Exposure Assessment Modeling for Volatiles—Towards an Australian Indoor Vapor Intrusion Model

Abstract

Human health risk assessment of sites contaminated by volatile hydrocarbons involves site-specific evaluations of soil or groundwater contaminants and development of Australian soil health-based investigation levels (HILs). Exposure assessment of vapors arising from subsurface sources includes the use of overseas-derived commercial models to predict indoor air concentrations. These indoor vapor intrusion models commonly consider steady-state assumptions, infinite sources, limited soil biodegradation, negligible free phase, and equilibrium partitioning into air and water phases to represent advective and diffusive processes. Regional model construct influences and input parameters affect model predictions while steady-state assumptions introduce conservatism and jointly highlight the need for Australian-specific indoor vapor intrusion assessment. An Australian non-steady-state indoor vapor intrusion model has been developed to determine cumulative indoor human doses (CIHDs) and to address these concerns by incorporating Australian experimental field data to consider mixing, dilution, ventilation, sink effects and first-order soil and air degradation. It was used to develop provisional HILs for benzene, toluene, ethylbenzene, and xylene (BTEX), naphthalene, and volatile aliphatic and aromatic total petroleum hydrocarbons (TPH) < or = EC16 fractions for crawl space dwellings. This article summarizes current state of knowledge and discusses proposed research for differing exposure scenarios based on Australian dwelling and subsurface influences, concurrent with sensitivity analyses of input parameters and in-field model validation.

Analytical modeling of the subsurface volatile organic vapor concentration in vapor intrusion

“…Shen et al (2013a, b). Vapor intrusion models (Turczynowicz and Robinson, 2007; Provoost et al, 2009) have been widely used in examining subsurface vapor concentrations. For example, some factors that have been hypothesized to influence subslab and soil gas vapor concentrations include those of spatial and temporal nature, such as the complexity of soil properties (Abreu and Johnson, 2005; Luo et al, 2009; Pennell et al, 2009), contaminant concentration gradients in groundwater (Little et al, 1992; Abreu and Johnson, 2005; Luo et al, 2009; Yu et al, 2009; Picone et al, 2012), contaminant source to building distance (Abreu and Johnson, 2005; EPA, 2012a; Yao et al, 2012a), temporal environmental changes (Little et al, 1992; DeVaull, 2007; Tillman and Weaver, 2007; Shen et al, 2012b).…”

Field data and numerical modeling: A multiple lines of evidence approach for assessing vapor intrusion exposure risks

“…However, the comparison of high-quality, temporally-correlated field data with model predictions remains a critical need within the vapor intrusion community (Turczynowicz and Robinson, 2007; Yao et al, 2013a). …”

Accuracy and Conservatism of Vapour Intrusion Algorithms for Contaminated Land Management

“…Some of the field validation has been undertaken for the JEM by Weaver and Tillman (2005), for four screening-level algorithms by Crump, Hartless, Ross, Scivyer, Davidson, and Pout (2005) and in Provoost et al (2008bProvoost et al ( , 2009Provoost et al ( , 2013. It would be helpful to extend the field validation to well documented sites from different countries similar to what Turczynowicz and Robinson (2007) did for Australia.…”

“…The algorithm predicts indoor concentrations by applying a 1D transport model where the source is infinite. Data from sites in Australian were used to address, dilution, ventilation and first-order soil and air degradation (Turczynowicz & Robinson, 2007). The sensitivity analysis revealed that mainly building parameters drive the VI predicted by the volatilization algorithm, and to a lesser extend the soil and physico-chemical properties (Turczynowicz & Robinson, 2001 (Johnson & Ettinger, 1991), predict indoor air concentrations for aromatic hydrocarbons up to 2 OoM higher than the observed concentrations.…”