|PARNELL, JR., C|
Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/5/2005
Publication Date: 6/20/2005
Citation: Wanjura, J.D., Buser, M.D., Whitelock, D.P., Armijo, C.B., Hughs, S.E., Green, J.K., Norman, B.M., Capareda, S.C., Hamm, L.B., Parnell, Jr., C.B., Shaw, B.W., Lacey, R.E. 2005. An engineering analysis of a method used to determine property line setback distances for cotton gins. In: Proceedings of the Beltwide Cotton Conference, January 4-7, 2005, New Orleans, Louisiana. p. 614-629. 2005 CDROM.
Interpretive Summary: The 1977 amendments to the Federal Clean Air Act required that all states implement a stationary source permitting program. This state permitting program is known as new source review (NSR) and requires all stationary sources to obtain a permit prior to beginning construction on new sources or making modifications to existing facilities. The goal of this permitting program is to protect public health through ensuring compliance with Ambient Air Quality Standards (AAQS). Cotton gins are stationary sources and are required to obtain minor source NSR permits in most states. In some states, cotton gins may fulfill their permitting requirements through a state registration process or by obtaining a general permit from the state. Several tools are available for the states to use in demonstrating that stationary sources are in compliance with their NSR permit, including air quality control equipment requirements, process weight allowable tables, visible emissions limitations, and dispersion modeling. New Mexico developed a new tool that the state uses to demonstrate that a cotton gin is in compliance with its permit. This new tool uses minimum property line setback distances to ensure that air quality standards are met at the cotton gin's property line. The property line setback is the distance between the gin's exhausts and the nearest property line. Under the New Mexico permit, cotton gins would be required to have a property line setback distance equal to, or greater than, the limit specified in the permit. Dispersion modeling and particulate matter (PM) sampling at a New Mexico gin (using federal reference method samplers) were used to develop the required setback distance equations. The state identified problems with current dispersion modeling techniques that result in inaccurate concentration estimates. Thus, the developers attempted to correct for these errors. New Mexico used a conservative correction factor based on a single data point to adjust dispersion modeling results to match sampler concentrations. This manuscript focuses on deriving a correction factor based on sound science which accounts for the errors resulting from dispersion modeling and particulate matter sampling. The results of this work indicate that the setback distances determined by New Mexico were over estimated by a factor of three. Adoption of the findings of this manuscript will help to ensure the appropriate regulation of cotton gins based on required property line setback distances.
Technical Abstract: The US Environmental Protection Agency (EPA), under authority granted by the Federal Clean Air Act, delegates the responsibility of regulating and enforcing ambient air quality standards to the states. States are required by EPA to submit state implementation plans (SIP) detailing how a state will implement and enforce regulatory actions to ensure that the National Ambient Air Quality Standards (NAAQS) are achieved. The NAAQS list federal ambient concentration limits for six criteria pollutants including particulate matter less than or equal to 10 micrometers aerodynamic equivalent diameter (PM10). The primary criteria pollutant emitted by a cotton gin is PM10. In 1987, the NAAQS for particulate matter were changed from a total suspended particulate (TSP) concentration limit of 260 ug/m3 to the current standard for PM10 of 150 ug/m3 (Federal Register, 1987). The primary PM10 NAAQS of 150 ug/m3 is a 24-hour average ambient concentration limit established to protect public health. State air pollution regulatory agencies (SAPRA) regulate cotton gins by requiring minor source permits under the new source review (NSR) process. When granted the NSR minor source permit, the owner/operator has permission from the state to begin construction on either a new facility or modifications to an existing facility. States have granted cotton gin pre-construction permits based on permit by rule, standard permit, or individual facility permit. Recently, the state of New Mexico developed a new tool to use in permitting cotton gins. This new tool involves a property line setback distance. The property line setback distance is the distance from the emission point to the nearest property line. The results of field sampling and dispersion modeling taken from four days identified as worst case scenarios were used to determine the required setback distance for a New Mexico gin. The ratio of the modeled concentrations to the measured concentration (using FRM PM10 samplers) was determined for the four days and used to correct the concentration predictions from the model. The required setback distance for the gin was determined to be 41 meters corresponding to a 12 lb/hr PM10 emission rate. The method used to determine this setback distance did not account for the sampler errors that occur when using FRM PM10 samplers to measure concentrations of PM emitted from agricultural sources. The purpose of this manuscript is to evaluate the methods used by the NMED to determine the required property line setback distance and to provide guidance based on sound science and engineering for all parties involved in the permit application process for a "permit by rule" via a minimum property line setback distance regulation. The method described in this manuscript shows that a gin emitting 24 lbs/hr PM10 would have a required setback distance of 58 meters if only modeling errors were accounted for. The same gin would have a required setback distance of 13 meters if both modeling errors and sampler errors were accounted for. Accounting for modeling and sampling errors results in a more appropriate minimum setback distance for cotton gins.