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(2) skin contact([mg•yr]/[kg•d]: <br /> ED, X AF X SA_ + (ED, - ED,) X AF X SA, <br /> SFS,dj ` BW, BW, <br /> (3) inhalation ([m'•yr]/[kg•d]): <br /> ED, X IRA, . (ED, - ED,) X IRA, <br /> InhF,dj BW, BW, <br /> 4S PRC Equations <br /> The equations used to calculate the PRGs for carcinogenic and noncarcinogeaic contaminants <br /> are presented in Equations 4-1 through 4-8. The PRG equations update RAGS Part B <br /> equations. Briefly, PM are risk assessments run in reverse. The methodology <br /> backcalculates a soil, air, or water concentration level from a target risk (for carcinogens) or <br /> hazard quotient (for noncarcinogens). For completeness, the soil equations combine risks <br /> from ingestion, skin contact, and inhalation simultaneously. Note: the electronic version of <br /> the table also includes pathway-specific PRGs, should the user decide against combining <br /> specific exposure pathways; or, the user wants to identify the relative contribution of each <br /> pathway to exposure. <br /> f <br /> To calculate PRGs for volatile chemicals in soil, a chemical-specific volatilization factor is <br /> calculated per Equation 4-9. Because of its reliance on Henry's law, the VF, model is <br /> applicable only when the contaminant concentration in soil is at or below saturation (i.e. there <br /> is no free-phase contaminant present). Soil saturation ("sat") corresponds to the contaminant <br /> concentration in soil at which the adsorptive limits of the soil particles and the solubility <br /> limits of the available soil moisture have been reached. Above this point, pure liquid-phase <br /> contaminant is expected in the soil. If the PRG calculated using VF, was greater than the <br /> calculated sat, the PRG was set equal to sat, in accordance with Soil Screening Guidance <br /> (USEPA 1996 ab). The updated equation for deriving sat is presented in Equation 4-10. <br /> 15 <br />