Human and Ecological Risk Assessment - Earthjustice

Section 4.0Risk Characterizationin this analysis does not include impoundment water samples, and the direct exposure pathwaycould not be addressed for ecological risk. However, the CCW risk assessment conducted in1998 (U.S. EPA, 1998a,b) did consider direct exposure of ecological receptors to surfaceimpoundment waters. The approach in the 1998 study restricted the analysis to terrestrialreceptors that obtain food and prey from the surface impoundments and excluded aquaticreceptors living in the water column because surface impoundments are not intended to be ahabitat for aquatic species. For the terrestrial and aquatic receptors considered, the 1998 analysisused the same CSCLs and a similar methodology to that used in the CCW screening analysis(e.g., comparison of 90th percentile waste concentrations with CSCLs).The 1998 direct exposure results are provided in Figure 4-1 and show HQs greater than100 for boron, selenium, lead, barium, and cadmium. This, along with the damage case resultspresented in Section 4.2.4, show a clear likelihood of risks to terrestrial organisms that obtainfood and prey from CCW surface impoundments. It is probable that ecological receptors eat anddrink from CCW surface impoundments in some settings. In addition, ecological receptors,particularly amphibians who may lay their eggs in surface impoundments, are probably exposedthrough chronic contact with wastewater. Because amphibians are prey to a large variety ofanimals (e.g., raptors; wading birds; mammalian omnivores, such as foxes, raccoons, andweasels), this exposure is transferred up the food chain. Aquatic plants, although not often afocus of this ecological risk assessment, are directly exposed in surface impoundments. Plants, inturn, may be ingested by vertebrates and invertebrates at higher trophic levels.April 2010–Draft EPA document. 4-27