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Amid growth in the Portland-metro area, Hillsboro-based public utility Clean Water Services is investing nearly $70 million in its 10-year West Durham Basin Improvement Program. A large portion of that is a $30 million effort to improve the existing Tualatin Interceptor that serves Beaverton, Tigard, Tualatin, Sherwood and King City, and connects to the Durham wastewater treatment plant in Tigard.

鈥淚t’s the start of rebuilding our largest-diameter interceptor pipeline that was put in during the early ’70s,鈥� said Wade Denny, project manager for Clean Water Services. 鈥淚t’s being built in concert with all the development that’s occurring in the South Durham basin.鈥�

The project calls for replacing sections of pipe along a route stretching from just west of Oregon Route 99W in King City east to Tigard’s Cook Park and the Durham wastewater facility.

Old reinforced concrete pipe with diameters from 24 inches to 42 inches are being replaced with new pipe up to 66 inches in diameter. That will increase capacity to up to 20 million gallons of wastewater daily.

General contractor Mortenson Construction is carrying out the project along with partners hand-picked under a progressive design-build contract with Clean Water Services. Tom Paul, Mortenson’s General Manager of Environmental, oversees the company’s environmental division. The delivery method is noteworthy, he said.

鈥淲ade (Denny) gave us a list of problems to solve, and said, 鈥楲et your team go solve them,’鈥� Paul said. 鈥淭here was no preconceived notion on what the problems were and what to solve. I speak about this all over the country, and what it means is pick a team you want to work with for the next three or four years. It’s not about trenchless technology; it’s about how the team addressed the challenges.鈥�

The project is unique in that three tunneling methods are being used. Two 鈥� jack and bore, and horizontal directional drilling 鈥� are traditionally used in North America; however, a third 鈥� micro-tunneling 鈥� is relatively uncommon.

On the ground, a team led by Mortenson and Brownsville, Wisconsin-based Michels Corporation carried out the micro-tunnel crossing of the Tualatin River just west of Oregon Route 99W in King City during the spring. Using an 84-inch diameter Herrenknecht AG micro-tunnel boring machine, crews dug the longest vertical curve tunnel in North America. It’s 470 feet long and roughly 30 feet below the bed of the Tualatin River.

Similar to the jack and bore method, micro-tunneling involves installation of both a large casing pipe as well as internal carrier pipe (three carrier lines in this case). A second crossing of the river was excavated at Cook Park using horizontal directional drilling.

Instead of boring and then filling the tunnel with pipe, however, micro-tunneling crews install sections of pipe behind the boring machine as it works. Once the casing is in place, crews ram the carrier lines through.

鈥淲ith the cutting face, you take water and you pump what you’ve cut back through the pipe,鈥� Paul said. 鈥淲hen we came out on the big tunnel we came out within an inch horizontally and vertically, and we did it in nine days with a crew from around the world.鈥�

After the casing pipe was installed under the river, crews then placed a relatively new type of carrier pipe 鈥� a total of three, with diameters of 14, 16 and 30 inches. This pipe, made of high-density polyethylene (HDPE), is designed to be both seismically resilient and resistant to the buildup of hydrogen sulfide (H2S) and other acidic compounds. Such substances can gradually erode pipes.

鈥淭here are a couple of companies that make a centrifugal wrap polymer pipe, so in essence it’s a mortar pipe that has walls about an inch thick, but it’s wrapped in fiberglass,鈥� Paul said.

Currently, approximately 10 people are working in Tualatin’s Jurgens Park 鈥� roughly the midpoint between the project’s east and west ends. There, they are simultaneously pulling up old pipe and laying new pipe via horizontal directional drilling.

Officials expect the project to be completed by the end of the year.

鈥淲e do a lot of pipeline enhancements,鈥� Denny said. 鈥淏ut this is a lot more unique. It’s our first go-round in replacing these large-diameter pipelines, and what was really new was the design-build methodology; that was a first for us.鈥�