The Minnesota Pollution Control Agency (MPCA) has fined American Crystal Sugar Company $135,000 for repeatedly violating its state permits by releasing excess hydrogen sulfide — the gas known for its noxious rotten egg smell — at two sugar beet processing plants along the state's western border.

The company, which faced a similar enforcement action in 2008, agreed to continue efforts to fix the problems at its East Grand Forks and Crookston facilities and to meet yearly with state pollution officials to update them on its progress.

Under a stipulation agreement with the state, Crystal Sugar did not admit wrongdoing, and it denied that any of the alleged violations were intentional. It also said that since 2008 it has invested $61 million at its three Minnesota plants, including one that was not cited. That paid for pond aeration systems, pond covers, wastewater treatment upgrades and other equipment.

However, a state review of the company's air monitoring data showed that it exceeded its hydrogen sulfide limits 280 times between 2013 and 2016. In addition to the smell, hydrogen sulfide can cause burning eyes, coughing and shortness of breath even at low concentrations.

The company said in the enforcement document that the violations represented only one-tenth of 1 percent of the 320,000 air samples it's taken since 2008, meaning that the vast majority of the time it was in compliance.

But MPCA environmental specialist Jenna Ness said the agency has been working with the company for several years. The fine, which is significant, was warranted because "they didn't work on the problems in a way that would fix them," she said.

She acknowledged that solutions at complex facilities like sugar beet processors are difficult. But part of the agreement includes regular discussion on hydrogen sulfide strategies that the company can pursue, a provision that took a year to negotiate, she said.

American Crystal Sugar did not respond to a request for comment for this article.

The company faced MPCA enforcement actions in 2008 for hydrogen sulfide violations that occurred from 2005 to 2007.

Other air permit violations addressed in the stipulation agreement include emissions of fine particle pollution, failure to take corrective action when emission thresholds were exceeded, failure to use fabric filters to control emissions, and problems with reporting and documentation.

Earlier this year, the MPCA completed an enforcement action involving the Moorhead facility for violations that included exceeding permit limits for hydrogen sulfide and fine particle pollution and operating a pulp dryer without controlling emissions with a fabric filter.

That action included an $8,700 fine.

Josephine Marcotty • 612 673 7394