40 CFR 112.8 · 264.175 · EPA Vic 1698

Secondary containment and bund calculator

Size the bund before the drums arrive, not after the spill.

Enter the containers stored in one area and your bund size to get the minimum containment volume under the US and Australian rules, in litres and gallons, with a pass or fail for each.

Last updated 2026-09-28. Math runs in your browser, no data leaves your computer.

Work one bund, spill pallet or storage area at a time, and list every container that drains into it. A 208 litre drum is a 55 US gallon drum, and a standard IBC is 1,000 litres, but use the capacity on the container's own marking where you have it.

Units

Containers in this bund

Enter the count and the capacity of each container in gallons, one size per line, because every rule turns on the largest single container as well as the total.

Pick packages for drums and IBCs, because the Australian package store rules scale with the total stored while the tank rules follow the largest tank.

Leave 0 for a roofed or indoor bund. For an open one, EPA suggests the 24-hour 25-year storm for the site, which NOAA and local water authorities publish.

The bund dimensions below are optional. Add them to check a bund you already have, or leave them blank to get the minimum volume only.

Measure inside the walls, since the wall thickness holds nothing and the rain volume uses the same floor area.

Use the inside width at the floor, which is the conservative figure where the walls lean or taper.

Take the lowest point of the wall or the sill at a doorway, because the spill leaves at the lowest point.

Enter the volume of everything below the wall top except the container that fails, as EPA Victoria 1698 and the SPCC worksheets both deduct it.

Before the booking, screen the name on the invoice. Shipment pre-check is on the paid plans, from USD 59 a month.

General guidance only. Verify against the cited primary sources before you commit to a shipment, declaration, or contract.

The five sizing rules side by side

RuleApplies toMinimum volume
40 CFR 112.8(c)(2), SPCCOil in containers of 55 US gallons or more at a facility over 1,320 gallonsLargest single container plus freeboard for rain
40 CFR 264.175(b)(3), RCRAHazardous waste container storage areasGreater of 10% of all containers with free liquids or the largest container
EPA Victoria 1698Liquid storage in Victoria, used as a guide elsewherePackages: greater of 25% of total or 110% of largest. Tanks: 110% of largest plus 10% of the second largest
AS 1940:2017 clause 4.4.3(d)Flammable and combustible liquid package stores100% of largest package plus 25% of capacity to 10,000 L, 10% from 10,000 to 100,000 L, 5% above
AS 3780:2023 clause 4.4(a)Corrosive substance package storesGreater of 25% of total or the largest container, capped at 5,000 L where only packages are kept

The SPCC rule in 40 CFR 112.8(c)(2) sets no number for the rain allowance. The tool follows the method in EPA's secondary containment worksheets: rainfall depth times the bund floor area, added to the largest container. The RCRA line adds the same rain figure only as an allowance, because 264.175(b)(4) asks you to keep run-on out or hold extra capacity for it.

The EPA Victoria figures come from publication 1698, pages 22 to 26, where the 10 percent freeboard and the 10 percent of the second largest tank are suggested minimums. The AS 1940 and AS 3780 lines follow the clause text as quoted by Storemasta, because Standards Australia sells the standards and Sourzi has not checked a licensed copy. Treat those two lines as a guide until you do.

Your bund's available volume is length times width times wall height, less the displacement you enter. Conversions use 1 US gallon = 3.785 litres and 1 cubic foot = 7.48 US gallons, the same 0.1337 cubic feet per gallon EPA's worksheet uses.

Worked example. The open bund that forgot the rain

The booking. A US plant keeps two 330 gallon IBCs and twelve 55 gallon drums of hydraulic oil in an open bund 12 ft by 10 ft with 8 inch walls. The bund holds 12 × 10 × 0.667 = 80 cubic feet, or 598 gallons, and the drums and the second IBC take up about 18 cubic feet, or 135 gallons, below the wall top. That leaves 463 gallons against a largest container of 330 gallons, or 140 percent, which looks fine on paper.

The failure. 40 CFR 112.8(c)(2) also wants freeboard for rain. If the site's design storm is 5 inches, rain on 120 square feet adds 50 cubic feet, or 374 gallons, so the bund needs 330 + 374 = 704 gallons and holds only 463. The choice is simple: keep the rain out, or build a bigger bund.

The fix. The plant puts a roof over the bund with enough overhang to keep driving rain off the floor, which EPA Victoria also recommends. With no rain allowance the requirement drops back to 330 gallons, and the 463 gallons on hand pass with room to spare, while the SPCC plan records the roof as the reason.

Storing solvents in the bund rather than oil? The flammable liquid storage limit calculator tells you how many cabinets or what size of inside storage room OSHA allows, and the chemical storage compatibility chart shows which drums should never share one bund.

Frequently asked

How do you calculate secondary containment capacity?

Work out the rule's required volume from the containers stored, then work out what the bund really holds: length times width times wall height, less the space the containers and plinths take up below the top of the wall. Under the US SPCC rule the required volume is the largest single container plus freeboard for rain, per 40 CFR 112.8(c)(2). The bund passes when the available volume is at least the required volume.

Is 110 percent a legal requirement for SPCC containment?

It is not a legal figure. EPA's own SPCC worksheet example says the rule does not set a method or a storm size for the rain allowance, that industry often uses 110 percent of the tank as a rule of thumb, and that 110 percent may not be enough in a wet area. EPA suggests a 24-hour 25-year storm if you want a conservative figure, which is why the tool asks for a rainfall depth.

What is the RCRA secondary containment rule for drums of hazardous waste?

For a hazardous waste container storage area, 40 CFR 264.175(b)(3) requires capacity for 10 percent of the volume of the containers or the volume of the largest container, whichever is greater. Containers with no free liquids are left out of the sum. Run-on has to be kept out, or the system needs extra capacity for it on top of that figure.

What bund capacity does Australia require?

The free official guide is EPA Victoria publication 1698, which asks for 25 percent of the total stored or 110 percent of the largest container, whichever is greater, for drum stores, and 100 percent of the largest tank plus suggested allowances for bulk tanks. AS 1940 for flammable liquids and AS 3780 for corrosives set their own package store rules, and the tool runs both as quoted by a supplier, because the standards themselves are paid documents.

Do the containers inside the bund reduce its capacity?

They do, and by a lot. Any drum, IBC, tank or plinth that sits below the top of the bund wall takes up space a spill cannot use. EPA Victoria spells this out as calculated volume less the volume taken up by the containers, and the SPCC worksheets for several tanks in one dike subtract the displacement of every tank except the one that fails. Enter that figure in the displacement box.

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Sourzi shows what official files say. It is not customs or legal advice. For a binding answer, ask a licensed customs broker, a CBP ruling or an Australian Border Force Tariff Advice.

File dates and links are on Data sources.