SWPPP Requirements in Washington

Who needs a SWPPP in Washington?

Any construction project that disturbs one acre or more — or is part of a larger common plan of development reaching one acre — needs a SWPPP under Washington permit WAR300000.

Washington runs its own delegated stormwater program. Operators obtain coverage from Washington State Department of Ecology under Construction Stormwater General Permit (WAR300000), not directly from the EPA. A small subdivision, a solar pad, and a road-widening project all clear the same one-acre line.

Washington adds requirements worth flagging early: Weekly turbidity or transparency sampling at discharge points (turbidity meter required at 5 acres or more); benchmark 25 NTU (33 cm transparency), 250 NTU reporting trigger — discharges to waters on the 303(d) list for turbidity, fine sediment, low dissolved oxygen, or phosphorus are instead held to a numeric turbidity effluent limit (S8.C); Sites discharging to a TMDL or 303(d)-listed water are eligible for coverage only if the operator prevents exposing stormwater to the impairment pollutants, documents that those pollutants are not present on site, or gives Ecology data showing the discharge will not cause or contribute to an exceedance — with the documentation kept in the SWPPP — and Ecology makes an affirmative determination (S8.B); Stabilize exposed soils within 2 days (Oct 1-Apr 30) or 7 days (May 1-Sep 30) west of the Cascades; Apply via the Ecology Water Quality Permitting Portal.

What the plan must contain

A Washington SWPPPis the site's compliance binder — the document an inspector opens first. It documents:

1. 1Site & project descriptionTotal and disturbed acreage, soils, slopes, and the sequence of construction.
2. 2Receiving waters & discharge pointsWhere stormwater leaves the site and the waterbodies it reaches.
3. 3Erosion & sediment control BMPsSilt fence, stabilized entrances, inlet protection, and stabilization measures.
4. 4Inspection schedule & recordsDated, signed inspection logs and the corrective actions taken.
5. 5Operator certificationThe SWPPP is signed by the legally responsible party before work begins.

Required and conditional BMPs

Filing your Notice of Intent

Apply for coverage via the Ecology Water Quality Permitting Portal.

A Notice of Termination closes coverage once the site reaches final stabilization. Keeping the SWPPP and its inspection records on site is what keeps a project clear of stop-work orders.

Inspection requirements

Inspect at least once every calendar week and within 24 hours of any discharge from the site (a calendar week starts at 12:01 a.m. Sunday; an individual discharge event lasting more than one day does not require daily inspections) (WA CSWGP Special Condition S4.B.3; Appendix A (“Calendar Week”)). Every inspection is dated and signed, and any failed control is corrected before the next storm.

How Washington differs from the federal permit

Because Washington administers its own program, the federal EPA Construction General Permit does not apply directly here — the state permit governs. Sites inside a regulated municipal storm sewer system may carry additional local ordinance requirements on top of the state permit.

Frequently asked questions