‘Big week’ ahead for Asheville' water: Turbidity drops some; curtain installation and upcoming mineral treatment should bump it down more • Asheville Watchdog

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Asheville Water Resources faces “a really big week” in its effort to reduce the murkiness in its North Fork Reservoir, department spokesperson Clay Chandler said Monday.

Chandler said at the daily Buncombe County Helene briefing that a type of in-lake filtration system — three layers of suspended curtains in the reservoir — is being installed “as we speak.” After the curtains are fully installed, a Georgia company will conduct another round of dosing an area of the lake with aluminum sulfate, a compound that coagulates the floating sediment and facilitates it sinking to the bottom, leaving clearer water up top.

The 350-acre lake, which provides drinking water for 80 percent of Asheville’s water system, has remained stubbornly murky with suspended sediment since Tropical Storm Helene deposited and stirred up sediment in the reservoir Sept. 27. All city water customers remain under a boil water notice.

“This is a different company than the first round,” Chandler said. “They have a little bit bigger boat, and hopefully can get to every area that needs to be covered a little more quickly.”

The curtain installation should take 24 to 36 hours, meaning the mineral application could possibly start by late Tuesday afternoon.

“Never having done this before, we’re kind of learning as we go,” Chandler said. “The good news is we did buy the curtains so they’re ours. If we ever need them again, they’ll be on site. So we are learning, just like everybody else is, as this process moves along.”

Turbidity, a measurement of water clarity, is measured in Nephelometric Turbidity Units (NTUs), and the city’s target for being able to treat the water in the reservoir is 1.5 to 2. At that point the city could resume normal filtration and water treatment, returning potable water to customers.

On Sunday afternoon the NTUs level stood at 23.3, down from 26 in about a week.

“So it’s coming down,” Chandler said. “Obviously, it’s not dropping fast enough, and if everything goes well this week with the second round in-reservoir treatment, that process will speed up.”

All city water customers should continue to boil city water and should not consume it. The city is treating the water with chlorine, and it is safe for flushing commodes, showering and other non-potable uses.

The pace of the turbidity clearing up will not be a linear drop at a set rate, Chandler said. Between the mineral treatments and the curtain installation, the reservoir could see a significant drop in a short period of time. But Chandler stressed that workers are learning as they go, as the city has never used a curtain installation.

Regarding the mineral treatment, the “target is to complete treatment by either late Friday, early Saturday.

“And I think during the first round, within 48 or so hours, we had a general idea about how effective it was going to be,” Chandler said. “So using that timeline, Monday, maybe Tuesday of next week, we should have a pretty good idea of how effective it was.”

The first round of treatment, conducted Oct. 16 and 17, was not very effective, partly because high winds stirred up the water closest to the surface. Water did clear more at the reservoir’s deeper level, which was unexpected.

As has been the case since Helene wiped out the city’s two main transmission lines from North Fork and a backup bypass line, Chandler gave no estimate on full potable water restoration, and even declined to offer a timeline on giving a timeline, as one reporter suggested.

“I would love to be able to say that with certainty,” Chandler said. “I wish we could, but that’s just a total unknown right now.”

Chandler said “it’s not completely out of the question that we do a third round, especially if the second round is particularly effective.

“I mean, if it shows it’s going to drop the turbidity, let’s just say eight points in a week, I don’t see how we couldn’t do a third round if it worked that well,” Chandler said.

Last week the city noted that it has increased water testing in multiple locations, and it is testing daily for aluminum, iron and manganese. While these minerals do cause discoloration and cloudiness in the water, they are generally safe in low levels.

The city has extensive information about the outage, water safety and testing on its Helene recovery and response page.

North Fork’s direct filtration system was made for clear water, as that’s what the reservoir’s heavily forested 20,000-acre watershed generally provides. Chandler said the city continues to work with the U.S. Army Corps of Engineers on alternatives for reducing turbidity, but he said installing a filtration system designed for high turbidity would cost in the “nine-digit” territory, or over $100 million.

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