Mukilteo Ferry Terminal Deep Stormwater Utility

Project Summary

IMCO performed improvements to the SR 525 Mukilteo Ferry Terminal by constructing a deep stormwater utility line. The team installed a 50-foot outfall pipe during night work, timing activities against the tides, and a tight fish window. 200 yards of concrete was poured underwater to form a tremie slab in two pits to allow for work inside the pits without the need to maintain a dewatering system. The tremie slab provides a solid working platform for the trenchless machine to rest on. The team used a trenchless installation method to install 36-inch casing pipe and 24-inch carrier pipe. 



Mukilteo, WA


WSDOT – Washington State Ferries

Contract Amount

$2.3 Million


December 2017 - October 2018