SEDIMENT BASIN SIZING CALCULATOR: EPA CGP STORAGE REQUIREMENTS (FREE CALCULATOR)
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summary     Free sediment basin sizing calculator using the EPA Construction General Permit standard: 3,600 cubic feet per acre drained or the 2-year, 24-hour storm runoff, in cubic feet, cubic yards and gallons.

sections
- Other EPA CGP basin requirements
- Sediment trap or basin?

faq
Q: How do you size a sediment basin?
A: Under the EPA Construction General Permit, provide storage for either the runoff volume from a 2-year, 24-hour storm or 3,600 cubic feet per acre drained. State permits and BMP manuals may set additional or different sizing standards.
Q: What is the 3,600 cubic feet per acre rule?
A: It's one of the two storage options for sediment basins in EPA's Construction General Permit: 3,600 cubic feet of storage for every acre that drains to the basin, roughly equal to an inch of runoff over the drainage area.
Q: Why do sediment basins need surface outlets?
A: The cleanest water sits at the surface while sediment settles below. Surface outlets such as skimmers discharge the clearest water, and the EPA CGP requires them unless infeasible.

note        Free general education based on the Clean Water Act, EPA NPDES rules and the EPA Construction General Permit. Your governing permit (EPA, state, tribal or local) controls. This is not legal advice, not EPA-approved, and not a California QSP/QSD or other state credential, and it does not issue a certificate. Nothing you enter on this page is saved or sent.

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Free Calculator

Sediment Basin Sizing Calculator: EPA CGP Storage Requirements

Enter the drainage area to see the storage a construction sediment basin needs under the EPA Construction General Permit, by either sizing option.

  • Runs in your browser
  • Nothing is saved
On this page
  1. Calculator
  2. Other EPA CGP basin requirements
  3. Sediment trap or basin?
  4. FAQ

Under Part 2.2.12 of the EPA Construction General Permit, a sediment basin or similar impoundment must provide storage for either the calculated runoff volume from a 2-year, 24-hour storm, or 3,600 cubic feet per acre drained.

Other EPA CGP basin requirements

  • Locate the basin outside receiving waters and natural buffers.
  • Design it to avoid collecting water from wetlands.
  • Use outlet structures that withdraw water from the surface (such as a skimmer or floating riser), unless infeasible.
  • Use erosion controls and velocity dissipation at inlets and outlets.
  • Maintain it to keep its sediment storage capacity.

Sediment trap or basin?

Many state manuals use sediment traps for small drainage areas and sediment basins for larger ones, with engineered outlets and embankments. Thresholds vary by state, so follow your state's BMP manual and permit, which may require more storage than the federal minimum.

Learn the full set of sediment controls in the free sediment control lesson.

Sources and official references

Last reviewed: October 25, 2026 · Free general education based on the Clean Water Act, EPA NPDES rules and the EPA Construction General Permit. Your governing permit (EPA, state, tribal or local) controls. This is not legal advice, not EPA-approved, and not a California QSP/QSD or other state credential, and it does not issue a certificate. Nothing you enter on this page is saved or sent.

FAQ

Frequently asked questions

Under the EPA Construction General Permit, provide storage for either the runoff volume from a 2-year, 24-hour storm or 3,600 cubic feet per acre drained. State permits and BMP manuals may set additional or different sizing standards.

It's one of the two storage options for sediment basins in EPA's Construction General Permit: 3,600 cubic feet of storage for every acre that drains to the basin, roughly equal to an inch of runoff over the drainage area.

The cleanest water sits at the surface while sediment settles below. Surface outlets such as skimmers discharge the clearest water, and the EPA CGP requires them unless infeasible.

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