Human and Ecological Risk Assessment - Earthjustice

Section 1.0Introduction1.3.6 Modeling ApproachThe full-scale analysis was implemented using a site-based probabilistic approach thatproduces a distribution of risks or hazard for each receptor by allowing the values of some of theparameters in the analysis to vary. Input parameters were varied in the analysis using datacollected at or around CCW disposal facilities or, when site-based data were not available, fromdistributions representing the variability of parameters across the United States. This approachwas ideal for this risk assessment because there are many CCW facilities across the UnitedStates, and site-based data collection can capture both the variability in waste managementpractices at these facilities and the differences in their environmental settings (e.g.,hydrogeology, climate, hydrology).This probabilistic approach was implemented through seven primary steps:Problem Formulation1. Characterize the CCW constituents and waste chemistry, along with the size and linerstatus of the WMUs in which each waste stream may be managed2. Characterize the environmental settings for the sites where CCW landfills and surfaceimpoundments are located3. Identify scenarios under which contaminants are released from a WMU andtransported to a human receptorAnalysis4. Screen risks to select CCW constituents for full-scale analysis5. Predict the fate and transport of constituents in the environment once they arereleased from the WMUs at each site6. Quantify the exposure of human and ecological receptors to the contaminant in theenvironment and the risk associated with this exposureRisk Characterization7. Estimate the risk to receptors from the exposure and characterize this risk in terms ofexposure pathways, health effects, and uncertainties8. Identify the waste disposal scenarios and environmental conditions that pose risks ofpotential concern to human health or the environment. Evaluate risks at the 50th and90th percentiles.April 2010–Draft EPA document. 1-6