North Seattle Lateral Project


Northwest Pipeline LLC (Northwest) is one of three interstate natural gas pipelines operated by The Williams Companies. The Northwest system extends from the San Juan Basin in northwestern New Mexico and southwestern Colorado through the states of Colorado, Utah, Wyoming, Idaho, Oregon and Washington to a point on the Canadian border near Sumas, Washington. Northwest provides natural gas transportation service to the Seattle, Washington, Portland, Oregon and Boise, Idaho, markets.

Northwest consists of various diameter pipelines buried underground within a common pipeline right of way. Northwest’s bi-directional system provides access to British Columbia, Alberta, Rocky Mountain and San Juan Basin gas supplies.


  • Growth of Snohomish and King Counties population and housing is forecasted to exceed the peak capacity of the North Seattle Lateral in the 2018-19 heating season. This lateral delivers natural gas to Puget Sound Energy’s customers.
  • The lateral, which was built in 1956 (prior to construction of Interstate 5 and the Everett Boeing plant), is operating beyond its intended peak capacity on cold winter mornings and days, when PSE’s customer demand for natural gas is highest.
  • Pipelines are built and sized to serve peak demand – when PSE’s customers use the maximum amount of natural gas in one moment. While actual PSE customer demand is relatively low most of the year (i.e., spring, summer and fall), it increases in the winter.
  • Now that the lateral is upgraded and in service, Northwest will be able to meet the heating demands of PSE’s customers.

To meet the growing demand for natural gas in the North Seattle market area, Northwest proposed the North Seattle Lateral Upgrade Project. Northwest has executed firm agreements with PSE for the project to expand the delivery capabilities of Northwest Pipeline’s North Seattle Lateral, which serves PSE customers. PSE operates Washington’s largest natural gas distribution system serving nearly 800,000 gas customers in six counties.


The North Seattle Lateral Upgrade Project was mechanically completed and placed into service on Nov. 15, 2019.


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