STP1317

    Prediction of Risk-Based Screening Levels for Infiltration of Volatile Subsurface Contaminants into Buildings

    Published: Jan 1997


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    Abstract

    A Risk-Based Corrective Action (RBCA) approach is increasingly being used for the management of contaminated sites. Fundamental to this approach is the prediction of risk-based screening levels (RBSL) for operable exposure pathways. Screening level models currently used (e.g., ASTM ES-1739-95) indicate that RBSLs for the indoor inhalation pathway can be significantly lower than other pathways typically considered. This paper presents the results of a screening level spreadsheet model used to predict human health risks resulting from infiltration of volatile organic compounds (VOCs) into buildings. The model was developed to derive RBSLs for soil and groundwater for possible future incorporation into the regulation of contaminated sites in British Columbia. Key features of the semi-analytical VOC infiltration model are steady-state diffusive mass transfer through soil coupled with advective and diffusive mass transfer through a cracked building floor slab or wall, source mass depletion of soil contaminants present using a mass balance approach, and the capability to incorporate multi-component chemical partitioning for soils containing non-aqueous phase liquid (NAPL). The critical factors affecting VOC infiltration and resulting health risks are presented. In terms of model assumptions, the estimated VOC infiltration rates can be unrealistically high when mass depletion or multi-component partitioning is not considered. The effect of building characteristics (concrete cracks and underpressurization) on VOC infiltration rates is shown to be of minor significance for the cases investigated. Soil properties that are sensitive in terms of their effect on resulting screening levels are organic carbon content and air-filled porosity. A significant limitation pertaining to models used to predict infiltration of VOCs into buildings is the lack of fundamental research and field validation.

    Keywords:

    soil gas infiltration, partitioning, diffusion, risk-based screening level


    Author Information:

    Hers, I
    Golder Associates Ltd., Burnaby, B.C.

    Zapf-Gilje, R
    Golder Associates Ltd., Burnaby, B.C.

    Petrovic, S
    Golder Associates Ltd., Burnaby, B.C.

    Macfarlane, M
    British Columbia Ministry of Environment, Victoria, B.C.

    McLenehan, R
    British Columbia Ministry of Environment, Victoria, B.C.


    Paper ID: STP12245S

    Committee/Subcommittee: E47.05

    DOI: 10.1520/STP12245S


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