A group of divers spent hours under water to do what many people don’t think of – making sewer upgrades.

As part of the ongoing sewer system improvements the SFPUC is doing at Islais Creek, last week saw a phase of work with divers, cofferdams and barges. 

Divers were called to install plugs on an existing 36-inch diameter force main pipe that is buried across Islais Creek. The plugs have been installed so that the pipe could be filled with concrete and abandoned in place in preparation for future system improvements. 

In addition to the divers, the marine contractor installed valves (also known as knife gate valves) inside temporary cofferdams (metal structures to isolate bay water and keep the work area dry) so that crews could cut a portion of the existing 36” pipe and replace it while continuing to allow the adjacent 42-inch diameter force main pipe to discharge final treated effluent into San Francisco Bay. 

This work had to be carefully executed and involved a number of operational constraints that had to be carefully coordinated such as a temporary shutdown of Booster Pump Station, custom installation of the knife gate valves on both the north and south side of the creek, maneuvering a specialized barge-crane to facilitate activities, and confined space entry into a 36” diameter pipe to install plugs.