The Heartland Biogas Project operates southeast of LaSalle, Colo. The plant converts cow manure and food scraps into natural gas. A yellow sign posted by the county indicates an upcoming meeting with commissioners. Neighbors of the plant have lodged hundreds of complaints about the smell.

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The Heartland Biogas Project looks different from anything else you’d see in rural Weld County. The six white domed digesters stand out among oil and gas wells, farms and fields.

“It’s unique. It’s sustainable. It’s solving an organic waste problem,” said plant manager Jason Thomas. “There are a lot of really good things about this facility.”

Ask any of the residents in the surrounding prairie and they’ll tell you there’s something rotten about the green energy plant: the smell. Which is really saying something, given that Weld’s history is built on agriculture. Herds of livestock, feedlots and dairies dot the landscape.

“I’m not offended by odor easily. They can say what they want, they can say that they can prove that it’s getting better,” said neighbor Rena Arens. “I don’t see it.”

Arens has called for the plant to be shut down until the odor issue is resolved. She isn’t alone, more than 600 odor complaints have been lodged — the largest such case in recent memory, county officials said — and yet Weld has recorded only one violation, from April 2016. The public complaints and the one odor violation prompted state officials to step in. In November, the state and Heartland Biogas finalized a 10-page Compliance Order on Consent. The document outlines a number of changes Heartland Biogas has agreed to make, including an odor capture and control system for the plant’s digester processing system.

Fed up with the slow governmental process, neighbors started pouring through the county code to identify additional potential violations they believe the plant may have committed. Weld County Commissioners will wade through those violations during a Dec. 19 meeting.

Rena Arens is one of several rural residents who live near the Heartland Biogas Project. She said the occasional smells can be overpowering.

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The public dispute has been a long, winding detour for Heartland Biogas. When the plant launched the message was about green technology and innovation.

The Heartland Biogas Project is one of the country’s largest biogas production facilities; it transforms cow manure and food scraps into natural gas. Biogas is billed as one of the few consistent green energy sources, unlike solar or wind.

Standing next to a maze of pipes, manager Thomas said the plant’s “goal is to control odors as much as possible.” The tangle of pipes leads to large metal box that collects the biogas. This is the final step before natural gas from this plant, operated by EDF Renewable Energy, is injected into a pipeline. Sacramento Municipal Utility has an agreement to purchase the gas.

The part of the plant that you’d think would smell, didn’t on my visit. Next to the six white digesters say open pits of manure and boiling food scraps.

“What small amount of odor does come off the pit is controlled with an odor control we’ve got in place,” Thomas said.

Open pits of manure and boiling food scraps are waiting to be fed into the digester. After neighbors’ complaints, Heartland started misting the pits and the digester processing system with a chemical to reduce the smell.

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The digester processing system is also misted with the chemical. EDF expanded a fabric canopy over the DPS so food scraps are unloaded inside instead of outside. The company changed ventilation of its digesters to filter the air. And yet there are still strong putrid smells in parts of the plant. I asked Thomas if the plant will ever be completely void of odor.

“We anticipate there will always be odors that come from a facility such as this,” he said. “We will continue to pursue improvement in the odor generation in light of being a good corporate neighbor.”

American Biogas Council executive director Patrick Serfass said more than 2,000 biogas plants operate across the United States.

“For a well-operating system, outside of the plant gates you should be able to smell virtually nothing,” he said.

Biogas plants can use different materials. Manure and human solids are most common, but recently, Serfass explained, there are different biogas plant configurations. For years cities built biogas facilities at wastewater treatment plants. They had to do something with human solids. In recent years, newer biogas plants like Heartland have started taking in food scraps. Something that’s not always a consistent fuel source, which may prompt an operator to ask “OK, how am I going to tweak my system to make sure I keep everything operating really well,” Sefrass said.

County and state laws say that industrial facilities can smell. But when smells drift over to neighbor’s properties, that’s when companies can run afoul of the law – or Rena Arens. The promise of green energy doesn’t erase the regular reality of bad smells she said she experiences.

“It’s like scorched manure… why not throw in a dead animal on top of that, and scorch it and cook it and burn it a little?” she said. “That’s what it smells like.”

Arens is used to the smell of rural life. She and her husband manage a herd of beef cows. Their neighbors are feedlots and dairies. She said what is unpleasant are occasional odors from biogas plant. She also claimed she’s gotten headaches from the smell. Another neighbor who lives closer to the plant, Nancy Flippin, said the smell has interrupted her daily life.

“There are some days it’s so bad you just want to get in the car and drive away,” Flippin said. “The one good thing is that it seems to go in bands. [The smell] will be real bad on one side of the house, but not on the other,” she said.

Nancy Flippin can see Heartland Biogas from her back yard and said the smell sometimes comes in “bands” onto her property. “There are some days it’s so bad you just want to get in the car and drive away.”

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Sitting in her kitchen, Flippin pours over documents and emails related to the smell at the plant. At the commissioner hearing, she and her neighbors plan to explore other issues they said were related to the plant. The county’s show cause hearing notice lists 11 issues, many of which have little to do with the smell. The potential issues range from alleged plant design deficiencies to blowing trash to an invalid Certificate of Designation.

Biogas plant manager Jason Thomas has plans to address the new issues at the hearing, including the potentially invalid Certificate of Designation. He said the plant was sold in 2013, and the name of the owner changed. The CD was not updated to reflect the new owner.

“It’s a matter of interpretation,” he said. “We’re going to go in and we’re going to say a lot of what we have before. We’d like to be a good corporate neighbor, we are aggressive attacking the odor sources at the facility, and will continue to do so.”

The Dec. 19 meeting is expected to be long and contentious. Ultimately it’s up to Weld Commissioners to decide whether to continue on the current path or take more drastic steps.