Through the use of chemicals, Marler said she and her staff will be able to control the mussels between the pump station and the treatment plant.
“What we can’t control is the intake structure on the right side of the dam,” Marler said. “There’s a butterfly valve inside the dam, then 200 feet of pipe into the pump house.
“We are going to have to change the outlet valve that’s in the dam and do some stuff to their structures,” she added. “That in itself dictates that we’re going to have to have an engineering firm do the work for us and work closely with the Corps of Engineers because we will be altering the pestilences within their dam structure.”
The cost of the project likely will be shared by the cities of Hillsboro and Marion, Marler said. She did not know if the project would qualify for any federal assistance.
Marler said she is expecting responses within 60 days from engineering firms that have experience with zebra-mussel control.
Asked by Mayor Delores Dalke whether any lake has “won the battle” against zebra mussels, Marler replied, “It depends on what you mean by won the battle. Completely eradicate them? No. But we can win the battle within our own structure.”
She said nuclear power plants and certain dam structures have been successful in that sense. But as far as eradicating them from the lake itself, “No, we will never win the battle with them,” Marler said. “They’re here to stay and we’ll be battling them from here on out.”
Zebra mussels have no natural enemies, Marler said. They can be controlled in limited environments through the use of chemicals and by controlling temperature and levels of dissolved oxygen and phosphorus.
“Our treatment strategy for this problem will end up being two or three of those different methods,” she said.
In addition to encrusting manmade structures in the water, the growth of the zebra mussels population in the lake also will compound the problem of blue-green algae blooms.
“These (mussels) filter the water to a level that allows the blue-green algae blooms to increase in strength and durability,” she said. “They also contribute to the nitrogen and phosphorus levels in the water.”
Another negative consequence will be the growth of the razor-sharp mussel shells along beaches, she added. Footwear will be necessary to protect bare feet.
The council agreed to authorize the invitation for engineering bids with some resignation but no opposition.
“I don’t like it, but I don’t think we have a lot of choice,” Councilor Bob Watson said. “We can’t dink around until they plug up everything.”