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Arbeitsbericht NAB 09-13

Reference pore water for the Effingen Member (Standortregion Südjura) for the provisional safety-analysis in the framework of the sectoral plan – interim results (SGT-ZE)

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Two reference pore water compositions are defined for the Effingen Member for the Jura-Südfuss area. One is a "low-salinity" (approximately sea water salinity) composition relevant for the upper and lower part of the Effingen Member towards the upper and lower bounding aquifers, and that is reasonably constrained by experimental data. A "high-salinity" pore water of twice sea water chlorinity is proposed as upper bound for the central part of the Effingen Member. Except for chlorinity and possibly Na concentrations, this composition is very poorly constrained, including sulphate and Ca concentrations, as well as pH and alkalinity. The compositions are listed in Table 7-8 and Table 8-1.

To further constrain the compositional uncertainty, variants with high sulphate concentration or with a higher partial pressure of CO2 (lower pH) are also provided, as well as a high-chloridehighsulphate combination (Table 9-1). Also, a lower-saline pore water is specified to reflect the uncertainty towards larger Cl-accessible porosity (Table 9-1). Full speciation details for these reference pore waters and variants are provided in Appendix 1-6.

The main uncertainties relate to the poorly constrained anion-accessible porosity (at least as low or lower than Opalinus Clay) and the Ca-sulphate-carbonate system (including pH, alkalinity and PCO2). This is largely rooted in the uncertainty to interpret laboratory data, and the inability to measure the composition of the exchangeable cations in borehole samples due to interference with mineral-water reactions during extraction procedures. Specifically, sulphate concentrations are poorly constrained and contradictory between experimental methods.

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