Secondary containment is a backup barrier that catches and holds oil, chemicals or hazardous waste if the primary container, such as a tank, drum or pipe, leaks or fails. Common examples include berms and dikes around tanks, spill pallets under drums, double-walled tanks and containment curbs around loading areas.
Secondary containment matters because tanks and containers eventually leak, overfill or get struck by equipment. A well-designed and maintained containment system keeps a spill from reaching soil, storm drains and waterways, which protects the environment and avoids costly cleanups and enforcement.
What Is Secondary Containment?
Primary containment is the container that normally holds a liquid. Secondary containment is the second layer of protection that holds the liquid if the first layer fails. Federal rules require secondary containment in several situations, most notably under EPA's Spill Prevention, Control, and Countermeasure (SPCC) rule for oil and RCRA rules for hazardous waste tank systems and storage facilities. OSHA's flammable liquids standard and fire codes also include requirements for diking or spill control around certain tanks.
Containment can be active, such as spill kits, sorbent booms or drain covers deployed when a spill happens, or passive, such as permanent dikes and double-walled tanks that work without anyone taking action.
SPCC Secondary Containment Requirements
The SPCC rule in 40 CFR Part 112 applies to non-transportation-related facilities that store more than 1,320 gallons of oil in aboveground containers (counting only containers of 55 gallons or more), or more than 42,000 gallons in completely buried tanks, and that could reasonably be expected to discharge oil to navigable waters or adjoining shorelines. Key containment provisions include:
- General containment (112.7(c)): areas where oil could be discharged, such as piping, transfer areas and oil-filled equipment, need appropriate containment or diversionary structures sized for the most likely discharge.
- Bulk storage containers (112.8(c)(2)): secondary containment must hold the entire capacity of the largest single container plus sufficient freeboard to contain precipitation. Dikes and other structures must be sufficiently impervious to contain oil.
- Mobile and portable containers (112.8(c)(11)): must be positioned to prevent a discharge and have secondary containment for the largest single compartment or container plus sufficient freeboard for precipitation.
- Tank truck and rail car loading racks (112.7(h)): where present, containment must hold at least the maximum capacity of any single compartment of a tank car or truck loaded or unloaded there.
Many facilities size bulk storage containment at 110 percent of the largest container as a rule of thumb, but the rule itself requires the largest container plus enough freeboard for precipitation, which a professional engineer should evaluate for the site's rainfall. Where secondary containment is impracticable, the SPCC rule allows alternatives such as a contingency plan, with conditions.
RCRA Containment Rules for Hazardous Waste
- Tank systems: hazardous waste tank systems, including those at large quantity generators, generally need secondary containment that holds 100 percent of the capacity of the largest tank within its boundary. Outdoor systems must also handle precipitation from a 25-year, 24-hour rainfall event unless run-on is otherwise prevented. Leaks must be detected and removed promptly.
- Container storage at permitted facilities: under 40 CFR 264.175, container storage areas holding wastes with free liquids must have containment that holds 10 percent of the total volume of containers or the volume of the largest container, whichever is greater.
Federal generator rules do not require secondary containment for every container accumulation area, but many states do, and it is a common best practice. See our page on RCRA hazardous waste generator requirements for more on accumulation rules.
Common Types of Secondary Containment
- Dikes and berms: concrete, earthen or synthetic walls around tanks or tank farms.
- Double-walled tanks: an outer shell around the primary tank, often with interstitial leak monitoring.
- Spill pallets and decks: portable platforms with built-in sumps for drums and totes.
- Containment curbs and trenches: for loading docks, transfer areas and process equipment.
- Remote impoundment: drainage that channels spills to a separate holding area.
- Sorbents, booms and drain covers: active measures used during a spill response.
How to Inspect Secondary Containment Step by Step
- Follow your schedule. Inspect containment on the frequency set in your SPCC plan, permit or procedures, using a written checklist.
- Check the structure. Look for cracks, gaps, eroded earthen walls, failed joints and damaged liners.
- Check for liquid. Note any oil, chemical or water in the containment area, and find the source.
- Confirm capacity. Make sure debris, stored materials or accumulated rainwater are not reducing the usable volume.
- Check drain valves. Confirm valves on diked areas are closed and secured when not in use.
- Inspect before draining rainwater. Check accumulated water for oil sheen or contamination before releasing it, and record the inspection and drainage as your SPCC plan requires.
- Record and fix. Document findings, assign repairs and confirm they are completed.
Common Mistakes to Avoid
- Leaving dike drain valves open, which turns containment into a direct path to the environment.
- Letting rainwater fill containment so there is no room for a spill.
- Adding a larger tank without checking whether existing containment is still big enough.
- Storing incompatible chemicals in the same containment area.
- Ignoring cracks in concrete or damage to coatings that make containment permeable.
- Skipping documentation of inspections and rainwater drainage.
How SMS360 Helps
SMS360's Audits & Inspections module lets teams build secondary containment checklists and complete them on mobile devices, with findings stored as records. Issues found can be assigned in Actions Management, and Document Library keeps SPCC plans and inspection logs in one place.
Frequently Asked Questions
Does secondary containment have to be 110 percent of the largest tank?
Not exactly. For SPCC bulk storage containers, the rule requires the capacity of the largest container plus sufficient freeboard for precipitation. Many facilities use 110 percent as a rule of thumb, but the right size depends on the site and its rainfall.
Do drums need secondary containment?
Under SPCC, oil drums of 55 gallons or more at a covered facility need appropriate containment. For hazardous waste drums, federal rules require containment at permitted storage facilities, and many states require it at generator sites too. Flammable liquid storage may also be subject to OSHA flammable liquids and fire code rules.
Can I drain rainwater from a containment dike?
Yes, but under SPCC you must keep drain valves closed when not in use, inspect the water to make sure it is not contaminated before draining, and keep records of the drainage.
