## 3 Results and Discussion  
### Microcosm Testing Results  
The effects of the addition of different slow-release substrates on environmental parameters are depicted in Figure 3. The testing results revealed that the use of emulsion products may accumulate organic acid, thus decreasing the pH in groundwater. The effect was particularly substantial with the addition of SOE+FL. The microcosm was an enclosed nonflowing space, which further increased the likelihood of acid accumulation. Regardless, the pH value in each of the groups was higher than 5.5, falling into a range suitable for microbial growth. The initial ORP of each group was approximately 200 mV. After the addition of different chemicals, the ORPs were reduced to 0 mV or lower. The greatest decrease was observed in the SOE+FL group. Because the in situ groundwater originally contained approximately 70 mg/L TOC, the blank group (BK) also exhibited a decreasing trend in ORP. However, the ORP of the BK group remained higher than 0 mV for the duration of the test, which was different from that of the other groups with emulsions added. The initial DO of each group was 6.48 mg/L. The results revealed that the CEVO and SOE+FL test groups showed lower DO levels compared with the other groups. Moreover, the groups with emulsions added (CEVO, SOE, and SOE+FL) had higher EC values, with the SOE+FL group having the highest EC. The higher EC in these groups was assumed to be caused by the electron donors provided by FL. The overall results indicated that the addition of FL accelerated ORP and DO reduction; however, the addition of FL also caused lower pH values. The water quality variation of each group during the testing period is depicted in Figure 4. The initial TOC of the groundwater used in this test was 76.8 mg/L. After the addition of various slow-release substrates, the TOC concentration in each of the non-BK test groups was higher than 3000 mg/L. The TOC concentrations following the addition of CEVO and self-made SOE were similar (approximately 3500 mg/L). The addition of FL further increased the TOC concentration to 4936 mg/L, suggesting that carbon sources in FL increased the electron donor content in emulsions. Additionally, on day 45 of the test, the chemical consumption rate of the SOE+FL group was faster than the consumption of the pure SOE or CEVO groups. It is possible that adding FL accelerated the environmental reduction, thereby increasing the chemical consumption rate. The nitrate concentration in each testing group increased in the initial period of the testing, possibly because nutrients were added in all groups. The nitrogen, phosphorous, vitamin B12, and  
Figure 2: In situ geological structure and layered formation of the injection well: (**a**) in situ biological field geologic structure; (**b**) double packer injection well structure. The TCE removal rates and derivative concentration variations in each group of the microcosm test are depicted in Figure 5. The BK group exhibited a TCE removal rate of approximately 22% on day 45 because the groundwater used contained TOC. The TCE removal rate of the self-made SOE, CEVO, FAE, and SOE+FL groups was approximately 71%, 64%, 52%, and 94%, respectively. The results indicated that adding FL accelerated environmental reduction and increased biodegradation efficiency. The TCE removal rates of the self-made SOE and CEVO were similar, suggesting that the self-made SOE was as stable as the commercial product. Moreover, the self-made SOE reached 95% and 99% TCE removal on days 65 and 90, respectively, which were higher than the 87% and 82% TCE removal rates, respectively, of the CEVO. According to the CEVO degradation tendency and the approximately 2500 mg/L TOC in the CEVO group on day 90, the CEVO group might have been able to reach 99% removal of TCE if the testing period had been extended. The FAE group reached approximately 55% TCE removal without any further increase in removal because of its low oil content.