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The WIAC will provide the analyses it collected to U.S.EPA for use in developing new AP-42 values. Since it is recognized that this process will require time,it is recommended that the U.S. EPA make the results contained in this report available on its Internet site as an interim reference. Report Objectives This report documents actual landfill gas concentrations for compounds of concern using a national database derived from laboratory analyses employing U.S.EPA standard methods. Herein we establish that differences between the data presented in this report and the current AP- 42 default values warrant their full-scale review by U.S.EPA.WIAC believes that the data presented here far better represent current conditions for many compounds and that such a review is well warranted. Procedures and Results AP-42 data management procedures were applied to the portion of the WIAC data set having AP- 42 default values.The data management procedures address,for example,data screening,air dilution,and data averaging methods.The results of these procedures follow. Data Collection and Screening WIAC collected LFG analyses from 75 landfills in sixteen states.This information was processed using U.S.EPA's AP-42 data management procedures.U.S.EPA uses a screening process to remove analytically unacceptable,poorly documented or questionable results 4 A review of the collected data indicated that the sample analyses would likely pass the AP-42 data screening process.The reported samples.were normal,untreated LFG derived from typical gas collection systems.The analytical methodologies appeared to be consistent with those accepted by U.S. EPA. The analytical results were corrected for air dilution using fixed gas analyses(specifically, methane and carbon dioxide).Several samples lacked either or both methane and carbon dioxide and were excluded.Additionally,some results appeared to be default values(e.g.,50%methane and 50%carbon dioxide)or were unusually high;these were excluded as well.In all,analyses from 27 landfills were omitted from subsequent evaluations. Data Rating The data for compounds from the remaining 48 landfills were rated from"A"(strongest)to`B" (weakest)using U.S.EPA's rating system.This process largely depends on the number of`good' results(A for 20 and up,B for 10 to 19,C for 6 to 9,D for 3 to 5,E for 1 to 2).U.S.EPA also adjusts the rating for a compound's variability.If the arithmetic standard deviation is twice or greater than EPA's default value,then the rating is decreased by one letter.Table 1 summarizes the WIAC rating results and compares these with U.S.EPA's AP-42 data set for 43 compounds. 4`EMISSION FACTOR DOCUMENTATION FOR AP-42 SECTION 2.4 MUNICIPAL SOLID WASTE LANDFILLS REVISED"Office of Air Quality Planning and Standards,Office of Air and Radiation,U.S. Environmental Protection Agency,Research Triangle Park,North Carolina 27711,August 1997;see Table 4-1 2