Washington Statewide Rule

Washington Stormwater NPDES Permit Requirements

Heavy RestrictionsApplies statewide across Washington (2026)

Key Facts

Authority: Department of Ecology
Construction Trigger: 1+ acre disturbed
Max Penalty: $10,000 per day
Statute: RCW 90.48

Last verified: August 21, 2026Source: Washington State Legislature

Summary

Washington Department of Ecology administers federally-required NPDES stormwater permits statewide, setting minimum standards for municipal, construction, and industrial stormwater that all jurisdictions must implement.

(b) Issue an updated national pollutant discharge elimination system municipal stormwater general permit applicable to western Washington municipalities for any permit first issued on January 17, 2007. An updated permit issued under this subsection shall become effective beginning August 1, 2013. (i) Provisions of the updated permit issued under (b) of this subsection relating to new requirements for low-impact development and review and revision of local development codes, rules, standards, or other enforceable documents to incorporate low-impact development principles must be implemented simultaneously. These requirements may go into effect no earlier than December 31, 2016, or the time of the scheduled update under *RCW 36.70A.130(5), as existing on July 10, 2012, whichever is later.

Source: Washington State LegislatureView official code

Full Breakdown

Under RCW 90.48 (Water Pollution Control Act) and the federal Clean Water Act, the Washington State Department of Ecology issues NPDES Phase I and Phase II Municipal Stormwater Permits, the Construction Stormwater General Permit, and the Industrial Stormwater General Permit. Construction sites disturbing one or more acres require coverage and a Stormwater Pollution Prevention Plan (SWPPP). Permittee cities and counties must adopt and enforce stormwater management programs meeting the Stormwater Management Manual for Western or Eastern Washington. Local jurisdictions may impose stricter requirements but cannot weaken state minimums.

Violations & Penalties

Discharging pollutants without a permit or violating permit conditions can result in civil penalties up to $10,000 per day per violation under RCW 90.48.144, and potential criminal charges for knowing violations.

Frequently Asked Questions

Do I need a stormwater permit for my Washington home construction project?

If your project disturbs one or more acres, you need a Construction Stormwater General Permit from Ecology. Smaller projects may still need local stormwater approvals depending on jurisdiction.

Who enforces stormwater violations in Washington?

The Department of Ecology enforces statewide permits, while local jurisdictions enforce their municipal stormwater programs. Both can issue notices of violation and assess penalties under RCW 90.48.

Sources

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