###### Abstract  
The refined characterization of groundwater pollution is an important prerequisite for efficient and effective remediation. A high-resolution survey of a contaminated site in a chemical pesticide factory was carried out using non-invasive geophysical sensing technology. Modern electrical resistivity tomography (ERT) technology can rapidly identify and characterize the groundwater pollution plumes of organochlorine pesticides, which was demonstrated in this study by the significantly abnormal resistivity sensing in stratums and aquifers under the raw material tanks, production, and loading areas. The results were found to be highly consistent with the ERT sensing results achieved via incorporating borehole sampling and hydrochemical analysis. With high abnormal resistivity, the range of contamination within the profile was characterized on the meter level. We also unexpectedly found new pollution and explained its source. This study confirmed that the modern refined ERT method has a high feasibility and accuracy in characterizing the spatial distribution of organochlorine pesticide plumes in groundwater. electrical resistivity tomography; contaminated sites; pesticides; groundwater; apparent resistivity +
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result in a more extensive pollution effect and pose a more severe challenge for environmental remediation and governance [25; 26]. Therefore, pesticide safety has become a hot environmental issue of global concern [27; 28]. Traditional hydrogeological survey methods have inherent limitations. Due to the closedness and concealment of groundwater, it is very difficult to detect groundwater pollution. Groundwater samples have to be collected through drilling and then analyzed in a laboratory. The process is complex and time-consuming and has a high cost, and the number of sampling points and data acquisition are limited and discontinuous. Moreover, there is a risk of aggravating the diffusion of pollutants. Geophysical techniques that have the advantages of remote sensing, rapid deployment, and the ability to record higher density and continuous data have been used in hydrogeological exploration and water investigation for many years. Due to the significant differences between the contaminated strata and the surrounding environment, geophysical exploration techniques can respond efficiently. Some common methods, including the modern high-density electrical method (ERT), ground-penetrating radar (GPR), and induced polarization (IP), have been applied to the field of contaminant hydrogeology [29]. These geophysical investigations have been applied in many fields, including: the application of 2D imaging technology to detect the leakage area of petroleum pollutants and the monitoring of their degradation process [30; 31; 32; 33; 34; 35]; monitoring the diffusion channels of heavy metal ions in tailings ponds and slag piles and establishing the relationship between their resistivity and ion concentration [36; 37]; detecting the integrity of the impervious layer at the bottom of landfill plants and finding pathways of leachate leakage [38; 39]; and determining seawater intrusion channels [40; 41]. ERT is a non-invasive and non-intrusive way to access specific underground conditions. ERT remotely explores underground conditions that are tens of meters deep by placing multiple electrodes on the ground and arranging them in a row. Rather than directly contacting the object underground, ERT maps the profile and underground features from a long way off. [PERSON] et al. [42] used ERT to monitor abandoned hydrocarbon-contaminated sites. Combined with the results of geochemical methods, they showed that hydrocarbon degradation products and the enhanced weathering of ones would lead to a decrease in regional resistivity, proving that electrical methods can effectively describe pollution in aging contamination sites. [PERSON] et al.