Comparison of RCRA Corrective Action Levels for Soils With Superfund Risk-Based Preliminary Remediation Goals and Soil Screening Levels. D. J. Marino, Eastman Kodak Company, 1100 Ridgeway Ave., Rochester, NY 14652
Under its RCRA Corrective Action and Superfund programs, the USEPA has developed risk assessment methodology to estimate acceptable concentrations of chemical contaminants in soils. Drafted under Superfund as potential no-further-action levels, Soil Screening Levels (SSLs) reflect the lowest calculated concentration resulting from either direct soil ingestion or inhalation of volatiles and particulates from contaminated residential soils or saturation of the organic carbon fraction in residential soils. Action levels potentially requiring further investigation as proposed under RCRA Corrective Action consider ingestion of contaminated residential soils. Preliminary risk-based remediation goals (PRGs) developed under the Superfund program for residential soils are based on ingestion of contaminated, soil while industrial soil PRGs reflect soil ingestion and inhalation of vapors and particulates from contaminated commercial sites. Given their intended purposes, it was assumed that SSLs would be lower than Corrective Action Levels which would, in turn, be lower than Superfund Residential or Industrial PRGs. To evaluate the quantitative relationships between these levels, all chemicals on the RCRA Appendix IX list with both oral and inhalation toxicity parameters (either a chronic oral Reference Dose (RfD) and a chronic inhalation Reference Concentration (RfC) or an oral Slope Factor and an inhalation Unit Risk factor) were selected, and allowable soil concentrations using the four methodologies were calculated and compared. There were 56 chemicals, mainly volatile organics and pesticides, that satisfied the selection criteria including 24 USEPA Group A or B carcinogens, 8 Group C carcinogens, and 24 noncarcinogens. For all 56 chemicals, SSLs were lower than RCRA Corrective Action levels and were less than or equal to residential PRGs. The median SSL concentration was 4.1 mg/kg, while median values for RCRA Corrective Action Levels and residential PRGs were 76 and 47.5 mg/kg, respectively. For Group A and B carcinogens, RCRA Corrective Action levels were approximately 9% higher than residential PRGs, while RCRA Corrective Action levels for Group C carcinogens were over tenfold higher than residential PRGs, reflecting a tenfold difference in target risk levels. For noncarcinogens, RCRA Corrective Action levels were approximately 3.4-fold lower than Superfund preliminary risk-based remediation goals. Quite surprisingly, industrial soil PRGs were lower than allowable concentrations in residential soils for 35/56 (62.5%) chemicals using RCRA Corrective Action methodology, for 42/56 (75%) chemicals using Superfund residential PRG methodology, and for 26/56 (46%) chemicals using Superfund SSL methodology. The median industrial soil PRG was 3.4 mg/kg. Exposure parameters responsible for the lower industrial soil PRGs compared to residential soil PRGs will be discussed along with the implications of these findings for risk assessment purposes.