通过无线电大地电磁和电阻率层析成像数据的 3D 联合反演研究了未经处理的污水灌溉和废物处理实践对地下水的影响。在这个案例研究中，电阻率断层扫描和无线电大地电磁场测量是在废物处理场附近的几个剖面上进行的，该场被未经处理的污水灌溉用于农业目的。此外，在远离垃圾场的地方进行了无线电大地电磁和电阻率层析成像测量，以得出未受污染的地质。之前使用 2D 反演技术对数据进行了分析。然而，对于电阻率层析成像和无线电大地电磁数据的 2D 反演，需要对走向方向进行假设。由于没有明显的污染走向，我们将问题视为 3D，并使用 3D 反演算法“AP3DMT-DC”解释当前数据集。倒置的 3D 电阻率模型显示了低电阻率的无承压含水层，其上覆盖着不饱和的低电阻近地层。随着与废物场地距离的增加，可以观察到浅层非承压含水层的电阻率增加。预计离垃圾场最远的地方是未受干扰的地质。我们导出了一致且有意义的 3D 电阻率模型。未受污染的参考地点表明含水层的电阻率增加。进行了合成 3D 研究以演示和验证算法性能以及收敛能力。研究表明，这两种方法，电阻率断层扫描和无线电大地电磁，相得益彰。此外，与单独的 2D 和 3D 反演相比，通过 3D 联合反演获得了更好解析的反演模型。