Methyl Tertiary Butyl Ether
December 9, 1997

Senator Boxer, I appreciate the opportunity to appear before the Senate Committee on Environment and Public Works to testify on the subject of methyl tertiary butyl ether--commonly referred to as MTBE--and water quality. My name is John Zogorski. I'm a hydrologist with the U.S. Geological Survey (USGS). As you may know, the mission of the USGS is to assess the quantity and the quality of the earth resources and to provide information that will assist resource managers and policy makers at the Federal, State, and local levels in making sound decisions. Assessment of water-quality conditions and trends is an important part of this overall mission. I am working on the National Water-Quality Assessment Program--often referred to as NAWQA. More specifically, I am responsible for the aspect of the NAWQA Program that is focused on synthesizing information on the occurrence and distribution of volatile organic compounds (VOCs) in ground water and surface water. MTBE is one of about 60 VOCs that we are assessing. The building blocks for the NAWQA assessment are comprehensive water-quality investigations of more than 50 large river basins and aquifers distributed across the United States (Figure 1). The San Joaquin-Tulare, Sacramento, and Santa Anna River basins in California are 3 of the study units that NAWQA is assessing.

In 1995, the NAWQA Program published a report discussing the occurrence of MTBE in shallow ground water in urban and agricultural areas from the first set of 20 study units. Chloroform and MTBE were the two most frequently detected VOCs in samples from about 200 shallow wells in 8 urban areas and about 500 shallow wells in 20 agricultural areas. MTBE was detected in about 25 percent of the urban wells and about 1 percent of the agricultural wells. Concentrations ranged from the detection level of 0.2 micrograms per liter to as high as 23,000 micrograms per liter. MTBE was most frequently detected in shallow ground water in Denver, Colorado and urban areas in New England. In Denver, about 80 percent of the samples from shallow urban wells had detectable concentrations of MTBE and in New England, about 35 percent of the samples from urban wells had detectable concentrations. Only 3 percent of the wells sampled in urban areas had concentrations of MTBE that exceeded 20 micrograms per liter, which is the estimated lower limit of the U.S. Environmental Protection Agency (USEPA) draft drinking water health advisory level (figure 2.).

I believe my colleagues from the USEPA will more fully discuss what is known about the human and aquatic health effects of MTBE and other fuel oxygenates. The initial sampling did not include information from urban areas in California. An urban ground water study is a component of the Sacramento River basin investigation, however, and our data collection in Sacramento will be completed at the end of this fiscal year.

Last year, at the request of the USEPA and the Office of Science and Technology Policy (OSTP), I co-chaired an interagency panel to summarize what is known and unknown about the water-quality implications associated with the production, distribution, storage, and use of fuel oxygenates and their movement in the hydrologic cycle (figure 3).





The results of our efforts were published as a chapter in a report entitled "Interagency Assessment of Oxygenated Fuels" prepared by the National Science and Technology Council, Committee on Environment and Natural Resources. The chapter summarizes the scientific literature and data on the sources, concentrations, behavior, and the fate of fuel oxygenates in ground water and surface water. We also discussed the implications for drinking water quality and aquatic life and we identified areas where the data are too limited to make definitive statements about the costs, benefits, and risks of using oxygenated gasoline in place of conventional gasoline. Recommendations for further data-base compilation, monitoring, assessment, research and reporting were made that we believe would reduce uncertainties and allow a more thorough assessment of human exposure, health risks and benefits, and environmental effects.

I'd like to briefly summarize for the Committee the major findings, conclusions and recommendations of this interagency assessment that was completed in late 1996:

MTBE is the most commonly used fuel oxygenate. U.S. production in 1995 was estimated to be about 9 million tons. Essentially all of the MTBE that is produced is used for fuel oxygenation. Ethanol is the second most used oxygenate in gasoline blending. Ethanol production in the U.S. in 1994 was estimated to be about 4.5 million tons or roughly half the production of MTBE. No data are available to estimate the portion of this production used in gasoline.

Like other hydrocarbon components of gasoline, fuel oxygenates are introduced to the environment during all phases of the petroleum fuel cycle: production, distribution, storage, and use. Releases of gasoline containing oxygenates to the subsurface from, for example, underground storage tanks, pipelines, and refueling facilities provide point sources for entry of oxygenates as well as gasoline hydrocarbons into the hydrologic cycle. Urban and industrial runoff and wastewater discharges also represent potential sources of oxygenates to the environment. In a few instances, such as in Santa Monica, California, high concentrations of MTBE have caused the shutdown of a drinking-water production wells and the source of contamination is believed to be leaking underground gasoline storage tanks.

Exhaust emissions from vehicles and evaporation from gasoline stations and vehicles are sources of MTBE and other oxygenates to the atmosphere. Because of their ability to persist in the atmosphere for days to weeks and because they will, in part, "mix" into water, fuel oxygenates are expected to occur in precipitation in direct proportion to their concentration in air. Hence, fuel oxygenates in the atmosphere provide a non-point, low concentration source to the hydrologic cycle. MTBE is much less biodegradable than ethanol or the aromatic hydrocarbon constituents of gasoline and, therefore, it will persist longer in ground water. MTBE also adsorbs only weakly to soil and aquifer materials. Consequently, MTBE will move with the ground-water flow and migrate further from sources of contamination.

MTBE was detected in 7 percent of 592 storm-water samples in 16 cities surveyed by the USGS between 1991-1995. When detected, concentrations ranged from 0.2 to 8.7 micrograms per liter, with a median of 1.5 micrograms per liter. A seasonal pattern of detections was evident, as most of the detectable concentrations occurred during the winter season. MTBE was detected both in cities using MTBE-oxygenated gasoline to abate carbon monoxide non-attainment and in cities using MTBE-oxygenated gasoline for octane enhancement.

At least one detection of MTBE has occurred in ground water in 14 of 33 states surveyed. MTBE was detected in 5 percent of about 1,500 wells sampled, with most detections occurring at low micrograms per liter concentrations in shallow ground water in urban areas.

Limited monitoring by Federal, State, and local agencies and organizations has shown that drinking water supplied from ground water is a potential route of human exposure to MTBE. As of 1997, MTBE has been detected in 51 public drinking water systems based on limited monitoring in 5 states including New Jersy, Iowa, Colorado, Illinois, and Texas. However, when detected, the concentrations of MTBE were, for the most part, below the lower limit of the current USEPA health advisory. This indicates that the consumption of drinking water was not a major route of exposure for these few systems. Because of the very limited data set for fuel oxygenates in drinking water, it is not possible to describe MTBE's occurrence in drinking water nor to characterize human exposure from consumption of contaminated drinking water for the Nation. There is not sufficient data on fuel oxygenates to establish water quality criteria for the protection of aquatic life, however, the petroleum industry is sponsoring research to complete needed studies.

The presence of MTBE and other alkyl ether oxygenates in ground water does not prevent the clean up of gasoline releases: however, the cost of remediation involving MTBE will be higher than for releases of conventional gasoline. Also, the use of natural bioremediation to clean up gasoline releases containing MTBE may be limited because of the difficulty with which MTBE is biodegraded.

The OSTP chapter on fuel oxygenates and water quality includes three broad recommendations.

First, more complete monitoring data and other information is needed to:

A. Identify and characterize major sources of MTBE to the environment;

B. Characterize the relation between use of MTBE (and other alkyl ether oxygenates) in gasoline and water quality; and

C. Enable an exposure assessment for MTBE in drinking water.

Completing the exposure assessment for MTBE in drinking water should be given high priority. Monitoring of MTBE in drinking water for this purpose should initially be targeted to high MTBE use areas, and to those environmental settings that are otherwise thought to be most susceptible to contamination.

Second, additional studies are needed to expand current understanding of the environmental behavior and fate of MTBE and similar oxygenates. For example, these studies are needed to help determine the significance of the urban atmosphere and land surface as non-point sources of contamination to surface and ground water, and to identify environmental settings where MTBE will be of concern.

Finally, studies of the aquatic toxicity of MTBE and similar oxygenates are needed for a broad range of aquatic animals and plants indigenous to surface waters to define the extent of any threat and to form the basis of Federal water-quality criteria, if warranted.

Again, I appreciate the opportunity to testify at this hearing. I'd be happy to try to address any questions of the Committee.