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Seattle City Light DEBRA SMITH, General Manager and CEO
Denny Substation Project
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Future Transmission

As part of the Environmental Impact Statement (EIS), City Light is evaluating three alternative routes for a new transmission line to connect from the new Denny Substation to the existing Massachusetts Substation located in the SODO area. The remaining SEPA/EIS work regarding the transmission line is specific to implementing City of Seattle’s the RSJI/Racial Equity Tool Kit process. Public outreach efforts will be coordinated to engage affected communities along the route during the selection of the Preferred Route option and prior to final design and construction. Once constructed, the transmission line will operate at 115 kilovolts (kV) with the capability to operate at 230 kV in the future as electrical demand increases and more areas of North Downtown Seattle are switched to a network distribution system.

The three transmission alternatives being considered include the following options:

  • Option 1 - A route primarily running along the east side of Interstate-5 (I-5)
  • Option 2 - A route primarily running along the eastern edge of the downtown commercial core
  • Option 3 - A hybrid route that combines the northern section of Option 1 & the southern section of Option 2 that crosses beneath I-5 at James St

Each of the three alternatives, as currently conceived, transition from underground to overhead structures at the southern end before entering the Massachusetts Substation. The Denny Substation Program map shows the three alternatives currently being considered.

Design of the final route of the transmission line will begin once the preferred alternative is selected within the completed SEPA/EIS & RSJI process. The design process is anticipated to take place from late-2019 through mid-2020. Construction of the transmission line is anticipated to start mid-2021 and to be complete in late 2022. The new Denny Substation is connected to the regional transmission grid by the Broad-Denny transmission line and the E Pine-Denny transmission line.


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Project Hotline:
(206) 257-2142

Email Address:
SCL_DennySub@seattle.gov

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