RD&D-Programme 2004 - SKB

of the concentrations of the individual solutes are in some cases indicative of specific ongoing
chemical processes.
More knowledge is obtained by statistical processing using multivariate analysis, which results
in a subdivision into different classes. The different classes represent water which has undergone
a certain evolution. By comparing the different classes with each other, their different
evolutionary pathways can be identified regardless of where in the volume they occur. A typical
water is defined for each class. Typical waters comprise the basis for continued calculations
of reactions and mixing ratios. Measurement data for e.g. the ten most important components
can be included in these calculations /19-76/. The calculated mixing proportions and the actual
measured composition comprise the basis for calculating the scope of chemical reactions. It is
then assumed that a discrepancy in the concentration of any of the components is the result of
a chemical reaction that occurs after the water has been mixed. It may be a question of dissolution
or precipitation of different minerals or microbial processes which generate e.g. sulphide,
carbonate, divalent iron etc. The code M3 (Mixing and Mass balance Modelling), which has
been developed with Matlab as a base, is used for this hydrochemical modelling, see section
19.2.11. The reasonableness of the results is checked by alternative modellings, for example
geochemical simulations with the code Phreeqc.
Knowledge of the microbial processes has increased in recent years /19-88/. They have been
found to have a great influence on the hydrogeochemical evolution and thereby on the hydrogeochemical
interpretation.
A constantly recurring question is whether the groundwater samples really represent the
groundwater at the depth where they have been taken. Studies of fracture-filling minerals
can contribute to evaluating the stability and representativeness of the hydrogeochemical
system. The main task of the EU project Equip /19-77/ has been to propose suitable methods
for gathering paleohydrological information, i.e. information from fracture-filling minerals
concerning current and historical water chemistry. The investigations of fracture-filling minerals
that have been done on Äspö indicate a division into three zones, where the zone below a depth
of 800 metres appears to be relatively isolated.
Conclusions in RD&D 2001 and its review
Taken together, the results of specific hydrochemical modellings based on data from Äspö and
Olkiluoto have yielded a picture of what changes in groundwater composition can be expected
in the future /19-98/. The present-day situation is expected to prevail during the coming
1,000-year period. In a 10,000-year perspective, land uplift and possible climate change will
influence today’s situation in a way that can be calculated with available hydrogeological and
hydrochemical models. In a 100,000-year perspective, assumptions concerning then-prevailing
climatic conditions completely determine what situation can be expected. In this time perspective,
it is meaningful to identify which climate situations may cause the greatest changes and
analyze their effects.
Newfound knowledge since RD&D 2001
New data gathered within the site investigation programme do not contradict the mixing pattern
that has emerged from data from other investigated sites in Sweden and Finland. But the number
of chemical analyses available is still too small to allow any definite conclusions to be drawn.
Programme
There are no plans for method development in the field. The methodology is being applied in
the site investigation programme.
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