The Lake Oswego Interceptor Sewer project is getting its final touches, according to project Citizen Information Coordinator Jeff Selby. The lake is slated to be filled and ready for recreation by Memorial Day.

The project has replaced an old interceptor sewer line with a new one that will float 8 to 17 feet below the lake’s surface. The line is connected to bedrock under the lake with steel tethers. In addition to the pipe replacement, the project includes the rehabilitation and strengthening of onshore sewer pipes, replacing manholes and construction of the Bryant Road Pump Station.

“Right now the major remaining task is to clean the new interceptor and inspect it,” Selby said. The lake was drained in September 2010 and started being refilled in February. Currently the lake is filled to 93.5 feet and will be at its full pool level of 98.6 feet by Memorial Day, he said.

“The schedule for this project had to be done with the lake residents’ boating and recreation schedules in mind,” Selby said.

When the “Lake Down” work is finished, on-shore work will continue until January 2012.

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A local project has earned bragging rights as the most significant project in the country for 2010, according to the Associated General Contractors.

The Lake Oswego Interceptor Sewer project was named winner of the Grand Award when the Aon Build America awards were handed out by AGC last week.

was the contractor for the project, which also earned a top award in the best new municipal and utilities category. Work consisted of the replacement of a 50-year-old hazardous sewer line and required crews to drill 270 feet into bedrock to install system anchors. The project, which required more than 1,200 commercial dives, was completed without any lost-time accidents.

Ted Aadland, AGC president and CEO of Portland-based , said the Lake Oswego project and the others honored were jobs that most contractors “dread starting” but “dream of completing.”

Nineteen other projects, including two in Oregon, were named Aon Award winners in individual categories. The Round Butte Dam Selective Water Withdrawal project handled by was honored as best new environmental construction while ‘s Savage Rapids Dam Removal project was selected as the best environmental renovation.

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The city of Lake Oswego today began draining Oswego Lake in preparation for the next round of work on the city’s new sewer line.

The new sewer line is made of 10,000 feet of buoyant material and is tied down and suspended 15 to 20 feet below the lake’s surface. It will replace an older line that was constructed along the floor of the lake. Water will be drained for the next three weeks so that crews can access to the new pipe for the next round of work, but as crews wait for the lake draw down, they will work on other parts of the project on shore.

Crews will work to rehabilitate and strengthen several thousands of feet of onshore sewer pipes, said Joel Komarek, project director for the city of Lake Oswego. While these pipes are 30 to 40 years old, they are not as susceptible to seismic activity as the pipe fixed to the lake floor, Komarek said. So instead of removing the pipes, the pipes will be cured in place, a process will strengthen the pipes and give them 30 to 40 additional years of life, Komarek said.

As part of the curing process, the existing pipes are impregnated by a heavy, felt-like liner and then filled with water. The water is then heated up, causing a chemical reaction in the liner that hardens the felt around the inside of the pipe like fiberglass.

Crews are also constructing six new debris manholes. The manholes, which are 15 feet by 8 feet and look like large concrete vaults, will be placed at strategic locations around the lake and will remove debris from the lake that would otherwise flow into the sewer line.

Once the lake is drawn down, contractors will begin demolishing old manholes in the lake and building new ones to better fit the new sewer pipe’s configuration.

The lake will be refilled after the completion of the project in March 2011.

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Up to 24 lineal feet of Oswego Lake will disappear beginning Sept. 7, when the city will begin to draw the lake down to attach a sewer interceptor to a new pipeline.

“It’s the first buoyant, submerged, gravity-flowing pipeline in the world,” said Joel Komarek, project director for the city of Lake Oswego.

The new pipe is comprised of nearly 10,000 feet of buoyant, high-density polyethylene material, which is tied down and suspended 15 to 20 feet below the lake’s surface by stainless-steel rope. The rope is attached to ground anchors, which were drilled down into the lake’s bedrock and grouted into place.

A major portion of the pipe was placed in the lake from November 2009 to April 2010. But additional pipes need to be placed and attached, a process that requires the lake to be drawn down. The water will be pumped into the Willamette River through a creek known as both Oswego Creek and Sucker Creek. The overall goal of the project is for the new pipeline to be attached and running by May 2011.

“The old line, which runs through the lake, was installed in the early 1960s,” said Jeff Selby, citizen information coordinator for the Lake Oswego Interceptor Sewer project. “The old one doesn’t have enough capacity and is structurally at risk. It is sitting on steel and lumber (that) is deteriorating. Even a mild earthquake could rupture the pipe and fill the lake with sewage.”

By remaining suspended in water and not fixed to support piles, the new pipe will not be susceptible to such risks. The pipeline is in a horizontal s-shape to allow the high-density polyethylene to expand and contract as the lake’s temperature changes. The horizontal bends allow the pipe to fluctuate in size without disrupting the consistent slope that is required for the pipeline to be gravity-based.

“The lake falls two feet over a distance of 10,000 feet, and we had to install the pipe and maintain that grade over a long distance,” Komarek said. “Every 25 feet there was an anchor installed and attached to the pipe. The contractor had to then survey the pipe at every anchor to make sure the proper slope was acquired.”

Each of the 428 tethers, which are attached to the anchor points, can be individually adjusted to maintain the required grade.

Advanced American Construction Inc. was awarded the $26 million bid for the project’s first phase, which included bending, sinking, and adjusting the pipe to get the proper grade required. Over 17,000 linear feet of pipe was fused together into 1,200-foot strings and anchored into the lake.

J.W. Fowler will be the contractor for the project’s second phase, which is known as the “lake down” – the pipe will be connected to a new, pile-supported, submerged pipe on the lake’s west end and to an existing interceptor on the east end.

The lake will be filled back up beginning in March 2011 with a combination of rainwater, Tualatin River water, runoff and water from local streams and creeks.

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The first phase of the Lake Oswego Interceptor Sewer project is completed, and the Portland general contractor is preparing for a lake drawdown of 22 feet in September so that the next phase can begin. LOIS, built in the early 1960s, collects sewage from a wide area and transports it beneath the lake surface to a treatment plant. The upgrade work will increase the capacity of the system and ensure its structural soundness.

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