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Digging Up the Dirt on Underground Storage Tanks

Let's start with the basic question, "What is an underground storage tank (UST)?" A UST is any tank, including any connected underground piping, with at least 10% of its volume underground and which stores a regulated substance, such as petroleum products or hazardous chemicals.

Double Walled Underground Storage Tanks
DW-Fiberglass USTs During Installation

Underground storage tanks have 3 primary components: the tank, integral piping and fuel dispensing pumps.

The tanks must be double-walled (DW) or installed within an approved secondary containment system. This is because unprotected steel can corrode causing leaks to occur.

With the exception of the fuel dispenser pumps, most components, are underground and not readily visible or easily accessible. Since they cannot be easily maintained, it is important to ensure that they are also made of or coated with noncorrodible materials.

Sumps are designed to provide access to equipment underground and sometimes prevent liquids from leaking into the surrounding soil and groundwater. There are various types of sumps that perform different functions for the UST system.

Some of these types are:

  • Turbine Sumps: These are designed to provide access to the turbine area directly above the tank. This area may contain the submersible turbine pump head, piping, line leak detectors, interstitial monitoring devices, wiring and other equipment.

  • Dispenser Sumps: These are designed to provide access to piping, flex connectors, shear valves and other equipment located directly beneath the dispenser.

  • Transition/Intermediate Sumps: These are less common that other types, but can be found along the piping running underground from the USTs to the dispensers. They are used to transition from one type of piping to another or reveal key points in the piping itself.

  • Spill Buckets: These are contained sumps, meaning they have sides and a bottom that are designed to be liquid tight. They are installed at the fill connection points to contain drips and spills of fuel that can occur during delivery.

Source:EPA 510-R-16-001
Underground Storage Tank System

Sumps can also provide access to the ATG, or automated tank gauge, which monitors the fuel level in the tank as well as temperature, water level and more. These are usually connected to a console located inside the facility that allows trained individuals to print read-outs of the tank's stats.

Shutoff flapper valves are used to prevent overfills during fuel deliveries. These systems restrict or stop flow into the tank, along with sounding an alarm, when the capacity reaches a certain level.

Another part of the UST system is the vent line. Vent lines may be per tank or may be manifolded. These allow pressure within the tank to equalize when product is removed or introduced to the tank.

It's important to remember that even the best equipment can become faulty if not properly operated and maintained. Even a small leak can result in large amounts of contaminated soil and groundwater over a period of time.

As of October 13, 2018, new requirements for monitoring USTs and their components will be in place. Every 30 days, you must perform an inspection of your spill equipment, the fill pipe, and the interstitial area of double-walled tanks. You must also ensure that release detection equipment is operating correctly. Annual inspections must be performed to check for issues with the containment sumps such as damage, leaks, or liquid.

You may choose to hire an environmental compliance company to perform these inspections for you. These companies, like our own AET Compliance, LLC., can conduct inspections to ensure facilities maintain equipment upgrades, leak detection systems are functioning properly, reconciliation records are up to date and new discharges are handled properly. A properly managed program can result in potential reduction in insurance premiums, an increase in safety and reduced liability due to regular maintenance.


-Broward County Environmental Protection and Growth Management Department Pollution Prevention Division Compliance Assistance Section. (2017, October). Your Florida Petroleum Storage Tank Facility Inspection Guide [PDF]. Broward County for the Florida Department of Environmental Protection.

- United States Environmental Protection Agency. (2016, February). Operating And Maintaining Underground Storage Tank Systems [WORD]. Washington D.C.: United States Environmental Protection Agency.

-U.S. EPA, Office of Underground Storage Tanks. (2005, May). UST Systems: Inspecting And Maintaining Sumps And Spill Buckets [PDF]. Washington D.C.: United States Environmental Protection Agency.


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