In-Situ Chemical Oxidation to Address Residual VOC Plumes.

Groundwater plumes containing volatile organic contaminants (VOCs) such as trichloroethylene (TCE) remain a major groundwater remediation challenge. Therefore, a field-scale technology demonstration was conducted to evaluate the utility of in situ chemical oxidation using persulfate to address residual VOC contamination.  The demonstration site was located within an area with an extensive VOC plume with a TCE concentration ranging from 10 to 40 ppm. The test site consisted of an injection well and three observation wells. The persulfate reactant was injected intermittently over a ten day period (230 g/L Na-persulfate) totaling 18,168 L. After injection, the observation wells were sampled periodically with the pH, electrical conductivity (EC) and ORP determined in the field, and samples were collected for VOC, persulfate, chloride, sulfate, and metals analyses. The current discussion focuses on the results from OW1 located closest (≈15 ft) to IW, the only observation well clearly impacted by persulfate injection. Persulfate was only detected in OW1 approximately two weeks after injection, peaking at ≈ 150 ppm and then slowly decreasing over the next 295 days. Injectate breakthrough in OW1 was also evident in the EC and Na, with ORP increasing initially and then becoming more variable with continued monitoring. TCE and PCE concentrations in OW1 were much lower than observed in OW2 and OW3 throughout the duration of the study. Although some dilution is inherent in the in situ chemical treatment of aqueous phase contaminants, elevated concentrations of Cl and SO₄ observed in OW1 are indicative of VOC destruction resulting from chemical oxidation