Human and Ecological Risk Assessment - Earthjustice

Executive SummaryHuman and Ecological Risk Assessment of Coal Combustion Wastes• CCW comanaged with coal refuse insurface impoundments• FBC waste managed in landfills.This risk assessment was designed andimplemented to identify and quantify humanhealth and ecological risks that may resultfrom groundwater contamination from currentmanagement practices for high-volumeCCWs. The risk assessment usesmathematical models to represent either alandfill or a surface impoundment, and torepresent the movement of chemicalconstituents from the CCW placed into alandfill or surface impoundment through theenvironment, up to an exposure point wherethe chemical constituent comes into contactwith a person (such as in a glass of drinkingwater from a well) or an aquatic organism(such as a fish swimming in surface water thathas become contaminated by groundwater thatdischarges into the stream near a CCWlandfill). In this analysis, EPA evaluatedhuman health exposures that occur by thegroundwater-to-drinking-water pathway,human health exposures that occur by fishconsumption, ecological exposures of aquaticorganisms in direct contact with contaminatedsurface water or sediment, and ecologicalexposures of organisms that eat contaminatedfood items from those contaminated nearbysurface water bodies.Because the infiltration from a landfill orsurface impoundment can significantlyinfluence how much, and how quickly,leachate flows out of a waste managementunit, the models also account for three types ofliner scenarios: unlined, clay-lined, andcomposite-lined. An unlined wastemanagement unit has native soils as thebottom and sides; a clay-lined unit has acertain amount of clay present to slow theflow of leachate; and a composite-lined unit isconstructed from various layers, includinghuman-made materials, which are assumed toretard the leachate flow to a significantlygreater extent than a clay liner.The risk assessment provides a distributionof estimated risks for each of the fivescenarios and three liner types. EPA modeledCCW waste management units that werelocated across the United States, in locationsthat represent a subset of the coal-fired powerplants that were in use in the mid-1990s. Themodels used to represent the movement ofchemical constituents from a landfill orsurface impoundment through theenvironment rely on data such as weatherpatterns, soil types, and subsurface geology,which influence the speed and direction inwhich the chemical constituents move. Thus,the environmental setting, or geographiclocation, of a landfill or surface impoundmentcan influence the resulting estimated risk. Byconducting the analysis at a national scale,EPA estimated risks at locations across theUnited States.Risk Assessment MethodologyTo estimate the risks posed by the onsitemanagement of CCW, the risk assessmentdetermined the release of CCW constituentsfrom landfills and surface impoundments,estimated the concentrations of theseconstituents in environmental media, andestimated the risks that these concentrationspose to human and ecological receptors. Toevaluate the significance of these risks, theywere compared with a risk range or singlecriterion as follows:• For constituents that cause cancer(carcinogens), the typical cancer riskevaluated was a range from 1 excesslifetime cancer case per 1,000,000 exposedindividuals (i.e., 10 -6 excess cancer risk) to1 case per 10,000 exposed individuals(i.e., 10 -4 excess lifetime cancer risk). 44 This is the typical cancer risk range used by theOffice of Solid Waste and Emergency Response -(10 -6 to 10 -4 ).April 2010–Draft EPA document.ES-2