Underground storage tanks (USTs) play a critical role in how fuels and hazardous liquids are stored safely across industries. But if you’re wondering, what is underground storage tank exactly—and how are they used, regulated, or maintained—you’re not alone.
Whether you’re in construction, fuel distribution, or just trying to understand compliance rules, this guide breaks it all down with clarity and sources you can trust.
Keep reading to learn what USTs are, who uses them, what they’re made of, and why regulations around them are so strict.
What Is an Underground Storage Tank (UST)?
An underground storage tank (UST) is any tank (plus connected piping) that has at least 10% of its total volume buried beneath ground level. These systems are commonly used to store petroleum products like gasoline or diesel, as well as certain hazardous substances regulated under U.S. law (EPA).
A complete UST system includes:
- The main storage tank – the structure that holds the liquid.
- Piping and connections – for filling and dispensing fuel or chemicals.
- Spill and overfill protection – to prevent accidental releases during transfers.
- Leak detection equipment – to identify problems before they become hazards.
USTs are commonly found at gas stations, airports, fleet fueling stations, and industrial facilities. Because of the potential risks to soil and groundwater, they are tightly regulated under federal and state laws to ensure safe design, installation, and ongoing monitoring.
What Is Underground Storage Tank Used For?
USTs are primarily used to store fuels and chemicals underground to save space and reduce fire hazards. Specific uses include:
- Gas stations: Storing large volumes of gasoline or diesel for retail fueling.
- Fleet services: Companies with internal fueling operations.
- Airports and transit depots: Fuel storage for planes, buses, or emergency generators.
- Municipal or military sites: Diesel or chemical storage for essential operations.
Because they’re underground, USTs offer a discreet storage solution—but with that comes a need for strict monitoring.
What Is Underground Storage Tank Made Of?
The materials used in constructing underground storage tanks are selected based on the intended contents, environmental conditions, and regulatory standards. Each option offers different advantages for durability, cost, and corrosion resistance:
Bare Carbon Steel
Common in older tanks, this material is structurally strong but highly susceptible to corrosion when exposed to moisture and soil acidity. Without additional protection, it poses a significant risk for leaks over time.
Coated Carbon Steel
To reduce corrosion, many modern steel tanks are coated with protective layers such as epoxy or polyurethane. These coatings serve as a barrier between the steel surface and corrosive soil or water, though they must be regularly inspected for wear or damage.
Fiberglass-Reinforced Plastic (FRP)
FRP tanks are non-corrosive and lightweight, making them ideal for a variety of petroleum products and chemicals. Their resistance to rust and compatibility with a wide range of substances makes them a popular choice for both new installations and replacements.
Composite Tanks
These combine steel and fiberglass layers, offering the strength of steel with the corrosion protection of FRP. The inner steel wall provides structural integrity, while the outer FRP layer acts as a corrosion barrier.
In addition to the base material, modern USTs are built to meet stringent EPA and state-level standards. They often include:
Double-wall containment systems
These feature an inner and outer wall with a space between them to detect leaks before they reach the environment.
Corrosion protection systems
Including sacrificial anodes or impressed current systems for steel tanks.
Leak detection sensors and monitoring ports
These help identify potential failures early, ensuring compliance and minimizing environmental risks.
Types of Underground Storage Tanks
USTs are classified based on their application, material, and structural configuration. The main types include:
Fuel Storage Tanks
Used for petroleum products such as gasoline, diesel, and kerosene. Found in gas stations, fleet fueling stations, and industrial sites.
Hazardous Substance Tanks
Designed to store chemicals regulated by the EPA under Subtitle I of RCRA. These require specialized materials and containment systems to prevent contamination.
Steel Tanks
Constructed entirely of carbon steel, typically coated or combined with cathodic protection to meet corrosion resistance standards.
FRP Tanks
Non-metallic tanks designed to resist corrosion, commonly used in locations with aggressive soil conditions or where metal is unsuitable.
Composite USTs
Multi-layered tanks combining the benefits of steel and fiberglass for enhanced structural performance and corrosion protection.
Double-Wall Tanks
Feature a secondary shell surrounding the primary tank to contain and detect leaks. Required in many states for new installations.
Jacketed Tanks
Jacketed tanks are a type of double-wall UST where the outer jacket provides secondary containment and space for leak monitoring. They are common in modern fuel storage installations to improve environmental protection and meet stricter regulations.
Single-Wall Tanks
Older models that consist of just one layer. These are being phased out due to leak risk and evolving regulations.
USTs with or without secondary containment
Secondary containment systems (e.g., liners, outer shells) are mandatory for many new installations to prevent environmental damage from leaks.
All of these types must comply with EPA and state regulations regarding design, installation, and monitoring to ensure environmental safety.
Who Uses Underground Storage Tanks?
A wide range of industries rely on USTs, including:
- Fuel retailers (gas stations)
- Construction firms (on-site fueling)
- Logistics and transportation companies (private depots)
- Government and municipal departments (backup fuel or chemical storage)
- Agricultural operations (fertilizer and pesticide storage)
USTs are essential where space is limited or above-ground tanks are impractical.
How Deep Are Underground Storage Tanks Buried?
The depth of a UST depends on its size and the soil type, but generally:
- Tanks are buried 2 to 7 feet below ground.
- Shallower depths are used for smaller tanks.
- Heavier-use sites (e.g., airports) may require deeper installation.
Shallow installations risk exposure or surface damage, while deeper tanks need stronger access systems for inspections and repairs.
What Are the Disadvantages of Underground Storage Tanks?
While USTs are widely used and regulated, they come with a range of operational and environmental challenges:
- Corrosion Risk: Steel tanks without proper protection can corrode over time, leading to structural failure or leaks.
- Leak Detection Complexity: Leaks may go undetected for long periods due to their underground location unless sophisticated monitoring systems are in place.
- Environmental Contamination: A leaking UST can release hazardous substances into soil and groundwater, triggering costly cleanup and regulatory penalties.
- High Installation and Maintenance Costs: Excavation, lining, monitoring, and repairs require significant upfront and ongoing investment.
- Regulatory Burden: USTs are subject to strict EPA and state rules regarding inspections, recordkeeping, leak detection, and financial responsibility.
These disadvantages make it crucial for UST owners to ensure tanks are built to current standards, maintained properly, and inspected regularly.
Underground Storage Tank Regulations
USTs are heavily regulated to protect environmental and human health:
- EPA UST Rules: Set national standards under RCRA Subtitle I (EPA Regulations).
- Energy Policy Act of 2005: Requires secondary containment and operator training.
- State-Level Oversight: States like California, Texas, and Florida have their own stricter rules.
- Standards from API and NFPA: Used to ensure tank performance and safety.
Operators are legally required to install leak detection, corrosion protection, and financial assurance measures.
What You Should Know About UST Safety and Use
If you operate or plan to install a UST, keep these best practices in mind:
- Always use compatible materials for the substance stored.
- Ensure secondary containment is installed for leak protection.
- Perform regular inspections and maintenance.
- Keep up with recordkeeping and compliance filings.
- Work with certified installers and inspectors.
Final Thoughts
Understanding what is underground storage tank used for goes beyond fuel—it’s about compliance, safety, and infrastructure. Whether you’re storing diesel, chemicals, or water, USTs provide a powerful tool for space-saving and fire-safe storage.
Just remember: with underground tanks comes high responsibility. From choosing the right materials to following EPA rules, proper management is non-negotiable.
For more regulatory information, visit the official EPA UST resource page.
Looking for reliable underground storage tank solutions? Call at (512) 731-1412 or request a quote from our team in Austin, TX. We provide UST design, installation, and compliance support for industries across United States, Latin America, and Canada.