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Metal floodwall set to protect treatment plant

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A grand ceremony to mark the construction of a steel wall to protect a wastewater treatment plant from flooding isn’t the sexiest governmental ribbon cutting, but it is a needed wall.

Tacoma’s Central Treatment Plant will soon be surrounded by a steel wall to protect the wastewater facility from flooding whenever the Puyallup River floods the tideflats as it did twice in the last 20 years, most recently in 2009.

The $9 million wall was funded with $6 million from the Pierce County Flood Control District’s tax of 10 cents per $1,000 in property value and $2.7 million from the City of Tacoma’s utility fees fund. That’s a lot of money for a wall few people will ever see, but a flood without the wall would threaten a $1 billion facility and potentially cause environmental damage.

“This was a very important project for us,” Tacoma Mayor Marilyn Strickland said, noting that a large flood that shut down the facility could force wastewater from Tacoma, Fife and surrounding areas to flow untreated into Commencement Bay. “It would be devastating for the entire region.”

During large storms the plant treats more than 135 million gallons of wastewater a day before discharging the treated water into Commencement Bay. The plant treats sewage from Tacoma Fife, Ruston, Fircrest and unincorporated Pierce County. The plant’s location on the tideflats makes sense because of its central location and its proximity to Commencement Bay, but the being just yards from the Puyallup River and Commencement Bay is a liability when flood rains come because the river could crest its banks and send water into the facility. An overflow could send untreated sewage into Puget Sound with potentially negative impacts to water-based businesses, recreation consequences for residents and impacts to wildlife. It’s that threat that placed it high on the flood control district’s list of priorities even if the wall itself won’t be much to look at when its completed.

The 2,500-foot-long wall will only be between one and eight feet high, but will be driven some 25 feet into the ground to prevent water from seeping below it. Three automatic lift gates will be the first constructed in the state and help control floodwater during heavy rains.

The wall is the second project funded through the flood control district, right behind levee improvements in Orting. The district’s 2014 budget includes $10.2 million for capital projects mostly involving flood control project related to the Puyallup River.