Secondary containment: how to size a spill berm

A spill berm has to hold what can leak from the containers inside it, plus rain if it stands outdoors. How much that is depends on where the site is and what is stored. This guide summarises the main US, UK and German rules and works through the arithmetic.

Last reviewed 17 September 2026. This is a summary, not legal advice: check the current regulation text, your SPCC Plan or permit, and your local regulator.

Five steps to size a berm

Find the rule that applies to the site, the country and the liquid (sections below).
Work out the liquid volume the rule requires, from the container sizes.
Add room for rain if the berm is outdoors and uncovered, or plan to remove rainwater promptly.
Subtract displacement: anything standing inside the berm below the top of the wall takes up volume.
Choose the inner size and wall height that give at least that volume.

Capacity (US gallons) ≈ inner length (ft) × inner width (ft) × wall height (ft) × 7.48. For a wall height in inches, divide it by 12 first. Capacity (litres) = inner length (m) × inner width (m) × wall height (m) × 1,000. One US gallon is 3.785 litres; one imperial gallon is 4.546 litres.

United States: EPA SPCC

The Spill Prevention, Control, and Countermeasure (SPCC) rule, 40 CFR Part 112, applies to facilities that store oil above set thresholds. The duties fall on the facility, not on the containment product.

Rule	Applies to	Required capacity
40 CFR 112.8(c)(11)	Mobile or portable oil storage containers (drums, totes, portable tanks) at SPCC facilities, except mobile refuelers and other non-transportation-related tank trucks	Capacity of the largest single compartment or container, plus sufficient freeboard to contain precipitation
40 CFR 112.8(c)(2)	Bulk storage tank installations at onshore facilities (other than oil production)	Entire capacity of the largest single container, plus sufficient freeboard to contain precipitation
40 CFR 112.7(c)	General secondary containment duty at SPCC facilities; lists dikes, berms, curbing and drip pans among acceptable methods	Designed for the typical failure mode and the most likely quantity of oil discharged
40 CFR 264.175(b)(3)	Container storage areas at permitted hazardous waste facilities (RCRA), not oil SPCC	10% of the volume of containers or the volume of the largest container, whichever is greater

What “sufficient freeboard” means

The SPCC rule does not define it. EPA’s guidance for inspectors describes two common design approaches, neither of which is a legal requirement: sizing for the rain from a 25-year, 24-hour storm, and the rule of thumb of 110% of the container’s capacity. EPA notes that 110% may not be enough where storms are heavy. The owner or operator decides the freeboard for the site.

Worked example: drums on a portable berm

Four 55-gallon drums of hydraulic oil stand outdoors at an SPCC facility. Under 112.8(c)(11) the berm must hold the largest container, 55 US gallons, plus freeboard for rain.

Berm: 6 ft × 6 ft inner floor, 8 in walls = 180 US gallons geometric capacity.
The drums cover about 12 sq ft of floor, displacing 60 gallons below wall height.
Net capacity: about 120 gallons. After the 55-gallon drum, about 65 gallons are left, which is about 2.9 inches of rain falling on the berm.

Compare that rainfall depth with the design storm you use for the site. Where heavier rain is expected, choose a larger berm or higher walls, cover the berm, or remove rainwater promptly.

United Kingdom: oil storage regulations

England, Wales, Scotland and Northern Ireland each have their own regulations for storing oil. The capacity figures are the same in all four; who is covered differs.

Situation	Minimum bund or tray capacity
Single container (tank, IBC, mobile bowser)	110% of the container’s capacity
Several containers in one bund	110% of the largest container or 25% of the combined capacity, whichever is greater
Drums on a drip tray	25% of the drum capacity, or of all drums used with the tray together

Where the rules apply

England: The Control of Pollution (Oil Storage) (England) Regulations 2001. They do not apply to containers of 200 litres or less, containers inside a building or wholly underground, private dwellings with up to 3,500 litres, agricultural oil on farms, or refineries and oil distribution depots.
Wales: The Water Resources (Control of Pollution) (Oil Storage) (Wales) Regulations 2016. They cover containers over 200 litres and have no general exemption for containers inside a building. They do not apply to wholly underground containers outside buildings, storage covered by an environmental permit, oil distribution depots, refineries or certain existing domestic tanks.
Scotland: The general binding rules in Schedule 9 of the Environmental Authorisations (Scotland) Regulations 2018, which replaced the earlier oil storage regulations. Check SEPA guidance for which activities and exemptions apply.
Northern Ireland: The Control of Pollution (Oil Storage) Regulations (Northern Ireland) 2010. They cover containers over 200 litres, including indoor containers, but not private dwellings with up to 3,500 litres, agricultural oil on farms, wholly underground containers, or very large storage at major-hazard sites.

GOV.UK guidance adds that double-skinned or twin-walled tanks do not count as secondary containment.

Worked example: two IBCs in one bund

Two 1,000-litre IBCs of diesel stand together outdoors at a business in England.

110% of the largest container = 1,100 L; 25% of the total = 500 L. The larger figure applies: 1,100 L.
Bund: 3.2 m × 2 m inner floor, 400 mm walls = 2,560 L geometric capacity.
Each IBC stands on a 1.2 m × 1.0 m footprint. Counting that whole footprint up to the top of the wall as displaced, the two IBCs take up 960 L.
Net capacity: about 1,600 L, above the 1,100 L requirement. Rainwater is not included, so keep the bund drained or size it larger.

Worked example: drums on a drip tray

Four 205-litre oil drums are used together on one drip tray. The tray needs at least 25% of 820 L, which is205 L. Drums of 200 litres or less fall outside the English regulations, although a drip tray is still good practice.

Europe: national rules, not one EU rule

We have not found an EU-wide rule that sets bund capacity. Member states set their own, and the approaches differ.

Germany: AwSV

Installations handling water-hazardous substances need liquid-tight retention without drains, sized for the volume that can escape until safety measures take effect (§ 18).
Drum and container stores up to 100 m³ need retention of 10% of the total volume, and at least the largest container (§ 31).
Retention areas that are not covered need extra volume for rainwater (§ 19).

Other countries

In France and other member states, requirements depend on the type of installation and its permit. Ask your importer or local authority for the rule that applies before you fix a bund size.

Common questions

Does the EPA SPCC rule require 110% secondary containment?

No. For bulk storage tanks and portable containers, 40 CFR 112.8(c)(2) and (c)(11) require the capacity of the largest container plus sufficient freeboard for precipitation. EPA inspector guidance describes 110% as a common rule of thumb and warns that it may not hold the rain from larger storms.

Are spill berms EPA certified or EPA approved?

No. The SPCC rule places the duty on the facility owner or operator, and EPA does not certify containment products. A berm helps meet the rule when it is sized and maintained for the containers it serves.

Who has to follow the SPCC rule?

Broadly, non-transportation facilities that could reasonably discharge oil to US waters and store more than 1,320 US gallons of oil above ground, counting only containers of 55 gallons or more, or more than 42,000 gallons in completely buried storage. See 40 CFR 112.1 for the full applicability rules.

Does the UK 25% drum rule apply to every drum?

No. In England the oil storage regulations do not apply to containers of 200 litres or less, to containers inside a building, or on private dwellings with up to 3,500 litres. Wales, Scotland and Northern Ireland have their own regulations with different exemptions.

Is there one EU rule for bund capacity?

We have not found an EU-wide sizing rule; each member state sets its own. Germany, for example, sizes retention under the AwSV for the volume that can escape before safety measures take effect, and requires extra volume for rain where the retention area is not covered.

Sources

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