U.S. EPA Region 10, 81 pp, 2018

Chromium, the hazardous substance of primary concern at the FHC site, is present in two forms, Cr(III) and Cr(VI). Although the 1987 OU-1 ROD called for excavation, stabilization, and replacement of all soils with concentrations greater than 550 mg/kg total Cr (~7,400 yd³ of soil) and the OU 2 ROD called for groundwater pump and treat from the area of greatest contamination (levels of Cr >50,000 µg/L), testing demonstrated the remedy would be insufficiently effective; hence, the remedy selected in the 2001 ROD Amendment was implemented in 2003. Injections of a blend of sodium dithionite and ferrous sulfate were performed to create an in situ redox manipulation (ISRM) treatment zone for the Cr-contaminated groundwater, followed by similar injections in source and hot spot areas. These treatments were effective. EPA issued a Notice of Deletion of the Frontier Hard Chrome Inc. Superfund Site from the National Priorities List on August 6, 2018. https://semspub.epa.gov/src/document/10/100092362 Details of the ISRM field work are available in the 2003 remedial action report at https://semspub.epa.gov/work/10/500010197.pdf.