Underground Storage Tanks

1. When was gasoline that contains MTBE first stored in USTs?

   Answer: Gasoline containing MTBE has been stored in underground storage tanks (USTs) since the 1970s. MTBE was first used as an octane-enhancing replacement for lead, primarily in mid- and high-grade gasoline at concentrations as high as 7% (by volume). Now, however, MTBE is mainly used as a fuel oxygenate at higher concentrations (11% to 15% by volume) as part of the Federal RFG and Wintertime Oxyfuel programs. he Oxyfuel and RFG Programs were initiated by the U.S. EPA in 1992 and 1995, respectively, to meet requirements of the 1990 Clean Air Act Amendments.

2. What is the difference between Oxyfuel and RFG?

   Answer: The Oxyfuel Program requires the use of gasoline with 2.7-percent oxygen (by weight) in areas with high levels of carbon monoxide during the fall and winter. When MTBE is used to meet this requirement, it is used at a concentration of 15 percent (by volume) in gasoline. Because ethanol has a higher oxygen content, it can meet this requirement with a concentration of 7.3 percent (by volume). The RFG Program requires 2.0-percent oxygen (by weight) throughout the year in the most polluted metropolitan areas. MTBE meets this level with an 11-percent (by volume) concentration, and ethanol can be used with a 5.4-percent (by volume) concentration.

3. Where are USTs which store gasoline containing MTBE located?

   Answer: MTBE is a common and widely used additive in gasoline. MTBE has been used in conventional gasoline to boost the octane since the 1970s. Given MTBE's widespread use as a gasoline additive and the large volumes of gasoline that are stored, transported, and used in all areas of the country, MTBE could have been (or is now) in virtually any UST anywhere in the U.S., not just areas required to use RFG or Oxyfuel.

   Studies by the U.S. Geological Survey have found that water supplies are more likely to be contaminated with MTBE in areas where RFG or Oxyfuel is required than in other areas. The Clean Air Act (CAA) mandates that reformulated gasoline (RFG) be sold in the 10 largest metropolitan areas with the most severe summertime ozone levels. The CAA also allows any other area classified as a marginal, moderate, or serious ozone nonattainment area to opt into the RFG program. In addition to the RFG program, certain areas in the nation that have not attained the National Ambient Air Quality Standards (NAAQS) for carbon monoxide are required under the CAA to implement the Wintertime Oxyfuel program. EPA's Office of Transportation and Air Quality (OTAQ) maintains a list of reformulated gasoline areas which are required to use oxygenated fuels at least part of the year.

4. Other than regulated USTs, what are some other sources of MTBE releases?

   Answer: As a large industrialized nation, the United States produces, distributes, and consumes extensive quantities of gasoline, and much of that gasoline contains MTBE. After production, gasoline may travel through thousands of miles of pipelines, or be transported by truck, to any of roughly 10,000 terminals and bulk stations. From there it may be distributed to one of 180,000 retail outlets and fleet storage facilities, or to any of hundreds of thousands of above ground or underground tanks at farms, industrial facilities, businesses, and homes. Finally, gasoline is removed from bulk storage into individualized storage units associated with such products as cars, trucks, boats, planes, lawn mowers, brush cutters, and chain saws. Residual gasoline in transport conduits may contaminate different types of fuels (e.g., home heating oil) that is transported through the same conduits at different times. There are opportunities for leaks wherever gasoline (or a product containing gasoline) is stored and there are opportunities for spills whenever fuel is transported or transferred from one container to another. Gasoline is released to the environment every day.

   Although releases (through leaks, spills, and overfills) from underground storage tank systems is a major source of MTBE contamination there are many other potential sources. Other potential sources of MTBE releases include: farm and residential tanks of 1,100 gallons or less, home heating oil tanks, tanks in basements, tanks of 110 gallons or less, emergency spill and overfill tanks, above ground tanks, automobile accidents, tank truck spills, consumer disposal of "old" gasoline, spills during refueling operations, motorized water craft, and storm water runoff.

5. Is funding available for LUST (Leaking Underground Storage Tank) prevention and remediation projects?

   Answer: The Office of Water has produced a Fact Sheet about the Clean Water State Revolving Fund (CWSRF) program (PDF) (2 pp, 36K, About PDF) that addresses this question.

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