## 3 Results and Discussion
### Pollution Identification Based on ERT  
According to the literature and application examples, the resistivity of organic compounds, such as vinyl chloride and hexachlorocyclohexane, can reach 10\({}^{6}\)-10\({}^{7}\)\(\Omega\)-m [32,33]. After injecting into the soil, different soil particles also change the resistivity. The resistivity of pollutants in the sand is often higher, between 200 and 350 \(\Omega\)-m, then silty loam is between 100 and 200 \(\Omega\)-m, and silty soil is lower, often below 10 \(\Omega\)-m [54]. The resistivity of the pollution plume distribution or residual position of organic compounds in most sites often exceeds 100 \(\Omega\)-m. The resistivity here was higher and the concentration of pollutants was greater. When there is a clay lens at the actual site, it hinders the migration of organic compounds and the resistivity may be as high as 1000 \(\Omega\)-m; therefore, it can  
Figure 4: The site resistivity background value that was used as reference setting for further work. be used to identify contaminated areas [32; 50]. The background resistivity value in our profile was mainly between 20 and 40 \(\Omega\)-m. After some organic pollutants enter the soil, they are adsorbed onto the soil and remain in the soil for a long time, leading to parts of the profile being extremely high. Below the depth of the water table, some areas also show relatively high values, which could be due to the high concentration of pollutants entering the aquifer and being adsorbed onto the medium, thereby increasing medium resistivity. In the near-surface area of our study, the resistivity of some parts reached 200 \(\Omega\)-m, which could be caused by the accumulation of construction waste on the surface. The decrease in resistivity at the bottom was caused by proximity to the aquifer and the increase in water content. The ML-II section had an obvious high-resistance anomaly area at a distance of 0-25 m and a depth of 2-6 m, where the resistivity exceeded 600 \(\Omega\)-m. It could be the underground part of the acid tank. In the range of 25-30 m, there was a high-resistance area near the surface, which could be caused by the accumulation of surface construction waste. The resistivity below this area dropped significantly, but then rose significantly at a depth of 5-10 m, reaching 140 \(\Omega\)-m. Compared to its right side, there was a significant increase, which was connected to the high-resistance area on the left side. This could be caused by the diffusion of pollutants in the tank. At the same time, it tended to diffuse to the east and the whole area was similar to a strip. There were two obvious high-resistance abnormal areas at 25-35 m and 40-50 m on the ML-III section where the resistivity was 200 \(\Omega\)-m. Both of these areas tended to go down and east. It was close to the semi-open unloading platform, which could be due to the leakage of raw materials during loading, unloading, transportation, and migration. The pollutants permeated from the surface to the depths of the ground, resulting in high concentrations of pollutants in the soil and groundwater. This profile was parallel to the flow direction of the groundwater. Due to the flow of groundwater, it diffused from upstream to downstream. Pollutants flowed through the entire profile and were adsorbed onto the soil. Therefore, the resistivity of the entire profile was higher than those of ML-I and ML-II and the overall resistivity was above 90 \(\Omega\)-m. The overall resistivity on the cross-section was relatively high and the pollution in this area was severe. At 5-15 m, the resistivity was 500 \(\Omega\)-m, which is relatively high. Similarly, the overall resistivity of the ML-IV profile was relatively high, which was also due to contamination. At the same time, in the range of 20-40 m and at a depth of 2-5 m underground, the resistivity of the center position was more than 200 \(\Omega\)-m, which tended toward infiltration. The resistivity of the east side gradually decreased, which could be caused by the diffusion of pollutants.