Tier 2 Exposure Assessment
A tier 2 Exposure Assessment will involve identifying
and quantifying exposure-source pathways and distribution around the
site. This will include:
- preliminary quantitative descriptions of the mode and timing of
contaminant releases, transport and fate
- integration of exposure values for receptors of concern
- undertaking a site review to determine if all considered pathways for
benchmark criteria are relevant to the site
- identification of specific human health or biological information from literature,
ingestion, inhalation and dermal absorption rates
- measurement of media properties affecting contaminant
mobility and availability
- calculation of contaminant concentration at the
At this point the exposure assessment should be able to provide a
quantitative estimate of exposure for important receptors through important
pathways, including estimates of uncertainty (e.g. confidence or tolerance
Tier 3 Exposure Assessment
Tier 3 Exposure Assessment principally involves the complex modelling of
pathways, transport and fate, to determine:
- present and future transport
- transformation of contaminants (dilution,
- environmental partitioning between media and into
biota or people.
The model should be integrated with the other components of the
RA and will
involve the collection of further field data to refine and calibrate the model
through iterations as required.
Field data may include receptor ingestion,
inhalation and absorption rates using food, air and water sampling to provide a
specific exposure assessment for each human or biotic component.
At this point the
analysis of potential receptor body tissues and fluids may be appropriate. In
addition, the key physical/chemical properties that determine a contaminants
fate, as outlined in Section 4.3.1 of Environment Canadas ERA Framework
(1994), should be determined at this stage.
The model should characterise existing exposures and predict future exposures
under each remediation option. A comprehensive uncertainty analysis and estimate should also be undertaken.
Finally, the default assumptions of the benchmark criteria
should be modified appropriately to calculate a modified criteria specific to