Zebra Mussels On the Move: What Are Water Utilities Doing to Stop Them?

For water utilities, zebra mussels can become more than just a nuisance. Find out how cities across the country are controlling this invasive species and learn more about some of the monitoring programs in place.
Zebra Mussels On the Move: What Are Water Utilities Doing to Stop Them?
Photo courtesy of U.S. Fish and Wildlife Service

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The Fargo, North Dakota, water utility had an unwelcome visitor recently.

A zebra mussel showed up in the intake structure that draws raw water from the Red River.

“We weren’t really surprised,” says Troy Hall, Fargo’s water utility director. “We knew it was coming. We only found one, but there are probably more.”

Hall says the state’s Department of Fish and Game has been monitoring for zebra mussels all along the Red River, which flows north into Canada. “They had found some veligers (larvae) in the south, but when they pulled one of our seven intake screens they found an adult and notified us.”

Fargo joins a growing list of water utilities affected by the invasive zebra mussel. Originally detected in the Great Lakes after they were transported from Europe in the ballast water of ocean-going ships, zebras are spreading.

In Texas, the City of Denton reports the invasive mollusks were discovered in its source water — Lake Ray Roberts — two years ago. According to news reports in the Denton Record-Chronicle, the city has budgeted up to $500,000 to clean and remove zebras from raw water piping, and plans to spend more on mitigating and controlling the invasive species in the lake.

Also in the Lone Star State, the Upper Trinity Regional Water District is investing in improvements to keep zebras from attaching to water infrastructure in Lewisville Lake, according to news reports. Zebra mussels were first detected in Texas in 2009.

Out West, the critters are starting to appear, as well. Zebras have been found in Lake Mead and Lake Havasu, and have recently been found in a reservoir in San Bernardino County, California, and a reservoir near Pueblo, Colorado. These findings, reported by the National Oceanic and Atmospheric Administration, suggest that efforts to control the spread of zebras beyond the Great Lakes watershed have not been entirely effective.

Most states now require boat owners to clean vessels and equipment whenever they pull out of a lake or river, and federal law requires ships to flush their ballasts with seawater — thought to be a natural preventive to fresh water organisms — before they enter the Great Lakes.

It takes a veliger
Some of the solutions to the zebra problem tend to be aimed at deterring or eliminating the mussels at their early, or veliger, stage of development.

One company working on antifouling solutions is AMIAD filtration systems. The company promotes compact mechanical pressure filtration of the veligers. Using 40 micrometer absolute stainless steel wire-mesh screens and continuous flushing with clean water, the company says zebras can be prevented from clogging intake structure and piping without the use of chemicals, scraping devices or forcing high velocity flows of air or water through the pipes.

Another company, Bollyky Associates of Stamford, Connecticut, has researched the use of ozone to wipe out veligers. According to company president and owner L. Joseph Bollyky, laboratory and pilot tests have demonstrated the ability of the company’s patented ozonation process to kill veligers, which can then be filtered out of the water stream.

The company’s literature states that ozone is effective at small dissolved ozone concentrations (0.1 to 0.3 mg/L). It’s an environmentally safe process, which also disinfects pathogenic microorganisms, which will not leave or produce undesirable or harmful chemicals in the water, according to the company.

In Minnesota, officials are experimenting with chemical treatment to eliminate zebras from small lakes. Keegan Lund, invasive species specialist with the Minnesota Department of Natural Resources, says that experiments to chemically treat veligers in small sections of Strawberry and Independence lakes in the Twin Cities area are promising.

“We are treating a 10-acre section (of the lake) very aggressively with potassium chloride,” he says. “We are actively monitoring for veligers and not finding any.”

His team is also diving and snorkeling, looking for adult mussels. “So far, so good,” he reports. “But it’s like a needle in a haystack.”

Lund says the research indicates the mussels tend to locate in one place in the lake, not spreading or reproducing elsewhere. That’s a good thing, he says, because once adult zebras get settled and colonize, there’s no viable treatment. And, he adds, treating a whole lake with chemicals is not environmentally viable or cost-effective.

St. Paul solution
The work in Minnesota is prompting St. Paul Regional Water Services to try chemical treatment in its water intake conduits. The utility draws raw water from a series of small lakes that are fed by the Mississippi River.

Ben Feldman, project engineer, says that every winter St. Paul must shut down each conduit and hand scrape zebra mussels off the pipe walls, and then use vacuum trailers to remove the debris.

“There’s quite a buildup,” he says. “It’s very labor-intensive.”

He says the utility also gets zebra buildup on its intake screens.

The plan is to use a product called EarthTec QZ — a chemical control method approved by both the EPA for open water use and NSF for drinking water — to control zebra development in pipes and screens.

According to the EarthTec website, the product was selected as one of the Top 10 water treatment technologies at the 2014 AWWA conference. It is said to provide 100 percent mortality for adult zebra and quagga mussels.

St. Paul has the proper piping in place and is currently pursuing the permits required to begin testing.

Meanwhile, back in Fargo where Troy Hall’s 11 mgd (average flow) plant provides drinking water to 115,000 people, the utility has hired a design consultant to come up with a plan for countering zebra mussels.

“We expect to have something in place by next spring,” Hall says. “We’ve been thinking about this for some time. We might try coated screens or some type of chemical treatment to keep them from colonizing on the piping. We’ll be examining the regulations and see what is allowed.”


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