Human and Ecological Risk Assessment - Earthjustice

Section 4.0Risk Characterizationcertain constituents from further consideration, a 1 in 100,000 (10 -5 ) excess lifetimecancer risk) was used. 1• For constituents that cause adverse, noncancer health effects (noncarcinogens), thecriterion is an HQ of greater than 1, with the HQ being the ratio of the average dailyexposure level to a protective exposure level corresponding to the maximum level atwhich no appreciable effects are likely to occur.• An HQ greater than 1 for was used to identify constituents with adverse effects toecological receptors.In general, the full-scale analysis showed lower risks than the screening analysis, but stillshowed risks within or above the cancer risk range or above an HQ of 1 for certain CCWconstituents, WMU types, pathways, and receptors at the 90th percentile. At the 50th percentile,risks are still above these levels for both WMU types, but for fewer constituents and pathways.The results presented herein are subject to further interpretation, as EPA queries the CCW riskinputs and outputs to investigate how the results may be affected by (1) waste types andenvironmental and waste management conditions, (2) assumptions made about these conditionsin designing the probabilistic analysis, and (3) the availability of newer facility data.4.1 Human Health RisksThis section presents the 90th and 50th percentile risk results for the two human exposurepathways evaluated in the full-scale analysis: (1) groundwater-to-drinking-water and(2) groundwater-to-surface-water (fish consumption). Results are presented for the two WMUtypes addressed in the analysis: landfills and surface impoundments, and show the distribution ofrisks across all waste types by liner type from the EPRI survey data (see Section 4.1.3 for furtherdiscussion of liners).4.1.1 Groundwater-to-Drinking-Water Results by Waste Type/WMU ScenarioAs described in Section 3.3, the CCW risk assessment was organized by waste type sothat different waste chemistries could be accounted for in the fate and transport modeling. Theresults discussed so far in this report address conventional CCW (fly ash, bottom ash, boiler slag,FGD sludge) and conventional CCW codisposed with coal refuse. 2 Section 4.1.1.1 presents theseresults by waste type. FBC wastes were also modeled in this assessment. However, there was avery small number of FBC waste disposal sites (seven) in the EPRI/EPA database. For thisreason, the FBC results are treated separately in Section 4.1.1.2. Groundwater results arereported for a resident’s child because these consistently led to higher HQs, with the exception ofarsenic cancer values, which were consistently higher in adults. Thus, the cancer risks reportedare for adults.12The typical cancer risk range used by the Office of Solid Waste and Emergency Response is 10 -4 to 10 -6 .Coal refuse is the waste coal produced from coal handling, crushing, and sizing operations, and tends to have ahigh sulfur content and low pH. In the CCW constituent database, codisposed coal refuse includes “combinedash and coal gob,” “combined ash and coal refuse,” and “combined bottom ash and pyrites.”April 2010–Draft EPA document. 4-2