Skip to main content

SR 520 – Montlake Project – 54-inch water line

This summer, the installation of a new 54-inch water line under SR 520 will be complete. Crews have been working since early 2020 to bore a tunnel between the north and south sides of the highway, then feed the 250-foot water line through. Activities since the fall have focused on connecting this new line to the existing one.

Graphic showing path of 54-inch water line under SR 520
The 54-inch water line runs under the lanes of SR 520.
Crews excavate pit for 54-inch water line
Excavating the south pit for the 54-inch water line
Soil frozen to keep it in place while digging pit for 54-inch water line
Freezing the soil helps stabilize the north excavation.
Crews in pit, using equipment to bore hole for 54-inch water line
The “jack and bore” method was used to push a casing under SR 520. The permanent water line was then threaded through the casing.
Casing lowered into pit for 54-inch water line
Steel casings were lowered into the pit and pushed under SR 520.
Pieces of water line await installation
The water line shown here was inserted under the ground, under SR 520, through the casing.
Crews in vault through which 54-inch water line emerges
Crews install a concrete water vault.
54-inch water line installed
The 54-inch water line is installed in the concrete vault.