PORT ANGELES — When it’s preparing to do its job, the nearly eight-story-high, 14-foot-wide column built in the center of the city’s 5 million-gallon storage tank on Rayonier’s former mill property feels like a rocket about to take off.

Looking down from the top of the concrete structure during a recent test, it sort of looks like one, too.

The column, construction on which wrapped up in December, and the metal gangway leading to it shudder as the structure prepares to release roughly 20 vertical feet of water stored within.

The shaking then stops, and the only noise that can be heard is the water flowing across the bottom of the tank into a moat built around the inside of the tank’s base.

CSO project

From there, it’s taken to the city’s nearby water treatment plant in a process that will eventually play a key role in the city’s $42 million combined sewer overflow, or CSO, project.

“The CSO tank has been successfully tested,” City Engineer Mike Puntenney said.

“The tank works as it was designed to.”

Testing of the tank’s flush column has been underway since the beginning of this month, city project manager James Burke said, and is expected to be wrapped up in the coming week as part of the $16.7 million first phase of the CSO project.

The city expects crews from Ferndale-based IMCO General Construction to be completely off-site by the end of February, Puntenney said.

IMCO has been working since September 2012 on the project, which also snaked new underground stormwater and wastewater lines across the Rayonier Inc. property to downtown Port Angeles.

Tank’s operation

The city anticipates the tank can be operational after permitting for phase one is finished, estimated at between three to six months, Puntenney said.

The tank will not be able to take stormwater and sewage from the downtown area until a new pump station, part of phase two of the CSO project, is built at the west end of Front Street, Puntenney explained.

The city has an application in for a roughly $11 million low-interest state loan for phase two, Puntenney said, which the city expects to hear about in the coming months.

The goal of the CSO project, slated to be completed by 2016, is to increase sewage and stormwater capacity between downtown and the wastewater treatment plant to reduce the number of CSO events that historically have sent untreated sewage into Port Angeles Harbor during heavy storms.

During these times, the tank will take sewage and stormwater from the city’s downtown area and hold it until it can be treated at the nearby treatment plant and released into the harbor, Burke explained.

Flow into tank

Depending on the amount of rainfall, water would flow into the tank at between 5,000 and 20,000 gallons per minute, said Keith Parker, the on-site CSO project manager with Vanir Construction Management Inc.

At the highest flow, that’s enough water to fill Port Angeles’ 200,000-gallon William Shore Memorial Pool once every 10 minutes.

The water in the flush column is released to clear sediment and other residue from the floor of the tank after it has stored sewage and stormwater, Burke said.

The water used to test the flush column has already been treated, Burke said, though the column will use the same water the tank will store to clear the tank’s bottom when officially brought online.

The flushing is triggered automatically after the tank empties, Burke added.

Water cannons

The tower also is equipped with four water cannons city crews will use to spray down the sides of the tank as needed after the tank is drained following a heavy storm.

“Most of our CSO events take place in the wintertime,” Burke said. “The chance of odor is unlikely.”

Parker estimated that water would not be held in the tank for more than a couple of days at the most.

The state Department of Ecology has given the city until 2016 to complete the CSO project or face fines of up to $10,000 for each additional combined sewer overflow that happens after the deadline.

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Reporter Jeremy Schwartz can be reached at 360-452-2345, ext. 5074, or at jschwartz@peninsuladailynews.com.