Geothermal
Scanning for Groundwater Flow
Geothermal
methods to classify the subsurface of Germany with
respect to the ability for nuclear waste deposits.
Joint
research project with RWTH Aachen University and
LIAG Hannover funded by the German Federal
Environment Ministry (BMU) and the German Federal
Office for Radiation Protection (BfS)
The
subsurface temperature increases with depth with
an average gradient of 30°C per kilometre.
Locally, strong deviations from this average value
can occur, resulting from following factors:
Ground
water flow: Water has a high heat capacity.
Even small ground water flows (~ mm/a) can
transport great quantities of stored heat.
Groundwater flow therefore might result in a
strong deformation of the temperature field. The
strongest effects are observed in the surrounding
of thermal springs or gushing springs, which
transport hot water to the earth's surface.
Paleoclimate:
During history of earth the average surface
temperature strongly changed. These variations
produce temperature signals which are slowly
transported with time from earth's surface to
greater depth. The temperature increase after the
end of the last ice age is still measurable in
boreholes of 1-2 km depth. Later events, such as
the little temperature drop at about the 15th
century or the warming within the last century are
detectable in boreholes of a few 100 m depth.
Subsurface
heterogeneity: The thermal properties of rocks
strongly change depending on the mineralogical
composition and the rock porosity. Thus the heat
flow, having normally a vertical direction, is
refracted at bed boundaries. To separate of
effects of ground water flow and paleoclimate from
the temperature field needs a good knowledge of
the thermal properties of the formations as well
as of their geometry.
By
planning a conventional or a nuclear waste deposit,
one of the main targets is to protect the
environment from pollution. Pollutants can easily
be transported be streaming groundwater. Therefore,
main restrictions for nuclear waste deposits are
areas with ground water flow. The objective of
this study was to investigate temperature profiles
from boreholes in Germany and to the separate all
factors of subsurface heterogeneities and
paleoclimate from the temperature logs in order to
detect and quantify of groundwater flow on a
regional scale.
Instituts
für Höchstleistungsrechnen,
RWTH Aachen
GGA-Instituts
Hannover
Bundesministerium
für Umwelt, Naturschutz und Reaktorsicherheit
(BMU)
Bundesamt
für Strahlenschutz (BfS)
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