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McMillin Reservoirs

Structural, Water


Tacoma, WA

Tacoma Water


Structural, Water



Tacoma Water needed to cover the last of its existing open air storage reservoirs. After an extensive study of various cover options, Tacoma Water decided to construct two 33 MG pre-stressed, strand-wrapped concrete reservoirs inside the footprint of the existing McMillin Reservoir No. 2.

Construction of the tanks resulted in the world’s largest diameter, pre-stressed, post-tensioned tanks. The project included 64 separate roof and floor slab pours, 664 columns, and more than 300 miles of strand wrapped around the tank.

Site work included the demolition of portions of the existing 100 MG open top, concrete McMillin Reservoir No. 2, site grading to backfill the proposed reservoirs within 2 feet of roof levels, site drainage, and reconfiguration and extension of the steel inlet, outlet and drain piping, which measure 60, 48 and 36 inches in diameter, respectively.

Due to economies of scale in the design, RH2 completed engineering for less than 1.5 percent of the overall project cost. RH2 completed the design and permitting to within a day of the originally established project schedule. Funding for this project included bond sales, Public Works Trust Fund loans and American Recovery and Reinvestment Act monies.

The design of the two 33 MG concrete reservoirs was completed in the spring of 2009, and the substantial completion date of the two reservoirs was near the end of 2011.

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