Tetra Tech EC, Inc. (Tetra Tech) conducted field surveys and prepared the joint National Environmental Policy Act/Washington State Environmental Policy Act (NEPA/SEPA) EIS for the Methow Transmission Project under contract with the Public Utility District No. 1 of Okanogan County (PUD). The proposed action and ultimately the selected alternative involved construction of approximately 28 miles of 115-kV electric transmission line, associated access roads, and an electric substation in Okanogan County in eastern Washington. The EIS evaluated the proposed action and six alternatives.

Alternatives included two different transmission corridors, distribution upgrades, and construction of a temporary diesel generation facility. A number of the alternatives involved rebuilding the existing Loup Loup transmission line.

Tetra Tech scientists conducted a number of detailed field studies, including wintering bald eagle surveys along the Methow River, and general wildlife, vegetation, noxious weeds, rare plants, riparian vegetation, wetlands, and soil surveys along all three alternative transmission line corridors. These surveys also included the proposed construction laydown, substation, and temporary generation sites. Tetra Tech staff conducted cultural resource surveys of all three alternative transmission line corridors and worked with the PUD, Forest Service, BLM, and Confederated Tribes of the Colville Reservation to identify and assess potential effects to Traditional Cultural Properties (TCPs) within the project area. Tetra Tech also prepared a detailed analysis of the potential visual impacts of the proposed alternatives.

Tetra Tech engineering staff worked with the PUD in the field to identify suitable access locations and developed a GIS access layer using GPS data collected in the field. Tetra Tech GIS specialists developed GIS coverage for the project area based on partial coverages from a number of different sources, aerial photography, and field data and conducted detailed GIS analyses for most potentially affected resources.

Tetra Tech public involvement specialists supported the PUD and Forest Service with all public involvement activities required under NEPA and SEPA.

Tetra Tech used the information from the field surveys along with numerous other secondary data sources to develop a Draft EIS that fully evaluated the potential impacts of the proposed action and alternatives. The Final EIS was published in March 2006.

Despite the controversial nature of the project, the EIS prepared by Tetra Tech withstood 3 legal challenges.