When is a sediment basin required on a construction site?

EPA's 2022 CGP does not require one, but sets rules if you install one. Texas requires one where feasible for a common drainage location serving 10 or more acres disturbed at one time; Florida and Mississippi require one for drainage locations with 10 or more disturbed acres at one time.

How big does a sediment basin need to be?

Under EPA's permit, storage for the runoff from a 2-year, 24-hour storm or 3,600 cubic feet per acre drained. Florida and Mississippi use 3,600 cubic feet (133 cubic yards) per acre drained; Texas uses the 2-year, 24-hour runoff, with 3,600 cubic feet per acre where a calculation cannot be done.

When must a sediment basin be cleaned out?

EPA requires removing accumulated sediment to keep at least one-half of the design capacity. Texas requires removal before design capacity is reduced by 50%.

Can SWPPP Desk write a SWPPP for a site with a sediment basin?

No. We do not take sites that need a sediment basin or engineered BMPs, and the checkout's site check stops those orders before payment.

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Sediment basin requirements for construction sites

EPA's 2022 Construction General Permit does not require a sediment basin, but if you install one it must sit outside receiving waters and natural buffers, avoid collecting water from wetlands, store either the runoff from a 2-year, 24-hour storm or 3,600 cubic feet per acre drained, draw water from the surface unless that is infeasible, and be cleaned out to keep at least half its design capacity. EPA 2022 CGP Part 2.2.12 Several state permits go further and require a basin where 10 or more disturbed acres drain to one point, including Texas (where feasible), Florida and Mississippi. TXR150000 Part III.F.2(c)i(A) FDEP CGP Part 5.6 MSR10 ACT5 T-6(2)(A)

National guide. The rules cited are from EPA's 2022 Construction General Permit (as modified in 2025), checked October 20, 2026, which applies where EPA is the permitting authority. Most states issue their own permit with different details; check your state before relying on a number.

Sources last checked October 19, 2026. Prepared by our team led by Mohamed Elansary, PhD, with AI research tools. We are not a licensed engineering firm and do not seal plans.

General information; your permit text controls. Not legal advice and not engineering judgment. We make no promise of permit coverage, agency acceptance or compliance.

When a basin is required

Permit	Trigger	Minimum storage	Other rules
EPA 2022 CGP	None; rules apply if you install one	2-year, 24-hour runoff, or 3,600 cubic feet per acre drained	Outside receiving waters and buffers; no water from wetlands; surface outlets unless infeasible; erosion controls and velocity dissipation at inlets and outlets; keep at least half the design capacity. EPA 2022 CGP Part 2.2.12
Texas TXR150000	Required where feasible for a common drainage location serving 10 or more acres disturbed at one time	2-year, 24-hour runoff from each disturbed acre drained; 3,600 cubic feet per acre where rainfall data or a calculation is not available	Capacity calculations go in the SWP3. If a basin is not feasible, document why and use equivalent controls, which may be a series of smaller basins. TXR150000 Part III.F.2(c)i(A) Remove sediment before design capacity is reduced by 50%. TXR150000 Part III.F.6(c)
Florida CGP	Drainage basins with 10 or more disturbed acres at one time	3,600 cubic feet per acre drained, until final stabilization	Where that is not attainable, a combination of smaller basins, traps, wet detention or other practices. Under 10 disturbed acres, basins and traps are recommended but not required. FDEP CGP Part 5.6, 5.6.1
Mississippi MSR10	Drainage locations serving 10 or more disturbed acres at one time	At least 3,600 cubic feet (133 cubic yards) per acre drained	Installed before initial grading; surface-withdrawal outlets designed for at least a 2-year, 24-hour storm; baffles where flocculants are used; capacity, drainage acreage, plan location and outlet diagram shown in the SWPPP. Linear projects are not required to use basins. MSR10 ACT5 T-6(2)(A)-(C)

Runoff from off-site areas, and from undisturbed or stabilized on-site areas, does not count toward the volume in Texas and Florida when it is diverted around both the disturbed area and the basin. TXR150000 Part III.F.2(c)i(A)(1) FDEP CGP Part 5.6

What 3,600 cubic feet per acre means

3,600 cubic feet is 133 cubic yards, the figure Mississippi's permit prints next to it. MSR10 ACT5 T-6(2)(A) One acre is 43,560 square feet, so 3,600 cubic feet spread over an acre is about one inch of water. For a drainage location serving 12 disturbed acres, the default storage is 12 x 3,600 = 43,200 cubic feet, or 1,600 cubic yards. This is arithmetic on the permits' default number, not a basin design; the 2-year, 24-hour option uses local rainfall data, and EPA points to its CGP tools page for that figure. EPA 2022 CGP Part 2.2.12, footnote 34

Sediment trap or sediment basin

The permits use both terms without a size line between them. EPA lists sediment traps as one way to slow water in site drainage features, and says storm drain inlets that drain to a sediment basin, sediment trap or similar control do not need separate inlet protection. EPA 2022 CGP Part 2.2.10, footnote 33 Texas allows traps and basins for drainage locations serving under 10 acres; at 10 acres or more, the basin rule above applies. TXR150000 Part III.F.2(c)i(A), ii(A) Florida recommends either under 10 disturbed acres. FDEP CGP Part 5.6.1

Surface outlets

EPA, Texas and Mississippi all call for outlets that draw water from the surface of the basin, where the cleanest water sits. EPA 2022 CGP Part 2.2.12 TXR150000 Part IV.F MSR10 ACT5 T-6(2)(A) EPA says cases where this is infeasible are rare, such as extended cold weather, and any exception must be documented in the SWPPP with the conditions or time periods it covers. EPA 2022 CGP Part 2.2.12, footnote 35; 7.2.6

Who designs a basin

A sediment basin is a design element. Texas requires capacity calculations in the SWP3, and Mississippi requires the outlet diagram. TXR150000 Part III.F.2(c)i(A)(1) MSR10 ACT5 T-6(2)(A) Check your state permit for who may design a basin.

SWPPP Desk does not take sites that need a sediment basin or BMPs that require engineering design; the checkout's site check stops those orders before payment. If your site needs a basin, a design professional sizes it and the SWPPP references that design.

What this page does not cover

Basin design, hydrology, outlet sizing, dam safety rules and local drainage criteria. Sites that need a sediment basin are outside our scope.

Have it written for you

SWPPP Desk prepares site-specific SWPPPs from your drawings for construction sites in the states we cover (coverage by state), for a fixed price, delivered the next business day after your inputs are complete. Small site (1 to under 5 acres): $449. Large site (5 acres or more): $749. Background: all guides.

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