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MONITORING TO ASSOCIATE A PLUME OF MTBE IN GROUNDWATER WITH A VAPOR RELEASE
Citation:
WILSON, J. T., J. HWANG, M. MILLER, A. WARDLE, AND R. CHAPMAN. MONITORING TO ASSOCIATE A PLUME OF MTBE IN GROUNDWATER WITH A VAPOR RELEASE. Presented at The API Soil and Groundwater Technical Task Force, Houston, TX, February 06, 2007.
Impact/Purpose:
To inform the public.
Description:
There is a class of MTBE plumes in ground water that have little of the BTEX compounds. It has been proposed that these MTBE plumes are caused by release of gasoline vapors from underground storage tanks. However, a mechanism to carry MTBE vapors into ground water has not been established. In the winter season, the gasoline in the tank is cold with respect to the tank fill material. We postulate that water vapor in the fill condenses on the side of the tank, that the MTBE vapors dissolve in the condensed water, and the water and dissolved MTBE drains into the ground water. To test the hypothesis, we installed gelled heavy water under the covers of the fuel drop, the dry break, the sump for the automatic tank guage, and the pump sump at three underground storage tanks at a site in Virginia. Over time the gelled heavy water evaporated. In the spring we determined the concentration of heavy water in the ground water in the fill of the tank pit. Approximately half of the heavy water that evaporated found its way into the water in the tank pit. We also installed passive diffusion samplers to measure the concentrations of heavy water vapor and MTBE vapor in the air under the covers. From the ratio of the concentration of vapors we calculated the concentration of MTBE that would drain with the condensed water. The calculated concentrations explained the measured concentration of MTBE in the ground water in the tank pit.