RD&D-Programme 2004 - SKB

A field study of permafrost and its importance for hydrology and groundwater composition
is being conducted in cooperation with Posiva, Nirex and OPG at a gold mine in Canada, the
Lupin Mine. Besides field investigations, the study includes laboratory experiments /21-23/. The
results can above all be used to show how permafrost can affect the groundwater composition.
Programme
Possible depth and extent of permafrost is planned to be studied with the aid of a numerical
model developed at Helsinki University /21-24/. The purpose of the study is to survey to what
extent permafrost and frozen ground can be expected to occur on the two sites being investigated
by SKB. The study consists of two parts. In the first part, the factors that can affect the
evolution of permafrost will be identified. Examples of such factors are: topography, soil layers
(materials, depth), watercourses (depth, extent, flow and salinity), groundwater composition
(salinity), groundwater flow, heat flow (surface, geothermal) and temperature climate including
annual variations. In the second part, permafrost on the two candidate sites will be studied in
the light of obtained results. Important site-specific parameters will be included in these studies.
They will also analyze how the heat from the deposited fuel can influence the evolution of
Permafrost.
The occurrence of periglacial permafrost will be analyzed to begin with, but subglacial permafrost
will also be studied. Information from the aforementioned ice sheet project will comprise
important input data for the latter analyses. Results of simulations of permafrost will be used in
geohydrological and geochemical analyses.
21.3 Temperate/boreal domain
A temperate/boreal climate domain prevails in all of Sweden today, with the exception of parts
of the Caledonide mountains. Today’s variations in the north-south direction, from northernmost
Sweden down to Central Europe, are judged to cover the full amplitude of the variation that
could possibly occur in the country and this climate domain, even in a long-term perspective.
The process judged to have the greatest importance for conditions in the deep repository in this
climate domain is shoreline displacement. The consequences of shoreline displacement are
described schematically in Figure 21-5. The position of the shoreline affects the hydrological
boundary conditions for the deep repository. The figure illustrates what happens in connection
with regression, i.e. when a water-covered area becomes dry land. The course of events is
reversed in the case of transgression, i.e. when water covers the land.
(m)
20
10
0
−10
−20
~100
Brackish water
(m)
20
10
0
−10
−20
~100
Fresh water
Brackish water
Fresh water
Brackish water
~1,000
Very saline water
~1,000
Very saline water
0 5 10 (km) 0
5
10 (km)
Flows are density-driven.
The groundwater table follows the topography.
Figure 21-5. Schematic illustration showing variations of hydrology and salinity in connection
with regression on a hypothetical site on the present-day coast of the Baltic Sea.
RD&D-Programme 2004 299