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How We Built a Filtration Plant

Before breaking ground on its filtration plant, Tacoma Water had to make a big decision: whether to go traditional or progressive in the design and construction phase of the plant.

“Design, bid, build” is the traditional process for public projects. Through it, each piece of a project is separate, with little or no crossover between designers, builders and operators. There was also a relatively new way to deliver a public works project: the general contractor/construction manager (GC/CM) method. With it, a general contractor is selected based on qualifications early in the design process to collaboratively develop and discuss the project’s cost, schedule and constructability.

After a rigorous preparation process, Tacoma Water received permission from the state to use the GC/CM route. And from start to finish, the benefits have been significant.



One of the first challenges to tackle using the GC/CM method was the facility’s layout. With a relatively small site and one where the existing water treatment facility was already running, putting things in the right place was like a puzzle. The original concept suggested buildings be sited in a way that would require two tower cranes for construction. But having the builder (Hoffman Construction) involved early meant they had the opportunity to suggest shifting buildings around, the result requiring only one crane.

Valuable suggestions also came from Tacoma Water employees. A water treatment operations supervisor suggested repurposing a 10-million-gallon water storage tank for cleaning the filters or for use as an emergency water supply. The suggestion replaced the need for a new storage tank and pumps, and saved $2 million. 

Another savings came from having an independent group run two value engineering sessions during design. In that time, experts analyze the design and examine options to bring more value. That was when repurposing the tank was evaluated, along with other ideas and modifications that saved about $10 million.


Project of a Lifetime

The looming question during the planning and construction was how to tackle the challenge of running an existing facility while building a new one.

With two pipes that run water out, the decision was to run both unfiltered and filtered water for a time. That required moving our chlorine feed system in order to install a new one, move the fiber optics and electrical – all while giving our customers, good, clean uninterrupted water.

Tacoma Water engineers and plant operators ran a pilot plant on site while the new design was underway. Findings from that were incorporated into the facility, which started providing some filtered water on Dec. 16, 2014. By Jan. 15, 2015, all of the water supplied from the Green River became fully filtered.