Trying to determine the potential for odor from a feedlot is similar to trying to predict the weather - there are many different factors that go into who will smell what and where it can be smelled, said Mae Petrehn, feedlot program coordinator at Douglas County Land and Resource Management.
There also is a lot of science and regulations regarding the odor impact of a feedlot, such as the proposed expansion of beef cattle operation near Millerville.
Joe Wagner's farm currently houses about 680 animal units (AU). The plan is to expand to 6,800 AUs, which is about 8,000 head of cattle.
Odor was of the biggest concerns with the proposed expanded feedlot at a recent open house hosted by Wagner on the project.
Through a process called air modeling, an analysis is done to determine the estimated amount of hydrogen sulfide concentrations, ammonia concentrations and odor intensities at the expanded feedlot's property lines, as well as 29 of the expanded feedlot's nearest neighbors.
The details about air/odor emissions is part of the mandatory Environmental Assessment Worksheet (EAW), Petrehn said. The EAW is mandatory for the construction of any new feedlot that has a capacity of 1,000 or more AUs or any expansion of an existing feedlot, such as the Wagner expansion, by 1,000 or more AUs.
The air quality modeling, according to the EAW, also considers the gaseous emissions from eight feedlots within a 9-square-mile grid surrounding the project site.
"The process takes several months to complete, and there is a lot of science that goes into it," said Petrehn.
Some of the factors weighed in air modeling include size of the facility, air temperature, the amount of rainfall, how many head of cattle, what type of cattle and type of manure - solid or liquid. The analysis performed used the AERMOD (a specific software) air dispersion model for a five-year period using historical weather data, as well.
Although the state does not regulate odor, Petrehn said, the gasses produced from the odor is monitored by the Minnesota Department of Health. The process is based on a protocol that is approved by the Minnesota Pollution Control Agency (MPCA). The state then regulates the amount of gasses produced, as in the hydrogen sulfides and ammonia, which Petrehn called the "trademark smells" of a farm.
"It's pretty recognizable," she said.
Odor is measured by odor units (OU) and can be described anywhere from faint, which is about 83 OUs, to moderate, which is roughly 244 OUs.
According to the EAW, the air modeling estimated the ground-level odor intensities at the expanded feedlot property line and at the adjacent neighbors.
The maximum hourly odor intensity at the feedlot's property line is 180 OUs, which is above the faint odor threshold but is below the moderate odor threshold. The EAW also indicated that the maximum frequency at which the odor intensity exceeded the faint odor threshold is about 0.20 (less than 1) percent of the time.
The EAW concluded that the proposed facility will comply with the ambient air quality standard for hydrogen sulfide and is also indicated that it would not create exceedances of ammonia.
The full EAW is available for viewing on the MPCA's website at www.pca.state.mn.us.
After the EAW is fully reviewed, the Douglas County Planning Commission will make its recommendation on whether or not to approve the project. It then goes before the Douglas County Board of Commissioners for final approval. No date has been set as to when that will happen.