“Green” proposal for CSO control in Barton basin
Barton CSO basin project area
Examples of streets with GSI (Seattle and Port Townsend) - Slide 27
Example GSI concept in Barton subbasin 416 - Slide 25
Typical GSI construction area - Slide 44
Source: Green Stormwater Infrastructure presentation, August 5, 2010 (PDF)
King County plans to design and build green stormwater infrastructure (GSI) to control combined sewer overflows (CSOs) in the Barton basin. The GSI project will consist of planted areas between sidewalks and curbs in the Sunrise Heights and Westwood neighborhoods in West Seattle. Also known as “raingardens,” GSI refers to engineered infrastructure used to manage stormwater. GSI uses soils and vegetation, in combination with other decentralized storage and infiltration approaches to infiltrate, evaporate, capture, and reuse stormwater. In the Barton basin, raingardens, plantings, and street trees in the City of Seattle-owned right-of-way will be designed to capture and reduce the amount of peak stormwater flows that would enter the combined sewer system to reach the control target of no more than one overflow per year on a long-term average. This is the first “green” project King County Wastewater Treatment Division will implement for flow control in the conveyance system. King County will work closely with project neighbors and the West Seattle community throughout design, construction, and into operations.
How community input informed the decision process
Since late 2009, county staff has been meeting with neighborhood residents. In March 2010, King County presented three proposals for CSO control in Barton. The county’s project team hosted a public meeting, a technical information session to help people more fully understand the GSI option, and a meeting in fall 2010 to hear about an additional alternative proposed by the community. People had opportunities to provide feedback at a public meeting, on the Web, and by email, mail, and phone to project staff.
King County’s project team used input from the community along with a range of selection factors and updated technical information to evaluate alternatives. Community questions and concerns related to project design and construction will be carried forward as King County continues to work with the Barton community throughout the project.
Barton CSO Control Project- Green Stormwater Infrastructure
The recommended proposal involves use of planting strips in the City-owned right-of-way on approximately 66 blocks (see map). This option for CSO control provides a number of benefits:
- Vegetation allows stormwater runoff to infiltrate into soil rather than entering the combined sewer system. By maximizing use of natural processes, the project supports the region’s commitment to energy conservation and sustainability.
- King County will work with the neighborhood to enhance street aesthetics, minimize parking impacts, and respond to neighborhood preferences for the project.
- The project does not require any operating facilities, and responds to many West Seattle residents who expressed strong support for a “green” solution.
- This approach significantly reduces the risk of combined sewer overflows at Barton and reduces flows to the Murray Basin.
Project elements (see map) include:
- Existing planting strips landscaped and planted for retention of stormwater
- Widened planting strips on some streets
- Curb cuts allowing water to enter and exit raingardens
- Access to residences from the street, as needed
What is next
- King County continues to work with project neighbors and the Barton community throughout design and construction
- Many opportunities to be involved in this project are still to come, beginning in early 2011, when the State Environmental Policy Act (SEPA) review of the recommended proposal will begin with a threshold determination and formal comment period.
- Construction may take up to 2 years and is expected to begin no later than December 2013.
- King County will monitor and maintain GSI installed for CSO control in this area.
What we heard from Barton stakeholders
Community members provided King County with a robust level of input during the alternatives evaluation process, attending meetings, contacting staff, taking online surveys, and mailing in comment forms.
- For the GSI alternative,
- Support for this approach to control CSOs
- Concerns about potential for flooding, drainage, or landslide problems associated with infiltrating stormwater
- Concerns about potential impacts to cultural resources, vegetation, and green space adjacent to the proposed storage alternative for Upper Fauntleroy Way SW
- Support for locating an underground storage facility at the former Fauntleroy School site, and also concerns about impacts of this alternative on businesses and nearby areas
- Concerns about the proposed Lincoln Park alternative due to potential construction impacts on traffic, public recreation access, vegetation and wildlife