Environmental groups are asking Oregon regulators to deny the air pollution permit for a project that would turn cow manure into renewable natural gas.

Oregon’s largest dairy operation is already collecting the manure from more than 30,000 cows and turning it into biogas in a digester.

Right now, Threemile Canyon Farms in Boardman is using that gas to generate electricity. The company has applied for a permit to produce renewable natural gas instead. That way, it can go into a natural gas pipeline while reducing greenhouse gas emissions from normal dairy operations.

Tarah Heinzen with Food & Water Watch said she doesn’t see that gas being clean or renewable.

“This is a production method that is reliant on producing vast amounts of manure and housing huge numbers of animals in intensive confinement,” she said. “It’s an inherently dirty energy source.”

Her group and others are asking the Oregon Department of Environmental Quality to include the air pollution from the rest of the mega-dairy operations in the permit for the new facility – or deny the permit altogether.

Threemile Canyon Farms spokeswoman Anne Struthers said her company would invest $30 million in the conversion, which would remain under the state limits for air pollution.

She said current laws would give the state no basis for regulating dairy operations outside the company’s renewable natural gas and electrical power plant operations.

DEQ spokeswoman Laura Gleim said the state hasn’t required air pollution permits for dairy farm operations in the past but has not made a decision yet on the permit for the proposed facility.

Heinzen said the project will generate revenue for the dairy farm that will incentivize expansion of the operation in the future, and that could increase unregulated air pollution over time.

“The vast majority of the emissions from this operation are not captured or addressed in any way by this digester, and they’re not regulated and will not be regulated by the permit as proposed,” she said.

Struthers said her company has no plans to expand its herd size and estimates the conversion to a renewable natural gas facility will reduce an additional 20,000 tons of carbon emissions from its dairy operations.

“It is a clean, renewable energy source which contributes to our closed-loop system and sustainable farming strategy,” she said in a written response.

The existing biogas digester and the proposed renewable natural gas facility are both eligible for carbon offset credits under programs such as California’s cap and trade system because they reduce methane emissions from dairy operations.