Unique Drainage System Will Filter Capitol Hill Stormwater
‘Swale on Yale’ Will be Nation’s First Large-scale
Urban Biofiltration System

For immediate release: 9/30/08
For more information, Contact:
Seattle Public Utilities Customer Service, (206) 684-3000

SEATTLE —Seattle Public Utilities (SPU) is preparing to build the nation’s first large-scale biofiltration swale in an urban streetscape — a project that will treat more than 188 million gallons of stormwater annually from upper Capitol Hill, one of the city’s most densely developed neighborhoods.

The innovative project will apply SPU’s proven natural drainage practices in a new setting, piloting a novel approach to integrating a public drainage system with private property redevelopment — maximizing construction efficiencies, sharing maintenance requirements, and reducing overall project costs.

Nicknamed the “Swale on Yale,” the project will be built in conjunction with adjacent redevelopment by Vulcan Inc. that will transform existing one-story warehouses and offices into multi-story mixed-use retail, office and/or residential buildings.

As part of its redevelopment, Vulcan is required to make street improvements; and by partnering with SPU, those funds will go towards a complete street redesign which also achieves water quality improvements.

“The project looks like four extra-wide, nicely vegetated planting strips,” said Chris Woelfel, SPU’s manager for the $8 million project. “In fact, it’s also a stormwater treatment facility that removes pollution from over 160-acres of Capitol Hill runoff. We can create a neighborhood amenity at the same time we improve water quality in Lake Union. It’s a win-win.”

Currently, stormwater flows across the streets of upper Capitol Hill collecting silts, oils, heavy metals and other pollutants before being piped downhill, under the Cascade Neighborhood and into Lake Union, untreated. As part of the Swale on Yale project, a portion of this Capitol Hill runoff will be routed to a system of four biofiltration swales —wide, flat-bottomed ditches planted with thick vegetation.

As a first step, the diverted water will be sent through an underground chamber called a pretreatment vault where trash, gravel and large sediment will be removed. The runoff will then flow into one of the four biofiltration swales. The thick vegetation and gentle slopes in the swales will reduce the speed of the water flow, allowing sediments and pollutants to settle out. The Swale on Yale project will remove an estimated 25 cubic yards of sediments and pollutants per year from the stormwater before it enters Lake Union — the equivalent of 2 ½ dump truck loads.

The Swale on Yale will provide a neighborhood amenity and additional green space in the Cascade Neighborhood. This is in keeping with Mayor Greg Nickels’ goal of encouraging pedestrian-friendly streets and additional green space.

Construction is slated to begin in 2009 with construction of storm drains which will convey the stormwater to project site. Other phases will be constructed between 2010 and 2012 and will be coordinated with adjacent private redevelopment. There will be opportunities for public input along the way.

The Swale on Yale is part of Seattle’s Restore Our Waters Program, launched by Nickels in 2004. The city’s commitment is to take action and promote partnerships that protect and improve urban water bodies, based on science. The program goals are to reduce stormwater runoff and water pollution, and restore aquatic habitat in the city's waters. For more information please visit the Restore Our Waters website.

Vulcan Inc. may be contacted through Lori Mason Curran, manager of market research and investment strategy for Vulcan Real Estate, (206) 342-2265, LoriC@vulcan.com.

In addition to providing a reliable water supply to more than 1.3 million customers in the Seattle metropolitan area, SPU provides essential sewer, drainage, solid waste and engineering services that safeguard public health, maintain the city’s infrastructure and protect, conserve and enhance the region's environmental resources.

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Seattle Public Utilities