Human and Ecological Risk Assessment - Earthjustice

Section 2.0Problem Formulationonsite CCW landfills and surface impoundments at coal-fired utility power plants, but does nothave data on typical distances (or the distributions of distances) of domestic drinking water wellsfrom CCW disposal facilities. (The potential impact on the results of this assumption is discussedas an uncertainty in Section 4.4.3.3).Figure 2-3. Conceptual site layout for residential groundwater ingestion scenario.The angle off the contaminant plume centerline ( rw in Figure 2-3) was based on auniform distribution ranging from 0 to 90°. The depth of the well below the water table was setwithin the groundwater model based on assumptions that are generally typical of averageconditions for surficial aquifers across the United States. These limits are discussed inSection 3.6.3. In this assessment, receptors were always located within the lateral extent of theplume.The soil and aquifer characteristics needed for the groundwater model were based onavailable data on soil and groundwater conditions collected around the 181 modeled sites, asdescribed in Appendix C.2.2.2.2 Recreational Fisher and Ecological Risk ScenarioThe recreational fisher 4 scenario, shown in Figure 2-4, was used to estimate risks torecreational fishers (and their children) who live near the CCW landfills and surfaceimpoundments and catch and consume fish from a waterbody located adjacent to the buffer andcontaminated by CCW constituents through the groundwater to surface water pathway. The4 Only recreational fishers were considered as the reasonable maximum exposed individuals. Subsistence receptorswho eat fish were not modeled, but could be expected to have higher risks than the recreational fishers for whomwe present results.April 2010–Draft EPA document. 2-10