Human and Ecological Risk Assessment - Earthjustice

Executive SummaryHuman and Ecological Risk Assessment of Coal Combustion Wastescaptures the variability in both wastemanagement practices and environmentalsettings (e.g., hydrogeology, climate,hydrology). This probabilistic approach wasimplemented through the following steps:1. Characterize the CCW constituents andwaste chemistry, along with the WMUs inwhich each waste stream may be managed(i.e., the size and linear status of CCWlandfills and surface impoundments).2. Characterize the environmental settingsfor the sites where CCW landfills andsurface impoundments are located (i.e.,locations of coal-fired power plants).3. Identify how contaminants are releasedfrom a WMU through leaching andtransported to human and ecologicalreceptors by groundwater and surfacewater.4. Predict the fate, transport, andconcentration of constituents ingroundwater and surface water once theyare released to groundwater from theWMUs and travel to receptors at each site.5. Quantify the potential exposure of humanand ecological receptors to thecontaminant in the environment.6. Estimate the potential risk to each receptorfrom the exposure and characterize thisrisk in terms of exposure pathways andhealth effects.Based on this approach, EPAcharacterized the potential risks associatedwith the waste disposal scenarios andexposure pathways, including the uncertaintiesassociated with the results.Results and CharacterizationThe CCW risk assessment presentedresults at a typical exposure (50th percentile)as well as a high-end exposure (90thpercentile). CCW risk assessment results atthe 90th percentile suggest that managingCCW in unlined or clay-lined WMUs result inrisks greater than the risk criteria of an HQgreater than 1 for noncancer effects to bothhuman and ecological receptors (for humansdrinking groundwater, 90th percentile HQs upto 3 for antimony, 7 for boron, 9 for lead, 8 formolybdenum, 20 for nitrate, and 4 forthallium; for ecological receptors, 90thpercentile HQs up to 2,000 for boron, 300 forlead, 100 for arsenic, 30 for cadmium, and 12for selenium). With respect to arsenic inCCW, the 90th percentile results suggest thatmanaging CCW in unlined or clay-linedWMUs results in human excess cancer riskswithin or above a range of 1 in 1 million to 1in 10,000 (i.e., ranging from 6 in 100,000 to 1in 50 excess cancer risk). Clay-lined unitstended to have lower risks than unlined units,but still had 90th percentile arsenic III excesscancer risks ranging from 6 in 100,000 to 7 in1,000.However, it was the composite-linedunits that effectively reduced risks from allpathways and constituents, below1 in 100,000excess cancer risk or an HQ of one.The tables that follow present selected riskresults only for chemicals that exceed anexcess cancer risk of 1 in 100,000 (arseniconly) or an HQ of 1.As shown in Table ES-1, arsenic was theconstituent with the highest risk for landfills.Clay-lined landfills presented 90th percentilearsenic III cancer risks as high as 1 in 5,000and thallium HQs as high as 2. When landfillswere unlined, they additionally presentedarsenic III cancer risks as high as 1 in 2,000and a maximum thallium HQ of 3. In additionto arsenic and thallium, clay-lined FBClandfills also presented 90th percentile risksabove an HQ of 1 for antimony. However,unlined FBC landfills differed in that theyonly exceeded a 1 in 100,000 excess cancerrisk for arsenic and did not exceed an HQ of 1for any of the noncarcinogens modeled. 6 Atthe 50th percentile (see Table ES-2) arsenic6 Unlined FBC units showed less risk as modeled.April 2010–Draft EPA document.ES-4