172-8 CO2 Releases from Abandoned Coal Mines in Pennsylvania and West Virginia

Session: Urban Geochemistry

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Abstract:

The presence of gaseous CO₂ in coal mines has long been known from the standpoint of mine safety, and many have measured elevated CO₂ levels emitting from the air-filled shafts of abandoned mines. However, elevated concentrations of CO₂ also persist dissolved in water discharging from abandoned coal mines where sulfuric acid associated with mine waters interacts with carbonate rocks in the associated strata. This can result in elevated concentrations of CO₂ which degas to the atmosphere when the mine water discharges at the land surface. In this study we report over 200 measurements of CO₂ from ~50 unique locations in Pennsylvania and West Virginia. The CO₂ concentrations ranged from 0.2 to 13 mM (8 - 570 mg/L CO₂) with a median concentration of 4.5 mM (198 mg/L CO₂). These concentrations are up to 1300 times greater than CO₂ that would be expected due to equilibrium with atmospheric CO₂ concentrations. For comparison, CO₂ measured in 19 karst discharges, where carbonic acid is predominately responsible for weathering the carbonate rocks, had a median of <1 mM.  Thermal-mineral springs had a maximum CO₂ concentration comparable to the mines (11 mM) but a lower median concentration (2.1 mM). Longitudinal data, collected downstream of the discharges at numerous mine sites, demonstrate that the CO₂ concentration decreases rapidly as the mine water flows away from the point of discharge.

At the Phillips Mine near Uniontown, PA, there are two discharges from the same mine: one discharge taps a vadose portion of the mine while a second discharge rises under pressure from the flooded mine. The shallower discharge has lower CO₂ concentrations and is more variable over time. In the Irwin Syncline, located southeast of Pittsburgh, the mine water evolves along its flow path from an acidic, oxidized water in the recharge area to a basic, reducing water downgradient. Over that distance, the CO₂ decreases as DIC increases and pH rises. Previous studies have suggested that cumulative flux of CO₂ from coal mines may be significant; the current data illustrate the range in regional concentrations along with the importance of understanding changes spatially, with hydrologic conditions, and through time.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-10087

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