Development of an odor rating system to estimate setback distances from animal feedlots: Odor from feedlots setback estimation tool (offset)

The odor ratings systems, now called the "Odor from Feedlots - Setback Estimation Tool" (OFFSET), has been developed to estimate the setback distance from animal production sites in Minnesota. It is based on numerous odor emission measurements from more than 200 animal buildings and manure storage units on nearly 80 farms in Minnesota during 1998 to 1999 and an air dispersion model. The geometric means of the measured odor emission rates are used to represent odor emissions for different animal housing systems and various manure storage units. Source type and dimensions estimate the odor emissions from a specific source. The dispersion model was validated for short-distance (<0.25 mile) and long-distance (0.25 to 2.0 miles) odor dispersions by extensive Held odor measurements. Setback distances from animal sites are presented in graph form as a function of the total odor emission factor and the desired odor annoyance free frequency of the neighbors. The odor annoyance free intensity level is set at odor intensity 2 (faint odor) on a 0 (no odor) to 5 (very strong odor) intensity scale. Odor annoyance free frequencies are based on the average weather data for Minnesota from 1984 to 1992. A step by step process is described that first identities all of the different odor sources at a site, selects the odor emission number on a per square foot basis, determines the total surface area of the barn or storage units, credits any odor control technology, and then calculates the total odor emission factors for each source. This number is found on the hortizontal axis of the frequency figures and. depending on the odor annoyance free frequency desired from a high of 99% to a low of 93%, the setback distance in miles can be selected.