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Tacoma Water’s $187 million filtration plant almost ready

The journey a glass of Tacoma tap water takes from the Green River watershed to your home is about to take a little longer.

Tacoma’s water comes from the Green River, northeast of Enumclaw. Right now the water supply is unfiltered.

That will change in December, when Tacoma starts filtering some of the water it supplies to 300,000 people in Pierce and south King counties. By 2015, all of the utility’s water will be filtered.

A 2006 Environmental Protection Agency rule requires all surface water utilities, like Tacoma Water, to treat the water for a bacteria called cryptosporidium.

A crypto infection can be serious. In 1993, more than 400,000 people in Milwaukee became sick and at least 69 people died after drinking water infested with the parasite.

Here in Tacoma, the parasite has been found in low amounts three times since testing began after the Milwaukee outbreak. A $187.5 million water filtration plant will remove the parasite from the water supply.

An ultraviolet light system could have removed the threat of crypto for about half the price, but going that route could have eventually backfired. UV doesn’t fix a big problem with Tacoma Water’s supply: sediment. And without that fix, the threat remained that the EPA could require the more expensive disinfection method of filtration in the future.

“UV light is cheaper than filtration to kill crypto,” said Chris McMeen, deputy water superintendent. “It still was a lot of money, and this river gets very dirty.”

RELIABILITY

Even when the river runs clear, the current unfiltered system sends 1,000 pounds of fine sediment through Tacoma Water’s pipes every day, McMeen said. That sediment settles out in low-flow areas and gets stirred up during construction mishaps or when a fire hydrant opens. It then flows through people’s taps.

There are 700 to 800 water quality complaints each year, McMeen said. Most of them are from people reporting that their water looks dirty. But for businesses, the stirred-up sediment can have bigger consequences.

Last year, several restaurants in North Tacoma temporarily closed after maintenance operations caused “flow changes” that disturbed the fine sediment. And Boeing’s Frederickson plant’s finishing line was closed twice in 2005 after heavy sediment in the water clogged the filters the company uses to purify tap water.

When the Green River is even dirtier or turbid than usual, Tacoma Water takes preventive measures by diluting the river water with cleaner water from nearby shallow wells. But that’s not always a sure-fire answer.

In 2006, the utility came “perilously close” to shutting down the Green River intake because the water was “completely muddy,” McMeen said, and the water from shallow wells was almost too dirty to send through the system. The city would have then relied on groundwater wells in town, which would have served “most of the customers,” McMeen said.

The new filtration plant buys reliability, he said.

In 2010, the Tacoma Public Utilities board approved $211 million for the plant, which can process up to 150 million gallons of water per day. Favorable construction bids and suggestions by the winning bidder, Hoffman Construction, drove down costs.

Construction crews broke ground more than two years ago. Crews worked below the water table for a year — no small feat when pouring an average of 50 truckloads of concrete per day.

“This is not a high-rise medical center or a Costco,” said Bryan Shirley, project superintendent with Hoffman Construction. “You’re constructing a giant machine.”

About one-third of the plant’s cost will be paid by project partners: the city of Kent, Lakehaven Utility District and Covington Water District. Those partners buy water to serve residents and businesses. The rest is covered by low-interest bonds and loans.

The plant’s cost is expected to increase water rates by 16.4 percent from 2011 through 2018, said Chris Gleason, TPU spokeswoman.

Tacoma Public Utilities board member David Nelson said the utility got a good price on the massive plant because of lower recession-era construction prices. The filtration plant will not only answer concerns about crypto and sediment in the water, but also ease water managers’ concerns that other contaminants could reach the system’s reservoir above Howard Hanson Dam.

“I think this is going to add a level of security to the water supply,” Nelson said. “If somebody did something to that reservoir, the filtration might grab it out of there before something happens.”

MORE THAN DIRT

Once all of the water supply is filtered through the plant next year, most of the dirt and silt that now enters water distribution pipes will be removed prior to the filtration stage.

At the point the water is removed from the river, Tacoma Water will add chemicals “that help those particles find each other and become bigger particles and settle out in settling tanks,” McMeen said.

Then the sludge will be pushed through a 20-foot-long screw press, separating the dirt from most of the rest of water. McMeen said he expects that process to produce one or two truckloads of soil per week during much of the year.

“During turbid water events, we may be hauling solids multiple times per day,” he said. The soil will be sent to a landfill because of the chemicals it contains.

The water, once free of larger particles of dirt and debris, will filter through 4 feet of anthracite coal and 2 feet of special sand. The filter medium, housed in a 30-foot-tall building about five times the area of a basketball court, strains out the crypto and almost all remaining debris.

The trip through the filter also will remove dissolved iron and manganese that oxidize during the treatment process and can cause discolorations.

“People will say, ‘It’s always been kind of tea-colored,’ ” McMeen said of Tacoma’s water.

As cleaner water enters the water distribution system, the existing sediment will be gradually flushed out. McMeen said it could take a year or two to get rid of most of the sediment.

Another benefit of filtration is fewer suspected carcinogens in the water.

The plant will use about a quarter less chlorine than it does today, which will be added after water filters through the sand and coal. Chlorine can react with certain organic molecules, like decayed fish slime or leaves. That reaction creates what the EPA calls “disinfection byproducts,” which are suspected to cause cancer.

Using less chlorine means fewer of these byproducts, McMeen said.

Perhaps the most important question to Tacoma Water’s customers: How will the water taste and look when filtration is in place?

“The water quality is good to start with,” McMeen said. After filtration, “some will notice. Probably many will not.”

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