Disposal of Fly Ash and Fly Ash Alkali FGD Waste in a Western Decoaled Strip Mine

摘要

The potential impacts of fly ash and fly ash-generated FGD waste on groundwater quality by disposal in various surface mine settings is being evaluated by an ongoing study at the Center Mine near Center, North Dakota. Of concern is the generation and potential impact on groundwater of highly mineralized leachate characterized by very high concentrations of sodium and sulfate. Also of concern is the potential for generation of leachate characterized by elevated concentrations of certain toxic trace elements, particularly arsenic, selenium and molybdenum. The research involves detailed field studies and computational geochemical studies. The field study is evaluating two hydrogeologically distinctive types of disposal settings in the Center Mine: the pit bottom and the vee-notch between spoil ridges. This study has demonstrated that water in contact with both the fly ash and fly ash FGD waste is characterized by very high TDS concentrations. Predominate major species in solution are sodium, magnesium, calcium and sulfate. Sulfate concentrations in waste-effected groundwater are sufficiently high so that the water would be unfit to drink. Data from this project indicate that neither the fly ash nor the fly ash FGD waste from the Milton R. Young Plant constitute a hazardous waste as defined by RCRA regulations. Disposal in a pit-bottom position increases the potential for contact between the wastes and laterally migrating water in the base of the spoils and results in relatively slow, but continuous, dissolution of the waste material. Disposal in pit-bottom sites which contain standing water, due to groundwater inflow, will result in initial rapid dissolution, followed by relatively slow but continuous dissolution of the wastes. Vee-notch disposal sites are typically above the post-closure water table. The effect of evapotranspiration in semi-arid settings will be to minimize infiltration into vee-notch sites, thereby minimizing the potential for leachate generation. (ERA citation 07:059136)