North Seattle Lateral Upgrade 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.


To meet the growing demand for natural gas in the North Seattle market area, Northwest is proposing the North Seattle Lateral Upgrade Project (Project) located in Snohomish County in the state of Washington. Northwest has executed firm agreements with Puget Sound Energy (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.

project map

Click image for larger map.

Regulatory Process

On July 18, 2017, Williams Partners L.P. announced that Northwest had filed an application with the Federal Energy Regulatory Commission (FERC) seeking authorization for its North Seattle Lateral Upgrade project in south Snohomish County in the state of Washington.


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




Lead Applicant: Northwest Pipeline LLC

Filing Type:         Formal Notice

Description:        Notice of Availability of the Environmental Assessment for the Proposed North Seattle Lateral Upgrade Project re Northwest Pipeline LLC under CP17-44.


To download the document for this Issuance, click here.


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


Proposed Schedule

Second-quarter 2019                     Expect pipeline construction to begin

Fourth-quarter 2019                      Target in-service date for pipeline