Figure 2. Cold-regions boundaries as determined by frozen
ground. (From Bates and Bilello 1966.)
Alaska. Discontinuous permafrost or permafrost is found under most of the land surface of
that state.
Permafrost. Areas of permafrost, in which no seasonally thawed land occurs, are found in
the northernmost parts of Alaska.
Importance to contaminant-transport modeling
A model is a mathematical expression of the developer's understanding of the system
being simulated. Accordingly, contaminant-transport models valid for cold regions differ
from those appropriate for warmer climates because the system being described is conspic-
uously different. The following modeling aspects differentiate contaminant-transport
models valid in cold regions:
1. Much of what is understood about the hydrology of cold regions is qualitative. Be-
cause there have been comparatively few studies in cold regions, the physical, chem-
ical, and biological processes that determine the contaminant hydrology of cold re-
gions are not completely understood. This lack of quantitative knowledge hinders
the development of physically based contaminant-transport models valid for cold
regions. Much basic research is needed to support the development of simulation
models that are appropriate for these regions.
2. The energy flow and aqueous-solution phase transitions must be included explicitly
in the development of solute transport models.
3. In unfrozen porous media, liquid water moves largely in response to hydrostatic gra-
dients. In frozen porous media, liquid water movement in response to osmotic or
thermal gradients may be dominant.
4. The physical chemistry of electrolyte solutions in natural porous media above freez-
ing temperatures is well understood, and models describing them are generally
available. For systems below 0C, there are comparatively few physical chemical data
(aside from freezing-point depression determinations) for even simple electrolyte so-
lutions.
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