Fate and Transport of Chloroform in VI Evaluations

Abstract

Chloroform is frequently detected in indoor air in vapor intrusion (VI) studies. At many sites, initial screening shows potential indoor air impacts for chloroform at unacceptable levels. During follow‐up site characterization, however, the VI pathway for chloroform is rarely found to be the primary source of chloroform in indoor air. This paper sets forth a conceptual model for understanding these results and summarizes data from 10 field sites from various US Environmental Protection Agency regions to illustrate the concepts. Chloroform is a volatile organic compound (VOC) that is categorized as being a trihalomethane. It is well documented that it can be formed when chlorine is used to disinfect water. Chloroform also may be emitted directly into indoor air from treated water and may be formed and/or emitted from various cleaning products. The typical indoor air background concentration in residential buildings is approximately 0.5–1 µg/m3, but results will vary, and values of 10 µg/m3 or higher have been measured. The indoor air background concentrations presented in the literature are well above typical screening level concentrations for residential buildings. Field data are presented that demonstrate that the attenuation factor for chloroform often differs widely from attenuation factors of other VOCs that may pose a potential risk via the VI pathway.