6th and 9th Avenue Pump Station Replacement

Owner/Client: City of Poulsbo Public Works Department

The City of Poulsbo’s 6th and 9th Ave Sanitary Sewer Pump Stations located on Fjord Drive along Liberty Bay had far exceeded their useful life. The City contracted with CHS Engineers to determine if the 9th Ave Pump Station could be decommissioned and a gravity sewer main installed to redirect wastewater to the 6th Ave Pump Station.  CHS and a geotechnical sub-consultant completed a pre-design study to evaluate the feasibility of installing the gravity sewer main between the two pump stations and rebuilding the 6th Ave station to accommodate increased depth and flow.

The study included an extensive geotechnical evaluation to determine soil characteristics, ground water levels (including confirming the influence of the tide and artesian pressure on ground  water levels) and proposed shoring methods. Because of the required depth of the sewer main and significant dewatering and shoring work, CHS concluded the gravity sewer main would be too costly to construct and recommended constructing new submersible pump stations at both station sites. An onsite standby generator was proposed to provide alternate power for the 6th Ave Pump Station. CHS coordinated with the City to size the force main as part of this project, including hydraulic surge analysis. CHS is currently designing both pump stations.

Dates:
Pre-design 2011-2012, Design 2014 – Construction pending
CHS Staff:
Rodney Langer, P.E., Principal-in Charge/Project Manager
Darrel Frame, P.E., Project Engineer
Nadine Firestine, P.E., Project Engineer
Erik Andersen, P.E., Geotechnical Engineer, Aspect Consulting LLC

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