Human and Ecological Risk Assessment - Earthjustice

Appendix CSite Dataeach site, either through direct calculations or by applying established relationships in lookuptables.EPACMTP utilizes three soil textures to represent variability in hydrologic soil propertiesand (along with climate data) to assign infiltration rates to each site. Because STATSGO soilsare classified into the 12 U.S. Soil Conservation Service (SCS) soil textures, the crosswalkshown in Table C-3 was used to assign the SCS textures to the EPACMTP megatextures and tocalculate the percentage of each megatexture within the 5-km data collection radius. Thesepercentages were sampled for each site when preparing the source data file for each site.Both soil pH and soil organic matter were derived for each EPACMTP soil megatextureat a site. During source data file preparation, when a megatexture was picked for a particulariteration of a site, the corresponding pH and organic matter values were selected as well.Table C-3. EPACMTP Soil Texture CrosswalkSTATSGO TextureSandLoamy sandSandy loamSilt loamSiltLoamSandy clay loamClay loamSilty clay loamSandy claySilty clayClayEPACMTP MegatextureSandy loamSilt loamSilty clay loamC.3.3 ResultsAttachment C-1 lists the STATSGO soil textures and EPACMTP megatextureassignments and percentages for each CCW disposal site.C.4 Hydrogeologic Environments (Aquifer Type)To assign aquifer properties used by EPACMTP, it was necessary to designatehydrogeologic environments (or aquifer types) for each of the locations modeled so thatcorrelated, national aquifer property data could be used in the analysis. EPACMTP uses theHydrogeologic Database (HGDB) developed by the American Petroleum Institute (API) (Newellet al., 1989; Newell et al., 1990) to specify correlated probability distributions, which were usedto populate the following four hydrogeologic parameters during the Monte Carlo analysis:• Unsaturated zone thickness• Aquifer thicknessApril 2010–Draft EPA document. C-6