In Situ Anaerobic Transformation of Trichlorofluoroethene in Trichloroethene-Contaminated Groundwater

Abstract

Methods are needed to obtain in situ information on the transformation rates of trichloroethene (TCE), the most commonly detected organic groundwater contaminant. The objective of this research was to investigate the potential for determining TCE transformation rates in groundwater by measuring the transformation rate of its fluorinated surrogate, trichlorofluoroethene (TCFE). To explore this hypothesis, the in situ transport behavior, transformation pathway, and transformation rate of injected TCFE were determined in TCE-contaminated groundwater using single-well, push-pull tests. Although transport behavior varied between wells, TCFE, dichlorofluoroethene (DCFE), and TCE were transported similarly to each other. In the shallow water-bearing zone, TCFE was reductively dechlorinated to cis-DCFE, trans-DCFE, and (E)-1-chloro-2-fluoroethene (CFE), while co-injected TCE was concurrently transformed to cis-dichloroethene (DCE), trans-DCE, 1,1-DCE, and a trace amount of chloroethene (CE). With added formate and the injected TCFE concentration being a factor of 20 higher than that of TCE, the TCFE transformation rate ranged from 0.053 to 0.30 mumol/L-day, while that of TCE ranged from 0.009 to 0.012 mumol/L-day. Without added formate, the TCFE transformation rate decreased to 0.036 mumol/L-day. In the deeper water-bearing zone, TCFE transformation occurred only after a lag time of 55 days with added formate. No TCFE transformation occurred in groundwater that had not previously been exposed to TCE. The potential applicability for TCFE as an in situ transport and transformation surrogate for TCE was demonstrated.

Detecting and Quantifying Reductive Dechlorination During Monitored Natural Attenuation at the Savannah River CBRP Site

“…These rates are orders of magnitude slower than TCFE transformation rates (0.05 to 1.6/day) reported in previous field tests by Hageman et al (2001Hageman et al ( , 2003 and Field et al (2005). The slower rates in this study may be attributed to differences in aquifer and experimental conditions dechlorination.…”

Respiration of 13 C-Labeled Substrates Added to Soil in the Field and Subsequent 16S rRNA Gene Analysis of 13 C-Labeled Soil DNA

“…As mentioned in the introduction, a long-standing criticism of this approach is that resultant data may be misleading because of artifacts imposed on microbial reactions by unrealistic laboratory conditions (34,55). Other approaches to measure biodegradation have ranged from empirical observation of diminished effectiveness of intentionally released chemicals (e.g., herbicides [38]) to rare field release of 14 C-labeled substrates (8,30) to the use of conservative tracers during injection and retrieval of substrates in subsurface environments (16,22,25,47). Issues surrounding the effectiveness and interpretations of such assays have been previously addressed (34,39).…”

“…In field-based investigations, the prospects for radiolabeling of active microbial populations are dim due to the unlikelihood of quantitative isotope retrieval from the field and to safety and environmental regulations. If experiments that release substrates to field sites are implemented, then nonradioactive surrogate compounds are likely to be employed (with or without conservative tracers that assist in mass-balance accounting [16,49]). …”

Push-Pull Tests for Evaluating the Aerobic Cometabolism of Chlorinated Aliphatic Hydrocarbons

“…Push-pull tests have been previously used to obtain quantitative information on a variety of aquifer physical, chemical, and microbiological characteristics (Istok et al, 1997;Schroth et al, 1998;Istok et al, 1999;Schroth et al 2001;Hageman et al, 2001). Currently, the push-pull method is under investigation as a tool for measuring in situ rates of microbially mediated uranium reduction (Istok et al, 2004) and of anaerobic BTEX degradation (Reusser et al, 2002).…”