January 20, 2022
Final Reports
San Mateo Courts - Civil Grand Jury 1998 Final Report: Use of Methyl Tertiary-Butyl Ether (MTBE) as a Fuel Additive
Background | Findings | Recommendation
The Environmental Protection Agency (EPA) was formed by the Federal government in the 1970’s. It was formed to clean up air, water, and soil pollution.

Air pollution was a common problem in areas of concentrated populations. To solve this problem, Federal laws and regulations were adopted which regulated the emissions allowable from internal combustion engines. To achieve these standards, catalytic exhaust systems along with more efficient combustion in the engines were required. These standards made for a sizeable decrease in the emissions. Despite implementing these measures, smog remained a problem in certain geographical areas.

In the 1920’s, ethanol and lead were used to prevent premature combustion commonly referred to as “knocking.” To combat this problem, lead quickly became the additive of choice until the 1970’s. The discovery of the adverse health effects of lead required its withdrawal.

In 1979, methyl tertiary-butyl ether (MTBE) was first employed to boost octane rating. MTBE is a member of a class of chemical compounds, ether, whose unique properties are enhanced solubility in water and chemical attraction to water molecules. As a consequence, MTBE does not readily attach to soil and is extremely resistant to natural degradation. From the 1970’s through the 1980’s, gasoline was blended using 1% to 5 % MTBE. In 1990, amendments to the Federal Clean Air Act were adopted that included programs to oxygenate and reformulate gasoline which mandated the inclusion of MTBE. Ethanol was an alternative in a 10% blend, a practice encouraged by a Federal tax credit of 5.4 cents per gallon of ethanol. At its peak, ethanol accounted for only 5% to 6% of the additive market, or 70 million gallons per year in California. MTBE became the oxygenate of choice because of its ability to increase octane rating, its low cost of production, its ability to readily mix with other gasoline components, its dilution effect on undesirable components (aromatics, sulfur, olefin, and benzene) and its evaporative qualities. Oxygenated winter gasoline was introduced in California in November 1992 and currently has from 11% to 15% of MTBE by volume. This represents a substantial increase since its inception.

In 1996, legislation was passed that gave California an exemption from EPA rules if its own criteria were more stringent. This legislation created the California Air Resources Board.

The states of Alaska, New Jersey, and Texas have banned the sale of gasoline containing MTBE.


In 1997, a Federal court in North Carolina awarded $9.5 million and an undisclosed amount of punitive damages to 178 residents of two mobile home parks whose drinking water had been contaminated with MTBE. The presence of MTBE has caused the closure of two well fields that supply 80% of the drinking water for Santa Monica, California. In South Lake Tahoe, California, 35% of the city’s groundwater wells have been contaminated with MTBE. The presence of MTBE has been detected at a depth of 100 feet in Lake Tahoe. The town of Glenville, California, has been devastated from the result of water contamination by MTBE and has shut down its only gas station, its single restaurant, and its only grocery store. Property values have been devalued as a consequence. The annual parade has been cancelled. Fearing the specter of a collapse of the wine industry, the Sonoma County Board of Supervisors has adopted a resolution banning the sale of gasoline that includes MTBE as the oxygenate.

MTBE contamination is easily detected from its odor and turpentine like taste. The threshold at which MTBE can be smelled in water has been reported in three different studies at 15 parts per billion (ppb), 45 ppb and 95 ppb. The same studies found the taste threshold was 39 ppb, 40 ppb and 134 ppb.

A process to biodegrade MTBE has been allegedly discovered by a U.C. professor which may expedite its removal from water supplies.

The California Air Resources Board announced a temporary suspension of the requirement that MTBE be included in gasoline for the period October 1, 1998 to January 31, 1999. As a consequence, regular grade gasoline with no MTBE is currently for sale in parts of the Bay Area. The Governor has announced a program to gradually eliminate the inclusion of MTBE over a six-year period.

Recommendation 31: The San Mateo County Board of Supervisors should adopt by January 1, 1999, a resolution to eliminate the sale of any gasoline in the County of San Mateo that includes Methyl Tertiary-Butyl Ether as the oxygenate.


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