Guide to SPCC Containment Requirements (40 CFR 112)

Who Needs an SPCC Plan

An SPCC plan is required for any facility that meets all three of the following criteria: (1) the facility stores oil in containers or tanks, (2) the total aboveground oil storage capacity exceeds 1,320 gallons in aggregate, and (3) the facility could reasonably be expected to discharge oil into navigable waters of the United States or adjoining shorelines. The third criterion is broadly interpreted. If your facility has storm drains, ditches, or any drainage path that connects (however indirectly) to a stream, river, lake, or wetland, you meet it.

Containers counting toward the 1,320-gallon threshold include: aboveground storage tanks (ASTs), drums (55 gallons each), IBCs (totes), day tanks, transformers containing oil, and hydraulic reservoirs. Containers smaller than 55 gallons are exempt from the count. Underground storage tanks (USTs) have a separate 42,000-gallon threshold and are subject to different containment rules under 40 CFR 280.

Common facilities that trigger SPCC requirements include: farms with diesel and gasoline storage, manufacturing plants with hydraulic oil and lubricant storage, power generation facilities with fuel and transformer oil, fleet maintenance operations with used oil tanks, and construction yards with fuel storage for equipment. Even a facility with twenty-four 55-gallon drums of oil (1,320 gallons) needs a plan.

Secondary Containment: The 110% Rule

The core SPCC containment requirement is that secondary containment must be sized to hold the contents of the largest single tank within the containment area, plus a sufficient allowance for precipitation. The industry-standard interpretation is 110% of the largest tank volume, which provides a nominal margin for rainfall. Some state regulations require larger containment (125% is common in several states).

When multiple tanks share a common containment area, the containment must hold the volume of the largest single tank, not the sum of all tanks. The reasoning is that a simultaneous failure of multiple tanks is not a credible scenario. However, the containment must also accommodate the displacement volume of any other tanks, equipment, piping, and structural supports within the diked area.

The net containment volume is the gross volume of the diked area minus the displacement volume of all objects inside it: other tanks, pipe supports, pumps, and foundations. The formula is: Net Volume = (Length × Width × Wall Height) − Σ(displacement of each object). The net volume must be ≥110% of the largest tank.

For areas with significant rainfall, additional freeboard may be needed. EPA recommends accommodating the 25-year, 24-hour rainfall event in addition to the 110% tank volume. In areas like the Gulf Coast where this event can exceed 8 inches, the precipitation allowance significantly increases the required containment size.

Dike and Berm Design Considerations

Secondary containment is most commonly provided by earthen dikes, concrete curbs, or prefabricated steel berms. Each approach has advantages depending on the tank size, site conditions, and budget.

Earthen dikes are the most common for large tank farms. The dike must be constructed of compacted, impervious material (clay or clay-lined soil). Dike walls are typically 2 to 6 feet high with 2:1 or 3:1 side slopes for stability. The floor of the diked area should be graded to drain toward a sump or low point for water removal. Earthen dikes require regular maintenance, as burrowing animals, root growth, erosion, and freeze-thaw cycles can compromise impermeability.

Concrete containment is preferred for smaller tanks, drum storage areas, and locations where earthen dikes are impractical. Concrete floors and curbs provide excellent impermeability and are easy to inspect. Joints must be sealed with oil-resistant caulk or expansion joint material. Concrete containment areas need a drain valve for rainwater removal. The valve must remain closed except during active, attended drainage.

Prefabricated berms (flexible spill containment systems) are used for temporary storage, portable tanks, and construction sites. They consist of a chemically resistant liner with foam or rigid walls. Prefabricated berms must be inspected for tears, punctures, and chemical degradation before each use.

Inspections, Plans, and PE Certification

SPCC plans require regular inspections of all oil storage containers, containment systems, and associated piping. The inspection frequency depends on the equipment type: bulk storage tanks require monthly visual inspections, integrity testing on a schedule appropriate to the tank material and age (typically API 653 for steel ASTs), and annual review of containment condition.

Tier I plans (self-certified) are available for facilities that meet all of the following: total aboveground oil storage capacity of 10,000 gallons or less, no single container larger than 5,000 gallons, no history of reportable spills in the past 3 years, and no discharge to navigable waters. A Tier I plan can be prepared and self-certified by the facility owner/operator without a Professional Engineer (PE).

Tier II plans and all plans that do not qualify for Tier I must be certified by a licensed Professional Engineer (PE). The PE reviews the plan, inspects the facility, and certifies that the plan meets all SPCC requirements. The PE certification must be renewed whenever the plan is amended due to facility changes.

Plan amendments are required within 6 months of any facility change that affects oil storage or spill potential: new tanks, relocated tanks, changes in containment, new oil types, or changes in facility drainage. Plans must also be reviewed and recertified at least every 5 years, even if no changes have occurred.