Human and Ecological Risk Assessment - Earthjustice

Appendix CSite DataAppendix C. Site DataThe site characteristics used in this analysis were based on site-specific, regional, andnational data sources to provide the environmental parameters necessary for modeling the fateand transport of coal combustion waste (CCW) constituents released in landfill or surfaceimpoundment leachate. Site-specific data were collected for the area in the immediate vicinity ofthe waste management unit (WMU), and included the geographic relationship among importantfeatures such as the WMU boundary, residential well location, and streams and lakes. These datawere collected at each of the 181 coal-fired power plants selected for the analysis. These 181locations across the continental United States were intended to represent the geographicdistribution of onsite WMUs used for disposal of CCW and were used to capture nationalvariability in meteorology, soils, climate, aquifers, and surface waterbodies at the disposal sites.C.1 Data Collection MethodologyThe CCW risk assessment employed site-specific, regional, and national data. Sitespecificdata were collected around CCW plant locations from the Energy InformationAdministration (EIA) database to obtain data for each facility that were representative of theenvironment immediately surrounding the plant. When site-specific data were not available,regional or national scale data sources were used. Where appropriate, distributions were used inthe Monte Carlo analysis to capture site-to-site, within-site, and national variability in theparameters collected.Data were collected around each CCW site using a geographic information system (GIS)that allowed (1) site-specific data to be assembled from the area immediately surrounding thefacility and (2) the site to be assigned to a region to collect regional data. To account forlocational uncertainty for the CCW WMUs 1 , a 5-km radius was used to define the data collectionarea for aquifer type and soil data. If multiple soil or aquifer types occurred within this radius,multiple types were sent to the model, weighted by the fraction of the collection area that theyoccupied. Surface waterbody type and stream flows also were collected for each site byidentifying the nearest stream segment.Climate and water quality data were collected by assigning each site to a HydrologicEvaluation of Landfill Performance (HELP) model climate station and a U.S. Geological Survey(USGS) hydrologic region. The EPA STOrage and RETrieval (STORET) database was used asthe source for water quality data, with parameters selected from distributions queried from thisdatabase for each region.Because the EIA locations were not exact for the WMUs being modeled, a nationaldistribution of stream distances was developed by manually measuring the distance between the1 The EIA latitudes and longitudes usually represent a facility centroid or front-gate location for each power plant.Because these facilities are often large, the WMUs are frequently located some distance from the plant itself andnot at the EIA location.April 2010–Draft EPA document. C-1