IDENTIFICATION OF AN ACCURATE SOIL SUSPENSION DISPERSION MODELING METHOD FOR USE IN ESTIMATING HEALTH-BASED SOIL CLEANUP LEVELS OF HEXAVALENT CHROMIUM IN CHROMITE ORE PROCESSING RESIDUES/

The primary health concern associated with chromite ore processing res idues (COPR) at sites in Hudson County, NJ, is the inhalation of Cr(VI ) suspended from surface soils. Since health-based soil standards for Cr(VI) will be derived using the inhalation pathway, soil suspension m odeling will be necessary to estimate site-specific, health-based soil cleanup levels (HBSCLs). The purpose of this study was to identify th e most appropriate particulate emission and air dispersion models for estimating soil suspension at these sites based on their theoretical u nderpinnings, scientific acceptability, and past performance. The iden tified modeling approach, the AP-42 particulate emission model and the fugitive dust model (FDM), was used to calculate concentrations of ai rborne Cr(VI) and TSP at two COPR sites. These estimated concentration s were then compared to concentrations measured at each site, The TSP concentrations calculated using the AP-42/FDM soil suspension modeling approach were all within a factor of 3 of the measured concentrations . The majority of the estimated air concentrations were greater than t he measured, indicating that the AP-42/FDM approach tends to overestim ate on-site concentrations. The site-specific Cr(VI) HBSCLs for these two sites calculated using this conservative soil suspension modeling approach ranged from 190 to 420 mg/kg.