North Beach force main maintenance

Project need

 
North Beach Force Main (PDF). December 2011


King County crews installed a new manhole in order to evaluate the force main. August 2011.


Launching the acoustic listening device (Smartball) at the access point to the force main. August 2011.


The North Beach force main runs parallel to the Burlington Northern Railroad tracks for approximately 4,700 feet within the tidal zone of Puget Sound. Flows from the North Beach Pump Station are conveyed through the 14-inch diameter, 7,490-foot long cast iron force main to the Carkeek Wet Weather Facility where they are either pumped to the county’s West Point Treatment Plant or, in large storm events, treated on site.

King County is carrying out a project to evaluate the condition of the North Beach Force Main, installed in 1963.

Project status

In Summer 2011, crews installed a new air relief valve and manhole to the force main pipe at the North Beach pump station, providing improved access to evaluate the pipeline. A specialized acoustic listening device (ALD) was launched at that access point and used to detect sound patterns along the pipeline. Signature patterns are associated with potential leaks or trapped air. While no leaks were found, the ALD did identify seven areas of trapped air which may lead to pipeline corrosion over time. This information allows King County to focus pipeline condition assessments to areas with the highest potential for corrosion inside the pipeline. For more information, view the force main inspection report issued in August 2011.

Targeted assessments will provide a more accurate estimate of remaining service life, and reduce impacts to the sensitive nearshore environment where the pipeline is located.

King County will provide updates on plans for this work in 2012.