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Underground Storage Tanks (USTs)

Emerging Fuels and Underground Storage Tanks (USTs)


Hundreds of thousands of USTs nationwide store regulated substances, primarily automotive fuels made from petroleum or a mixture of petroleum and other regulated substances. EPA’s regulations require that USTs are constructed, maintained, and operated in a manner which ensures petroleum and other regulated substances are stored safely.

EPA refers to new or different fuel formulations as emerging fuels. Those fuels enter the market for various reasons, such as policy changes or technical requirements. Emerging fuels include biofuels, like ethanol; new formulations of petroleum based fuels, like ultra-low sulfur gasoline; combinations of multiple types of fuels, like ultra-low sulfur diesel; or others. Emerging fuels may not always be compatible with all UST systems, and storing emerging fuels can sometimes increase corrosion in UST systems.

This website helps UST owners and operators understand emerging fuels and the responsibility of preventing leaks or releases of regulated substances possibly caused by emerging fuels.

Biofuels Are Emerging Fuels

The use of biofuels in the United States is growing, partly because federal mandates required incremental increases in biofuel blending into the fuel supply beginning in the mid–2000s. Biofuels include all substances listed in the 2015 UST regulation that require additional actions by owners and operators to ensure compatibility:  gasoline blends containing greater than 10 percent ethanol; diesel blends containing greater than 20 percent biodiesel; or any other substance identified by an implementing agency now or in the future.

Two biofuels, primarily ethanol and biodiesel, have significantly increased their volume share of the total national vehicle fuel market over the last decade. Isobutanol is projected to become more prevalent in the fuels market in the future. Ensuring compatibility of UST systems with these fuels — knowing the materials that make up the UST system will maintain their respective chemical and physical properties when in contact with the substance they are storing — is essential. Storing a fuel that is not compatible with an UST system may jeopardize the integrity of the UST system and cause a release to the environment. All UST systems must be compatible with the regulated substances they store. The 2015 UST regulation requires additional notification, demonstration, and record keeping actions of owners wishing to store biofuels.

In addition to biofuels, a small percentage of emerging fuels are also made from renewable feedstocks, but are not regulated by EPA as biofuels according to the federal UST regulation. Those emerging fuels — such as green or renewable gasoline, or green or renewable diesel — are chemically very similar to petroleum based fuels and meet the same industry specification as their petroleum based counterpart. 

The table below provides information about common emerging fuels.

Emerging Fuel Common Name Does it contain biofuel? Must UST owner meet additional compatibility requirements because the fuel contains more than 10% ethanol or more than 20% biodiesel, or another substance identified by the implementing agency?
Ultra-low sulfur diesel (ULSD) Diesel Possibly biodiesel up to 5%. No. This fuel is common across the US.
Ultra-low sulfur gasoline (ULSG) ULSG, E10, gasoline Yes, usually ethanol at 10%. No. This fuel is common across the US.
E15   E15 Yes, 15% ethanol. Yes. Must demonstrate compatibility of the UST system.
E85 E85 Yes, 51-83% ethanol. Yes. Must demonstrate compatibility of the UST system.
B20 B20 Yes, 6-20% biodiesel. No. Up to B20 is commonly stored by fleet operators.
B50 B50 Yes, 50 percent biodiesel. Yes. Must demonstrate compatibility of the UST system.
B99 B99 Yes, 99 percent biodiesel. Yes. Must demonstrate compatibility of the UST system.
Isobutanol Isobutanol, biobutanol Yes Yes. Must demonstrate compatibility of the UST system.
Renewable diesel Renewable diesel No No. Made from biocomponents, but chemically similar to diesel.
Renewable gasoline Green gasoline No No. Made from biocomponents, but chemically similar to gasoline.

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Compatibility Requirements for Storing Biofuels

EPA’s underground storage tank regulation requires that tank systems are compatible with the substances — usually petroleum or a mixture of petroleum and other regulated substances, such as biofuels — stored in them. EPA required compatibility beginning with the 1988 UST regulation. In an UST system, the regulated substances stored must not interact with the materials comprising the system in any way that would cause the system’s performance to change. In the 2015 federal UST regulation, EPA clarified those compatibility requirements, and owners storing or intending to store certain fuels are required to meet three additional requirements. Prior to storing biofuel blends, UST owners and operators should be aware of the federal UST regulation and potential issues to ensure fuels are stored safely in USTs.

Each biofuel fuel blend has unique chemical characteristics different from purely petroleum derived gasoline or diesel fuel. Those chemical characteristics may affect how the fuel interacts with UST systems. USTs contain many components made of different materials. If any of these materials are incompatible with the regulated substance stored and even temporarily lose their manufactured properties such as shape or flexibility, the UST system may fail to contain the regulated substance. This could result in a release to the environment and possibly a failure to detect the release. Incompatibility between fuels stored and UST system materials can result in equipment or components such as tanks, piping, gaskets, or seals becoming brittle, elongated, thinner, or swollen when compared with their condition when first installed.

Many retail facilities, such as gas stations, and non-retail fueling facilities already store ethanol and biodiesel in their UST systems. Ethanol and biodiesel are commonly blended with gasoline and diesel, respectively. Petroleum-biofuel blends are referred to by a number that usually refers to the approximate biofuel percentage of the overall blend:  E10, E15, or B20. Gasoline blended with 10 percent ethanol is called E10, and is ubiquitous around the country. Biodiesel may be blended in diesel up to 5 percent without any special labeling, and it is also increasingly found in concentrations such as B10 or B20. These fuels are also available in some retail markets and non-retail uses as even higher blends, such as E85 or B50.

2015 Compatibility Requirements

EPA revised the underground storage tank regulations in 2015. Part of that revision reinforced and clarified the UST compatibility requirement by requiring that owners and operators must use an UST system made of or lined with materials that are compatible with the substance stored in the UST system.

Compatibility is the ability of two or more substances (for example, the tank or piping material and petroleum) to maintain their respective physical and chemical properties when in contact with one another.  The UST tank and piping material and substances stored must remain compatible for the design life of the tank system and under conditions likely to be encountered in the UST.

The compatibility requirement has been in effect since 1988. EPA incorporated elements of our 2011 guidance into the 2015 federal UST regulation. The 2015 regulation clarified the compatibility requirement in the 1988 regulation. Since October 2015, owners storing or intending to store certain regulated fuels or substances are required to meet three additional requirements:  notify their implementing agency; demonstrate compatibility; and keep records.

  • Notify their implementing agency at least 30 days prior to storing one of the following:
    • Regulated substances containing greater than 10 percent ethanol;
    • Regulated substances containing greater than 20 percent biodiesel; or
    • Any other regulated substance identified by the implementing agency.

This notice gives the implementing agency an opportunity to inquire about the compatibility of the UST system before an owner and operator begins storing the regulated substance.

  • In addition, owners and operators storing one of these regulated substances must demonstrate compatibility by meeting one of the following:
    • Demonstrate compatibility of the UST system — including the tank, piping, containment sumps, pumping equipment, release detection equipment, spill equipment, and overfill equipment — by using one of these options:
      • Certification or listing of UST system equipment or components by a nationally recognized, independent testing laboratory for use with the regulated substance stored
      • Equipment or component manufacturer approval, which must be in writing, indicate an affirmative statement of compatibility, specify the range of biofuel blends the equipment or component is compatible with, and be from the equipment or component manufacturer
    • Use another option determined by the implementing agency to be no less protective of human health and the environment than the two options above
  • Keep records that document compliance with the compatibility requirement if they store regulated substances containing greater than 10 percent ethanol, greater than 20 percent biodiesel, or any other regulated substance identified by the implementing agency. Owners and operators must keep these records for as long as the UST system is used to store these regulated substances.

For more information, contact Ryan Haerer at or 202-564-0762.

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Corrosion Issues in Storing Emerging Fuels, including Diesel and Gasoline Blends

In 1984, Congress directed EPA to create a federal program to regulate USTs storing petroleum and other hazardous chemicals, including preventing external corrosion of metal components in contact with soil. The corrosion requirement was part of the 1988 UST regulation, and EPA allowed owners 10 years to comply with the requirement.

Over the past couple decades, many fuel formulations have entered the market and corrosion on the insides of tanks and other UST components not required by law to have corrosion protection has become extremely common. Below we provide information on more recent corrosion risks to UST systems, offer explanations, and discuss potential prevention and responses actions.

Corrosion has been commonly reported in USTs storing diesel fuel and gasoline-ethanol blended fuels. Anecdotes suggest when storing diesel fuel, corrosion generally appears on metal components inside USTs. When storing ethanol blended fuels, corrosion generally appears in sumps. Instances of this corrosion began appearing about a decade ago.

The federal UST regulation requires UST owners have corrosion protection for their UST systems’ metal components in contact with the ground. But corrosion protection is not required for metal components inside USTs or in sumps. Corrosion in USTs storing emerging fuels does not violate federal UST requirements.

However, UST owners and operators must ensure corrosion does not affect the functionality of their equipment. If UST equipment does not function as intended, it may violate the federal UST regulation or lead to releases into the environment. Owners and operators should contact their state UST implementing agencies because they may have requirements that differ from the federal regulation. 

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Corrosion of Internal Components in USTs Storing Diesel Fuel

EPA conducted research on 42 actively operating underground tanks storing diesel fuel at facilities all across the United States and found that 83 percent (or 35 USTs) exhibited moderate or severe corrosion of metal components inside the tank system. EPA’s July 2016 report discusses that research. Industry provided invaluable assistance to EPA in research design, operational coordination, and report reviews over the course of the research effort. EPA will continue to coordinate with industry to understand the corrosion issue and identify solutions.

EPA cannot project the actual percentage of USTs storing diesel that are affected by corrosion nationwide. However, this could be a widespread and potentially significant problem for owners of underground tanks storing diesel fuel.

The corrosion may cause metal components inside both steel and fiberglass UST systems to corrode. This can possibly shorten the lifespan or affect the serviceability of components, including limiting the movement of floats on automatic tank gauging systems, operability of mechanical devices designed to prevent the chance of overfilling the tank, or ability of shear valves to shut off flow of product in the event of a release. Corrosion may cause dispenser filters to clog and be replaced more frequently and could potentially limit the proper functionality of equipment designed to test for leaks in fuel product lines. EPA recommends UST owners check for corrosion in their tank systems storing diesel fuel, and if they find corrosion, repair or replace equipment as necessary to ensure proper functionality. 

Other Resources

These industry documents contain practices, technologies, or treatments to minimize the risk of release of diesel fuel from underground tanks.

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Corrosion in Submersible Turbine Pump Spaces in USTs Storing Ethanol Blended Fuels

External corrosion is commonly found coating metal components in the submersible turbine pump spaces, also called sumps, of USTs storing gasoline blended with ethanol. This type of corrosion can be caused by bacteria through a process called microbiologically-influenced corrosion and may impact the serviceability or functionality of equipment in the sumps. The information below may be helpful to minimize corrosion in sumps storing ethanol blended fuels.

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Additional Reading and Resources

EPA is providing these resources to help owners and operators learn more about UST system compatibility and emerging fuels. 

On this page: 

You may need a PDF reader to view some of the files on this page. See EPA’s About PDF page to learn more.

EPA Office of Underground Storage Tanks Historical Compatibility Documents

EPA's 2011 guidance, which is superseded, provided UST owners and operators with assistance in complying with the federal compatibility requirement for UST systems storing gasoline containing greater than 10 percent ethanol or diesel containing greater than 20 percent biodiesel. See the updated compatibility requirement in the 2015 federal UST regulation. 

EPA's November 2007 memorandum to regions and states responds to questions from states on the regulatory status of underground storage tanks containing E85, which is a blend of approximately 85 percent ethanol and 15 percent gasoline.

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Resources for Determining Equipment Compatibility

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  • UL Fuel Compatibility Tool
    This tool, developed by UL (formerly Underwriters Laboratories), provides information to help manufacturers and fueling stations meet EPA, state, or other code authorities’ fuel compatibility requirements. UL provides information in order to assist fuel stations and local code authorities. The tool provides access to UL’s Listing Category Control Numbers (CCN’s) and individual UL Listings.
  • UST Component Compatibility Library
    This library, developed by Petroleum Equipment Institute, contains information on equipment compatibility with ethanol and biodiesel-blended fuels. Listings include product specifications and links to manufacturers.
  • Affirmative Statement of Compatibility by Manufacturer
    Prepared by California State Water Resources Control Board, this resource provides links to manufacturer statements supporting compatibility of their products with alternative fuels.
  • Alternative Fuels Storage Information and Links
    Prepared by Steel Tank Institute, this web page provides links to alternative fuels storage resources from federal, state, and nongovernmental agencies.
  • Biodiesel Handling and Use Guide (PDF) (72 pp, 1.7 MB)Developed by the Department of Energy’s National Renewable Energy Laboratory, this document provides basic information on the proper and safe use of biodiesel and biodiesel blends in engines and boilers; it is designed to help fleets, individual users, blenders, distributors, and those involved in related activities understand procedures for handling and using biodiesel fuels.
  • Handbook for Handling, Storing, and Dispensing E85 and Other Ethanol-Gasoline Blends (PDF) (44 pp, 1.0 MB)
    Developed by National Renewable Energy Laboratory, this document provides information on ethanol fuel properties, standards, codes, best practices, and equipment information for those who blend, distribute, store, sell, or use E15 (gasoline blended with 10.5% to 15% ethanol), E85 (marketing term for ethanol-gasoline blends containing 51% to 83% ethanol, depending on geography and season), and other ethanol blends.
  • Materials Compatibility (PDF) (4 pp, 156 K)
    This fact sheet, prepared by National Biodiesel Board, provides guidance on UST system compatibility with biodiesel blends and includes several tables of material compatibility ratings
  • National Ethanol Vehicle Coalition (PDF) (5 pp, 72 K)
    This is a listing of E85-compatible tank equipment and manufacturers, prepared by National Ethanol Vehicle Coalition.

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Compatibility Research

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Additional Reading about Emerging Fuels

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