Underground storage tank systems

Underground storage tanksIn Minnesota, there are about 13,000 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 most recently amended in 2019 to conform with the 2015 revisions to CFR 40, pt. 280 which is administered by the U.S Environmental Protection Agency (EPA). Amendments also reflect new technologies, codes of practice, and industry standards. The following fact sheets summarize what's new for tank owners and tank contractors:

Which USTs are subject to regulation?

USTs that contain petroleum or hazardous substances 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
  • 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, secondary containment, cathodic protection system testing, release detection, operation and maintenance testing, inspections, 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

A 10-day pre-notification is required for installations, replacement, or repair of a UST system, excluding dispensers and exposed components below grade. A Certified Contractor must oversee all work, which must be in accordance with applicable codes.

After December 22, 2007, all new and replacement UST systems (tanks, piping, submersible pumps, and dispensers) must be secondarily contained and designed to conduct interstitial monitoring. Heating oil tanks and piping, and safe suction piping do not have to be secondarily contained.

Tanks and piping must be constructed of approved non-corrosive materials, or steel that is protected from corrosion. Release detection, corrosion protection, spill prevention, overfill prevention and Stage 1 vapor recovery (metro area only), must also be installed as described on this website. Owners need to submit a UST notification form to the MPCA within 30 days of project completion.

Internal lining inspections

Some USTs had an internal lining as the sole method of corrosion protection installed to meet the 1998 upgrade requirements. These internal linings must be internally inspected every five years.

Dispenser and submersible pump containment

After December 22, 2007, 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.

After April 29, 2019, containment beneath the dispenser is also required if the concrete or base material beneath any dispenser is replaced, or if new or replacement piping is connected to any dispenser.

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

Spill and overfill prevention

Tanks are required to have a 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), high level alarm, or a flow restrictor device in a vent line (ball float).  Existing ballfloat devices can continue to be used if functioning properly, but cannot be installed or repaired in the future

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 tester. Cathodic protection system test results must be submitted to the MPCA within 30 days on one of the following forms:

Details on cathodic protection installation, testing, and repair:

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 for leaks every 30 days.

Tanks installed after December 22, 2007, must be  secondarily contained (double-wall) and interstitial monitoring must be conducted as the primary method of tank leak detection. Acceptable release detection methods for tanks installed prior to December 22, 2007:

  • Automatic tank gauging
  • Statistical inventory control (SIR)
  • 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

All pressure piping (any installation date) must have an automatic line leak detector (mechanical or electronic), that can detect a leak at 3 gallons per hour (gph) at 10 psi line pressure within an hour. A function test of the automatic line leak detector must be done annually to verify it meets this threshold.

Pressurized piping installed after December 22, 2007, must be secondarily contained (double-wall), and continuous or monthly  interstitial monitoring must be conducted.

Pressurized piping installed prior to December 22, 2007, must use one of the following options:

  • annual line tightness testing at 0.1 gph by an agency-approved tester
  • monthly line tightness test at 0.2 gph (electronic line leak detector or SIR)
  • continuous or monthly interstitial monitoring (for double wall pipe systems)

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 or monthly interstitial monitoring (for double wall pipe systems)

The following fact sheets provide further information:

Underground storage tank system compatibility

Notification to the MPCA is required at least 30 days prior to storing fuel greater than 10% ethanol or 20% biodiesel. Use the change in status form.

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

Periodic inspections and maintenance testing

As part of the 2019 rule amendments, the MPCA added rule language requiring periodic inspections and maintenance testing.

Monthly walk-through inspections

The following requirements will be effective April 29, 2019 and may be conducted by the owner or operator of the tank system:

  • All spill buckets, dispenser sumps, and submersible pump sumps must be visually checked on a monthly basis for leaks. Any product, water, and debris must be cleaned out. The source of any leaks must be immediately investigated and repaired.
  • Note: A secondarily contained submersible pump sump with an automatic leak sensor only needs to be checked on an annual basis, provided the leak sensor is function tested on an annual basis as well Check all riser caps are tight and no obstructions are in the fill port (drop tube) of the tank
  • Ensure release detection equipment is operating with no alarms or unusual operating conditions, and that release detection records are reviewed and current
  • Ensure the tank bottoms are monitored for water, and the source of water is investigated.  Removing water from the tank is very important.

Below is a monthly inspection form to help comply with these requirements

Annual release detection operability testing and inspections

A test of mechanical and handheld release detection components is required to assure serviceability and proper operation.  The annual testing described below must be conducted by October 13, 2020 and must be done by an agency-approved tester:

  • Automatic Tank Gauge (ATG)- test controllers, alarms, and system configuration
  • Test probes, sensors, and automatic line leak detectors for functionality and communication with controller
  • Vacuum pumps and pressure gauges must have proper communication with sensors and controllers
  • Hand-held release detection devices (gauging sticks and fuel paste) are functional
  • Visually inspect all spill buckets and containment sumps used for interstitial monitoring for liquid tightness and deficiencies

Below are inspections forms to comply with these requirements

Three year functionality and integrity testing

The functionality and integrity testing described below must be conducted by October 13, 2020 and must be done by an agency-approved tester:

  • An integrity test is required every three years on all spill buckets to assure liquid tightness
  • An integrity test is required every three years on containment sumps used for interstitial monitoring to assure liquid tightness.  Interstitial monitoring is required on pressure piping, and non-safe suction piping, installed after December 22, 2007
    Note: Double-wall spill buckets or containment sumps used for interstitial monitoring are exempt from three year integrity testing, provided the interstice is checked monthly for liquid, and leak sensing devices are checked annually for proper function
  • Overfill protection devices must be checked every three years to ensure the equipment is set to activate at the correct level and that it functions properly

Below are inspections forms to help comply with these requirements.

Agency-approved testers must apply and be approved to conduct annual or three year testing and inspections as described above.  Please see the following application on how to become an agency-approved tester.

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).

The MPCA encourages you to contact your local government unit and fire code official, which may require permits or have additional requirements for UST closures.

Heating oil tanks

Tanks larger than 1,100 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 a regulated substance which is used solely for emergency power generation purposes on the premises must follow all applicable requirements for UST design and operation. Facilities with emergency generator USTs must implement a tank and piping release detection method by October 13, 2020, if a release detection method is not currently implemented. Tanks containing a regulated substance which is used for both emergency power generation and heating (dual-use), must also follow all applicable requirements for UST design and operation with a few exceptions.

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.

Record keeping

When a facility is inspected by the MPCA, records will be requested to determine compliance with all applicable requirements. Without proper records tank compliance cannot be demonstrated. Some records such regarding installation, repairs, compatibility, and use of alternative methods must be retained for the life of the tank system. Other records such as release detection, and operation and maintenance testing must be retained for 5 years.

Underground Storage Tank Quality Assurance Program Plan

This document provides general guidance for our internal staff as well as our external clients.

Selecting a certified contractor

It is unlawful for an owner or operator to hire a contractor not certified by the MPCA.