As North Fork turbidity improves, Asheville also pursues Army Corps of Engineers filtration plan • Asheville Watchdog

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As the murkiness of North Fork Reservoir continues to improve — some residents noticed clearer tap water over the weekend — the City of Asheville is pursuing a filtration plan from the Army Corps of Engineers that could be in place by the end of the month.

“Some good news is Water Resources now has a second option at its disposal for treating the turbid water at North Fork reservoir,” city Water Reources Department spokesperson Clay Chandler said at the Monday Buncombe County Helene briefing. “The U.S. Army Corps of Engineers is in the early stages of implementing an alternative treatment project that could possibly — and I want to stress possibly — be operational in very late November, very early December. That’s based on information the Corps of Engineers has given us.”

The city has installed turbidity-reducing curtains in North Fork, which supplies 80 percent of Asheville’s drinking water, and it has completed two rounds of treatment with aluminum sulfate and caustic soda, which cause coagulation of sediments and reduce sedimentation. That allowed the city to put 10 million to 15 million gallons of treated water a day into Asheville’s system over the weekend, which likely accounted for the clearer water customers say they saw over the weekend, Chandler said.

The Corps of Engineers system will rely on mobile treatment units, which will be staged at North Fork in a clearing above the dam. The exact number of the units, which Chandler described as “generally shaped like a shipping container,” and precise layout are still being determined. He said the city hopes the system is operational by early December.

“We will pursue this option concurrently with the in-reservoir treatment process, and we’re absolutely not giving up on that, not by any means,” Chandler said. “And it’s possible that the in-reservoir treatment process clears up the lake enough for us to start treating water on a very large scale before the Corps of Engineers system is even operational.”

At the briefing, Chandler said the reservoir’s turbidity had dropped to 18.5 by Monday morning, down from 21.2 on Oct. 31. Measured in Nephelometric Turbidity Units (NTUs), turbidity needs to hit about 1.5-2.0 for the city to be able to fully treat the water to make it potable.

Chandler stressed that the Corps of Engineers’ plan is a construction project, so weather, equipment procurement and other variables could cause delays. Planning started Oct. 1.

Despite the variables, Chandler said, “We are very, very hopeful and optimistic that by early December, based on the information that we have right now, that system will be operational.”

The goal is to reach a capacity of 25 million gallons of treatable water a day.

“That’s enough to keep the system pressurized and provide flushing capacity,” Chandler said, referring to clearing the system of non-potable water. “The flushing part of this is going to be very, very important.”

Once the city starts pushing out nothing but potable water into the system, “we’re going to have to completely replace the water in the tanks and our main transmission and all auxiliary transmission lines,” Chandler said.

That process will take a couple of weeks.

“I think the latest timeline we have for that is two and a half to three weeks, so even though we start pushing potable water, that does not mean that the boil water notice will be lifted immediately,” Chandler said. “We will have to again flush the system and perform some extensive back-end testing before we can lift that boil water notice.”

The entire system, which serves 63,000 residential and commercial customers, remains under a boil water notice. The tap water available now is safe for showering and flushing commodes, but bottled water is recommended for consumption.

Chandler stressed that the Corps of Engineers’ installation timeline may change. The federal agency is in the process of procuring materials, equipment and personnel.

“Over the next couple of weeks, equipment, materials and personnel will begin arriving at North Fork for construction and setup,” Chandler said. “Once construction and setup begins, the contract’s terms will require the contractor who’s going to do all this work to work for 24 hours a day until the system is operational. So we’re trying our best to move this process along as quickly as possible.”

A third round of aluminum sulfate/caustic soda treatment is planned. The city will give the second round more time to work, so the third round will likely take place Monday or Tuesday of next week.

“I want to emphasize again, it is important to note that the in-reservoir treatment process could clear up the reservoir before the Corps of Engineers project is operational,” Chandler said. “However, to maximize redundancy, we are going to pursue the Corps of Engineers project regardless. And keeping that system in place until we have the upgraded filters that we’ve been seeking is a possibility that we’re going to pursue.”

FEMA will pay for the Corps of Engineers system, but the cost was not available at the briefing.

North Fork, which opened in 1955, uses a “direct filtration” system designed for extremely pure water, which the reservoir normally delivers, mainly because of its pristine 20,000-acre wooded watershed. The system cannot handle higher turbidity.

The Corps of Engineers systems works with a system of “sedimentation plates” that removes sediment. The lake sediment is mostly very fine clay particles that have stubbornly remained in suspension, and the plates can filter that out.

“To simplify that, it will basically remove not 100 percent but pretty close to 100 percent of the sediment that’s in the water, which is what’s causing it to be turbid right now,” Chandler said.

Chandler said previously that installing a permanent filtration system designed for high turbidity would cost the city more than $100 million. The city does have a “filter upgrade wish list” for North Fork and its other reservoir, Bee Tree in Swannanoa.

“Essentially, if we were to get that project funded, the technology that we would be using at that point is the same technology that the Corps of Engineers will use with their system,” Chandler said. “We would absolutely love to keep this Corps of Engineers system in place until those filter upgrades are made. And if it’s up to us, we will. It’s not completely up to us, though, but we’re going to make that case.”

Asheville City Councilmember Maggie Ullman broke the news about the Corps of Engineers equipment installation and timeline in a Friday Instagram post. Chandler addressed the county briefing the day before but didn’t mention the Corps of Engineers plan.

“It became viable Wednesday night and made its way down to me after the briefing on Thursday,” Chandler said. “We didn’t have a community briefing until today. There was no immediate deadline for any kind of action or anything like that, so we felt comfortable waiting until today to detail it.”

He noted that the timeline was provided by the Corps of Engineers, not the city, which has steadfastly refused to offer a timeline on potential potable water restoration other than to say it is weeks away.

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