Introduction
Stringent measures have been created by the American Environmental Protection Agency (EPA) to prevent raw sewerage from running into streams and rivers in heavy rainfall. In compliance with this requirement, Portland, Oregon, developed a Combined Sewer Overflow (CSO) program in 1991 and can thus be regarded as the project’s owner. The project’s designers were J.W. Fowler, Inc., and McMillen Jacobs Associates, the contractors that offered construction engineering services. A vital constituent of this city’s CSO program is the Balch Consolidation Conduit Shafts and Pipeline project (Balch).
It involved the construction of a novel pipeline that carries stormwater and sewerage overflow to the west side of a big pipe from the Balch drainage basin. Wastewater and floodwater will be temporarily stored in underground tunnels if water accumulation overwhelms the sewage treatment plant’s capacities. The water that has been amassed is then propelled to the sewage cleaning plants where it is treated. This prevents the pollution of the Willamette River by sewerage and wastewater.
The 5.7-kilometer-long westside tunnel collects the water that accumulates in the city’s western side. Similarly, the East Side tunnel is in charge of the city’s eastern side. The project uses a total of five tunnel-boring machines from Herrenknecht. Foundation Engineering offered information to illustrate the subsurface conditions along the orientations of the tunnel. Early work entailed the geologic valuation of the projected alignments founded on geologic mapping and subsurface data. Identification of wetlands, topography, streams, and historic shorelines was made in the downtown area to locate buried structures and pilling and asses fill depth that could influence tunnel construction and design.
The second stage entailed extensive subsurface surveys: the tunnel explorations of the westside consisted of 13 cone penetration tests, 13 topography borings, and 101 geothermal borings to support geophysical surveys for subsurface impediments. The investigation involved the Willamette River tunnel crossing’s four barge-mounted borings. It also explored the frequency and size of boulders using the huge diameter borings. The borings were penetrated, ensuring they suited the conditions for the drop and access shafts: The Tanner Extension, the Peninsular Force Main, the Swan Island Pump stations, and the Southwest Parallel Interceptor. Single-point diffusion and groundwater response monitoring were done to examine the Swan Island Pump station’s state of groundwater.
Various agencies, including federal, state, and local governments, worked with foundation engineering and other contractors to ensure traffic control and drilling permits were obtained while drilling within the city parks and streets. The CSO also involved an eastern side with a 6-mile-long tunnel that spreads between the Westmoreland area and Swan Island (City of Portland, Oregon, 2023). This phase’s exploration involved seven slope inclinometer installations, 29 monitoring wells, and 75 mud rotary boring (City of Portland, Oregon, 2023). Geophysical examinations were also offered to aid in locating steel piles adjacent to tunnel configurations.
In Willamette River’s eastern shore, vacuum excavations and test pits were conducted to detect and examine micro tunneling man-made debris, train trestles, and historic piling. Microtunnel connections comprised 84-inch reinforced concrete pipe (RCP) of 6,921 feet installed in 1690 five feet drives. The drives were of 1,194 feet, 1,134 feet and 1, 308 feet and 1595 feet. Additionally, a 54-inch, 1,115-foot RCP was also fitted; they were of varying depths ranging from 20 to 75 feet (City of Portland, Oregon, 2023). Every drive ends with the annular space between the ground and concrete pipe plastering.
Advantages and Issues of The City of Portland Balch Consolidation Conduit Program
The Combined Sewer Overflow (CSO) program presented Portland, Oregon, with many advantages related to the environment. Spanning over two decades with an investment of $1,4 billion (City of Portland, Oregon, 2023). The big pipe project has lessened sewer overflow to the Willamette River by 94% and by 99% to the Columbia Slough (Wheeler, Ryan, Mapps, et al., 2022). Having eliminated most of the overflows, the Willamette River is at one of its cleanest levels in decades. Prior to the Balch Consolidation Conduit project, it did not need much rain to cause an overflow.
The City of Portland Bureau of Environmental Services examined various choices before settling on the CSO Balch program as the preferred choice to tackle sewage and wastewater overflow. Figure 1 below indicates the efficacy of the project by illustrating the number of overflows after its completion; Figure 2 compares overflows before and after the project. The program was the most cost-effective method while maintaining efficiency by eradicating most but not all run-off (Wheeler, Ryan, Rubio, et al., 2022). Table 1, on the other hand, shows some important facts and advantages that the project has presented. This link indicates a map of the area that the project covered in Portland, Oregon https://www.portland.gov/bes/about-csos and has benefits offered by the project.
Table 1 – Portland Oregon’s Combined Sewer Overflow (CSO) Quick Facts.
Regarding budget issues, a significant consideration was the cost of having a system that eliminates 100% of CSOs. However, as pointed out in Table 1, when determining that it would not positively impact residents’ health, 94% to 99% was settled for. There were no major schedule issues; the Portland city entered into an Amended Stipulation and Final Order (ASFO) through the Department of Environmental Quality in 1991.
The ASFO mandated the program’s completion by December 1, 2011, and the project was completed as planned in 2011. Environmentally, the project was meant to mitigate environmental pollution. The issues encountered by the project include choosing an appropriate contracting method, coordinating and relocating utilities in its area, obtaining permits and easements, doing ground modification, and ensuring optimum public interaction.
Choosing the Appropriate Contracting Method
Micro tunneling is known to be risky with associated perils, including the collapsing of borings. The risks are even more hazardous when it comes to Balch consolidation conduit (BCC) projects. Thus, to avert these risks, getting it right when it comes to procurement of construction contractors is inevitable. The Balch project ensured responsible risk-sharing between the city and the contractors. For a month between December 2007 and January 2008, representatives of the Bureau of Environmental Services (BES) assessed several techniques for the execution of the project and selection of the construction contractors.
By mid-January 2008, BES decided to go for a competitive proposal that was qualification-based. The project construction utilized the Cost Reimbursable Fixed FEE(CRFF) contract and the contractor selection process (Cozzi, Moore, & Jossis). After selecting the contractor through the competitive process, the city entered into a construction services agreement with the contractor. During the preconstruction period, the contractor took part in the final design of the projects and negotiated an estimated reimbursable cost (ERC) between the city and the contractor. The contractor and the town also negotiated the construction contract, with the contractor’s compensation being set on a fixed fee based on the ERC.
The main issues that this contracting method addresses include the capacity to have an equitable risk-sharing approach between the city and the contractor. It enables a simultaneous selection of the contractor during design, lessening the project schedule’s overall requirement. It allowed for procuring long lead time materials and equipment early (Cozzi, Moore, & Jossis). It permitted the simultaneous working on inter-linked work elements such as constructability review, risk evaluation, value engineering, and the development of estimated reimbursable costs. The contracting method also nurtured a cooperative working relationship between the design team, contractors, and BES during construction and design.
Utilities in The Projects Area
Utilities situated in the area of the project’s scope posed a significant issue. The area on which the project was to pass through was examined to identify all types and locations of utilities. This helped establish the need for utility relocation and the impacts they would have. Gas pipelines, waterlines, underground telecommunications, railroad lines, and overhead power were of significant concern. These utilities were identified in conjunction with Northwest Natural Gas, Portland Water Bureau, QWEST, Burlington Northern Railroad, and Portland General Electric. The issue was addressed by removing the utilities in the project area.
Obtaining Permits and Easements
A project touching such a vast area and involving many risks would inevitably need permits. To ensure permits were acquired in time, division of labor was adopted. Notably, the responsibilities were split between those that the design team could accomplish in the course of design and those that the BES could undertake. Against those more linked to the methods and means the contractor could perform. Those that the Portland Bureau of Environmental Services offered include clearing permits, utility permits, land use approval permits, railroad crossing, encroachments and easements permits, and non-park use permits. The provider provided a contaminated media disposal permit, utility services connection permit, discharge permits, NPDES construction stormwater permit, noise variance permits, and excavation disposal permits. Building demolition permits, site grading permits, and other permits linked to construction staging areas and permits for pumping water from River Willamette. This way, the issue of obtaining permits was dealt with and alleviated.
Ground Modification
As far as ground modifications are concerned, the issue was posed by the existence of highly variable soft soil, which threatened micro tunneling. To address this, it was recommended that a prolonged zone of micro tunnel break-out ground alteration be made about shaft B and for the micro tunnel drive amid B and GLI. These modified areas spread over a 60-foot area towards the direction of shaft GLI. Grout column panels were also recommended along the drive from GLI to B to enable safe micro tunneling. A 15-feed clear space amid every panel was recommended, and the spacing was founded upon the proposed BCC machine project, which comprised an airlock cylinder and a secondary steering joint. Additionally, ground modification was inevitable to ensure all shafts’ break-in/break-out (BU/BO). This is a standard industry practice and was not to be avoided.
Ensuring Optimum Public Interaction
Within the 20-year construction span, different parties would be affected by the program; failure to inform them would result in issues, including court cases against the project. Thus, the project incorporated a general public education and information program with a well-planned approach to offer timely coordination and information with the directly affected parties. The emphasis of outreach before and during BCC construction was the conveyance of particular construction information and the building of a bond with property and business owners affected by the construction activities. Through continuous and well-calculated outreach, community disruption and impact were reduced.
Conclusion
In conclusion, the Portland, Oregon City, Combined Sewer Overflow (CSO) program was delivered for a 20-year period, up to 2011. The project has been discussed above, offering a short case study and later expanding on the advantages and issues encountered during the project. The project has contributed to the overall health and well-being of the people in the area. The alternative contracting method enabled a competitive process that hugely led to the project’s success.
References
City of Portland, Oregon. (2023). About the big pipe project. Web.
Cozzi, R., Moore, B., & Jossis, B. (n.d.). Another success for the city of portland using alternative contracting methods to deliver the balch consolidation conduit. Paper E-2-01 – 2, 3-5.
Wheeler, T., Ryan, D., Mapps, M., Rubio, C., Hardesty, J. A., & Caballero, M. H. (2022). Proposed Budget City of Portland,Oregon: FiscalYear2022-23. City of Portland,Oregon, 22-25. Web.
Wheeler, T., Ryan, D., Rubio, C., Hardesty, J. A., Mapps, M., & Caballero, M. H. (2022). Adopted Budget City of Portland, Oregon. City of Portland, Oregon, 1, 1-11. Web.
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