OLR Research Report

December 11, 2003




By: Paul Frisman, Associate Analyst

You asked for information about contamination of groundwater by MTBE (methyl tertiary butyl ether).

MTBE, a volatile, organic chemical, is a gasoline additive that promotes more complete burning of gasoline, thereby reducing carbon monoxide and ozone levels. It is added to gasoline in certain areas of the country that do not meet national air quality standards (including Connecticut) to comply with federal Clean Air Act requirements that these areas reduce air pollution.

However, while MTBE succeeded in reducing air pollution, leaks of the chemical from underground storage tanks have polluted nearby water sources in a number of states. Because the U. S. Environmental Protection Agency (EPA) considers MTBE a possible human carcinogen, a number of states, including Connecticut are banning the use of MTBE. For more information on Connecticut’s ban, which is scheduled to take effect on January 1, 2004, please see OLR Reports 2003-R-0643, 2003-R-0693, and 2003-R-0858.


According to a May 2002 report by the U. S. General Accounting Office (GAO), a majority of states have reported finding MTBE at contaminated underground storage tank sites. GAO says that while the full extent of MTBE contamination is unknown, most states have reported finding it in groundwater, and some states have detected it in drinking water. According to the report, half the states reported finding MTBE even at underground gasoline storage tanks for which there was no documented gasoline leak. About half the states also reported finding MTBE that they could not attribute to a leaking underground tank.

Some states also found that MTBE had reached their drinking water supplies. The report noted that this problem may be more widespread than reported, because only 24 states routinely analyze drinking water sources for MTBE. According to GAO, California, Kansas and Maine have had some of the most extensive MTBE problems. Santa Monica, Calif. had to close seven wells, supplying half the city’s water, because of MTBE pollution. (EPA has not regulated MTBE, but has advised people not to drink water with MTBE concentrations greater than 20 to 40 parts per billion).

The GAO report notes that this extent of MTBE contamination occurred even though only certain communities in about one-third of the states use gasoline with MTBE as required under the Clean Air Act. GAO speculates that this may be because MTBE was used in the past as an octane enhancer, and because it is carried through the same fuel pipes and by the same trucks that deliver gasoline throughout the country. MTBE travels faster and farther than other gasoline contaminants, and GAO reports that, as a result, finding MTBE at a leaking tank can increase the cost and time of a site cleanup. Several states have reported their cleanup costs doubled because of MTBE. We have attached a copy of the GAO report, which can also be obtained on-line at http: //www. gao. gov/new. items/d02753t. pdf.

We also have attached a summary of MTBE groundwater contamination compiled by the Environmental Working Group (EWG), a Washington, D. C. -based not-for-profit environmental research organization. EWG reports that 28 states have detected MTBE in drinking water supplies. The organization, which says it obtained the data under state and federal Freedom of Information laws, reports that a total of 1,513 drinking water systems, serving a population estimated to range from 15 million to 41 million customers, were affected. (However, MTBE contamination may affect only a small number of a water system’s customers). States with the largest number of affected water systems were: Arkansas (129), California (127), Maryland (119), Massachusetts (221), New Hampshire (280), New Jersey (138) and New York (170). The report, dated October 2003, is attached, and can be found on-line at http: //www. ewg. org/issues/mtbe/20031001/statelist. php.

We are also including a link to the September 1999 report of the Blue Ribbon Panel on Oxygenates in Gasoline, which goes into great detail on the issues presented by the use of MTBE. The report can be found on-line at Blue Ribbon Panel. More information on MTBE in general can be found on the EPA web site.

PF: ro