Laserfiche WebLink
EXHIBIT 3-1 <br /> SUGGESTED READINGS FOR EVALUATING SOIL CONTAMINANT <br /> PATHWAYS NOT CURRENTLY ADDRESSED BY REGION 9 PRGs <br /> EXPOSURE PATHWAY REFERENCE <br /> Migration of contaminants to an underlying Soil Screening Guidance: User's Guide <br /> potable aquifer and Technical Background Document <br /> (USEPA 1996a b) <br /> Ingestion via plant uptake Technical Support Document for Land <br /> Application of Sewage Sludge (USEPA <br /> 1992a) <br /> Ingestion via meat or dairy products Estimating Exposure to Dioxin-Like <br /> Compounds - Review Draft (1994a) <br /> Inhalation of volatiles that have migrated Soil Screening Guidance: User's Guide <br /> into basements and Technical Background Document <br /> (USEPA 1996a b) <br /> Terrestrial environmental pathways Role of the Ecological Risk Assessment in <br /> the Baseline Risk Assessment (USEPA <br /> 1994b) <br /> 3.2 Background Levels Evaluation <br /> A necessary step in determining the usefulness of Region 9 PRGs is the consideration of <br /> background contaminant concentrations. EPA may be concerned with two types of <br /> background at sites: naturally occurring and anthropogenic. Natural background is usually <br /> limited to metals whereas anthropogenic (i.e. human-made) background includes both organic <br /> and inorganic contaminants. Before embarking on an extensive sampling and analysis <br /> program to determine local background concentrations in the area, one should first compile <br /> existing data on the subject. Far too often there is pertinent information in the literature that <br /> gets ignored, resulting in needless expenditures of time and money. <br /> Generally EPA does not clean up below natural background. If natural background <br /> concentrations are higher than the PRGs, the generic PRGs may not be the best tool for site <br /> decisionmaking. Or, an adjustment of the PRG may be needed. For example, naturally <br /> occurring arsenic frequently is higher than the soil PRG set equal to a one-in-one-million <br /> cancer risk (the point of departure), thus an alternative PRG for arsenic is provided in the <br /> lookup tables based on non-cancer endpoints that is still protective of cancer risks as well (i.e. <br /> falls within EPA's "acceptable" risk range). Because of the problems associated with <br /> adjusting PRGs to an alternate risk level, this procedure is not recommended without first <br /> 8 <br />