Role of back diffusion and biodegradation reactions in sustaining an MTBE/TBA plume in alluvial media

Journal of Contaminant Hydrology
By: , and 



A methyl tert-butyl ether (MTBE) / tert-butyl alcohol (TBA) plume originating from a gasoline spill in late 1994 at Vandenberg Air Force Base (VAFB) persisted for over 15 years within 200 feet of the original spill source. The plume persisted until 2010 despite excavation of the tanks and piping within months after the spill and excavations of additional contaminated sediments from the source area in 2007 and 2008. The probable history of MTBE concentrations along the plume centerline at its source was estimated using a wide variety of available information, including published details about the original spill, excavations and monitoring by VAFB consultants, and our own research data. Two-dimensional reactive transport simulations of MTBE along the plume centerline were conducted for a 20-year period following the spill. These analyses suggest that MTBE diffused from the thin anaerobic aquifer into the adjacent anaerobic silts and transformed to TBA in both aquifer and silt layers. The model reproduces the observation that after 2004 TBA was the dominant solute, diffusing back out of the silts into the aquifer and sustaining plume concentrations much longer than would have been the case in the absence of such diffusive exchange. Simulations also suggest that aerobic degradation of MTBE or TBA at the water table in the overlying silt layer significantly affected concentrations of MTBE and TBA by limiting the chemical mass available for back diffusion to the aquifer.

Study Area

Publication type Article
Publication Subtype Journal Article
Title Role of back diffusion and biodegradation reactions in sustaining an MTBE/TBA plume in alluvial media
Series title Journal of Contaminant Hydrology
DOI 10.1016/j.jconhyd.2011.08.006
Volume 126
Issue 3-4
Year Published 2011
Language English
Publisher Elsevier
Contributing office(s) Branch of Regional Research-Western Region, Toxic Substances Hydrology Program
Description 13 p.
First page 235
Last page 247
Country United States
State California
Other Geospatial Vandenberg Air Force Base
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