What Are Underground Storage Tanks (USTs)?

Underground storage tanks (USTs) are containers with at least 10 percent of their volume, including connected piping, located underground. They primarily hold petroleum or other hazardous substances. USTs are used in various industries, such as fueling stations, vehicle maintenance shops, industrial facilities, and commercial buildings. Their underground presence and stored substances make them a topic of public interest.

Definition and Components

An Underground Storage Tank (UST) system safely contains regulated substances beneath the earth’s surface. Tanks are typically constructed from steel, fiberglass, or composite materials. Early steel tanks were prone to corrosion, leading to the development of corrosion-protected steel, fiberglass, and composite tanks that combine steel with fiberglass coatings to enhance durability and prevent leaks. Single-wall tanks have largely been replaced by double-wall tanks or those with secondary containment systems, providing additional protection against releases.

A network of piping connects to the tank, facilitating the transfer of substances in and out. This piping includes suction piping, which draws product, and pressure piping, which pumps product under pressure. Piping materials are typically steel, fiberglass, or flexible plastic, chosen for resistance to the stored substance and structural integrity. Connections between pipe sections and to the tank are sealed to prevent leaks, often using specialized fittings and sealants.

The UST system incorporates various ancillary equipment for its operation and safety. Dispensers are where product is dispensed to the user. Pumps, either submersible (inside the tank) or suction (above ground), move product through piping. Fill pipes deliver new product into the tank, while vent pipes release vapors to prevent pressure buildup. Gauges measure the quantity of product within the tank.

UST systems are equipped with monitoring and spill prevention devices. Spill buckets are installed around the fill pipe to capture small spills during delivery, preventing them from reaching the soil. Overfill prevention devices, such as automatic shutoff valves or flow restrictors, prevent tanks from being overfilled, which could lead to significant spills. Interstitial monitoring systems detect leaks in the space between double-wall tanks’ primary and secondary walls or within secondary containment liners. Automatic tank gauging (ATG) systems use probes to continuously monitor tank levels and detect potential leaks by tracking inventory changes.

Regulatory Framework

Underground storage tanks are extensively regulated due to environmental and public safety risks from potential leaks or spills. The Environmental Protection Agency (EPA) oversees USTs in the United States under Subtitle I of the Resource Conservation and Recovery Act (RCRA). This federal mandate establishes a comprehensive program to prevent, detect, and clean up UST releases.

EPA regulations mandate specific requirements for UST systems, beginning with registration. Owners must notify state or local agencies about their tanks, providing details on age, size, type, and contents. This registration process helps regulatory bodies track USTs and ensure compliance throughout their operational life. Design standards require new and upgraded tanks and piping to incorporate corrosion protection and secondary containment to minimize leak risk.

Installation requirements are stringent, often necessitating certified professionals. This ensures tanks and piping are correctly placed and connected, reducing the likelihood of future operational failures or releases. Leak detection is a critical component, with regulations stipulating that owners and operators must regularly monitor their tanks for leaks using approved methods, such as automatic tank gauging or statistical inventory reconciliation. These detection methods identify releases early, before widespread contamination.

Spill and overfill prevention regulations require specific equipment, such as spill buckets and overfill prevention devices, to contain spills during product delivery and prevent tanks from being overfilled. Financial responsibility is a key regulatory requirement, obligating UST owners and operators to demonstrate they have the financial means to cover potential cleanup and third-party damages from a release. This can be achieved through various mechanisms, including environmental impairment liability insurance, state assurance funds, or self-insurance.

While the EPA sets federal standards, state and local agencies play a substantial role in implementing and enforcing these regulations. Many states operate their own EPA-authorized UST programs, which must be at least as stringent as federal requirements. This delegated authority means specific rules and compliance procedures can vary by state, though they generally align with federal goals of preventing and addressing UST releases.

Environmental and Safety Concerns

Leaks or spills from underground storage tanks pose environmental and public health threats. When petroleum products or hazardous chemicals escape a compromised UST, they can migrate through surrounding soil. This leads to extensive soil pollution, rendering affected land unsuitable for certain uses and potentially harming local ecosystems. Cleanup of contaminated soil is often a complex and costly process, requiring specialized excavation and treatment methods.

Groundwater contamination is a significant environmental consequence. Many communities rely on groundwater as a primary source for drinking water and agricultural irrigation. Leaking USTs can introduce hazardous substances, such as BTEX compounds, directly into groundwater aquifers. Once contaminated, remediation efforts become substantially more challenging and expensive, sometimes requiring long-term treatment or the development of alternative water sources.

Beyond environmental damage, these releases present public health risks. Exposure to hazardous substances from contaminated groundwater or soil can occur through ingestion of tainted drinking water, inhalation of vapors, or direct skin contact. Such exposures are linked to a range of health issues, including neurological problems, respiratory illnesses, and an increased risk of certain cancers, depending on the specific contaminants and exposure levels. Children and vulnerable populations are particularly susceptible to these health impacts.

Fire and explosion hazards are another serious safety concern associated with USTs. Petroleum products, especially gasoline, release flammable vapors that can accumulate in confined spaces, such as basements, utility conduits, or sewer lines, if a leak occurs. The ignition of these vapors can lead to devastating fires or explosions, posing immediate danger to life and property. These risks underscore the necessity for robust leak detection, prevention, and response protocols.

Risks associated with USTs arise from various factors, including aging infrastructure, improper installation, and inadequate maintenance practices. Older single-wall steel tanks are more susceptible to corrosion and structural failure over time. Failure to conduct regular inspections or maintain leak detection equipment can allow small leaks to go unnoticed for extended periods, leading to widespread contamination. Proper management throughout a UST’s lifecycle is essential to mitigating these environmental and safety concerns.

Operational Aspects

Safe and compliant operation of underground storage tank systems requires diligent attention to routine inspection and maintenance. Owners and operators perform daily checks, such as visual inspections of spill buckets and dispensers, to identify immediate issues. Monthly inspections involve checking alarms and ensuring monitoring equipment functions correctly. Annual testing of various components, including line tightness tests for pressure piping and functionality checks of spill and overfill prevention devices, is a standard practice to confirm system integrity.

Leak detection is a continuous aspect of UST operations. Automatic Tank Gauging (ATG) systems use probes within the tank to measure product levels and temperatures. These systems can detect leaks as small as 0.1 or 0.2 gallons per hour with high accuracy. For double-wall tanks, interstitial monitoring involves placing sensors in the space between the tank’s walls or secondary containment liner to detect any fluid that might escape the primary containment.

Other leak detection methods include manual tank gauging for smaller tanks, which measures tank levels over a period to identify discrepancies. Vapor monitoring and groundwater monitoring wells can be installed around the tank to detect petroleum vapors or product in the soil or water. Statistical Inventory Reconciliation (SIR) analyzes inventory data, delivery records, and sales records to identify potential losses that could indicate a leak. Each method contributes to a comprehensive leak detection strategy tailored to the specific UST system.

Spill and overfill prevention procedures are important during product deliveries. Operators must ensure spill buckets are empty and clean before a delivery begins to effectively contain any drips or minor spills. Overfill prevention devices, such as automatic shutoff valves, flow restrictors, or high-level alarms, must be regularly inspected and maintained to ensure they activate correctly, preventing the tank from being filled beyond its safe capacity. Proper communication between the delivery driver and the operator is also important to prevent overfills.

Record-keeping is a mandatory element of UST operations. Owners and operators must maintain comprehensive records, including maintenance logs for all equipment, results of all leak detection tests, delivery receipts, and inspection reports. These records serve as proof of compliance with regulatory requirements and are often reviewed during compliance inspections by regulatory agencies. Maintaining accurate and accessible records is a common requirement for demonstrating adherence to environmental protection standards.

When an underground storage tank is no longer in use, proper closure procedures are essential to prevent future environmental contamination. Closure involves either permanent removal of the tank from the ground or abandonment in place. Tank removal typically requires excavation, cleaning the tank’s interior to remove residual product and vapors, and proper disposal of the tank and any contaminated soil. If abandonment in place is chosen, the tank is thoroughly cleaned and then filled with an inert solid material, such as sand or concrete slurry, to prevent collapse and future contamination. Both closure methods usually require a site assessment to confirm that no contamination has occurred; if found, remediation efforts are initiated to clean up the affected area.