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CityLink Seattle

Divers, Crews Install Conduit for City Light Data Line in Portage Bay



 

Photo of diver preparing to enter tunnel below Portage Bay.

A diver from Associated Underwater Services prepares to enter the tunnel beneath Portage Bay to help install a Seattle City Light fiber optic data line.

Seattle City Light saved about $480,000 by using an innovative approach to install conduits for a fiber optic data line beneath the waters of Portage Bay.

“This project provides an important data link that will allow Seattle City Light to expand its use of technology,” Superintendent Jorge Carrasco said. “It also demonstrates a creative solution for meeting that goal and using an efficient approach for installation and reducing costs.”

City Light crews worked with contracted scuba divers from Associated Underwater Services to install the flexible conduits Thursday inside a flooded concrete tunnel built across the Ship Canal about 60 feet below the surface of Portage Bay.

When the tunnel was first built decades ago, water would be pumped out for any maintenance or construction work. Changes in environmental law would require offsite disposal of any removed water and sediment if that approach was used today, with an estimated cost of $500,000.

Instead, City Light hired the dive team to help install the conduits while the tunnel remained flooded. The dive team guided a pull rope and the conduit through the tunnel while City Light crews fed the conduit from large rolls on one side of the Ship Canal and used a winch to pull the conduit to the other side. That approach cost less than $20,000.

City Light crews will come back later to install the fiber optic cable. The cable will provide a dedicated data link for City Light and enhance reliability. Three other data lines City Light uses are carried on overhead wires and shared with other city departments. Large construction projects can interrupt service on some of those overhead wires. 

Seattle City Light is the 10th largest public electric utility in the United States.  It has some of the lowest cost customer rates of any urban utility, providing reliable, renewable and environmentally responsible power to nearly 1 million Seattle area residents.  City Light has been greenhouse gas neutral since 2005, the first electric utility in the nation to achieve that distinction.