Human and Ecological Risk Assessment - Earthjustice

Section 3.0AnalysisTable 3-11. Aluminum Solubility as a Function of Waterbody pH aMinimum pH Maximum pH Solubility (mg/L)3.5 4.5 26.24.5 5 1.845 5.5 0.1965.5 6 0.01126 6.5 0.001436.5 7 0.0006627 7.5 0.0009157.5 8 0.002298 8.5 0.006828.5 9 0.02129 9.5 0.06669.5 10 0.21110 10.5 0.668aComputed using MINTEQA2Only the water column concentration for aluminum was used in subsequent exposure andrisk calculations, because there is no available ecological benchmark for aluminum in sediment.The water column concentration was used to calculate human exposure via drinking wateringestion, as well as risk to ecological receptors exposed via direct contact.3.8 Human Exposure AssessmentThe human exposure component of the full-scale analysis assessed the magnitude,frequency, duration, and route of exposure to CCW contaminants that an individual mayexperience. The term “exposure,” as defined by the EPA exposure guidelines (U.S. EPA, 1992),as the condition that occurs when a contaminant comes into contact with the outer boundary ofthe body. The exposure of an individual to a contaminant completes an exposure pathway (i.e.,the course a constituent takes from the WMU to an exposed individual). Once the body isexposed, the constituent can cross the outer boundary and enter the body. The amount ofcontaminant that crosses and is available for adsorption at internal exchange boundaries isreferred to as the “dose” (U.S. EPA, 1992).This risk assessment evaluated the risk from CCW contaminants to receptors in thevicinity of a WMU. The individuals evaluated were those residents closest to the WMU. Thedistances from the WMU to the residents were taken from a distribution of distances to thenearest residential drinking water well measured for municipal landfills and, for the recreationalfisher, a distribution of the distance of the nearest surface water body from CCW landfills andsurface impoundments (see Appendix C).Section 3.8.1 presents an overview of the receptors and selected exposure pathwaysconsidered for this assessment, including a discussion of how childhood exposure wasconsidered in the analysis. Section 3.8.2 presents exposure factors (i.e., values needed tocalculate human exposure) used in the analysis. Section 3.8.3 describes the methods used toestimate dose, including average daily dose (ADD) and lifetime average daily dose (LADD).April 2010–Draft EPA document. 3-40