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Fate of MTBE Relative to Benzene in a Gasoline‐Contaminated Aquifer (1993–98)
Author(s) -
Landmeyer James E.,
Chapelle Francis H.,
Bradley Paul M.,
Pankow James F.,
Church Clinton D.,
Tratnyek Paul G.
Publication year - 1998
Publication title -
groundwater monitoring and remediation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.677
H-Index - 47
eISSN - 1745-6592
pISSN - 1069-3629
DOI - 10.1111/j.1745-6592.1998.tb00168.x
Subject(s) - gasoline , microcosm , environmental chemistry , biodegradation , aquifer , benzene , chemistry , contamination , groundwater , dilution , environmental engineering , environmental science , geology , ecology , organic chemistry , geotechnical engineering , biology , physics , thermodynamics
Methyl tert ‐butyl ether (MTBE) and benzene have been measured since 1993 in a shallow, sandy aquifer contaminated by a mid‐1980s release of gasoline containing fuel oxygenates. In wells downgradient of the release area, MTBK was detected before benzene, reflecting a chromatographic‐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 release area, and also up to 10 feet (3 m) below the water table surface in nested wells located farther from the release area. This distribution of higher concentrations at depth is caused by recharge events that deflect originally horizontal ground water flowlines. In the laboratory, microcosms containing aquifer material incubated with uniformly labeled 14 C‐MTBE under aerobic and anaerobic. Fe(III)‐reducing conditions indicated a low but measurable biodegradation potential (<3% 14 C‐MTBW as 14 CO 2 ) after a seven‐month incubation period, Tert ‐butyl alcohol (TBA), a proposed microbial‐MTBE transformation intermediate, was detected in MTBE‐contaminated wells, but TBA was also measured in unsaturated release area sediments. This suggests that TBA may have been present in the original fuel spilled and does not necessarily reflect microbial degradation of MTBE. Combined, these data suggest that milligram per liter to microgram per liter decreases in MTBE concentrations 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 gasoline release site.