A Section 112(f) Residual Risk Assessment of Hazardous Air Pollutant Emissions from Hill Air Force Base, Utah

摘要

Hill Air Force Base (AFB) recently took part in a mandatory residual risk assessment of theAerospace National Emission Standards for Hazardous Air Pollutants (NESHAP). As the largestmaintenance depot west of the Mississippi River, Hill AFB is a major and compliant sourcesubject to the Aerospace NESHAP. The emphasis of the residual risk assessment was todetermine whether the current Maximum Available Control Technology (MACT) standards asimplemented under the NESHAPs are sufficient to provide an ample margin of safety betweenthe allowable emissions of hazardous air pollutants, the resulting concentrations, and subsequenthuman health risks.Engineering data were collected and analyzed to determine mass emission rates from AerospaceNESHAP sources. These mass emission rates were evaluated as a function of human inhalationpathways and Hill AFB site-specific weather data utilizing Environmental Protection Agency(EPA) Human Exposure Model (HEM-3) software. Following the evaluation of HEM-3 results, arisk characterization of the data was performed to characterize human health inhalation pathwayrisks from Hill AFB Aerospace NESHAP sources.In the course of the assessment, Hill AFB's unique meteorological environment elicitedinnovative modeling solutions. The EPA's preprocessor programs were used to combine sitespecificsurface data and Salt Lake City upper air data for 1991-1995. The resultantmeteorological data represented the actual weather conditions at Hill AFB. Running HEM-3using this data provided an accurate representation of the effects of dispersion along withrealistic locations for the areas of highest concentrations. Relative to using genericmeteorological data, the use of site-specific meteorological data resulted in a more robust riskassessment of the area surrounding the facility while producing an accurate and site-specificassessment of risk values and only requiring a minimal increase in effort.