Replacement of the Fremont Siphon, by King County Wastewater Treatment Division, continues, and construction of the outer wall of the tunnel shaft has begun.
Crews will drill holes 90-feet into the ground and replace the soil with four-foot-wide concrete cylinders, called secant piles. These lock together to create a watertight ring that controls groundwater. The ring at the Fremont site will be 32-feet wide. King County has a short video, on YouTube, on how secant piles are used to control groundwater.
Construction of the secant piles is expected to take six weeks, with work being done from 7a – 6p on weekdays. After the shaft is excavated, the tunneling machine will begin digging for the new pipe to go under the Lake Washington Ship Canal. All this work will increase the noise and activity levels at the Fremont site, at Canal Street and 2nd Ave NW, with equipment accessing the site from NW 36th St.