One Project, Four TBMs

Story by Carl Molesworth | September 28, 2010

The massive Brightwater Treatment System project passed a major milestone in September when the first of four tunnel boring machines that will dig the 12.6-mile-long Brightwater conveyance tunnel began grinding their way under neighborhoods in northern King County, Wash.

The TBMs will dig a tunnel up to 16 feet in diameter that runs from the Brightwater treatment plant's south Snohomish County location north of Woodinville to a deepwater outfall off Point Wells in Puget Sound. The tunnel, to be completed under four separate contracts, is scheduled to be completed by fall 2010 at a construction cost of approximately $450 million. Meanwhile at the Brightwater plant site, the 1 million-cubic-yard earthmoving job in preparation for construction of the plant structures is nearing completion after more than a year of cut-and-fill work (see PB&E Nov. 6, 2006).

The Brightwater system, most recently estimated to cost $1.7 billion, will treat wastewater from about 250,000 homes and businesses in north King and south Snohomish counties. Its conveyance tunnel will have the dual purpose of connecting existing sewage-collection pipes to the treatment plant and also conveying treated wastewater from the plant to the outfall in Puget Sound. Force mains inside the tunnel will send influent to the treatment plant, and effluent will flow from the plant by gravity feed to the outfall. A separate contract has been let to build a 170-mgd influent pump station at the North Creek Portal, as well as smaller contracts for improvements to existing facilities, said Judy Cochran, King County's project manager for the conveyance system.

Kenny/Shea/Traylor joint venture of Wheeling, Ill., has a $131-million contract to build a 14,000-linear-foot East Tunnel from Portal 41, also called the North Creek Portal, in Bothell to the south end of the Brightwater property. The contractor started work at the North Creek Portal site in April 2006. The first order of business was to drill two shafts, one for the Influent Structure and another next to it for the Influent Pump Station, using slurry diaphragm wall construction.

The 80-foot-deep IS shaft measures 75 feet in diameter with a 14-foot-thick concrete slab at the bottom. The IPS shaft is a more complex binocular configuration, measuring 76 feet across and 133 feet long. Its floor will be 85 feet below grade.

When the IS shaft was completed, the contractor launched a microtunneler that will dig 2,300 feet in length, 65 feet deep under North Creek Parkway to the existing North Creek Pump Station. Then the Lovat TBM "Luminita" was launched with a public ceremony on Sept. 26 to dig the East Tunnel from the portal to the Brightwater plant. Inside the tunnel will be two influent forces mains, a gravity-feed effluent main and a gravity-feed reclaimed water main, Cochran said.

The IPS shaft will become the below-ground portion of a new pump station for the conveyance system.

At the North Kenmore Portal, Central Tunnel contractor Vinci Parsons Frontier-Kemper joint venture has also launched at TBM nicknamed "Helene." It is tunneling eastward to the North Creek Portal, where it is expected to be retrieved in February 2009. A second TBM, "Rainier," will launch in December from the North Kenmore Portal and will tunnel west toward the Ballinger Portal, where it is expected to be retrieved in November 2009.

The fourth tunnel boring machine, yet to be named, will launch at Point Wells in April 2008 and dig east to the Ballinger Portal, where it is expected to be retrieved in December 2009. Jay Dee/Coluccio/Taisei has the contract to complete that portion of the tunneling.

"It takes a special kind of organization to participate in a construction project of this magnitude, and I am grateful that our staff has been able to pull together the world's leading tunneling firms to perform this portion of the project," said Christie True, director of the King County Wastewater Treatment Division.

Hanson/CSI joint venture has built a plant to produce the precast concrete segments that will create all three sections of the conveyance tunnel, Cochran said. The 10-inch-thick tunnel walls are designed to be built by the TBMs in rings of six segments each, she added.

Civil engineering firms that helped design the conveyance tunnels for the Brightwater system were Montgomery Watson Harza and Jacobs Associates; and Camp Dresser McKee, the geotechnical engineers. Jacobs Civil, an engineering firm, is overseeing construction management on the project.

A Change of Plans at Plant

At the 114-acre Brightwater treatment plant property, GC/CM Hoffman Construction and its subcontractors have spent the past year moving dirt — lots of dirt — in order to prepare the site for construction of the treatment facilities to begin.

As crews from subcontractor Northwest Construction were excavating along the east side of the property for the structures that will be built there, large land forms and berms have been rising along the west side that will block the plant from sight by motorists traveling on Highway 9. In addition, the 350,000-cubic-yard "Alpha Mound" at the south end of the property will provide materials for backfill and other purposes later in the project.

"The plan is to not export any materials," said Dave Johnson, project manager for Hoffman Construction.

The effluent drop structure at the south end of the site also was completed, along with extensive shoring, trenching and a backup stormwater system.

Darlene Septulka, King County's project manager for the treatment plant, said the desire to expedite progress on the site led the county to break out a portion of the work to be completed under a separate contract. Previously, all the work had been under Hoffman's contract, but now the solid stream and odor control will be built under a hard bid contract of an estimated $150 million to $175 million. Bids for the solid stream/odor control contract were set to open Oct. 25, with work beginning in January 2008.

Hoffman will continue to be responsible for all of the excavations plus building the liquid stream portion of the plant, which will total about $300 million. Also under that contract, Hoffman Structures will perform extensive tenant improvements to an existing building on the property to convert it for use as the Brightwater Operations Center.

"We wanted to take advantage of the summer to get the excavation done," Septulka said in explaining the change in plans.

At this point, Hoffman has reached about 70 percent buyout on the contracts under its management. Johnson said the contracts still to come are for site yard piping, yard electrical work, instruments and controls, exterior closures and architectural finishes, and final site improvements and landscaping.

For neighbors, the most visible change at the site during 2008 will be the erection of tower cranes, eventually numbering five — as construction of the plant facilities gets under way. That work will continue into 2010, with the plant expected to commence operation in early 2011.

The plant configuration features primary treatment, secondary treatment using aeration and membrane bioreactor (MBR) technology, plus disinfection of wastewater.

When it comes online, Brightwater will be the largest MBR wastewater treatment plant in the world. As a result of this advanced treatment process, effluent leaving the plant will be of a high enough quality for use in irrigation and certain industrial applications. In addition, a digester will produce methane for powering the plant, and solids removed from the wastewater during the treatment process will be collected and hauled off-site for compost and other uses. Enclosed odor-control structures, costing $65 million alone, will be the most sophisticated in the nation and will emit no odors to the surrounding community.


Key Project Participants

Brightwater Treatment Plant Site

Design Team:

Civil/site engineering design: CH2M Hill

Process design: Brown and Caldwell

Architectural design: Mithun

Landscape design: Hargreaves

Effluent Drop Structure design: HDR

Construction Management:

CM consultant for King County: CDM

Construction Team:

GC/CM: Hoffman Construction

Earthwork and Utilities: Northwest Construction

Yard Piping: University Mechanical

Effluent Drop Structure Shoring: Condon Johnson

Effluent Drop Structure Concrete: Harbor Pacific

Temporary Power: Elcon

BOC Tenant Improvements - Hoffman Structures

Contractors who will be working on the structures:

Concrete: Hoffman Structures

Structural Steel: McClean Ironworks

Waterproofing: Division 7 Waterproofing

Masonry: Fairweather Masonry

Roofing: Snyder Roofing