The City of Montesano will soon announce a call for bids for two projects designed to protect the city’s wastewater treatment plant along the Wynoochee River, said public works director Mike Olden.

“We’re trying to get the project bids out right away to prevent a short-term ecological disaster,” said Olden at the July 24 council meeting.

The river has migrated greatly over the past decade or so, threatening to breach the treatment plant and send waste into the river, which could have devastating effects not just for Montesano but for downriver communities along the Chehalis River, including Cosmopolis and Aberdeen.

The plan is two-fold: The construction and installation of log jacks to shore up the riverbank and protect the plant, and the removal and disposal of existing waste in the treatment facility’s lagoons. The biological waste includes coliform bacteria like E.coli, which could be deadly to salmon, steelhead and other fish species if it found its way into the river.

A study from WEST Consultants Inc. in 2017 said the log jacks — log and boulder barriers designed to prevent flows from eroding the river bank — placed along the north side of the river near the ordinary high-water line should keep the river out of the treatment plant for eight years, longer than the five years the city has decided it will take to put in place more permanent solutions to keep the plant out of the flood plain.

According to a 2017 presentation to the City Council, the cost of emergency replacement or relocation of the treatment plant would exceed $50 million; the cost of addressing the environmental impacts of a breach could top $500,000. According to a City Council presentation earlier this year, the cost of the log jacks and effluent removal would run about $3 million.

The plan calls for more than 100 of the log jacks along the most vulnerable part of the riverbank. According to a diagram produced by Parametrix Engineering, the jacks are constructed with four logs that are 16 to 20 feet long and about 16 inches in diameter, anchored to the bank with boulders at least 8 tons each. Bolts and chains are used to hold the assembly shape together as needed. They are placed in two layers, about 65 on the bottom tier and 45 at the top.

Olden said additional log jacks could be placed along the sheet pile wall, which further protects the plant, to shore it up if another major flood event hits the region.

Olden added the cost of the project would be covered by Chehalis River Basin Flood Authority funding.