Virginia environmental officials are investigating how a colony of zebra mussels found its way into the Millbrook Quarry near Haymarket, and whether they were deliberately brought in by divers.

The nuisance mollusks were discovered in September in the quarry, the only place in Virginia where the shellfish species has been found.

Once established in rivers and lakes, the mussels rapidly multiply and kill off marine life. But they also dramatically increase water clarity and visibility, making the environment better for divers.

In two similar cases in Pennsylvania quarries, divers are suspected of introducing the mussels. The Millbrook Quarry is used extensively for scuba training and practice.

Maj. Mike Bise, an investigator with the Virginia Department of Game and Inland Fisheries, said the role of the divers would be one aspect of the investigation. “We’ll have some conversations with the folks there, and I’m sure we’ll ask questions,” But the first priority, he said, is getting rid of the aggressive species.

A representative of the Fairfax dive shop that manages access to the quarry denied introducing the mussels or knowing of any effort to do so.

John Wall, training director of the Dive Shop, told The Washington Post that he was upset with state officials for implying at meetings that divers were responsible. “They’ve worked with a lot of innuendo,” he said. “They talked like we were responsible.”

The state General Assembly this year approved a bill to outlaw the possession of zebra mussels and other invasive species and would set a civil penalty of up to $25,000.

The dime-size zebra mussels, which were discovered in the Great Lakes in the 1980s, may have been brought from the waters of Russia and Ukraine in the ballast tanks of cargo ships.

Since then, the mussels have spread like a plague through the Great Lakes and major rivers, killing off marine life, clogging drinking water intakes and costing billions of dollars to control. They were discovered in Prince William by a diver who recognized the species and the problem.

“In the Great Lakes, the dive community has benefited from the infestation, which has sharpened the clarity of the water,” said Ann Swanson, executive director of the Chesapeake Bay Commission. “One of the concerns has been that the zebra mussels have been introduced [to new areas] by someone who didn’t know the ecological problems.”

“The farther you get away from known distribution sites, the harder it is to explain that it is accidental,” said Tony Shaw, zebra mussel coordinator for the Pennsylvania Department of Environmental Protection.
Shaw knows of two mussel-infested quarries, one outside Allentown and another in Lebanon County. Both are used extensively by divers.

“It’s almost a similar situation as in Virginia,” he said. At one site, the Willow Springs dive park in Richland, PA, a single rock was found that was covered with mature zebra mussels. “There’s no real good explanation how it got there,” Shaw said. Like the Prince William location, the Richland quarry featured sunken boats and vehicles as underwater diving attractions.

Dive Shop spokesman Wall said there could be other explanations for the infestation. He said juvenile zebra mussels can be transported by waterfowl or in excess water in equipment used by divers. Juvenile zebra mussels can be as small as a grain of sand.

For months, investigators have been denied access to the quarry in a dispute over legal liability, but an agreement was worked out with the owners in March. State biologists were hoping to begin work at the quarry by mid-April.

The first steps are creating a detailed map and depth chart of the quarry and gathering samples. An accurate estimate of water volume is necessary to figure out how much poison would be needed to kill the mussels, if a chemical approach is approved, said Ray Fernald, an official with the Virginia Department of Game and Inland Fisheries.

Another possibility under discussion is draining the quarry. “That would reduce the amount of water that would have to be treated chemically and kill the exposed mussels,” Fernald said.

Further investigation also is needed to see to what extent the quarry is connected to nearby Broad Run, a tributary of Lake Manassas and the Occoquan Reservoir, which together provide drinking water for 600,000 people.