Dredged channel helps clear water for Corvallis

Of the Corvallis Gazette-Times

CORVALLIS — A dredging project in the Willamette River south of Corvallis appears to be doing exactly what it was designed to do: providing a steady flow of water to the intake pipe for a large Linn County pulp and tissue operation and diluting the treated wastewater from the plant where it enters the river.

Cascade Pacific Pulp invested $1.3 million in the undertaking, which carved a new channel through a gravel bar that had built up near the company's water handling facility on the Willamette at American Slough.

The river was backing up behind the gravel bar during periods of low flows, allowing effluent from the outfall pipe to mix with the intake feeding Cascade Pacific's Halsey pulp mill and the adjoining Georgia-Pacific tissue plant, which together employ about 600 workers.

The reduced flow also created a coffee-colored, foul-smelling plume of concentrated effluent that was not being dispersed before leaving the designated mixing zone below the outfall pipe, which enters the Willamette about 15 miles upstream of Corvallis. The river supplies about 70 percent of the city's drinking water.

Cascade Pacific tried to address the problem by dredging a small temporary channel in 2011, but it needed permits from the U.S. Army Corps of Engineers before it could attempt a larger-scale, longer-term solution.

In August 2012, Willamette Riverkeeper threatened to sue the company under the Clean Water Act unless it acted quickly to resolve the problem. The nonprofit environmental watchdog also wanted Cascade Pacific Pulp to post signs marking the outfall site and identifying itself as the responsible party.

The suit was dropped after Cascade Pacific paid $20,000 and agreed to complete the dredging project and modernize the fish screens on its intake pipe. After meeting with an arbitrator, the company agreed to post signs identifying the intake facility as Cascade Pacific property, but with no reference to the effluent mixing zone.

The new side channel was opened last August, and the project was completed in late October. The channel has a meandering course to mimic the shape of a natural waterway, with a number of massive tree trunks anchored in the banks to provide fish habitat. Native grasses were planted on both sides along with about 4,000 young willow trees.

“We think the project was very successful,” said Pat Rank, general manager of the Cascade Pacific mill. “It provides good flow to our intake as well as past our outfall pipe.”

The dredging permit requires the company to maintain the channel for a 10-year period, but Rank is optimistic it will continue to function much longer than that.

“The river kind of has a mind of its own,” he cautioned. “You can't look too far into the future when it comes to river flows. But it was designed to be a permanent solution.”

So far, the project is also passing muster with Willamette Riverkeeper director Travis Williams, who took a canoe through the new side channel earlier this month. He said it seems to be moving enough water through the mixing zone to disperse the effluent, even though there's still a noticeable odor around the outfall pipe.

“I think they implemented what everybody thinks will work — it appears they did a good job of creating that side channel and establishing some good woody debris in the bank and shoring it all up,” Williams said.

“The test will be when the river is at average to low flows — is the mixing zone backing up in that immediate area, or is it mixing as it was designed to do?”


Information from: Gazette-Times, http://www.gtconnect.com

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