 When it rains, it pours: how heavy rain can impact sewer systems
 Rainy street scene
What do rainwater runoff and sewage have in common? In many parts of Seattle, they use the same system. Parts of our “Emerald City” use a combined sewer system, meaning stormwater (aka rain) and sewage (yep, we mean poop) use the same pipes to travel to the region’s treatment plants. This means that during heavy rain events there is more flow going into the system. When the system gets overwhelmed, to prevent the combined sewage and stormwater from backing up into homes and streets, it is released into our local waterways. These are called “combined sewer overflows” or “CSOs.” CSOs usually happen between the months of October and May and are typically made of about 90% stormwater and 10% sewage.
This is why King County and Seattle Public Utilities (SPU) are working hand in hand to better the quality and health of our beautiful waterways on the Ship Canal Water Quality Project. During a heavy storm, the new 18-ft diameter tunnel will capture and temporarily store more than 29 million gallons of untreated stormwater and sewage until the treatment plant is ready for it. The tunnel will improve water quality regionally by keeping an average of more than 75 million gallons of polluted stormwater (from rain) and sewage each year from flowing into Lake Washington Ship Canal, Salmon Bay, and Lake Union. Based on data from the last five years, the Ship Canal Water Quality Project would have removed about 70% of SPU’s total combined sewer overflow volume.
Visit our project website to learn more about the project and check out our Flickr albums for recent construction photos. A gentle reminder that Seattle’s mountain reservoir levels are still significantly below average for this time of year and we continue to ask our customers to use less water until we get enough rain this fall. Thank you!
Ballard
Crews continue to dismantle, clean, and remove the equipment that was needed to build the tunnel.
You should anticipate:
- Nighttime truck movements may be necessary to remove large equipment over the next few months
- Noise and vibrations typical of a construction site
Crews continue working two shifts, 20 hours a day, six days a week. Some work may occur on Sundays.
East Ballard
Crews continue to build the adit, install the conveyance pipe on NW 45th St, and build the isolation maintenance hole structure on 11th Ave NW. In the next few weeks crews will begin replacing a segment of water main in NW 45th St between 11th Ave NW and 9th Ave NW.
Local closures and detours:
- There continues to be a one-lane traffic configuration on 11th Ave NW at NW 45th St. Traffic signals and flaggers will direct traffic at the intersection during single lane closures.
- NW 45th St remains closed to traffic between 11th Ave NW and 9th Ave NW. Vehicles must detour onto NW 46th St
- Burke-Gilman Trail (BGT) remains detoured to the north side of NW 45th St through the project area. For safety, bicyclists should either dismount or cross train tracks at a 90-degree angle. Please take extra caution in wet weather as ramps may be slippery.
You should anticipate:
- Heavy equipment in the area
- Noise and vibrations typical of a construction site
Regular work hours will be Monday through Friday, from 7 am to 6 pm. Night and weekend work may occur.
Fremont
Crews are building the permanent structure inside the shaft, constructing the adit, and installing the conveyance pipes that connect to the storage tunnel. They also continue to build the large underground mechanical and electrical vault.
Crews have nearly completed installation of the vent shaft which connects to the top of our new 18-ft diameter tunnel underneath Leary Way NW at N 36th St. Crews have begun work replacing a segment of water main in Leary Way NW.
Local closures and detours:
- Leary Way NW is reduced to one lane each direction for several weeks for water main work
- The water main work will also require short-term overnight work to connect the new water main to the existing system. Customers will be notified of any water service interruptions.
- On 2nd Ave NW, between Leary Way NW and NW Canal St, the street remains closed to vehicle and pedestrian traffic through 2023
- NW Canal St is open to two-way traffic during this closure
- NW 36th St, between Leary Way NW and 3rd Ave NW, remains closed through 2023
- Pedestrian detours are in place on Leary Way NW; please follow all detour guidance
You should anticipate:
- Truck traffic on Leary Way NW as trucks bring materials and equipment to and from the site
- Concrete trucks entering and leaving the site
- Fans running during work hours to provide fresh air to crews working in the shaft
- Heavy equipment in the area
- Noise and vibrations typical of a construction site
Regular work hours will be Monday through Friday, from 7 am to 6 pm; and some Saturdays from 9 am to 6 pm.
Wallingford
Our contractor continues installation of a maintenance hole structure and conveyance pipes on N 35th St between Interlake Ave N and Stone Way N. We understand that traffic is a challenge in this area. We continue to keep an eye on neighborhood impacts and added new signage for ongoing and safe access to businesses, as businesses are open and ready to service the community. Please follow all detour signage and safety directions when traveling through the work area.
See our detour routes for cyclists and pedestrians in our detour maps.
N 35th St closure vehicle detour:
- Check out the vehicle detour map
- Traffic is detoured via N 40th St and Wallingford Ave N, and via Woodland Park Ave N and N 34th St
- The all-way stops remain in place at Woodland Park Ave N at both N 35th St and N 34th St, and also at Wallingford Ave N and N 35th St
- Stone Way N between N 34th St and N 35th St remains closed to vehicles and bicycles
- Please adhere to the Road Closed, Local Access Only, and Traffic Revision Ahead signage and follow marked detour routes
N 35th St closure bicycle detour
- Check out the bicycle and pedestrian detour map
- Bicyclists are detoured to the west on N 35th St and to the south on Woodland Park Ave N
- Access to the Burke Gilman Trail is on N 34th St at Stone Way N and at Troll Ave N
- Please dismount and walk if you use the sidewalk
You should anticipate:
- N 35th St between Stone Way N and Interlake Ave N and the intersection of N 35th St and Stone Way N are closed
- Trucks coming in and out of the site
- Heavy equipment in the area
- Vibrations typical of a construction site
- Road and periodic sidewalk closures
- Temporary bus stop on Woodland Park Ave N is being relocated and Metro bus routes 31, 32, and 62 have been detoured. Please view service advisories on King County Metro’s website.
Regular work hours at the Wallingford shaft site will be Monday through Friday, from 7 am to 6 pm. Crews also work a second shift in the tunnel and there will be occasional surface work at the shaft site.
Regular work hours on N 35th St and Stone Way N will be Monday through Friday, 7 am to 6 pm. Night and weekend work may occur periodically.
Queen Anne
Crews continue to build the permanent structure and pipes inside the shaft. They have also begun installation of some utilities at the site.
Local closures and detours:
- Localized Ship Canal Trail detour at least through 2023 (see map). Please continue to remain alert when moving through this area.
- West Ewing Mini Park parking closure through 2023
You should anticipate:
- Trucks coming in and out of the site
- Heavy equipment in the area
- Noise and vibrations typical of a construction site
Regular work hours will be Monday through Friday, from 7 am to 6 pm. Night and weekend work may occur.
Contact Us
Please email SPU_ShipCanalProject@seattle.gov with questions or comments or call our hotline at (206) 701-0233. You can also find information online at spushipcanal.participate.online.
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