Michels Pipe Services, a division of Michels Corp., is nearing completion of a $4.5 million cured-in-place pipe (CIPP) project in the upscale, lakefront community of Lake Oswego, Ore., that is part of a overhaul of the Lake Oswego Interceptor Sewer (LOIS).
What made this project a challenge — beyond its overall size — was that the pipes to be rehabbed are under the lake, forcing CIPP crews and engineers to design a creative plan to complete the job.
The project, which is scheduled for completion in December, involves the rehabilitation of two 48-year-old, deteriorated sewer lines: 2,150 ft of 16-in. pipe and 3,900 ft of 36-in.
Logistics and access have played critical roles in this project, which has necessitated the use of barges, tug boats and construction of piles/steel shoring to anchor the barges while the CIPP work was taking place.
“Access to the lake has been the most challenging part,” said Kelly Odell, vice president of Michels Pipe Services.
Lake Oswego is 400-acre, privately owned lake that was formed by the damming of Sucker Creek in 1921, creating one of the most affluent suburbs of Portland. In 1962, the lake was drained to install the existing sewer pipe on the lake bottom. Over the years, deterioration has caused the pipe to become increasingly and dangerously fragile, resulting in leakage from the line.
The Lake Oswego Interceptor Sewer lies submerged some 14 to 21 ft below the surface of Lake Oswego. The LOIS system includes over 13,000 ft of 16- to 36-in. diameter pipe traversing Lake Oswego and over 5,000 ft of smaller diameter trunk sewers constructed through canals and bays. Today, the LOIS system collects flows from a 4,500-acre service area and transports these flows down to the City of Portland’s Tryon Creek Wastewater Treatment Plant (TCWTP) by gravity, where it is then treated and discharged to the Willamette River. While some of the pipe is buried, nearly 9,000 ft is pile-supported above the lake bed to maintain a uniform slope to the treatment plant. About 40 manholes are scattered across the lake, canals and bays to provide access for maintenance and inspection.
Brown and Caldwell is the design engineering firm handling the project and the firm developed a unique sewer line to replace a major portion of the old one. The replacement pipe is anchored and tethered to the lake bottom but will float about 8 to 17 ft below the water’s surface. Like the existing interceptor sewer, the new system will be a gravity line, meaning that changes in elevation from the west end of the lake to the east will keep material moving through the line without pumping. In the LOIS design, tethers restrain the pipe from bowing up, the buoyancy pipe restrains the pipe from bowing down and installation in an s-curve limits the side to side movement. These elements acting in unison ensure the right grade all the way to the treatment plant. Work has been ongoing for this project for the last year and even required the lake to be drained for a portion of it.
According to Odell, several sections of the pipe were not conducive to this unique system and for these sections, CIPP was determined to be the best solution.
Michels tackled the 2,150-ft, 16-in. CIPP installation first, starting in the spring. A large bypass was set up before the CIPP work could begin; the bypassinvolved an 18-in. pump and HDPE pipe that wound clear around the lake. On a barge, there were twelve 16-in. pumps to assist with dewatering.
The 2,150-ft CIPP section took approximately eight weeks to complete — an incredibly slow pace due to the limited access. This section was done during what was called the “Lake Up” phase of the project, meaning the lake was not drained as this was taking place during the summer season. “All the pipes that could be rehabilitated by land access were,” Odell said. “But for those under water, we had to put all of our equipment and crew onto barges to do the work on the lake. Everything that you would normally use on a land-base install, we had to take out onto the middle of the lake. If you didn’t bring it with you, you’d have to get back in the boat and go back to shore to get it, [adding more time].”
The logistics for this section were time-consuming for each manhole access point. Some of the access points were in the lake and some of them were on the shore line right behind the homes or had docks and walkways that were located behind the houses. Crews had to install steel piling around the barge to anchor it and then drain the manhole, clean and video the sewer line section and then rehab it. Normally, each phase for the entire pipe would be done before moving on to the next. This project didn’t permit that, Odell said.
The second phase of the CIPP work — for the 3,900 ft of 36-in. pipe — is currently under way, beginning in October. For this phase, the lake was drained, as it was the off-season. “The lake was drained through the dam and by active pumping to a level it had not seen since 1962,” Odell said. “This revealed roads installed for the original pipe installation. These roads were rebuilt to allow heavy equipment access to the locations required for pipeline rehabilitation.”
Odell noted that because the window for the “Lake Down” portion of the project is short, the schedule is very tight, the work must be completed to allow the lake to be entirely refilled by Memorial Day 2011. The CIPP work must be completed by December. “The progression of the lake drawdown and refilling is further complicated by these activities [pipe cleaning, pipe videoing and CIPP] being performed in different stages, requiring critical path sequencing,” he said.
Working in the “Lake Down” phase in what would have been 24 ft under water during normal conditions, Michels crews had new challenges to face. According to the contract, the liner could not be impregnated onsite. So that facet of the project was done some 40 miles away at Michels Pipe Services’ Salem, Ore.-facility and then brought to the site in refrigeration trucks.
One section of pipe was so long that the weight would not have been feasible to haul by highway. Michels decided to break that run in two, installing each pipe from a land-based location and meeting in the middle of the lake. “This allowed a pipe spool to be installed to join the two CIPP sections, minimizing disruption on the sensitive lake bottom,” Odell said.
How much did the logistics and limited access slow down the work? Odell estimates that under normal land conditions and projects of similar size, his crews could reline approximately 5,000 ft a week. “In this particular case, that’s not happening,” he said. “We are lucky to get 500 ft done in a week due to the access and working off of barges. It has just slowed everything down. It’s difficult to move the barges and set up the pilings for each manhole. But overall, the project has gone extremely well.”
Nearly 400,000 lbs of Interplastic Corp. resin was used for the two CIPP projects and Applied Felts liners through Premier Pipe were also used. All in all, things went smoothly, Odell said, noting that the surrounding community has been kept informed of their progress.
“This project has been unique,” Odell said. “The coordination and scheduling have been difficult.”
Sharon M. Bueno is managing editor of Trenchless Technology.