Human and Ecological Risk Assessment - Earthjustice

Section 4.0Risk Characterization• Appropriateness of CCW leachate data. Data on another highly sensitive parameter,leachate (porewater) constituent concentration, were available and used for CCW surfaceimpoundments. However, available data for landfills were mainly TCLP analyses, whichmay not be representative of actual CCW leachate. Comparisons with recent (2006 and2008) studies of coal ash leaching processes show very good agreement for arsenic.However, although the selenium CCW data are within the range of the 2006 and 2008data, some of the higher concentrations in both Vanderbilt data sets are not representedby the TCLP data, and U.S. EPA (2008c) show similar trends for barium andmolybdenum. This suggests that risks for these metals may be underestimated, which isconsistent with selenium as a common driver of the damage cases.• Impacts of mercury rules (CAIR and CAMR). While CAIR and CAMR will reduceemissions of mercury and other metals from coal-fired power plants, mercury and othermore volatile metals will be transferred from the flue gas to fly ash and other air pollutioncontrol residues, including the sludge from wet scrubbers. EPA ORD has researchunderway to evaluate changes to CCW characteristics and leaching of mercury and othermetals from CAIR and CAMR. Data from the first report (U.S. EPA, 2006c) suggest thatalthough total mercury will increase in CCW from the use of sorbents as mercurycontrols, the leachability of mercury may be reduced. Data from U.S. EPA (2008c) add tothis assessment by supporting similar findings.• Mercury and nondetect analyses. Because of a high proportion of nondetect values anda limited number of measurements, the risks from mercury in CCW could not beevaluated for either landfills or surface impoundments and for antimony and thallium insurface impoundments. The 2006 leaching study data suggest that mercury levels arefairly low in fly ash from coal combustion, a conclusion generally confirmed by the 2008study report (U.S. EPA, 2008c), although that study did find higher mercury leachateconcentrations from scrubber sludge than other coal wastes and found that blending flyash and lime can increase mercury leaching from scrubber sludge.Uncertainties that are more difficult to evaluate with respect to CCW risk results includethe following:• Well distance. Nearest well distances were taken from a survey of MSW landfills, asdata were not available from CCW sites. EPA believes that this is a protectiveassumption because MSW landfills generally tend to be in more populated areas, butthere are little data available to test this hypothesis.• Liner conditions. Liner design and performance for CCW WMUs were based on dataand assumptions EPA developed to be appropriate for nonhazardous industrial wastelandfills. EPA believes that CCW landfills should have similar performancecharacteristics, but does not have the quantitative data to verify that.• Data gaps for ecological receptors. Insufficient data were available to developscreening levels and quantitative risk estimates for terrestrial amphibians, but EPAacknowledges that damage cases indicate risk to terrestrial amphibian and plantcommunities through exposure to selenium and boron.April 2010–Draft EPA document. 4-60