Human and Ecological Risk Assessment - Earthjustice

Section 2.0Problem Formulationdata sources) and screened to develop the waste disposal scenarios modeled in the full-scaleanalysis.2.1.1 Identification of Waste Types, Constituents, and Exposure PathwaysTo identify the CCW constituents and exposure pathways to be addressed in this riskassessment, we relied on a database of CCW analyses that EPA had assembled over the pastseveral years to characterize whole waste and waste leachate from CCW disposal sites across thecountry (see Appendix A). The 2003 CCW constituent database includes all of the CCWcharacterization data used by EPA in its previous risk assessments, supplemented with additionaldata collected from public comments, data from EPA Regions and state regulatory agencies,industry submittals, and literature searches up to 2003.The CCW constituent database represents a significant improvement in the quantity andscope of waste characterization data available from the 1998 EPA risk assessment of CCWs(U.S. EPA, 1998a,b). For example, the constituent data set used for the previous risk assessments(U.S. EPA, 1999a) covered approximately 50 CCW generation and/or disposal sites, while the2002 CCW constituent database covers approximately 140 waste disposal sites. 1 The 2002database also has broader coverage of the major ion concentrations of CCW leachate (e.g.,calcium, sulfate, pH), that can influence CCW impacts on human health and the environment.2.1.1.1 Waste TypesTable 2-1 shows the waste types included in the 2002 CCW constituent database, alongwith counts of the number of sites with wastes of each type with constituent measurements inlandfill leachate, surface impoundment porewater, and whole waste.Comments received by EPA on the previous CCW risk assessment pointed out that theanalysis did not adequately consider the impacts of CCW leachate on the geochemistry andmobility of metal constituents in the subsurface. Commenters stated that given the large size ofthe WMUs and the generally alkaline nature of CCW leachate, it is likely that the leachateaffects the geochemistry of the soil and aquifers underlying CCW disposal facilities, which canimpact the migration of metals in the subsurface. To address this concern, EPA statisticallyevaluated major ion porewater data from the CCW constituent database for the waste streamsshown in Table 2-1. Based on this analysis and prevalent comanagement practices, EPA groupedthe waste streams into three statistically distinct categories: conventional CCW (fly ash, bottomash, slag, and FGD sludge), which has moderate to high pH; codisposed CCW and coal refuse,which tends to have low pH; and FBC waste, which tends to have high pH. As shown in Table2-1, each of these waste types included several waste streams that are usually codisposed inlandfills or surface impoundments. Note that some sites in the CCW database have more thanone waste stream, so the site counts for the different waste streams in a waste type category sumto more than the total site count for that waste type.1 Although EPA believes that the 140 waste disposal sites do represent the national variability in CCWcharacteristics, they are not the same sites as in the EPRI survey. During full-scale modeling, data from the CCWconstituent database were assigned to each EPRI site based on the waste types reported in the EPRI survey data.April 2010–Draft EPA document. 2-2