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

Appendix D
Derivation of Dilution Factor for Recharge Water in
Groundwater
1.0 Guiding Assumptions and Rationale
Equilibrium partitioning concepts predict the concentration of a non-polar organic chemical in water
draining from a soil at a contaminated site (See Appendix C). Estimating the effect of this recharge on
groundwater quality requires that dilution be considered. Several assumptions are made to allow a
generic treatment of the dilution problem:
1. Site is underlain by an unconfined aquifer.
Rationale: This is a fairly common arrangement and is among the most sensitive. Other
stratigraphic arrangements that commonly occur should also be protected if
guidelines are developed under the unconfined aquifer assumption.
2. Entire site has been remediated to the preliminary soil quality guideline concentration.
Rationale: Residual contamination may be found in hotspots or throughout a site. However, a
generic approach to groundwater protection must address the more severe
condition.
3. Groundwater for drinking is or could be withdrawn from a well located along the down gradient
boundary of the remediated site.
Rationale: A general objective for remediation guidelines is that they will not result in off-site
movement beyond relevant generic guidelines. This is compatible with regulations in
most Canadian jurisdictions.
4. Compliance with objectives set under assumption three is required now and in the future.
Rationale: If groundwater is to be protected for drinking, a generic remediation exercise must be
effective at the time of completion — i.e., management of contamination plumes that
would render the water unpotable for any period of time would normally be
conducted under risk assessment procedures.
5. Soil organic matter in the zone of contamination is the principal attenuating factor.
Rationale: Soil conditions presented in the protocol ensure that in the zone of contamination
organic matter should prevail over other sorbent properties. It is also assumed that
significant sinks for contamination do not exist between the aquifer and the
contaminated zone. If significant attenuation is expected by virtue of buried,
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