MTBE And Underground Storage Tanks
The use of methyl tertiary butyl ether (MTBE) in gasoline sold in the U.S. has virtually ceased in recent years. EPA's federal underground storage tank (UST) regulations have contributed greatly to reducing soil and ground water contamination by MTBE and other fuel components from USTs. However, not all UST systems are regulated and not all components of regulated UST systems are regulated. Even with the most ideal regulations, there will continue to be equipment failures and installation mistakes which will result in releases of fuel into the environment. EPA continues to work with states to increase the compliance rate with the spill, overfill, and corrosion protection requirements of the federal UST regulations. EPA is also working with states to improve the compliance rate with the leak detection requirements; we are jointly undertaking a major multi-year effort to increase UST owners' and operators' compliance rates through compliance assistance, UST inspections, and enforcement.
MTBE was found in gasoline (and other petroleum fuels) that was commonly stored in USTs. MTBE was typically added to reformulated gasoline, oxygenated fuel, and premium grades of unleaded gasoline. EPA has not set a national standard for MTBE in drinking water, although some states have set their own limits. In December 1997, EPA issued a Drinking Water Advisory. This advisory established a taste threshold of 40 ppb and an odor threshold of 20 ppb.
Although leaking USTs are the primary source of MTBE contamination, there are many other potential sources as well, such as discharge of unburned fuel from watercraft (especially two-stroke engines); gasoline spills from automobile and tanker truck accidents; gasoline spills and drips when refueling automobiles, lawnmowers, tractors and other machines; plus leaks from pipelines and aboveground storage tanks.
EPA is continuing to study both the potential health effects and the occurrence of MTBE, and MTBE is on a list of contaminants (Contaminant Candidate List) for which EPA is considering setting drinking water standards.