Remediating a PCE Source Area in Clay Using Electrokinetically Enhanced In Situ Bioremediation

Abstract

The success of in situ remediation techniques such as bioremediation and chemical oxidation is often limited by the presence of contaminants in low-permeability silts and clays, as remediation reagents cannot be effectively delivered into these materials to promote and achieve treatment. A novel electrokinetic (EK) technique, referred to as EK-BIO, was demonstrated at full-scale to overcome the limitations of conventional in situ bioremediation with respect to reagent delivery. Electron donor and dehalorespiring bacteria (KB-1®) were effectively and uniformly delivered throughout a tetrachloroethene (PCE) source area in clay till using the EK-BIO technique. Lactate, as electron donor, was effectively delivered through the clay soils over a sustained operational period of 720 days. A one-time bioaugmentation of the treatment area with KB-1® dehalorespiring culture was conducted within the first month of operation. Vinyl chloride reductase functional gene counts increased by several orders of magnitude in treatment area wells, with ensuing PCE dechlorination to ethene and chloride observed at all treatment area wells. Remediation goals for site soil of 10 mg PCE/kg were met within 2 years of system operation. Average soil concentrations in the treatment area were reduced by 98.75% (PCE eq.). Rebound testing 6 months after cessation of EK-BIO operation showed sustained dechlorination and compliance with remedial goals. These results document the first large field-scale remediation of a PCE source area in clay using EK-BIO.