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Swan Island CSO Pump Station Phase 1 and Phase 2 Projects

Client
City of Portland Bureau of Engineering Services
Location
Portland, Oregon
Pump Station Interior

Project Overview

Carollo designed the 220-mgd Swan Island CSO Pump Station (SIPS). As part of the City of Portland’s combined sewer overflow (CSO) program; the largest capital construction project in the City’s history, the SIPS serves as the terminus of two large CSO conveyance and storage tunnels deep beneath the city (in excess of 120 feet underground), designed to collect and store over 100 million gallons of combined sewage. The pump station consists of a 135-foot diameter circular cast-in-place, 150-foot deep below grade concrete structure, located adjacent to the Willamette River. The circular pump station is one of a kind, and at the time of construction was believed to be to be the deepest of its type in the United States.

The wet well design features several special attributes that benefit pump station operation. The distinguishing attribute is its self-cleaning design, which simplifies operation and reduces maintenance and risk to personnel by minimizing the need to enter the wet well. The pump station utilizes a trench-style self-cleaning wet well making it the largest self-cleaning pump station in the Pacific Northwest. Because of its uniqueness, Carollo used physical hydraulic modeling using a 1:7 scale to test for hydraulic inefficiencies, vortices, and other adverse flow phenomena to optimize wet well and pump performance.

Designed in two phases, the primary function of the SIPS is to provide a balance between tunnel conveyance, storage, and treatment plant capacity, requiring a wide-ranging suite of operational modes. The pump station’s performance and reliability is the linchpin to the success of the City’s CSO Control Program.

The Phase 1 pumping system, put in Service in December 2006, consists of two 42.7 mgd, vertical extended shaft, 2000 hp wet weather pumps, and two horizontal, 16 mgd, 800 hp dry weather pumps, for a total pumping capacity of 100 mgd through parallel 30-inch and 48-inch interconnected forcemain system. The design included alternatives analysis, preliminary and final design of the Mechanical, Electrical, and Structural infrastructure to accommodate an ultimate capacity of 220-mgd. During early phases of construction, Carollo lead a VE effort that cut 3 months from the critical path, resulting in an estimated savings of $3M.

Phase 2 pumping system, put in Service in December 2011, consists of three 40 mgd, vertical extended shaft, 2250 hp wet weather pumps to provide an additional 120 mgd through a 66-inch forcemain; to achieve it’s its ultimate capacity of over 220 mgd, at a combined motor load of 12,350 horsepower. The design included alternatives analysis, preliminary and final design for the complete buildout of the pump station which included civil, mechanical, structural, electrical, and instrumentation engineering. included the selection of major components, requiring a thorough evaluation and optimization of various existing infrastructure and systems to ensure functional compatibility between the existing Phase 1 and Phase 2 pumping systems.

Significant cost savings resulted from the innovative design of the pumping systems to take advantage of significant variance in static head associated with high water levels (or surcharge) within the wet well.  As surcharging occurs, the static head that the pumps must overcome begins to decrease, increasing pump station output. Carollo’s design approach took advantage of the varying static head associated with tunnel storage by eliminating the need for a standby pump, which minimized the overall footprint of the 150-foot deep pump station, resulting in an estimated $14 million reduction in constructing the pump station structure.

Results and Highlights

The 150-foot deep, 130-foot diameter circular below grade superstructure, located adjacent to the Willamette River, is one of a kind and is believed to be the deepest of its type in North America.

220 million gallons per day pump station, with a combined medium voltage motor load of 12,350 horsepower.

8-220 million gallons per day pumping range through a multi-forcemain system required a wide ranging suite of operational modes.

The 150-ft below grade enclosed trench-type self cleaning design reduces maintenance and risk to personnel by minimizing the need to enter the wet well.

Carollo’s design approach took advantage of deep tunnel hydraulics to eliminate the need for a standby pump to reduce the size of the structure at significant cost savings.

One-of-a kind pump intake was validated through physical modeling, to meet Hydraulic Institute standards and optimize the performance and life of pumps.

During construction of the first phase of the project, Carollo lead a VE effort to cut 3 months from the critical path, resulting in an estimated savings of $3M.

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