NPDES Construction General Permit
A Clean Water Act permit required for any construction activity disturbing one acre or more of land, or a smaller site that's part of a larger common plan of development that will ultimately disturb an acre or more, requiring a stormwater pollution prevention plan and erosion/sediment controls in place before any ground disturbance begins.
Why it matters
The "common plan of development" rule means several small, individually under-an-acre lots inside one larger development can still require permit coverage together, even though no single lot would trigger it on its own.
On a real project
A developer building six half-acre residential lots inside a ten-acre subdivision needs NPDES permit coverage for the whole development, even though each individual lot disturbs less than an acre by itself.
Who this matters most to
A Civil Engineer designs the erosion and sediment control plan the permit requires before a single acre of ground gets disturbed.
Where this goes wrong
A general contractor starts clearing and grading a three-acre site before the NPDES permit and its required stormwater controls are actually in place. A state inspector cites the project for an unpermitted discharge, and work stops until the paperwork and controls catch up to where the grading already is.