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Show INTRODUCTION The electric utility industry was singled out in the federal Clean Air Act Amendments of 1990 (CAAA) for further study to a sess the impact of hazardous air pollutant (HAP) emissions on human health. Title III of the CAAA defined a list of 189 substances or classes of substances as hazardous air pollutants. The CAAA mandated that U.S. Environmental Protection Agency (EPA) prepare three reports to Congress. These are known as the Electric Utility Study; the Mercury Study; and the Great Lakes Study. The Mercury Study and the Electric Utility Study recently have been completed in draft fonn for scientific peer review [1,2]. When the CAAA was promulgated, much of the existing HAP emission data base for coal-fired power plants was questionable. Data were not available for all of the HAPs listed in Title Ill, and existing data were subject to considerable uncertainty due to unknown or poor measurement methods, and incomplete or absent data quality documentation. The potential ramifications of HAP - emission control regulation of the electric utility industry were economically significant. Therefore, in a cooperative effort, the industry and U.S. government embarked on a series of comprehensive assessments of HAP emissions from coal-, oil-, and gas-fired power plants between 1990 and 1993 [3,4]. A total of 52 tests were conducted at 48 sites using conventional and advanced sampling and analysis methods under programs performed by the Electric Power Research Institute (EPRI), U.S. Department of Energy (DOE), Northern States Power Company, and EPA [1] . The tests encompassed a wide range of coal types, boiler designs, and emission control technologies. These data form the basis for the human health risk assessment in EPA's Report to Congress [1]. Subsequently, tests also have been perfonned at additional sites under EPRI and DOE sponsorship [5,6,7,8,9]. In all of these tests, validated EPA test methods were employed to the extent they were available. For many pollutants, however, the published test methods have been developed for other types of combustion sources. The characteristics of coal-fired power plants are sufficiently different from the sources on which these methods are based are sufficiently different that significant modification to sampling and analytical procedures are required. This paper discusses the performance of method modifications used by Energy and Environmental Research Corporation in several of the test programs described above. 2 |