Frequently Asked Questions

An underground storage tank (UST) system is a tank and any underground piping connected to the tank that has at least 10 percent of its combined volume underground. The federal UST regulations apply only to underground tanks and piping storing either petroleum or certain hazardous substances.

Until the mid-1980s, most USTs were made of bare steel, which is likely to corrode over time and allow UST contents to leak into the environment. Faulty installation or inadequate operating and maintenance procedures also can cause USTs to release their contents into the environment. The greatest potential hazard from a leaking UST is that the petroleum or other hazardous substance can seep into the soil and contaminate groundwater, the source of drinking water for nearly half of all Americans. A leaking UST can present other health and environmental risks, including the potential for fire and explosion.

The following USTs are excluded from regulation and, therefore, do not need to meet federal requirements for USTs:

• Farm and residential tanks of 1,100 gallons or less capacity holding motor fuel used for noncommercial purposes
• Tanks storing heating oil used on the premises where it is stored
• Tanks on or above the floor of underground areas, such as basements or tunnels
• Septic tanks and systems for collecting storm water and wastewater
• Flow-through process tanks
• Tanks of 110 gallons or less capacity
• Emergency spill and overfill tanks

The state regulations for USTs are found in the Arkansas Pollution Control and Ecology Commission (APC&EC) Regulation 12. The federal regulations (40 Code of Federal Regulations, Part 280, 281) are adopted by reference in APC&EC Regulation 12. In 1988, EPA issued regulations setting minimum standards for new tanks (installed after December 22, 1988) and requiring owners of existing tanks (installed before December 22, 1988) to upgrade, replace, or close them. The regulations are divided into three sections: technical requirements, financial responsibility requirements, and state program approval objectives.

EPA designed part of the technical regulations for USTs to make sure releases or leaks from USTs are discovered quickly before contamination spreads from the UST site. Owners and operators are responsible for detecting leaks from their tanks and piping.

All USTs must have leak detection. USTs installed after December 22, 1988, must have leak detection when they are installed. USTs installed before December 22, 1988, had compliance deadlines that varied with the age of the USTs. By December 22, 1993, all of these "older" USTs had to be in compliance with leak detection requirements.

Owner/operators of petroleum USTs must use at least one of the seven leak detection methods listed below:

1. Secondary containment and interstitial monitoring involves placing a barrier between the UST and the environment. The barrier provides secondary containment and can be a vault, liner, or double-walled structure. Leaked product from the UST is directed toward a monitor located in the interstitial space between the UST and the outer barrier. Interstitial monitoring methods range from a simple dip stick to automated vapor or liquid sensors permanently installed in the system. New USTs holding hazardous substances must use this method.
2. Automatic tank gauging systems use monitors permanently installed in the tank. These monitors are linked electronically to a nearby control device to provide information on product level and temperature. During a test period of several hours when nothing is put into or taken from the tank, the gauging system automatically calculates the changes in product volume that can indicate a leaking tank.
3. Vapor monitoring senses and measures product vapor in the soil around the tank and piping to determine the presence of a leak. This method requires installation of carefully placed monitoring wells. Vapor monitoring can be performed periodically using manual devices or continuously using permanently installed equipment.
4. Groundwater monitoring senses the presence of liquid product floating on the groundwater. This method requires installation of monitoring wells at strategic locations in the ground near the tank and along the piping runs. To discover if leaked product has reached groundwater, these wells can be checked periodically by hand or continuously with permanently installed equipment. This method is effective only at sites where groundwater is within 20 feet of the surface.
5. Statistical inventory reconciliation uses sophisticated computer software to determine whether a tank system is leaking. The computer conducts a statistical analysis of inventory, delivery and dispensing data collected over a period of time and provided by the operator to a vendor.
6. Manual tank gauging can be used only on tanks 2,000 gallons or smaller. This method does NOT work on tanks larger than 2,000 gallons or on piping. This method requires taking the tank out of service for at least 36 hours each week to take measurements of the tank’s contents. Tanks 1,000 gallons or less can use this method alone. Tanks from 1,001 to 2,000 gallons can use this method only when it is combined with periodic tank tightness testing and only for 10 years after installation or upgrade of the UST. After 10 years, these USTs must use one of the leak detection methods listed above in 1-5.
7. Tank tightness testing and inventory control combines two methods. Tank tightness testing requires periodic tests conducted by vendors who temporarily install special equipment that tests the soundness of the tank. Tank tightness testing must be used in combination with inventory control. Inventory control is an ongoing accounting system, like a checkbook, kept by the UST owner/operator to detect leaks. Inventory control requires taking daily accurate measurements of the tank’s contents and performing monthly calculations to prove that the system is not leaking. Tank tightness testing and inventory control can be used only for 10 years after installation or upgrade of an UST. After 10 years, these USTs must use one of the leak detection methods listed above in 1-5.

The leak detection requirements for the two types of piping systems are as follows:

1. Pressurized piping needs automatic line leak detectors (these can be automatic flow restrictors, automatic flow shutoffs, or continuous alarm systems). Pressurized piping also needs one of the following: groundwater monitoring, vapor monitoring, secondary containment and interstitial monitoring, statistical inventory reconciliation, or an annual tightness test of the piping.
2. Suction piping needs no leak detection if it meets two design requirements: 1) piping slopes so that the product drains back into the tank when suction is released, and 2) piping has only one check valve located closely beneath the pump in the dispensing unit. Suction piping not meeting these design requirements must use one of the following: tightness test of the piping every three years, groundwater or vapor monitoring, secondary containment, and interstitial monitoring or statistical inventory reconciliation.

There are three areas that had to be addressed by December 22, 1998, for existing tank systems to either be in compliance or be properly closed. The three areas and their required upgrades are described below:

1. Corrosion protection for tanks and piping must be provided by being constructed of non-corrodible material, having a corrosion-resistant coating, and having cathodic protection, or the steel tank can be clad with a thick layer of non-corrodible material (this option does not apply to piping). There are three other options that existing tanks could have chosen from to comply with the corrosion protection requirements:
   1. Add cathodic protection to a tank that was proven to be structurally sound. Cathodic protection can be provided by adding an impressed current system that protects the UST by introducing an electrical current into the soil around the UST. Cathodic protection systems must be periodically inspected and tested.
   2. Add interior lining, which is a thick layer of non-corrodible material, to the interior of the tank. This interior lining must be periodically inspected.
   3. Combine cathodic protection and interior lining. USTs using this option are not required to have the interior lining periodically inspected.
2. Spill protection must be provided by the addition of catchment basins to contain spills and the use of good filling practices when product is delivered to the USTs. Basically, a catchment basin is a bucket sealed around the fill pipe.
3. Overfill protection must be provided by following good filling practices and the installation of overfill protection devices. USTs must have one of the following devices that guard against overfills: automatic shutoff devices, overfill alarms, or ball float valves.

Steel piping must have cathodic protection. Piping made entirely of (or enclosed in) non-corrodible material does not need cathodic protection.

To properly close a UST:

• Notify DEQ’s Regulated Storage Tanks (RST) 30 days before closing. DEQ will provide you with the proper forms.
• Use a contractor licensed by DEQ for all closure procedures.
• Proper assessment of the tank excavation must be conducted to determine if the tank has leaked and damaged the environment. If the tank has leaked, appropriate notification must be given and corrective action must be taken.
• Proper closure procedures (according to a recommended code of practice) must be followed to assure the tank system is emptied, cleaned, assessed, and closed in a safe and correct manner.
• Follow the instructions in Guidelines for the Permanent Closure of Underground Storage Tank Systems.