This is the first in a series of articles about King County Wastewater Treatment Division’s sewer construction projects that use trenchless technology. The benefit is in the name: instead of disrupting the surface to excavate an open trench for a pipeline, trenchless construction gets the job done mostly underground.
King County Wastewater Treatment Division (WTD) spent 4.5 years preparing for a critical mission: replace 100 year old pipes that carry high volumes of wastewater across the Lake Washington Ship Canal. In January 2015, WTD hired Stellar J Corporation to construct the project . About a year later, Stellar J’s subcontractor, Northwest Boring Company, Inc., lowered one of the Fremont Siphon Replacement Project’s most critical team members underground. That team member’s name is SWIZY, and her mission was to drill two new 450 feet-long tunnels from Fremont to Queen Anne, traveling 80-90 feet beneath the surface of the Ship Canal.
On July 12, WTD’s project team and contractor celebrated SWIZY’s second triumphant return to the surface. Mission accomplished.
You’ve probably guessed SWIZY isn’t a person. SWIZY is a microtunnel boring machine (MTBM). Microtunneling is a trenchless construction method that builds underground tunnels while crews work safely at the surface.
What’s in a name?
SWIZY is named after one of the contractor’s family members. It is common for contractors to name tunneling machines, in the same tradition as naming ships.
THAT WAS THEN, THIS IS NOW
Before World War I, workers built a tunnel using shovels and pickaxes with materials hauled in by iron horse and four-legged horse. They completed the tunnel and installed three pipes- two for sewage, one for drinking water- before the Ship Canal was in service. Today, the Fremont Siphon carries flows from a service area of up to 100 square miles, making up half the volume treated at the West Point Treatment Plant in Discovery Park.
The existing 100-year old tunnel and pipelines under the Ship Canal
After nearly a century of service, the siphon needed an upgrade. Today, public health rules require separation of drinking water and wastewater pipes and there was nowhere to temporarily transfer the sewage while the existing pipes were upgraded. WTD’s project team had to find a new route under the Ship Canal. In 2010, the team rolled up their sleeves and got to work.
DESIGNED FOR SUCCESS
“These types of complex projects need a wide range of subject matter experts on the team during design,” says Project Manager Will Sroufe. The Fremont Siphon Replacement Project included project management and project control, engineering, flow modeling, construction management, operations, environmental planning, permitting, property acquisition, and community relations experts who shape each decision along the path of a project. Each subject matter expert weighs in on decisions, follows the project through construction, and contributes to lessons learned at each step.
The first step in design is to set a pathway, or alignment for the pipeline. Trenchless construction is anchored at the entry and exit points, where shafts are built to launch and retrieve equipment and soils. The team evaluates potential locations for these points, which constrain where the pipe can travel between them.
The Fremont Siphon project team had two major goals. They needed to set a new path for the Fremont Siphon to keep the existing siphon operating during construction and to move away from the drinking water pipelines. Additionally, the team needed to put in odor control to scrub foul air pushed out of the wastewater pipes on the Fremont side.
In a highly developed area, siting new shafts and buildings presents some hard choices. The team could locate the exit shaft on King County property in Queen Anne, but the odor control facility needed to be located at the high point, on the Fremont side. The Fremont side also had more room to accommodate the entry shaft and associated equipment. These constraints required the County to acquire property and relocate a Fremont business.
Trenchless pipeline construction- tunneling, drilling, and ramming- requires careful analysis of soils and groundwater. Two types of studies help set the alignment for the pipeline. Geotechnical experts first carry out desk studies of historical information and other projects in the area. Second, geotechnical tests in the field sample the soils and groundwater on potential routes. This information tells the team whether the proposed route is feasible, and helps decide the best trenchless construction method to use.
Since the Fremont Siphon travels under a waterway and includes work on the shoreline, environmental planners and permitting staff work with an alphabet soup of agencies: USACE, DOE, WDFW*. Consultations include tribal governments with fishing rights in the area, in this case the Muckleshoot Indian Tribe.
King County’s contract bids call for highly qualified contractors with a record of success. Northwest Boring of Woodinville was started in the 1950’s and has completed successful trenchless construction projects for King County and other agencies.
“Every microtunneling project has its own unique challenges,” according to Dennis Molvik, Vice President of Northwest Boring. In 2010, the company completed a record microtunneling project installing 1,903 linear feet of steel casing for a City of Portland force main project. “While the Fremont Siphon tunnels were only a fraction of that length at about 450 feet each, we faced huge challenges,” says Molvik. These challenges including building those tunnels only 3-6 feet apart, in glacial soils with the potential for machine-stopping boulders, and no easy way to build an intervention shaft in the Ship Canal.
“We didn’t expect to run into problems, but if we had, there were contingency plans in place that would solve the problem underground without an intervention shaft,” says Marty Noble, King County’s Project Representative.
Close collaboration between King County’s construction management team and the contractor was critical to successfully address these challenges. “It’s really critical on these projects to have ongoing dialogue and coordination with the contractor,” says Noble. “A good working relationship between the County and the Contractors really helped avoid problems.” Dennis Molvik agrees that, “Open communication and working thru challenging circumstances helped ensure that the microtunneling stayed on track and got completed on time.”
WTD required that the contractor purchase a new MTBM to ensure successful tunneling in such a busy waterway. Seven-feet in diameter, weighing approximately 63,000 pounds, SWIZY tunneled approximately 15 feet every hour returning 650 cubic yards of soil- about 65 dump trucks-from each tunnel drive. SWIZY completed her job while boat traffic continued unimpeded through the Ship Canal.
The Community Relations team worked with the Fremont and Queen Anne project neighbors throughout design and construction of the project, taking input and addressing questions and concerns. But the team also found ways to have some fun and to celebrate. On February 16, 2016, the team invited the public to a launch party to christen SWIZY. Crowds of neighbors, tourists, and regional visitors signed the machine before she began her journey underground.
The signatures on SWIZY disappeared into the earth beneath the Ship Canal and she emerged triumphant but a little faded from her journey. With a little maintenance, scrubbing, and a fresh paint job, she’ll be ready to go back to work again on another tunneling job. The tunnels she built under the Lake Washington Ship Canal will begin the next century of service for our bustling region.
*USACE=United States Army Corps of Engineers; (WA) DOE = Washington State Department of Ecology; WDFW = Washington State Department of Fish and Wildlife.
Watch SWIZY get removed from the shaft after her final tunnel run in Fremont!