Is the half acre limit the same for every nationwide permit?

No. It applies to a defined subset of nationwide permits, currently 19 of the 57 active permits. Several permits carry no acreage limit at all, and a few use a different number entirely.

Does temporary impact count toward the acreage loss limit?

No. The loss limit applies to permanent loss of waters of the United States. Temporary impact, such as a construction easement that is later restored, is recorded separately and does not count toward the loss limit, though it still has to be disclosed.

Is the pre-construction notification threshold the same as the acreage loss limit?

No. 1/10-acre pre-construction notification threshold triggers a PCN requirement on several permits well before the project reaches the permit's overall loss limit. They are two different tests.

The half acre limit, explained

Q: Which nationwide permits use a full acre limit instead of half an acre?

NWP 46 (Discharges in Ditches) and NWP 60 (Activities to Improve Passage of Fish and Other Aquatic Organisms) both carry a loss limit of 1 acre rather than the half acre figure used elsewhere.

The half acre limit is not universal. It caps permanent loss of waters of the United States under a defined subset of nationwide permits, currently 19 of the 57 active permits, and even within that subset the number is not always 0.5 acres. 2 permits use a full acre instead, and NWP 14 drops to a smaller limit specifically in tidal waters.

What counts as a loss

The limit applies to permanent loss of waters of the United States, meaning fill, excavation or other conversion that removes the area's aquatic function on an ongoing basis. Temporary impact, such as a construction easement, a cofferdam, or a work pad that is removed and the area restored, is recorded separately and does not count toward the loss limit, though it still has to be disclosed and may still trigger a PCN in its own right. Confusing temporary disturbance with permanent loss is one of the more common ways a project is misjudged against these limits.

The permits that carry an acreage limit

1/2-acre limit on loss of waters of the United States applies to the permits below. Per single and complete project, for those NWPs that carry an acreage loss limit (NWPs 12, 14 (non-tidal), 21, 29, 39, 40, 42, 43, 44, 50, 51, 52, 57, 58, 59). Not all NWPs have an acreage limit; several are self-limiting. Several other nationwide permits carry no acreage limit at all because they are self-limiting by activity type, and are not listed here.

NWP	Title	Loss limit	Note
NWP 18	Minor Discharges	0.1 acres	Overall limits: 25 cubic yards and loss of no more than 1/10-acre; discharge may not be placed for the purpose of a stream diversion.
NWP 12	Oil or Natural Gas Pipeline Activities	0.5 acres	1/2-acre loss limit applies per single and complete project.
NWP 14	Linear Transportation Projects	0.5 acres	1/2-acre limit applies in non-tidal waters; a lower 1/3-acre limit applies in tidal waters.
NWP 21	Surface Coal Mining Activities	0.5 acres	1/2-acre limit applies to non-tidal waters; valley fills are not authorised.
NWP 29	Residential Developments	0.5 acres	For residential subdivisions the aggregate total loss authorised cannot exceed 1/2-acre, including loss associated with development of individual subdivision lots.
NWP 39	Commercial and Institutional Developments	0.5 acres	1/2-acre limit applies to non-tidal waters of the United States.
NWP 40	Agricultural Activities	0.5 acres	1/2-acre limit applies to non-tidal waters of the United States.
NWP 42	Recreational Facilities	0.5 acres	1/2-acre limit applies to non-tidal waters of the United States.
NWP 43	Stormwater Management Facilities	0.5 acres	1/2-acre limit applies to non-tidal waters of the United States.
NWP 44	Mining Activities	0.5 acres	1/2-acre applies separately to non-tidal wetland loss and to mined area in non-tidal open waters, and to the combined total.
NWP 50	Underground Coal Mining Activities	0.5 acres	1/2-acre limit applies to non-tidal waters of the United States.
NWP 51	Land-Based Renewable Energy Generation Facilities	0.5 acres	1/2-acre limit applies to non-tidal waters of the United States.
NWP 52	Water-Based Renewable Energy Generation Pilot Projects	0.5 acres	Floating solar panels in navigable waters: each single and complete project cannot exceed 1/2-acre of water surface area covered. Placement of a transmission line on the bed of a navigable water is not a loss of waters for the purposes of applying the 1/2-acre limit.
NWP 57	Electric Utility Line and Telecommunications Activities	0.5 acres	1/2-acre loss limit applies per single and complete project.
NWP 58	Utility Line Activities for Water and Other Substances	0.5 acres	1/2-acre loss limit applies per single and complete project.
NWP 59	Water Reclamation and Reuse Facilities	0.5 acres
NWP 46	Discharges in Ditches	1 acre	Loss limit is one acre of waters of the United States.
NWP 60	Activities to Improve Passage of Fish and Other Aquatic Organisms	1 acre	New NWP this cycle; proposed as NWP A and issued as NWP 60. Loss limit is one acre of waters of the United States.
NWP 34	Cranberry Production Activities	10 acres	Cumulative total acreage of disturbance per cranberry production operation must not exceed 10 acres of waters of the United States.

NWP 14's tidal wrinkle

NWP 14, Linear Transportation Projects, is the clearest example of why you cannot assume a single number across a whole permit. 1/2-acre limit applies in non-tidal waters; a lower 1/3-acre limit applies in tidal waters. A road crossing sized correctly for a non-tidal reach can be over the limit the moment the same design is applied in a tidal waterway. Always read the limit that applies to your specific water type on the NWP 14 page rather than carrying a number over from a different project.

The 2 permits that use a full acre

NWP 46, Discharges in Ditches, and NWP 60, Activities to Improve Passage of Fish and Other Aquatic Organisms, both carry a 1 acre loss limit rather than the half acre figure used elsewhere. Do not import a half acre ceiling onto either of these by habit; check NWP 46 and NWP 60 directly. A small number of other permits, cranberry production activities among them, carry a materially larger limit again, which is exactly why this page renders the table from live data rather than printing a single memorised figure.

The PCN threshold sits below the loss limit

1/10-acre pre-construction notification threshold: For NWPs that have an acreage PCN threshold, the Corps set that threshold at 1/10-acre (e.g. NWPs 12, 14, 51, 57, 58, 60). NWP 18 also carries a 1/10-acre loss limit as a permit condition. A project can be comfortably inside its permit's acreage limit and still owe a PCN, because the notification trigger is set well below the ceiling on several permits. Treat the loss limit and the PCN threshold as two different tests, not one, and read both for the specific permit in play; see the pre-construction notification guide for how the two clocks that follow actually run. To check your own numbers against the permit you have in mind, use the determination tool.