Approach for Determining Generic Health Based Soil Action Levels for Trivalent and Hexavalent Chromium at Residential and Industrial Sites. D. M. Proctor, P. K. Scott, and B. L. Finley, ChemRisk Division, McLaren/Hart Environmental Engineering, 29225 Chagrin Blvd., Cleveland, OH 44122
Many state regulatory agencies are currently developing generic health-based cleanup levels for soils at hazardous waste sites. Likewise, the U.S. Environmental Protection Agency (USEPA) has developed draft Soil Screening Levels (SSLs) for thirty chemicals commonly found at Superfund sites. An SSL is defined as a chemical concentration above which there is sufficient concern to warrant further site-specific study. Consistent with the guidance for SSLs, we contend that any generic standards should be considered "action levels" or "points of departure," rather than universally applied remediation objectives or cleanup criteria. Sites which contain significant quantities of material above these standards should still require a site-specific risk assessment for the purpose of developing site-specific cleanup levels. We suggest that probabilistic analyses of exposure and risk should be used to develop any action levels in order to more fully describe the range and distribution of the calculated levels. Many regulators and risk assessors believe that characterizing estimated risks and developing cleanup standards in terms of probable ranges, rather than as "point estimates," is the next step in refining the risk assessment process. Herein, we evaluated appropriate action levels for hexavalent and trivalent chromium [Cr(VI) and Cr(III), respectively] in soil. These valence states have very different toxicological and environmental fate and transport characteristics, and therefore, standards for each valence should be set separately. We have selected chromium as a case study because of our familiarity with this metal and because it is often a chemical of concern at State and Federal hazardous waste sites. These action levels are protective of chemical uptake by ingestion, inhalation of suspended soil particulates, and dermal contact. Action levels suggested here for Cr(VI) are 130 and 210 mg/kg, for industrial and residential sites, respectively. As expected, inhalation of Cr(VI) was the most critical route of uptake for Cr(VI), and more critical at industrial sites where traffic on unpaved areas may be of concern. The action levels calculated for Cr(III) were 270,000 and 342,000 mg/kg for residential and industrial sites, respectively, where the most important route of exposure is ingestion. These soil action levels for Cr(III) and Cr(VI) are compared with proposed and promulgated state cleanup levels and the USEPA SSLs.