North Henderson Basins
The North Henderson area projects will reduce the amount of untreated sewage and polluted stormwater that is overflowing into Lake Washington at combined sewer overflow (CSO) outfalls near Seward Park (Basin 44) and Martha Washington Park (Basin 45).
The North Henderson area CSO-reduction projects incorporate additional storage, conveyance pipeline and system upgrades to control about 10.5 million gallons that currently overflow into Lake Washington during rainstorms. The projects are planned for completion in 2018.
Because of topography and other factors, Green Stormwater Infrastructure (GSI) opportunities are limited in North Henderson Basins. Some opportunity may exist for small-scale projects, such as RainWise.
Selecting a Preferred Alternative
After nearly two years of study and discussions with residents, Seattle Public Utilities has decided to address the neighborhood’s ongoing stormwater and sewage storage issue by pursuing construction of an underground storage tank across the street from Martha Washington Park, at 5560 S. Holly St.
To reach a decision, the SPU project team weighed community impacts, environmental considerations, technical feasibility and cost. At the onset of the siting process in 2010, storage options included Seward Park and Martha Washington Park, under streets (the right-of-way option), and on private property.
Since May 2010, SPU has held six public meetings, four briefings and two drop-in events at Martha Washington Park, in addition to one-on-one meetings with immediate neighbors of the park.
In response to community feedback, SPU separated the review processes for Basin 44, which drains toward Seward Park, and Basin 45, which drains to a pump station on the south side of Martha Washington Park. By mid-2011, siting alternatives for the project in the Martha Washington Park vicinity were narrowed to storage under 57th Avenue South, private property and the park itself.
As the project team evaluated these three options, a property owner offered to sell the parcel at 5560 S. Holly St. This property ranked the highest when scored against the storage options in Martha Washington Park and under 57th Avenue South.
Frequently Asked Questions
North Henderson - Frequently Asked Questions - October 2010 (pdf)
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- February 26, 2012 Basin 45 (Martha Washington vicinity) Staff-Recommended Alternative Open House - possible restoration concepts and conceptual layouts, comment summary (pdf)
- June 9, 2011 Basin 45 (Martha Washington Park Vicinity) Alternatives Workshop - meeting summary, alternatives comparison, display boards, comment form (pdf)
- June 7, 2011 Basin 44 (Seward Park) Open House - public scoping summary, project guide, presentation, display boards, comment form (pdf)
- March 10, 2011 North Henderson Workshop #4 - presentation, summary of project cost estimates (pdf)
- January 19, 2011 North Henderson Workshop #3 - agenda, presentation, meeting summary, meeting summary appendices, evaluation criteria, scoring, weighting sheet, cost summary (pdf)
- December 14, 2010 North Henderson Workshop #2 - meeting summary, presentation, display boards (pdf)
- November 18, 2010 North Henderson Workshop #1 - meeting summary, presentation, display boards( pdf)
- October 4, 2010 Friends of Seattle's Olmsted Parks Briefing - presentation (pdf)
- October 2, 2010 Friends of Seward Park Briefing – presentation pdf)
- September 16, 2010 North Henderson Basin Community Briefing - notice, presentation (pdf)
- June 23, 2010 Southeast District Council Meeting - presentation (pdf)
In response to community feedback, SPU is conducting separate siting and environmental processes for Basin 44, which drains to Seward Park, and Basin 45, which drains to Martha Washington Park. Public comments received at meetings in late 2010 and early 2011 supported managing CSOs for Basins 44 and 45 separately, rather than combined solutions (e.g. a large storage tunnel to convey and store).
Seward Park Area (Basin 44) Project Alternatives
SPU proposes to build an underground storage facility in Seward Park to temporarily hold combined sewage and stormwater runoff. SPU is currently developing a Draft Environmental Impact Statement (EIS) under the State Environmental Policy Act (SEPA) to document how the project could impact people and the environment. SPU anticipates releasing the Draft EIS in late 2011. SPU is currently studying two project locations in Seward Park.
View the Community Guide to the Project (pdf) to learn more about the Seward Park (Basin 44) alternatives.
Martha Washington Park Vicinity (Basin 45)
After nearly two years of study and discussions with residents, Seattle Public Utilities has decided to address the neighborhood’s ongoing stormwater and sewage storage issue by pursuing construction of an underground storage tank across the street from Martha Washington Park, at 5560 S. Holly St. In mid-January 2012, SPU will hold an informal open house near the intersection of 57th and South Holly Street to provide the most up-to-date project and schedule information. Please sign up for a listserv message with the exact date, time and location.
SPU will prepare an Environmental Checklist under the State Environmental Policy Act (SEPA) to document how the project could impact people and the environment. SPU anticipates issuing a determination of findings (threshold determination) in late 2012.
There will be two opportunities to provide public input about the recommended alternative. As part of the State Environmental Policy Act (SEPA), SPU is moving ahead with the environmental review process for Basin 45. The SEPA environmental review documents will be available in early March/April 2012 for the public’s review and comment.
In May, the Seattle City Council will hold a public hearing prior to finalizing purchase of the property. Construction is tentatively scheduled to begin in 2015. Additional opportunities for input on site restoration and construction impacts will take place during the design phase. We hope to see you in January to talk further about the project.
View the Alternatives Summary (pdf) to learn more.
We Want to Hear From You
Public input is an important part of our decision process. Email SPU_HCSO@seattle.gov to share your thoughts on the project alternatives:
- What do you like about each of the project alternatives?
- Are there any changes to the project alternatives you would like the project team to consider?
- Are there any environmental, community, or neighborhood issues you would like us to consider?
- Do you have a preference for any of the proposed project alternatives?
To help the project team best understand your concerns and interests, please specify the project (Basin 44 or Basin 45) and alternative(s) your comments address.
Seward Park Area (Basin 44)
Martha Washington Park Vicinity (Basin 45)
- North Henderson (Basin 45) Determination of Non-Significance (pdf)
- North Henderson (Basin 45) SEPA Checklist (pdf)
- North Henderson (Basin 44) Geotechnical Evaluation (pdf)
- North Henderson (Basin 44) Determination of Significance (pdf)
- Genesee & Henderson - Initial Estimation of Overflow Control Volumes (pdf)
- Genesee & Henderson - Preliminary Geotechnical Evaluation (pdf)
- Henderson - CSO Flow Monitoring Report - October 2009 (pdf)
- Henderson - Flow Monitoring Study (pdf)
- Henderson - Modeling Alternatives (pdf)
- Henderson - Modeling Plan (pdf)