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.
Moving that dirt from the distant pits to the site requires a fleet of trucks specially equipped for the project. Over the life of the project, those trucks will make a total of 350,000 trips between the airport and the pits, Rothnie said. That means 40 to 60 trucks arriving at the airport site every hour during the day and as many as 90 an hour at night when the freeways are clearer. The filling continues 20 hours daily, six days a week. The port has built a special "construction vehicles only" off-ramp from the Washington 509 freeway at South 176th Street west of the airport to serve those trucks.
The trucks must be 1998 models or newer and must be powered by diesel engines specially equipped to burn ultra-low-sulphur diesel. That fuel, said the port, is available at only two sources in Western Washington.
To accommodate the new runway, Weyerhaeuser Co. had to relocate its corporate hangar from the middle of the west side of the airport to the south end, where the port has built a parking area for the few private aircraft that use Sea-Tac.
The port is building several mammoth walls as tall as 135 feet and up to 1,460 feet long to contain the fill at strategic places. By building the walls -- which are almost vertical from bottom to top -- the port has minimized the area of wetlands that it would have covered if it had built conventional sloped sides to the fill. The walls are faced with 5-by-5-foot cross-shaped interlocking concrete panels. Attached to those panels are steel straps extending deep into the mountain of fill. Those straps are longer and more numerous at the bottom of the walls and fewer and shorter at the top.
This network of straps helps tie the fill together to prevent it from sliding during an earthquake, Rothnie said.
The straps are laid out according to a plan, bolted to the wall and then covered with a shallow layer of fill. The fill is compacted with a mechanical roller, and the compression is tested. If the compressed earth doesn't meet the rules, it is dug out and replaced.
On the outside of some of the panels, the concrete forms designs of Northwest symbols -- birds, fish and other objects pleasing to the eye.
To allow the aircraft sufficient overrun areas on the north end of the runway, the port has also had to relocate 154th Street some 300 feet farther north and built a new bridge over Miller Creek.
The project has taken extraordinary measures to restore the two creeks to pristine condition, said Robin Kordik, senior environmental program manager for the port.
The port claims that for each of the 21 acres of wetlands that it is covering with the new runway fill, it is creating 5 acres of new wetland either on the site or in Auburn near the Green River. The Auburn site will be a more swamplike wetland conducive to bird life. The port couldn't build such a wetland near the runway because of the danger birds pose to airliners.
Kordik said the new creeks will be far more productive than the old ones -- which in some places were just tire-lined ditches farmers excavated from their lands.
The new creek beds provide a relatively narrow channel where the creeks run during the summer when water is low. The design also creates a larger flood plain where water can spread during winter and spring rains.
In creating those creek beds, the port has lined the banks with a woven coconut fabric called coir to stabilize the banks and provide a secure place for new plants to take root.
The beds have been lined with spawning gravel. Here and there, the construction crews have anchored fallen trees, called LWD (or larger woody debris in envirospeak), to give fish a refuge from the sun and predators.
When construction crews are rebuilding a section of the creek, biologists remove all the fish from that section by trapping and gently shocking them. After counting and tagging them, the fish are transplanted to other sections.
After the port demolished the homes on the site, it removed hundreds of septic tanks that were contaminating the soil. Workers also eliminated non-native vegetation -- including blackberries, decorative shrubs and ornamental plants -- from the forest floor.
When the fall rains come, the port will plant some 168,000 native trees and plants to shade the streams and control erosion in the forest. Those plants will get a boost from an underground watering system that will provide supplemental moisture for at least three years until the plants are established.
Once the plants and trees are large enough to shade the water, the yearly installation of the shade cloth will be unnecessary.
Runoff from the construction site is captured in a drainage system. Oil is skimmed off, and larger solids settle out in ponds. The water is then pumped through large treatment facilities where it is filtered through crushed crab and shrimp shells and then passed through a layer of sand. The water that emerges is clear, Kordik said.
In Lora Lake, the port is removing several concrete bulkheads. To keep mud from that removal project from spreading into the lake waters, the port has hung silk curtains in the water within a few feet of the bulkheads to catch the sediment.
The port has built two truck washes on the site. Each dump truck is washed before it returns to the highways. Nine water trucks continually wet down the site to keep stray dust from blowing into nearby neighborhoods or toward the runways, where dust can be sucked in by jets taking off.
The water from the washes is routed to settling basins, then filtered and reused. The sludge accumulating in those basins is removed and trucked off the site once a week, Kordik said.
The permits require the port to monitor the mitigation site for 15 years after the runway goes into service in 2008.
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