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Institute of Water Security and Science


Impaired drainage from active and abandoned mines degrades the water quality of receiving streams and aquifers. Coal mine drainage (CMD) has been studied for decades in Appalachia, but unknowns and uncertainties are still present, including the influence of mine hydrogeology on the outflow chemistry of above-drainage mines. To evaluate the influence of recharge type on above-drainage mine dissolved inorganic carbon chemistry, samples were collected every two weeks at a CMD outflow treatment system in Harrison County, West Virginia. Samples were collected to measure geochemical changes taking place in the mine workings and along the flowpath of the passive treatment system. Samples were divided into two groups based on the dominant type of recharge entering the mine during sample collection. Calculated PCO2 along the treatment system flowpath approximated a degassing trend during periods of direct recharge. During diffuse recharge periods, dissolution of carbonate minerals in the first 10 meters of the flowpath was evident prior to degassing of DIC as CO2. Throughout the study period, 89% of DIC in the system was degassed to the atmosphere as CO2 before leaving the treatment system. This study demonstrates how varied recharge mechanisms can influence the chemistry of CMD outflows, with implications in system design, interpretations of routine chemical data, and extrapolation of CO2 efflux from CMD outflows for large-scale carbon balance studies.