Development and Validation of a Controlled Pressure Method Test Protocol for Vapor Intrusion Pathway Assessment.

Controlled pressure method (CPM) testing is a building-specific diagnostic tool for vapor intrusion (VI) pathway assessment which offers advantages over traditional pathway assessment approaches. By manipulating the building pressure conditions, the CPM creates the worst-case VI impact and provides rapid insight into the type of vapor source(s). The primary barrier to general acceptance and use of this tool is the need for definitive guidance on test design parameters, such as the indoor-outdoor pressure difference (or exhaust fan flow rate), CPM test duration, exhaust fan location, and air sampling location(s) and conditions. This study focused on a systematic evaluation of each of these factors, which then led to the formulation of proposed CPM testing guidelines. The results suggest that CPM tests should be conducted with both negative and positive pressure indoor-outdoor differentials of about 10-15 Pa, and the tests should last for at least nine indoor air exchanges for negative pressure difference testing and four indoor air exchanges for positive pressure difference testing. Although exhaust fan intake sampling is sufficient to provide critical information to assess impacts during negative pressure testing, adding room-specific indoor air sampling to both negative and positive pressure difference testing can provide insight into vapor entry locations and indoor source contributions.

Long-term evaluation of the controlled pressure method for assessment of the vapor intrusion pathway.

Vapor intrusion (VI) investigations often require sampling of indoor air for evaluating occupant risks, but can be confounded by temporal variability and the presence of indoor sources. Controlled pressure methods (CPM) have been proposed as an alternative, but temporal variability of CPM results and whether they are indicative of impacts under natural conditions have not been rigorously investigated. This study is the first involving a long-term CPM test at a house having a multiyear high temporal resolution indoor air data set under natural conditions. Key observations include (a) CPM results exhibited low temporal variability, (b) false-negative results were not obtained, (c) the indoor air concentrations were similar to the maximum concentrations under natural conditions, and (d) results exceeded long-term average concentrations and emission rates under natural conditions by 1-2 orders of magnitude. Thus, the CPM results were a reliable indicator of VI occurrence and worst-case exposure regardless of day or time of year of the CPM test.