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

Part C, Section 5
Y p = C w (K d + ? m ) [3]
where
Y p = total contaminant concentration in soil at equilibrium with pore water at the
drinking water guideline concentration (mg/kg)
? m = mass moisture content
The critical soil concentration in terms of the pore water concentration guideline, partition coefficient,
and the mass moisture content at drainage is illustrated in Equation 3. For all but very weakly sorbing
contaminants (i.e., hydrophilic chemicals) K d is much larger than q m and the moisture content can be
ignored.
Using Equation 3 with a relevant soil organic matter content, it is possible to calculate for non-ionic
organic contaminants a soil concentration at which the equilibrium pore water (which ultimately will drain
to groundwater) exceeds the water quality guideline. However, this drainage water will dilute when it
reaches the aquifer. The soil concentration yielded by substituting the drinking water guideline value in
Equation [3] is then multiplied by a generic dilution factor before comparing it to the PSQG HH :
Y a = DF × C wa (K d + ? m ) [4]
where
Y a = total contaminant concentration in soil at equilibrium with groundwater at the
drinking water guideline concentration (mg/kg)
DF = generic dilution factor (50)
C wa = the critical contaminant concentration in groundwater -- set equal to the relevant
drinking water guideline. (mg/L)
The magnitude of dilution at a particular site will vary with respect to a number of factors including
recharge, groundwater flow, and distance from source. To develop generic guidelines, the
Subcommittee reviewed data for important input parameters from across Canada. Based on this
review, a number of assumptions about a generic site (e.g., site size, stratigraphy), and an analysis of
uncertainty, a dilution factor of 50 has been proposed for this generic protocol. The rationale for the
generic dilution factor, including generic site assumptions, protection goals, and analysis of uncertainty
are examined in Appendix D.
The preceeding derivation equations apply to non-dissociating organic contaminants. Some ionizing
organic compounds can also be accommodated provided that sorption of the dissociated and nondissociated
forms can be simply described (i.e., weak organic acids, such as chlorophenols). In this
case, the phenol is sorbed, whereas the dissociated (anionic) form -- the phenate -- is negligibly sorbed.
An arithmetic treatment of this case appears in Appendix C.
5.3.2.3 Data Requirements. The data necessary to perform the organic contaminant check are:
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