The North Creek Interceptor Sewer is a 2-mile pipeline that has served the Bothell area continuously since 1970. This sewer line has been generally well utilized; however, recent issues with the sewer as well as anticipation for population growth pushed King County to improve its water and sewage infrastructure. One of the projects was the North Creek Interceptor Sewer, which was due for a replacement. The improvement increased the reliability, especially with issues such as sewer overflow, and accommodate population growth.
James W. Fowler Co., was ultimately awarded the contract via an emergency declaration after the original contractor was terminated from the project. The emergency declaration waives the competitive procurement process, and the core compensation to complete the project was discussed and negotiated by James W. Fowler Co. and King County.
The primary objective was to construct 3,443 ft of new sewer line and connect it to the previously built pipeline. The previous contractor’s work was first completed through the open-cut method and completed by installing 85 ft of 42-in and 155 ft of 36-in Hobas pipe, sliplining 85 ft of 12-in PVC, and 250 ft of 8-in ductile iron pipe and miscellaneous 8-in laterals which were tied into the main sewer pipelines. Once all the pipes were in place, cellular concrete was grouted in the annular space between the pipe and excavation.
Pipelines in this project were mainly constructed using open-faced shield tunneling with 72-in casing and 42-in and 48-in Hobas carrier pipe in deep sections and under state freeways. Four drives of 1,103 ft, 1,002 ft, 881 ft, and 547 ft were required.
Aside from pipework, JWF was also responsible for asphalt paving, traffic control, landscaping, and wetland restoration. The construction took place in the City of Bothell as well as an unincorporated Snohomish country. The geotechnical characteristics of the area includes cobbles and mixed face conditions, high water table, artesian, and multiple layered aquifers requiring extensive dewatering.
JWF was faced with a challenge with dewatering as we had to eliminate the impact of construction activity on nearby wetlands and the North Creek to be compliant to the environmental requirements. JWF was successful in treating and discharging the output to the North Creek with no impact to the water quality. Aside from environmental requirement compliance, JWF also performed extensive public outreach and coordination with property owners to obtain over 30 easements and rights of entry to access the project site.