Human and Ecological Risk Assessment - Earthjustice

Executive SummaryHuman and Ecological Risk Assessment of Coal Combustion WastesIII from CCW codisposed with coal refuseexceeded an excess cancer risk of 10 -5 , withcancer risks of 1 in 50,000.As shown in Table ES-3, arsenic andcobalt were the constituents with the highestrisks for surface impoundments. Clay-linedsurface impoundments presented 90thpercentile excess cancer risks above 1 in10,000 for arsenic and exceed the HQcriterion of 1 for boron, cadmium, cobalt,molybdenum, and nitrate. Here, arsenic excesscancer risks were as high as 1 in 500, andcobalt had HQs as high as 200. When surfaceimpoundments were unlined, they alsoshowed risk above the HQ criterion for leadand selenium. Here, arsenic excess cancerrisks were as high as 1 in 50, and cobalt hadHQs as high as 500. As seen in Table ES-4,the 50th percentile surface impoundmentresults exceeded a 1 in 100,000 cancer risk forarsenic and only cobalt exceeded an HQ of 1.Here, unlined units had arsenic excess cancerrisks as high as 6 in 10,000 while clay-linedunits had arsenic excess cancer risks as highas 1 in 5,000. Cobalt HQs were as high as 20and 6 for unlined and clay-lined surfaceimpoundments, respectively.For the groundwater-to-drinking-waterpathway, composite liners, as modeled in thisassessment, effectively reduced risks from allconstituents to below a 10 -5 cancer risk or HQof 1 for both landfills and surfaceimpoundments at the 90th and 50thpercentiles.For the groundwater-to-drinking-waterpathway, arrival times of the peakconcentrations at a receptor well are muchlonger for landfills (hundreds or thousands ofyears) than for surface impoundments (mostless than 100 years).For humans exposed via the groundwaterto-surface-water(fish consumption) pathway,unlined and clay-lined surface impoundmentsposed risks above the HQ criterion and anexcess cancer risk of 1 in 100,000 at the 90thpercentile (see Table ES-5). For CCWmanaged alone in surface impoundments,these exceedences came from selenium (HQsof 3 and 2 for unlined and clay-lined units,respectively), while for CCW comanaged withcoal refuse, these exceedences came fromarsenic (3 in 100,000 and 2 in 100,000 excesscancer risks for unlined and clay-lined units,respectively). All 50th percentile surfaceimpoundment risks are below an HQ of 1 andan excess cancer risk of 1 in 100,000. Noconstituents pose risks above these levels forlandfills (including FBC landfills) at the 90thor 50th percentile.Waste type has a much larger effect whenmanaged in surface impoundments than whenmanaged in landfills. In the case of surfaceimpoundments, some constituents presentedhigher risks from CCW managed alone(boron, molybdenum, nitrate, and selenium).However, others presented higher risks whenCCW is comanaged with coal refuse (arsenic,cadmium, cobalt, and lead).The higher risks for surface impoundmentsthan landfills are likely due to higher wasteleachate concentrations and the higherhydraulic head from the impounded liquidwaste. This is consistent with damage casesreporting wet handling as a factor that canincrease risks from CCW management.April 2010–Draft EPA document.ES-5