Environmental Permit Support for Port of Seattle’s Third Runway

Client:
Port of Seattle

Location:
King County (Seattle), WA

Project Background & Challenges

The Port of Seattle’s Master Plan Update calls for the construction of a new 8,500-foot runway at Sea-Tac Airport — a project that entails placing over 20 million cubic yards of fill for an embankment. Because the new runway will lie within the Miller, Walker, and Des Moines Creek watersheds, the Port must comply with water-quality permits issued by Ecology and the U.S. Army Corps of Engineers. Consequently, before the project can move forward, the Port must address various environmental conditions.

Solution

Using GIS methods, Aspect helped evaluate the potential for contaminant migration via subsurface utility lines. In addition to showing the utility line distribution, our maps effectively presented complex information about groundwater and geologic conditions. They were also used to support testimony on contaminant fate and transport issues presented to the Pollution Control Hearings Board (PCHB) in a case involving Ecology’s 401 Water Quality Permit. After this hearing, Aspect helped address additional permit conditions that required an analysis of preferential groundwater pathways, annual database updates, and mapping.

Aspect also developed a work plan outlining protocols for qualifying fill materials to be used in the embankment. This plan applies to materials imported for a variety of improvements — the third runway, runway safety areas, and the south aviation support area, among others. It also establishes a two-part process that satisfies requirements of Ecology, the PCHB, and the U.S. Fish and Wildlife Service regarding the quality of imported fill. The work plan has been incorporated into construction bid specifications for pre-approval of fill sources.