Field Application of the Digital Opacity Compliance System (DOCS) For Fugitive Emissions Opacity Determination

摘要

Most regulated facilities currently employ the US Environmental Protection Agency (EPA)Reference Method 9 (Method 9) to demonstrate compliance with enforceable fugitive emissionvisible opacity limits. However, Method 9 was neither designed nor intended by the EPA to beused to determine the visible opacity levels associated with fugitive emissions.Maintenance of Department of Defense (DoD) weapon systems, battlefield training exercises andconstruction/demolition activities invariably lead to the generation of fugitive emissions. DoDreliance on Method 9 for certifying compliance with fugitive emissions opacity regulationsleaves installations and their vital combat readiness programs vulnerable to unnecessarilyrestrictive regulatory oversight including environmental enforcement actions.Recently, the DoD, working in conjunction with the EPA and several western states, hasembarked on a technology field demonstration program focused on evaluating the ability of theDigital Opacity Compliance System (DOCS) to reliably determine the visible opacity associatedwith fugitive emissions. The DOCS technology utilizes digital photographs taken by standardcommercial-off-the-shelf digital cameras to determine visible opacity. The photographs areanalyzed using an innovative yet simple computer algorithm that compares the differences inspatial color intensity between scenes with and without the presence of fugitive emissions toquantify the level of visible opacity.Using an industrial fog generator to produce fugitive emissions of variable density, a fieldcomparison of the DOCS technology and Method 9 was conducted at Hill Air Force Base, UT.Results demonstrated that the two methods yielded mixed findings under turbulent windconditions. In the first set of opacity measurements (i.e., taken at 30 foot off-set distance), theDOCS technology and Method 9-certified observers were found to generate opacitymeasurements that were statistically different and that, on average, indicated that the DOCStechnology consistently yielded a higher opacity value. The fact that all three digitalcamera/Method 9 stations generated similar results suggests that the downwind location did notaffect the performance of one method more than the other.To document the inherent variability of the individual test methods, the average standarddeviation of the opacity measurements was estimated. At an off-set distance of 30 feet, allDOCS Camera/Method 9 opacity stations reported DOCS opacity measurements that were lessvariable than Method 9 opacity results regardless of down wind distance. As the off-set distancewas increased, the variability and inconsistency in performance between the DOCS technologyand Method 9-certified observers increased.Preliminary evaluation of the field data suggests that development of a fugitive emissionsopacity method must take into account the impact of local climatic conditions (e.g. wind shear)on opacity determination. Moreover, method development must also balance the need to complywith prescribed regulatory protocols (e.g., maintaining sun's position to the back of the opacityobserver) when determining the visible opacity associated with fugitive emissions.