Biomedical Engineering Reference
In-Depth Information
rates compared to BTEX biodegradation in MTBE-containing and
oxygenate-free groundwater. Laboratory experiments found no signifi-
cant biodegradation of BTEXin the presence of 7000 ppmofmethanol but
some BTEX biodegradation was noted when the methanol concentration
was only 1000 ppm. It was concluded that the mechanism for greater
BTEX persistence in the presence of methanol is the initial inhibition of
BTEX biodegradation by toxic methanol concentrations followed by
inhibition due to the removal of oxygen by preferred methanol bio-
degradation. Such results are particularly important in assessing the fate of
benzene, a known carcinogen (Dean, 1985) and the most recalcitrant
monoaromatic under anaerobic conditions.
In another laboratory microcosm study, the biodegradation of BTEX
was reportedly impaired at 1.4% (14,000 ppm) methanol and was
completely inhibited at higher methanol levels (Novak et al., 1985).
In conclusion, the biodegradation rate of BTEX compounds in a
gasoline plume that has become commingled with a methanol plume
(Scenario 3) could be significantly retarded in the presence of high
methanol concentrations. This reduction in BTEX biodegradation could
effectively increase the length of BTEX plumes. A complete evaluation
of this effective plume elongation has not been completed for this
evaluation, but is likely to be a function of the distance between the
methanol leaking UST (LUST) and the gasoline LUST, and of the
locations of the two USTs relative to groundwater movement.
2.3.2 Surface Water Release
2.3.2.1 Sources of Methanol in Surface Water
The potential domi-
nant source of methanol in surface water is the direct release of neat
methanol into a surface water body following accidental release or
catastrophic failure during transport, such as is outlined in Scenario 2.
Nonpoint sources of methanol include precipitation from the atmo-
sphere, which is not expected to be important, as noted earlier.
2.3.2.2 Losses of Methanol in Surface Water
The processes that
contribute to methanol losses from surface water bodies include bio-
degradation, abiotic degradation, volatilization, and bioaccumulation.
