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A 25-million-gallon underground concrete reservoir under construction in Southeast Portland is slated to go online this spring. Hoffman Construction is the contractor on the Portland Water Bureau’s $90 million project, which replaces a 10-million-gallon steel tank formerly at the site.

Work on the project began in late 2012 with the demolition of the 43-year-old tank. Following the demolition, nearly a year of excavation at the site took place, while concrete for the reservoir began being poured in fall of 2013.

Around 2,000 truckloads of concrete were brought in to pour a total of 266 squares, each measuring 20 feet by 20 feet. The squares were poured in a checkerboard pattern to control shrinkage cracking. The reservoir’s walls, roof, and 252 support columns were completed in summer 2014.

Backfilling around the sides of the reservoir began last fall, and continues with the installation of mechanically stabilized earth walls. The reservoir will begin operations after being disinfected and commissioned. Work at the site will continue with construction of access roads, fencing, landscaping and mitigation plantings. Total completion of the project is slated for this fall.