# Effect of Water Content on Light Nonaqueous Phase Fluid Migration in Sandy Soil
## 3 Experimental Results and Analysis
### Residual LNAPL  
The results of the soil residual LNAPL content versus water content at different water contents are shown in Figure 7. The results show that when a certain volume of diesel went into the medium, \(Q_{r}\) decreased gradually with increasing water content in the medium, and the relationship between them was nonlinear. When the medium's water content was above 12%, and the initial quantity of oil exceeded 5%, part of the diesel oil in the soil occurs in a solid phase by residual, and part of the LNAPL migrates from the unsaturated zone to the saturated zone via vertical migration. As the water content increased, the residual oil content in the soil column gradually decreased. When the water content of the medium was greater than 12%, the residual LNAPL content in the medium decreased further.  
The results (Figure 8) show that when the water content of the medium is fixed, as the oil content through the medium increases, \(Q_{r}\) gradually decreases, and a nonlinear  
\begin{table}
\begin{tabular}{c|c c c c c c c} Water Content (\%) & & & & & & & \\
**Oil Content (\%)** & & & & & & & \\
5 & \(\times\) & \(\times\) & \(\times\) & \(\times\) & \(\times\) & \(\times\) & \(\surd\) \\
6 & \(\times\) & \(\times\) & \(\times\) & \(\times\) & \(\times\) & \(\surd\) & \(\surd\) \\
7 & \(\times\) & \(\times\) & \(\times\) & \(\times\) & \(\surd\) & \(\surd\) & \(\surd\) \\
9 & \(\times\) & \(\times\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) \\
10 & \(\times\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) \\
11 & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) \\
13 & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) \\ \hline \end{tabular}
\end{table}
Table 4: Experimental results.  
Figure 7: Residual rate versus water content.  
relationship was observed between the two. As the oil content increased, the residual LNAPL content in the soil column gradually decreased. When the water content exceeded 12%, and the initial oil content exceeded 5%, the residual LNAPL content of the test medium was less than 40%, and the residual LNAPL content in the medium with different water content decreased gradually as the oil content increased. This indicates that at least 60% of the LNAPL migrates downward in a free phase state. Notably, when the medium does not reach saturation, the large pores in the medium are filled by the water phase, but the small and medium pores are not filled. When LNAPL leakage occurs, a fluid channel forms, and as the LNAPL leakage increases, the pores in the medium will gradually be filled by the oil phase, eventually migrating to the saturated zone under the action of gravity and capillary forces. Soil water content during downward migration has a strong influence on the occurrence state of LNAPL.  
Figure 9 displays a surface chart of the relationship between water content, oil content, and oil flow. Analysis of Figure 10 indicates that when the initial discharge rate of LNAPL is fixed, the water content has a greater influence on the oil flow, and the oil flow increases as the water content increases, but when the water content reaches 16%, the oil flow reaches 85%, attributed to the downward migration of LNAPL under the action of gravity. As time passes, the water phase in the soil column is gradually replaced by the oil phase, which gradually increases oil saturation in the soil column and increases the pressure of the oil phase; however, with the migration of LNAPL, the diesel saturation in the soil column will not reach complete saturation due to the hysteresis saturation effect under the action of capillary force.