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is 10 and the acceptable ground water concentration is 0.05 mg/L, the target soil leachate concentration would be 0.5 mg/L. The partition equation (presented in the Soil Screening Guidance document) is then used to calculate the total soil. concentration (i.e. SSL) corresponding to'this soil leachate concentration. The SSL methodology was designed for use during the early stages of a site evaluation when information about subsurface conditions may be limited. Because of this constraint, the methodology is based on conservative, simplifying assumptions about the release and transport of contaminants in the subsurface. For more on SSLs, and how to calculate site- specific SSLs versus generic SSLs presented in the PRG table, the reader is referred to the Soil Screening Guidance document (USEPA 1996ab). 4.4 Exposure Factors Default exposure factors were obtained primarily from RAGS Supplemental Guidance Standard Default Exposure Factors (OSWER Directive, 9285.6-03) dated March 25, 1991 and more recent information from U.S. EPA's Office of Solid Waste and Emergency Response, U.S. EPA's Office of Research and Development, and California EPA's Department of Toxic Substances Control (see Exhibit 4-1). Because contact rates may be different for children and adults, carcinogenic risks during the first 30 years of life were calculated using age-adjusted factors ("adj"). Use of age-adjusted factors are especially important for soil ingestion exposures, which are higher during childhood and decrease with age. However, for purposes of combining exposures across pathways, aMtional age-adjusted factors are used for inhalation and dermal exposures. These factors approximate the integrated exposure from birth until age 30 combining contact rates, body weights, and exposure durations for two age groups - small children and adults. Age- adjusted factors were obtained from RAGS PART B or developed by analogy (see derivations next page). For soils only, noncarcinogenic contaminants are evaluated in children separately from adults. No age-adjustment factor is used in this case. The focus on children is considered protective of the higher daily intake rates of soil by children and their lower body weight. For maintaining consistency when evaluating soils, dermal and inhalation exposures are also based on childhood contact rates. (1) ingestionQmg•yr]Jkg•d]: IFS - ED, x IRS: F (IDr - ED,) x IRS. id� - BW, BW, 14