Written by John Boyle, Asheville Watchdog.
The North Fork Reservoir’s capacity for providing treated water to city customers continues to rise, but the water is still not potable and likely won’t be for weeks.
“North Fork’s capacity to push treated and filtered water into the system has risen to 17 million gallons a day,” Asheville Water Resources Department Clay Chandler said at the Buncombe County Helene briefing Wednesday. “That’s extremely significant. And that’s almost double what the capacity was when we first started pushing filtered water into the system last Wednesday.”
As the murkiness continues to improve, the city also has significantly dropped the amount of chlorine it’s using to treat the water.
The 350-acre reservoir, which provides drinking water to 80 percent of Asheville’s 63,000 customers, was hit hard by Tropical Storm Helene on Sept. 27, leaving it with extremely silt-laden water and without its three main distribution lines.
The city restored water service in mid-October, but only with heavily chlorinated lake water that is not potable. Chandler said workers have reduced chlorine levels from 8 parts per million initially to 2.5 this week.
The city has installed a “turbidity curtain” near the intakes to help still the reservoir, and it has conducted two treatment sessions with aluminum sulfate, a coagulant that helps clay particles sink, and caustic soda, which provides the optimum pH for that to work.
“We have ordered additional aluminum sulfate and caustic soda for next week’s treatment,” Chandler said. “We hope to get that underway Monday afternoon.”
Work continues on mobile filtration system
Additionally, Chandler said the city continues to work with the U.S. Army Corps of Engineers to install a mobile filtration system that can handle more turbid water. Turbidity is measured in Nephelometric Turbidity Units (NTU), and ideally the city needs that level to hit 1.5 to 2.0 for optimum filtration with the city’s direct filtration system. On Tuesday, turbidity stood around 18, down from 18.5 Monday morning and a previous high of 30.
The contractor will treat the reservoir near Black Mountain every day next week, “or until the treatment chemicals run out, whichever happens first,” Chandler said. “But we expect that to be a minimum of four days staying at North Fork.”
Previously, the city said it could not filter water until the 1.5-2.0 NTU range was reached, but Chandler said Wednesday that workers have discovered, with the Army Corps of Engineers’ help, that the plant can handle more turbid water.
The system needs to reach 27 million gallons a day in production to fully pressurize the system and provide potable water. The Army Corps set up a small, portable pilot treatment system at North Fork “that has the same kind of filters on it that we have,” Chandler said.
“And we just started testing pushing water through it, seeing how the filters handled it, seeing how long we could run the filters before we had to take them offline and backwash them,” he continued. “And once we got comfortable with the results, and how that small amount translated to a large amount, that’s when we started pushing filtered water through the system. That was a week ago today.”
The city would still be “most comfortable” pushing the full amount of water through the system with turbidity at 1.5-2.0 NTU. In normal times, the reservoir’s water hovers around 1.0, but it was deluged with silt during Helene and the lake essentially turned upside down, Chandler has said previously.
The Army Corps continues to work to install a mobile filtration system at North Fork designed for high-turbidity water. Chandler said previously that it could be ready in late November or early December, and the Corps’ procurement process for that equipment is ongoing.
Chandler also noted that one of the city’s contractors, T&K Utilities, completed installation of new primary transmission main lines from the reservoir, a 24-inch pipe and a 36-inch pipe. The previous transmission lines, along with a 36-inch bypass line, all washed out in the storm.
Chandler said the two main lines do follow “the same general route” as before.
“The bypass location — same thing, same general area,” Chandler said. “But when this process is finished, it will be more heavily armored and buried deeper than it was previously.”
Eventually the city would like to work toward an additional bypass line that would be “geographically separate” from the current main lines and the bypass line, but the area around North Fork is mountainous and geographically challenging, Chandler said.
Once the city can filter the full 27 million gallons of water daily through North Fork, it will take two to three weeks to fully flush, refill and repressurize the system to deliver potable water, the city has said previously.
Asheville Watchdog is a nonprofit news team producing stories that matter to Asheville and Buncombe County. John Boyle has been covering Asheville and surrounding communities since the 20th century. You can reach him at (828) 337-0941, or via email at [email protected]. To show your support for this vital public service go to avlwatchdog.org/support-our-publication/.