Montesano Wastewater Treatment Plant Project

City of Montesano, Washington

Wastewater Treatment Plant Protection Project

The City of Montesano’s Wastewater Treatment Plant (WWTP) is currently threatened by the migration of the Wynooche River toward the WWTP. Failure or loss of critical elements of the treatment plant as a result of ongoing river migration will have severe environmental consequences from raw sewage contamination of the local ecosystem.  The extent of river encroachment on the WWTP is shown in the following photo:


The City has been working with the local flood protection authority and resource agencies on an evaluation of various alternatives to either move or protect the WWTP.  The evaluation found that protecting the existing WWTP through river bank process modification is estimated to cost $8 Million to $10 Million.   Moving the WWTP plant is estimated to be in the range of $20 Million to $30 Million.

The selected alternative is the protection and modification of the existing WWTP. The selection of this alternative is primarily based on relative cost but is also predicated on the understanding that the river bank protection is also needed to make sure that the river does not impact a significant state transportation corridor and WWTP effluent outfall piping.  The scope of the proposed project includes riverbank protection, moving sludge handling and effluent piping away from river encroachment, and opening a relic channel to the west of the site.  The riverbank protection will be completed using “log jacks”. The log jacks are an innovative method of implementing stream bank protection that mimics natural processes.   The relic channel work is expected to provide flow relief during flood events.

The project cost will have a significant impact on the community.  The City has obtained tentative funding approval of up to $5 Million of the needed $8 Million to $10 Million and is working on obtaining funding from other sources. Project costs will also be refined during the initial permitting and design development phase.  It is critical that the City moves forward on this project as soon as possible to avoid the pending environmental disaster that can occur if the local environment becomes polluted from a breach at the WWTP.

It is anticipated that the project will be completed in four phases:

Permitting and Design Development – February 18’ to July 18’
North Bank Protection (Log Jacks) – April 18’ to October 18’
Biosolids and Effluent Relocation – July 18’ to September 19’
Relic Channel Opening and Habitat Restoration – July 19’ to September 20’
The above timelines for each phase include design through construction.
The conceptual evaluation of WWTP options can be found here

City Councilman Robert Hatley recently flew his drone over the site, the aerial view gives a clearer picture of the rivers path, here is the video: