The Washington Department of Ecology released the draft 2026 Construction Stormwater General Permit (CSGP) on March 19, 2025. This permit release opens the public comment period, which will close on April 9. This post will go over everything you need to know to navigate this permit reissuance process. Carefully review the proposed changes in the permit documents and get involved by submitting a public comment regarding any proposed permit language!
Key Permit Documents & Links:
Ecology Construction Stormwater General Permit Home Page
2026 Draft Permit Redline(Use the redline to quickly identify changes)
Fact Sheet for the Draft Permit
Small Business Economic Impact Analysis
Public Comment Submission Link
Key Dates
Ecology will host 2 public comment hearings before the end of the public comment period. These sessions typically involve a brief presentation going over the key changes in the permit followed by Q&A and a formal comment period where comments can be verbally submitted for review.
The first session will be on April 21, 2025 at 1:30 at Ecology’s headquarters in Lacy.
The second session will take place on April 24, 2025 at 5 pm virtually. Register Here.
The public comment period will end on March 9, 2025 at 11:59 pm.
Permittees must reapply for permit coverage at least 180 days before the current permit expires. This means that all existing permit holders must reapply for the permit by July 3, 2025. Renewal Instructions
Key Proposed Permit Changes
The following is a summary of changes proposed in the 2026 draft permit. It is important to remember that these are proposed changes, and are subject to change in the final version of the permit. Always review the permit and accompanying factsheet for more context on these proposed changes.
1. New emphasis on construction support areas needing permit coverage
Draft language places emphasis on obtaining permit coverage for construction support activity and using best practices to prevent erosion and sediment issues from these areas.
2. Site map updates for modification of permit coverage that have an increase in acreage or a partial transfer of coverage
The draft permit proposes that sites submitting for a partial transfer of coverage or increase in acreage should provide ecology with an updated site map that include these new boundaries with their modification of permit coverage.
3. Additional language on what constitutes a contaminated site for application purposes
The draft permit state that applicants filling out an NOI must notify ecology about contamination “…including sites with known, remediated, or historically contaminated groundwater and or soil.”
4. Changes to PH sampling techniques
The draft permit now limits pH sampling methods to calibrated pH meters only. If incorporated this would require sites measuring pH using alternative methods such as pH paper or pH kits to modernize and get a digital pH meter.
5. Updated sampling requirements
The draft permit proposes that all sites under 5 acres must conduct weekly sampling for turbidity (and pH if they meet the permits pH sampling threshold). Under the 2021 permit, permitted sites under one acre in size were exempt from weekly sampling.
6. CESCL requirements for small sites
The draft permit requires all permitted sites, regardless of disturbed acreage to have site inspections performed by an inspector with CESCL certification. Under the 2021 permit, smaller permitted sites under one acre could have inspections done by a person without CESCL certification.
7. Removal of S3.A from the permit
The draft permit has removed section S3.A from the 2021 permit that read: “Discharges must not cause or contribute to a violation of surface water quality standards (Chapter 173-201A WAC), groundwater quality standards (Chapter 173-200 WAC), sediment management standards (Chapter 173-204 WAC), and human health-based criteria in the Federal water quality criteria applicable to Washington. (40 CFR Part 131.45) Discharges that are not in compliance with these standards are prohibited.”
8. Changes to sampling triggers for 303(d) listed/ TMDL waterbodies
Sites discharging to a water body impaired for low dissolved oxygen (DO) would now trigger turbidity sampling limits. This would require sites discharging into these waterbodies to be subject to numeric effluent limits, or the surface water quality standard for turbidity. Low DO is an addition to the triggers in the 2021 permit of phosphorus, turbidity, and fine sediment.
9. Construction Entrance BMPs
The draft permit states that crushed concrete shouldn’t be used for the establishment of stabilized construction entrances. This wasn’t explicitly restricted in the 2021 permit.
10. Wheel Wash BMPs
The draft permit has added language stating that wheel wash BMPs “must comply with special condition S9.D.9.d to prevent discharge to surface
waters and ensure appropriate treatment and disposal methods of wash water.” S9.D.9.D states: “Discharge wheel wash or tire bath wastewater to a separate on-site treatment
system that prevents discharge to surface water, or to the sanitary sewer with local sewer district approval.”
11. Pipe sizing for BMPs protecting slopes and channels / outlets
The draft permit has clarified the acceptable methods for calculating pipe drains using either the “Single Hydrograph Method” or the “Continuous Simulation Method” and expanded the explanation of utilizing these methods.
12. Protect Infiltration BMPs
The draft permit has changed language from “protect low impact development (LID) BMPs” to “protect infiltration BMPs”. This language is a little more broad but would continue to include the protection LID BMPs that are required to be protected under the 2021 permit.
13. Additional/ Modified Definitions
There are a number of additional definitions in the draft permit including:
• Construction Support Activity
• Date of Receipt
• Day (compliance period interval)
• Operational Hours
Questions or Concerns about the new permit? Reach out to Brandon Boyd via email at [email protected].
