Underground storage tank systems

Underground storage tanksIn Minnesota, there are about 18,000 regulated underground storage tanks (USTs) in use. The Underground Storage Tank Program helps to prevent contamination caused by leaking tanks by focusing on technical assistance and compliance.


The MPCA promulgated UST rules in 1991. The rules were amended following the Energy Policy Act of 2005 (Act) and became effective on March 24, 2008. The UST rules were again amended in 2009 to address expanded training requirements. The following fact sheets summarize what's new for tank owners and tank contractors:

The MPCA will revise existing UST rules and is considering revisions to address federal amendments and may also include language clarifications or other updates. Further information on this effort is available on the Underground Storage Tanks Update Rulemaking webpage.

Which USTs are subject to regulation?

USTs which contain petroleum or hazardous materials are subject to the MPCA’s design and operating rules for USTs. Tank appurtenances such as piping and dispensers are also covered. Definitions in the rules are found at Minnesota Rules, Chapter 7150.0030.

Some types of USTs are exempt from the regulations:

  • Tanks with capacity of 110 gallons or less
  • Farm and residential tanks with capacity of 1,100 gallons or less, storing motor fuel for non-commercial purposes
  • Tanks with capacity of 1,100 gallons or less, storing heating oil for consumptive use on the premises
  • Tanks that contain a minimum concentration of regulated substances
  • Flow-through process tanks
  • Oil-water separators

What are the requirements?

Design and operating rules for regulated USTs include tank and piping corrosion protection, overfill prevention, dispenser and pump containment, cathodic protection system testing, release detection, and other requirements. A brief summary of each requirement and links to forms and fact sheets follows. The complete rules are available at Minnesota Rules, Chapter 7150, Underground Storage Tanks.

New installations

Prior to installing or replacing any UST system or component, owners must provide 10-day pre-notification to the MPCA. A Certified Contractor must oversee all work, which must be in accordance with applicable codes.

After March 24, 2008, all new and replacement UST systems (tank, piping, submersible pumps, dispensers) must be secondarily contained with interstitial monitoring. Pressure piping must have an automatic line leak detector or a sump sensor design. Fill pipes must have a drop tube, a liquid-tight spill catchment basin, and employ an overfill prevention device. Gasoline tanks must have Stage 1 vapor recovery (metro area only). Owners need to submit a post-installation notification to the MPCA, and retain appropriate design documentation from installation contractors.

Corrosion protection for tanks and piping

Tanks and piping are required to use a corrosion protection design, to prevent degradation and rusting of metal components and leaks to the environment.

After March 24, 2008, all new and replacement tanks and piping must use a secondary containment design with interstitial monitoring, except for heating oil tanks and piping, and safe suction piping. Acceptable secondary containment designs:

  • Double-walled fiberglass-reinforced plastic (FRP)
  • Double-walled steel with cathodic protection
  • Double-walled steel with a composite FRP jacket
  • Single-walled steel with a composite FRP jacket designed to contain and detect leaks through steel wall
  • Double-walled flexible nonmetallic (piping)

For more information:

  • Secondary Containment for Underground Storage Tanks (t-u3-19) (pending)

Acceptable materials for UST systems installed prior to March 24, 2008:

  • FRP
  • Steel with cathodic protection
  • Steel with a composite FRP jacket
  • Steel with an internal lining (tank)
  • Flexible nonmetallic (piping)
  • Secondary containment design

Internal lining inspections

USTs with an internal lining as the sole method of corrosion protection must be internally inspected within ten years after being lined, and every five years thereafter.

The MPCA has now specified inspection procedures, effective March 24, 2008, for these tanks, intended to ensure that these tanks are structurally sound with the lining still performing to original design specifications. Required procedures include: pre-notification to the MPCA, designated inspection code, inspector qualifications, manned entry with visual evaluation, specific tests such as holiday testing, ultrasonic testing, and hardness testing, post-inspection leak testing after repairs, and report submittal to the MPCA. Minor abnormal lining conditions may be repaired; however if more extensive lining failure occurs, the tank must be permanently closed.

Dispenser and submersible pump containment

After March 24, 2008, new and replacement dispensers must have secondary containment underneath the dispenser, and submersible pumps must have secondary containment surrounding the pump head, in order to prevent contamination from leakage at these locations. Dispenser containment is not required where an existing dispenser is replaced and no work is performed beneath the shear valve. Containment must be made of synthetic materials (not concrete or metal) and have liquid-tight sides, bottom and points of piping penetration.

  • Secondary Containment for Underground Storage Tanks (t-u3-19) (pending)

Spill and overfill prevention

Tanks are required to have a catchment basin (spill bucket) surrounding the fill pipe, to catch spills that may occur when the delivery hose is disconnected from the fill pipe. Spill buckets must be kept clear of debris and storm water, and spilled product must be removed. Tanks are also required to have an overfill prevention device to minimize the chances of delivering more product to a tank than the capacity of the tank allows. Three options for overfill prevention include an automatic shutoff device (flapper valve), flow restrictor (ball float valve), and a high level alarm.

Cathodic protection systems

Cathodic protection systems protect metallic UST system components buried in soil from corrosion. Two types of cathodic systems are commonly used on UST systems, impressed current and sacrificial anode.

Cathodic systems must be properly maintained and tested periodically to ensure effectiveness. Sacrificial anode systems must be tested every 3 years by a qualified Cathodic Protection Tester. Impressed current systems must be tested annually by a qualified Cathodic Protection Expert. Cathodic system test results must be submitted to the MPCA within 30 days on one of the following forms:

More information about certified cathodic protection testing and testers can be found at the and STI website. Please be aware, however, that not all of the individuals included on these lists provide cathodic protection testing services for hire. The MPCA suggests contacting your tank service provider who may be able to direct you to individuals in your area that are certified to conduct cathodic protection testing, and many tank service providers are certified to conduct the test themselves.

Minnesota accepts certification of Cathodic Protection Experts and Testers from the National Association of Corrosion Engineers (NACE) and the Steel Tank Institute (STI). Individuals must have education, experience, and documented competence in topics relating to soil resistivity, stray current, structure-to-soil potential, and component electrical isolation measurements of buried metal piping and tank systems.

  • Cathodic Protection of Aboveground and Underground Tanks (pending)

Release detection for tanks

Tank owners must provide a method that can detect a release from any part of the tank, and the connected piping, pumps, and dispensers, that routinely contains regulated substances. Systems must either be monitored continuously or checked every 30 days for leaks.

For secondarily contained tanks installed after March 24, 2008, monitoring of the interstitial space for leaks is required, using an automatic leak sensor or a monthly manual check. Any sensor must be function tested annually.

Acceptable release detection methods for tanks installed prior to March 24, 2008:

  • Automatic tank gauging
  • Inventory control (first 10 years only, tightness testing at 5 years)
  • Statistical inventory control (SIR)
  • Manual tank gauging for 1,000-2,000 gallon capacity tanks (first 10 years only, tightness testing at 5 years)
  • Manual tank gauging for less than 1,000 gallon capacity tanks
  • Interstitial monitoring (secondary containment tanks)

For more information, use the following fact sheets on leak detection methods.

Release detection for piping

Pressurized piping installed after March 24, 2008, must be secondarily contained, and the interstitial space must use a gravity drain design to a sump. The interstitial space must be monitored using one of the following options:

  • Continuous interstitial monitoring (sump sensor with alarm, flow restrictor, or shutoff).
  • Continuous automatic line leak detector plus monthly sump monitoring.

Pressurized piping installed prior to March 24, 2008, must use one of the following options:

  • Continuous automatic line leak detector plus annual line tightness testing;
  • Continuous automatic line leak detector plus monthly SIR;
  • Continuous automatic line leak detector plus monthly sump monitoring; or
  • Continuous interstitial monitoring.

Automatic line leak detectors and sump detectors must be function tested annually.

Release detection is not required for properly designed "safe suction" piping. Other suction piping (any installation date) must use one of the following options:

  • Line tightness testing every three years
  • Monthly SIR
  • Continuous interstitial monitoring
  • Monthly interstitial monitoring.

The following fact sheets provide further information:

Underground storage tank system compatibility

Underground storage tank (UST) systems are required by law to be compatible with the product they store and dispense. The following compatibility form needs to be completed for UST systems that use fuel greater than 10% ethanol or 20% biodiesel.

Sump checks

All spill catchment basins (spill buckets), dispenser sumps, and submersible pump sumps must be visually checked on a monthly basis for leaks, water, and debris. A secondarily contained submersible pump sump with an automatic leak sensor need only be checked on an annual basis. Any leaked or spilled product, water, or debris must be cleaned out.

Temporary and permanent closure

Certain requirements must be followed by owners when leaving a tank inactive for a period of time (“temporary closure”) or taking the tank out of service permanently (permanent closure).

  • If a tank is not being actively used for more than 90 days, the owner must notify the MPCA of temporary closure status, empty the tank, lock out fill lines, and continue to maintain cathodic protection.
  • Temporarily closed tanks must be permanently closed at the end of one year, unless the owner has received written MPCA approval to continue in temporary closure.
  • A tank that has been temporarily closed more than one year needs written MPCA approval to return to service. Temporary closure may not extend beyond 5 years. If temporary closure requirements are not met, the tank is considered an active tank and normal operating requirements should be followed.

The MPCA must receive advance notice of permanent tank closure. Permanent closure involves emptying and cleaning the tank and piping, and either removing the tank and piping from the ground or filling them with an inert substance.

Heating oil tanks

Tanks larger than 1100 gallons containing new fuel oil or waste oil which are used solely for heating purposes on the premises, are subject to notification and corrosion protection requirements, but are exempt from most other requirements including spill and overfill prevention and release detection.

Emergency generator tanks

Tanks containing new fuel oil or waste oil which are used solely for emergency power generation purposes on the premises, or which are used for both emergency power generation and heating (dual-use), must follow all UST requirements except that tanks installed prior to March 24, 2008, are exempt from release detection. Tanks installed after March 24, 2008, must be secondarily contained and use interstitial monitoring.

Used oil tanks

Used oil (waste oil) tanks are regulated and must follow all applicable UST design and operating rules. If a used oil tank is used solely for heating purposes on the premises and no used oil is pumped from the tank for recycling or re-use elsewhere, it must follow the requirements for heating oil tanks (see Heating Oil Underground Storage Tanks).

Vapor recovery for metro gasoline USTs

Stage 1 Vapor Recovery is the process of recovering hydrocarbons that are emitted during the transfer of gasoline from the delivery vehicle into the underground storage tank (UST) holding petroleum products. Vapors in the tank are displaced as the gasoline fills the tank. During Stage 1 Vapor Recovery, the vapors are routed through a hose back into the tanker instead of venting directly into the atmosphere.

All retail locations selling gasoline to automobiles in the Twin Cities seven-county metro area must perform Stage 1 Vapor Recovery. The seven-county metro area includes the following counties: Anoka, Carver, Dakota (excluding the city of Northfield), Hennepin (excluding the city of Hanover), Ramsey, Scott (excluding the city of New Prague), and Washington.

Underground Storage Tank Quality Assurance Program Plan

This document provides general guidance for our internal staff as well as our external clients. Please review the document:

Selecting a certified contractor

It is unlawful for an owner or operator to hire a contractor not certified by the MPCA. A list of MPCA-certified underground storage tank contractors is available. The MPCA is not endorsing these companies nor providing testimonials about the work quality of these companies. This list is supplied as a public service and only includes companies which have completed certification requirements.