Project Profile: Redmond, WA, Leverages Precast Concrete for Stormwater Management

Water is our most precious natural resource. Protecting it within our urban environment requires the proper management and treatment of stormwater runoff. In Redmond, WA, precast concrete is playing a vital role.

One such example is the new Overlake Village park-and-ride, which received a 10-foot-wide by 36-foot-long by 18-foot-deep StormCapture PV panel vault system with 65 stacked 30-inch-tall PerkFilter cartridges for stormwater treatment as well as a 12-foot-diameter Downstream Defender for trash and debris capture. As designed, the PerkFilter system has a design flow rate of 1,428 gallons per minute, while the Downstream Defender has a treatment flow rate of 18 cubic feet per second.

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PerkFilter vault

Located adjacent to the Overlake Village park-and-ride on 152nd Avenue NE will be a new light rail station, with a targeted open date of 2023. The station’s entrance will be along 152nd Avenue NE, just south of State Route 520. Once completed, the new light rail line will link Overlake Village to Pioneer Square, with the ride taking about 30 minutes. Contemporary in design, the station was devised in accordance with the City of Redmond’s 152nd Avenue Corridor Study and the associated Overlake Village Neighborhood Plan.

Working together, general contractors Kiewit-Hoffman and Marshbank Construction, along with McMillen Jacobs Associates, designed the deep underground stormwater vault while also meeting the regulatory requirements of the Washington State Department of Ecology (WADOE). After review, the team concluded that a segmented precast concrete panel vault system would be easier to install with its reduced overall pick weight while also saving months of installation time over a cast-in-place system. The precast solution with the PerkFilter cartridges would also remove total suspended solids and phosphorous in accordance with General Use Level Designation (GULD) requirements of WADOE.

Panel vault installation

WADOE issues guidelines for how stormwater runoff is treated before being discharged off job sites. As a developed site with impervious surfaces, the park-and-ride facility ensured that its stormwater runoff would be as clean as from an undeveloped site with its new stormwater treatment system.

The Oldcastle Precast plant in Auburn, WA, designed, engineered, manufactured, and delivered the precast concrete components of the underground detention system. Oldcastle Precast Auburn Project Manager Rick Roof remarks, “Using precast provided a variety of benefits including strength, durability, and flexibility of design, and it vastly improved the construction schedule, operational efficiencies, and overall quality of the detention structures for this project.”

In total, the Auburn plant supplied the StormCapture PV flat-base slabs, wall panels, and top slabs, as well as ladders, cast-iron covers, and risers for the underground detention vault. The Oldcastle Precast plant in Stockton, CA, supplied the PerkFilter cartridges and associated installation hardware.

Once completed, the precast concrete stormwater vault will hold about 48,000 gallons of rainwater before slowly releasing it into the downstream storm drain system to prevent flooding. Each precast panel was sealed using hydrophobic sealer, ensuring a watertight system. As soon as water touches the sealer, it triggers the sealer to spread, harden, and cure between panels so there is no accidental seepage.