Origin of carbon dioxide gas contamination in groundwater and building spaces in western Pennsylvania – implications for subsurface carbon sequestration

Christopher D. Laughrey, Bureau of Topographic and Geologic Survey, 500 Waterfront Drive, Pittsburgh, Pennsylvania 15222; Fred J. Baldassare Pennsylvania Department, of Environmental Protection, Environmental Cleanup, 400 Waterfront Drive, Pittsburgh, Pennsylvania 15222; and William C. Ehler and Steve Rathburn, Office of Surface Mining, U.S. Department of the Interior, Three Parkway Center, Pittsburgh, PA 15220

Subsurface CO2 sequestration involves three potential carbon storage reservoirs: 1) petroleum reservoirs; 2) coal seams; and 3) deep brine aquifers. Assuring the environmental safety of CO2 storage in the subsurface is critical. Sequestered CO2 might migrate and contaminate drinking water or accumulate as free gas in buildings.

Investigations of CO2 migration from subsurface sources in western Pennsylvania are relevant to research with CO2 sequestration. There are several possible sources of CO2 in the petroleum and coal fields there and it is crucial to recognize these before storing CO2 underground. Carbon isotope geochemistry, in combination with site-specific geologic studies, can help specify source. These techniques are useful for establishing baseline data for CO2 sequestration and for discriminating this gas from other sources of CO2.

A case study from Lawrence County, Pennsylvania is instructive. Here, CO2 from a subsurface source contaminated ground water and building space at several private residences. Over 25% CO2 was measured in the air above the water table in monitoring wells, and ambient CO2 in the homes exceeded 14% during low barometric pressure episodes. Potential sources of the CO2 included organic matter and carbonate in spoil from a strip mining operation, an abandoned deep coal mine, reactions of AMD from the mine with carbonate in bedrock, the spoil and/or local glacial till, active deep gas wells, and an abandoned oil field. The d13CO2 of the contaminant ranged from -7.01 to +2.86 permil indicating a carbonate source for the gases. The site-specific investigation suggested that AMD reacting with carbonate in the glacial till was the source of the gas.

Poster paper presented at North-Central Section (36th) and Southeastern Section (51st), GSA Joint Annual Meeting (April 3–5, 2002)