Evaluation of Vapor Intrusion Using Controlled Building Pressure

Abstract

The use of measured volatile organic chemical (VOC) concentrations in indoor air to evaluate vapor intrusion is complicated by (i) indoor sources of the same VOCs and (ii) temporal variability in vapor intrusion. This study evaluated the efficacy of utilizing induced negative and positive building pressure conditions during a vapor intrusion investigation program to provide an improved understanding of the potential for vapor intrusion. Pressure control was achieved in five of six buildings where the investigation program was tested. For these five buildings, the induced pressure differences were sufficient to control the flow of soil gas through the building foundation. A comparison of VOC concentrations in indoor air measured during the negative and positive pressure test conditions was sufficient to determine whether vapor intrusion was the primary source of VOCs in indoor air at these buildings. The study results indicate that sampling under controlled building pressure can help minimize ambiguity caused by both indoor sources of VOCs and temporal variability in vapor intrusion.

Influence of Soil Moisture on Soil Gas Vapor Concentration for Vapor Intrusion

“…The assessment of extent and hazard posed by vapor intrusion of VOCs into buildings has received increasing attention in recent years (Murphy and Chan, 2011;Eklund et al, 2012;McHugh et al, 2012;Picone et al, 2012;Turczynowicz et al, 2012;Wang et al, 2012). With *500,000 contaminated sites in the United States presenting uncertain VOC vapor intrusion risk (Schuver, 2007), the assessment of risk from inhalation of these vapors has been a topic of recent discussion, field investigations (Fitzpatrick and Fitzgerald, 2002;Sanders and Hers, 2006;William et al, 2007), and modeling studies (Abreu and Johnson, 2005;DeVaull, 2007;Tillman and Weaver, 2007;Bozkurt et al, 2009;Pennell et al, 2009;Yao et al, 2011).…”

“…In other words, there is no simple linear dependency observed between the source vapor concentration and the soil gas vapor concentration. The weak dependency can be the consequence of various specific site and sampling conditions, such as sampling locations (Abreu and Johnson, 2005), source concentration distribution (Yu et al, 2009), soil heterogeneity , open ground surface capping effects , transient effects, such as groundwater fluctuations (Picone et al, 2012), barometric changes (Garbesi and Sextro, 1989;McHugh et al, 2012), and so on. On the other hand, there is one major factor that often does not receive sufficient attention-that of soil moisture content.…”

Use of On-Site GC/MS Analysis to Distinguish Between Vapor Intrusion and Indoor Sources of VOCs

“…Building pressure control may then be used as a tool to control the advective flow of soil gas into the building. If advection (rather than diffusion) is the primary mode of vapor intrusion for a building, then building pressure control can provide an improved understanding of the potential for vapor intrusion (McHugh et al, 2012;USEPA, 2011b). Building pressure control can also be used to support the findings from the baseline evaluation.…”

“…Therefore, in order to further illustrate the utility of the on-site analysis protocol for distinguishing between vapor intrusion and indoor sources of VOCs, we have included results from several supplemental studies which show how the method can be used for indoor source identification and vapor entry point identification. Additional examples are also provided for the building pressure manipulation (McHugh et al, 2012;USEPA, 2011b) option of the protocol.…”

Assessment of Public Health Risks Associated with Naphthalene Entering Residences and Commercial Space from Vapor Intrusion at MGP Sites

“…Since compounds like naphthalene may be present in non-aqueous phase liquids (NAPL), the concern has expanded from possible soil and groundwater contamination to the potential for soil vapor intrusion [4]. Inhalation exposure via soil vapor intrusion to the chemicals commonly found at MGP sites is a concern because of the potential for adverse effects on human health [5][6][7][8][9].…”