Abstract

Abstract: Screening for vapor intrusion potential is likely to be required at a large number of sites in the future, due to federal or state requirements, real estate transactions, or voluntary cleanups. At most sites, the authors expect that only groundwater data will be available in sufficient quantity to conduct initial screening (as opposed to soil vapor or indoor air data). Therefore, groundwater data will tend to drive the need for additional vapor intrusion investigations at most sites. The current EPA subsurface vapor intrusion screening guidance (EPA 2002) assumes that soil vapor concentrations immediately above the water table are at equilibrium with groundwater concentrations (based on Henry’s Law Constant) and that indoor air concentrations in overlying buildings are 1000 times lower (an attenuation factor of 1/1000), due to attenuation through the soil column and building shell. According to EPA (2002), attenuation factors based on empirical groundwater and indoor air measurements are less than 1/1000 approximately 95 % of the time. Unfortunately, the resultant