Cary and Apex are using a new tactic – a $4.1 million aeration system – to address Jordan Lake’s inconsistent water quality in the wake of the state’s failed SolarBees experiment.
The SolarBees attempted to improve water quality by disrupting algal blooms caused largely by upstream runoff. The Cary Town Council approved an aeration system Thursday that will tackle the separate issue of water taste and odor for a utility system that serves 300,000 Triangle residents.
“One of the differences is we’re not trying to solve all the lake’s problems,” said Robert Hirt, Cary’s utility engineering manager. “The EPA has classified the lake as impaired. We recognize we can’t do anything about the bigger picture, but we’re trying to help our part of it.”
While the towns’ water is safe, it has seasonal fluctuations in taste and odor related to a variety of factors that also make treating the lake water more cumbersome and unpredictable.
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Cary and Apex will use the ResMix system, manufactured by the Australian firm, WEARS. The system will circulate water near the intake, just north of where U.S. 64 crosses Jordan Lake, disrupting water stratification that occurs in the summer. The project was put out to bid in November, although Hirt said a solution to the problem had been discussed on a staff level since the decision was made in 2010 to expand the treatment facility.
Cold, oxygen-deprived water sinks to the bottom of the lake, where it dissolves naturally occurring minerals in the lakebed. The ResMix system will vertically mix the warm, oxygen-rich water near the surface to help keep taste- and odor-causing minerals, such as phosphorous, iron and manganese, from being dissolved into the water nearest the intake, according to a Cary town staff report.
Hirt said this circulation guarantees that the water reaching the treatment plant has a more consistent chemical makeup year-round, allowing the plant to treat it more efficiently. Hirt said this approach would be more cost effective than upgrading the treatment plant.
Cary and Apex also considered deploying their own fleet of two dozen SolarBees, but Hirt said placing them near the intake’s position in open water would have created a dangerous “slalom course” for boaters. Hirt also said SolarBees’ results have been less reliable than those yielded by ResMix aerators.
For almost two years, 36 of the algae-busting SolarBees bobbed on the lake’s surface before they were pulled from the water in August after a Department of Environmental Quality report in May said they weren’t successful in improving water quality. The state spent $1.7 million to maintain the leased SolarBees and is saving $854,000 by ending the lease before the October 2018 end date, a state spokeswoman said in August.
After nixing the SolarBees, the state commissioned studies last year from UNC-Chapel Hill to help evaluate and revise water-quality standards and practices. A study of Jordan Lake’s water quality and management tactics is to be delivered to the state by the end of 2018.
Thursday, Cary’s Town Council approved a $4.12 million contract with Crowder Construction Company to buy and install the aeration equipment.
The bid was $950,000 higher than what Cary and Apex had budgeted, but the Cary council unanimously approved the extra expense. Apex approved its share of the aerator’s cost in its 2015-16 budget.
According to the cost-sharing arrangement between Cary and Apex, Cary will take on $732,000 of the overrun, while Apex will be responsible for the remaining $218,000.
Both towns use the lake as a source of drinking water and treat it at the shared Cary/Apex Water Treatment Facility at 1400 Wimberly Road in Apex. All expenses related to that facility and its upkeep are split between the towns. Apex typically pays 23 percent, while larger Cary pays 77 percent. Morrisville residents also drink water treated at the plant.
Though the contract was unanimously approved in Cary, Councilman Don Frantz expressed some skepticism about the aeration technology.
“SolarBees were supposed to work, too, and we found out they were a joke,” Frantz said. “I just want to know what kind of track record this thing has.”
Hirt said there are few case studies for the ResMix approach in the United States, where the technology is relatively new. The city of Denver has recently installed a pair of aerators, he said, but aeration systems have been used with success in Australia and in the Middle East.
Gargan: 919-460-2604; @hgargan