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Environmental Geosciences

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Some applications of isotope geochemistry for determining sources of stray carbon dioxide gas

¹ Pennsylvania Department of Conservation and Natural Resources, Bureau of Topographic and Geologic Survey, 500 Waterfront Drive, Pittsburgh, Pennsylvania 15222; claughrey{at}state.pa.us
² Pennsylvania Department of Environmental Protection, Environmental Cleanup, 400 Waterfront Drive, Pittsburgh, Pennsylvania 15222

Christopher D. Laughrey is a senior geologic scientist with the Pennsylvania Geological Survey, where he has worked since 1980. He worked as a geophysical analyst for the Western Geophysical [Company] in Houston, Texas, before taking his present position in Pittsburgh, Pennsylvania. He also teaches sandstone petrology at the University of Pittsburgh. Laughrey's research interests include isotope and organic geochemistry, carbonate and clastic petrology, and borehole geophysics.Fred Baldassare is a hydrogeologist with the Pennsylvania Department of Environmental Protection. He has 15 years experience investigating incidents of subsurface stray gas migration. Fred currently serves as a project manager providing technical reviews of chemical and hydrological data generated at industrial sites with ground-water contamination. He also serves as an advisor on the regulations and technical guidance for Pennsylvania's Land Recycling Program. Fred's current research interests include natural gas isotope geochemistry and contaminant fate and transport.

High concentrations of stray carbon dioxide in buildings are an emerging environmental hazard in some areas of the Appalachian coalfields. In western Pennsylvania, potentially lethal concentrations of CO₂ (>25%) and low volumes of O₂ (<10%) have caused several private homes to become uninhabitable. The CO₂ is primarily anthropogenic, although the specific source is commonly uncertain. Carbon isotope geochemistry provides the most useful technique for identifying the specific gas source.

Carbon dioxide derived from organic substrates by microbial activity is enriched in ¹²C, whereas CO₂ derived from carbonate materials is enriched in ¹³C. The activity of ¹⁴C can support the identification of geologically recent microbial gas generation. Ground-water chemistry can support interpretations of an inorganic CO₂ source based on stable-isotope data. Case studies from western Pennsylvania demonstrate the utility of isotopic analyses in identifying specific sources of stray CO₂ in buildings.