Human and Ecological Risk Assessment - Earthjustice

Section 4.0Risk CharacterizationEcological Criteria. CSCLs were developed for constituents when sufficient data wereavailable. In many cases, sufficient data were unavailable for a receptor/constituent combination,and therefore, the potential risk to a receptor could not be assessed. In particular, insufficientdata were available to derive chronic effects CSCLs for amphibians. Because the risk results canonly be interpreted within the context of available data, the absence of data cannot be construedto mean that adverse ecological effects will not occur.In addition to the effects of data gaps on ecological benchmarks, the ecological criteriatend to be fairly conservative because the overall approach is based on “no effects” or “lowesteffects” study data. In site-specific assessments, a de minimis effects approach is often replacedwith an effects level similar to natural population variability (e.g., sometimes as high as a 20percent effects level). As a result, the CSCLs used in this analysis are likely to overestimate risksfor representative species and communities assumed to live in surface waters impacted by CCWWMUs. Because the difference between a LOAEL and a NOAEL is often about a factor of 10,an HQ exceedance of roughly 10 may not be ecologically significant. In contrast, CSCLs basedon no effects data that are developed for the protection of threatened and endangered species arepresumed to be protective.4.5 Summary and ConclusionsCCW risk assessment results at the 90th percentile suggest that the management of CCWin unlined or clay-lined WMUs result in risks greater than 1 in 100,000 for excess cancer risk tohumans or an HQ greater than 1 for noncancer effects to both human and ecological receptors.Key risk findings include the following:• For humans exposed via the groundwater-to-drinking-water pathway, risks from claylinedunits that dispose CCW or CCW comanaged with coal refuse are lower than thosefor unlined units. However, the 90th percentile risks for clay-lined units are still wellwithin or above the range of concern (10 -6 to 10 -4 ) for cancer risk and above an HQ of 1for noncarcinogens. For example, arsenic III cancer risks in clay-lined units range from1 in 5,000 for landfills to 9 in 10,000 in surface impoundments. The thallium HQ wasas high as 2 for clay-lined landfills, and the clay-lined surface impoundment HQ was ashigh as 200 for cobalt and 4 for boron.• Arsenic was the constituent with the highest risk for landfills. Clay-lined landfillspresented 90th percentile risks above an excess cancer risk of 1 in 100,000 for arsenic(risks as high as 1 in 5,000) and an HQ of 1 for thallium (HQ of 2). When landfills areunlined, they also present risk above an HQ of 1 for antimony and molybdenum, eachwith an HQ of 2. Here, arsenic cancer risks were as high as 1 in 2,000. Clay-lined FBClandfills also presented 90th percentile risks above and HQ of 1 for antimony (HQ = 3)and thallium (HQ = 4) and showed excess cancer risks of 3 in 50,000 for arsenic.However, unlined FBC landfills differed in that they only exceeded a 1 in 100,000 excesscancer risk for arsenic. 14 At the 50th percentile, arsenic III from CCW codisposed with14 As modeled, unlined FBC units showed less risk than clay-line FBC units.April 2010–Draft EPA document. 4-57