BOARDMAN, Ore. — A proposal to turn cow manure into natural gas at Oregon’s largest dairy is moving forward after state regulators approved a key permit for the project.

Threemile Canyon Farms, near Boardman, Ore., already operates the largest manure digester in the western U.S., capturing methane from the dairy’s 65,000 cows and using the biogas to generate 4.8 megawatts of electricity.

Now the dairy wants to expand its digester facility and install new equipment to convert the methane into “pipeline quality” natural gas, a process that entails removing carbon dioxide and other impurities from the gas stream so it can be injected into a pipeline and transported to consumers.

The Oregon Department of Environmental Quality approved a modified air quality permit for Threemile Canyon on June 25, despite objections from environmental groups that claim pollution from the dairy and manure digester pose a public health and safety risk.

A coalition of groups opposed the permit, including Columbia Riverkeeper, Friends of Family Farmers, Friends of the Columbia Gorge, Humane Voters Oregon, Food & Water Watch, the Center for Food Safety, Center for Biological Diversity, Animal Legal Defense Fund, Farm Forward and Factory Farm Awareness Coalition.

In its comments to DEQ, the coalition argued that Threemile Canyon is a significant source of air pollution.

DEQ maintains the permit only regulates digester gas emissions. Emissions limits will not change under the modified permit, allowing for up to 74,000 tons of greenhouse gases per year, which is equivalent to 57,608 passenger cars.

Threemile Canyon has not come close to exceeding that limit, emitting just 32,529 tons of greenhouse gases in 2017.

Tarah Heinzen, staff attorney for Food & Water Watch, said DEQ is “shirking its responsibility to regulate Threemile’s overall air pollution emissions.”

Anne Struthers, spokeswoman for Threemile Canyon Farms, said the project should be finished by later this year. She said natural gas that will be produced at the dairy is “100% contracted,” though buyers are confidential.

Marty Myers, general manager of Threemile Canyon, previously said the farm plans to sell the gas to make fuel for vehicles.

The dairy is working with Equilibrium Capital, a Portland investment firm, on funding for the $30 million digester expansion. Struthers said they have not received any state financing.

According to the American Biogas Council, Oregon has seven biogas production systems on farms, handling 8 million gallons of manure per day. Washington has eight systems on farms handling 7.2 million gallons per day.

Patrick Serfass, executive director of the organization, said there are 2,200 biogas systems spread across all 50 states, including farm, wastewater and food waste digesters. He said there is enough raw organic material to build another 14,000 projects, including 8,000 manure digesters on farms.

“That’s a pretty conservative number,” Serfass said. “We’re looking at just the biggest (producers) or organic material.”

Serfass said these systems not only produce renewable energy, but are actually a net positive on the environment because they reduce methane emissions, kill pathogens, reduce odor and create a safe soil amendment to spread on cropland.

“We can make a farm of any size be more environmentally friendly, responsible and make great products that will protect our air, water and soil,” he said.