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September 28, 2018
Oak Harbor clean water facility
Location: Oak Harbor
Owner/developer: City of Oak Harbor
Team: Hoffman Construction Co., general and concrete contractor; MWA Architects, architect; Carollo, structural engineer; Miles Sand & Gravel, ready-mix supplier
The Oak Harbor clean water facility broke ground in 2016. The facility will be capable of processing twice the daily flow of the facility it replaces when it begins serving the island’s 24,000 residents by the end of 2018.
The facility’s footprint covers just over 2 acres. It houses six membrane tanks, three aeration basin tanks, two WAS/RAS storage tanks, a cylindrical vortex chamber with a complex influent, wet well and effluent channel, as well as a two-chambered odor-control structure.
The two most complex and difficult structures within the complex are the membrane tanks and the vortex chamber. These structures were built using a combination of Peri and handset formwork.
The membrane tanks are supported by a sloping elevated concrete deck above a dry gallery below, supported by large cast-in-place walls and columns. The upper walls for the membrane follow the same sloping profile and tie into the effluent channel for the membrane tanks. Peri formwork was used to form the majority of the walls, but a combination of handset and Peri had to be used to form the connections between the trough, channel and supports below.
The large concrete conical vortex chamber consists of 1-foot-thick,14-foot-radius walls that transition into a 5-foot radius. The structure had to be poured in three stages due to intersecting concrete beams and deck.
Built-in-place hand-set forms were chosen due to the unique structure and the need to tie into adjacent Peri-formed walls that had to pour monolithically with the vortex.