Biomedical Engineering Reference
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mixtures such as M85. Results show that M85 released into the
subsurface may produce high concentrations of aqueous methanol as
well as elevated aqueous BTEX concentrations near the front of the
plume. However, the BTEX distribution in the plume would change as a
function of the aqueous/gasoline phase volume ratios (Poulsen et al.,
1992; Chen et al., 1997; Beck, 1991). The American Petroleum Institute
(API) published a study that evaluated the effect of methanol on the
cosolubility of BTEX compounds for M85 (Barker et al., 1991). API
concluded that for aqueous methanol concentrations below 8.5% (v/v)
(i.e., about a 10-fold dilution factor), BTEX solubility was not
increased. As the concentration of methanol increased from 8% to
25%, the BTEX solubility increased linearly with the methanol con-
centration. Above 25% (v/v) concentration of methanol, the BTEX
solubility increased exponentially with the methanol concentration,
specifically, to 933 ppm at an equilibrium methanol concentration of
44%. In conclusion, the magnitude of BTEX cosolubility is controlled
by the concentration of the methanol plume at the point of
BTEX/methanol plume interaction, which is a function of the dilution
factor (Barker et al., 1991).
Cosolvency experimentation with M85 was also conducted at the
Canadian Forces Base in Borden, Ontario. Similar to previous studies,
the Borden study concluded that for methanol concentrations below
0.7% (i.e., below 7000 ppm), there was no distinguishable change in the
mobility or solubility of the BTEX components. However, this study
concluded that enhanced mobility would likely occur for methanol
concentrations > 25% (i.e., > 250,000 ppm) (Barker et al., 1990;
Hubbard et al., 1994). While these concentrations are unlikely in
most of a plume area, they can be anticipated in the source area of
an M100 or M85 plume with a low dilution factor.
2.3 FATE AND TRANSPORT OF METHANOL
IN THE ENVIRONMENT
The chemical and physical properties of methanol are described in
Sections 2.1 and 2.2 and summarized in Table 2.3. The following three
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