An examination of the building pressure cycling technique as a tool in vapor intrusion investigations with analytical simulations.

The building pressure cycling (BPC) technique has been developed and applied by vapor intrusion (VI) site investigators to obtain estimates of reasonable maximum exposures and to identify possible background sources of contaminant vapors. This method assumes that by application of consistent indoor depressurization one can increase the average contaminated soil gas entry rate into a building of interest. In this study, a one-dimensional analytical model was developed to examine this assumption and explore the mechanism of BPC application. We have established that contaminant entry rate can typically reach a new pseudo-steady state on a time scale of one day following the imposition of enhanced indoor depressurization. Considering the traditional source-soil-building pathway, the results indicate that BPC can increase building loading rate in the first 3-5 hours, to an extent linearly related to the strength of depressurization, and after half a day, the normalized rate would reach a pseudo-steady state of about twice the value before application of depressurization. More significant and substainble increases in building loading rate indicate alternative pathways such as land drain or sewer pipeline. These findings are fully consistent with available field observations, and could help investigators optimize the performance of the BPC operation.