Landslides are all about water in the ground.

This fact is front of mind for leaders of the Washington Park Reservoir Improvements Project, the eight-year, $190 million effort to bury a major source of drinking water in the hills west of Portland. The whole job site lies in the path of an ancient, slow-moving landslide, and the six months since the project began have been six of the wettest on record.

Project managers and consulting engineers are eyeing multiple monitoring systems, on high alert for irregular movements in the slide.

Cement is being added to the fill dirt for stability. Loaders are working in up to two feet of water.

“I’ve worked in Alaska – I’ve worked everywhere, and I tell you, it’s tremendously wet,” said Cary Bubenik, project manager for Hoffman Construction. “It’s the toughest job, weather-wise, that I’ve ever done.”

Watered down

Leaders of the Washington Park Reservoir Improvements Project say it will involve, for the most part, mostly uninteresting, below-the-radar earthwork. But there will be milestones when the thrust of work shifts. With a project as complex and challenging as this, those moments also represent challenges overcome, Bubenik said.

Last week featured one of those moments, as a crew with Gonzales Boring & Tunneling concluded jacking and boring three tunnels beneath the park’s historic dam – a critical piece of prep work. Eventually, almost all water poured from faucets in Portland west of the Willamette River will first flow through these inlets.

The main goal of the project is to construct a 12.5-million-gallon drinking water reservoir below the footprint of the city’s existing Reservoir 3 and add a reflecting pool on top. The reservoir will be engineered to withstand the ongoing landslide occurring at the site as well as effects of a major earthquake.

Then Washington Park’s other reservoir, Reservoir 4, will be disconnected from the city’s grid, and a stormwater management area will be built.

Heavy work on the reservoirs is scheduled to continue until 2020, when a two-year pause will begin to allow soils to settle. Work will resume in 2022 with construction of the “interpretive features,” like the reflecting pool.

“What soil does when it’s unloaded is rebound and swell a little bit,” said Stan VandeBergh, head of the Portland Water Bureau’s capital projects division. “And when you put stuff on it, it goes back down. So if we don’t let it settle before we do the reflecting pool, it would all crack.”

Adding to the complexity are the site’s relatively small size (only between 75 and 100 workers have been working), access issues with the surrounding residential streets, and mandates to preserve historic features and relocate more than 170 trees.

But the biggest issue, by far, for construction manager-general contractor Hoffman Construction has been the weather, which has been unpredictable, though predictably wet.

Robotic survey monitoring equipment is spread around the site, sending out prisms to different points and up to satellites in space.

“We can look at the movement of the slide real time; I mean, it’s going on right now,” Bubenik said. “How many projects are you constantly monitoring a landslide with both piezometers and vibrating wires?”

The city even has retained a landslide stabilization consultant (Cornforth Consultants) to do work that would normally be done in-house.

Bubenik, VandeBergh and much of the team came directly from the Kelly Butte Reservoir Replacement Project. That means the team is familiar with the challenges of covering a drinking water reservoir VandeBergh said. But nothing can really prepare a team for a project like the one at Washington Park.

“I’ve been with the Water Bureau for 34 years, and this is by far the most challenging project I’ve seen,” he said.

Material advantage

The schedule is highly segmented, with the next big segment involving cutting the earth down to where the reservoir will go and forming a toe-block wall tied into the landscape with cables and rods.

The first step was drilling 172 pilings to a depth of 100 feet below where the reservoir will go. At 3.5 feet to 5 feet in diameter, they are the “big boys,” according to Bubenik.

Necessitating this heavy work is the fact that far below the now-damp park, soils under Washington Park are flaky, and not competent enough to support the 50-foot-tall reservoir.

The walls, floor and ceiling of the basin will be made of reinforced concrete – around 30,000 yards – between 2 and 5 feet thick. The No. 18 rebar needed to reinforce it will require use of a tower crane because human workers can’t work with steel so thick. Two cranes are called for (foundations for them are being dug).

Engineers opted to design the reservoir in a dogleg shape, which led to a design problem in anticipating how it will perform in an earthquake.

“The engineer of record told me he had to run 85,000 iterations of this project in the modeling every time we’d make a change,” Bubenik said. “That wouldn’t occur if it was a square or a rectangle or a circle.”

With the landslide moving about one-eighth of an inch annually, engineers opted to encase the reservoir in a compressible foam, which will be crushed slowly until it needs replacement – in about 75 years. It’s a highly-advanced, lightweight plastic. Just don’t call it Styrofoam around VandeBergh.

Portlanders don’t mess around with their drinking water, and might not feel comfortable with the thought that it’s being protected from an earthquake by a relatively thin layer of Styrofoam, he said.

But this foam is strong – it’s nearly impossible to dent samples kept at the Portland Water Bureau job trailer. It only looks like Styrofoam.

“It’s an engineered plastic,” VandeBergh said, “not Styrofoam.”

Eliminating the slide altogether would have been “tremendously expensive,” he added.

But the project’s steep price tag reflects the seriousness of its goal. With reservoirs in Arlington Heights being temporarily bypassed, the system is operating at a risk. The project is also just one chunk of a larger effort to shore up the city’s drinking water system. Another major one – providing a new pipe crossing of the Willamette River – is in early design stages, with a request for proposals set to go out soon.

“We’re fairly vulnerable at the moment,” VandeBergh said. “If a subduction zone event occurred today, I’m not going to say we wouldn’t have water (on the west side of the Willamette River), but if I was a betting person, I’d say it would be pretty limited.”

Washington Park Reservoir Improvements

Cost: $190 million

Contractor: Hoffman Construction

Architect: city of Portland

Consulting engineer: Cornforth Consultants

Structural engineer: AECOM

Expected completion: 2022

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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.”

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