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GeoInsighter Fall / Winter 2000 Newsletter
Volume 5 Number 3

The Rise and Fall of MTBE

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In a classic case of the law of unintended consequences, methyl-tertiary-butyl ether (MTBE) was initially introduced and supported as an environmental savior and, today, MTBE is regarded as an environmental villain. MTBE is added to unleaded gasoline as an octane booster, and use of MTBE expanded enormously throughout the 1980s and 1990s, as leaded gasoline was phased out and the USEPA required improvements to air quality. However, in March 2000, the USEPA proposed to sharply reduce or eliminate MTBE entirely due to risks to ground water and drinking water sources.

MTBE was first synthesized in the early 1960s; however, commercial production of MTBE did not begin until 1979. Due to its high-octane value, MTBE was initially used to replace tetra ethyl lead used in leaded gasoline. Testing data indicated that MTBE was compatible with all types of automotive and tank liner materials, did not have a phase separation problem with water (a problem with ethanol), and reduced carbon monoxide and hydrocarbon emissions. Based upon these characteristics, MTBE use became very attractive to gasoline distillers, and by 1984, MTBE had become one of the top 50 chemicals produced in the United States (47th by weight in 1984). MTBE use continued to expand in the 1980s as additional production plants were brought on-line and leaded gasoline was phased out.

Congress enacted the Clean Air Act of 1990, which required that areas of the United States with the worst ozone smog problems use reformulated gasoline (RFG) with an increased oxygen content to improve air quality. In addition, several areas of the country voluntarily chose to use RFG to increase air quality. MTBE, and to a lesser extent, ethanol, are added to gasoline to produce RFG. Approximately 87 percent of the RFG in the United States is produced with MTBE, with ethanol used primarily in the midwestern portion of the country, such as Chicago and Milwaukee. Since the 1990 Clean Air Act, MTBE use has more than tripled to the present volume of approximately 4.5 billion gallons of MTBE used each year in gasoline.

Compared to other gasoline components, such as benzene or toluene, MTBE is very soluble in water (4.3 percent) and does not sorb or "cling" well to soil. At gasoline releases, MTBE dissolves quickly into ground water and migrates further and faster than other gasoline components. Due to its high solubility, MTBE is very difficult to treat in ground water once dissolved. MTBE does not adsorb well onto activated carbon or charcoal filters, and other technologies, such as air stripping or ultraviolet treatment, generally require redundant backup systems to ensure treatment. New synthetic resin and polymer filters have been developed specifically to treat MTBE, but these filters are expensive and this technology is still under development. MTBE also does not naturally biodegrade well, although new research is focusing to develop strains of MTBE-consuming bacteria. Due to these limitations, it is important that remediation systems for MTBE releases be carefully designed.

As a result of MTBE's high solubility and fast migration, MTBE has been detected in water supplies across the country, including 137 water supply wells in New Hampshire and 23 public water supply wells in Massachusetts. Maine researchers found approximately 15 percent of wells in the state impacted by MTBE. Based upon impacts to wells and threats to water supplies across the country, USEPA Administrator Carol Browner announced on March 20, 2000 that the USEPA recommended congressional action to develop legislation limiting MTBE use. Specifically, the USEPA recommended to 1) amend the Clean Air Act to provide the authority to significantly reduce or eliminate the use of MTBE, 2) ensure that air quality gains are not diminished as MTBE is phased out, and 3) replace the existing oxygen requirement contained in the Clean Air Act with a renewable fuel standard for all gasoline. In addition to the legislation, the USEPA is proposing to regulate MTBE use under the Toxic Substances Control Act, which gives the USEPA authority to ban, phase out, limit, or control the manufacture of any chemical substance deemed to pose an unacceptable risk to the public or the environment. 

Ironically, the USEPA and environmental groups such as the Sierra Club, which support reducing or banning MTBE to protect water supplies today, strongly supported MTBE in the early 1990s to reduce air pollution.

Kevin D. Trainer
kdtrainer@geoinc.com

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