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

Part C, Section 5
Volatile organic compounds have migrated into basements of homes from underground storage tanks
leaking petroleum-based fuels, and from hazardous waste landfills where vinyl chloride was improperly
disposed (Stephans et al., 1986). The SEQCCS attempted to ensure that guidelines for residential
soils will not pose a potential indoor air contamination risk. A gas infiltration model is used to estimate
the indoor air contaminant concentration and adjust a preliminary guideline as necessary.
Exposure via ingestion of soil contaminated by volatile organic substances is not likely to be significant
since these compounds are expected to volatilize rapidly from dry surface soil. It is, therefore, the
position of Health Canada that human health soil quality guidelines for volatile organic substances, based
on soil ingestion, are not required. Health Canada considers contamination of indoor air by volatilization
from contaminated soil to be the primary pathway of exposure for volatile organic chemicals. Human
health soil quality guidelines for volatile organic chemicals are therefore derived primarily on the basis of
inhalation following the migration of volatile contaminants from soil into buildings.
The concentration of volatile compounds in the soil gas (air) can be estimated. The following equations
to partition from the soil (absorbed) phase and dissolved phase to the soil gas phase:
where:
C sw = C s /(K oc × f oc ) [1]
C s = contaminant concentration absorbed to soil (mg/kg)
C sw = contaminant concentration dissolved in soil water (mg/L)
K oc = organic carbon partitioning coefficient (L/kg)
f oc = organic fraction of dry soil (g/g)
where:
C sg = 1000 x (C sw x H)/(R x T) [2]
C sg = contaminant concentration in soil gas (mg/m 3 )
H = Henry's Law constant (atm⋅m 3 /mol)
R = Gas constant (atm⋅1m 3 /mol°K)
T = absolute temperature (°K)
Once in the gas phase, volatile organic compounds migrate into basements via diffusion and barometric
pressure differentials between the soil gas and the indoor air. The migration into indoor air is also a
function of a variety of factors including soil type, depth or distance of contamination from the house
foundation, type of building foundation, the building air exchange rate, and building volume. All these
factors vary greatly and no standardized defaults exist. However, using known ranges of these
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