MONMOUTH -- Crews with NW Natural Gas are continuing replacement and installation of a pipeline along Highway 99W through Monmouth.
The very visible activity happening between Hoffman and Parker roads represents the first of a four-stage project that entails nearly 30 miles of reinforced 12-inch steel pipe being laid down between Bethel Road east of Perrydale and Corvallis.
In recent weeks, contractors have set up staging areas along the highway on massive timbers to accommodate heavy equipment and materials.
The length of pipe will eventually link to another transmission line that runs east to west from the valley to the coast. NW Natural is replacing 12 miles of bare steel pipe with one that's thicker and coated with an anticorrosion agent.
The entire "Mid-Willamette Valley Feeder" project will cost about $47 million, said Jon Huddleston, director of operations and engineering for the Portland-based utility.
The new system would increase capacity of the pipeline by 25 percent and improve "reliability and long-term supply to the area," Huddleston said.
In spots where it's impractical or disruptive to dig trenches for pipe, workers will use a practice called horizontal directional drilling.
That involves boring down into the ground between 20 feet and 50 feet deep and steering a drill head horizontally until it reaches an entrance pit, where the pipe is located.
The pipe is then attached to the drill and pulled back into the hole and into place.
The process is less invasive than traditional trenches, Huddleston said. To cross Avery Park in Corvallis, for example, the pipe is being laid down perhaps 30 feet below tree roots, according to the Corvallis Gazette-Times.
"We do it in areas that aren't easy to dig in, if there's an environmentally sensitive spot or if there's a railroad crossing," he said. "We're trying not to impact citizens."
The Monmouth phase will wrap up in August, Huddleston said. A line will be installed between Bethel Road and Rickreall between June and October.