## 4 Conclusions  
In this paper, we presented a study on the monitoring of the dielectric properties of soil contaminated with biodiesel-diesel blends. The focus of the study is on using commercial grade diesel B7 to contaminate a sample of sand soil and measuring the dielectric properties of the contaminated soil using a dual electrode plate-based radio frequency heating system. This allowed us to observe the behavior of the contaminated soil with biodiesel-diesel blends before and after RF heating treatment. For our experiment, soil samples were contaminated with commercial grade diesel B7 and were heated using a dual electrode plate-based RF heating system with various electric field intensities of 112.5 kV/m, 150 kV/m, 225 kV/m, and 450 kV/m to observe the dielectric properties of contaminated soil with biodiesel-diesel blends. The results showed that the RF heating system using an electric field intensity of 450 kV/m provided the highest reduction in the volumetric content of commercial grade diesel B7 in the soil. This is because a higher electric field intensity leads to improved power absorbed per unit volume in the dielectric material. These results suggest that using RF heating on contaminated soil samples leads to the evaporation of the commercial grade diesel B7 in the soil and improves the air in the pore space and blocking air spaces compared to unheated contaminated soil samples. This strategy may be useful for soil treatment in Thailand using a RF heating system with dual electrode plates. In future work, we plan to use a high-performance heating system that can be adjusted to electric field intensity values higher than 450 kV/m. Additionally, we will use GC [2], Fourier Transform Infrared Spectrometer [34], and Thermogravimetric Analysis [35] to further investigate the contaminated soil with biodiesel-diesel blends heated by RF heating. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Contaminated Soil Condition** & **Frequency** & \multicolumn{2}{c}{**None**} & **112.5 kV/m** & **150 kV/m** & **225 kV/m** & **450 kV/m** \\ \cline{3-10}  & **\(\varepsilon^{\prime}\)** & \(\varepsilon^{\prime\prime}\) & \(\varepsilon^{\prime}\) & \(\varepsilon^{\prime\prime}\) & \(\varepsilon^{\prime}\) & \(\varepsilon^{\prime\prime}\) & \(\varepsilon^{\prime}\) & \(\varepsilon^{\prime\prime}\) & \(\varepsilon^{\prime}\) & \(\varepsilon^{\prime\prime}\) \\ \hline \multirow{4}{*}{Unsaturated} & 200 & 3.06 & 0.73 & 2.94 & 0.60 & 2.74 & 0.47 & 2.68 & 0.43 & 2.59 & 0.40 \\  & 400 & 3.21 & 0.65 & 3.05 & 0.50 & 2.90 & 0.43 & 2.88 & 0.39 & 2.75 & 0.38 \\  & 600 & 3.27 & 0.53 & 3.13 & 0.43 & 3.00 & 0.37 & 2.98 & 0.36 & 2.85 & 0.34 \\  & 800 & 3.27 & 0.47 & 3.14 & 0.42 & 3.02 & 0.36 & 3.02 & 0.34 & 2.88 & 0.33 \\  & 1000 & 3.26 & 0.43 & 3.10 & 0.36 & 2.99 & 0.31 & 3.03 & 0.30 & 2.88 & 0.29 \\ \hline \multirow{4}{*}{Saturated} & 200 & 3.29 & 0.77 & 3.22 & 0.67 & 3.11 & 0.54 & 3.01 & 0.57 & 2.99 & 0.59 \\  & 400 & 3.69 & 0.89 & 3.45 & 0.60 & 3.35 & 0.51 & 3.25 & 0.51 & 3.23 & 0.55 \\ \cline{1-1}  & 600 & 3.80 & 0.82 & 3.54 & 0.50 & 3.45 & 0.43 & 3.35 & 0.44 & 3.32 & 0.46 \\ \cline{1-1}  & 800 & 3.78 & 0.62 & 3.57 & 0.47 & 3.48 & 0.39 & 3.39 & 0.41 & 3.35 & 0.43 \\ \cline{1-1}  & 1000 & 3.68 & 0.51 & 3.58 & 0.42 & 3.50 & 0.35 & 3.41 & 0.36 & 3.37 & 0.39 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Dielectric properties of heated soil samples based on the highlighted frequencies. We will also study different types of soil and various types of other biodiesel-diesel blends used in Thailand. Conceptualization, T.Y., S.S., C.T., T.T. and N.S. ; methodology, T.Y., S.S. and N.S. ; validation, T.Y., S.S., C.T., T.T. and N.S. ; formal analysis, T.Y., S.S. and N.S. ; investigation, T.Y., S.S. and C.T. ; data curation, T.Y. and S.S.; writing--original draft preparation, T.Y. and S.S.; writing--review and editing, T.Y., S.S., C.T. and N.S. ; visualization, T.Y. ; supervision, C.T. and N.S. ; project administration, S.S., C.T. and N.S. ; All authors have read and agreed to the published version of the manuscript.