Have you taken a good look at the tank integrity program described in your facility’s Spill Prevention Control and Countermeasure (SPCC) plan? Does your tank integrity testing program still reference a 2004 U.S. Environmental Protection Agency (EPA) document in lieu of an industry standard? If so, it may be time to give your tank integrity testing program a facelift.

Since 2003, the Steel Tank Institute (STI) SP001 has gradually become the industry standard for tank integrity testing of shop-fabricated tanks. While some facilities have avoided incorporating the standard into their program, the requirements of STI SP001 are actually very similar to the concepts in the 2004 EPA letter.

Incorporating Initial Standards

Let’s briefly review how facilities began to incorporate the 2004 EPA methodology into their SPCC plans in the first place. In the SPCC regulations first proposed in 2002 and finalized in January 2010, 40 CFR 112.8(c)(6) added a requirement for regular tank integrity testing in accordance with industry standards on aboveground storage containers with oil-containing capacity greater than 55 gallons. Integrity testing is a way to determine the structural soundness of the storage container and its ability to continue to store oil. For example, unidentified tank corrosion on an older storage tank could lead to an inadvertent release of oil.

Many industry standards at the time required tank integrity testing by a certified inspector, which can be expensive. Not surprisingly, many facility owners with multiple small storage tanks were not content with the new regulation.

Consequently, a 2004 letter from EPA to the president of the Petroleum Makers Association of America, as well as a 2005 version of EPA's SPCC Guidance for Regional Inspectors, addressed the matter. In those documents, the EPA proposed this method as an environmental equivalent to tank integrity testing: If a shop-built container had a capacity of 30,000 gallons or less and was elevated so all sides were visible, or a non-permeable barrier was located between the tank and container, with a licensed professional engineer's certification, visual inspections could be considered environmentally equivalent to non-destructive tank integrity testing methods.

Many companies chose to work with professional engineers to incorporate this approach in their SPCC plans to avoid the requirements of hiring a certified inspector to conduct visual external tank inspections, or the more burdensome out-of-service internal inspections, on small storage tanks. Now that the SPCC regulations have been finalized and STI has a well-established industry standard, referencing the methodology discussed in the 2004 EPA letter has become outdated. EPA revised the integrity testing regulation in 40 CFR 112.8 in 2008 to allow inspection requirements outlined in industry standards without the need for an environmental equivalence determination by a PE. While the current SPCC regulations do not stipulate which industry standards should be followed for a facility’s tank integrity testing program for shop-fabricated tanks, today STI SP001 is considered good engineering practice. It should be noted that the 2004 environmental equivalence approach is still valid, so long as the environmental equivalence determination is certified by a PE.

Developing Three Categories

STI SP001 was issued in 2003, and last revised in January 2018, to provide a standard for the inspection of shop-fabricated tanks with storage capacities of 30,000 gallons or less. STI SP001 provides an inspection schedule for shop-fabricated storage tanks based on risk; the highest risk tanks require the most inspections. The standard sorts tanks into three categories based on container capacity and the presence of spill control, a continuous release detection method (CRDM), and a release prevention barrier (RPB).

  • Category 1 tanks are the lowest risk and have spill control and CRDM.
  • Category 2 tanks have spill control.
  • Category 3 tanks are the highest risk and do not have spill control.

If a tank is a Category 3 tank, it is not compliant with the sized secondary containment requirements in 40 CFR 112.8. To understand the tank categories specified in STI SP001, one must understand CRDM and spill control.

CRDM is a passive means of “detecting a release of liquid through inherent design” and allows a release to be visually detected. The standard identifies CRDMs to include an aboveground storage tank of double-wall construction, an elevated tank, a storage tank located within a steel containment dike, or a containment area with a release prevention barrier (RPB). An RPB is a nonpermeable barrier (concrete, steel, liners) installed beneath the storage container and the ground with the purpose of diverting a release toward the container’s perimeter for easy detection. Earthen materials do not meet the requirements of a CRDM.

Spill control is the container’s secondary containment and can include an earthen berm, steel or concrete containment dike, closed-top steel dike with overfill protection, double-walled tank with overfill protection, or concrete exterior tank with overfill protection. While overfill protection would ideally consist of high-level alarm or automatic shutoff devices, having an individual present to manually control a shutoff device while filling a tank is acceptable.

Examples of Category 1 tanks include horizontal or vertical tanks in steel or concrete containment dikes, an elevated horizontal tank placed over a secondary containment structure, and a tank of double-walled construction. An example of a Category 2 tank is a storage tank located within earthen berm containment. A Category 3 tank is simply a tank without secondary containment.

STI SP001 uses the tank category and capacity to suggest inspection schedules for shop-fabricated tanks, including periodic inspections by the owner’s inspector, formal internal and external inspections by a certified inspector, and formal leak testing by an owner’s designee. If facility personnel are familiar with tank inspection procedures, the owner’s inspector can be someone who works at the facility.

Conducting Appropriate Inspections

Suggested annual and monthly inspection forms are included in the standard. A certified STI inspector has undergone extensive training and passed an exam. Certified API 653 inspectors may only qualify as a certified STI inspector if they have also received STI certification. Monthly, the inspector will examine the tank, piping, tank equipment and secondary containment. On an annual basis, the inspector will examine the tank foundation, as well as its shell/heads/roof and manways/piping/equipment. Inventory and release detection procedures are also examined annually. Many facilities that are following STI SP001 combine the requirements of the monthly and annual inspections into one monthly inspection for simplicity.

Many of the tanks at facilities throughout the nation tend to be in Category 1. For Category 1 tanks with capacities of 5,000 gallons or less, monthly and annual visual inspections are required. If Category 1 tanks have a capacity from 5,001-30,000 gallons, the monthly and annual visual inspections are required, in addition to an external inspection by a certified inspector every 20 years. These requirements are very similar to the requirements of the 2004 EPA document, with the additional preventive measure of having a certified inspector inspect the storage tank. If a shop-fabricated tank has been stored outside for 20 years, it might be more effective to replace the tank.

Storage tanks sitting on a concrete foundation within an earthen containment area with no lining are considered Category 2 tanks because they do not have a CRDM. If these tanks have capacities of 1,100 gallons or less, the monthly and annual inspections are all that is required. Because of the greater risk of a release to the environment not being easily detected from one of these tanks, Category 2 tanks with capacities of 1,101-30,000 gallons require more frequent certified internal and external inspections.

The standard also addresses the integrity of portable steel containers, such as drums. Drum storage areas require monthly inspections. A suggested monthly inspection form is included in the standard and includes documentation that the drum and containment areas are in good condition.

While STI SP001 imposes some burdens on facilities, it’s a better choice and good engineering practice to follow an industry standard rather than use the 2004 environmental equivalence approach. In some instances, it will encourage facilities to improve containment for tanks or consider replacing Category 3 tanks.


Developing and following an SPCC program can be critical to environmental protection and compliance, but many facilities fall short of what’s necessary. Read more about how to implement SPCC.

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Amy Reed, PE, is an associate environmental engineer, compliance audit team member and project manager at Burns & McDonnell. A chemical engineer by training with over 20 years of experience, she specializes in helping industrial and utility clients comply with EPA regulations.