Enhancing a Groundwater Remedy for TCE with ISCO

This paper will describe the results of an in situ chemical oxidation (ISCO) remedial action currently in progress to address subsurface contamination by trichloroethene (TCE). The U.S. Department of Energy is responsible for the cleanup of environmental media at the Portsmouth Gaseous Diffusion Plant (PORTS) in southern Ohio. During construction of the PORTS facility in the early 1950's, an electrical substation was constructed in the area of the X-740 Solid Waste Management Unit. The switchyard was removed upon completion of the X-530A Switchyard located directly north of the area. Adjacent to the area, the X-740 Waste Oil Handling Facility was constructed in 1982 and was in operation until 1992. Groundwater contamination at the X-740 area was first discovered during the Quadrant III RCRA Facility Investigation (RFI) Phase I field investigation conducted in 1992. The size of the TCE plume has remained relatively unchanged since 1999. The maximum detection of TCE concentration in a single monitoring well is 7600 ug/L. The RFI process began in 1992 and was completed in 1997. The Cleanup Alternatives Study/Corrective Measures Study (CAS/CMS) report was approved on July 1998. The selected remedy for the X-740 groundwater plume, phyto-remediation, was presented in the Decision Document for Quadrant III, approved in May of 1999. The major components of the selected remedy include phyto-remediation by planting one-year-old hybrid poplar trees in the area of groundwater contamination; groundwater monitoring to confirm that the containment and treatment of contaminants sufficiently protect human health and the environment; and site deed restrictions that include retaining the existing security fencing to restrict access to prevent exposure to contaminated media, and to limit disturbance of the area, ensuring the integrity of the remedial action. The X-740 Phyto-remediation System was constructed and implemented in 1999. Based on the monitoring results, the 2007 evaluation determined that the X-740 Phyto-remediation System has not performed as predicted by the Quadrant III CAS/CMS groundwater model. In a letter, Ohio EPA stated the current remedy is not achieving the goals outlined and required DOE to evaluate other remedial alternatives in conjunction with the current remedy. To enhance the remediation of groundwater at the X-740 SWMU, a new remediation approach is being implemented for the unit. The new approach involves the injection of Modified Fenton's Reagent, using temporary direct push injection points, directly into the portion of the groundwater plume that currently contains TCE concentrations of 50 parts per billion (ppb) or higher. This new approach overcomes limitations imposed by heterogeneities in the subsurface by injecting relatively small quantities of reagent into a large number of temporary injection points over the area. These injections are then repeated as necessary on a grid pattern until performance goals are achieved. Baseline and post-injection groundwater data from three complete Phase injection events are expected to be available in time for the conference. These data will be compared against the remediation end point as defined in the work plan to determine the progress of the remedy. (authors)