QUANTIFYING THE RELATIVE REACTION RATES AND PATHWAYS OF TRICHLOROFLUOROETHENE DEGRADATION BY PYRITE IN COMPARISON TO TRICHLOROETHENE

Trichloroethene (TCE) is a solvent used in cleaning and a carcinogenic groundwater contaminant that has infiltrated more than 60% of sites designated as a Superfund site by the U.S. Environmental Protection Agency. At the former Naval Air Warfare Center (NAWC), Trenton, NJ, high TCE concentrations in groundwater continue to be observed despite decades of pumping, leaving uncertainties about how much contaminant is left. This study presents the results of research done to investigate the abiotic degradation of TCE by pyrite (FeS₂), with a comparison to the abiotic degradation of trichlorofluoroethene (TCFE). The TCE abiotic degradation rate is uncertain in the relatively shallow, low permeability strata, and the development of a TCFE tracer will help to quantify the in situ TCE reactions going on in the fractured sedimentary mudstones of the Newark Basin. The TCFE tracer could determine likely situations for why TCE is still observed at NAWC, such as potential contaminant diffusion out of low-permeability strata into the high permeability fractures. Significant concentrations of pyrite found in the low permeability rocks at NAWC make it a viable reactant in testing the abiotic degradation pathways. Two batches of pyrite with water and TCE or TCFE were monitored and the samples from the batches were analyzed by gas chromatography. Significant degradation by pyrite was observed in both batches. The products of the abiotic degradation by pyrite will indicate the relative rates of TCFE degradation compared to that of TCE. Knowledge of TCFE’s behavior during the abiotic degradation presented here will be used to quantify the processes affecting TCE at the NJ site during in situ tracer tests that incorporate TCFE. If the tracer proves useful in NJ, its applications can be extended to any other fractured sedimentary rock contaminated sites with reduced iron minerals, such as pyrite.