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Regulated Underground Storage Tanks

An underground storage tank (UST) is defined as one or any combination of tanks and connective pipes used to contain petroleum or other regulated substances with 10% or more volume (including underground pipes) beneath the ground surface. A storage tank does not need to be buried to be considered a regulated UST.

Certain USTs are exempt from the “Rules Regulating Underground Storage Tank Systems” (IDAPA 58.01.07):

  • Farm and residential tanks with capacities of 1,100 gallons or less of motor fuel used for noncommercial purposes.
  • Tanks storing heating oil for on-site consumption.
  • Tanks on or above the floor of underground areas (e.g., basements).
  • Septic tanks and systems for collecting stormwater and wastewater.
  • Emergency spill and overfill tanks that are immediately emptied after use.

Each regulated UST or UST compartment is assessed a tank fee of up to $100 per tank or compartment for continued environmental protection through the Idaho UST Program. DEQ invoices fees annually in November with payment due by the first business day of each year.

Aboveground storage tanks
not regulated by DEQ.

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New or different fuel formulations are referred to as emerging fuels. Those fuels enter the market for various reasons such as policy changes or technical requirements. Emerging fuels include biofuels (e.g., ethanol), new formulations of petroleum-based fuels (e.g., ultra-low sulfur gasoline), combinations of multiple types of fuels (e.g., ultra-low sulfur diesel), and others. Emerging fuels, including 15% ethanol, 85% gasoline (E15), may not be compatible with all UST systems, and storing emerging fuels can increase corrosion in UST systems. Regulations require that USTs are constructed, maintained, and operated in a manner that ensures petroleum and other regulated substances are stored safely.

Stage 1 vapor recovery captures gasoline vapors that otherwise may escape into the environment. DEQ’s Air Quality Program manages the Stage 1 Vapor Recovery Program in Ada and Canyon Counties under the “Rules for the Control of Air Pollution in Idaho” (IDAPA 58.01.01). EPA regulations apply statewide. For more information, contact the DEQ Boise Regional Office at (208) 373-0550.

It is important to determine if an UST (even one that is no longer in use) exists or existed on a property before the purchase or sale. The issue of contamination from a leaking UST (past or present) may come up in a property transaction.

We maintain a database of regulated UST sites in Idaho, but potential buyers/sellers often hire a contractor to conduct an environmental site assessment. Lenders may require site assessments for loans on certain types of properties. Any past or newly-discovered contamination must be disclosed to a potential buyer and reported to DEQ to determine if remedial action is required.

DEQ does not regulate or track residential heating oil tanks, and current state regulations do not address heating oil tanks on residential property unless a leak has been confirmed.

Although a residential heating oil tank may not be regulated for operation and maintenance purposes, the current property owner is still responsible for cleaning up leaks under IDAPA 58.01.02 and 58.01.24.

An  underground residential heating oil tank can cause several issues:

  • The property owner may be liable for damage caused by contamination from the tank system.
  • Leaks can contaminate soil on the property and adjoining properties.
  • Leaks can contaminate ground water and residential well water.
  • Cave-ins can occur when tank walls collapse due to corrosion.
  • Most lending institutions and buyers require the closure of unused heating oil tanks before finalizing a residential sale.

Underground residential heating oil tanks still in use should be monitored and/or actively checked for signs of leakage (e.g., furnace using more fuel than usual, unusual weather, furnace malfunction).

For more information on residential heating oil tanks, see Real Estate and Underground Storage Tanks or contact your regional office.

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UST Compliance Officer

Mark Olsen
Mark.Olsen@deq.idaho.gov
(208) 373-0138

UST/LUST Program Manager

Kristi Lowder
Kristi.Lowder@deq.idaho.gov
(208) 373-0347

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