Impact of ISCO Treatment on PFAA Co-Contaminants at a Former Fire Training Area.

The effects of an in situ chemical oxidation (ISCO) treatment aimed predominantly at remediation of chlorinated volatile organic compounds (cVOCs) and perfluoroalkyl acids (PFAAs) co-contaminants were investigated. Soil and groundwater samples were collected before and after an ISCO pilot-scale field test of a peroxone activated persulfate (OxyZone) technology. Statistically significant decreases in PFAA groundwater concentrations were observed in post-treatment samples. Reductions in PFAA aqueous phase concentrations were also supported by decreases in soil concentrations. Importantly, there was no evidence for increased aqueous PFAA concentrations due to mobilization from soil or conversion of precursors into PFAAs. As indicated by chloride data from inside and outside the treatment zone, displacement and/or dilution could not explain the observed decrease in PFAA concentration. Also, relatively constant pH values, due to using a buffered oxidant solution, did not support increased PFAA removal via soil sorption. Overall, the use of peroxone activated persulfate to treat cVOCs had no discernible negative impacts on PFAA co-contaminants at the Site. Rather, the data suggest that PFAA concentrations decreased due to ISCO treatment.

Peroxone activated persulfate treatment of 1,4-dioxane in the presence of chlorinated solvent co-contaminants.

1,4-dioxane is often found as a co-contaminant with chlorinated volatile organic compounds (VOCs) at solvent release sites such as landfills, solvent recycling facilities, or fire training areas. Historically, soil and groundwater samples were not routinely analyzed for 1,4-dioxane and therefore the number of known 1,4-dioxane sites is still increasing. Due to its co-occurrence with chlorinated compounds, remediation strategies are needed that simultaneously treat both 1,4-dioxane as well as chlorinated VOC co-contaminants. In this proof of concept laboratory study, the fate of 1,4-dioxane was examined during the targeted destruction of aqueous phase VOC, using a peroxone activated persulfate (PAP) chemical oxidation method. Bench-scale experiments were carried out to evaluate the treatability of 1,4-dioxane as both a single-contaminant and in the presence of trichloroethene (TCE), and 1,1,1-trichloroethane (1,1,1-TCA). Possible dependencies on oxidant concentration and reaction kinetics were studied. The oxidative destruction of 1,4-dioxane, TCE and 1,1,1-TCA in single-contaminant batch systems followed pseudo-first-order reaction kinetics and even at the most dilute oxidant concentration lasted for at least 13 days. The rate of oxidation for each contaminant increased linearly with increasing persulfate concentration over the range of oxidant concentrations tested. The rate of oxidative destruction, from most easily degraded to least, was: TCE > 1,4-dioxane > 1,1,1-TCA. Oxidation rates were up to 87% slower in a mixture of these three compounds. Although additional tests are necessary, our data suggest that PAP oxidation of 1,4-dioxane might aid in the cleanup of VOC contaminated sites.