Since the discovery of zebra mussels at the South Dakota Big Bend powerhouse intake gates in the summer of 2019, the U.S. Army Corps of Engineers has conducted an internal analysis of the potential alternatives to control the invasive species.
According to the U.S. Fish and Wildlife Service zebra mussels can grow up to 1.9 inches as full adults. The first instance of the invasive species in the United States was 1988 in Lake St. Clair, Michigan. They were believed to be brought in by the larvae in the ballast water the barges discharged. The barges then continued to spread the zebra mussels as they traveled through the channels.
In 2015 the hydroelectric powerhouse at Gavins Point Dam on the Missouri River near Yankton, South Dakota, found established adult zebra mussels at the Lewis & Clark Reservoir cited by the Big Bend Zebra Mussels Mitigation report issued by USACE in May 2020. The report also states that due to the zebra mussels clogging up the powerhouse raw water systems, generator air cooler and thrust bearing oil coolers, the dam must take frequent outages in order to rid the raw water system of the invasive species. These increased outages result in decreased power generating potential.
Two projects within USACE Omaha District’s area of operations are finding alternative ways to combat the rapidly increasing population of zebra mussels. Big Bend Dam is in the planning phases of installing copper ion generators while Fort Randall in South Dakota is in its planning phase for direct injection of copper-based sulfate pentahydrate.
Fort Randall found its first zebra mussels in 2020 and received information from the Gavin Point dam on the severe impact zebra mussels were having there.
Russell Kieffer, operations project manager, Fort Randall Project, said, “If a similar situation occurs at Fort Randall, this will result in additional loss of power production for the Omaha District and increased frequency in maintenance to mechanically clear zebra mussels from attached surfaces inside piping and equipment. Furthermore, if the powerhouse generators are shut down for zebra mussel removal, reservoir releases may occur through the spillway or flood tunnels resulting in additional wear on those structures.”
Due to the discovery of zebra mussels at Gavins Point Dam, an ultraviolet light system was installed in 2019. This system, which did not require a discharge permit was designed to kill larval stage zebra mussels from entering the raw water system and prevent the invasive species from developing and settling in powerhouse pipes and coolers. However, this does not eradicate existing zebra mussels already developed in the system.
“Further investigation is being done to address zebra mussels that have been established in the Gavins Point powerhouse piping and coolers,” Kieffer said. “This includes looking at dosing the system this winter with a copper sulfate solution.”
In the BBZMM report, it was reported that the copper ion generators were developed as a means of preventing zebra mussel biofouling in the raw water systems and have seen success in other power plant, industrial and agricultural facilities.
Scott Wik, operations project manager for the Big Bend Dam said, “One of the big advantages to the copper ion generator is that it will kill [zebra] mussels that are established within the system already. UV systems only treats water that is coming through the UV lights. It won’t take care of any zebra mussels that are established past the location of the UV lights.”
Currently Gavin Point’s UV system is incapable of removing already established colonies of adult zebra mussels in the raw water piping. The BBZMM report also found significant disadvantages to using the UV system at project sites like Big Bend. The initial equipment cost with generating units and additional raw water intakes would run approximately $880,000 and yearly maintenance contracts of $80,000 per year and yearly component replacements such as UV bulbs between $25,000- $30,000.
“Another piece of this that is critical is timing. We found the very first zebra mussels at Big Bend in 2019,” said Wik. “Gavins Point found their first zebra mussels three years before and they are having significant cooling water problems.”
Big Bend has received environmental permitting from the South Dakota Department of Environment and Natural Resources and the South Dakota Department of Agriculture.
“My goal in this whole situation was to have a system operational by zebra mussel season in 2021 which is the very beginning of May. So, we are shooting for mid-April to be operational,” Wik said.
Fort Randall is currently developing their environmental permitting for the use of a copper-based sulfate pentahydrate injection system.