In 1991, the City of Portland (“City”) entered into an Amended Stipulation and Final Order (“ASFO”) administered by the Oregon Department of Environmental Quality which mandated completion of the Combined Sewer Overflow (“CSO”) program by December 1, 2011. The ASFO required the City to construct facilities to control combined sewer overflows into the Willamette River. The Balch Consolidation Conduit Shafts and Pipelines project (“Balch”) was a key component of the City’s CSO program and required construction of a new pipeline to carry sewage and stormwater runoff from the Balch Drainage Basin to the West Side Big Pipe, which collects combined sewage from the west side of the Willamette River for conveyance to the Columbia Boulevard Wastewater Treatment Plant on the east side of the river.
The microtunnel installation included 6,921 feet of 84-inch RCP installed in five drives of 1,690 feet; 1,595 feet; 1,308 feet; 1,194 feet and 1,134 feet. An additional 1,115 feet of 54 inch RCP was also installed. The depths varied from 20 to 75 feet. Each drive ended with grouting of the annular space between the ground and concrete pipe.
Portland’s ground conditions are renowned for being extremely challenging and this site was no exception. Located in a former landfill, the five launch/ reception shafts were constructed thru fragments of glass, brick, wood, wire and sheet metal in addition to the expected cobbles, boulders and soft soils.
During the final microtunnel drive, the machine encountered an unidentified steel object which halted the progress. JWF performed over 250 separate compressed air man interventions where a team of two people went over 900 feet within the pipe 75 feet underground, pressurized the face of the tunnel machine and entered the crushing chamber through a door 16 inches by 19 inches to repair the machine and resume the tunneling process. This process is similar to a deep sea dive and is extremely dangerous. JWF is the only tunneling contractor in the United States to have performed compressed air interventions of this magnitude on a microtunneling machine.
As a means of managing the risks of the project and reducing cost and schedule, JWF offered Cutter Soil Mixing (“CSM”) as an alternative shaft shoring method of the tunnel access shafts – a method untested in Oregon or the types of soils on site. The City agreed to use the new technology enabling Balch to be the first project in Oregon to use CSM for shaft support. Additionally, this project was the first use in the United States of the CSM panels to support the machine and pipeline and for tunnel break-in / break-out zones. This new technology fit well with the City’s sustainability initiatives by eliminating waste to landfills, reducing fuel consumption, and containing hazardous waste and contaminated groundwater.
The project included construction of five shafts, the first was 36 feet long, 24 feet wide, and 30 feet deep; the second was 45 feet long, 32 feet wide, and 46 feet deep. The remaining three were round shafts including a 36 feet diameter and 62 feet deep shaft, a 24 feet diameter and 68 feet deep shaft, and a 31 feet diameter and 78 feet deep shaft.
The City prides itself on promoting historically under-utilized minority, women and emerging small businesses (“MWESB”). At the beginning of the project, JWF identified a goal of $3.4 million of MWESB participation. We also identified firms to mentor during the project, offering assistance in the form of estimating, deciphering plans and specifications, and business management which allowed these entities to remain in business in a challenging economic environment. At the end of the project, JWF had awarded $16.3 million to MWESB firms, a 448% improvement on the original goal! The Balch project exceeded the City’s expectations by finishing ahead of schedule, under budget and within specifications. Most importantly, the City was able to meet the ASFO mandated completion date and their commitment to healthy working rivers for future generations.
Final estimates of all project sustainability measures included reducing the amount of contaminated spoils destined for landfills by 36,700 tons, which in turn saved 25,200 gallons of fuel and reduced road congestion by over 2,400 trips.