U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of
the Technical Meeting Charleston South Carolina March 8-12, 1999--Volume 3
of 3--Subsurface Contamination From Point Sources, Water-Resources
Investigations Report 99-4018C
Transport of Methyl Tert-Butyl Ether (MTBE) and Hydrocarbons to
Ground Water from Gasoline Spills in the Unsaturated Zone
By Matthew A. Lahvis and Arthur L. Baehr
ABSTRACT
At point-source gasoline-release sites, methyl tert-butyl either
(MTBE), a fuel oxygenate, is commonly found in ground water at
concentrations that exceed those of benzene, toluene,
ethylbenzene, and xylenes (BTEX). A mathematical model is
developed to explain such occurrences. Type curves are developed
to predict benzene and MTBE transport across the water table and
to evaluate the relative importance of the advection diffusion and
biodegradation pathways. In general, the mass flux of benzene is several orders of magnitude less
than that of MTBE, if biodegradation of MTBE is assumed to be
negligible. Consequently, ground-water plumes of MTBE could
potentially extend several orders of magnitude farther
downgradient than BTEX plumes at a gasoline-spill site. Depth to
the water table has the greatest effect on the selective removal
of hydrocarbons in the unsaturated zone.
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