SPCC plan template › SPCC secondary containment
SPCC secondary containment requirements
The SPCC rule asks for two kinds of containment. Every bulk storage container (tanks, drums and totes of 55 gallons or more) needs sized containment: room for the entire capacity of the largest single container plus enough freeboard for rain. Everywhere else oil could escape, such as transfer areas, piping and equipment, you need general containment sized for the most likely spill.
General vs sized containment
| General containment | Sized containment | |
|---|---|---|
| Rule | 112.7(c) | 112.8(c)(2) for fixed tanks, (c)(11) for drums, totes and portable tanks; 112.6(a)(3)(ii) at a Tier I site |
| Where | Any part of the facility where oil could be discharged: loading and unloading areas, piping, pumps, oil-filled equipment, drum handling | Bulk storage containers, except mobile refuelers and other tank trucks used only on site |
| How big | The typical failure mode and most likely quantity of oil | Entire capacity of the largest single container plus sufficient freeboard for precipitation |
| Active measures allowed? | Yes: spill kits, sorbents, drain covers, if they can be deployed in time | Rarely: EPA's guidance says active measures for larger containers may not meet good engineering practice, so dikes, curbs, pits or double walls are the norm |
Section 112.7(c) lists acceptable methods for onshore facilities: dikes, berms or retaining walls sufficiently impervious to contain oil; curbing or drip pans; sumps and collection systems; culverting, gutters or other drainage systems; weirs, booms or other barriers; spill diversion ponds; retention ponds; and sorbent materials. The whole system, walls and floor, must hold oil long enough for cleanup.
What "sufficient freeboard" means
The rule doesn't define it. In 2002 EPA said the proper standard is room for a 25-year, 24-hour storm, but chose not to make it binding, so its own inspector guidance calls that standard "not enforceable." The guidance adds that a 110 percent of the largest tank rule of thumb "may be an acceptable design criterion in many situations," that many state tank rules require at least 110 percent, and that in wet climates 110 percent may not hold a real storm. Some states require you to design for storm events. Where rainfall data are available, EPA suggests considering the 25-year, 24-hour storm anyway; NOAA publishes those depths by location in its precipitation frequency atlas.
Worked example: one tank in a dike
A 1,000-gallon vertical diesel tank in a concrete dike with a 10 ft by 8 ft floor. One cubic foot holds 7.48 gallons.
Tank volume: 1,000 gal ÷ 7.48 = 133.7 ft³ Wall height for the tank alone: 133.7 ft³ ÷ 80 ft² = 1.67 ft (20.1 in) At 110%: 1,100 gal ÷ 7.48 = 147.1 ft³ ÷ 80 ft² = 1.84 ft (22.1 in) For the tank plus a 4 in storm: 20.1 in + 4 in = 24.1 in
A 2-foot wall (24 in) meets the 110 percent rule of thumb. Whether it holds your 25-year storm depends on your rainfall: if that storm drops more than about 3.9 inches in a day, build higher.
Worked example: two tanks sharing a dike
When other containers sit inside the same dike, their footprint takes space the spilled oil can't use. EPA's own worksheets and its inspector guidance (Figure 4-6) subtract that "displacement" before checking freeboard.
Add a 500-gallon vertical tank, 4 ft across, to the dike above and raise the walls to 2.5 ft.
Gross dike volume: 10 × 8 × 2.5 = 200 ft³ = 1,496 gal Displacement of the 500-gal tank: (π × 4² ÷ 4) × 2.5 = 31.4 ft³ = 235 gal Net capacity: 1,496 − 235 = 1,261 gal (126% of the 1,000-gal tank) Freeboard left: 261 gal = 34.9 ft³ ÷ 80 ft² = 0.44 ft (5.2 in of rain)
The largest tank still governs; the smaller tank only shrinks the room. Tanks that are permanently manifolded so they work as one unit count as one container, so their combined capacity is the "largest single container."
The rule doesn't make you show these numbers in the plan, but EPA's worksheet page says to keep the calculations so you can show an inspector. EPA publishes four blank worksheets (single vertical tank, multiple horizontal tanks, remote impoundment, new construction) that assume a flat floor and square corners.
Worked example: general containment at a transfer area
For a hose or pump, size containment from the failure you expect. EPA's guidance (Figure 4-10) uses a delivery truck pumping heating oil at 150 gallons a minute, with an attendant who can close the valve within 15 seconds of a hose rupture: 150 ÷ 60 × 15 = 37.5 gallons, so the measure must hold at least that much, more if the shutoff takes longer.
Spill kits and sorbents: know their limits
Active measures count for general containment only if your crew can deploy them before oil reaches water. EPA's guidance warns that most commercial spill kits handle about 150 gallons, and a single "high-capacity" sorbent pad absorbs less than 0.7 gallons: a 600-gallon spill would take more than 900 pads. Write in the plan where kits are kept, how much they hold, and who deploys them.
Common setups and how EPA treats them
- Double-walled tanks. Still subject to secondary containment, but the outer wall serves as it. EPA's guidance says shop-built double-walled tanks of any size may generally meet both the general and the sized requirement, with overfill protection such as alarms or flow shutoff and watched transfers. The outer wall doesn't catch an overfill out of the vent, so plan for that during deliveries.
- Earthen and clay berms. EPA's farm answers say an unlined clay dike or berm that holds the largest tank is sufficient protection, as long as it's impervious enough to hold oil until cleanup. Size it for rain on top, like any dike.
- Loading racks. If tank trucks or rail cars load or unload at a rack, its containment must hold at least the largest single compartment of a truck or car loaded there (112.7(h)(1)). Tier I plans skip this rule.
- Drums and totes. Spill pallets and containment sheds count, sized for the largest drum or tote on them plus room for rain if they're outside.
- Vaults. Whoever prepares the plan must decide whether the vault meets 112.7(c), including any drains or sump pumps that could carry oil out.
- Oil-filled equipment. Transformers, hydraulic systems and similar equipment with a clean three-year record may skip containment under 112.7(k), if the plan sets out an inspection or monitoring program, an oil spill contingency plan under part 109 and a written commitment of manpower, equipment and materials.
Draining rainwater out of a dike
Diked areas must drain through manual open-and-closed valves, never flapper valves; pumps must be started by hand after checking the water (112.8(b)). If rainwater from the dike goes to a storm drain or open water rather than a treatment system, keep the bypass valve sealed closed, inspect the water for sheen before releasing it, open and reseal the valve under supervision, and keep a record of each event (112.8(c)(3)). EPA's Tier I template has a dike drainage log for this in Attachment 3.3.
When containment isn't practicable
If you can't build containment somewhere, 112.7(d) lets the plan explain why and use an oil spill contingency plan plus a written commitment of manpower, equipment and materials instead; for bulk storage containers you also need periodic integrity testing of the containers and integrity and leak testing of their valves and piping. Only a PE may make that call: a Tier I plan can't contain it at all, and in a Tier II plan a PE must certify that section in writing (112.6(b)(4)).
ePlan's SPCC draft lists each container with the containment you describe and flags any without it; it doesn't size dikes for you or replace a PE where one is needed. The inspection checklist covers what to look at in the dike every month.
Questions
Does the SPCC rule require 110% secondary containment?
No. It requires the entire capacity of the largest single container plus sufficient freeboard for precipitation. EPA's guidance calls 110 percent an acceptable rule of thumb in many situations, and many state rules require it, but in wet places it may not be enough.
Do 55-gallon drums need secondary containment?
Yes. A 55-gallon drum is a bulk storage container, so under 112.8(c)(11) (or 112.6(a)(3)(ii) at a Tier I site) it needs containment that holds the largest drum or container in the area, plus freeboard if it's exposed to rain.
Do double-walled tanks need secondary containment?
They're subject to the requirement, but the outer wall usually meets it. EPA expects overfill protection and monitored transfers along with it.