Je. Landmeyer et al., FATE OF MTBE RELATIVE TO BENZENE IN A GASOLINE-CONTAMINATED AQUIFER (1993-98), Ground water monitoring & remediation, 18(4), 1998, pp. 93-102
Methyl tert-butyl ether (MTBE) and benzene have been measured since 19
93 in a shallow, sandy aquifer contaminated by a mid-1980s release of
gasoline containing fuel oxygenates. In wells downgradient of the rele
ase area, MTBE was detected before benzene, reflecting a chromatograph
ic-like separation of these compounds in the direction of ground water
flow. Higher concentrations of MTBE and benzene were measured in the
deeper sampling ports of multilevel sampling wells located near the re
lease area, and also up to 10 feet (3 m) below the water table surface
in nested wells located farther from the release area. This distribut
ion of higher concentrations at depth is caused by recharge events tha
t deflect originally horizontal ground water flowlines. In the laborat
ory, microcosms containing aquifer material incubated with uniformly l
abeled C-14-MTBE under aerobic and anaerobic, Fe(III)-reducing conditi
ons indicated a low but measurable biodegradation potential(<3% C-14-M
TBE as (CO2)-C-14) after a seven-month incubation period. Tert-butyl a
lcohol (TBA), a proposed microbial-MTBE transformation intermediate, w
as detected in MTBE-contaminated wells, but TEA was also measured in u
nsaturated release area sediments. This suggests that TEA may have bee
n present in the original fuel spilled and does not necessarily reflec
t microbial degradation of MTBE. Combined, these data suggest that mil
ligram per liter to microgram per liter decreases in MTBE concentratio
ns relative to benzene are caused by the natural attenuation processes
of dilution and dispersion with less-contaminated ground water in the
direction of flow rather than biodegradation at this point source gas
oline release site.