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Construction is slated to begin in 2016 on a $67 million project to replace one of Washington Park’s historic, open drinking water reservoirs.

The Portland Water Bureau shared the project plans with the public at an open house last week. City officials sought input on whether to include a reflecting pool, walking paths or other park features on top of the new underground concrete reservoir.

The project is scheduled to finish in 2021.

The open house drew members of the Friends of the Reservoirs advocacy group; they expressed concerns that replacing the reservoir is costly and unnecessary.

City officials announced last month that they would proceed with the project after receiving a mandate from the Oregon Health Authority to follow a federal regulation that outlaws the use of uncovered reservoirs to store finished drinking water. The rule is intended to reduce the risk of exposure to contaminants.

City officials made numerous attempts to obtain a variance or delay in rule compliance because of cost. OHA refused the request in May.

The Portland Water Bureau started making plans to construct a new Washington Park reservoir and two others in 2006, after the Environmental Protection Agency established the Long Term 2 Enhanced Surface Water Treatment Rule. It required additional treatment for all open-air reservoirs.

Work is under way on the $138 million Powell Butte reservoir scheduled to be completed this fall, and the $70 million Kelly Butte reservoir slated to be finished in late 2014, Water Bureau spokesman Tim Hall said. The new reservoirs will replace the 75-million-gallon, open-air Mount Tabor reservoir, which will be decommissioned in December, he said.

The northern Washington Park reservoir currently holds 16 million gallons. It will be replaced by a reservoir with a capacity of 15 million gallons, said Alan Peck, project manager with Portland-based AECOM, which the city contracted for engineering services.

Washington Park’s 17-million-gallon reservoir will be decommissioned and used for overflow, dechlorination and stormwater management.

The city is seeking public input on how else to reuse the space, Hall said.

“We wanted folks to give us some ideas for what happens with the lower reservoir because we don’t need all the space in the facility,” he said. “We wanted to see what folks wanted in there.”

Although both reservoirs have been upgraded and repaired over the years, the concrete continues to crack and deteriorate, Peck said. The structures also aren’t seismically sound, he said.

“We’re much more aware that earthquakes happen in the Pacific Northwest,” Peck said.

Floy Jones, a founding member of Friends of the Reservoirs, said the group believes recent upgrades to the reservoirs are sufficient. The construction project will unnecessarily raise water rates, she said.

“There’s absolutely no reason to be (replacing) them now,” Jones said. “Really, the bottom line is saving the ratepayers money for projects that don’t need to happen.”

The city should continue to seek a deferral to the OHA mandate, she said.
“They’ve been proven safe for over 115 years,” she said. “You don’t fix what isn’t broken.”

The new underground reservoir will be rectangular, with thick concrete walls, Peck said. The base will be 4 feet thick, the walls about 3 feet thick and the roof 2 feet thick, he said. The walls of the existing reservoir are only about a foot thick, he said.

“It’s going to look a lot more like a concrete box,” Peck said. “It’s just a vastly more robust structure because we understand the seismic needs. We understand the needs to contain water.”

Like the existing reservoir, the new one will be about 40 feet deep, Peck said. A concrete slab over the water will be covered with 4 or 5 feet of earth, he said.

Efforts will be made to preserve historic structures surrounding the reservoirs, which were built in 1894, Peck said. The reservoirs have been listed as part of the Washington Park Reservoirs Historic District on the National Register of Historic Places since 2004.

“One of the project goals is to maintain as much of the historic character as possible,” Peck said.

The new reservoir will be built slightly east of the existing one to avoid the path of a shifting hill that is prone to landslides, Peck said. Construction in the late 19th century caused a significant landslide, he said.

The hill still moves downward about one-quarter inch to one-half inch a year, he said. The new reservoir will be built about 20 feet east of this landslide, and earth will be added to the bottom of the slide, he said.

“We have to design it to get away from that,” Peck said.

He said the new reservoir will retain the shape of the original one.

“It’s still going to look like a sock,” Peck said. “It’s very hard to design because it’s unusually shaped.”

Another challenge will be ensuring that the structure can withstand the weight of the water it will hold, he said.

“We’re working on the issues of loading and reinforcing,” Peck said. “One of the issues is to equalize pressure from the inside and the outside.”
To help solve this problem, AECOM will use computer models, he said.

“You can come out with an answer for what the stresses are on the reservoir,” Peck said.

Work is under way to sample the soil that will be under the new reservoir, he said.

“The strength of the soil under this is key to everything,” Peck said. “We’re going to have to run piles down into the soil to take the load because the soil doesn’t have enough strength to hold the weight.”