Discussion on the suitability of electrical resistivity tomography method to detect DNAPLs contaminantion

Due to the high resistivity of dense non-aqueous phase liquids (DNAPLs),there is a significant difference in electrical properties between the underground medium and the groundwater. Because of this difference, electrical resistivity tomography (ERT), which is a non-intrusive monitoring method, has shown its potential in detecting organic contaminated sites . However,in field survey ,the ERT couldn’t reveal the obviously high resistivity anomaly sometimes, or the high resistance anomaly is caused by the heterogeneity of the medium rather than the DNAPLs, thus caused the result of the miscarriage of justice.In order to explore the suitability of the ERT in DNAPLs contaminated site, this paper calculates the total true resistivity under different DNAPLs saturation conditions by using effective medium resistivity model. It is theoretically explained that there is no significant high resistance anomaly when the DNAPL saturation is small. Then, an ideal ERT forward model is established to disscuss the suitability of ERT. Results show that the heterogeneity of the medium (such as high resistance of gravel, etc) on the ERT detection has a strong interference, which may cause the miscarriage of justice of the DNAPLs distribution of the scope,and conventional static ERT detection of DNAPLs pollution is only applicable to the conditions which the DNAPLs saturation is high in homogeneous or heterogeneous medium. When the saturation of DNAPLs is small,if the DNAPLs saturation is low,the differential inversion method based on time domain can effectively weaken the influence of the heterogeneity of the medium, and recognize the distribution of DNAPLs accurately.