While the City of Asheville has restored potable water to its 63,000 customers, it’s still struggling with high turbidity at its main reservoir, North Fork.
Filtering that cloudy water remains a challenge, but major assistance is on the way this week in the form of a $39 million six-month project spearheaded by the Army Corps of Engineers to install a mobile filtration system at the reservoir. The city and the Corps planned to start testing the system this week, and Asheville Water Resources spokesperson Clay Chandler said it should be operational by Friday.
Chandler addressed the plan at the Monday Tropical Storm Helene briefing and then answered followup questions via email. Plans call for the system, which will be run by a contractor, to run continuously at North Fork Reservoir, which is located outside of Black Mountain and provides water to 80% of the city’s residents.
“Its production will start small, around 5 million gallons per day, and ramp up from there,” Chandler said. “Eventually, the Corps of Engineers system will do most of the heavy lifting, with North Fork’s existing processes providing support, to produce the average daily demand of 20-25 million gallons of water.”
The city restored untreated water to most customers in mid-October and potable water Nov. 18. But turbidity remains a concern.
“While North Fork has been able to meet system demand on its own for several weeks, we’re still one snowstorm or other especially windy weather event from the turbidity becoming unmanageable for our existing treatment processes,” Chandler said. “The Corps of Engineers system will provide a critical layer of security that will keep our customers in water should that happen.”
Chandler said the Federal Emergency Management Agency will cover the cost of the project.
Army Corps of Engineers spokesperson Patrick Moes said the North Fork Reservoir Turbidity Reduction Project contract was awarded to Ahtna/CDM Smith on Nov. 8.
“With respect to the design of the project, we provided the holistic performance requirements such as a gallons per day requirement (25 million), pumping requirements, etc., and the contractor executed the plan,” Moes said via email.
“The $39.2 million contract is for six months, with options to extend the work beyond the initial performance effort. The extension options include two additional six-month intervals, but we have not had those discussions at this point.”
Ahtna and CDM Smith have worked together on other projects. Ahtna’s website states the corporation is “one of 13 Alaska Native Regional Corporations established by Congress under terms of the Alaska Native Claims Settlement Act of 1971.
“Based in Glennallen, Alaska, Ahtna, Inc. is owned by more than 2,000 shareholders, the majority of whom are of Ahtna Athabascan descent,” the site continues. “Many Ahtna shareholders still reside in the Ahtna region, the traditional homeland of the Ahtna people.”
Ahtna’s subsidiaries provide a range of services across many industries, construction and government contracting, according to the website. It works in all 50 states.
CDM Smith is a privately owned engineering and construction company that offers service in “water, environment, transportation, energy and facilities,” according to its website. Its world headquarters is in Boston.
After Helene caused extreme flooding and heavy runoff into North Fork, on Sept. 27, essentially turning the 350-acre lake upside down, the measurement of turbidity, Nephelometric Turbidity Units (NTUs), stood at 79. The raw water coming into North Fork, which is surrounded by a largely undeveloped 20,000-acre watershed, usually has a measurement around 1. By Monday it had dropped to 12.7.
The city has taken several measures to reduce turbidity, including three rounds of in-lake chemical treatments to help sediment coagulate and sink, and the installation of “turbidity curtains” designed to help still the water and foster coagulation of clay particles.
With the Army Corps’ help in constructing a pilot plant at North Fork to see what level of turbidity the reservoir’s direct filtration system can handle, the city discovered it was able to filter and treat higher turbidity water than previously thought. Initially, the city said turbidity would have to drop to the 1.5-2.0 level before treatment began, but it realized via the pilot plant that it could treat water with NTU levels in the teens.
The three in-reservoir treatment applications at North Fork involved dispersing aluminum sulfate, a coagulant, and caustic soda, which regulates the water’s pH levels to ensure optimum coagulation and sinking of clay particles. The turbidity improved, but it has been slow going: It remained in the 20s through October before dropping into the teens in November.
The water coming to customers’ taps is potable now and has a very low turbidity level, about .1, the city said previously. That’s well under EPA requirements.
‘Seasonal flip” may help turbidity
On Monday, Chandler noted another phenomenon that could help with turbidity: “the seasonal flip.”
“So, when the water gets really cold, like it’s about to get because it’s really cold outside, it does exactly like the term ‘flip’ sounds. It takes everything that’s on or near the bottom and puts it near the top, and takes everything that’s at or near the top and puts it on the bottom,” Chandler said.
The city is fairly certain that a seasonal flip occurred at the Bee Tree Reservoir in the past few days.
“We believe that the reservoir at North Fork is going to do its seasonal flip sometime this week,” Chandler said Monday. “Bee Tree Reservoir did its seasonal flip, we are reasonably certain, last week, which drastically lowered the turbidity there — finally got it under 100 in the lower depths of the Bee Tree reservoir.”
It had stood near 500.
Bee Tree, located in Swannanoa, is much smaller than North Fork, but the seasonal flip results are encouraging for North Fork, Chandler said, because if the larger reservoir sees a similar shift, it could significantly lower turbidity.
The city announced it was awarding the contract to the Army Corps on Nov. 8. Chandler said the Corps is delivering the filtration system on time, “exactly fitting the timeline that they originally gave us.”
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 jboyle@avlwatchdog.org. The Watchdog’s local reporting during this crisis is made possible by donations from the community. To show your support for this vital public service go to avlwatchdog.org/support-our-publication/.
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