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

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 CO (sub 2) (>25%) and low volumes of O (sub 2) (<10%) have caused several private homes to become uninhabitable. The CO (sub 2) 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 (super 12) C, whereas CO (sub 2) derived from carbonate materials is enriched in (super 13) C. The activity of (super 14) C can support the identification of geologically recent microbial gas generation. Groundwater chemistry can support interpretations of an inorganic CO (sub 2) source based on stable-isotope data. Case studies from western Pennsylvania demonstrate the utility of isotopic analyses in identifying specific sources of stray CO (sub 2) in buildings.