## 3 Experimental Results
### Characteristics of Resistivity Change  
From Figure 7a-c, when the LNAPL leaks for 120 min, the resistivity change rate is 10-20% in the vertical direction. With the increase of leakage, the high-resistance region gradually spreads from the center point to both sides. After 2 h of leakage, the resistivity change rate near both sides of the leakage point becomes larger, indicating that the oil continued its slow horizontal migration after rapid vertical migration due to the fact that the migration of the LNAPL is subjected to the effect of the capillary force and the difference of its own density horizontally. In the vertical direction, the migration is affected by gravity, so the rate of change of resistance is mainly downward, supplemented by left-right migration. In general, under homogeneous conditions, the LNAPL migrates mainly in the vertical direction, supplemented by left-right migration, and the resistivity change rate reaches up to about 50% in the vadose zone (Figure 7). In the middle of the sand box (x = 0.5 m, y = 0.13 m), there is an area of reduced resistivity value. This phenomenon reflects the process of oil and water repulsion after the leakage of LNAPL. The water in the pore space has been displaced and migrated, resulting in the formation of an area of reduced resistivity value. Figure 6: Maximum migration distance for different test groups. Figure 7: Rate of change of resistance (no lens-shaped aquifer). (**a**) 30 min (**b**) 60 min (**c**) 120 min (**d**) 180 min (**e**) 240 min (**f**) 300 min. When there is a low-permeability lens in the medium, when LNAPL reaches this lens body, the vertical migration is blocked, and the resistivity change rate is 50%. When the diesel oil leaks for 100 min, it can be observed that the horizontal diffusion rate of the LNAPL is greater than the vertical diffusion rate. At this time, the resistivity change rate of the leak point is 50%, and the high resistance is mainly concentrated in the diffusion around the leak point as the center (Figure 8). When the leakage is 200-300 min, the LNAPL further accumulates and diffuses at the location of the leakage point, and due to the existence of the low-permeability lens [34], the vertical migration of LNAPL above the low-permeability lens gradually decreases, after which there is an obvious bypass phenomenon [35]. After the LNAPL bypasses the lens, both horizontal and vertical diffusion ranges expand, with resistivity changes between 10-25%. As shown in Figure 8d,e, after 300 min of leakage, diffusion increases further, though horizontal migration remains smaller than vertical. The resistivity change rate inside the low-permeability lens tends to rise due to the slow infiltration of the LNAPL, which does not reach saturation levels because of the lens's low permeability, maintaining the resistivity change rate at 10-25%. In contrast, the saturated state shows a resistivity change rate of around \(-\)40%. Figure 8f indicates that the resistivity change rate below the lens gradually increases, suggesting the LNAPL migrates to the lens' bottom under capillary action post-bypass. However, the top of the lens shows a resistivity change rate of 30-50%, while the bottom has about 10%, with the top exhibiting higher resistivity than the bottom of the lens. When there is a high-permeability lens in the medium, it forms a preferential channel within the lens, causing the LNAPL to migrate mainly vertically, with some horizontal migration. When leaking for 60 min, the LNAPL migrates downward through the inside of the lens to the buried depth of 0.15 m. Currently, the horizontal diffusion range also starts to increase, and the migration distance in the horizontal direction increases from 0.05 m to 0.15 m. When diesel oil leaks for 300 min, the resistivity rate of change reaches the maximum value, and the area of the resistivity growth area is obviously increased from Figure 9d,f.