Information session about Lake Iroquois herbicide coming up

Lake Iroquois is a beautiful location, but invasive Eurasian milfoil has presented challenges. Photo by David Jennings

When vacuuming and hand-cleaning don’t work, what’s the best way to get rid of a smelly mess? Eurasian milfoil, an invasive aquatic plant, has taken hold in Lake Iroquois, creating problems for lakefront homeowners and visitors alike. The Town of Williston has received a draft permit to use an herbicide in the lake and a public information session is coming up next week.

According to Vermont Department of Environmental Conservation Program Officer Dr. Perry Thomas, the final permit has not yet been issued; the draft permit is an indication that the agency does anticipate the permit being issued, she said, but public feedback also influences the final decision. This feedback includes what will be said at next week’s meeting, as well as comments that have come in through the website and via mail over the last month.

With the use of herbicide in a waterway come public concerns about the safety of drinking and swimming in the water. Such concerns have popped up on Front Porch Forum in recent days.
The fundamental concern, said Vermont Department of Health State Toxicologist Dr. Sarah Vose, is potential exposure. Vose noted that in the case of Sonar, the herbicide proposed for Lake Iroquois, the greatest risk of exposure is to the workers applying the pesticide, per EPA information.

Ann Bove of the Vermont DEC Lakes and Ponds Section noted that the label for fluridone, the active ingredient in Sonar, allows levels of 150 ppb. The Department of Health established the more-cautious action level of 20 parts per billion (ppb), said Vose, based on EPA information from a 2016 human health assessment.

“The 20 ppb is well below what the level of concern would be for drinking water,” said Vose.
DEC Permit Analyst Misha said that the Sonar treatments proposed for Lake Iroquois have a target concentration of five to eight ppb. Bove noted that Eurasian milfoil is highly susceptible to even low levels of the herbicide.

Other concerns include the potential movement of Sonar to downstream locations, including Sunset Lake, also known as Lower Pond. Movement of Sonar depends on multiple factors, said Bove, including amounts of sun and rain, as well as the water’s flow level. Sonar breaks down due to microbes and sunlight, Bove noted.

Water samples are to be taken following application of the herbicide, according to the draft permit submitted by the Town of Williston to the Vermont DEC. Bove noted that sampling locations are identified based on a determination of where Sonar may go once applied. Cetner said it’s unlikely that Sonar applied in Lake Iroquois would travel as far as the LaPlatte River.

On the other hand, Cetner noted that it’s not known in what concentration Sonar might reach Sunset Lake. The plants present in the two water bodies are similar, but breakdown of Sonar means that milfoil likely would not be as affected in Sunset Lake as it is expected to be in Lake Iroquois. Sampling will occur downstream of Lake Iroquois, Cetner added.

“There is no anticipated risk for people eating fish located in waters treated with fluridone,” Cetner noted.

Both liquid and pelletized forms of Sonar are available; the liquid formulation is planned for use in Lake Iroquois, according to the draft permit. The liquid form has been permitted for years, according to DEC Regional Permit Analyst Laura Dlugolecki, while the DOH continues to examine how the pellets have been used elsewhere.

Public information flyers will be posted near the lake, and property owners will be informed of upcoming treatments, per the draft permit. Notification may occur via hand-delivered notices, email, or U.S. mail. In any case, proof of notification is required. Following Sonar application, domestic use of Lake Iroquois water may not occur until fluridone is detected at or below 20ppb, according to the draft permit, and no use of the waterway or its outlet streams is recommended on treatment days.

Furthermore, treated water (from Lake Iroquois and one mile downstream) should not be used for irrigation or watering plants for 30 days. Cetner noted that, as an herbicide, Sonar could potentially affect vegetation besides the Eurasian milfoil it’s targeting in Lake Iroquois, leading to this longer-term use restriction.

The public information session will be held next Thursday, May 4 from 6 to 8pm at Hinesburg Town Hall. A final decision will be issued as quickly as possible after that, Perry said.

Leave a Reply

Shelburne News requires that you use your full name, along with a valid email address. Your email address will not be published, shared, or used for promotional purposes. Please see our guidelines for posting for full details.