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

Part C, Section 5
parameters, and stochastic analysis, the migration of contaminants from soil to basements can be
predicted probabilistically. This analysis is presented in detail in Appendix G.
Assuming that the contaminated soil is in direct contact with the basement foundation (i.e., depth or
distance = 0), the 5th percentile dilution factor from soil gas to indoor air is 10 000. In other words,
95% of the time, the contaminant in soil gas is diluted by more than 10 000 times when it enters and
contaminates air in a home. Therefore, dividing the estimated soil gas concentration for a volatile
organic compound (as calculated above) by 10 000 provides an estimated upper limit on the expected
indoor air concentration. Assuming that a person breathes, on average, 20 m 3 of air per day at this
indoor air concentration, then the total dose absorbed can be compared to published reference doses
for the inhalation of these compounds to ensure that no unacceptable exposure is likely to occur via this
route. The SEQCCS recommends that the indoor air concentration resulting from the soil guideline for
volatile organic compounds not exceed 20% of the inhalation reference dose for substances with
threshold effects, and not exceed an estimated incremental cancer incidence of one in one million for
carcinogenic substances.
For the complete derivation and discussion of the dilution of volatile compounds from soil gas to indoor
air, see Appendix G.
5.3.5 Off-site Migration of Soil/Dust from Industrial Sites
In deriving soil quality guideline for industrial sites, the SEQCCS used an exposure scenario which
considers on-site exposure only, (i.e., an adult worker on-site for a normal work week). However,
wind and water erosion of soil and subsequent deposition can transfer contaminated soil from one site to
another.
Therefore, the SEQCCS has developed a model to address the subsequent movement of soil from an
industrial to adjacent, more sensitive land sites (e.g., residential property). This procedure is briefly
described below. The full details and assumptions of the model are provided in Appendix E.
Calculations using the Universal Soil Loss Equation and the Wind Erosion Equation are used to estimate
the transfer of soil to an adjacent property. It is possible to calculate the concentration (C i ) in eroded
soil from the industrial site that will raise the contaminant concentration in the receiving soil to equal the
residential/parkland guideline within a specified period of time. Where the PSQG HH exceeds C i , SQG HH
should be set at C i. This may be viewed as multiplying the PSQG HH by a Management Adjustment
Factor for offsite soil migration defined by the ratio C i /PSQG HH . At specific industrial sites,
management actions may be taken to prevent or limit erosive losses of surface soils. Accommodation
for such situations is provided in the guidance for the development of site-specific objectives.
Professional judgement determined a number of the input parameters for this procedure. The use of
the Management Adjustment Factor in this check mechanism acknowledges the uncertainty surrounding
the assumptions used in the model.
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