Secondary containment calculations are required for SPCC plan compliance under EPA 40 CFR 112. Use this calculator to determine if your containment area provides sufficient capacity to hold the volume of the largest tank, plus precipitation and freeboard, after subtracting displacement from tanks, equipment, and other objects within the containment area. Supports rectangular dikes, circular berms, and custom-shaped containments.
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| Description | Type | Dim 1 | Dim 2 | Height in Cont. | |
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| Description | Volume (ft³) | |
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| Description | Type | Dim 1 | Dim 2 | Height in Cont. | |
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| Description | Volume (ft³) | |
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Conversions: 1 ft³ = 7.48052 US gal | 1 barrel = 42 US gal | SPCC threshold: 1,320 gal aggregate aboveground oil storage
Secondary containment is a structure — such as a dike, berm, vault, or double-walled tank — built around storage tanks to capture spills and prevent oil or hazardous substances from reaching the environment. EPA requires secondary containment under SPCC regulations (40 CFR 112) for facilities storing oil above certain thresholds.
Under SPCC regulations, secondary containment must hold the volume of the largest single tank within the containment area, plus sufficient freeboard for precipitation. Many facilities design for 110% of the largest tank to provide a safety margin. Some state regulations require capacity for the entire contents of all tanks within the containment.
You must subtract several displacements from the gross containment volume: the volume displaced by all tanks and equipment bases sitting inside the containment area (up to the wall height), the volume of accumulated precipitation for the design storm event, freeboard (safety margin below the wall top), and any other objects such as pipe supports, foundations, or equipment pads.
Multiply the containment surface area by the design rainfall depth. Most SPCC plans use the 25-year, 24-hour storm event for their region. For example, a 1,000 sq ft containment area with a 6-inch (0.5 ft) design storm displaces 500 cubic feet, or about 3,740 gallons. You can find your local design storm depth through NOAA Atlas 14.
Freeboard is the vertical distance between the top of the containment wall and the maximum expected liquid level. It provides a safety margin to prevent overtopping. Typical requirements range from 6 inches to 1 foot. Check your state and local regulations for specific requirements, as they may be more stringent than federal standards.
For cylindrical tanks: displacement = π × r² × h, where r is the tank radius and h is the lesser of the tank height or the containment wall height. For rectangular bases: displacement = length × width × h. Only the portion of the tank below the containment wall height displaces volume.
If containment cannot hold the required volume, options include: raising containment walls, expanding the containment area, reducing the number or size of tanks, installing a drainage system to a remote impoundment, or using alternative containment methods approved in your SPCC plan.
Yes. The custom shape drawing tool lets you trace the outline of any irregular containment area on a scaled grid. The calculator uses the Shoelace formula to compute the exact polygon area, then applies wall height and all displacement deductions. This is useful for L-shaped dikes, containments that follow building footprints, or any non-standard geometry.
Managing secondary containment requirements involves ongoing inspections, documentation, and regulatory reporting. EHS software streamlines these processes:
SPCC Plan Management - Maintain your SPCC plan digitally with tank inventories, containment specifications, facility diagrams, and secondary containment calculations. Track plan amendments, PE certifications, and ensure all locations have current documentation accessible to inspectors.
Containment Inspection Tracking - Schedule and document regular containment inspections including visual integrity checks, drainage valve status, liner condition, and accumulated precipitation removal. Assign corrective actions for deficiencies with automatic notifications and due date tracking.
Tank Inventory and Registration - Centralize your tank database with complete details: dimensions, capacity, contents, installation dates, last inspection, and containment assignment. Generate reports for state registration, EPA Tier II, and insurance requirements.
Spill Prevention and Response - Document spill incidents from initial notification through investigation, root cause analysis, corrective actions, and regulatory reporting. Track near-misses to identify patterns and prevent future spills.
Regulatory Compliance Calendar - Track deadlines for SPCC plan reviews (every 5 years or after changes), monthly containment inspections, annual integrity testing, Tier II reporting, and state-specific tank registration renewals.
Audit and Inspection Readiness - Maintain inspection-ready documentation with electronic records, photos, and corrective action histories. Generate compliance reports instantly for EPA inspectors, state auditors, or internal reviews.
Click on the "CONTACT US FOR HELP!" link below to see these benefits in action with a free trial of Ecesis EHS Software.
Please call us at (720) 547-5102 or complete the form below to learn more about how Ecesis can help you manage SPCC plans, containment compliance, and environmental reporting.
If you need help with secondary containment calculations or SPCC compliance, please call us at (720) 547-5102.
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