Gig Harbor completes 'milestone' infrastructure project

The public is invited to a ceremonial valve turning on March 16 at 3 p.m. at the Bogue Viewing Platform, 8803 N. Harborview Drive, in celebration of the latest milestone for the Gig Harbor Wastewater Treatment Plant — redirecting of treated effluent from the old marine outfall to the new marine outfall.

For more than a decade, the City of Gig Harbor has been planning and preparing for upgrades to the City’s wastewater treatment plant. These upgrades have been intended to increase the quality of the effluent that is discharged to Puget Sound while expanding the treatment capacity of the plant. A total of four large capital projects encompass the upgrades, including two revisions to the treatment process at the plant and two revisions to the outfall pipe that connects the treatment plant to the Puget Sound.

In the spring of 2008, the placement of a new outfall pipe between the plant and the shoreline was placed in North Harborview Drive. Soon after, the City awarded a public works contract for the first phase of revisions to the treatment process at the plant. By the end of 2009, the City contracted for the third project that placed a marine new outfall pipe on the sea bed from the shoreline to the middle of Colvos Passage. The fourth and final project in this series, which does not have a scheduled start date, includes more revisions to the treatment processes at the plant.

The construction of the new marine outfall pipe has been likely the most visible of all the treatment plant projects. This new marine outfall carries treated wastewater effluent out beyond the confines of Gig Harbor bay to the open waters of Colvos Passage. The pipe skirts along the edge of existing marinas to minimize impacts to potential anchorages within the harbor. Also, the pipe has been placed under the sand spit at the opening of the harbor so as not to inhibit the available water depth at the entrance to the harbor during low tides. Many citizens, businesses, and agencies have spent decades waiting for the outfall to be relocated. After years of planning, permitting, and design, the City and the contractor, Advanced American Construction, have reached the end of this project.

The marine outfall project consisted of the placement of 9,200 feet of 24-inch high density polyethylene pipe approximately 2,700 feet into Colvos Passage. During the course of construction, the contractor placed the pipe under the water in various ways, including directly anchored on the sea bed, placed in a trench then anchored and buried, and drilled directly under the sand spit.

Interesting construction facts from this project include: the total construction cost was $6,166,084.68; the project was completed on time (scheduled completion date: May 31, 2011); the City issued one change order in the amount of $8,130; three different types of concrete anchors were used to hold the pipe in place on the sea bed. A total of 675 anchors (weighing from 700 pounds to 8,000 pounds each) were used; the pipe was delivered from Nevada in 50-foot sections. More than 184 heat-fused welds were necessary to connect the pipe; this was the largest in-water endeavor ever taken on by the City; and the work is projected to have a life expectancy of more than 50 years and have the capacity to convey flows beyond the City’s anticipated buildout conditions.

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