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New stormwater storage tank construction in Capitol Hill starts next week | LEVY DOLLARS AT WORK

Photos of similar stormwater storage tanks recently built as part of the Madison RapidRide G Line project. Photos: SDOT.

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  • A new tank: We’re building a large stormwater storage tank in Capitol Hill, as part of the Madison RapidRide G Line project.
  • Environmental benefits: The new tank will collect stormwater and help ensure it’s treated before being released into local waterways and Puget Sound, particularly during major rain events.
  • Construction details: We’ll close two blocks of 10th Ave, between E Union St and E Madison St, for at least two months, beginning Monday, May 1.
  • Getting around: People can walk around the work zone, but should follow all posted signage and instructions.
  • Supporting local businesses: Nearby businesses like MoMo’s Kebab, El Chapulin, Lark, Drip Tea Market, Slab Sandwiches, Union Bar, Frankie & Jo’s, Fern Thai, and others remain open during this work, and we encourage you to stop by! We’re maintaining access for people walking and rolling around the site. This includes the adjacent Bright Horizons daycare facility.
  • Levy funding: This project is made possible thanks to Seattle voters who approved the Levy to Move Seattle. Thank you!

We’re building a new stormwater storage tank under the street on 10th Ave in Capitol Hill, starting Monday, May 1.

The tank will provide a significant environmental benefit by reducing flooding and helping contain stormwater runoff so it can be treated before it enters local waterways and Puget Sound. This blog highlights what you should know during construction, including how to get around the work zone safely.

Purpose and environmental benefits

We’re building this stormwater tank as part of the Madison RapidRide G Line project. The project has already built two similar stormwater storage tanks nearby under E Pine St (between 15th and 16th avenues) and underneath E Madison St (between 12th and 13th avenues), as pictured above. When we complete a major rebuild of a street to improve transit connectivity, we also want to make sure utilities like underground water lines and storage tanks are improved. This is a coordinated One Seattle approach to best serve the public, alongside our partners at Seattle Public Utilities and other City departments.

When complete, the new tank will collect stormwater from the street and slowly release it back into the sewer system. In this area, there is a combined sewer for both stormwater and sanitary waste. Sewer water is cleaned at treatment plants before it flows back into local waterways and Puget Sound.

During heavy rainfall, these combined sewers can sometimes overflow. This can lead to flooding and the release of sewer water into our natural water systems without being fully treated. Stormwater storage tanks like the new one under 10th Ave help hold stormwater and slowly release it back into the combined sewer system. The tanks help prevent overloading the treatment plants’ capacity and allow the sewer water to be fully treated before it goes back into local waterways and Puget Sound.

When complete, we expect the new storage tank to be able to hold up to nearly 57,000 gallons of water when needed.

Construction details

Building a large underground tank is no small effort! It requires using huge construction equipment and digging a major hole in the street. We need to close the street and fence off the work area for everyone’s safety.

Work will take at least 2 months to complete, and will look like this: 

  • Crews will start at the intersection of 10th Ave and E Madison St, and work their way north to just past the E Union St intersection.
  • Crews will dig a trench in the street and install piping to build the stormwater tank in sections. Once sections of the tank are installed, we’ll fill the trench with dirt and keep building north.  
  • Once the tank is fully installed, we need to test it. We’ll fill the tank with water and monitor how well it holds. It needs to pass the test!
  • After the tank passes the monitoring test, we’ll begin to repave the street.
  • First, we’ll remove the remaining portions of the street around the hole. Then we grade the whole street and repave it.

How to get around during the work

People walking, biking, and rolling:

Pedestrians will have continued access to travel around the fenced-off construction area along 10th Ave E. Local residents and businesses will also be able to access their buildings on foot. We’ll communicate any anticipated disruptions in advance via our project email listserv. Flaggers may also help people navigate around the work area during key activities.

People driving:

Once work begins, 10th Ave E will remain closed to vehicles between E Union St and E Madison St, until work on the stormwater drainage tank is complete. Drivers can use several adjacent streets to travel around the work zone. E Seneca St, between Madison St and Broadway Ct, will be open for local access only.

Map graphic showing the location of work. The graphic shows where 10th Ave is closed between E Madison St and E Union St; where local access only will be in place along E Seneca St from Broadway Ct to E Madison St; and where sidewalks will remain open on 10th Ave and E Seneca St.
Map of the closure area, local access areas, and sidewalks that will remain open. Graphic: SDOT

We encourage you to continue visiting local businesses in the area while this work takes place. As shown on the map above, we’ll maintain access for people walking and rolling around the site, so please stop by your favorite local shops during construction!

If you have any questions or want to discuss your specific access needs, please contact us at

Thank you for your interest and understanding as this important work moves forward!