Left: Construction of a third runway at Seattle's busy Sea-Tac Airport—for which trucks will haul in 17 million cubic yards of dirt fill—will help alleviate the nearly $100 million additional operating costs incurred yearly due to delays. Photo: Port of Seattle. Above: Stormwater runoff systems throughout the third-runway construction area include sand-filter tanks and an 8×10-foot monitoring station. Photo: Hach Co.
Miller Creek, a natural stream in the construction area, has been enhanced with poles and wires, which hold shade cloth during warmer months to keep the creek cool until native plants can provide natural shade. Photo: Port of Seattle

Imagine you're adding a runway at a busy international airport. Then, imagine doing it while saddled with the most stringent environmental impact mitigation permits issued in state history. You would be managing the third-runway project at Seattle-Tacoma (Sea-Tac) International Airport in Washington, an endeavor many involved consider one of the most complex public works projects in the state, if not the country.

The Port of Seattle—the public enterprise responsible for the $1.13 billion project—has faced enormous challenges during planning and construction of a third runway at Sea-Tac. Yet, what first appeared to be a win-or-lose showdown between transportation improvement and environmental interests morphed into a study in cooperation and innovation.

“In the end, we're very confident that the natural environment will be better, with cleaner water, because of the project,” said Ray Hellwig, director of the Northwest Region of the Washington State Department of Ecology.

To create the raised embankment for the runway, which will measure 150 feet wide and 8500 feet long, 17 million cubic yards of fill dirt will be brought to an area constrained by creeks, wetlands, and public roads. As of May 2005, 221,620 truck trips have brought in more than 3 million cubic yards of the 6 ½ million cubic yards of fill material contracted for delivery in 2004–2005. The more than 11 million miles driven under the contract has created a market for a local refinery to provide ultra-low-sulfur diesel fuel, specified for use in the project's trucks to minimize the air-quality impact.

Raising the Bar

According to Hellwig, Sea-Tac's permit that certifies compliance with Section 401 of the Clean Water Act (CWA) is the most stringent ever issued by the Washington State Department of Ecology.

“Typically, a 401 permit for a federal transportation project requires that ‘no toxic fill, in toxic amount, can be used,'” he said. “For this project, we specifically require that a state-certified laboratory screen the fill samples for arsenic, metals, and total petroleum hydrocarbons that might contaminate the groundwater through leaching. We've specified use of the synthetic precipitation leaching process test, a U.S. Environmental Protection Agency method usually applied in characterizing municipal solid waste and landfills.”

Permitting addresses not only quality but also quantity of area water. “We looked at the impact of the construction on subsequent flow of ground and surface water, at how the mechanically stabilized earth walls would change the way water expresses itself in nearby streams,” said Muffy Walker, now chief of the South Application Review Section of the Seattle District, U.S. Army Corps of Engineers, and project manager at the time permits were being processed for CWA Section 404 compliance.

According to Elizabeth Leavitt, manager of Port of Seattle Aviation Environmental Programs, “We are constructing vaults to hold well-sourced water for release during low-flow periods, to maintain water flow in the receiving creek.”

Leavitt also described the permit-required mitigation for the 21 acres of wetlands being consumed during runway construction. “We are replacing that area, which supports migratory and native birds, with 65 acres of wetlands offsite, in nearby Auburn. This restoration, with plantings that target avian species, moves the birds away from air traffic.”

“Onsite mitigation within the Des Moines/Miller Creek watersheds will minimize avian habitat and, instead, focus on fish habitat and other wetland functions such as natural filtration of organics and flood control, all to maintain the quality of the aquatic life of the basin,” said Walker.

Further, modifications to the Port of Seattle's renewable National Pollutant Discharge Elimination System permit will extend the mitigation measures. Ed Abbasi, permit engineer with the Department of Ecology Water Quality Program, said that by July 2007, the Port of Seattle must achieve a 99% reduction of the monthly average biochemical oxygen demand (BOD) of the water discharged from the airport's 300-acre drainage area. From a maximum of 85,000 pounds per day in 2003–2004, or more than 5000 mg/L, the BOD must be reduced to a maximum of 2000 pounds per day, or 30 mg/L. Plans call for constructing a conveyance line to direct runoff contaminated by organics such as de-icing agents, jet fuel, grease, and oil to a publicly owned treatment works a few miles away.

Even with these and other rigorous environmental impact mitigation requirements, the runway's 401 and 404 permits drew critical scrutiny by opponents of the Sea-Tac expansion. Argued over for years, the third-runway project permits eventually required Washington State Supreme Court approval. To compensate for the millions of dollars of added environmental mitigation costs, project proponents petitioned the Federal Aviation Administration for additional funding and have received a total federal commitment of $278.4 million—more federal funding than any other runway project in the country.