SHERMAN — A natural gas power plant under construction across the state border in Dover, N.Y., is worrying environmental activists and residents in border towns.

The Cricket Valley Energy Center’s potential to pollute the air in New Milford, Sherman and Kent alarms residents and activists, who say they had no input during the state approval process that led to the plant’s authorization.

Cricket Valley, which will burn natural gas to generate electricity, was proposed in 2009 and approved in 2012 by the New York Department of Environmental Conservation. Construction began this summer, and the plant is slated to go online in 2020.

The 1,100-megawatt natural gas-powered plant sits on a 193-acre property eight miles from Sherman, 10 miles from New Milford and six miles from Kent.

The plant will emit nitrogen oxides, carbon monoxide and volatile organic compounds, but all emission levels would be below state air quality standards and would have an “insignificant impact on air quality,” according to a 2012 findings statement by the agency.

“The project’s air emissions will comply with all applicable state and federal standards and, for most pollutants, will represent an insignificant impact,” said a draft environmental impact statement on the project. “Development of new, more efficient energy supplies like that represented by the project has the potential to displace the operation of older, less efficient and higher emitting power plants, reducing regional emissions of air pollutants and” greenhouse gases.

But that conclusion did not sway activists in New York and Connecticut, who contend the plant will pollute the area with “tons” of airborne chemicals.

Joel Tyner, a Dutchess County legislator who started a petition to kill the plant, said the plant will emit 279 tons of nitrogen oxide, 191 tons of particulate matter, 118 tons of volatile organic compounds and tons of other pollutants, citing the draft environmental impact statement.

“I understand that Cricket Valley got a bunch of permits, but anything is possible,” Tyner said. “We’re trying to light a fire under (New York Gov. Andrew) Cuomo and (New York Attorney General Eric) Schneiderman to shut down the plant.”

Linda Yannone, of Sherman, said she and more than 600 other people signed Tyner’s petition.

“We’re worried about the air, water and soil quality,” Yannone said. “There is no air quality monitoring and no talk across the border.”

Yannone is angry she learned only last month that the plant was going ahead — after construction already started.

“I had no idea that it was this far along,” she said. “We have to shut it down.”

She said she was aware of the project earlier, but was not given opportunities to comment or kept abreast of its progress.

First Selectman Clay Cope said he “would be happy to host an air quality station for monitoring.”

blytton@hearstmediact.com; 203-731-3411; @bglytton