# Effect of Water Content on Light Nonaqueous Phase Fluid Migration in Sandy Soil
## 3 Experimental Results and Analysis
### Relationship Between LNAPL Movement Rate and Water Content  
Figure 10 presents the relationship between LNAPL flow rate and time under different water content conditions. Analysis of the data in the Figure indicates that the LNAPL flow rate increases slowly with time when the water content is 4%, 6%, and 8%, and there is a power function (math) relationship between the two. The fitting curve is \(y=a\,\times\,x^{b}\). Nevertheless, as the water content in the soil column gradually increased, the LNAPL flow rate decreased and then increased at the water contents of 10%, 12%, 14%, and 16%. The nonlinear fitting curve was \(y=y^{0}+A\,\times sin\) (\(\pi\,\times\,(x-xc)/w\)). The details of the nonlinear fitting functions for different water content conditions are provided in Table 5.  
Figure 8: Residual rate versus oil content.  
To better understand the influence of water content in the soil column on the diesel flow rate, the duration of the experiment was increased, and the water content was found to have less effect on the LNAPL flow rate per unit time below 8%. After the water content exceeded 8%, the LNAPL flow rate decreased and then increased with an increase in time. At 10% water content, the diesel flow rate was 135 mL in 362.33 s when the flow rate inflection point occurred. The flow rate increased beyond this time and decreased at 362.33 s. When the water content was 12%, the diesel flow rate reached its lowest point at 204.05 s of 65 mL, and the flow rate exhibited an increasing trend beyond this point. When the water content was 14%, the diesel flow rate reached its lowest point at 783.47 s of 90 mL, and the flow rate presented a nonlinear increasing relationship beyond this point. At 16% water content, the diesel flow rate reached its lowest point at 55 mL in 1605.45 s, and the long-term flow rate had a nonlinear growth relationship with time beyond this point.  
Thus, the greater the oil content of the medium, the less the migration of diesel and the slower the migration rate because in the oil-water two-phase flow in the porous medium, due to the influence of interfacial tension, a transition zone forms between the oil-water interfaces, whose size is affected by fluid. The upper edge of the transition zone has good changing interface characteristics. The distribution of both water and oil phases above the transition zone is uniform, and the oil phase below the transition zone is influenced by the water phase. The pressure difference at the oil-water interface is considerable, so LNAPL will migrate horizontally due to the large pressure difference. As a result, the LNAPL flow rate first decreases and then increases when the water content exceeds 10%, but as the  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Water Content\%** & **Fitting Function** & \(\mathbf{a}\) & \(\mathbf{b}\) & \(\mathbf{R^{2}}\) \\ \hline
4 & & 5.19 & & 1.01 & 0.989 \\
6 & \(y=a\times x^{b}\) & 1.28 & & 1.63 & 0.993 \\
8 & & 3.77 & & 3.38 & 0.957 \\ \hline
**Water content\%** & **Fitting function** & \(\mathbf{y^{0}}\) & \(\mathbf{xc}\) & \(\mathbf{w}\) & \(\mathbf{A}\) & \(\mathbf{R^{2}}\) \\ \hline
10 & & 0.01 & \(-\)144.6 & 356.7 & 0.0039 & 0.998 \\
12 & \(y=y^{0}+A\times sin(pi\times\) & 0.015 & \(-\)85.95 & 54.23 & 0.0087 & 0.952 \\
14 & (\(x-xc\))/\(u\)) & 0.005 & \(-\)402.89 & 356.24 & 0.0017 & 0.922 \\
16 & & 0.001 & \(-\)290.58 & 559.64 & 0.0006 & 0.945 \\ \hline \hline \end{tabular}
\end{table}
Table 5: LNAPL flow rate and water content fitting functions.  
Figure 9: Surface chart of the relationship between water content, oil content, and oil flow.