For the Canadian Arctic, most areas of contamination outside of commu- nities or industrial activity sites are defined as parkland (Table 1.3). The majority of Arctic soils are coarse-grained in that the median grain size is greater than
75 μm. Soils are generally thin, particularly if permafrost is considered to be
the lower boundary layer. In the context of the guidelines, the subsurface soil
category applies if contamination is <1.5 m deep. Therefore, for most remote
Canadian Arctic sites applications contamination is of the surface soil. The most common terrestrial spills in Canada are diesel range fuels. Therefore, when using
Table 1.3 a level of 150 mg kg−1 would apply to most situations as the lowest
default guideline or trigger value. If the measured level exceeds the trigger value, there is then an option to use Tier 2 (Table 1.4) or Tier 3 risk assessment derived criteria.
Table 1.4 Detailed examination of CCME Tier 2 guidelines for F2 (C10-C16) (∼diesel range
fuel). Discussed further in the Nunavut case study (Section 1.3.2). Key issues discussed further in the text are shown in bold. TBD = to be decided
Exposure pathway
Concentration
mg kg−1 Comments Soil ingestion (by
children and animals)
8000 Ingestion by children only likely near communities. Ingestion by animals is limited by seasonal snow cover – but is of concern to indigenous groups. Dermal contact Free product Fencing the site could remove this pathway. Unlikely
to be of concern in remote sites. Vapor inhalation
(indoor)
240 Pathway can be removed at remote sites by
preventing entry into buildings This is problematic where there are heritage issues or prevention of entry cannot be enforced.
Vapor inhalation (indoor, slab on ground)
150 Only relevant where buildings present.
Protection of potable groundwater
1200 Of concern where the contamination is in the watershed of a drinking water source.
Protection of groundwater for aquatic life
150 Highly variable pathway in the Arctic where groundwater is ephemeral and of limited extent. Preventing sheen in surface water is important and distance to water body is the key determinant.
Nutrient cycling TBD No data available to guide or assess impacts.
Ecological soil contact
TBD Vascular plants are scarce in most Arctic sites. Faunal distribution is highly variable, but burrowing animals or insects could be of concern. Produce TBD Not important for Arctic Canada.
Canadian researchers from Queens University considered the application of Tier 2 guidelines for a remote DEW Line site on Resolution Island, Nunavut (Paudyn et al. 2006; Poland et al. 2004). Contamination was measured with mean
concentrations of 2140 mg kg−1 and a maximum of 19 000 mg kg−1, with both
mean and hotspots considerably above the 150 mg kg−1trigger value. The site is
hydraulically active each summer thaw, and a small stream passes through an area of petroleum-contaminated soil adjacent to an imploded fuel tank, although
fuel in water was<1.0 mg l−1 when sampled each year since 2001. Water flows
in the stream 300–400 m before flowing over a cliff top and into the sea. One active water course flows through a pond in the centre of the area. Fauna at this site are very limited; there are no earthworms, and even mosquito larvae are not
numerous in comparison to other Arctic locales. It is not known whether fuel spills have changed the ecology of this area. The various risk factors and exposure pathways in the Tier 2 assessment are summarized in Table 1.4, although only soil ingestion, protection of groundwater for aquatic life, ecological soil contact, and nutrient cycling are applicable for remote sites with no inhabited buildings.
For soil ingestion, the site is remote and ingestion by humans or animals is likely to be minimal. The animals in contact with the soil are polar bears, arc- tic fox, and birds such as guillemots, ptarmigan, raptors, and migratory geese.
Much of the contamination is<10 cm deep and the site is covered in snow for
eight months each year. Thus animals would be in contact with the contami- nated areas for only a short period of time. In any case, very little of the soil
contamination is as high as 8000 mg kg−1 (see Table 1.4).
With respect to the protection of groundwater for aquatic life, groundwater in the conventional sense is essentially absent in this part of the Canadian Arctic. Sea-
sonally unfrozen subsurface water to depths of∼1.5 m is important if there is
a link between the contaminant source and surface water because of the neces- sity to prevent free product or sheen on surface waters. This value is adjustable depending on the distance to a water body and factors such as: soil bulk density, soil moisture content, organic carbon fraction, depth to groundwater, saturated hydraulic conductivity of the underlying aquifer, hydraulic gradient, and dis-
tance to surface water. For instance, the remediation criterion of 150 mg kg−1
can be changed to 360 mg kg−1 if the organic carbon fraction is 0.7% rather
than the default value of 0.5%. The distance to surface water is the most signifi- cant parameter. The default is 10 m, but at 25 m, the calculated criterion is 890
mg kg−1 if all other default values are kept constant. For distances>55 m the
criterion exceeds the soil ingestion value of 8000 mg kg−1.
The ecological soil contact pathway is non-adjustable (450 mg kg−1). For ecologi-
cal soil contact to be important there must be flora and fauna present. At many sites in the Canadian Arctic vascular plants are scarce and mosses and lichens are the only species present. Fauna at many sites may be limited to bacteria and small insects, whereas at other locations larger animals (e.g. lemmings, ground squirrels) could inhabit a limited territory where exposure could be high. The relative importance of these criteria, however, is open to interpretation.
The nutrient cycling pathway currently has ‘‘insufficient data available for Tier 2 modification” and cannot therefore contribute to the Tier 2 adjustment.
Ecological soil contact and nutrient cycling may be excluded at the discretion of the jurisdiction, provided that the contaminated area is found to have ‘‘no adverse effect on the ecosystem.” In some cases, jurisdictions have allowed for the exclusion of soil organisms and related pathways from consideration where ‘‘no productive use of the soil system is anticipated or required” (CCME 2001).
For all sites, the collection of soil samples, the measurement of soil proper- ties, and the determination of various site characteristics can easily be obtained and used to re-calculate remediation criteria quantitatively for a Tier 2 adjust- ment. However, the issue considered by researchers at Queens University con- cerned the qualitative attribution of ‘‘importance,” especially whether the soil ecosystem in the area is important (ecological soil contact pathway), whether nutrient cycling might be significant if it was investigated as part of a Tier 3 investigation, and assigning a degree of significance to localized and tran- sient surface water sheen. In their assessment of the various risk factors, the group also considered much broader factors. Of key importance, trials indi- cated that low-cost bioremediation by landfarming (with tilling and nutrient addition) readily increased biodegradation rates at this site. A full-scale quanti- tative risk assessment was undertaken which calculated a cleanup criterion of
26 860 mg kg−1. In the end, however, a precautionary approach mitigated by
socio-political considerations of perceptions regarding pollution of indigenous land, coupled with access to low-cost bioremediation techniques established a
remediation criterion of 8000 mg kg−1 and the construction of a landfarm in
2003. Actual residual levels are much lower than 8000 mg kg−1 (Paudyn et al.
2006).