Inside the Powell Butte Reservoir construction project

Part 1: See many exclusive photos of the “construction ballet” being performed every day – as this new outer East Portland underground reservoir is being constructed …

Even from a distance, it’s easy to see the arch created by this gigantic concrete pump piping, as it’s fed by to cement mixer trucks on the “Powell Butte Reservoir Project”.

Story and photos by David F. Ashton
Since it began several years ago, following the story of the building of a 50,000,000-gallon underground reservoir high up on Powell Butte in outer East Portland has been fascinating for us to chronicle for you.

> See our February 27, 2012 update story, with links to many past stories: CLICK HERE.

When we again visited the project on August 1, it became clear that the “Powell Butte Reservoir Project” is actually made up of many projects – ranging from the grading of the lower and upper parking lots, to the building of new caretaker facilities, interpretive facilities, and other facilities – in addition to actually building the gigantic reservoir.

The brief shutdown of the Portland Water Bureau (PWB) Washington Park Reservoir in late July, due to contamination, underlined the need for this new water storage facility.

PWB Public Information Manager Tim Hall, and PWB Senior Engineering Associate and Assistant Construction Manager Rick Lapp, say that this construction is actually many projects, in one.

“A bacterial contamination event is more likely to happen in an open reservoir than in an enclosed reservoir,” commented PWB Public Information Manager Tim Hall, as he drove us from the base of Powell Butte up to the construction site.

“This project is on schedule to disconnect the Mt Tabor and Washington Park reservoirs,” Hall continued. “The two Powell Butte reservoirs, in combination with a new underground reservoir on Kelly Butte, will provide enough water capacity to disconnect the open reservoirs.”

Here’s a look into one of the two 28-foot-deep Inspection Vaults being constructed at the project. It’s not finished; they’ll pour walls extending up another 20 feet on the top, bringing the height up to what will be ground level when the project has been completed.

To give scale to the size of pipes being used, PWB’s Tim Hall stands in front of these pipes – which are made locally, by the way.

Hall was quick to point out that it’s up to the Portland City Council to decide the fate of the beloved open reservoirs – and he pointed out that both are listed in the National Historic Registry, “so there’s very little that can be done to make changes to them.”

At the worksite, Hall introduced us to PWB Senior Engineering Associate and Assistant Construction Manager Rick Lapp, who said he’s responsible for all the piping on the job.

“You’ve come at a good time,” Lapp said. “We’re coming to the completion of the floor of the facility, and starting to install walls and support columns.”

Under the watchful eye of an on-site inspector, a welder lays down an even bead on the metal connector sleeve of this 78 inch drain line pipe in a Drain Vault.

Here, from a viewpoint on higher ground at Powell Butte, is what will be the eastern “cell”, or tank, of the reservoir now under construction.

Every day, about 60 truck loads of concrete – roughly 600 yards – is brought to the site, and then offloaded into one of two huge concrete pumps, informed Lapp. In addition to the “floor”, a total of 520 columns will be poured to support the concrete top.

While it’s referred to as a reservoir, Lapp explained, “Actually it’s constructed as two separate “cells” – 25,000,000 gallons each. Each cell operates independently, so we can clean out or repair one side or the other, while keeping the system in service.”

Every five years, workers will drain a cell, go inside, inspect it for damage, and wash it down, to clear out the fine silt that accumulates, said Lapp.

“Compare that to our open reservoirs,” Hall added, “that must be closed and cleaned every six months – twice a year.”

Near what will be the top of this cell, workers fasten rebar over a water inlet pipe. What appears to be a silver electrical conduit above the inlet pipe is actually a small pipe that will be connected to pressure-sensing monitors.

When completed, this piping will allow water to flow out the bottom of the cell, much like a swimming pool floor drain.

When concrete covers these rows of rebar, they will form the walls that will divide the new reservoir into two independent cells.

Lapp guided us down from the construction offices, alongside the north edge of the project, while describing features along the way.

The reservoir will be more than just a couple of big tanks, we learned. Through a complex maze of giant pipes, water is controlled by huge valves that direct the flow from Bull Run into the top of each cell, and allow it to flow out through the bottom.

In addition to the water holding cells, each side of the reservoir also has both an Inspection Vault and Drain Vault.

In the background, “wall forms” have been erected in every other space. And, on either side of the poured concrete floor slab, rebar has been set in place – checkerboard fashion – here in the western cell of the reservoir.

“The floor of the reservoir is made up of 209 40′ x 40′ squares, each one better than 2 ½ feet thick. Both the floor and the walls are poured in a checker-board pattern,” Hall said. “Looking at historic construction photos, it’s clear that reservoirs were built using this technique 100 years ago.”

Lapp added, “Doing this, instead of pouring them contiguously, one next to one another, the concrete workers make a precision watertight seal.”

When we looked down into a Drain Vault, workers were welding together segments of a 7- inch drain line. “There’s also a weld inspector in the vault to check it, on-the-spot,” Lapp pointed out. “In addition, each welded pipe section is pressure-tested, and also has magnetic particle inspection (MPI), a non-destructive testing technique.”

Workers tie rebar tubes in half of what will become a concrete column form.

Looking over at rebar frames being wired together for the support columns, Lapp explained that they’re poured at the same time as the slabs. “Instead of placing the column forms on top of the slab, pouring them into the slab helps speed construction. But more importantly, it also provides a seamless, easy-to-clean joint between the floor and the column.”

Concrete streams from the pump truck into the rebar, as a worker holds a thick cable attached to an industrial-strength vibrator that’s poked into the fresh concrete to work out air bubbles.

After the last “square in the checkerboard” has been poured in the western floor, workers smooth and finish the concrete.

Lapp said the project is on schedule. “Even though we’re working with a California-based general contractor, this project is providing about 1,500 local jobs,” he added.

In addition to doing a “slump test” of newly-delivered concrete, these cylinders contain quality samples that are tested after curing to ensure each meets or exceeds specifications.

Coming in Part 2: Park amenities take shape

© 2012 David F. Ashton ~ East Portland News

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