A new 3 million-gallon concrete water reservoir is being built off of Southeast Verlie Street in Happy Valley, and it’s a jarring sight amid some single-family homes in the Clackamas County suburb.

A massive amount of earth has been scooped out of the hillside by Landis & Landis Construction, the excavation subcontractor for the new $8.5 million reservoir project being carried out by the Sunrise Water Authority and general contractor Ward-Henshaw Construction of Canby. In all, more than 44,000 cubic yards of dirt and 8,000 cubic yards of bedrock will be excavated and hauled from the site in order to allow the new reservoir to sit alongside an existing 2.5 million-gallon concrete tank at the same grade.

“It’s a huge amount of dirt and a huge amount of rock,” said Wade Hillard, senior superintendent in charge of the jobsite for Ward-Henshaw Construction. “The first step was just getting all the mass excavation out, and now we’re at the rock excavation.”

The project is one of the largest undertaken by the Sunrise Water Authority in recent years and comes in belated response to population growth.

“We’re a little behind on keeping up with that,” said Dan Fraijo, project manager for the water provider. “So, this will bring us up to par. But not too much extra.”

Space has been reserved for more than a decade for the new reservoir. The project is part of the agency’s 20-year capital improvement plan.

Excavation and construction is expected to take around 16 months to complete. A further five months will be needed for backfill and final grading, with a final goal, Fraijo said, of getting the new reservoir online by late summer 2019.

Because of its sensitive location in the middle of an affluent suburb, the project is being carried out with restrictions on noise and hours of operation. There even are a pair of decibel meters on fences to the east and west sides of the excavation site to ensure adherence to agreed-upon noise limits.

“This job is interesting just because it’s in the tight quarters of this neighborhood,” Hillard said. “So, the logistics and access and stuff has been a little bit of a fight keeping the neighbors happy, keeping the owners happy and keeping it on schedule. It’s a constant grind.”

Technically, a reservoir is little more than a round concrete tank placed atop a large concrete slab and footings. But this reservoir is being constructed with seismic resilience in mind; it’s not a conventional post-tensioned concrete structure.

“Everything is independent of each other,” Hillard said. “If you look at a house or a school, you have your concrete footing and your rebar sticking out and then your wall would sit on top of that rebar and everything’s tied together with steel and concrete. Whereas on this reservoir it’s completely independent of each other.”

Instead, the concrete core walls sit on rubber pads and are strengthened on the interior by vertical seismic tendons similar to post-tensioned cables.

“You don’t have any rebar connecting things, so you have the seismic cables and you have rubber,” Hillard said. “In theory, if there’s ever a seismic event the wall is independent of the footing.”

Concrete reservoirs are not only stronger than their steel counterparts, but also far easier to maintain over time.

“The biggest difference is there is basically zero maintenance on the concrete reservoirs; it’s all poured and done,” Hillard said. “If you have a steel tank you have to go in probably on a yearly basis because they’re coated and they’re not going to last as long.”

That’s a huge consideration in the face of regional population growth and the need to build further infrastructure in coming years, which is exactly what the Sunrise Water Authority is planning for. It has plans to build another reservoir and has already contracted with Clackamas River Water for storage space in a new 6 million-gallon reservoir that agency is building off of Southwest 152nd Avenue as part of an eight-year, $40 million series of infrastructure projects.

“There is another reservoir planned at this same elevation further east within the next five to 10 years just to keep up with that curve,” Fraijo said.

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