United States
Hong KongThe One-Acre Threshold for Construction Stormwater Permit Coverage
Under the federal NPDES construction-stormwater framework, permit coverage is generally required for construction activity that will disturb one acre or more and discharge stormwater, or for a smaller site that is part of a common plan of development or sale that will ultimately disturb one acre or more.
More key points
- State, tribal, or local permitting authority, waiver eligibility, and the project's discharge conditions matter.
On this page6 sections
A half-acre building pad may still be part of a project that crosses the stormwater permit threshold. The relevant question is not always the acreage disturbed by one contractor's parcel; it can include the larger common plan of development or sale.
The general federal threshold
Construction activities disturbing one or more acres of land generally need NPDES permit coverage for stormwater discharges, subject to the applicable permit's conditions and any eligibility rules. Clearing, grading, excavation, stockpiling, and related activities can count when they disturb land or create pollutant-generating conditions.
Smaller sites can be included in a larger common plan
A site disturbing less than one acre may still require coverage if it is part of a common plan of development or sale that will ultimately disturb one or more acres. A small lot in a subdivision is a familiar example. A common plan can be shown by documents, public announcements, plans, applications, or physical demarcation indicating that related construction will occur.
The threshold is not the only permit test
Permit coverage also depends on whether the activity discharges stormwater to waters covered by the permit and which permitting authority administers the program. Some states administer their own NPDES-authorized programs. Certain waivers may apply, but they have specific conditions; acreage alone does not establish that a site is exempt.
Plan controls before earthwork
The operator should determine permit eligibility early, identify the responsible operator, prepare the required stormwater pollution prevention plan, install erosion and sediment controls, and complete any required notice before construction discharge begins. Coordinate sequencing with subcontractors so controls stay in place as the site changes.
Exam example
A contractor disturbs 0.6 acre building a retail pad within a 12-acre shopping-center plan. The individual work area is under one acre, but the larger common plan may meet the threshold. The contractor must check permit coverage and jurisdiction rather than concluding that the pad is exempt.
Key takeaway
Think one acre at the project or common-plan level, then verify discharge, operator, jurisdiction, and any waiver conditions. Smaller parcels are not automatically outside the stormwater program.
Common questions
Does every construction site under one acre avoid an NPDES stormwater permit?
No. A smaller site can be part of a common plan that will disturb one acre or more, and other permit conditions still apply.
Does the one-acre threshold mean a permit is always required at one acre?
It is the general federal trigger for covered construction stormwater discharges, but determine the applicable authority, permit conditions, and any eligible waiver.