Contaminants of Concern (COC) at Underground Storage Tank (UST) Sites
Though their use is decreasing, fuel oxygenates are used as a fuel additive and octane enhancer in reformulated gasoline, oxygenated fuel, and premium grades of unleaded gasoline. Water-quality criteria for fuel oxygenates to protect aquatic life have not been established. Available data indicates the presence of MTBE in drinking water. However, limited or no data are available for any other fuel oxygenate.
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 for which EPA is considering setting drinking water standards.
Lead scavengers, ethylene dibromide (EDB) and 1,2-dichloroethane (1,2-DCA), also known as ethylene dichloride (EDC), were necessary additives in leaded gasoline to prevent buildup of lead oxide deposits within internal combustion engines. With the phase out of leaded gasoline the conventional wisdom was that lead scavengers and alkyl lead compounds would no longer occur in the environment as the result of leaks from underground storage tank (UST) systems. Data however, indicate that lead scavengers may persist for long periods of time in certain ground water environments and thus may still be present at UST sites that were in operation through the end of the 1980s. Leaded fuel containing lead scavengers is still used for certain off-road applications such as automobile racing and also aviation fuel (Avgas). EPA is currently working with states to determine the scope and magnitude of the occurrence of lead scavengers at leaking UST sites. Below are the following Lead Scavengers Team Publications:
- Lead Scavengers Team Mission Statement
- Phase 1: Lead Scavengers Compendium: Overview of Properties, Occurrence, and Remedial Technologies - May 2006
- Phase 2: Natural Attenuation of the Lead Scavengers 1,2-Dibromoethane (EDB) and 1,2-Dichloroethane (1,2-DCA) at Motor Fuel Release Sites and Implications for Risk Management - August 2008 (PDF)
- Phase 3: Recommendation for States, Tribes, and EPA Regions to Investigate and Clean Up Lead Scavengers When Present at Leaking Underground Storage Tank (LUST) Sites - May 2010 (PDF)
Underground storage tank (UST) systems that store substances identified as being hazardous under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) are subject to the same requirements as petroleum UST systems except that hazardous substance tanks must have secondary containment. Hazardous wastes are already regulated under Subtitle C of the Resource Conservation and Recovery Act (RCRA) and therefore are not covered by the UST regulations.
Currently about 1,200 substances (excluding radionuclides) are identified as hazardous under CERCLA (40 CFR 302, section 302.4).