EPA/600/R07/100
Monitored Natural Attenuation of
Tertiary Butyl Alcohol (TBA)
in Ground Water at Gasoline Spill Sites (PDF)
(55 pp, 2.4MB, About PDF)
Abstract
The state agencies that implement the Underground Storage Tank program rely heavily on Monitored
Natural Attenuation (MNA) to clean up contaminants such as benzene and methyl tertiary butyl ether
(MTBE) at gasoline spill sites. This is possible because the contaminants are biologically degraded in
anaerobic ground water at the site. Tertiary Butyl Alcohol (TBA) is generally considered to be more
readily degradable than MTBE, and there is a danger that the state agencies will consider contamination
from TBA a good prospect for MNA. A close examination of the available information indicates that a
default presumption that TBA is readily degraded in anaerobic ground water is not justified. Anaerobic
biodegradation of TBA will require a supply of an electron acceptor such as sulfate or biologically available
Iron(III) or Manganese(IV). The available survey data indicate that ground water in the source area of
the majority of known plumes is devoid of sulfate. Although a procedure to estimate biologically available
Iron(III) is commercially available, it is not routinely applied to gasoline spill sites. There is no established
procedure to estimate biologically available Manganese(IV). To date, the performance of available approaches
to document anaerobic biodegradation of TBA at specific field sites has been disappointing.
These include field monitoring to show a statistically significant attenuation in concentration with distance
along the flow path, microcosm studies conducted with sediment from the site, and analysis of stable
isotope ratios in TBA in the plume.
Contact
John T. Wilson , Wilson.JohnT@epa.gov
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