Human and Ecological Risk Assessment - Earthjustice

Section 1.0Introduction1.4 Document OrganizationThis document is organized into the following sections:• Section 2, Problem Formulation, describes how the framework for the full-scaleanalysis was developed, including identification of the waste constituents, exposurepathways, and receptors of concern; selection and characterization of waste managementpractices and sites to model; and development of the conceptual site models for themodeling effort.• Section 3, Analysis, describes the probabilistic modeling framework and the models andmethods used to (1) screen CCW constituents for the full-scale analysis, (2) estimateconstituent releases from CCW landfills and surface impoundments (source models),(3) model constituent concentrations in the environmental media of concern (groundwaterand surface water), (4) calculate exposure, and (5) estimate risk to human and ecologicalreceptors.• Section 4, Risk Characterization, characterizes the human health and environmentalrisks posed by CCW, including (1) discussion of the methods used to account forvariability and uncertainty and (2) identification of the scenarios and conditions modeledthat resulted in higher and lower risks. Results are presented as national estimates forCCW landfills and CCW surface impoundments, as well as by waste type and linerstatus. This section characterizes the risks posed by CCW constituents and pathwaysunder the conditions modeled, including factors (such as liners or facility environmentalsetting) that result in higher or lower risk levels. Finally, the risk characterizationevaluates the risk results in light of more recent research on CCW waste managementpractices and the environmental behavior of CCW constituents.The first three appendices provide detailed information on how wastes, WMUs, andsettings were characterized for the risk assessment. Appendix A describes the chemicalcharacteristics of CCW, including the CCW leachate concentration distributions used torepresent disposal conditions in landfills and surface impoundments. Appendix B describes howEPA characterized the CCW landfills and surface impoundments, including locations, surfacearea, capacities, geometry, and liner status. Appendix C presents the methodologies and dataused to characterize the environmental setting at each CCW site identified in Appendix B,including delineating the site layout and determining the environmental setting (e.g.,meteorology, climate, soils, aquifers, and waterbodies).The next five appendices provide detailed information on the specific models and dataused to calculate risk, including the nonlinear sorption isotherms (Appendix D), the surfacewater fate and transport and intake equations (Appendix E), the exposure factors (Appendix F),benchmarks for human health (Appendix G), and benchmarks for ecological risk (Appendix H).The next three appendices provide background and results for the screening analysis,including calculation of health-based numbers (HBNs, Appendix I), chemical-specific inputsused in the screening analysis (Appendix J), and the screening analysis results (Appendix K).Finally, Appendix L provides figures showing, for selected CCW constituents,cumulative percentiles of the time it took for the peak concentration to reach a receptor well foreach source type.April 2010–Draft EPA document. 1-7