## 3 Results
### Comparison of the Simulated and Filter Paper Method SWRC  
Table 2 shows the parameter \(n\) values for the van Genuchten model. Comparing the natural state of both the simulated restrictions and laboratory results, the most striking effect is the substantial increase in the parameter \(n\) value when the simulation is considered aside from the model. The value of the parameter \(n\), which used Mualem's approximation, was the closest to the filter paper method data, which also uses the Mualem restriction. However, the increase in the value of the parameter \(n\) was about 27%. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{
\begin{tabular}{c} **Arsenic** \\ **Concentration** \\ \end{tabular} } & \multicolumn{6}{c}{**Value of the Parameter \(n\)**} \\ \cline{2-7}  & **Filter-Paper** & **Burdine** & **Mualem** & **Geometric** & **Neutral Pore** & **Larger Pore** \\ \hline
0 mg/kg & 1.44 \(\pm\) 0.03 & 2.96 \(\pm\) 0.01 & 1.83 \(\pm\) 0.02 & 1.96 \(\pm\) 0.02 & 3.33 \(\pm\) 0.08 & 3.87 \(\pm\) 0.02 \\
25 mg/kg & 1.19 \(\pm\) 0.00 & 2.78 \(\pm\) 0.06 & 1.77 \(\pm\) 0.08 & 1.89 \(\pm\) 0.06 & 3.26 \(\pm\) 0.06 & 3.83 \(\pm\) 0.08 \\
50 mg/kg & 1.18 \(\pm\) 0.01 & 2.88 \(\pm\) 0.04 & 1.88 \(\pm\) 0.04 & 1.96 \(\pm\) 0.03 & 3.31 \(\pm\) 0.02 & 3.86 \(\pm\) 0.05 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Values of the parameter \(n\) for the van Genuchten data fitting. Figure 1: SWRCs of the natural and contaminated soils. SWRCs obtained by the filter paper and simulation methods of the (**a**) 0 mg/kg (natural soil), (**b**) 25 mg/kg, and (**c**) 50 mg/kg arsenic-contaminated soils. Similarly, the arsenic-contaminated condition increased the value of the parameter \(n\) on all the simulations. The difference was about 49% and 59% for the 25 mg/kg and 50 mg/kg arsenic concentration, respectively, compared to [PERSON]'s restriction. This resulted in a change in the SWRCs' slope. Such a difference can be explained through the correlation between the value of the parameter \(n\) and the pore-size distribution because the parameter \(n\) is a slope function [32; 41]. The comparison of the simulated SWRC and the filter paper SWRC is shown in Figure 2 for the three arsenic concentrations with [PERSON]'s restriction. Upon analyzing the SWRC obtained by the filter paper method (Figure 2), for the same saturation rate (\(s_{r}=1\%\)), it was observed that the natural soil reached its maximum \(\psi_{m}\) value at \(1.30\times 10^{8}\) kPa, while the estimated SWRC reached it at \(4.13\times 10^{5}\) kPa, indicating a difference of about three orders of magnitude (log scale). Moreover, at high saturation rates (\(s_{r}\geq 70\%\)), the estimated curves provided the suction values provided by the estimated curves were almost two times higher than those of the filter paper method curve, which was particularly notable in the shape of the SWRCs (Figure 1). In the case of the SWRC of the 25 mg/kg arsenic-contaminated soil, for \(s_{r}<45\%\), the simulated SWRC provided smaller \(\psi_{m}\) values than those obtained by the filter paper method curve. In contrast, for \(s_{r}>45\%\), the simulated SWRCs tended to overestimate the  
Figure 2: Simulated and filter paper SWRCs (using the Mualem’s restriction) of (**a**) 0 mg/kg (natural soil), (**b**) 25 mg/kg, and (**c**) 50 mg/kg arsenic-contaminated soils. \(\psi_{m}\) of the contaminated soil. The simulated SWRC provided a \(\psi_{m}\) value as high as eight times bigger (log scale) than the one obtained by the filter paper method SWRC for \(s_{r}\) = 99%. A similar tendency was observed for the SWRC of the 50 mg/kg arsenic-contaminated soil. The simulated curves overestimated the \(\psi_{m}\) for \(s_{r}\) > 65% in this case. The most significant \(\psi_{m}\) value difference was obtained at \(s_{r}\) = 99%, corresponding to three times the \(\psi_{m}\) obtained by the filter paper SWRC. The \(\psi_{m}\) decrease can be partially explained by the number of points used for the van Genuchten fitting at a low saturation rate in the filter paper curves.