1700R S DONOVAN ST
Oct. 30, 2025:
The local in-city electrical grid requires a connection between the westside (City of Seattle) and eastside (City of Tukwila) to meet energy demands, including forecasts for large increases in electricity usage, and a corresponding need for greater reliability of that electricity. Prior to 2003, an in-kind circuit provided connectivity via an overhead line, however attempts to reconstruct that line were stymied by a variety of factors. Electrification of fossil fuel power has already begun in the south Seattle area, and larger circuits with multiple paths of delivery, as provided by this circuit, are necessary to continue reducing fossil fuel use and to meet growing demands for clean energy. The project proposes installation of these circuits below the Duwamish River using trenchless methods, specifically (horizontal directional drilling [HDD]). This method avoids interference with other uses of the river (navigation, industry, habitat), and many potential environmental risks.
The project will install three circuits beneath the Duwamish River between two Boeing owned properties (1) South Park property on the west and (2) Thompson/Isaacson property on the east. Practically and economically, the circuits must be installed beneath the river using trenchless construction techniques (HDD) because overhead placement of the circuits is not possible within the height restrictions imposed by the U.S. Coast Guard, U.S. Army Corps of Engineers (USACE), and Federal Aviation Administration. Open-cut installation beneath the riverbed is not practical from a construction standpoint, and would be too environmentally disruptive, with a high degree of risk. The lines must also be greater than 10 feet below the authorized dredge depth (-15 feet MLLW or -17.33 NAVD 88) to accommodate USACE dredging of the waterway, and to meet safety and engineering requirements.
The crossing includes three circuits that will be placed in three 32-inch diameter HDPE or PVC casing pipes. Once the casings are in place, a conduit bundle consisting of six 6-inch PVC conduit and one 4-inch conduit will be sliplined inside the casing. The conduit bundles will terminate at the HDD pit at each end. Connections will be established from the HDD pits to the existing grid within adjacent road rights-of-way, utilizing either overhead or underground routes. All connections will be situated entirely in upland areas.
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