Yes, there's a very big hole at the site of the Seattle Center Fifth Avenue North Garage. Seeing the site from the sky is the best way to get the big picture. Here are some facts to fill in the details.

• The garage footprint
  The building will be rectangular: about 350 feet long from north to south along Fifth Avenue North and 240 feet wide.
  
  
• Plaza and a place for visitors
  The garage will feature a pedestrian entrance plaza with stair and elevator access for parking patrons, along with vehicle entrances and exits on two sides. An exhibit space along Fifth Avenue will house a Gates Foundation visitor learning center (expected to open in late 2010).
  
  
• The depth of the hole
  Because the site slopes, the excavation will be about 45 feet deep on the south end and 35 feet on the north end.

Dirt removal in progress

Ten to 18 dump trucks and trailers are hauling soil and debris from the site. Each truck driver plans to make approximately six round trips a day.

Crews are working long hours, aiming to get the mass excavation done by the first week in April and to minimize impact on the surrounding neighborhood as much as possible. The garage is expected to open in mid-2008.

On February 8, 2007, Mayor Greg Nickels (at left in photo above) joined Bill Gates Sr., foundation co-chair, Cheryl Scott, chief operating officer, and Seattle Center Director Robert Nellams in a ceremonial groundbreaking for the Seattle Center Fifth Avenue North Garage.

Public parking in the new structure--located between Harrison and Republican streets and across from Memorial Stadium--will replace a surface lot that the city sold last year for our future headquarters.

A public-private partnership

The 1,020-stall garage is a joint project of the City of Seattle and foundation affiliate IRIS Holdings, LLC. Expected to open in mid-2008, it will be owned and operated by Seattle Center.

The city and IRIS Holdings are sharing the construction costs of the garage. The city's share is $15 million (the estimated cost for the city to build a garage above ground). IRIS Holdings is paying $35 million to put the garage underground--as well as adding a planted "living roof" for the street-level structure, a coffee stand, a parking office, and our future visitor learning center.

Cleanup efforts to remove contaminants in the groundwater deep below the northern mid-section of the 500 Fifth Avenue North project site will begin the last week of March. Installing the cleanup equipment will take approximately six weeks of onsite construction.

What contaminants were found in the groundwater?

The site's past use as a bus barn (1939-1986) released gasoline, diesel, and oil into the soil beneath. Gasoline is more mobile (fluid) than diesel and oil, and it migrated deeper through the soil and reached the groundwater. The groundwater will be cleaned using a technique called air sparging and vapor extraction.

How air sparging works

Air sparging injects air directly into groundwater. It is similar to blowing bubbles from a straw into a bowl of water. As the bubbles rise, the contaminants are removed from the groundwater by physical contact with the air and are carried up into the soil in vapors. An extraction system then removes the vapors from the soil.

A combination of 50 air-sparge, vapor-extraction, and monitoring wells have already been drilled. The air-sparge and vapor-extraction wells will be connected underground to equipment housed in a fenced area of approximately 16 feet by 25 feet.

The primary equipment above ground--an air compressor and blower--will be enclosed in sound-dampening boxes. Three cylindrical containers (four feet in diameter and eight feet tall) will rise above the six-foot-high fence. These cylinders contain a filtering system for the exhausted fumes. The filters, which will be changed periodically, trap the gasoline vapors and allow clean air to be exhausted to the atmosphere.

Air sparging is a commonly used technique that takes time but has proven to be effective. Once the cleanup equipment is installed and operational, the process likely will go on for at least three to five years.

Environmental goals

Our goal is to design and build the new campus to reflect Seattle's citywide policy on sustainable building--emphasizing environmental and social stewardship. The City of Seattle and IRIS Holdings, LLC, are cleaning up the site as part of the state ecology department's Voluntary Cleanup Program, and the cleanup plan has been approved by the State Department of Ecology.

Interested in more details about upcoming construction work? You can stay up to speed by reading bulletins posted by Sellen Construction, the project general contractor.

The bulletins help our future neighbors know what to expect and when to plan for changes around the project site, including street closures.

Bulletins in PDF format are posted at:
http://www.sellen.com/gatesfoundation.html