The extent, mechanism(s), and rate of chlorinated ethene degradation in a large tetrachloroethene (PCE) plume were investigated in an extensive sampling campaign. Multiple lines of evidence for this degradation were explored, including compound-specific isotope analysis (CSIA), dual C-Cl isotope analysis, and quantitative real-time polymerase chain reaction (qPCR) analysis targeting the genera Dehalococcoides and Dehalogenimonas and the genes vcrA, bvcA, and cerA. A decade prior to this sampling campaign, the plume source was thermally remediated by steam injection. This released dissolved organic carbon (DOC) that stimulated microbial activity and created reduced conditions within the plume. Based on an inclusive analysis of minor and major sampling campaigns since the initial site characterization, it was estimated that reduced conditions peaked 4 years after the remediation event. At the time of this study, 11 years after the remediation event, the redox conditions in the aquifer are returning to their original state. However, the DOC released from the remediated source zone matches levels measured 3 years prior and plume conditions are still suitable for biotic reductive dechlorination. Dehalococcoides spp., Dehalogenimonas spp., and vcrA, bvcA, and cerA reductive dehalogenase genes were detected close to the source, and suggest that complete, biotic PCE degradation occurs here. Further downgradient, qPCR analysis and enriched δ¹³C values for cis-dichloroethene (cDCE) suggest that cDCE is biodegraded in a sulfate-reducing zone in the plume. In the most downgradient portion of the plume, lower levels of specific degraders supported by dual C-Cl analysis indicate that the biodegradation occurs in combination with abiotic degradation. Additionally, 16S rRNA gene amplicon sequencing shows that organizational taxonomic units known to contain organohalide-respiring bacteria are relatively abundant throughout the plume. Hydraulic conductivity testing was also conducted, and local degradation rates for PCE and cDCE were determined at various locations throughout the plume. PCE degradation rates from sampling campaigns after the thermal remediation event range from 0.11 to 0.35 yr⁻¹. PCE and cDCE degradation rates from the second to the third sampling campaigns ranged from 0.08 to 0.10 yr⁻¹ and 0.01 to 0.07 yr⁻¹, respectively. This is consistent with cDCE as the dominant daughter product in the majority of the plume and cDCE degradation as the time-limiting step. The extensive temporal and spatial analysis allowed for tracking the evolution of the plume and the lasting impact of the source remediation and illustrates that the multiple lines of evidence approach is essential to elucidate the primary degradation mechanisms in a plume of such size and complexity.

在广泛的采样活动中，研究了大型四氯乙烯（PCE）羽流中氯化乙烯降解的程度，机理和速率。多条证据为这种降解进行了探讨，包括化合物的特定同位素分析（CSIA），双C-氯同位素分析，并针对各属定量实时聚合酶链式反应（qPCR的）分析Dehalococcoides和Dehalogenimonas和基因vcrA，bvcA和cerA。在该采样活动开始之前的十年，烟羽源通过注蒸汽进行热修复。释放出溶解的有机碳（DOC），刺激了微生物的活动并在羽状流中产生了减少的条件。根据自最初现场表征以来对主要和次要采样活动的包容性分析，据估计，修复事件发生后4年，减少的条件达到了顶峰。在进行这项研究时，即补救事件发生11年后，含水层中的氧化还原条件已恢复到原始状态。但是，从修复源区释放的DOC与3年前测得的水平相符，羽状条件仍适用于生物还原性脱氯。Dehalococcoides spp。，Dehalogenimonas spp。和在源头附近检测到了vcrA，bvcA和cerA还原性脱卤素酶基因，表明此处完全发生了生物PCE降解。此外下坡，qPCR分析和富集δ ¹³为C值的顺-二氯乙烯（cDCE）表明，cDCE在烟羽中的硫酸盐还原带中被生物降解。在羽流中降解程度最低的部分，双重C-Cl分析支持的特定降解物含量较低，表明生物降解与非生物降解结合发生。另外，16S rRNA基因扩增子测序表明，已知含有机卤化物的细菌的组织分类单位在整个羽流中相对丰富。还进行了水力传导性测试，并确定了整个羽流中各个位置的PCE和cDCE的局部降解率。热修复事件后采样活动的PCE降解率范围为0.11至0.35 yr ^-1。从第二次到第三次采样的PCE和cDCE降解率分别为0.08至0.10 yr ^-1和0.01至0.07 yr ^-1。这与cDCE作为大多数羽状流中的主要子产物以及cDCE降解作为限时步骤相一致。广泛的时间和空间分析允许跟踪羽流的演变和源补救的持久影响，并说明多证据线方法对于阐明这种大小和复杂性的羽流中的主要降解机制至关重要。