UST System Components & Operations 3 — Questions and Answers
Question 1: What is the role of the interstitial space in a double-walled UST?
- To store additional fuel capacity
- To provide a secondary containment zone that can be monitored for leaks (Correct answer)
- To house the submersible pump motor
- To equalize pressure between the tank and product lines
Correct answer: To provide a secondary containment zone that can be monitored for leaks
The interstitial space between the inner and outer walls is a secondary containment area continuously monitored so that a leak from either wall is detected before reaching the environment.
Question 2: A shear valve (impact valve) on a dispenser is required to:
- Vent excess vapor pressure from the product line
- Automatically close the fuel line if the dispenser is struck or knocked over (Correct answer)
- Prevent overfilling of the underground storage tank
- Regulate flow rate to the nozzle
Correct answer: Automatically close the fuel line if the dispenser is struck or knocked over
A shear valve is designed to close automatically if a vehicle drive-off or impact severs the dispenser from its base, preventing a fuel spill.
Question 3: Which type of cathodic protection uses an external DC power source to protect a steel UST from corrosion?
- Sacrificial anode system
- Impressed current system (Correct answer)
- Dielectric coating system
- Fiberglass reinforcement system
Correct answer: Impressed current system
An impressed current cathodic protection system applies an external DC voltage to make the steel tank a cathode, stopping electrochemical corrosion.
Question 4: A spill bucket (spill containment manhole) at the fill pipe is intended to catch:
- Groundwater intrusion into the tank
- Product that overflows during delivery operations (Correct answer)
- Vapors emitted from the vent pipe
- Rainwater entering the tank sump
Correct answer: Product that overflows during delivery operations
The spill bucket collects product that drips or spills at the fill point during delivery, preventing it from reaching the soil.
Question 5: What does 'ullage' refer to in UST operations?
- The total tank capacity in gallons
- The empty space remaining in the tank available for product (Correct answer)
- The volume of product dispensed per day
- The interstitial volume between double walls
Correct answer: The empty space remaining in the tank available for product
Ullage is the unfilled portion of the tank—the space above the product level—which must be calculated before a delivery to prevent overfill.
Question 6: Which component in a pressurized piping system is designed to relieve excess line pressure and protect the piping from hydraulic surges?
- Overfill prevention valve
- Line leak detector
- Pressure relief valve on the STP head (Correct answer)
- Turbine sump sensor
Correct answer: Pressure relief valve on the STP head
The pressure relief valve on the STP head opens when line pressure exceeds the set limit, protecting piping and equipment from damage.
Question 7: A turbine sump (under-dispenser containment sump) is installed to:
- House the in-tank submersible pump
- Contain leaks or spills from under-dispenser piping connections (Correct answer)
- Monitor vapor concentrations in the dispenser area
- Provide emergency shutoff access for the STP
Correct answer: Contain leaks or spills from under-dispenser piping connections
The turbine sump provides secondary containment beneath the dispenser, catching any leaks from piping connections, flex connectors, or the dispenser base.
UST System Components & Operations 3
What is the role of the interstitial space in a double-walled UST?