In situ anaerobic transformation of trichlorofluoroethene in trichloroethene-contaminated groundwater

Methods are needed to obtain in situ information on the transformation rate s of trichloroethene (TCE), the most commonly detected organic groundwater contaminant. The objective of this research was to investigate the potentia l for determining TCE transformation rates in groundwater by measuring the transformation rate of its fluorinated surrogate, trichlorofluoroethene (TC FE). To explore this hypothesis, the in situ transport behavior, transforma tion pathway, and transformation rate of injected TCFE were determined in T CE-contaminated groundwater using single-well, push-pull tests. Although tr ansport behavior varied between wells, TCFE, dichlorofluoroethene (DCFE), a nd TCE were transported similarly to each other. In the shallow water-heari ng zone, TCFE was reductively dechlorinated to cis-DCFE, trans-DCFE, and (E )-1-chloro-2-fluoroethene (CFE), while co-injected TCE was concurrently tra nsformed to cis-dichloroethene (DCE), trans-DCE, 1,1-DCE, and a trace amoun t of chloroethene (CE). With added formate and the injected TCFE concentrat ion being a factor of 20 higher than that of TCE, the TCFE transformation r ate ranged from 0.053 to 0.30 mu mol/L-day, while that of TCE ranged from 0 .009 to 0.012 mu mol/L-day. Without added formate, the TCFE transformation rate decreased to 0.036 mu mol/L-day. In the deeper water-bearing zone, TCF E transformation occurred only after a lag time of 55 days with added forma te. No TCFE transformation occurred in groundwater that had not previously been exposed to TCE. The potential applicability for TCFE as an in situ tra nsport and transformation surrogate for TCE was demonstrated.