Secondary containment requirements: what your facility must meet

If your site stores oil or hazardous materials, secondary containment is the barrier that catches a spill before it reaches soil, storm drains, or navigable waters. Federal rules require it as a baseline. Miss the mark on sizing, materials, or inspections, and a single tank failure becomes a reportable discharge with penalties attached.

This guide breaks down the secondary containment requirements that apply to most industrial facilities: which regulations govern them, how to size a system correctly, and what inspectors look for. IRONCLAD Powered by Mersino builds and deploys containment systems across refineries, chemical plants, construction sites, and pipeline operations, so this reflects what holds up on real job sites.

What secondary containment does

Primary containment is the tank, drum, or tote holding the liquid. Secondary containment is everything built to catch that liquid if the primary fails: berms, dikes, liners, sumps, and containment pallets. The goal is to hold spilled liquid inside a controlled area long enough to recover it.

Two things make containment count as compliant: enough capacity to hold a worst-case release, and a surface that holds the liquid instead of letting it seep away. Bare earth rarely qualifies on its own.

Which regulations set the requirements

Three federal frameworks cover most facilities. State and local rules can add more on top.

EPA SPCC rule (40 CFR part 112)

The Spill Prevention, Control, and Countermeasure rule applies to facilities that store oil where a spill could reach navigable waters. The rule applies once a facility's aboveground oil storage tops 1,320 gallons, or once completely buried storage tops 42,000 gallons. Only containers of 55 gallons or larger count toward the aboveground total, measured by each tank's full shell capacity rather than how much oil is in it at the time. Aboveground, twenty-four 55-gallon drums are enough to cross the line.

RCRA hazardous waste standards (40 CFR 264.175)

If you store hazardous waste in containers, the Resource Conservation and Recovery Act sets its own containment standard. Size the containment to whichever is larger: 10 percent of the combined volume of all the containers, or the full volume of the single largest container. Because that formula isn't the same as the SPCC calculation, a site storing both oil and hazardous waste has to size each area separately.

OSHA (29 CFR 1910.120)

OSHA's standards govern worker safety during spill response rather than containment sizing. They cover how people handle a release once it happens: the training crews need before they respond, the protective equipment they wear, and the emergency response plan the site keeps on file. Employees expected to stop or clean up a hazardous spill generally need documented HAZWOPER training, and the level of training scales with the role they play in the response. So while SPCC and RCRA tell you how to build and size containment, OSHA tells you what has to be true about the people standing next to it. All three belong in the same planning conversation.

How to size secondary containment

Under SPCC, sized containment for bulk storage has to hold the full volume of the largest single container in the area. You size for the biggest tank, not the sum of every tank in the berm. If the area sits outdoors, it also has to hold enough extra room, called freeboard, to capture rain that collects in the containment.

This is where the familiar '110 percent' figure comes from: 100 percent of the largest container, plus a 10 percent cushion for precipitation. But that 10 percent is a common design convention, not a number written into the rule. The EPA doesn't require a specific freeboard method, and many engineers size it to a 25-year, 24-hour storm instead, which in wet regions can call for far more than 10 percent. Check the design storm for your location before settling on a number.

A quick reference:

• Oil, single tank in a berm (SPCC): largest container volume plus freeboard, commonly designed at 110 percent
• Hazardous waste containers (RCRA): 10 percent of all containers combined, or the largest container, whichever is greater
• Outdoor areas: add freeboard for the local design storm, not a flat 10 percent

You do not need a separate containment structure for every drum. One shared system sized to the largest container meets the requirement.

Materials and impermeability

Capacity means nothing if the liquid drains out the bottom. SPCC calls for containment that holds a discharge until it can be cleaned up, which rules out unlined earthen berms in most cases. A chemically compatible liner is the accepted way to make an area sufficiently impervious, and liner selection has to match the product being stored. A liner that resists diesel may fail against a solvent.

The same logic applies to prefabricated options. Steel and poly containment, frac tanks, and portable berms all carry known capacities and material ratings, which takes the guesswork out of proving compliance.

Double-walled tanks and alternative designs

A double-walled tank builds secondary containment into the tank system itself. The inner and outer shells form a monitored space, and a leak detection system flags a breach before hazardous liquid escapes. The EPA recognizes qualifying double-walled tanks as meeting the containment requirement for the tank, which suits sites tight on space or storing a hazardous chemical a standard berm cannot safely hold. Where standard containment is impracticable, SPCC also allows an alternative design, as long as a professional engineer certifies it in the facility's plan.

Inspection and drainage

Containment is not a set-and-forget install. Outdoor systems collect rainwater, and that water has to be checked for sheen before it is drained. Under SPCC, you inspect accumulated stormwater, confirm it is clean, drain it through a controlled valve, and keep records of every drainage event. Skipping the paperwork is its own violation, separate from any spill.

Build a routine around it:

• Inspect containment areas and stormwater accumulation on a regular schedule
• Keep drainage valves closed and locked between controlled releases
• Log each inspection and drainage event with date and observation
• Recheck sizing whenever you add tanks or change what you store

RCRA container storage areas call for weekly inspections, and facility personnel should be trained on the drainage and response steps before they are needed.

Containment options for the field

Fixed berms work for permanent tank farms. Temporary and mobile work needs assets that arrive rated and ready. That is where rental containment earns its place: turnarounds, emergency response, remediation, and construction dewatering all need capacity fast, without pouring concrete.

Ironclad's fleet covers the common cases:

• Frac tanks for bulk liquid storage with known capacities
• Vacuum and roll-off boxes for solids and sludge
• Spill containment berms for equipment staging and temporary storage
• Emergency response support when a release is already underway

With the largest specialty containment fleet in the United States and branches nationwide, Ironclad can size, deliver, and set up the right system before a compliance gap turns into a discharge.