Protocol for the Derivation of Environmental and Human ... - CCME

Appendix G
4.4 Application of the Results
The dilution factors presented above may be used to estimate the potential indoor air concentration
based on a known contaminant concentration in the soil vapour beneath a foundation. The dilution
factor is not significantly affected by the contaminant type. However, contaminant concentrations are
more commonly measured in soil or groundwater, and the partitioning of the contaminant from the soil
or groundwater to the soil vapour is dependent on certain contaminant-specific properties (K oc , Henry's
Law constant, molecular weight) as well as soil type (principally organic carbon fraction). For certain
groups of compounds, such as the common monocyclic aromatics benzene, toluene, ethyl benzene, and
xylenes (BTEX), the partitioning factor may be described by average or generic distribution factors that
do not vary significantly between compounds. To minimize uncertainty, however, it is recommended
that partitioning be evaluated on a contaminant-specific basis and that only the dilution factors be
applied in a generic manner. Partitioning may be evaluated using the relationships described in Section
3.2 and Table G.1.
It should be noted that calculations using this model must consider concentrations in the three soil phases
(soil gas, soil water, and soil particles) and utilize the total amount of contaminant in a given mass of total
soil as the basis for any comparisons or for the development of numeric guidelines.
5.0 Closure
The dilution factors presented in this report may be used to estimate the potential contaminant
concentrations in indoor air resulting from a known contaminant concentration in the soil vapour beneath
or near a foundation. This may be used in turn as a screening tool to assess the significance of vapour
infiltration and inhalation as an exposure pathway for the purpose of risk assessment or the development
or implementation of risk-based remediation guidelines. Caution should be exercised in the application
of the generic dilution factors in situations where subsurface, foundation, and building conditions differ
significantly from those assumed in the development of the relationships.
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