FUGITIVE OR STRAY GASES—SUMMARY OF A WORKSHOP ON ASSESSMENT STRATEGIES AND CASE STUDIES

During November 4-6, 2009, a technical workshop was held in Pittsburgh, Pa., to discuss tools and strategies for investigating fugitive or stray gases in groundwater and buildings. Stray gases can originate from oil and gas wells, surface and deep mines, gas-storage reservoirs, as well as buried organic debris and landfills, then migrate into aquifers and built infrastructure such as water wells and buildings. The workshop planners (authors of this abstract) and other scientists and specialists presented investigative techniques and the results of case studies that focused on the origins, migration, and accumulation of stray gases. The focus was on the source identification and mitigation of fugitive methane and carbon dioxide associated with resource extraction. Studies of volcanic or magmatic origins of carbon dioxide and a case study of carbon monoxide poisoning associated with coal mining also were presented. Gas composition including carbon and hydrogen isotopic chemistry, combined with geologic and site characteristics used to define plausible sources, were discussed as primary tools for assessing the origin of fugitive gas. For example, methane associated with thermogenic natural gas typically was enriched in both ¹³C relative to ¹²C and ²H relative to ¹H and percent modern carbon was negligible as indicated by ¹⁴C analyses. In contrast, methane associated with microbial natural gas was enriched in the light isotopes. Case studies from across the U.S. showed that tools and strategies used in one area are applicable elsewhere. The web site http://pa.water.usgs.gov/stray_gas/ serves as a clearinghouse for presentations from the workshop. This presentation summarizes the major themes from the workshop.