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Pacific Northwest Geologic Mapping and Urban Hazards

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Lifelines and earthquake hazards in the greater Seattle area

Lifeline systems
Earthquake hazards
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Lifeline Systems


The three largest water suppliers in the region are the cities of Everett, Seattle, and Tacoma. In all three cases, the primary supply comes from surface water gathered on the western slopes of the Cascade Mountains. Seattle and Tacoma also have supplementary groundwater supplies. The three suppliers' systems are substantially independent of one another, with only small interties. An intertie is planned between the Seattle and Tacoma systems. These three suppliers provide both retail and wholesale service. Smaller water purveyors depend on supplies from Everett, Seattle, and Tacoma, and (or) their own groundwater (and to a limited degree surface water) supplies.

The map shows source rivers and reservoirs where the surface water enters the transmission systems, and follows the transmission systems to their terminal reservoirs. The transmission systems generally run east to west and in all cases cross valleys with unconsolidated young alluvial deposits.


The largest wastewater system in the region is operated by King County, and serves most of the county's urban area. Gravity interceptors collect sewage and deliver it to large treatment plants in Renton and at West Point, in many places traversing liquefiable soils en route. The Renton plant, at the southern end of Lake Washington, serves the region east of Lake Washington and the Kent Valley. Its outfall parallels the Duwamish River and discharges into Puget Sound. The West Point plant, northwest of Elliott Bay, serves the area west of Lake Washington and discharges via a short outfall into Puget Sound.

The cities of Everett and Tacoma operate wastewater collection and treatment facilities. The Everett treatment plant is across the Snohomish River from the city. The Tacoma treatment plant is on former tide flats adjacent to the Puyallup River.

Electrical Power

The major electric power producer in the Pacific Northwest is the Bonneville Power Administration, which has hydroelectric plants along the Columbia and Snake rivers far to the east. BPA sells power to the major distributors in the region, including Puget Sound Energy, Seattle City Light, Snohomish County PUD, and Tacoma Public Utilities. Each of these distributors has some generation capacity. Much of the BPA power moves through the 500 and 345 kV substations shown on the map. A 230 kV grid also provides a significant level of redundancy.

Natural Gas

Natural gas is transported into the region from Canada, through a pair of high-pressure transmission lines (26-inch constructed in 1952, and 30-inch constructed in 1970) located in a common corridor. Williams Natural Gas Pipeline Company owns both lines. In the event of a failure, gas can be supplied from the south. These pipelines cross the east-west trending river valleys, which run from the Cascades to Puget Sound. Natural gas is distributed in the region primarily by Puget Sound Energy (PSE). PSE has connections to the Williams pipelines distributed along their length.

Liquid Fuel

Olympic Pipeline Company transports liquid fuel in a pair of pipelines (16-inch and 20-inch) from refineries at Ferndale, Cherry Point, and Anacortes (all north of the map) south to Renton. One line continues on to Portland. The pipelines carry about 14 million gallons per day. Lateral pipelines transport fuel to the Ports of Seattle and Tacoma, Seattle-Tacoma Airport, and distribution points from where it is trucked to gas stations. About 75% of the gasoline used in the region is delivered through these pipelines. Approximately 700 tank trucks per day would be required to move the fuel the pipeline transports south to Portland.


Primary regional vehicle movement is north-south. I-5 carries between 150,000 and 300,000 vehicles per day, depending on the location. I-405 carries about 200,000 vehicles in Bellevue. The east-west I-90 bridge carries nearly 150,000 vehicles per day while the SR-520 bridge moves approximately 125,000. Most of the I-5 bridges were constructed between the mid-1950s and the mid-1970s.


Both Burlington Northern-Santa Fe and Union Pacific railroads serve the region. More than 50 freight trains per day move through the Kent Valley south of Seattle, with more than 30 passenger trains per day expected once the heavy-rail component of Sound Transit is implemented in the next few years. Railroad bridges over the Duwamish, and Puyallup rivers were built before 1910. The railroad alignment between Seattle and Tacoma lies on liquefiable unconsolidated young deposits in the Kent and Puyallup River valleys. North of Seattle, the main Burlington Northern-Santa Fe route runs along the Puget Sound, where it is frequently impacted by landslides, particularly during the winter rainy season.


Seattle Tacoma International Airport, between Seattle and Tacoma, is the area's primary commercial airport, with approximately 25 million passengers and 200,000 landings annually. Boeing Field, along I-5 in south Seattle, services a significant air freight business. Boeing's 747 - 777 assembly plant is located at Paine Field south of Everett. McChord Air Force Base, south of Tacoma, supports large transport planes. All of these airports are on competent soils with the exception of Boeing Field, which is in the liquefiable Duwamish River valley.

Marine Facilities

The ports of Seattle and Tacoma are leaders in international trade, with each port shipping approximately 1 million twenty-foot equivalent units (TEUs) per year. About 60 percent of imports move through to inland domestic markets. The Port of Everett has some log-export traffic and is home to part of the U.S. Navy's Pacific fleet.

Most Port of Seattle marine facilities are located at the former estuary of the Duwamish River on Elliott Bay. The Port of Tacoma is located on the delta of the Puyallup River on Commencement Bay. Both locations are highly liquefiable.

Continue to Earthquake Hazards.

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1 U.S. Geological Survey, University of Washington, Box 351310, Seattle, WA 98195
2 EQE International, 1411 4th Avenue Building, Suite 500, Seattle, WA 98101
3 U.S. Geological Survey, University of Washington, Box 351650, Seattle, WA 98195

This site is maintained by the Pacific Northwest Urban Corridor Geologic Mapping Project, part of the Geology, Minerals, Energy and Geophysics Science Center

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