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Marine outfall work proceeding for Powell River's consolidated wastewater treatment plant

JJM Construction is deploying and sinking the offshore section, completing a critical piece of the project's infrastructure
CRITICAL INFRASTRUCTURE: Sinking of the consolidated wastewater treatment plant’s offshore section is taking place in the waters adjacent to the plant facility that is under construction.

Work is being undertaken to sink the offshore section of the marine outfall for the consolidated wastewater treatment plant.

The work was taking place on July 22.

According to information supplied by City of Powell River engineering technologist Mik Drosdovech, general contractor Graham Infrastructure’s outfall subcontractor, JJM Construction Ltd, is deploying and sinking the offshore section of the marine outfall, completing this critical piece of infrastructure.

Drosdovech stated this offshore section of the marine outfall is approximately 580 lineal metres (1,900 feet) and is constructed from 12.2-metre and 15.2-metre (40- and 50-foot) segments of 900mm high-density polyethylene pipe (36-inch diameter with 2.67-inch thick walls) that were butt-fusion welded together. 

According to Drosdovech, the offshore section of the marine outfall has 101 concrete weights attached to the pipe that will assist with sinking the outfall, and are ultimately designed to secure the outfall in its final position on the sea-floor. 

“The final resting place for the diffuser section (offshore end) of the marine outfall will be approximately 700 lineal meters (2,300 feet) from shore, at a depth of over 52 metres (170 feet),” stated Drosdovech.

He stated the deployment of the offshore section of the marine outfall began with JJM crews towing the weighted pipe section out from the millpond and into place at First Beach, then connecting the floating offshore section of the outfall with the intertidal section of the outfall that was installed in mid-May. The crews would then position the offshore section of the outfall pipe with two or three barges and tugs and begin filling the pipe at a set rate by pumping in seawater to allow the pipe to sink, according to Drosdovech.

There are a number of variables that could speed things up or slow them down, such as guiding the pipe around certain rock features or poor ground conditions on the seafloor as the divers guide it down, but for now the final placement is anticipated for early evening on July 22, stated Drosdovech.

“All in all, this will be a long day for the JJM and Graham crews, but given the significant effort they have put into planning, scheduling and organizing this significant step in the consolidated wastewater treatment plant project, we are collectively confident that all will go accordingly,” stated Drosdovech.