For the past five years, the U.S. Army Corps of Engineers Omaha District's Gavins Point project has been under attack! An invasion of an underwater invasive species known as zebra mussels has been slowly infiltrating the Gavins Point power plant.

"Back in 2014 there was an introduction of zebra mussels to the area; there was one single zebra mussel found on a dock at the boat ramp on the north end of the dam," said Michael Schnetzer, Gavins Point powerhouse senior mechanic, USACE-Omaha. "The following year out in our spillway we discovered a couple of small zebra mussels. The summer after that we started finding them inside the plant."

Native to Eastern Europe and Western Russia, it is believed zebra mussels were first brought to the United States during the 1980s. If left unchecked, they could cause extensive damage to the environment and manmade structures as well.

To help combat the invasive species, in February, Gavins Point installed a $1.045 million ultraviolet light filtration system.

Zebra mussels can:
• clog irrigation intakes and other pipes,
• attach to boat motors and boat hulls, reducing performance and efficiency,
• attach to rocks, swim rafts and ladders where swimmers can cut their feet on the mussel shells,
• attach to and smother native mussels, and
• eat tiny food particles that they filter out of the water, which can reduce available food for larval fish and other animals, and cause more aquatic vegetation to grow as a result of increased water clarity.

"A zebra mussel is an invasive species. It's a small mussel that when it gets to adult stage, as it's going through its stages it will attach to just about anything - boat docks, boats, intake pipes or water lines, concrete that might be in the water, just about anything it can find," said Gary Ledbetter, Chief of Natural Resources, USACE-Omaha Gavins Point project.

Before the introduction of zebra mussels into the system, Schnetzer said the power plant would shut down one of the plants three generators every six months for general cleaning. As the mussel infestation grew, those cleanings changed to every two weeks; thus reducing the amount of power the plant was able to produce.

"They'll attach to (the inside of) piping. If it's really small piping they'll completely block it up, stop the flow through it," Schnetzer explained. "They reduce the amount of flow through the system, they can completely block the heat exchangers or reduce the flows, which of course starts to make our unit temperatures creep up, forcing us to shut a generator down to clean it out.

"With the irrigation system it's the same thing. It can start to reduce the flow through the irrigation system. When the mussels slough off, or if they die, they'll layer up on top of each other. If you get enough resistance from all the shells, it can break a chunk off sending it down the line and either clog up our sprinkler heads that will also clog up the heat exchangers on the generators, or the generators for the HVAC system for the plant," he added.

With the new UV system, water comes in through the intake structure, passes through the strainer, and then passes through the UV lights. The UV light sends out a concentration of light that is strong enough to break down the protein chains in the cells of the villagers, which in turn kills the villager mussels, preventing them from passing through the system, attaching to and plugging up the piping in the heat exchangers throughout the plant.

"Villagers are the baby zebra mussels, the very microscopic organisms going through the water," said Lacey Gould, Gavins Point electronics mechanic, USACE-Omaha District. "They have about a three-week life cycle before they attach to a wall, a bearing, a valve or anything in the water. Those are the little tiny ones that we are trying to kill off before they attach to the system."

The UV light the mussels are exposed to through the system is highly more intense that the UV light that emits from the sun.

"You need safety if you're going to look into the unit or have the unit on with the lights on you have to have UV protection - eye protection, skin protection, because it will harm you, Gould warned. "That is how intense it is!"

It will take longer to rid the system of the adult mussels. Rather than kill them off, the UV light sterilizes them, preventing them from reproducing for the rest of their three-year life span.

In addition to the threat the mussels pose to the power plant, Ledbetter said the species also threatens the natural environment of the Missouri River, or any aquatic habitat it invades.

"They could clean the water through their life stage, eating those microscopic organisms and interrupting the natural progression of food that other marine life depends on," he explained.

The UV system has a 99 percent effective rate in controlling and killing off the zebra mussel population. However, the main source of zebra mussel contamination is through boaters transferring them from one water source to another.

Boaters can help curtail the spread of zebra mussels by:
• Thoroughly inspecting boats and trailers, removing any aquatic weeds and scrape off and throw away any suspected mussels.
• Drain all water from boats and equipment before leaving the recreational area.
• Do not reuse any live bait that has contacted infested water.
• Thoroughly rinse and dry boats, motors and trailers.