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

Part C, Section 5
The following section characterizes four indirect soil exposure pathways and includes a brief description
of the methods used for estimating the contaminant exposure or flux. More complete details are found
in the Appendices.
The SEQCCS developed these check modelling procedures to ensure that the final generic soil quality
guideline will not lead to excessive migration of a soil contaminant to another medium, (e.g., air, water,
and food). There are two check mechanisms for indirect exposures. The first check mechanism
directly calculates an amended soil concentration if the preliminary soil quality guideline fail the test.
Examples of these check mechanisms are the groundwater check (Section 5.3.2) and the infiltration of
volatile contaminants into indoor air check (Section 5.3.4). The SEQCCS employed probabilistic
analysis in determining input parameters for these models.
The second type of check mechanism uses Management Adjustment Factors (MAF). Modelling
procedures are used to estimate the effect of a soil concentration (e.g., PSQG HH ) on a model result.
This result is then compared as a ratio to the original soil concentration. This ratio is used as the
Management Adjustment Factor (MAF), and is applied to the PSQG HH . Examples of this second
check mechanism are the off-site migration of contaminants (Section 5.3.5) and the contamination of
backyard produce (Section 5.3.3).
5.3.2 Evaluation of Derived Guidelines Relative to Guidelines for Canadian Drinking
Water Quality
5.3.2.1 General. Soils are hydrologically linked to groundwater systems. Soil contamination can and
does lead to groundwater contamination, which may be technically, economically, or otherwise difficult
or impossible to remediate. Thus, soil quality guidelines must be designed to prevent unacceptable
transfers of contaminants to groundwater systems. A prudent assumption is that an aquifer underlying a
remediated site may be a drinking water source for humans. This assumption was incorporated into the
development of soil guidelines in the U.S. (e.g., Barkach et al., 1990; Henning, 1992; Commonwealth
of Massachusetts 1993) and The Netherlands (van den Berg and Roels, 1991).
5.3.2.2 Methodology. Different factors govern the mobility of metals and organic contaminants in
soils. These differences require different approaches for managing mobility. An explicit, mechanismbased
generic treatment of groundwater protection is presently proposed only for non-polar and certain
anionic organic contaminants.
Contaminant Metals
Partitioning of metal contaminants between sorbed and dissolved forms in soils is affected by many
factors {e.g., pH, mineralogy, redox potential, abundance of mobile ligands, and clay and organic
matter contents (Sposito 1989)}. Mathematical description of the important interactions among these
factors is complex and involves many site-specific parameters. Partitioning calculations for metals in
soils are generally iterative and require sophisticated computer programs to execute {see for example
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