Oil Containment
North America's Premier Oil Containment Association | 1,847+ Members | SPCC Compliance, Foam Berms & Containment Technology
Secondary containment, sized and proven
A dike that has not been calculated is a decoration. This is how capacity, freeboard and barrier selection are actually worked out, and what an inspector will ask you to show.
What sized containment means
40 CFR 112.8(c)(2) requires bulk storage containment to hold the capacity of the largest single container plus enough freeboard for precipitation. Industry practice, and most state programs, settle on 110% of the largest vessel.
Capacity
Largest single container, not the sum of all of them – plus displacement from every other tank and foundation inside the dike.
Freeboard
Enough additional depth for the 25-year, 24-hour storm at your location, unless the area is drained under an engineered procedure.
Demonstration
A written calculation in the plan. An inspector asks for the number and the basis, not a photograph of a wall.
Work out your required capacity
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Secondary containment sizing
SPCC sizing for a single-tank containment area — 110% of the largest vessel plus rainfall freeboard.
Planning aid only. 40 CFR 112 requires a sized, engineered design; most SPCC plans must be certified by a licensed P.E.
What to line it with
Permeability is only half the question. The other half is what happens at the joints, in the cold, and under a truck.
| Barrier | Seams | Elongation | Cold limit | Drive-over | Repairable in place |
|---|---|---|---|---|---|
| Spray polyurea | None | 300-600% | -60°F | ✓ | ✓ |
| Reinforced PVC liner | Heat-welded | 200-350% | 10°F | ✗ | ✓ |
| HDPE geomembrane | Fusion-welded | 500-700% | -40°F | ✗ | ✓ |
| Concrete, sealed | Control joints | Negligible | -40°F | ✓ | ✗ |
| Compacted clay | None | Negligible | Varies | ✓ | ✗ |
Typical values for containment-grade systems. Confirm against the manufacturer data sheet for your specific product.
The five failures we keep investigating
Nobody deducted displacement
Every additional tank, pump skid and foundation inside the dike takes volume away from the containment. On congested pads this routinely costs 10-15% of nominal capacity.
The drain valve was left open
A containment area with an open gravity outfall is not containment. Valves stay locked closed and are opened only under a written, logged procedure after inspection of the water.
The coating was sprayed below dew point
Condensation on the substrate is invisible and fatal to adhesion. Substrate temperature must be at least 5°F above the dew point through the whole application window.
Penetrations were never detailed
Pipe penetrations, conduit and anchor bolts are where liners leak. Each one needs a detail, and each one needs to be on the inspection route.
The wall was never re-checked after a tank change
Swapping in a bigger tank changes the required capacity. The plan is amended within six months of any change that materially affects discharge potential.
Monthly walk-around checklist
Tick these off as you go. Your progress is remembered in this browser.
Secondary containment inspection
0/10Frequently asked
Is it 100% or 110% of the largest tank?
The federal rule says the capacity of the largest single container plus sufficient freeboard for precipitation. It does not name a percentage. 110% is the convention that satisfies that wording in most climates, and several state programs require it outright. In a high-rainfall region 110% may still be short – run the storm number.
Do I count every tank in the dike?
For required capacity, no – only the largest single container. For available capacity, yes: every other tank and foundation displaces volume you would otherwise have.
Can I use a liner under gravel?
Yes, and it is common for transformer and fire-rated containment. Specify a cushion geotextile above and below the liner, and accept that inspection becomes indirect – you are relying on the outfall sample rather than a visual check.
How often must containment be inspected?
The rule requires inspections on a written schedule with records kept for three years. Monthly visual inspection plus an annual documented condition assessment is what most member facilities run.
Does a self-certified Tier I plan still need sized containment?
Yes. Tier I changes who signs the plan, not what the plan requires. Any deviation from the standard containment requirements needs a P.E.
Have the committee review your sizing
Members can submit a tank schedule and site plan for a no-cost technical review. We will tell you whether the calculation holds up before an inspector does.