## 4 Data Interpretation and Future Implications  
By the vapor concentration data and the cumulative mass extracted (Figure 5), several considerations can be drawn concerning the success and the general performance of the SVE system. Extracted concentrations show an initial spike (96,000 ug/Nm\({}^{3}\)) followed by a rapid decline towards concentrations ranging from 3-5% of the initial concentration (2800 \(\div\) 4800 ug/Nm\({}^{3}\)). As the time of SVE operation increased, the less mobile phases (i.e., more strongly adsorbed forms) or gasses from greater distances were removed. In fact, two primary physical mechanisms in SVE operations are mass transfer (as the partition of one phase to another) and mass transport. Desorption phenomenon from the soil particles may occur for long time [32]. During the Phase I, mass transfer provides little contribution until the extracted concentration decreases significantly as the advective soil volume is swept. At later times (Phase II), the extracted concentration changes very slowly. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & & \multicolumn{3}{c}{**C\(<\)12**} & \multicolumn{3}{c}{**C\(>\)12**} \\ \cline{3-8}
**Core** & **Sampling** & \multicolumn{3}{c}{**RT = 891 mg/kg**} & \multicolumn{3}{c}{**RT = 365 mg/kg**} \\ \cline{3-8}
**Sample n.** & **Depth (m)** & \begin{tabular}{c} **EC 2005** \\ **(mg/kg)** \\ \end{tabular} & \begin{tabular}{c} **PT 2018** \\ **(mg/kg)** \\ \end{tabular} & \begin{tabular}{c} **Efficiency** \\ **(%)** \\ \end{tabular} & \begin{tabular}{c} **EC 2005** \\ **(mg/kg)** \\ \end{tabular} & \
\begin{tabular}{c} **PT 2018** \\ **(mg/kg)** \\ \end{tabular} &
\begin{tabular}{c} **Efficiency** \\ **(mg/kg)** \\ \end{tabular} \\ \hline
**S291** & 4 & 1156 & 800 & 30.8 & 119.4 & 99.2 & 16.9 \\ \hline
**S291C** & 4 & 908 & 786 & 13.4 & 445.2 & 362 & 18.7 \\ \hline
**S293** & 4 & 7108 & 25 & 99.6 & 525 & 367 & 30.1 \\ \hline
**S293A** & 4 & 1855 & 412 & 77.8 & 404.4 & 350 & 13.5 \\ \hline
**S293B** & 4 & 569 & 478 & 16.0 & 406.5 & 335 & 17.6 \\ \hline
**S037** & 4 & 1608 & 623 & 61.3 & 658 & 491 & 25.4 \\ \hline
**S037A** & 1 & \textless{}0.1 & - & - & 34,177 & 50 & 99.9 \\ \hline
**S037B** & 1 & \textless{}0.1 & - & - & 4128 & 2381 & 42.3 \\ \hline
**S037B** & 4 & 408 & 366 & 10.3 & 3642 & 2953 & 18.9 \\ \hline
**SP028** & 5 & 410 & 360 & 12.2 & 749 & 622 & 17.0 \\ \hline
**SP028C** & 5 & 333 & 15 & 95.5 & 9812 & \textless{}5 & 99.9 \\ \hline
**P036A** & 3 & 785 & \textless{}5 & 99.4 & 52 & \textless{}5 & 99.9 \\ \hline
**P036B** & 4 & 1276 & 330 & 74.1 & 10,026 & 9572 & 4.5 \\ \hline
**Total** & - & 16,416 & 4195 & 74.4 & 65,096 & 17,582 & 72.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Efficiency of the remediation treatment for C\(<\)12 and C\(>\)12 hydrocarbons. As described above, the early rapid decay in concentration (Phase I) corresponds to the permeable soil volume holding volatilized vapors easily accessible. Instead, the mass removal from low-accessibility domains entails a mass transfer lower rate (Phase II). This implies that, during the first year of SVE treatment (Phase I), over 420 kg of VOCs were extracted, which corresponds roughly to the 78% of the total mass extracted (540 kg) in four years of treatment (Phase I + Phase II). In this case study, a small contaminant \"rebound\" effect was observed during the monitoring period. VOC IN concentration showed a spike (4000 \(\mathrm{\SIUnitSymbolMicro g/Nm^{3}}\)) after the facility shutdown. The compounds retained in the stagnant regions escaped slowly by diffusion and resulted in rebounding of concentrations in the gaseous phases. Experimental results indicated that the water saturation from rainfall is one of the important factors for contaminant volatilization; in fact, high water table causes significant mass transfer limitations. Consequently, the limited rate of mass transfer may be attributed to the reduction of the interfacial area available for VOC volatilization.