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HYH-07 Groundwater flow and water?rock interaction in compact fractured rocks: Storage of nuclear waste, field evidence and mathematical models - Part 1
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The hydrogeochemical modeling approach used within the Swedish site investigation programme
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Marcus Laaksoharju, Geopoint AB (Sweden)
John Smellie, Conterra (Sweden)
Eva-Lena Tullborg, Terralogica (Sweden)
Maria Gimeno, University of Zaragoza (Spain)
Javier Gomez, University of Zaragoza (Spain)
Luis Auque, University of Zaragoza (Spain)
Jorge Molinero, Amphos (Spain)
Ioana Gurban, 3DTerra (Canada)
Lotta Hallbeck, Micro Analytics (Sweden)
Gunnar Buckau, FZK-INE (Germany)
Mel Gascoyne, GGP (Canada)
Bill Wallin, Geokema (Sweden)
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Site studies for SKB's programme of deep geological disposal of nuclear fuel waste currently involves the investigation of two locations, Forsmark and Laxemar-Simpevarp, situated on the eastern coast of Sweden, to determine their geological, hydrogeochemical and hydrogeological characteristics. Present hydrogeochemical modelling employs hydrogeochemical methods such as conceptual postglacial modelling, explorative analysis, mathematical modelling (e.g. mass balance and mixing modelling) and construction of site descriptive models using a broad spectrum of hydrochemical data.
To various degrees, the sampled groundwater compositions reflect processes relating to ancient through to modern water/rock interactions and mixing. The major conclusion is that changes from glacial isostasy and, hence, hydrogeology seems to have a major influence on the groundwater chemistry. These complex data require a multidisciplinary approach to their interpretation. The results of the detailed hydrogeochemical modelling methodology are used to produce a hydrogeochemical site descriptive model (SDM) used, for example, in hydrogeological, transport and safety assessment modelling. The hydrogeochemical SDM should represent a site-scale hydrogeochemical interpretation that is fully integrated with the corresponding final site descriptive versions of the geological and hydrogeological models. This final hydrogeochemical model version should clearly show the following:
a) the major lithological and structural units comprising the site;
b) knowledge of the major groundwater flow directions from hydrogeological modelling
c) the relationship of chemistry (i.e. mixing of end members; chemical reactions etc.) to these major hydraulically conducting pathways;
d) a clear indication of the groundwater types representative of the main hydraulic rock mass units characterised by fractures (fracture zones) of lower transmissivities;
e) an indication of the chemistry of the rock matrix pore space fluid/groundwater.
The use of independent modelling approaches such as explorative analysis and mathematical modelling provides the possibility to compare the outcome of the different models and to use discrepancies between models to guide further modelling efforts. The use of independent and new modelling approaches, such as evaluation and modelling of the pore water chemistry and detailed hydrogeochemical and coupled modelling, has considerably facilitated the understanding of the complex groundwater system at these Swedish sites.
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