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Underground Storage Tanks (USTs)

Emerging Fuels and Underground Storage Tanks (USTs)

About Emerging Fuels

EPA provides this information about emerging fuels and the responsibility of UST owners and operators to help prevent leaks or releases of regulated substances possibly caused by emerging fuels. Emerging fuels may not always be compatible with all UST systems, and storing emerging fuels can sometimes increase corrosion in UST systems.

EPA uses the term emerging fuels to broadly describe new or different fuel formulations that enter the market for various reasons, such as policy changes, retail opportunities, or technical requirements. Emerging fuels include biofuels, like ethanol, biodiesel, and butanol; new formulations of petroleum-based fuels, like ultra-low sulfur gasoline and ultra-low sulfur diesel; renewable diesel; combinations of multiple types of fuels, and others.

Emerging Fuels in the United States Today

Ultra-low sulfur gasoline and ultra-low sulfur diesel are now the standard gasoline and diesel fuels nationwide.

Many retail facilities, such as gas stations, and non-retail fueling facilities also store biofuels, 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 letter representing the first initial of the biofuel—E for ethanol; B for biodiesel— followed 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 E10 and is ubiquitous around the country. Some fueling stations sell E15 or E85; although the number is small as a percentage of total fueling stations now, the number is growing quickly. 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.

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Existing and Proposed Compatibility Requirements for Storing Biofuels

EPA’s underground storage tank regulation requires that tank systems are compatible with the substances stored in them. 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. If any UST system 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.

2015 Compatibility Requirements

EPA required compatibility beginning with the 1988 UST regulation. EPA revised the underground storage tank regulation in 2015. Part of that revision reinforced and clarified the UST compatibility requirement 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.

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.

EPA's Proposed Rulemaking: E15 Fuel Dispenser Labeling and Compatibility with Underground Storage Tanks

EPA’s proposed rulemaking presented revisions to the 2015 UST regulation. Specifically, EPA proposed to grant certain allowances for owners and operators in demonstrating compatibility, making it easier for them to meet the current requirements. EPA also proposed a new requirement that in the future when UST systems are installed, or UST equipment and components are replaced, they must be constructed with equipment and components that are compatible with ethanol blends up to 100 percent; this requirement would be effective within one year of the effective date of the final rule.

EPA accepted comments on the proposed rulemaking through April 19, 2021.

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

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Emerging Fuels Regulatory Requirements Table

The table below provides information about requirements for demonstrating compatibility of 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 U.S.
Ultra-low sulfur gasoline (ULSG) ULSG, E10, gasoline Yes, usually ethanol at 10%. No. This fuel is common across the U.S.
E15  E15 Yes, 15% ethanol. Currently, yes. Must demonstrate compatibility of the UST system. See proposed rulemaking web page for more information.
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% biodiesel. Yes. Must demonstrate compatibility of the UST system.
B99 B99 Yes, 99% biodiesel. Yes. Must demonstrate compatibility of the UST system.
Isobutanol Isobutanol, biobutanol Yes No. 
Renewable diesel Renewable diesel No No. Made from biocomponents, but chemically similar to diesel. However, if renewable diesel is blended with more than 20% biodiesel, you must meet these additional requirements.
Renewable gasoline Green gasoline No No. Made from biocomponents, but chemically similar to gasoline.

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

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 were reported more frequently beginning 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 by itself 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’s July 2016 research found that 83 percent—or 35 USTs—storing diesel fuel exhibited moderate or severe corrosion of metal components inside the tank system.

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. EPA will continue to coordinate with industry to understand the corrosion issue and work to identify solutions.

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. 

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Resources for Determining Equipment Compatibility and Meeting Federal Requirements for Storing Biofuels

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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.
  • Flex Check by American Coalition for Ethanol
    This website, developed by the American Coalition for Ethanol, provides a way to see how E15 compatible your facility is. Flex Check contains information on equipment compatibility with ethanol, sorted by component. Listings include component manufacturer, model number, component category, and some manufacturer statements of compatibility.
  • Retailing Biofuels: A Guide to Reading Applicable Federal Regulations
    This report, developed by the Fuels Institute, compiles all of the federal regulations and third-party standards applicable to storing and selling biofuels, including those mandated by the U.S. Environmental Protection Agency, the Federal Trade Commission, and Occupational Safety and Health Administration. The report helps retailers and other interested stakeholders keep up with new liquid fuel offerings by serving as the single resource needed to navigate applicable federal regulations, liability concerns, penalties for non-compliance and compliance options.
  • 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) (40 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 percent ethanol), E85 (marketing term for ethanol-gasoline blends containing 51 to 83 percent ethanol, depending on geography and season), and other ethanol blends

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Compatibility Research

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Additional Reading about Emerging Fuels

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  • Biodiesel Facts
    This fact sheet, developed by Iowa Renewable Fuel Association, presents a list of biodiesel facts.
  • Biofuels: Release Prevention, Environmental Behavior, and Remediation (PDF) (157 pp, 3.6 MB)
    The Interstate Technology & Regulatory Council Biofuels Team developed this 2011 guide.  It explains how the different properties of biofuels and biofuel-blends cause them to exhibit different environmental behavior in comparison to conventional fuels.
  • Fuel Ethanol: Industry Guidelines, Specifications, and Procedures (PDF)(58 pp, 1.9 MB)
    This 2018 guide, developed by Renewable Fuels Association, presents comprehensive information on ethanol standards, equipment compatibility and conversion, handling and safety, quality assurance, and tax incentives. (See page 31 for E85.)
  • Converting Existing Underground Storage Tank (UST) Systems to Ethanol Compatible (PDF) (5 pp, 134 K)
    Prepared by Iowa Department of Natural Resources, this fact sheet provides guidance on equipment compatibility and conversion of USTs for storing ethanol.
  • E15 Retailer Handbook (PDF) (44 pp, 2.1 MB)
    This guide, developed by the Renewable Fuels Association, is designed to provide fuel retailers with guidance in order to legally store and sell E15 ethanol blends.
  • Keeping Water Out of Your Storage System (PDF) (13 pp, 192 K)
    Prepared by Steel Tank Institute, this resource discusses ways in which water can enter an underground storage tank system, economic impacts of water intrusion, and methods for the protection of UST systems against water intrusion. Microbial contamination and other issues related to storing ethanol and biodiesel blends are discussed.

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