POULSBO — Imagine one of the arteries that carries blood from your heart is weak and in danger of rupturing. Rather than opening you up, cutting out the bad section and replacing it, your surgeon may decide to simply insert a reinforcing tube called a stent.
Now, imagine that stretch of weakened artery is the big, mile-long sewer pipe that runs along Highway 305 and carries all of Poulsbo’s sewage.
Rather than dig it up and replace it, Poulsbo Public Works is going to put in a stent.
“Every bit of sewage from Poulsbo goes down that pipe,” Poulsbo Public Works Supervisor Mike Lund said. “If it were to blow out, it would be a really bad thing.”
And because it runs right alongside Highway 305, digging it up and replacing it would require what folks like to euphemistically call major “traffic revisions.”
The pipe was installed in the late 1960s-early ’70s, according to Lund. It’s buried 12 to 15 feet deep in places and about 2,322 lineal feet of it needs repair or replacing now; another 2,640 lineal feet of it will need repair or replacing within the next five years or so, he said.
The crumbling pipe was discovered as part of Public Works ongoing project to map the condition of all of the sewers and stormwater pipes in Poulsbo using its Utility Video Inspection Truck that it purchased in 2016. (See “Mapping underground Poulsbo,” at www.kitsapdailynews.com/news/mapping-underground-poulsbo-a-herald-series.)
The repair operation is called a CIPP, which stands for “Cured In Place Pipe Project.” Basically, workers line the pipe with a fiberglass “stent” which is then cured (hardened) with either boiling water or ultraviolet light, Lund said.
So what happens to all of the stuff inside the pipe while that’s going on?
Lund said the idea is to work from manhole to manhole. To work on a section, workers close off the pipe at the upstream manhole and route all of the effluent through a big hose down to the next manhole below where they are working.
No digging, no big traffic revisions, the work will be done at night and it should be completed in 45 days from the beginning of construction.
Three bids were received, the lowest being from Insta-Pipe, Inc. for $769,804. The base bid — estimated by city engineers to be in the range of $400,000 to $500,000 — is for repairing some 2,322 feet of pipe that are in the worst condition. Then there is an additive alternate bid for another $400,000 to $500,000 to install an additional 2,640 lineal feet or so of CIPP. This would completely rehabilitate the existing sewer main.
This may seem like a lot of money, but Lund estimated it would cost “three times that much” — $3 million — if the city had to dig up the pipe and replace it.
The project does not impact the budget, Lund said. The money for this project came from “shuffling some [other] CIPP monies around,” Lund said.
“It’s cheaper to be proactive than reactive,” he said.