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State permit
Washington Construction Stormwater General Permit (CSWGP)
The Washington State Department of Ecology's Construction Stormwater General Permit (CSWGP) was issued November 19, 2025, took effect January 1, 2026 and expires December 31, 2030. CSWGP cover page It covers construction disturbing one acre or more, or less in a larger common plan of one acre or more, that discharges to surface waters of the State. CSWGP S1.B.1.a Three conditions set its timeline and workload: the NOI goes in at least 60 days before discharge, a newspaper notice runs twice, and every site samples its discharge weekly. CSWGP S2.A.1.c, S2.B, S4.C Checked October 20, 2026.
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.
CSWGP at a glance
| Item | Rule | Source |
|---|---|---|
| Permit | Construction Stormwater General Permit, with Ecology's errata of February 5, 2026 | CSWGP permit text |
| Agency | Washington State Department of Ecology, Water Quality Program | CSWGP S2.A.1.b |
| Effective / expires | Issued November 19, 2025; effective January 1, 2026; expires December 31, 2030 | CSWGP cover page |
| How to file (NOI) | Electronic NOI on Ecology's CSWGP page, at least 60 days before discharging and before the first public notice. Paper only by waiver | CSWGP S2.A.1.b-c |
| Public notice | Newspaper of general circulation in the county, once a week for two consecutive weeks, at least 7 days apart, after the NOI is submitted, with the statements the permit lists | CSWGP S2.B |
| When coverage starts | The 30-day comment period begins on the second notice. Unless Ecology responds in writing, coverage starts on the 31st day after Ecology receives a complete NOI | CSWGP S2.A.1.c |
| Contamination | Tell Ecology about known, remediated or historical soil or groundwater contamination, with details, in the NOI | CSWGP S2.A.1.e |
| Fee | Permit fees set by Chapter 173-224 WAC, assessed until the permit is terminated | CSWGP S6 |
| Inspector | A Certified Erosion and Sediment Control Lead (CESCL), identified in the SWPPP and present on site or on call at all times | CSWGP S4.B, S4.B.1.b |
| Inspection frequency | At least once every calendar week and within 24 hours of any discharge; monthly for inactive, temporarily stabilized sites | CSWGP S4.B.3 |
| Sampling | Weekly at every discharge point when discharging. Under 5 acres: turbidity meter or transparency tube; 5 acres or more: turbidity meter. Benchmarks: 25 NTU or 33 cm | CSWGP S4.C, Table 3 |
| pH sampling | Only with significant concrete work (more than 1,000 cubic yards over the project) or engineered soils, where runoff reaches surface waters; benchmark 8.5 | CSWGP S4.D, Table 3 footnote 6 |
| Reporting | Monthly DMRs through WQWebDMR, received within 15 days after each month ends, including months with no discharge | CSWGP S5.B |
| Termination | NOT after final stabilization and removal of temporary BMPs, or transfer of all unstabilized areas, or (residential) temporary stabilization and homeowner possession. Effective on the 31st calendar day after Ecology receives it. No partial terminations | CSWGP S10 |
Sampling results and what they trigger
| Result | What the permit requires |
|---|---|
| Turbidity 25 NTU or less, or transparency 33 cm or more | At or better than the benchmark values. CSWGP S4.C.5 |
| Turbidity 26 to 249 NTU, or transparency 32 to 7 cm | Start source control or treatment BMPs at once and finish within 10 days; review and revise the SWPPP within 7 days; record it in the site logbook. CSWGP S4.C.5.a |
| Turbidity 250 NTU or more, or transparency 6 cm or less | Report to Ecology's regional ERTS line within 24 hours, address the problem with source control or treatment BMPs within 10 days, and sample daily until the discharge is back at the benchmark or meets the turbidity water quality standard. CSWGP S4.C.5.b |
The benchmarks do not apply to discharges to 303(d)-listed (Category 5) segments for turbidity, fine sediment, low dissolved oxygen or phosphorus; those discharges have a numeric turbidity limit under S8. CSWGP S4.C.5, S8
Soil stabilization clock
Exposed soil may not sit unworked longer than: west of the Cascade crest, 7 days from May 1 to September 30 and 2 days from October 1 to April 30; east of the crest, 10 days in the dry season and 5 in the wet season; in the Central Basin, 30 and 15 days. CSWGP S9.D.5
Concrete washout and dewatering have their own conditions: see concrete washout rules and construction dewatering. CSWGP S9.D.9.h, S9.D.10
What we do
We prepare Washington CSWGP SWPPPs. You supply the CESCL who inspects the site and does the sampling; we do not inspect, sample or file DMRs. Runoff and post-construction calculations, and the design of post-construction controls, come from your project designer. We do not calculate or design them (Terms 6.1); the plan lists them as items your designer supplies. We prepare the plan document. We do not stamp plans, visit sites or file the NOI; you file it. The site check at checkout applies the Washington limits shown on the Washington hub before payment.
Questions
How far ahead must I apply for Washington construction stormwater coverage?
Submit the NOI at least 60 days before discharging, and before the first newspaper notice. Coverage starts automatically on the 31st day after Ecology receives a complete NOI unless Ecology responds in writing.
Who has to inspect a CSWGP site?
A Certified Erosion and Sediment Control Lead (CESCL), at least once every calendar week and within 24 hours of any discharge.
Is pH sampling required on every Washington construction site?
No. Weekly pH sampling applies when the project places more than 1,000 cubic yards of concrete or uses engineered soils, and runoff from that area reaches surface waters (S4.D).
Do I file a DMR if nothing discharged?
Yes. The CSWGP requires monthly DMRs within 15 days after each month, including a no-discharge DMR when there was no discharge.
When does a Washington NOT take effect?
On the 31st calendar day after Ecology receives a complete NOT, unless Ecology denies it. Partial terminations are not allowed.