Remediation Status: Site closed

Why the technology was selected:
The consultant considered the injection of several different chemical oxidation commercial products. Based upon an examination of costs, time of remediation and site specific conditions, the consultant determined the use of potassium permanganate was the most cost effective means of remediating the solvent contamination at the site.

Date implemented:
1st injection (pilot test) 19 May, 2003; 2nd injection 10-19 December, 2003; 3rd injection 13-16 December, 2004

Final remediation design:
The initial pilot test consisted of the injection of 150 pounds of KMnO4 at four direct-push points in the vicinity of two monitoring wells (MW-3 and MW-5) to determine if this method would achieve the desired results as well as to determine the optimal amount of KMnO4 required to be injected on the remainder of the site. Subsequent sampling of the groundwater indicated that the initial results of the pilot test were successful. PCE concentrations in the source area (MW-3) decreased by more than 89% after application and PCE concentrations in the down gradient well (MW-5) were reduced to below the laboratory reporting limit (5µg/l). However, as expected the PCE concentrations in the source area did rebound through the course of the pilot study. The second event consisted of the injection of 1,450 pounds of KMnO4 at 29 additional points. As with the previous sampling events, the PCE concentrations declined significantly after this round of injections but rebounded. It was believed that the contaminant mass beneath the floor of the facility was substantially more than anticipated. It was determined that an additional injection event be conducted. During the third event, a total 1,200 pounds of KMnO4 were injected at four points around the source area, two near MW-1 and two near the building. Post injection sampling indicated that the PCE concentrations in the source area monitoring well (MW-3), decreased significantly, as PCE was not detected in the sample obtained from this well. PCE concentrations in several other wells (MW-1 and MW-4) slightly exceeded the original cleanup target level of 5 µg/L.

Results to date:
A fourth injection event was originally proposed to further reduce the PCE levels. However, at that time the department released its draft Missouri Risk-Based Corrective Action Technical Guidance document. A risk assessment was subsequently conducted of the site using this document. The evaluation eliminated the drinking water pathway and the representative concentrations of PCE were below the residential levels for the remaining completed pathways. The department therefore issued a Certification of Completion letter for unrestricted use of the site on June 9, 2005.