# Effect of Water Content on Light Nonaqueous Phase Fluid Migration in Sandy Soil
## 2 Materials and Methods
### Research Methods  
#### 2.3.1 Surface Infiltration and Subsurface Imbibition Experiment  
Two forms of LNAPL flow were simulated, surface infiltration and subsurface imbibition, to reproduce common types of LNAPL leakage in realistic scenarios (Figure 3). Introducing LNAPL into the test soil from the top of the column, the process simulates surface infiltration when LNAPL contamination occurs at or near the surface, and the LNAPL-contaminated fluid migrates downward into the subsurface porous medium primarily by gravity. Introducing LNAPL into the test soil from the bottom of the column simulates the process of LNAPL subsurface imbibition from a storage tank guide leakage, whereby LNAPL migrates upward under capillary force. When the weight of the water column and the component of surface tension in the vertical direction are equal, the liquid  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{\begin{tabular}{c} Fine \\ sand \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} Percentage of \\ particle size (\%) \\ \end{tabular} } & 2–0.5 mm & 0.5–0.25 mm & 0.25–0.075 mm & 0.075–0.005 mm & \textless{}0.005 mm \\ \cline{2-6}  & & 7.7 & 27.2 & 51.3 & 7.2 & 6.6 \\ \cline{2-6}  & Curvature & \begin{tabular}{c} Saturated moisture \\ content (\%) \\ \end{tabular} & \begin{tabular}{c} Saturated oil \\ content (\%) \\ \end{tabular} & \begin{tabular}{c} Average particle \\ size (mm) \\ \end{tabular} & \
\begin{tabular}{c} Unevenness \\ factor \\ \end{tabular} &
\begin{tabular}{c} Dry Density \\ (g \(\times\) cm\({}^{-3}\)) \\ \end{tabular} \\  & 7.79 & 25.432 & 21.221 & 0.175 & 31.71 & 1.63 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Media property index.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Diesel** & **Density** & **Dynamic** & **Surface Tension** & **Ignition Point** & **Boiling Point** & **Kinematic** \\
**Type** & **(g/mL)** & **Viscosity (cst)** & **(dyne/cm)** & **(\({}^{\circ}\)C)** & **(\({}^{\circ}\)C)** & **Viscosity (mm\({}^{2}\)/s)** \\ \hline
0\# & 0.84 & 2.54 & 27.8 & 220 & 180–370 & 3.92 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Basic physical properties of diesel.  
in the vertical tube rises to reach the maximum rise height. The maximum rise height can be calculated by the following equation [25]:  
\[h_{c}=\frac{2T_{s}\cos\theta}{\rho\text{g}d_{m}} \tag{1}\]  
\(T_{s}\) is the surface tension/N; \(\theta\) is the contact angle/rad; \(\rho\) is the density of the solution/ (g\(\cdot\)cm\({}^{-3}\)); \(g\) is the acceleration of gravity/(m\(\cdot\)s\({}^{-2}\)); and \(d_{m}\) is the radius of the capillary/cm.  
Before the start of the simulation, debris was removed from the test medium, and the sample was air-dried at 105 \({}^{\circ}\)C in an oven for 12 h. It was weighed every 2 h until  
Figure 3: Surface infiltration (**left**); subsurface imbibition (**right**).  
Figure 2: Laboratory model setup.  
the sample mass remained unchanged to exclude the influence of water content from the experiment process. The experimental process was monitored in real-time, and the height of pollutant migration was photographed and recorded at various times. The changing LNAPL migration rate over time was compared under different forces to analyze the change of force effect under different conditions.