Human and Ecological Risk Assessment - Earthjustice

Section 1.0Introduction1.3.2 Exposure PathwaysThe releases, and hence media concentrations and risk estimates in this report, werebased on leaching to groundwater and groundwater transport to nearby wells and surface waterbodies. This analysis did not address direct releases to surface water, which are permitted underthe National Pollutant Discharge Elimination System (NPDES) of the Clean Water Act. Thus,the estimated media concentrations and risks do not take into account contributions fromNPDES-permitted releases, including discharges due to flooding or heavy rainfall. Uncertaintiesassociated with this decision are described in Section 4.4.1 of this report.EPA recognizes that there are exposure pathways in addition to the groundwaterpathways addressed in this report that could be of concern to human health and ecologicalreceptors, including fugitive dust eroded and transported by wind from uncovered CCWlandfills, and erosion and transport of CCW constituents from uncovered landfills onto adjacentland and eventually into downslope waterbodies. These “aboveground” pathways were addressedin the 1998 risk assessment, and in 2002, EPA conducted a draft screening analysis (U.S. EPA,2002a) to evaluate risks from these pathways.1.3.3 Risk LevelsTo evaluate the significance of the estimated risks from the pathways assessed in thisassessment, EPA compared the risk estimates to a risk range (for carcinogens) or to a specificrisk criterion (for noncarcinogens) that are protective of human health and the environment:• An estimate of the excess lifetime cancer risk for individuals exposed to carcinogenic(cancer-causing) contaminants ranging from 1 chance in 1,000,000 (10 -6 excess cancerrisk) to 1 chance in 10,000 (10 -4 excess cancer risk). For decisions made to screen outcertain constituents from further consideration, a 1 in 100,000 (10 -5 ) excess lifetimecancer risk was used. 2• A measure of safe intake levels to predicted intake levels, a hazard quotient (HQ) greaterthan 1 for constituents that can produce noncancer human health effects (an HQ of 1 isdefined as the ratio of a potential exposure to a constituent to the highest exposure levelat which no adverse health effects are likely to occur)• An HQ greater than 1 for constituents with adverse effects to ecological receptors.1.3.4 MethodologyIn 1998, EPA conducted a risk assessment for fossil fuel combustion wastes (whichinclude CCWs) to support the May 2000 RCRA regulatory determination (U.S. EPA, 1998a,b).Since then, EPA has added to the waste constituent database that was used in that effort,expanding the number of leachate and total waste analyses for 41 CCW constituents. The CCWrisk assessment subjected these waste and leachate constituent concentrations to the tiered riskassessment methodology illustrated in Figure 1-1.2 The typical cancer risk range used by the Office of Solid Waste and Emergency Response is 10 -4 to 10 -6 .April 2010–Draft EPA document. 1-3