Physical and Chemical Factors Affecting
Contaminant Hydrology in Cold Environments
STEVEN A. GRANT
Definition of cold regions
Lexically, the adjective "cold" refers to an environment in which the ambient tempera-
ture is noticeably below body temperature. A cold region is one in which lower tempera-
tures have significant effects on the natural environment or human activities. While moder-
ate temperatures may be perceived as "cold," cold regions have been typically defined by
the intervals in which ambient temperatures are below the melting temperature of water,
because it is at these temperatures that the effects of cold temperatures are most pronounced.
Among the criteria that have been used to delineate cold regions are (Bates and Bilello
1. Air temperatures below 0C or 18C (32F and 0F, respectively) that had a 50% like-
lihood of being observed annually
2. Mean annual snow depth
3. Ice cover on navigable rivers
4. Isolines based on permanence, depth, and continuity of frozen ground.
Traditionally, the maps made from plotting isograms based on these criteria delineate
the changes in human activities due to cold. For example, isograms based on frozen ground
delineate changes in the construction requirements for building footings. Isograms based
on ice cover speak to the navigability of the waters during some portion of the year.
This report discusses how cold temperatures affect contaminant-transport modeling;
cold regions should be delineated by the cold-regions phenomena necessary to make the
model a valid representation of the pertinent chemical, physical, and microbiological pro-
cesses that determine the fate of contaminants in the environment. Cold temperatures af-
fect the physics of contaminant transport by freezing the water in the ground (sometimes to
great depths) and by blanketing the ground (seasonally or permanently) with snow. Since
no maps have been drawn delineating the cold-regions effects on contaminant hydrology,
the natural delineations would be those for snow covers and extents of ground freezing.
Extent of cold regions
In comparing the hydrologic systems of cold regions with those of warmer areas, two
factors distinguish the former systems:
1. Some of the annual precipitation occurs as snow, which completes its role in the hy-
drologic cycle during a comparatively brief period as snowmelt.
2. The ground freezes to some depth. Ground freezing reduces the soil's permeability and
its water-storage capacity. Accordingly, ground freezing dramatically decreases the
soil's infiltration rate and just as dramatically increases run-off from the soil of water
from rain and snowmelt.