Human and Ecological Risk Assessment - Earthjustice

Section 2.0Problem Formulationsmall sample is not sufficient to represent the universe of FBC disposal units and, if included inthe overall analysis, could bias the Monte Carlo results towards the environmental conditionsaround these few landfill units, FBC wastes were addressed separately from the moreconventional CCW types in the full-scale analysis and are not included with the conventionaland codisposal CCW management scenarios in the overall results. Section 4.1.3 compares therisk results for each of these waste types, including FBC.Table 2-3 shows how the plants were distributed across the waste type/WMU scenariosmodeled in the full-scale analysis. The distribution across the waste type/WMU scenarios, thegeographic distribution of these facilities, and the size and liner status of the WMUs wereassumed to be representative of all onsite CCW landfills and surface impoundments in thecontinental United States as of 1995. As mentioned previously, DOE and EPA have conducted anewer survey on CCW disposal facilities (U.S. DOE, 2006), but the scope of this survey was notas comprehensive as the EPRI survey (e.g., WMU areas and capacity data were not collected).Newer information (U.S. DOE, 2007a,b) suggest that there now may be up to approximately 500coal-fired electric utility power plants in the United States, the majority of which would beexpected to conduct some waste management activities in onsite landfills or surfaceimpoundments (U.S. EPA, 2010).Table 2-3. Coal Combustion Plants with Onsite CCW WMUsModeled in the Full-Scale AssessmentWaste Type and Liner StatusConventional CCW cunlinedclay-linedcomposite-linedCodisposed CCW and coal refuseunlinedclay-linedcomposite-linedFBC waste dunlinedclay-linedcomposite-linedNumber of Plants in 1995 EPRI Survey a with Onsite:Landfills7138281038201097331SurfaceImpoundments38241056552112Either WMUType b103603815100692111- 7331All waste types 108 96 181a EPRI (1997); note that some coal combustion plants have one or more onsite WMUs.bNumber of coal combustion plants with onsite landfill(s), surface impoundment(s), or both.c Fly ash, bottom ash, boiler slag, and FGD sludge.d Includes 3 EPRI Survey FBC landfills plus 4 additional FBC landfills added by EPA. FBC wastreated separately in the full-scale assessment because of the small number of FBC sites.2.2 Conceptual ModelThe waste stream/WMU combinations discussed above provided the waste managementscenarios evaluated in the risk assessment. The full-scale assessment used the EPRI survey datato place these scenarios at actual onsite CCW disposal sites across the country. These sites wereApril 2010–Draft EPA document. 2-6