Fate of MTBE Relative to Benzene in a Gasoline‐Contaminated Aquifer (1993–98)

Abstract

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 14C‐MTBE under aerobic and anaerobic. Fe(III)‐reducing conditions indicated a low but measurable biodegradation potential (<3%14C‐MTBW as 14CO2) 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.

Biotreatment of groundwater contaminated with MTBE: interaction of common environmental co-contaminants

“…However, this has lead to widespread groundwater contaminations. The relative high water solubility has resulted in frequent occurrences of MTBE and TBA in groundwater and raised public health concerns (Squillace et al 1996;Landmeyer et al 1998;EPA 1999). As a consequence, MTBE is being phased out in the United States.…”

Monitoring Biodegradation of Methyl tert-Butyl Ether (MTBE) Using Compound-Specific Carbon Isotope Analysis

“…For example, the solubility of MTBE from reformulated gasoline (11.1% MTBE by volume) is 4700 mg/L at 20°C, while the solubility of benzene from conventional gasoline is only 18 mg/L (1). Since it only sorbs weakly on solids (Koc ) 11 (2)) and appears difficult to biodegrade (5), it can travel nearly unretarded in groundwater and long plumes of dissolved MTBE are frequently observed (6,7). In several laboratory studies, biodegradation of MTBE by aerobic bacteria has been observed (8)(9)(10)(11), while in others, MTBE was reported to be recalcitrant, in particularly under anaerobic conditions (12)(13)(14)(15).…”

Methyl t -Butyl Ether Mineralization in Surface-Water Sediment Microcosms under Denitrifying Conditions

“…Although the potential for aerobic biodegradation of MTBE to nontoxic products has been demonstrated for a number of groundwater (3,9,18) and surface-water sites (5), the actual contribution of this process to natural attenuation of MTBE is unclear because the onset and subsequent predominance of anoxic conditions are characteristics of hydrocarbon-contaminated waters. Consequently, engineered systems are being developed to support aerobic MTBE biodegradation under otherwise anoxic conditions (18).…”

“…The U.S. Geological Survey national water use summary estimated that 60% of the drinking water consumed in the continental United States comes from surface water (20). Because these systems are not easily shielded from numerous point (5,9) and nonpoint (1, 2, 4, 6, 10, 13, 14, 16) sources of MTBE contamination, identifying natural sinks for MTBE in surface waters is particularly important. Although microorganisms in surfacewater bed sediments can mineralize MTBE to CO 2 under oxic conditions (5), geochemical constraints on oxygen transport (27) may limit the importance of aerobic MTBE mineralization in these systems (5).…”