Ambient odour testing of concentrated animal feeding operations using field and laboratory olfactometers

The Missouri Air Conservation Commission regulations include regulations that limit the amount of acceptable odor from confined animal feeding operations (CAFOs). The regulations concerning odor designate the use of a scentometer as a screening tool. The rules dictate that if an odor is detectable by an investigator at a dilution ratio of 5.4 using a scentometer then an air sample should be collected and sent to an olfactometry laboratory for an odor panel to determine the detection threshold and the intensity of the odor sample. The detection thresholds are determined following ASTM E679-91 and EN13725. The intensity is determined following ASTM E544-99. If the olfactometry laboratory determined the detection threshold of the sample to be above seven, then the CAFO would be in violation. If the olfactometry laboratory determined the intensity level to be above a level equivalent to 225 ppm of n-butanol, then the source of odor would be in violation. The CAFO odor rules came under scrutiny by representatives of the largest hog producer in the State of Missouri. Specifically, they argued that the detection threshold limit of seven in the CAFO portion of the rule was too low for the rule to realistically identify a violation. This paper presents the results of a study to find the appropriate regulatory level of odor as determined by laboratory olfactometry. The study took place from November 2001 to October 2002. Samples were collected from field locations that exhibited odor produced by confined animal feeding operations and from areas exhibiting no apparent odor. The odors were categorized based upon the scentometer level at which the odors were detectable, and then samples were sent to an odor evaluation laboratory for analysis by olfactometry.