Water and Pollution Control Department

MtBE and Drinking Water

Below are some of the most frequently asked questions about MtBE and their answers.

Q	What is MtBE?
A	MtBE stands for Methyl tertiary-Butyl Ether. It is a compound that is added to gasoline as an oxygenate. MtBE has been shown to reduce the level of air pollution (such as ozone and carbon monoxide) from automobile emissions. MtBE has replaced the use of lead as an octane enhancer since 1979. The 1990 Clean Air Act requires that gasoline sold in areas where smog levels are at their highest use an oxygenate additive to burn fuel more efficiently. Many gasoline producers add MtBE to gasoline, although other additives (such as ethanol) produce similar improvements in air quality.
Q	How could MtBE get into drinking water?
A	By far, the most common way for MtBE to enter a water supply is from leaking underground storage tanks. Since July 1, 1999, the Iowa Department of Natural Resources (IDNR) has required testing for MtBE in both soil and groundwater around known leaking gasoline tanks. Another source of MtBE water contamination is two-cycle engines, such as the kind used in personal watercraft. These engines can discharge up to 30% of their fuel unburned. If the unburned fuel contains MtBE, contamination is a possibility.
Q	What are the dangers of MtBE?
A	Currently, MtBE is not classified as a human carcinogen nor a reproductive toxin. The US EPA has adopted a preliminary Consumer Advisory Level for MtBE of 20 to 40 parts per billion (ppb) based on taste and odor. Early indications are that managing water supplies to avoid the unpleasant taste and odor effects of MtBE at levels in this range also provides protection against any potential adverse health effects with a very large margin of safety. There are no data on the effects on humans of drinking MtBE-contaminated water, but investigators are suspicious. In laboratory tests on animals, cancer and non-cancer effects occur at high levels of exposure. It is important to know that these tests were conducted by inhalation exposure or by introducing the chemical directly into the stomach. While these results indicate a reason for concern, because the animals were not exposed through drinking water there are significant uncertainties about the risk posed by the low concentrations that might be found in drinking water. Currently, a number of studies are underway by EPA, the Chemical Industry Institute of Toxicology (CIIT) and other organizations. These studies should allow for extrapolation from the inhalation studies to an assessment of risks associated with ingestion of drinking water. In addition, further study of potential health effects of MtBE and other fuel additives are underway by the petroleum industry as required under the Clean Air Act section 211.
Q	How much MtBE is used in Iowa?
A	There is no requirement that Iowa gasoline contain MtBE. In fact, gasoline sold in Iowa may contain no more than 2% MtBE (California blending is 11%). Prior to the new law taking effect, MtBE use in Iowa has occurred, but it was so infrequent that the amount of MtBE sold in Iowa is virtually untrackable. Basically, very little MtBE comes into Iowa.
Q	How is an MtBE spill cleaned up?
A	MtBE is proving to be a difficult contaminant to remove from drinking water sources, due to its affinity for water and its tendency to form large contamination plumes in groundwater. Because MtBE is highly resistant to biodegradation and remediation, gasoline releases with MtBE can be substantially more difficult and costly to remediate than gasoline releases that do not contain MtBE. This is a substantial concern in the United States, where approximately 40-46% of the population uses groundwater as a source of drinking water. Drinking water contaminated by MtBE requires much more aggressive management and treatment than do spills of conventional gasoline. One treatment method being evaluated is a granular activated charcoal (GAC) process. Activated charcoal is routinely used by water plants to remove a wide array of other organic compounds in addition to MtBE. However, the relatively low sorption rates for MtBE means that more GAC must be used than for other contaminants. It is important to remember that adding any additional treatment steps or chemicals to the water treatment process comes with an increased price tag for the consumer.
Q	If MtBE is banned, does that mean more air pollution?
A	EPA is currently reviewing other possible alternatives to MtBE as an oxygenate and octane enhancer. If the use of MtBE is limited or banned and the Clean Air Act oxygenate requirement remains in place, refiners will have to use a substitute oxygenate to meet the reformulated gasoline requirements. Ethanol and other ethers are the most likely oxygenate alternatives. The Department of Agriculture (USDA) has concluded that ethanol can fully meet all oxygenate requirements within 4 years. EPA is proceeding slowly on ethanol, to make sure similar problems are not repeated. Given that ethanol is formed naturally in the body at low levels, exposure to ethanol at low levels is not expected to result in adverse health effects.
Q	Is there any MtBE in Ames Drinking Water?
A	The Water Plant routinely tests for the presence of other gasoline compounds like benzene, toluene, ethylbenzene, and xylene. In the last 10 years, the Ames Water Plant has been unable to detect even trace amounts of these compounds in the groundwater used. Investigations have shown that MtBE may be more mobile in groundwater than other gasoline compounds. Because of this, the Ames Water Plant voluntarily conducted a quarterly monitoring program for MtBE in 2000. Four samples were collected during the year and were tested by the University of Iowa Hygenic Laboratory.
		Each time the results came back as "Not Detected." This means that the instruments used by the laboratory were unable to detect the presence of MtBE in finished drinking water for the City of Ames!
	As a part of the 1996 amendments to the Safe Drinking Water Act, the US EPA has included MtBE on the Screening Survey List 1 of the Unregulated Contaminant Monitoring Regulation. The UCMR is the US EPA's priority list in researching contaminants to determine if a regulated maximum contaminant level should be established. The rule requires most water suppliers across the country, including Ames, to conduct monitoring for MtBE. MtBE is also included in the EPA's Information Collection Rule, a regulation that requires utilities serving more than 100,000 people to test for a wide array of chemicals. US EPA will use the information gathered by these two programs to make future decisions about MtBE.

If you have additional questions about MtBE, or about any aspect of the Ames Water Treatment Plant please contact us.