INTEGRATED CORRECTIVE MEASURES AT A COMPLEX SITE

At a complex manufacturing site in the Southeast, being addressed under the RCRA corrective action program, 9 solid waste management units (SWMUs) and 3 areas of concern (AOCs) were examined in the corrective measures study (CMS). A variety of conventional and innovative technologies were selected for migration control and source control. The cornerstone of the corrective measures is a permeable reactive barrier (PRB) using zero valence iron to reduce chlorinated volatile organic compounds (VOCs) and hexavalent chromium. This migration control measure, which will be the largest of its kind at 8,700 tons of iron filings, will protect human health and the environment by treating groundwater in situ prior to its discharge to the adjacent stream.Given the nature of releases, chemical properties and distribution of contaminants, and hydrogeological characteristics of the site, complete groundwater clean-up would be difficult, and in some areas technically impracticable, to achieve within a reasonable timeframe. Furthermore, the Baseline Risk Assessment established that the site does not pose unacceptable human health risk, except for potential risks associated with hypothetical future use of the uppermost aquifer for drinking water purposes. Therefore, the primary objective in any evaluation of potential additional corrective measures was to focus on source and migration control of contaminants through containment, removal, or destruction, and “make progress toward the ultimate goal of returning contaminated groundwater to its maximum beneficial use” as stated in USEPA's groundwater protection strategy.In consideration of the site characteristics, land use, current conditions, and previous and on-going source control measures, the following principal objectives were recommended for corrective action at the facility: (1) implement corrective measures which are protective of human health and the environment, based upon current potential exposures; (2) for affected groundwater which has migrated beyond the facility boundary (i.e., downgradient from the PRB), clean up to state groundwater quality standards; (3) prevent further degradation of soil and groundwater with appropriate source control corrective measures, and utilize the PRB as a site-wide migration control measure; (4) comply with standards for management of waste during corrective measure implementation; (5) develop and implement use restrictions/institutional controls for site soil and groundwater to prevent future exposures; and (6) implement the approved Performance Monitoring Plan to track the progress of the corrective action program.Short-term protection goals, intermediate performance goals, and final cleanup goals have been formulated. Based upon the risk assessment, “Current Human Exposures Under Control,” an EPA environmental indicator (EI), has been achieved. As a short-term goal, the PRB will be installed to effect the other EI, “Migration of Contaminated Groundwater Under Control.”One intermediate performance goal is recommended: implement the selected corrective measures for source control. The final cleanup goals suggested for this facility are the state groundwater quality standards. The logical point of compliance is groundwater immediately downgradient of the PRB installation. A technical impracticability (TI) zone has been designated for upgradient areas.Based on the CMS evaluation process, eight site-specific components were selected as part of the final recommended corrective measures for the site. The EPA has unconditionally approved the CMS report.