Inside the cooling system of the Fort Randall Dam, about 600 gallons of a copper-based pesticide starts to work on the zebra mussels since last November. Russell Kieffer, projects manager at the dam, said they're using material that harms zebra mussels.
"As the water temperature increases, the zebra mussels become more active. It might make things worse, so we’re just kind of working through those issues now," Kieffer said.
The pesticide is released from four injection sites inside the dam based on the changing waterflow.
“There’s pretty significant dilution that happens when it hits our tailrace," Kieffer said. "It’s almost to the point where our water quality people can’t even, there’s no detection of these chemicals downstream of us.”
Zebra mussels are an invasive, fingernail-sized mollusk. Their name comes from the dark, zig-zagged stripes on each shell. When they invade a reservoir, they can clog power-generating systems and other machinery.
Fort Randall applied for a permit to use the pesticide called EarthTec QZ in the summer of 2021. At the time, the material was not approved, but it's now certified for use by the state. Even with the solution, Kieffer said some zebra mussels still survived when they took apart a generator air cooler.
"When we did take it apart, some of the clusters were still alive so right now we’re doing some trouble shooting on increasing our dose rate on the pesticide and staying within the limit of our permit,” Kieffer said.
He said the mussels were most likely established before they injected EarthTec QZ.
The pesticide costs about $1,000 every month. Other dams like Big Bend and Gavin's Point use different mitigation methods such as a copper-ion generator and ultraviolet light, but they all work relatively the same.
