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When is a SWPPP required? The 1-acre rule and its exceptions
A SWPPP is required when construction disturbs 1 acre or more of land, or less than 1 acre that is part of a larger common plan of development or sale disturbing 1 acre or more in total. Those sites need construction stormwater permit coverage, and every construction general permit requires a SWPPP before you file for it. Small sites in low-rainfall periods can sometimes waive out.
The two tests
1. Area disturbed. Federal rules call 1 to under 5 acres "small construction activity" (40 CFR 122.26(b)(15)) and 5 acres or more "construction activity" (122.26(b)(14)(x)). Both need permit coverage; the size can change what you file, not whether you need a plan. Disturbance means clearing, grading and excavating, and EPA's permit also counts grubbing, stockpiling fill and placing raw materials on the site.
2. The common plan. Under an acre still counts if it's part of a larger common plan of development or sale that will disturb an acre or more. EPA reads "plan" broadly: any announcement or document (a sign, a sales pitch, a drawing, a permit application, a zoning request) or physical marker (lot stakes, survey marks) showing that construction may happen on a specific plot. A home on a half-acre lot in a 40-lot subdivision is covered even though the lot is small.
Routine maintenance that keeps a facility's original line and grade, hydraulic capacity or purpose isn't small construction activity (122.26(b)(15)), so repaving a lot in place or regrading a ditch to its original profile usually doesn't trigger the rule.
Worked examples
| Project | SWPPP? | Why |
|---|---|---|
| Custom home disturbing 0.4 acre on a lot in a subdivision | Yes | Part of a common plan that disturbs more than an acre; EPA has a streamlined Small Residential Lot template for up to five homes |
| Standalone 0.8-acre commercial pad, no larger plan | No (federal) | Under an acre and not part of a common plan. A city or county erosion control permit may still apply |
| 2.5-acre warehouse addition | Yes | Small construction activity: 1 to under 5 acres |
| 3-acre site graded over six dry weeks | Maybe not | If the rainfall erosivity factor R is under 5 for the construction period, a Low Erosivity Waiver replaces the permit; recalculate if work runs long |
| 1.3 miles of water main in a 15-foot-wide trench and work zone | Yes | About 2.4 acres disturbed (1.3 mi × 5,280 ft × 15 ft); linear projects count area the same way |
| Milling and repaving a 3-acre parking lot to the same grade | Usually no | Routine maintenance of original line and grade is excluded; adding area or regrading isn't |
The waivers
Only sites disturbing under 5 acres can be waived, under Appendix C of EPA's permit and 40 CFR 122.26(b)(15):
- Low rainfall erosivity. The R factor from the Revised Universal Soil Loss Equation is under 5 for the period from first disturbance to final stabilization. EPA's rainfall erosivity calculator gives R for your coordinates and dates. File the waiver certification instead of an NOI, and redo it if the schedule extends.
- TMDL or equivalent analysis. Rare in practice: an EPA-approved TMDL for the receiving water finds that controls on small construction sites aren't needed, or, for unimpaired waters, your own equivalent analysis shows that allocations for your site aren't needed. Unlike the erosivity waiver, you can't start work until EPA approves it.
Some states drop the waiver or change it; check your state permit before relying on it.
When the plan has to exist
Before anything else. Under EPA's permit the SWPPP must be complete before you submit the Notice of Intent (Part 1.4.1), and the NOI is due at least 14 days before you break ground. "Breaking ground" includes clearing, grubbing and stockpiling fill, not just grading. The plan then stays current until you terminate coverage: changes go in within 7 days.
Where the rules differ
The 1-acre threshold is federal, so every state uses it, but what you file and what you can skip differ:
- Texas. Sites of 1 to under 5 acres still need an SWP3 but file no NOI: they post TCEQ's small site notice instead. Work in the low-erosion periods listed by county in the permit's Appendix A can be authorized automatically (Texas guide).
- California. Every site of an acre or more files in SMARTS, with a SWPPP written by a Qualified SWPPP Developer; the erosivity waiver for 1 to 5 acres costs $200 (California guide).
- Washington. The erosivity waiver only covers sites under 5 acres that aren't part of a 5-acre plan, and the permit application is due 60 days before you discharge.
- Virginia. Under an acre and outside a common plan there's no permit coverage, but disturbing 10,000 square feet or more, or 2,500 in a Chesapeake Bay Preservation Area, still needs local erosion and stormwater approval. A single-family home needs no registration statement but still follows the permit, SWPPP included.
- Colorado. Small sites in a qualifying local program (Arvada, Durango, Golden and Lakewood) are covered without applying to the state.
- Georgia, Florida and North Carolina. We found no rainfall erosivity waiver in their permits. North Carolina also requires an approved erosion and sedimentation control plan before the NOI.
Cities and counties often set lower thresholds of their own for erosion control or grading permits, so ask the local permit office too.
Construction SWPPP vs industrial SWPPP
A construction SWPPP ends when the site is stabilized and coverage is terminated. Factories, yards, airports and other facilities in the regulated industrial categories need an industrial SWPPP under EPA's Multi-Sector General Permit or their state's industrial permit, which runs for as long as the facility operates. The template on this site's main page is the construction one.
Once you know you need one, the NOI guide covers the filing order and the cost guide what each route costs. ePlan identifies which permit covers a site address and drafts the SWPPP from four answers; it's free to read and $49 to download (ePlan's SWPPP page).
Questions
Do I need a SWPPP for less than 1 acre?
Only if the site is part of a larger common plan of development or sale that will disturb 1 acre or more, such as a lot in a subdivision, or if your state or city requires one at a lower threshold.
What triggers a SWPPP?
Needing construction stormwater permit coverage: disturbing 1 acre or more, or less as part of a larger common plan. Every construction general permit then requires a SWPPP before you file for coverage.
Does a single-family home need a SWPPP?
If it disturbs an acre or more, or sits in a subdivision or other common plan that does, yes. EPA's Small Residential Lot SWPPP template is a shorter version for builders of up to five single-family or duplex homes, each disturbing under an acre.
Related guides
- SWPPP template: which one your permit wants, and how to fill it in
- SWPPP notice of intent: how to file the NOI, in order
- SWPPP cost: what a plan, the permit and the inspections cost
About this page
This guide is published by Winding AI, Inc., the company that makes ePlan, one of the ways to get a SWPPP drafted that this site compares. We make money when someone pays ePlan to download a document or subscribes; we earn nothing from links to agencies or other products, and links to ePlan carry a tag so ePlan can count visits from here. Every fact on this page was read from the source it links to on the date shown above.