Odor nuisance complaints are a significant issue for today's hog industry. The technology to completely prevent and remove odors either does not exist or is too expensive to install and/or manage. However, good design and management, and certain odor control technologies can minimize odors.

Properly sited buildings with enough setback distance to allow the atmosphere to dilute odor is one very effective odor control strategy. Initial site selection and facility location, therefore, is critical for reducing nuisance odor complaints.

It is difficult to determine the impact of odorous gas emissions because wind speed and direction change constantly. So judgments must be made based on statistical probabilities.

The determination of setbacks for livestock facilities is a very difficult and complex issue. Very little quality research data is available in the U.S. to develop setbacks. But European institutions have conducted extensive research during the last two or three decades. Several European countries have used both experience and scientific data to develop setback guidelines and models.

The latest development comes from Austria where they incorporate new variables such as wind frequency and topography. The site-specific Austrian guideline was modified and employed in the U.S. We used it to calculate setback distances for swine finishing buildings for comparison to setbacks established by several states. (See sidebar on page 63.)

Several potential improvements and the additional research needed to make the model more useful for the U.S. are discussed.

Existing Setbacks Community tolerance to odors can be assessed by surveying residents in the surrounding neighborhood along with simultaneous weather and odor monitoring. Such studies are very expensive and rare. But results include odor exposure in terms of hours per year when odors will or will not be tolerated.

One study surveyed neighbors around seven, 100- to 225-sow, farrow-to-finish operations to assess the relationship between the perception of odor nuisance, separation distance, and the size of the facility. About 20% of neighbors living about 2,200 ft. away from hog farms perceived them to be a nuisance. Farm size had no effect between 600 and 1,200 ft. away.

Sophisticated numerical models are available to predict odor concentration downwind of hog facilities. However, they cannot define what odor level constitutes a nuisance.

Setback models may consist of fixed setbacks or setbacks that consider at least some site-specific information. Some fixed setback distances based only on land use have been recommended. For example, the American Society of Agricultural Engineers recommends 1 mile from a housing development and 0.25-0.5 miles from neighboring residences. Other engineers recommend a 0.5-mile setback for units with more than 1,000 pigs, otherwise 0.25 miles from neighboring residences, in all directions.

Several states have incorporated setbacks into their environmental regulations. The setbacks depend on animal type, land use, and/or size of facility:

* Kansas 0.25 to 0.75 miles

* North Carolina 0.28 to 0.47 miles

* Iowa 0.14 to 0.47 miles

* Illinois 0.25 to 1.0 miles

* Missouri 0.19 to 0.57 miles

* Oklahoma 0.5 to 0.75 miles

* South Dakota 0.25 to about 1.5 miles and more (no maximum).

Detailed State Setbacks Iowa has setbacks for buildings, depending on land use and the total body weight of pigs, starting at 200,000 lb. (1,333 hogs weighing 150-lb.). For incorporated areas, setbacks increase from 1,250 ft. for 200,000 lb. (1,333, 150-lb. hogs) to 1,875 ft. for 625,000 lb. (4,167, 150-lb. hogs) and to 2,500 ft. for 1,250,000 lb. (8,333, 150-lb. hogs) or more. For unincorporated areas, the distances are 750, 1,000 and 1,500 ft. for 200,000, 625,000 and 1,250,000 lb., respectively.

Illinois specifies setbacks of 1,320 ft. from a non-farm residence and 2,640 ft. from a populated area for 125 to 2,500 finishing pigs. These setbacks increase by 220 and 440 ft. for every increase of 2,500 head up to a maximum of 2,640 and 5,280 ft., respectively. Provision is made for smaller setback distances if yet-to-be-determined, state-approved, odor-reducing innovative designs are employed. Waivers from residents living in the setback areas are allowed.

South Dakota's "model regulations" for counties set forth the highest setback requirements of all states. They specify setbacks of 1,320 ft. from dwellings, schools and churches, and 2,640 ft. from populated areas for 25-750 finishing pigs. The setbacks are 2,640 and 5,280 ft. for 2,500 finishers. For facilities with more than 5,000 finishers, setbacks increase for every 2,500 head by 220 ft. for units near residences and 440 ft. for units near towns. Producers may apply for variances and obtain waivers from neighbors.

Minnesota recently allocated $390,000 for the development of odor emissions ratings and setback curves for typical livestock production practices. Their proposed total odor emissions rating will ultimately be based on facility design and management, odor abatement technology, and facility size. The statewide system of total odor emissions ratings would exist as an option for local governments to adopt at their discretion, making the setbacks more or less restrictive than the state guidelines.

Good site selection should consider surrounding topography. Relatively level terrain, no obstacles, and areas with moderate to high wind velocity promote good odor dispersion. Confined valleys where sensitive sites are downslope of the facility are much more vulnerable. To date, no setback guidelines in the U.S. consider site-specific topography or prevailing winds.

New Setback Guideline A simple model is now available that can be used to calculate fair and reasonable setbacks for U.S. livestock industries. The setback model was developed recently for livestock confinement buildings in Austria. The model considers facility size, local topography, wind frequency and effects of building design and management and odor abatement techniques. It first estimates the strength of the odor source and then the dispersion of odor from the source. (See sidebar with Table 1 on page 63.)

The model can be used to determine conservative odor impact distances for swine buildings in different scenarios. Three scenarios are compared in Figure 1.

For example, the figure shows what the upper and lower bounds of what the model calculates for a site with 2,500 hogs is 0.43 and 0.12 miles (2,247 and 615 ft.), respectively. The upper includes a facility in a valley with neighbors. The lower bound is for a flat, windy area. A more typical odor impact distance is shown by the middle curve in Figure 1. This unit would be an average swine finishing unit.

Using the parameters for an "average" swine finishing unit and average odor dispersion, the model calculates recommended setbacks for populated areas:

* 0.17 mile (902 ft.) for one 1,000-head finishing unit;

* 0.34 mile (1,805 ft.) for four 1,000-head finishing units; and

* 0.51 mile (2,707 ft.) for nine 1,000-head finishing units.

Odor impact distances were calculated for hypothetical finishing facilities with 1,000, 4,000, and 10,000 head to illustrate the model (Figure 2). The annual wind frequency for Evansville, IN and hypothetical topography and land use factors were used. The resulting odor impact area is noncircular, and may or may not follow prevailing wind patterns because of the effects of topography and land use. It is obvious that setbacks calculated from the model are more accurate than arbitrary setbacks of 0.5 and 1 mile.

Discussion Nuisance complaints from swine odor depend on odor production at the facility, odor transport between the facility and neighbors, and odor tolerance by the neighbors. Each of these factors is highly variable and complicates the assessment of odor control for individual farms. A one-size-fits-all setback tends to meet the needs of the worst odor emission problem, the worst dispersion characteristics, and most sensitive neighborhoods.

Fixed setbacks disregard the ability of individual production facilities to achieve odor dilution or communities to accept detectable odors periodically.

Given the extremely complex nature of agriculture odor impact on surrounding communities, formalized judgment is needed to estimate setback distances. Several European countries have established such setback models, which are based on scientific odor measurements and neighbor surveys.

Can we assume that odor generation from swine confinement buildings in Europe are similar to those in North America so we can use their factors in the model? There are some differences that justify the need for research to establish the factors for U.S. livestock.

First, in the summer, U.S. buildings experience higher temperatures and air velocities, two important factors influencing odor emissions. The 2 "percent" temperatures (those exceeded only 2 "percent" of the time) for various countries and states are as follows: Austria 76-80 "degrees" F; The Netherlands 71-77 "degrees" F; Germany 72-83 "degrees"; Switzerland 71-80 "degrees"; Indiana and Illinois 85-90 "degrees" F; Iowa 85-89 "degrees" F; South Dakota 87-91 "degrees" F; North Carolina 83-92 F "degrees"; and Oklahoma: 93-97 "degrees" F.

The warmer temperatures in the summer creates more odor as manure decomposes at a higher rate. Plus, summer ventilation rates are at least twice as high in the U.S., producing higher indoor air velocities across emitting surfaces.

Another difference is facility size. Swine farms are much smaller in Austria than in the U.S. There are also differences in building design, manure handling and feed systems.

In spite of these differences, the proposed odor impact model appears to estimate reasonable distances of odor impact for livestock buildings and compare well with those established by state governments.

However, the interaction between odor production, separation distance, climactic and topographic data and local land use is a topic of research that urgently needs to be addressed. Meanwhile, this model is currently the best method for estimating reasonable setbacks. It allows incorporation of new information obtained from research.

A new model can now calculate setbacks for U.S. hog operations. The setback model was developed in Austria. It considers facility size, local topography, wind frequency and effects of building design and management and odor abatement techniques.

The model first estimates the strength of the odor source and then the dispersion of odor from the source:

* Odor Source - The odor source number (O) represents the strength of the odor source. It is calculated by multiplying the number of animals by the animal factor and a technical factor, as explained in Table 1.

The Austrian technical factor involves values based on ventilation, manure management and feed. But little guidance is given on how to judge and assign these values.

For this model to be used in the U.S., we should replace the technical factor with a building design and management factor and an odor abatement factor. These factors need to be developed from field test data conducted with American systems. Until such data becomes available, the model can be used conservatively with T=1, as shown in Table 1.

The building design and management factor depends on the manure, feed, ventilation and dead animal disposal systems. For example, a fully slotted floor with a long-term, deep-pit storage emits about 2.5 times as much ammonia as a pull-plug system with recharge in finishing houses. A deep-pit, finishing house with typical rations and tunnel ventilation might be assigned a factor of 1.0.

Technologies used specifically for reducing odor from the farmstead would be accounted for with the odor abatement factor. Odor abatement would include diet manipulation, feed and pit additives, manure storage covers, dust reduction, and other techniques.

* Odor Dispersion - Dispersion of odor is estimated by considering annual wind distribution and influence of land slopes and obstacles. Data from the nearest weather station is used to determine the regional wind patterns in all directions. The land topography surrounding the hog facility is assigned a score from 0-70 points in each of eight wind directions.

For example, a livestock building in a flat and windy area without any obstacles around it is dominated by the regional wind pattern so the topography score would be zero.

For land slopes greater than 5% and livestock facilities located in a valley, neighbors who live downslope and down valley from the facility are especially vulnerable during the night. In the case of steep slopes and narrow valleys, the topography score might be given the maximum value of 70.

The total score is determined for each direction by adding the topography score (range = 0 to 70) to the wind frequency, e.g. 10%. The odor dispersion factor (D) depends on the total score as explained in Table 1.

* Land Use Factor - The land use factor (L) ranges from 0 to 1 with 0 for full tolerance zones, 0.5 for commercial areas and 1.0 for purely residential areas. It would be most appropriate for local governments to assign the land use factors between 0 and 1. The site-specific land use factor also depends on direction from the facility.

* Odor Impact Distance - The odor impact distance in miles is calculated by multiplying the square root of the odor source number by 0.0155 and also by the odor dispersion and land use factors.

For example, if the odor source number is 350 and the dispersion and land use factors are 0.7 and 1.0, respectively, the odor impact distance is 0.20 miles.