Human and Ecological Risk Assessment - Earthjustice

Section 1.0IntroductionThis methodology implemented the following steps to assess the human and ecologicalrisk of CCWs:• Hazard Identification, which collected existing human health and ecologicalbenchmarks for the CCW constituents. Only constituents with benchmarks moved on tothe next step, constituent screening.• Constituent Screening, which compared very conservative estimates of exposureconcentrations (e.g., using leachate concentrations) to health-based concentrationbenchmarks to quickly and simply identify constituents with risks below the screeningcriteria.• Full-Scale Analysis, which characterized at a national level the human health andecological risks for constituents in CCW disposed onsite in landfills and surfaceimpoundments using a site-based probabilistic Monte Carlo risk analysis.This document focuses on the full-scale Monte Carlo analysis, but includes a discussion of thehazard identification and screening analysis (in U.S. EPA, 2002a) that led to the full-scaleassessment.1.3.5 Waste Management Scenarios AddressedThe full-scale analysis was designed to characterize waste management scenarios basedon two waste management options (disposal of CCW onsite in landfills and in surfaceimpoundments) and three waste types, as follows:• Conventional CCW, which includes fly ash, bottom ash, boiler slag, and FGD sludge• Codisposed CCWs and coal refuse, 3 which are more acidic than conventional CCWsdue to sulfide minerals in the mill rejects• FBC wastes, which include fly ash and the fluidized bed ash, and which tend to be morealkaline than conventional CCW because of the limestone mixed in during fluidized bedcombustion.Conventional CCW and codisposed CCW and coal refuse are typically disposed of inlandfills and surface impoundments that can be lined with clay or composite liners. FBC wastesare only disposed of in landfills in the United States; therefore, surface impoundment disposalwas not modeled for FBC waste.These three waste types, two waste management options, and three liner conditions(unlined, clay lined, composite lined) modeled in this analysis provide a good representation ofCCW disposal practices and waste chemistry conditions that affect the release of CCWconstituents from WMUs.3 Coal refuse is the waste coal produced from coal handling, crushing, and sizing operations, and tends to have ahigh sulfur content and low pH from high amounts of sulfide minerals (like pyrite). In the CCW constituentdatabase, codisposed coal refuse includes “combined ash and coal gob,” “combined ash and coal refuse,” and“combined bottom ash and pyrites.”April 2010–Draft EPA document. 1-5