Earth Tech was tasked to collect and analyze historical emissions data from Kelly Air Force Base (AFB), TX. They were limited in scope of work to certain years (1970 to 1975 and 1983 to 1989) with the assumption that these were 'peak production years' for the support of military actions in Southeast Asia and increased defense activities, respectively. These years would give a 'worst case' scenario of the air emissions at Kelly AFB. Earth Tech was also limited in scope of work to specific Air Force industrial processes (jet engine testing, painting, depainting, and degreasing). These industrial processes included the following air pollutants: benzene, toluene, ethylbenzene, xylene, methylene chloride, methyl ethyl ketone, perchloroethylene, components of burned jet fuel (cadmium, chromium, formaldehyde, benzene, arsenic, and 1,3-butadiene), and metals as applicable to painting, depainting, plating, and degreasing operations (to include cadmium and chromium). Based on the data that was analyzed, Earth Tech concluded that the data from the 1980s is the best available data to use for modeling purposes, specifically 1984, 1985, and 1986. Data from the 1970s is often sketchy, and although the confidence levels are the same for the 1970s data as the 1980s data, the 1970s data contains more uncertainty due to the extensive assumptions that were used when reviewing the data. Earth Tech recommends modeling the data using the Tier 1 approach. The Tier 1 analysis is the first part of an EPA three-tiered modeling process, defined in EPA-450/4-92-001, A Tiered Modeling Approach for Assessing the Risks due to Sources of Hazardous Air Pollutants.