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Trenchless sewer rehab in Woodstock piques interest

by: ELIZABETH USSHER GROFF - With a newly-assembled, deflated white bladder and a launcher pipe, on Ramona Street, are, from left, Rick Harris, Tyler Griffith, and (kneeling, preparing the launcher pipe) Brad Worthington.Neighbors on Ramona Street in the Woodstock Neighborhood wondered what was going on, when three or four large white City of Portland trucks sat for hours, several days in a row, as city workers lay long lengths of white and tan deflated tubes onto the ground and into manholes.

It turns out that this is called “trenchless sewer rehabilitation”, done by the Portland Bureau of Transportation (PDOT). The Bureau of Environmental Services (BES) operates the city sewer system, but contracts with the PDOT Maintenance for repairs.

And this particular method of repair is getting widespread attention! “People have come down from Seattle and British Columbia to see how we do trenchless repair. Portland is one of the leaders in the country in sewer lining,” said Rick Harris, crew leader for a Portland Bureau of Transportation Maintenance liner crew.

“Because broken, root-infested, and leaking sewers are a serious infrastructure issue, the City of Portland takes a proactive approach to sewer rehabilitation by using a safe, clean, and efficient liner system,” remarked Cheryl Kuck, spokeswoman for the Portland Bureau of Transportation.

Kuck says the “open-cut” method of digging up a street to repair a sewer pipe is made more difficult by high traffic volumes, depth, and utility conflicts, not to mention the cost.

“‘Dig and repair’ costs are approximately $500 per foot. Lining costs are under $200 per foot,” explained Kuck.

However, reconditioning an old sewer pipe by lining it is still a bit complicated. Liner crews, as they are called, composed of four or five workers, first do precise measurements, and then spend hours using bulk materials to construct bladders and cured-in-place liners.

They mix buckets of resin to coat a felt material, creating the liner which will simulate fiberglass. If it is raining, they do the construction inside a large white trailer that looks a little like a movie studio trailer. They then shoot the liner into the sewer pipe using air pressure – and wait for the resin to harden.

A truck with a robotic camera and cutter might sit as far away as two blocks from the actual repair site. It is equipped with a camera on a coaxial cable that is fed through the underground sewer pipe. The camera transmits images to a television screen in the truck, which allows workers to see inside the pipe and monitor the liner’s progress as it goes through the underground pipe. It also signals any blockage problem from a root or other obstacle in a line that might need to be cut out.

Finally, a worker in a special suit (and nerves of steel!) will then travel on a rolling platform through the narrow cured pipe to cut sewer access holes to restore service to homes and businesses on the street.

So, when curious neighbors see workers just sitting and standing around for periods of time, seeming to be doing nothing, they are in fact waiting for resin to harden (it takes 2 ½ - 4 hours to cure), and keeping an eye on air pressure to make sure the bladder hose doesn’t blow or collapse.

While it is a complicated and lengthy process as viewed from a layperson’s perspective, Harris says it is faster in the long run than digging up the street to repair the sewer pipe.

“We can do more footage in a day than a dig crew can,” remarked Harris. “The longest one we have ‘shot’ is 120 feet. We do pipes up to 24 inches in diameter.”

Harris explains that liner and repair crews take periodic classes to keep them up to date. Classes include details of construction, signaling for light rail and railroad tracks, soil analysis, confined space logistics, and basic first aid. All are designed to keep workers and pipes safe, and to make the process as efficient and effective as possible.

Portland has won a national award for its trenchless technology during the fourteen years that they have been using this method. Harris pointed out, however, that the city is always improving and changing. Evidently, it is this openness to learning and new technology that has gotten trenchless sewer repair to where it is today in the Rose City.