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The Sellwood Pump Station is a wet-weather pump station that is part of the overall City of Portland Bureau of Environmental Services’ (BES) 20-year Combined Sewer Overflow Abatement Program. On Thursday, 14 June 2012, the station had its grand opening to celebrate a cleaner, more sustainable way to deal with sewage outflow. In attendance at the ceremony were BergerABAM’s Tony Pritchett, Brian Board, and Hod Wells, team members in the design of the new pump station.
When the City of Portland was built in the mid-1800s, the sewer system constructed at that time was a combination of sanitary sewer and storm sewer—common in many U.S. cities. As a result, the city’s sewage and stormwater flowed directly to the Willamette River and Columbia Slough before the first treatment plant was constructed in 1952. Water quality improved after 1952, but heavy rainstorms still caused combined sewer overflow (CSO) discharge into the waterways.
The Oregon Department of Environmental Quality’s (DEQ) goal of reducing the amount of CSO to almost zero required the City of Portland to control 99 percent of CSO to the Columbia Slough and 94 percent of CSO to the Willamette River. Because it was impractical to completely separate stormwater from sewage everywhere in the city, BES undertook three “Big Pipe” projects to convey and treat the CSOs. Corollary to these mega-projects were dozens of other forcemain, pump station, and tunnel projects. The Sellwood Pump Station was one of these projects.
BergerABAM’s Portland office had been involved with this pump station design for over five years. Beginning in late 2006 with a small task order from BES to evaluate the Lents Trunk Sewer’s (LTS) capacity to be adapted for use as a storage conduit, BergerABAM later joined the team of West Yost Associates of Davis, California. Together, the team designed the system that intercepted the flow of the LTS (built in 1922) and the Sellwood Interceptor, and diverted that flow to a new pump station next to the Willamette River.
The LTS is a concrete tunnel with a brick-lined invert that drains 1,090 acres of combined sewer. The portion of the trunk sewer currently used as a storage conduit is the lower 4,400-foot-long reach that previously released untreated combined sewage directly into the Willamette River. Because the tunnel is over eight-tenths of a mile long between manholes, conventional closed-circuit television inspection of the sewer was not practical, and radio communication with topside personnel was impossible toward the middle of the tunnel.
Instead, at the onset of the pump station final design phase, BergerABAM engineer James Bohanek conducted, planned, and led a manned team inspection that included a pair of videographers and an industrial hygienist who continuously monitored air quality to ensure the safety of the personnel during this long-duration, confined space entry. The team travelled the length of the tunnel with self-contained breathing apparatuses should the industrial hygienist find the air quality unacceptable. In addition, the team was given air horns that they sounded periodically once radio contact was lost.
The inspection was conducted in mid-July after the spring rains had ceased. The team found large volumes of groundwater infiltration and significant localized deterioration along the length of the tunnel. The design team then thoroughly analyzed tunnel rehabilitation alternatives to alleviate this groundwater infiltration and make structural repairs. Ultimately, BES decided to rehabilitate the lower 1,000 feet of the tunnel using grout injection, localized crack and spall repair techniques, and masonry repair of the brick-lined invert. BergerABAM provided traffic control design for the project and structural engineering design of the new pump station control building (a 2,000-square-foot concrete masonry unit structure with an eco-roof) and the diversion structure, which is the 35-foot-deep structure that intercepts the LTS and diverts the flows to the pump station. The diversion structure extends 10 feet above ground and contains overflow weirs for the rare occasions in which storm event flows exceed the pump station’s capacity.
Because the pump station and diversion structure are in a residential neighborhood and adjacent to the Portland Rowing Club, every effort was made to create a facility with pleasing aesthetics and a high degree of odor and noise control. In addition to the adaptive resuse of the LTS and the pump station eco-roof, sustainable features of the project include the use of pervious concrete pavement, curb cuts, and infiltration swales. These features were incorporated to assure the community that BES would be a good neighbor.
Other members of the design team included MWA Architects, Jacobs Associates, Elcon Associates, Inc., and Vigil-Agrimis, Inc.