PHOTO BY NICK ROHLMAN/THE GAZETTE - Blake Iske takes a sample at the Marshall Ridge Renewable Energy Center in State Center, Iowa on Wednesday, September 18, 2024. The facility’s three anaerobic manure digesters extract methane from dairy cow manure. (Nick Rohlman/The Gazette)

STATE CENTER — Iowa OSHA is investigating a central Iowa biogas digester after a whistleblower alleged that a 2023 fire injured two employees and that the site has ongoing natural gas leaks that endanger workers.

Meanwhile, Marshall Ridge Dairy is seeking a state permit to nearly double its herd from 8,000 dairy cows to 15,000.

Marshall Ridge, a $42 million facility that extracts methane from cow manure and turns it into renewable natural gas, had a fire in September 2023 that burned through the roof of a million-gallon digester tank, released methane and other gases and injured two employees, according to a complaint filed with the U.S. Environmental Protection Agency.

Rodney Richwine, who said he is a project manager with Clean Energy Fuels — a California company that owns the digester along with BP — said in the complaint filed Dec. 5 that Marshall Ridge leaked greenhouse gases for months as the facility struggled to connect with a pipeline to pump renewable natural gas to states with low-carbon fuel standards (LCFS) to earn big-time profits.

“This means that instead of reducing methane produced by this dairy as the LCFS credits the company receives from the state of California would indicate, the site actually took that manure, held it in three, 1-million-gallon digesters, heated and mixed it to produce far more methane,” Richwine wrote. “It then allowed that gas to leak into the atmosphere for seven months.”

Clean Energy Fuels declined to answer questions about Richwine’s allegations, but said the company recently changed operators at Marshall Ridge.

“The owners of the renewable natural gas (RNG) digester at Marshall Ridge Dairy terminated their relationship with the operator earlier in February and have brought in one of the most well respected RNG operators in the country,” CE BP Renew Co said in an email Feb. 17.

“RNG is a fuel that brings tremendous environmental and economic benefits to the end users like the thousands of buses and trucks that cleanly operate on it and helps to mitigate methane emissions at dairy farms. We look forward to the new contractor with their vast experience taking over the operation of the RNG digester at Marshall Ridge.”

Safety issues under investigation

The Sept. 27, 2023, fire that burned through the roof of one of Marshall Ridge’s three digester tanks wasn’t reported to the State Center Fire Department, Fire Chief Brad Pfantz said.

“If it was something where the structure was on fire for a period of time, someone would have called 911,” he said. “I’m guessing the liner on the top of those is vinyl. It’s methane gas from manure that’s inside it. That gas somehow ignited and melted the vinyl roof. Once that burns off, there’s nothing left to burn.”

The same digester tank was without a roof for several weeks last fall as operators repaired a leak, the company said.

Richwine said in his complaint the 2023 fire “destroyed the roof membrane of digester 503 which held thousands of cubic feet of methane and injured two workers.”

Richwine said he was concerned gasses leaking from the Marshall Ridge site were dangerous to employees and visitors. He toured the site May 1, 2024, with stakeholders from Clean Energy, BP and a construction company when he noticed alarms were going off to indicate high levels of natural gas, which is toxic to inhale and can be an explosion risk.

“The operators told us it was a nuisance alarm and that it had been sounding for two months,” Richwine said in the complaint.

Iowa OSHA is investigating Marshall Ridge related to workplace safety.

“In November 2024, DIAL/IOSHA received a direct complaint from the complainant concerning the Marshall Ridge Energy Center,” Spokeswoman Stefanie Bond said in an email. “As the department is currently investigating this facility based on the November 2024 complaint, we are unable to provide further details at this time.”

Richwine’s allegations about the 2023 fire came too late for the agency to investigate.

“In December 2024, DNR (Iowa Department of Natural Resources) shared an incident tracking form with IOSHA regarding a fire that occurred in September 2023,” Bond said. “However, the information received by IOSHA in December 2024 was more than 14 months after the incident, and the statute of limitations had expired.”

How does a digester work?

Marshall Ridge, which started operations in February 2023, takes manure from Kevin and Holly Blood’s 8,000 dairy cattle, adds water and pumps the mix into one of three 1.3-million gallon digesters. The process releases gas, including methane, that is collected from the top of the digesters and filtered to remove water vapor, carbon dioxide and hydrogen to create renewable natural gas.

When The Gazette toured the Marshall Ridge site Sept. 18, Project Manager Mike Raymer said it was producing 250 to 325 Metric Million British Thermal Units (MMBTU) of renewable natural gas per day.

Black Hills Energy injects the compressed gas into the Northern Natural Gas pipeline that runs underground near State Center. Large facilities like these can earn more than $10,000 per day in credits designed to reduce greenhouse gas emissions from industries — including agriculture.

But it hasn’t always been smooth sailing.

“Getting commissioned and getting operations is always that rough,” Raymer said in September. “Everybody wants something yesterday. We were struggling.”

Iowa DNR monitoring air quality

When energy facilities like Marshall Ridge have trouble processing methane or are doing repairs on equipment, they are allowed to flare gas into the air. But Marshall Ridge exceeded its state limit of 2,000 flare hours per year in March 2024, according to DNR records. The site again flared too much in August, records show.

“Sometimes they can’t get it on the pipeline, so they have to burn it off,” said Bill Gross, senior environmental specialist with the DNR’s Region 5 office.

When Gross visited the site last May, he discovered that Marshall Ridge had installed a pressure release vent without getting a permit. After Gross received Richwine’s complaint to the EPA, he talked with an engineer in the Air Quality Bureau, and they decided in January Marshall Ridge needed to get a permit for the vent.

“Because they didn’t report it to us first, that’s kind of a penalty,” he said.

Dairy wants more animals

Iowa has permitted 15 new digester facilities since 2021, when the Legislature passed a law allowing animal feeding operations with digesters to exceed the state’s limit of 8,500 animal units.

Marshall Ridge Dairy, which is permitted to have up to 11,200 animal units (about 8,000 dairy cows), now plans to expand its herd by another 7,000 cows, according to a report the operators made to the Marshall County Board of Supervisors. Operators want to build a new confinement building, free stall, barn and milking parlor, according to a Jan. 16 story in the Times-Republican.

The DNR still is considering this permit application.

The Iowa Driftless Defenders, a group opposing a new on-farm digester in Winneshiek County, said in recent court petitions they are concerned for the safety of rural residents nearby because of potential manure leaks and incidents like fires. There have been several fires at Wisconsin digesters, including one in 2014 in Waunakee and one in 2020 near Kewaunee, according to news reports.