CitiesGoGreen - February 2009 - (Page 17) he “Swale on Yale” in Seattle, Washington, will be the first large-scale biofiltration system in an American city, according to Seattle Public Utilities (SPU). Spurred by Washington State’s new stormwater ruling requiring low impact development, the city paired with private real estate developer Vulcan Inc. to create four, 10-foot wide biofiltration ditches called “swales” to protect the local watershed. The four swales will filter 188 million gallons of runoff annually from 360 acres on Capitol Hill, in the heart of Seattle. The $8 million low-impact system T The Swale will capture about two and a half dump-truck loads of sediment, or about 4% of the polluted silt that would otherwise enter Lake Union, according to SPU. “Four percent is nothing to sneeze at,” said Chris Woelfel, SPU’s swale project manager, “but it’s not a magic answer for this lake.” Currently, untreated runoff flows into the lake, a heavily urbanized, 580-acre body of water just north of downtown Seattle, rimmed with roads, marinas, moorages, industries, commercial docks and dry On Yale by Sam McNeil docks. Woelfel said SPU chose to build the swales on Capitol Hill because of the neighborhood’s legacy of industrial pollution, “extra dirty runoff” from its high-traffic commercial and residential zones, and the opportunity created by the current South Lake Union redevelopment by Vulcan, which is required by law to incorporate “complete streets” in its plan. “The swales will be built in conjunction with the development,” said Market Research Manager Lori Mason Curran. Vulcan’s redevelopment of the neighborhood centers around renovating old warehouse industrial properties into multistory, mixed-use sites. The swales support the complete streets requirement by providing pedestrian-friendly space and adding green to the neighborhood’s aesthetic. “[The swales] will be an attractive landscape between the street and the sidewalk,” said Curran. After running off Capitol Hill the water goes into a pretreatment vault to “get the big gunky stuff out,” Woelfel said. “Beer bottle caps will fall out and cigarette butts will float.” Then the water flows through the swale in nine minutes, slow enough to allow particulates to settle. Every five to ten years the settled particulate layer will be scraped off, dumped and replaced with fresh soil by SPU, Woelfel said. Upkeep should only require two workers in a truck. Swales won’t work for every ecosystem, according to Woelfel. Swales can’t handle flash-floods, but are good for dealing with the sort of steady, light rain common in the Seattle area. The Pacific Northwest, Woelfel said, is leading biofiltration innovation partly because of its weather. v Sam McNeil is a freelance environmental convergence journalist based out of Seattle who is studying Arabic in hopes of furthering intercultural dialog. February/March 2009 17 http://citiesgogreen.com/issues/february-2009/current-features/the-swale-on-yale http://citiesgogreen.com/issues/february-2009/current-features/the-swale-on-yale http://citiesgogreen.com/issues/february-2009/current-features/the-swale-on-yale http://seattlepi.nwsource.com/local/380927_stormwater29.html http://www.seattle.gov/UTIL/About_SPU/News/News_Releases/SPU01_003989.asp http://green.kingcounty.gov/lakes/LakeUnion.htm http://www.seattle.gov/UTIL/About_SPU/News/News_Releases/SPU01_003989.asp http://www.ens-newswire.com/ens/aug2008/2008-08-12-093.asp http://www.ens-newswire.com/ens/aug2008/2008-08-12-093.asp http://vulcan.com http://www.worldchanging.com/local/seattle/archives/008770.html http://www.worldchanging.com/local/seattle/archives/008770.html http://www.CitiesGoGreen.com
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