Air modeling: The newest tool in proper hog barn siting

When Andy Muff opened his new 2,490-head finishing barns to pigs last month, he knew he had the best possible site available. The Ventura-area farmer had gone to great lengths to ensure that his operation was sited to minimize any impact on his neighbors and the surrounding communities of Ventura and Clear Lake. Muff was confident he had selected the proper site because of a new program that is gaining acceptance in determining the best possible locations for new or expanded livestock operations. The Community Assessment Model (CAM) is an air modeling tool that looks at multiple factors for siting a barn or expanding a current facility.
calendar icon 8 January 2007
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Farmers using CAM

Iowa State University Agricultural and Biosystems Engineering Professor Dr. Steven Hoff began developing CAM in 1998. "I've spent time since then with other funded research projects to help collect calibration data to validate the model," said Hoff. "It's always in development."

Hoff is putting the model to work in conjunction with the Coalition to Support Iowa's Farmers. "We started using the model for siting purposes in 2004 and have used it around 70 times in Iowa so far," Hoff said.

Proper siting is critical to the long-term success of an operation - from an investment standpoint and for community acceptance - and for minimizing the impact on neighboring residences and locations of public interest. Growth and management of livestock farms must be conducted in an environmental, economic and socially acceptable manner.

The state of Iowa has established minimum separation distances for livestock and poultry operations based on animal unit capacity. These required distances are minimums. However, when it comes to odor transport, it's important to note that distance is not equal in all directions. Orientation (barn layout and wind direction to neighboring residences) and topography are among the factors that must be considered.

Comprehensive Evaluations

The Community Assessment Model encompasses an evaluation of the site, including size of facility, species, average inventory and weight, and manure storage type. Community information gathered includes the direction and distance to residences, churches, cemeteries and places of frequent public gathering. Other livestock at the proposed site or other locations in the community also are reported.

Once this information is gathered, a computer model including local historical weather patterns with wind speed, duration and orientation is used to predict the total hours of potential odor exposure that a point of interest will receive. The hours of odor exposure is reported for three odor concentrations: 2 to1, 7 to1, and 15 to1. For example, an odor concentration of 2 to1 means that it would take two volumes of fresh-air mixed with one volume of odorous air to make the odor "barely detectable." A few states use an odor concentration of 7 to1 to assess whether an operation is in compliance relative to odor.

Modeling is conducted for odor release in the eight-month time frame of March to October. This is the time of year in which residents tend to spend a lot of time outdoors. The modeling procedure used is to assess a chosen siting location based on the percent time exposure of a residence to various levels of odor. Currently, site selections are judged based on a limit of a 1 percent time exposure to a 2 to1 odor and a 0.5 percent time exposure to a 7 to1 odor. These guidelines and results are given to the producer as a tool to help assess a potential site location.

This diagram shows the relative exposure of compass points from a
given emission source. (Courtesy of Dr. Steven Hoff)

This diagram represents the percentage of time winds are from a
given direction. The center is calm while the outer circle is 10%. The wind is from
the south (blowing due north) 15% of the time. (Courtesy of Dr. Steven Hoff)

A Useful Tool

CAM made a believer out of Muff. Air modeling of his site, about three miles north of Ventura, found that Ventura would detect odor from the facility for only two hours from March-September (the lake's busiest time of year). "It's one of the most useful tools we have available today," Muff said. "I recommend that it be used as much as possible."

Modeling potential building sites with CAM provides the farmer comfort in saying 'this is a good site' or 'we need to look at an alternate location.' The impact of odor reduction methods - including bio-filters, environmental vegetative buffers, manure storage covers, etc. - can be assessed with CAM to help producers achieve the 1 percent/0.5 percent guidelines provided above.

CAM modeling is based on field-collected odor data and work continues to refine the accuracy and usefulness of CAM. The CAM field work is conducted by Colin Johnson, extension program specialist with the Iowa Pork Industry Center at ISU. Hoff conducts the computer modeling and uses aerial maps to supplement the model. While CAM can help producers in the planning stages of siting new facilities, it is not EPA approved and it will not be recognized by law. However, CAM has been readily received by participating producers and, in a few cases, has given clear indications where alternate siting choices were needed.

"We need to have a recognized procedure for siting livestock buildings and I think this could be a tool that will eventually be adopted by agriculture and environmental agencies as the standard," said Hoff.

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