Human and Ecological Risk Assessment - Earthjustice

Section 4.0Risk Characterization4.1.2 Groundwater-to-Surface-Water (Fish Consumption) PathwayLike the drinking water results above, the fish consumption results are organized bywaste type so that different waste chemistries could be accounted for. Section 4.1.2.1 presentsthe results for conventional CCW and codisposed CCW by WMU and liner type. FBC wasteswere also modeled for the surface water pathway, and these results are treated separately inSection 4.1.2.2. Note that only the four constituents that failed the surface water screen wereprobabilistically modeled for this scenario. Of those, thallium risks are not presented for surfaceimpoundments because of a high proportion (>90%) of nondetects in the surface impoundmentdata (see Section 4.4.3.1 for further discussion). The screening analysis results in Section 3.2.4and Table 3-6 show which CCW constituents exceeded the surface water screening criteria.4.1.2.1 Conventional CCW and CCW Codisposed with Coal RefuseTables 4-8 and 4-9 present the 90th and 50th percentile risk results, respectively, bywaste type and liner type for CCW landfills for the fish consumption pathway. The resultspresented are for a fisher’s child because those risks were consistently higher than the risks forthe adult fisher. As seen in these tables, the results for landfills that codispose of CCW are notdrastically different from those that handle only conventional CCW. At the 90th percentile, onlyunlined landfills that comanage CCW present risks at an HQ of 1 (for selenium). The remainderof the modeled constituents had risks below an excess cancer risk of 1 in 100,000 or an HQ of 1at the 90th percentile. 50th percentile results were all well below these levels for both cancer andnoncancer risks.Tables 4-10 and 4-11 present the 90th and 50th percentile risk results, respectively, bywaste type and liner for CCW surface impoundments for the fish consumption pathway. Again,risks are higher for surface impoundments than for landfills because of the higher wasteconcentrations and the higher hydraulic head in these units, as discussed previously for thedrinking water pathway. Results at that 90th percentile exceeded an HQ of 1 for selenium inunlined (HQ of 3) and clay-lined (HQ of 2) impoundments managing conventional CCW, andalso exhibited excess cancer risks just above 1 in 100,000 for arsenic in unlined (3 in 100,000)and clay-lined (2 in 100,000) impoundments comanaging CCW. Fish consumption pathway 50thpercentile results are well below an excess cancer risk of 1 in 1,000,000 and an HQ of 1 for allconstituents, waste management scenarios, and liner types.Table 4-8. 90th Percentile Risk Results by CCW Type: Landfills,Groundwater-to-Surface-Water PathwayChemical bConventional CCW – 79 landfillsUnlined Units90th Percentile HQ or Cancer Risk Value aCancerClay-Lined UnitsComposite-LinedUnitsArsenic III 1E-06 1E-07 0Arsenic V 4E-07 3E-09 0(continued)April 2010–Draft EPA document. 4-13