## 3 Results and Discussion
### In Situ Biological Field Test Results
#### 3.2.3. TCE and Derivatives' Concentration Variations  
The TCE concentrations monitored after injection during the in situ biological field test are presented in Figure 7. Following the first injection, because the injection volume was insufficient, the TCE concentrations in OW1, OW2, and OW3 did not decrease in the first 30 days. After the second injection, the TCE concentrations in OW1, OW2, and OW3 decreased. As the CW lacked electron donors, the TCE concentration at CW remained at 0.8-1.0 mg/L, suggesting a low natural attenuation rate of TCE at the site. The distance between OW1 and the IW was the shortest, so TOC concentrations at OW1 were higher than those at OW2 and OW3. TCE concentrations at OW1 decreased from 0.225 mg/L to 0.033 mg/L on day 60, reaching a TCE removal rate of approximately 85%. The results of the microcosm test revealed that SOE+FL accelerated the TCE degradation rate, corresponding to the substantial decrease in TCE concentrations. On day 160 of the in situ field test, TCE concentrations at OW1 were lower than 0.01 mg/L, which is lower than the TCE monitoring standard of groundwater-related regulations. Prior to day 90, TOC concentrations at OW2 and OW3 were already substantially low, so further decreases in concentration were not observed. After day 90, TCE concentrations at OW2 decreased observably. On day 160, TCE concentrations at OW2 decreased from 0.164 mg/L to 0.0685 mg/L, reaching a TCE removal rate of approximately 58%. At OW3, TOC concentrations increased slowly and, as a result, TCE concentrations at OW3 did not decrease in a notable manner. On day 140 (OW3 was not analyzed on day 160), the TCE concentration of OW3 decreased from 0.636 mg/L to 0.048 mg/L, satisfying the groundwater regulation standards of TCE, Taiwan Groundwater Pollution Control Standards, as shown on Table 2[30]; however, the removal rate was a mere 25%. A possible cause of the low removal rate can be attributed to the long distance between OW3 and the IW, which required a long transmission time for the chemicals to reach OW3, thus shortening the time allotted for stabilizing the groundwater environment. A longer testing time was required for observable effectiveness to be achieved. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Well**} & **Sampling** & \multirow{2}{*}{**pH**} & **DO** & **ORP** & **Nitrate** & **Nitrite** & **Fe** & **Sulfate** & **Sulfide** \\  & **Day** & & **(mg/L)** & **(mV)** & **(mg/L)** & **(mg/L)** & **(II)(mg/L)** & **(mg/L)** & **(mg/L)** \\ \hline \multirow{6}{*}{OW2} & 0 & 6.41 & 1.94 & 328 & 7.92 & ND & 0.09 & 45.7 & ND \\  & 29 & 6.42 & 2.32 & 316 & 8.99 & 0.002 & 0.06 & 43.7 & ND \\  & 61 & 6.41 & 0.52 & 72 & 9.49 & ND & 0.5 & 39.8 & ND \\  & 119 & 6.44 & 1.83 & 85 & 8.62 & 0.005 & 0.18 & 44.1 & \textless{}0.04 \\  & 140 & 6.26 & 1.11 & -2 & 0.84 & ND & 3.6 & 50.3 & 0.22 \\ \hline \multirow{6}{*}{CW} & 0 & 6.78 & 1.6 & -5 & 0.02 & ND & 0.08 & 122 & ND \\  & 29 & 6.67 & 1.73 & 23 & 0.03 & ND & 0.35 & 128 & ND \\ \cline{1-1}  & 61 & 6.57 & 0.65 & -8 & 0.02 & ND & 1.05 & 130 & 0.02 \\ \cline{1-1}  & 92 & 6.26 & 0.07 & 103 & 0.05 & N.D. & 0.02 & 122 & 0.03 \\ \cline{1-1}  & 119 & 6.45 & 1.38 & 202 & 0.08 & 0.003 & 0.35 & 127 & \textless{}0.04 \\ \cline{1-1}  & 140 & 6.16 & 1.8 & 64 & 0.04 & ND & 1.98 & 127 & ND \\ \hline \hline \end{tabular} Note: Class I is for groundwater in drinking water resource protection area; Class II is for groundwater outside the Class I area.  
\end{table} 
Table 1: Environmental water quality parameter comparison of OW2 and CW in the in situ field testing. Anaerobic reductive declhorination of TCE derives chlorinated byproducts. Scientific literature has indicated that microbial degradation of soybean oil may generate organic acid and hydrogen atoms, which replace the chlorine atoms. During the reductive declhorination process, intermediates such as _cis_-1,2-DCE, VC, and the final product ethene are produced [11; 31].