West Tisbury moves a plan to clean up Mill Pond
After hearing a biologist's report on the deteriorating condition of Mill Pond last week, the West Tisbury selectmen directed the conservation commission to continue working on a plan to clean up the pond.
The selectmen said they were inclined to support comprehensive dredging of the pond next to the West Tisbury police station, even though the cost of the dredging would be high. The selectmen and the conservation commission heard an assessment and management plan prepared by Keith Gazaille, senior biologist of Aquatic Control Technology (ACT) of Sutton at the Wednesday night meeting.
Mr. Gazaille's estimates for the dredging ranged from $400,000 to $600,000 the first year, with additional costs totaling $25,000 to $38,000 for the second and third years of clean-up, plus permitting costs of $2,500 to $3,000.
Shoaling endangers Mill Pond, and dredging may be needed to clean it up. Photo by Ben Scott
The pond is overgrown with vegetation, and it has reduced water depths due to heavy sedimentation, according to the company's survey of the pond.
Selectman Jeffrey "Skipper" Manter said the first step for the conservation commission will be to draft a warrant article for the initial permitting for the pond work that would be presented at town meeting this spring. "We need to appropriate money to see where we're going," he said. Selectman Glenn Hearn also said the town needs to find the best approach in order to get Conservation Preservation Act (CPA) funding.
Mr. Gazaille said the next step in the assessment process would be a dredging feasibility study to see if the work can actually be done. He also will do a watershed assessment at the urging of conservation commission members. They said the report lacked a study of Mill Brook and the adjoining watershed area.
The pond survey findings showed the water depth ranged from less than one foot at the north end to seven feet in the southeast corner. The sediment depth ranged from 2.8 feet to more than four feet in some areas.
Mr. Gazaille also reported that the plant cover, both visible and under water, increased from 50 percent in the north end to 90 percent in the south end of the pond. Water samples showed elevated levels of phosphorous and nitrogen.
Mr. Gazaille presented several possible techniques for cleaning up the pond, including weeding, herbicides, dry dredging and hydraulic raking, in addition to the comprehensive dredging. All the methods except for the comprehensive dredging would be less expensive, but would likely have to be repeated more often, perhaps every two to three years.