Pump Station and Water Quality Facility
This project is a first step toward protecting people in South Park from flooding and protecting the Duwamish Waterway from polluted stormwater runoff.
The northwest industrial and residential area of South Park experiences chronic flooding for three reasons:
- The main drainage pipe to the Lower Duwamish Waterway is underwater during high tide. When it rains during high tides, the main pipe cannot drain out to the river and water backs up in the drainage system. Rain falling in the lower areas of the basin can't flow out and runoff from the upper areas of the basin can sometimes flow back out of inlets and catch basins, flooding the neighborhood. A pump station will allow the main pipe to drain during high tides and relieve flooding.
- Not all streets in the area have a drainage collection system. Additional connections cannot be built until the pump station is installed so that the pipes can drain at high tide. The new flood control pump station will not correct this problem by itself. If additional roadway drainage is built in the future, it will connect to the main and the pump station will allow the system to drain when the tides are high.
- Many private properties in the basin do not have drainage pipes connected to the public drainage system. Some properties are lower than the street or there is no existing street collection system. In these areas, individual property owners may need to make site improvements and connect to a public drainage system in the street, when one is available.
Water Quality Facility
From the pump station, stormwater will be sent through the facility where it will be treated to remove a variety of pollutants that are common in urban runoff. The treated stormwater will then be released through the existing outfall to the waterway. This will result in cleaner water and a healthier Duwamish River.
The site for this project was selected because of its location on the main stormwater drainage pipe where it empties into the Duwamish. The facilities will be located along the edge of 7th Avenue South near Riverside Drive and on adjacent land parcels already owned by Seattle Public Utilities.
The project will have underground equipment and above-ground structures including a small electrical controls building and a concrete structure, about 12 feet tall, 50 feet wide and 110 feet long. The facility will be fenced for security and will have security lighting. It will be run remotely so staff will only visit the site periodically to check and maintain it.
In 2012, new information on the performance and maintenance needs of the selected treatment technology became available, that indicated it might not perform as effectively or affordably as anticipated. Design and construction of the South Park Pump Station and Water Quality Facility were delayed so that our technical team could reevaluate appropriate technologies, and consider new technologies which recently became available.
SPU follows a deliberate process for making transparent decisions fully informed by:
- Project risks
- Financial, environmental, and social impacts and benefits
- Project life-cycle cost
SPU needed to evaluate treatment technologies to balance water quality treatment and protection of the Duwamish River with project costs. We needed to compare options based on the new information.
Project Update - December 1, 2014
In order to provide some flooding relief as early as possible, SPU has decided to build the flood control pump station before the water quality facility. Here are SPU’s projected next steps:
- Complete design and construct the flood control pump station. The current schedule for this project anticipates design will be complete in spring 2016 and construction complete in fall 2017. The flood control pump station will reduce flooding in areas where drainage systems are in place. It will not eliminate flooding in the in all areas of the lower 7th Ave S basin, which includes the industrial area nearest the river.
- Identify the best water quality treatment technology. SPU needs to test three possible technologies side by side to see how they would perform in this location. The current schedule calls for pilot testing to be complete in spring 2016 and a technology selected by fall 2016. Design and construction schedules will be developed once a technology is selected.
To ask questions or let us know what you think, email the project manager or give her a call: Sheila Harrison, (206) 684-5899.