The decision came as a blow to homeowners who have been battling airport expansion for years, and they have vowed to appeal the DOE's ruling. But it was a blessing for the port, which has been bucking for a third runway to handle increased traffic.

Only one hurdle - a federal permit from the Army Corps of Engineers - remains before final work can begin. The port wants to build an 8,500-foot runway west of SeaTac's existing runways by building up the airport's property with more than 17 million cubic yards of dirt. Wetlands and three streams with fish are in the vicinity.

According to the DOE permit, the port will protect and restore nearby wetlands, as well as manage stormwater to avoid polluting three salmon-bearing creeks contiguous to the runway site.

The port also will create a 60-acre wetland on property it owns along the Green River near Auburn.

"We are confident that the port's proposal satisfies all local, state and federal environmental regulations," Tom Fitzsimmons, state ecology director, said in a prepared statement.

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