Human and Ecological Risk Assessment - Earthjustice

Section 3.0Analysisfor the screening analysis: an HQ of 1 (for noncarcinogens) or an excess cancer risk level of 10 -5 .CSCLs were calculated based on an HQ of 1. A full description of the development of the HBNscan be found in Appendix I. Development of the CSCLs used for screening based on ecologicalrisks is provided in Appendix H.Screening involved developing these HBNs and CSCLs, as well as developing the wasteconstituent or media concentrations to be used in the comparison and estimating the riskassociated with these concentrations. Pathways and waste streams evaluated in the analysisinclude those summarized in Table 3-4, along with the basic assumptions and methods used toevaluate each pathway in the screening analysis.Table 3-4. Exposure Pathways Evaluated In CCW Constituent ScreeningExposure PathwayGroundwater-to-drinking-waterGroundwater-to-surface-water (fishconsumption; ecological)Direct exposure to surfaceimpoundment CCW (ecological only)MethodologyCompared drinking water HBNs to landfill leachate and surfaceimpoundment porewater concentrationsCompared surface water HBNs and CSCLs to landfill leachateand surface impoundment porewater concentrationsCompared surface water CSCLs to CCW surface impoundmentconstituent concentrations from the 1998 CCW risk assessment3.2.3.1 HBN CalculationsHBNs represent media concentrations that are protective of human health from exposurepathways that are relevant to that particular medium. The exposure scenarios assumed for CCWmanagement (see Section 2.2) defined the media of concern for the analysis. Human exposurescenarios included the following:• Drinking of groundwater contaminated by leachate from CCW landfills and surfaceimpoundments• Consumption of fish by recreational fishers fishing in streams and lakes contaminated byCCW leachate through the groundwater-to-surface-water pathwayThe CCW screening analysis used HBNs calculated for groundwater and surface waterexposure. The CCW HBNs represent reasonable maximum exposure (RME) scenarios for anoffsite receptor:• Groundwater HBNs are protective for residential drinking water exposure from adomestic well immediately downgradient from a CCW landfill or surface impoundment• Surface water HBNs are protective for fish caught (and consumed) by a recreationalfisher from a river, lake, or stream adjacent to a CCW landfill or surface impoundment.Key features and assumptions of the HBN calculations included the following:• HBNs were calculated based on a target cancer risk of 10 -5 or target HQ of 1April 2010–Draft EPA document. 3-10