Human and Ecological Risk Assessment - Earthjustice

Section 3.0Analysis• Soil and aquifer type were collected within a 5-km radius of each site location to accountfor locational uncertainty for the WMUs (site location are often facility centroids or frontgate locations).• Surface water type and flows were collected using a geographic information system(GIS) to identify the nearest stream and by matching plants to the Permit ComplianceSystem (PCS) database to get the stream segment for each plant’s NPDES dischargepoint.These site-based data were supplemented with regional data on surface water quality andwith national distributions of receptor distances (i.e., distance to drinking water well anddistance to nearest surface waterbody). Appendix C describes the site-based approach and datasources used for these site-specific, regional, and national-scale data collection efforts.The five 10,000-record scenario-specific source data files were then combined with theCCW constituent data for each constituent in the appropriate waste type to develop the finalsource data files for each scenario. With 12 constituents modeled for most scenarios, thisresulted in over 600,000 records in the final input data set.3.4 Landfill ModelReleases from landfills were modeled using a landfill source-term model contained inEPACMTP. EPA has used EPACMTP and its predecessor models for almost 20 years to conductgroundwater risk assessments in support of regulations for land disposal of hazardous andnonhazardous wastes. In that context, EPACMTP has undergone numerous peer reviews,including multiple reviews by EPA’s Science Advisory Board (SAB). Each of these reviews hassupported and approved the use of this model for developing national regulations and guidance,including verification that the model and model code are scientifically sound and properlyexecuted. Some of the more important reviews include• A 1989 review by SAB of the component saturated zone (groundwater) model used inEPACMTP• A 1993 review by EPA’s Office of Research and Development (ORD) of EPACMTP forpotential Hazardous Waste Identification Rule applications, which resulted in a numberof improvements in the computational modules of EPACMTP• A 1994 consultation with SAB on the use of EPACMTP for determination of dilutionattenuationfactors for EPA’s Soil Screening Guidance• A 1994 review by expert modelers Dr. Fred Molz (Auburn University) and Mr. ChrisNeville (SS Papadopoulos & Associates), who verified that the mathematical formulationof the model and the code verification testing are scientifically sound• The peer-reviewed publication of EPACMTP in the Journal of Contaminant Hydrology(Kool et al., 1994)April 2010–Draft EPA document. 3-19