Skip Navigation Links Home / Leaking Underground Storage Tanks / MTBE


CLICK HERE to go to a full, illustrated report on Electrical Resistance Heating (ERH) Technology Coupled with Air Sparging and Soil Vapor Extraction for Remediation of MTBE and BTEX in Soils and Groundwater in Ronan Montana.


Most gasoline used in Montana, except that used in Missoula County, contains methyl tertiary butyl ether, "MTBE," an additive used to raise the octane rating of gasoline. With the phase-out of lead in the 1970s, oil companies had to find a replacement octane enhancer that also met the air quality requirements of the federal Clean Air Act and its amendments. Most oil companies chose to use MTBE. MTBE is not made in Montana. Montana refineries either inject MTBE directly into the fuel prior to transportation via truck or pipeline or add the compound at refinery terminals located throughout the state. Fuel made in Montana refineries that use ethanol rather than MTBE as an octane enhancer can be contaminated with MTBE in the transportation and distribution systems. MTBE-blended gasoline is also trucked into the state from other states. Due to its use as an octane enhancer, MTBE concentrations are typically highest in super-unleaded gasoline (unless ethanol is used).

EPA Drinking Water Health Advisory

MTBE in drinking water is a problem because it tastes and smells bad at low concentrations, making the water undrinkable. MTBE may cause cancer in humans, and serious allergic reactions have been documented. If MTBE encounters groundwater, it will dissolve and spread more rapidly than other components of gasoline. MTBE does not easily degrade, and may remain in groundwater for a long period of time.

Although there is no established drinking-water regulation for MTBE, the U. S. Environmental Protection Agency (EPA) has issued a health advisory ( recommending that MTBE levels in drinking water be limited to 20 to 40 micrograms per liter (µg/L). This level corresponds to taste and odor thresholds. EPA health advisories are used only for information and guidance on contaminants for which there are no national regulations, and are not legally enforceable. This MTBE advisory concentration is intended to provide a large margin of safety for noncancer effects and is in the range of margins typically provided for potential carcinogenic effects. EPA is continuing to evaluate information, and is conducting research to determine the impacts to human health from exposure to MTBE in drinking water at levels equal to and below this advisory level.

Late in 1999, EPA recommended municipalities begin testing for and reporting the presence of MTBE even though it is only proposed for listing as a regulated drinking water contaminant. Contamination of drinking water at levels that make water unpotable have resulted from petroleum storage tank and pipeline releases. The Montana Department of Environmental Quality (DEQ) has documented the presence of MTBE in soil and groundwater samples at many sites of petroleum releases that are being actively cleaned up. Monitoring for MTBE is only required at petroleum release sites. In these locations, DEQ is working closely with public drinking water suppliers to test their supplies for MTBE.

Montana's MTBE Groundwater Cleanup Standard

In November 1998, DEQ adopted a standard requiring that MTBE found in groundwater at petroleum spill sites be reduced to no more than 30 micrograms per liter (ug/l) in order to be considered "cleaned up." Although municipalities are not required by federal or state law to test for and report the presence of MTBE in drinking water, sites of accidental petroleum releases must meet the 30 ug/l state standard. This standard also applies to any groundwater used for drinking water purposes. Parties responsible for petroleum releases must take action to prevent MTBE from impacting drinking water supplies. If concentrations at or above 30 ug/l are detected in nearby drinking water supplies, parties responsible for a release of gasoline which contains MTBE will be required to reduce MTBE concentrations to comply with the standard.

Winter Oxyfuels Program

Amendments to the Clean Air Act established a Winter Oxyfuels Program to reduce unhealthy levels of carbon monoxide pollution in areas with significant wintertime air pollution. Oil companies used either MTBE or ethanol blends to meet these EPA requirements. Missoula County is the only area in the state designated as part of the Winter Oxyfuels Program where an oxygenate is required to reduce carbon monoxide pollution from vehicles.

Under this program the Missoula area is required to use a minimum of 2.7 weight percent oxygen (weight oxygen/weight fuel) in gasoline. To achieve this concentration of oxygen, gasoline is blended with 15 percent (by volume) of MTBE, or a blend of 7.7 percent (by volume) ethanol. Missoula implemented the program using MTBE as its primary oxygenate in 1992. The use of MTBE created a large number of complaints by consumers who experienced health problems related to vapor inhalation of MTBE fuels during the winter of 1992-1993. As a result, the Missoula City-County Health Department worked with marketers to acquire ethanol blends of gasoline to meet the oxygen requirement, and stopped using MTBE in fuels distributed in the area.

EPA Reformulated Gasoline Program

EPA also recently started a reformulated gasoline (RFG) program in much of the country to reduce pollution and ozone from vehicles. Reformulated gasoline contains 2 percent (by weight) oxygen content. This requirement will be met by using oxygenates like those used in the Winter Oxyfuels Program. Oil companies may choose to use MTBE. RFG is not required for use in Montana, but is produced in Montana refineries for use in other states.

Fuel Labeling

People have asked how to tell if MTBE is in their fuel. Montana law administered by the Montana Department of Commerce requires that petroleum products retailed in the state containing 1.5 weight percent or higher concentrations of oxygen must be labeled with the type of oxygenate used. Based on this law, petroleum pumps at service stations must be labeled to show the type of oxygen containing compound dispensed in gasoline. The labels typically read "gasoline contains ethanol" or "gasoline contains methyl tertiary butyl ether (MTBE) or other ethers."

Related Information and Internet Websites

A great deal of information about MTBE is available on the internet. EPA's Office of Underground Storage Tanks ( is a good place to look for additional information. Another EPA website contains numerous links to other sources of MTBE information ( For more information about MTBE in Montana contact Jeff Kuhn at the DEQ Petroleum Release Section (406) 444-6567, or Howard Haines in the DEQ Pollution Prevention Bureau (406) 444-6478.