Located near Seattle, Wash., the Lynnwood Convention Center was the first project undertaken by the Lynnwood Public Facilities District. The District was created to spur economic growth through the development of public facilities and will lead the planned revitalization of the City of Lynnwood.
The success of the convention center project hinged on finding a stormwater management system that met site challenges while maximizing usable land. The existing 5.3 acre site was comprised almost entirely of existing commercial development, and the design of the convention center would result in 4.6 acres of impervious area. No land was available for above ground detention.
The District, working with Perteet Engineering, explored underground stormwater storage. However, the location available on the site was under access roads in the front of the building, and elevation constraints required shallow cover. This was primarily a concern because of the loading requirements required to accommodate the City’s fire trucks, amongst the heaviest in the state due to additional equipment. In order to meet these requirements, the lids on the detention facility would have to be specially designed to handle loading requirements in excess of H-20.
“We were looking at pretty excessive costs for constructing the detention vaults,” said Project Manager Erik Emerson, PE, from Perteet. “With a fixed budget for the project, the cost was really starting to impact the ability of the architect to build the building that the client wanted.”
During geotechnical explorations at the site, geotechnical engineers from Zipper Zeman Associates, Inc, found a sand lens, or layer, 26 feet deep. Using this information, Perteet designed an infiltration facility that saved the District about $300,000. A 26-foot-deep, 60-foot-wide, and 100-foot-long underground infiltration gallery was excavated.
“Right in the middle of the city we dug this monstrous hole,” said Emerson. “Then we backfilled it with clean drain rock to create a filled infiltration gallery.”
During construction, a full scale live test was completed using a Lynnwood Fire Department truck pumping water at a flow rate of 1500 gallons per minute. The gallery was found to exceed design expectations for infiltration.
To protect the gallery and prevent blinding over time, Perteet installed the Stormwater Management StormFilter® upstream. The StormFilter is a passive media filtration system that removes pollutants from stormwater, including TSS, soluble heavy metals, oil and grease, and total nutrients. Two 8 by 16 foot StormFilter vaults were installed in series, and house a total of 59 perlite-filled cartridges with a filtration rate of 7.5 gpm per cartridge.
“As the gallery is very deep there is really no way to maintain it. Our goal was to put the cleanest water as we could into it,” said Emerson. He researched stormwater treatment systems and found that the StormFilter can achieve treatment levels that others can not.
In addition to garnering interest from surrounding property owners with upcoming redevelopment plans of their own, the Lynnwood Convention Center’s innovative stormwater system won an Engineering Excellence Silver Award in 2005 from the Washington Chapter of the American Council of Engineering Companies.
As the first step to building a downtown core, the Lynnwood Convention Center is leading the way as both the model for public facilities and for improving and protecting urban watersheds.
About the Product
The Stormwater Management StormFilter® is a passive media filtration system that removes TSS, soluble metals, oil and grease, and total nutrients from stormwater. Siphon-actuated filter cartridges, which trap and adsorb pollutants, feature a surface cleaning system that prevents blinding and extends maintenance intervals.