Neighbors engaged in a pitched battle against a big hog feedlot in Goodhue County say that four other facilities owned by the same company may have routinely violating state air standards over a five-week period this summer.

Using a hand-held air quality monitor, neighbors took turns checking the air just outside six hog facilities owned by Kohlnhofer Farms in southeast Minnesota for a total of 15 hours. During that time, they said they found the air frequently exceeded maximum emissions levels for hydrogen sulfide.

It shows that "there is little or no enforcement of state feedlot air quality rules, and it's up to citizens to determine that there is a problem," said Katie Doody of the Land Stewardship Project, a farm and rural community advocacy group that has joined local residents in opposition to the proposed 4,700-hog facility in Zumbrota Township.

The company said in a statement that its preliminary review of the group's air monitoring results show that they "do not show any violations."

"This study is little more than a thinly veiled attempt to use incomplete and questionable data to create supposed air quality concerns by intentionally misreading applicable health and legal standards," the company said.

The proposed hog farm, Circle K Farms, is one of several large animal feedlots in the state that have generated fierce opposition in their communities. While officials from the livestock industry say that such conflicts are the exception, the growth in the number of increasingly large hog facilities in Minnesota may be driving the controversy.

Hog production in the state nearly doubled between 2006 and 2014, according the Minnesota Department of Agriculture. And the number has continued to grow in recent years as operators in Iowa and other states seek less dense regions to expand and escape the risk of infectious livestock disease.

The largest facilities, like the proposed Circle K, must operate under state permits that regulate manure storage and handling and air emissions. They also require a conditional use permit from the county to ensure they comply with zoning and land use laws.

The Kohlnhofers have complied with all the regulations, county and state officials say. But their project has still generated intense controversy among nearby residents who fear the potential smells, dust and risk of increased water pollution from manure spread on local farm fields.

After Goodhue County commissioners approved the conditional-use permit earlier this year, local residents filed suit, charging that the facility does not comply with the county's ordinance.

Now they are asking the state to step up monitoring of the other facilities to determine if their emissions do violate state standards, and are asking the Kohlnhofers to withdraw their proposal "because their other facilities may be endangering public health," Doody said.

The air monitoring report said that the residents found levels of hydrogen sulfide — a gas produced by manure and known for its rotten egg smell — to be above the state's limit in more than 30 measurements taken during the five-week period at two of the Kohlnhofers' operations. State rules say emissions cannot exceed 30 parts per billion more than 30 minutes twice a week, and cannot exceed 50 parts per billion for 30 minutes more than twice a year.

Even more concerning, Doody said, is that they found the hydrogen sulfide levels exceeded the much lower health risk level of 7 parts per billion in 122 measurements at four sites. The state standard says hydrogen sulfide can be a health risk if the average air concentration exceeds that limit over 13 weeks.

The company said in a statement that it has not received any air quality complaints from government agencies or neighbors in the past year. The owners of Circle K live on two of the sites listed in the report.

Circle K, it said, "will remain committed to managing its farms in a manner that is consistent with all applicable laws and that protects the health and well-being of its neighbors."

Steve Schmidt, a feedlot supervisor for the Minnesota Pollution Control Agency, said the agency monitors air emissions only if someone complains. Then, if there's sufficient reason to suggest there's a problem, the agency will monitor the feedlot. If violations are documented, it will work with the feedlot owner to mitigate the problem.

Schmidt said the agency does not track complaints but typically gets them when a new facility goes into an area that hasn't had one. And most of the time, the complaints stop.

"I don't know if that's a function of people giving up or if people move," he said, or if the operator solves the problem.

He said that the agency would likely review the air monitoring report from the Land Stewardship Project and conduct more comprehensive sampling around the Kohlnhofers' facilities if it is warranted.