A proposal by Mount Sunapee Resort to expand parking has drawn attention to a half-century old portion of the sewage treatment system that includes three wastewater lagoons next to the access road, near a brook that flows into Lake Sunapee.

“This is a method that was conceived in the 1960s. The three lagoons were put in, in the 1970s. At that time in the state park, there wasn’t even snow-making. Now it’s a year-round resort,” said Katherine Holmes, chairman of the Newbury Conservation Commission. The group is one of several that have raised concerns about the system in recent weeks.

The system, known as a spray irrigation site, is one of seven that are licensed by the state Department of Environmental Services.

At Sunapee Resort, water from septic systems at the various buildings run through pipes into three open lagoons, which store the water until the resort sprays it on nearby fields when weather is appropriate. The lagoons do not perform any treatment, aside from when the wastewater is diluted by rain or runoff. They can be seen as above-ground alternatives to the underground pipes that carry water away from septic tanks in a leach field.

“The solids are collected in tanks. The liquid fraction, instead of going into a leach field, they drain into lagoons,” said Andrew Koff, a hydrogeologist with the state’s Drinking Water & Groundwater Bureau.  “It’s still a viable option and frankly, it can be a beneficial reuse. Rather than irrigating a golf course with water from the public water system, they can use this.”

One of the spray systems licensed by the state is used for irrigation at the Atkinson Country Club, and one to wash gravel at the Brox Industries site in Hooksett. They also exist at Crotched Resort in Francestown, the Rockingham County Complex in Brentwood, and wastewater treatment facilities in Wolfeboro and Grantham.

Mount Sunapee Resort is on state-owned land, mostly in the town of Newbury, and operated by Vail Resorts under a long-term lease. The resort is in the midst of a five-year development plan, notable for the possibility of the long-discussed West Bowl expansion. The development plan includes building a new parking lot near the lagoons and expanding another lot to better deal with crowds.

The state’s Department of Natural and Cultural Resources is accepting comments on the parking lot proposal through June 17 at MountSunapeeComments@dncr.nh.gov

The expansion has drawn concern from several groups because it would require cutting trees and would affect some wetlands. The question of the wastewater system is more recent.

The lagoons are not easily visible from the road and had escaped the town’s attention until officials joined a site visit as part of the parking expansion proposal, Holmes said. “The Conservation Commission would have never known about the lagoons except for the parking lot.”

The lagoons are not lined, Holmes said, leading to concern that material might leak into groundwater. A small earthen dam holds back the water, another area of possible concern. “We think the contents of the lagoon are slowly and constantly seeping out of the toe of the slope of the dam, within 30 feet of Beck Brook,” said John Magee, a member of the commission.

Koff said the state’s major concern with spray irrigation sites involves lack of a backup alternative if the system is overwhelmed, such as during a flood.

“Variable weather can make spray irrigation harder,” Koff said. The Sunapee system has never been reported to have overflowed, he said.

Koff noted that wastewater lagoons like Sunapee’s, which hold water taken off the top of septic tanks, are different from septage of sludge lagoons, which hold all the material of sewage and act like open septic tanks.