North Seattle Lateral Upgrade Project

Quick Facts

  • The North Seattle Lateral consists of two lines (laterals) branching off the 30-inch Northwest mainline at milepost (MP) 1,397.1. The first lateral measures 20 inches in diameter to MP 2.0, at which point the diameter measures 8 inches. The second lateral measures 16 inches in diameter.
  • This project will replace a portion of this existing 8-inch line with new 20-inch pipe, beginning near MP 2.0 and extending up to approximately 5.85 miles.
  • An in-line inspection facility, currently located at MP 2.2, will be relocated to the end of the expanded portion of the line as part of the project.
  • All pipe installed during the project will use the existing Northwest right-of-way corridor. Work space or other use of land outside Northwest easements will be relatively minimal and temporary.
  • The maximum peak daily volume of the expansion will not exceed 408,000 Dth/day.

News & Updates

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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.

Impact & Benefits

  • 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.
  • 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.
  • The lateral, which was built in 1956 (prior to construction of Interstate 5 and the Boeing Everett plant), is operating beyond its intended peak capacity on cold winter mornings and days, when PSE’s customer demand for natural gas is highest.
  • If the lateral is not upgraded, Northwest will not be able to meet the heating demands of PSE's customers.
  • Failure to act now will place PSE’s residential and business customers at risk for service disruptions (i.e., gas stops flowing to furnaces and equipment, requiring house-by-house re-lights).


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.

Pipeline Safety
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Pending all federal, state and local regulatory approvals, construction-related activities are scheduled to begin in summer 2019 and would be completed in the fourth quarter of 2019.

Summer 2019                      Expect pipeline construction to begin

Fourth-quarter 2019            Target in-service date for pipeline

Regulatory Process

On July 19, 2018, the FERC issued its Certificate of Public Convenience and Necessity:

On Feb. 12, 2018, FERC issued its Environmental Assessment for the project: