Development of the Offset Model for Determination of Odor-Annoyance-Free Setback Distances From Animal Production Sites: Part I. Review and Experiment

The objective of the study was to develop a science-based model, OFFSET (Odor from Feedlot - SetbackEstimation Tool), to establish setback distances from animal production sites based on the use of an air dispersion model(INPUFF-2) and the actual odor emission data from these sites. Extensive research was conducted to obtain representativeodor emissions from various animal facilities and to evaluate the air dispersion model. Odor emissions were measured from280 animal buildings and manure storage units on 85 farms in Minnesota during 1998 to 2001. The geometric means of theodor emission rates for each type of odor source were obtained to represent odor emissions of that source. The efficienciesof some odor control technologies were summarized. The air dispersion model was evaluated for short-distance (<0.5 km)odor dispersion prediction against the odor plumes measured by trained field assessors on 20 farms and also for long-distance(4.8 km) odor dispersion prediction against odor data recorded by trained resident observers living in the vicinity of livestockoperations in a 4.8 4.8 km rural area. The relationship between odor detection threshold and intensity was obtained forswine and cattle odors in order to convert odor intensity to detection threshold. The results indicated that the INPUFF-2 modelwas capable of simulating odor dispersion downwind from animal production operations for low-intensity odors. Six stableor neutral weather conditions that favor odor transport were identified, and their historical occurrence frequencies in all 16directions at six weather stations in Minnesota were obtained. The occurrence frequencies of these weather conditions wereused to determine odor occurrence frequencies in the OFFSET model.