Port of Seattle to Give $1.2B Airport Project Environmental Safeguards

The port won the final go-ahead for the third runway at Sea-Tac Airport in 2004. The job is expected to be done sometime in late 2008.

Aug. 22--When the sun starts lingering longer each April, biologists working for the Port of Seattle carefully install hundreds of feet of shade cloth on a wooden superstructure straddling Miller Creek near Sea-Tac Airport.

In October, as the days grow shorter and the skies get grayer, they remove the protective cloth.

The twice-yearly shade cloth ritual is a critical part of the largest public works undertaking in the Puget Sound area, the $1.2 billion Sea-Tac Airport third runway construction project.

Without the shade cloth, the water in Miller Creek -- which in August gurgles downhill at barely more than bathtub volumes -- would become overheated. The native bream and sticklebacks, cutthroat trout and coho salmon could die. If they died, the project, its 900 workers and hundreds of pieces of machinery could come to an abrupt halt.

The shade cloth is one of hundreds of environmental safeguards built into the permits that allow the port, the airport's owner, to build the third runway. Those permits and the conditions that accompany them took years to reach final form. Those conditions were the subject of dozens of public hearings and nearly a decade of battles in federal and state courts.

The port won the final go-ahead for the third runway in mid-2004, and the project is beginning to take its final form.

When the job is done sometime in late 2008, the runway will be among the most expensive.

There are two reasons for the high price tag: the sheer scale of the project itself and the extraordinary environmental safeguards necessary to build an airport in the watershed of two salmon-bearing creeks.

From the expansive windows of the airport's new Central Terminal, the third runway will hardly seem spectacular. At 8,500 feet long and 150 feet wide, it will be shorter than either of the existing parallel runways.

The runway will be built using standard construction techniques. Slip-form paving machines will apply a layer of concrete 18 inches thick over a base of gravel. The runway will be strong enough to take years of pounding from aircraft landings. The runway shoulders will be made of asphalt strong enough to support the wheels of the occasional taxiing aircraft but not stout enough to take the beating the main runway will absorb, said John Rothnie, the airfield program manager.

Though the runway itself won't be extraordinary, the huge fill necessary to bring the west side of the airport level with the existing runways will be.

Until recent years, Sea-Tac's west side was a neighborhood populated with a mixture of small and medium-size homes and urban farms amid a forested wetland. That cool forest was crossed by Miller Creek on the north and Des Moines Creek on the south. At the north, a man-made impoundment, Lora Lake, was the backyard for several homes.

Most of the neighborhood was located below existing runway levels. To expand, the port bought and demolished more than 500 homes and businesses and is filling in some of the wetlands where the neighborhood once stood.

In some places, that fill is 140 feet deep, as tall as the Pacific Towers condominiums overlooking downtown Tacoma from Pacific Avenue.

The fill will amount to some 17 million cubic yards of carefully tested dirt. That dirt is coming by truck and barge from seven sites in the Puget Sound area as distant as DuPont. Before the dirt can be used as part of the runway fill, the pits where it is obtained must be geologically mapped and tested for contamination.

Only the cleanest fill need apply.

The material must have a specific consistency. For instance, too much organic matter in the fill would disqualify it because the decaying vegetation could compress and cause an uneven runway base. Too much clay, and the fill could become saturated with water and slide during heavy rains or an earthquake.

The fill nearest the edge must have rocks included, no larger than 6 inches in diameter because of the chance that larger rocks could tumble down the slopes and injure those below.

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