Examination of the influence of environmental factors on contaminant vapor concentration attenuation factors using the U.S. EPA's vapor intrusion database.

Those charged with the responsibility of estimating the risk posed by vapor intrusion (VI) processes have often looked to information contained in the U.S. Environmental Protection Agency (EPA)'s VI database for insight. Indoor air concentration attenuation factors have always been a key focus of this database, but the roles of different environmental factors in these attenuation processes are still unclear. This study aims to examine the influences of these factors in the context of the information in the VI database. The database shows that the attenuation factors vary over many orders of magnitude and that no simple statistical fluctuation around any typical mean value exists. Thus far, no simple explanation of this phenomenon has been presented. This paper examines various possible contributing factors to the enormous range of observed values, looking at which ones can plausibly contribute to explaining them.