Human and Ecological Risk Assessment - Earthjustice

Section 4.0Risk CharacterizationMercury0.10.0195th %0.001Hg (mg/L)0.00010.00001maxNaturalpHmin50th %5th %0.0000010.0000001BraytonPointPleasantPrairieSalemHarborVanderbilt StudyFacility C St. ClairFacilityFacility L CCW -LFEPRI -LFCCW -SIOther Data SetsEPRI - SIKey to data sets:Vanderbilt = U.S. EPA (2006c)CCW = CC Constituent Database (this analysis)EPRI = EPRI Leachate data (from U.S. EPA, 2006c)EPA = Leach 2000 data (from U.S. EPA, 2000, as cited in U.S. EPA, 2006c)LF = landfillsSI = surface impoundmentsFigure 4-3. CCW mercury concentrations compared with other leachate data.4.4.3.2 WMU Locations and CharacteristicsThe locations of the specific sites in the United States where CCW is disposed areknown, and EPA used the soil and climatic characteristics of these sites in the Monte Carloanalysis. Because most locations were facility front gates or centroids, the exact location of theCCW landfill or surface impoundment was not known. To account for this uncertainty, soil datawere collected for an area around the plant and soil type distributions were sampled in the MonteCarlo analysis. Climate center assignments were combined with the soil texture distributions toselect infiltration and recharge rates to use in the analysis.WMU area, depth, volume, and liner type were not varied in the Monte Carlo analysisbecause values for these variables were known from the EPRI survey data. More uncertainparameters, such as depth below grade, were varied within reasonable ranges. These data wereused in the source model calculations to generate the distribution of environmental releases usedby the fate and transport modeling.Three standard WMU liner scenarios (clay, composite, and unlined) were assigned toeach facility based on best matches to data in the EPRI survey on liner type. Infiltration throughthese liners was then modeled using assumptions, models, and data developed in support ofEPA’s Industrial Subtitle D guidance. How well these assumptions and models represent theperformance of CCW WMU landfills and surface impoundments is an uncertainty in thisanalysis.April 2010–Draft EPA document. 4-51