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Seattle Seahawks football complex features 8-layer “sandwich”

Case Studies | April 1, 2009 | By:

The ‘sandwich’ includes liner, grids and textiles.

Among the hundreds of projects judged at the national competition for the American Council of Engineering Companies (ACEC) in Washington, D.C., in April was an athletic compound in Washington state featuring several geosynthetic components.

The engineering involved brownfield remediation, as well as construction of a major structure on an ecologically sensitive site on the southeast shores of Lake Washington in Renton, Wash. The training facility and headquarters for the Seattle Seahawks — the Virginia Mason Athletic Complex — is described by engineers on the job as the most ecologically responsible facility in the National Football League (NFL), showcasing natural ecology on the site of a previously contaminated brownfield.

For Magnusson Klemencic Associates (MKA), the primary challenge was the contaminated soils resulting from the 20-acre site’s decades of use as a timber creosoting facility. The high levels of contamination required significant excavation and handling of the soils, as well as carefully engineering a stormwater conveyance system to protect native salmon migratory routes and to repair a neighborhood flooding problem. The stormwater system re-established the historic Gypsy Creek’s salmon migratory route by developing a fish-safe underground pipe to provide passage through the site’s toxic soils, a railroad line, city street, and other impediments.

Throughout the process, MKA’s strategies to handle soil and water provided a new creative model using natural techniques to protect against contamination and to purify water runoff. Instead of hauling contaminated soils offsite to a landfill, MKA developed a 3-ft-deep clean soil cap formed into a spectator viewing platform, ensuring spectator safety while also enhancing the site. This innovation alone saved the client $1.7 million in disposal fees, according to MKA.

A PVC liner was used to cap the ground under the indoor field and at specific locations where pre-excavation was prohibitive. For the rest of the site, MKA worked with an environmental consultant and the state Department of Ecology to place 3ft of imported soil above an “indicator fabric,” which designates the presence of contaminated materials.

Under the fields is a complex eight-layer “sandwich” containing cement-treated soils, geogrids, geotextiles, the indicator fabric, capping soils, gravel, sand, and turf (Figures 1, 2, 3). Figure 1 | Photo courtesy of Football Northwest. Figure 2 | Photo courtesy of Football Northwest. Figure 3 | Photo courtesy of Football Northwest. The layering not only ensured detoxification, but mitigated any potential uneven soil settlement.

The traditional parking lot storm drainage system channels runoff through environmentally friendly surface sand filters, cleaning the water in a vertical percolation process. In addition, MKA created six outfall points along the shoreline to reduce the outfall rate and minimize the deluge flows that inhibit habitat. The capping and filtration designs mean that rain falling on the site flows to the shores of Lake Washington as clean runoff.

The team successfully transformed this previously toxic area into an athletic destination as well as a scenic waterfront development. The complex includes three natural turf outdoor practice fields as well as a full-size, synthetic-turf indoor field.

The layout of the outdoor fields allows for rotation throughout the season to reduce wear. The fields are located immediately adjacent to the shores of Lake Washington and include additional sand layers for water quality filtration. The drainage system has six zones and includes access ports for a portable subsurface air ventilation system.

This system can function in either forced-air or suction mode and allows for both temperature moderation in the root zone as well as accelerated moisture removal from the field’s surface. The automatic irrigation system includes valve-in-head sprinklers so each field area can be controlled separately, thus providing maximum flexibility in field layout to rotate wear.

The indoor practice field was installed on a paved base with a supplemental pad system.

The northernmost 20 acres of what is called the Port Quendall project area is the site for this new privately funded complex that houses the headquarters and state-of-the-art training facilities for the Seattle Seahawks. A three-story building houses the administrative offices and features a cafeteria, weight room, team auditorium, locker room, lounge, team meeting rooms, indoor turf field, and media production studios. The facility is approximately 200,000ft2, nearly five times larger than the previous Seahawks facility in Kirkland, Wash. The new complex was completed in the summer of 2008.

Ron Bygness is the editor of Geosynthetics. He can be reached at 800 225 4324 or 1 651 225 6988, or via e-mail at

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