Project Summary

IMCO used innovative methods to reuse existing infrastructure in order to construct a new combined sewer overflow project for the City of Port Angeles. The Project was part of the City’s approved CSO Reduction program to increase storage capacity of combined sewer overflows to better protect the city against major rain events inundating the sewer system. This was the first phase of a two-phase project valued at over $40 Million and was the city’s largest public works construction project to date.

This project included a diverse and complex scope of work, 85% of which IMCO self-performed. The project involved wastewater treatment plant modifications, a new bridge over Ennis Creek, sliplining, a five-million-gallon tank rehabilitation, and open-cut installation of nearly 35,000-feet of pipeline.

Crews used the technique called sliplining to install nearly 17,000 feet of pipe. The slipline required simultaneous installation of one 30-inch and two 14-inch HDPE pipes pulled through an abandoned 48-inch industrial waterline. The pipeline parallels the Olympic Discovery Trail located within 10 feet of the Port Angeles shoreline. A major concern for IMCO’s client was the potential for typical open-cut construction methods to disturb native artifacts that may be in the area. There was also concern about the risk of environmental damage with open-cut excavations in close proximity to the shoreline. The solution was to slipline the existing waterline. The scale of the slipline made it particularly complex, with only a few inches of tolerance to fit the three new pipes through the existing pipeline. IMCO General Construction self-performed this scope, with support from Advanced Boring Specialists.

The Olympic Discovery Trail goes right through the jobsite is on the course for the Boston Marathon qualifying race that takes place every May. IMCO was able to sequence and accelerate the work to meet the milestone dates. The Boston Marathon qualifies specific courses, so the race couldn’t take place without the course being restored to its original condition.

The project also included the rehabilitation of a five-million-gallon steel tank that was part of the Rayonier Mill. The tank was previously used for industrial processing in the old pulp mill. The tank was being converted to CSO storage in order to avoid overwhelming the existing treatment plant. Innovative design by the City of Port Angeles allowed for the reuse of existing infrastructure, saving resources and protecting the marine environment.

“There have been changes and challenges that could have de-railed the relationship, but the project team has been dedicated to maintaining a strong relationship. This is something we are very proud of,” said IMCO President, Tyler Kimberley.



Port Angeles, WA


City of Port Angeles

Contract Amount

$16.3 Million


Brown & Caldwell


July 2012 - January 2014

Project Highlights

IMCO’s biggest success on this project is having a solid working relationship with the City of Port Angeles on a complicated project. Because this is an environmental cleanup project many special requirements had to be followed to keep the public, the crews, and the environment as safe as possible. Keeping the waterfront trail accessible to the public was a huge project priority. There was always part of the trail open throughout the duration of the project.