172 Urban Geochemistry

This session encourages presentations dealing with the geochemistry and biogeochemistry of urban and suburban water, soil and air as well as the impact of urban geochemistry on ecosystem and human health.

Tuesday, 21 October 2025
8:00 AM - 12:00 PM
HBGCC, 302A

CO2 Releases from Abandoned Coal Mines in Pennsylvania and West Virginia

Paper number: 172-9
Program: Technical Sessions
Time: 10:05 AM – 10:20 AM

Authors

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 Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-414181

© Copyright 2025 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.