PORTSMOUTH – In a move aimed at protecting the city’s largest single water supply, the City Council voted unanimously to move forward with plans to purchase a conservation easement on a 72-acre parcel of land next to the Bellamy Reservoir in Madbury.

Deputy Public Works Director Brian Goetz told the City Council this week that the reservoir accounts for about 60 percent of the city’s water supply.

“Land protection is the most important step to protecting a water supply resource,” Goetz told the council.

The council voted unanimously to authorize City Manager John Bohenko to negotiate a purchase and sale agreement with the Southeast Land Trust, which is working with the city on the transaction.

The council also voted to accept a $200,000 grant from the state of New Hampshire’s Drinking Water and Groundwater Trust Fund to be used toward the purchase price of $390,000.

Lastly it voted to set up a public hearing at its next council meeting on Feb. 5 to authorize Bohenko to use $223,130 from the city’s water enterprise fund for the balance of the purchase price, and the $33,130 fee to the Southeast Land Trust to administer the transaction.

“The subject parcel is ranked as the third most valuable parcel with respect to protection of the Bellamy Reservoir based on an assessment of abutting parcels,” Bohenko said in a memo to the City Council. “ … Development has the potential to greatly affect surface water quality through direct impacts of chemical runoff, septic system leachate, and storm water sediment loading, and indirect affects in terms of higher nutrient loading, which can cause an increased likelihood of harmful algal blooms and impacts to dissolved oxygen concentrations.”

“For these reasons, efforts to protect land that has the greatest potential to impact water quality … is important for the long-term management of the Portsmouth water supply,” Bohenko said.

The land is owned by a retired UNH forestry professor, Goetz said, who will be allowed to continue using about 10 acres to grow Christmas trees.

Goetz noted that city staff intends to keep working to acquire conservation easements around the reservoir in Madbury to “lock them up from development.”

“Seventy-five percent of properties that abut the reservoir are privately owned,” Goetz said, and could potentially be developed.

The conservation easement will forever “protect the land from being developed,” Goetz said.