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Monitoring Production of Methane from Spills of Gasoline at UST Release Sites.
Citation:
JEWELL, K. P., J. T. WILSON, AND J. Skender. Monitoring Production of Methane from Spills of Gasoline at UST Release Sites. Presented at The 22nd National Tanks Conference, Boston, MA, September 20 - 22, 2010.
Impact/Purpose:
The long term goal is to develop a robust and affordable sampling protocol that can be used by contractors or consultants to evaluate methane accumulation in soil gas at the same time that they sample water in wells for contamination.
Description:
ORD-362 (Rev 06/10/05) (Webforms v2.4) Abstract: Anaerobic biodegradation of the BTEX compounds can produce substantial concentrations of methane in ground water at gasoline spill sites. This methane can escape the ground water, move through the unsaturated zone and potentially produce explosive concentrations of methane in confined spaces or facilitate the intrusion of BTEX vapors in buildings. Biofuels such as ethanol, butanol, or biodiesel are readily degraded in ground water to produce copious quantities of methane. As biofuels become more prevalent in the market place, we can expect more methane production at fuel spill sites. Methane is rarely measured at fuel spill sites, and most commonly the measurements are made on samples of ground water. Many ground water monitoring wells are intentionally screened across the water table. This was done to allow them to sample free product. However, if there is sufficient screen interval above the water table, a conventional monitoring well can be used to sample soil gas. We developed a sampling approach that allows us to pump soil gas from the riser of monitoring wells, and then use field equipment to monitor the concentrations of methane, oxygen and carbon dioxide in the soil gas in real time. We are in the process of comparing the readings from different field meters to results from laboratory analyses to determine which meters are reliable and accurate. The long term goal is to develop a robust and affordable sampling protocol that can be used by contractors or consultants to evaluate methane accumulation in soil gas at the same time that they sample water in wells for contamination. We visited twelve gasoline service stations in Oklahoma that have had recent confirmed releases from the UST. We sampled soil gas from monitoring wells in the UST tank pit, or in the aquifer immediately adjacent to the tank pit. When the concentration of methane in gas is 14% or higher, it can mix with air to form an explosive mixture. At four of the thirteen sites, the soil gas from at least one monitoring well had methane concentrations above 14%. We had the methane from wells at four sites analyzed for the concentration of 14C, which would come from biofuels. At one of the sites, the concentrations of 14C in the methane suggest that a substantial portion of the methane came from a biofuel.