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The City of Portland, Bureau of Environmental Services (BES), is nearing the end of its 1.4 billion program to reduce combined sewer overflows (CSOs) to the Columbia Slough and Willamette River. The City has constructed an extensive infrastructure system to reduce the CSOs, including deep tunnels, pumping stations, large diameter interceptors, large diameter force mains, and treatment plant improvements. When this program is complete, the average annual overflow volume of 6 billion gallons per year will be reduced by 94 percent. As part of its agreement with the Oregon Department of Environmental Quality (DEQ), the City has agreed to reduce the number of overflows that occur through different areas of system in accordance with established milestones.

One of the last projects needed is the Portsmouth Force Main Project. The Portsmouth Force Main is being designed to convey up to 120 million gallons per day (mgd) of flow from the newly constructed Swan Island Pump Station (SIPS) to the existing Portsmouth Tunnel over 3 miles away from the pump station. The Portsmouth Force Main is a vital component of the system and will serve to convey peak wet weather flow from the SIPS. The force main will include approximately 16,000 feet of 66-inch-diameter pipe, odor control and air management facilities, as well as numerous other appurtenances. Because of the nature of the overall CSO system and how the system was developed and built, the Portsmouth Force Main is expected to operate only about 1 week a year. Due to size and nature of this facility and its relatively infrequent use, there are a number of important considerations that must be addressed, including understanding force main operations and their implications related to air management, odor and corrosion control systems, as well as various pipeline and materials considerations. Each of these aspects of Portsmouth Force Main system will be explored further as part of this paper.

Document Type: Research Article


Publication date: January 1, 2007

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