Aboveground storage tank facilities with less than one million gallons capacity

Tank requirements at facilities storing less than one million gallons of liquid substances are found at Minnesota Rules, Chapter 7151. The following fact sheet provides a summary of the requirements.

Secondary containment

All ASTs must have a secondary containment area surrounding the tank that can hold 100 percent of the contents of the largest tank located within the containment area, plus 10 percent capacity where secondary containment areas are exposed to precipitation. Double-walled tanks satisfy the secondary containment requirement. Acceptable materials for secondary containment depend on the tank’s date of installation, and in some cases, the type of substance stored and hydrogeologic characteristics of the site. For a list of materials that can be used for secondary containment see the fact sheet below.

Aboveground Storage TanksFor clay and earthen containment areas, which must be tested to meet a maximum acceptable permeability rate, see the fact sheet below for more information.


All tanks must be routinely monitored to ensure they are not leaking. If the secondary containment area is made of impermeable materials such as concrete or a synthetic liner, a weekly check of the containment area is required. For any other containment design, a containment area check is required every 72 hours.

All tanks, piping and containment areas must be visually inspected monthly to ensure they are in good condition. There are also monitoring requirements for field-erected tanks and internal tank floor liners that don’t have corrosion protection.

All tanks must have a leak detection system. Acceptable systems include: double-walled construction with interstitial monitoring; elevated tank; an impermeable barrier underneath the tank (concrete pad or synthetic liner); underfloor vapor monitoring; monthly inventory reconciliation; and statistical inventory reconciliation.

Corrosion protection

Corrosion on a tankSteel ASTs greater than 1,100 gallons in capacity must have corrosion protection for the floor of the tank. Corrosion protection options include:

  • elevating tanks above the ground;
  • resting tanks on a continuous concrete slab designed to prevent water accumulation around or under the tank;
  • installing double-walled tanks;
  • cathodically protecting and internally lining tank floors;
  • cathodically protecting and internally inspecting according to American Petroleum Institute (API) Standard 653 protocol; or
  • internally lining and internally inspecting according to API Standard 653 protocol.

All lines or piping connected to the tank must be double-walled, located aboveground or cathodically protected. Also, all underground lines must be tested for leaks annually. More information about corrosion protection is available in the following fact sheet:

Substance transfer

Transfer stationAreas where vehicles (tanker trucks or rail cars) are parked to transfer substances to and from ASTs must be equipped with spill containment to contain a release should it occur. The following fact sheet explains these requirements:

Additional requirements apply to facilities that have one or more ASTs of 2,000 gallons or greater and ASTs used for storage and subsequent resale of petroleum products. (See the PDF icon Petroleum Product Delivery Law fact sheet for further information.)

Overfill protection

Most ASTs owners are required to have procedures or equipment in place to prevent overfills during tank loading operations. With a few exceptions, tanks filled by transfers of more than 55 gallons at one time need to have one of the following systems:

  • high-level alarm
  • automatic shut-off
  • permanently-mounted site gauge during fueling
  • manual sticking of the tank during the product transfer

If double-walled tanks don’t have an additional secondary containment area, only a high-level alarm or automatic shut-off device can be used for overfill protection. Otherwise the overfill protection options are based on the tank installation date and the permeability of the additional secondary containment area. More information can be found in the fact sheet below.

Out-of-service tank systems

If a tank becomes inactive or is to be permanently closed, the tank owner must continue to follow requirements for an active tank, unless the tank owner follows closure procedures including: removing the product, sludge, and residuals; cleaning and degassing the tank; bolting all manways and valves; blinding piping; and labeling the tanks as out of service.

If the tank is later reactivated, the tank must be inspected and leak testing must occur before putting it back into service.

If the AST is dismantled or removed, with some exceptions, the area under the tank must be sampled for contamination. Although there is not a specific guidance document for smaller ASTs, the Petroleum Remediation Program has a number of guidance documents that may be helpful. The fact sheet below explains more:

Temporary tanks

Tanks that store product for longer than 30 days, but less than one year, are considered temporary tanks. These tanks must be labeled, have a facility sign posted, provide secondary containment, and be maintained. The following fact sheet explains more:


Piping that is two inches or greater in diameter that is connected to a regulated tank must have certain design and operational safeguards.

  • To protect against corrosion hazards, piping must be cathodically protected, double-walled, or located entirely above ground.
  • Buried piping must be tested annually for leaks.

Small tanks near surface water

Tanks that are greater than 500 gallons in capacity and less than or equal to 1,100 gallons in capacity and located within 500 feet of a Class 2 Surface Water must meet the labeling and secondary containment requirements only. A Class 2 Surface Water includes any waters used for fishing, fish culture, bathing, or any recreational purpose for which quality is or may be necessary to protect aquatic life, terrestrial life, or the public health, safety and welfare. More information is available in the following fact sheet:

Other regulated substances

Tanks storing products that have the potential to pollute the waters of the state, but are not hazardous materials or petroleum, are considered other regulated substances. Examples of these liquid substances include food-based products and chemicals with lower levels of toxicity such as: corn oil and soy oil, beet molasses, ethyl alcohol, paper pulp, waxes, and calcium chloride.

These tanks have limited regulations because they have limited risk. Other regulated substance ASTs are required to have labeling and secondary containment, and are subject to monitoring during product transfer, weekly monitoring, and monthly monitoring. These ASTs are not required to have leak detection, corrosion protection, substance transfer area safeguards, or overfill protection.

The following fact sheet explains more:

Asphalt cement tanks

Asphalt cement is defined in the AST rules as a mixture of bituminous obtained from native deposits or as a petroleum by-product used for roofing or paving that is solid at 100 degrees Fahrenheit or less.

These tanks have limited regulations because they have limited risk. Asphalt cement ASTs are required to have secondary containment and are subject to monitoring during product transfer, weekly monitoring, and monthly monitoring. These ASTs are not required to have leak detection, corrosion protection, substance transfer area safeguards, or overfill protection. Also, asphalt cement ASTs are not required to test for contamination when tanks are removed if the tank only stored asphalt cement or #6 fuel oil.

Record keeping

Owners of regulated ASTs larger than 1,100 gallons are required to keep records about the system design, containment area evaluation, tank monitoring and tank inspections. The following fact sheets explains more:

Inspecting field-erected tanks

Tanks that are constructed on-site are considered field-erected tanks. These tanks are generally greater than 50,000 gallons in capacity. Tank inspections are critical to identifying corrosion and other maintenance problems that could eventually lead to tank failure. Most field-erected steel tanks must participate in an on-going inspection program in accordance with American Petroleum Institute (API) Standard 653, a petroleum industry standard. Inspection type and frequency varies with the tank’s design, contents, and installation date.

Inspections must be performed by a person trained and certified by the API (an API 653 authorized inspector). Below is a list of companies that provide API 653 inspection services. MPCA does not endorse any of the companies that appear on this list.

Other requirements

Here are some additional requirements that apply to regulated ASTs.

  • New tanks and piping must be designed to applicable industry standards and guidance.
  • Tank owners must clearly label all tanks and piping.
  • Underground storage tanks (USTs) of any size cannot be used as ASTs.
  • AST contractors must follow any applicable industry standards in upgrading and repairing tanks and piping.
  • When an older tank is moved to a new facility, the tank must be upgraded and the tank integrity verified.

Tank owners may petition the MPCA commissioner to approve an alternative design or operating procedure for a tank, such as use of a new technology, that achieves the same result as a specific rule requirement.

Spill planning and response

Facilities with hazardous substance or petroleum ASTs greater than 10,000 gallons of capacity are required to have a spill plan addressing release prevention and spill response. Spill response and planning guidance material is available from the MPCA’s Emergency Management Unit.

Reporting leaks and spills

AST owners are required to report a leak or spill of more than 5 gallons of petroleum or any amount of a hazardous substance from any tank or piping. To report a leak or spill, call the Minnesota Duty Officer at 800-422-0798 (Minnesota only) or 651-649-5451.

Cleanup of leaks and spills

All leaks and spills from ASTs and associated piping must be cleaned up to protect the environment and public health. Petroleum-related cleanup at facilities with less than one million gallons capacity is managed by the Petroleum Remediation Program.

For sites with petroleum contamination, the Petroleum Brownfield Program provides technical assistance and liability assurances necessary to expedite and facilitate the development, transfer, investigation and/or cleanup of property.

Who to call

For questions about AST requirements call the MPCA at 651-296-6300 or 800-657-3864.