Local- and Repository-Scale Hydrodynamic Modeling for Geoscientific Characterization of a Candidate ILW/HLW Repository S

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/RFDODQG5HSRVLWRU\6FDOH+\GURG\QDPLF0RGHOLQJIRU*HRVFLHQWLILF&KDUDFWHUL]DWLRQRI D&DQGLGDWH,/:+/:5HSRVLWRU\6LWHLQ1RUWKHUQ6ZLW]HUODQG Ulrich Kuhlmann1, Paul Marschall2 1 TK Consult AG, CH-8050 Zürich, Switzerland 2 National Cooperative for the Disposal of Radioactive Waste, CH-5430 Wettingen, Switzerland 6,7('(6&5,37,21 Recent investigations within the scope of the Swiss program for disposal of high- and intermediate-level radioactive waste have concentrated on the Opalinus Clay located in the =UFKHU:HLQODQG of Northern Switzerland (Figure 1). The candidate host rock, a moderately over-consolidated claystone, is part of a thick sequence of Mesozoic and Tertiary sediments in the Molasse Basin with exceptional isolation properties resulting from its low hydraulic conductivity and homogeneity. The geoscientific information stems from a comprehensive site investigation program, including a 1000 m deep exploratory borehole at the village of Benken and a 3-D seismic survey of the surrounding area [1]. Hegau Bo

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Zürich Legend:

Opalinus Clay investigation area in northeastern Switzerland

Location of profiles shown in next figure Exploratory borehole Benken

3D seismic survey area (Zürcher Weinland)

Border Switzerland – Germany



)LJXUH. Principal tectonic units of Northern Switzerland and adjacent areas. The Opalinus Clay investigation area lies in the tectonically stable Tabular Jura and is predominately covered by the sediments of the Molasse Basin. Also shown is the 3D seismic investigation area in the Zürcher Weinland and the location of the borehole at Benken.

1

Depth [m]

Hydraulic Head

LithoLog

Lithostratigraphy

Hydraulic Conductivity [m s -1]

[m asl] 404 m 500

10 -13

700

10 -11

10 -9

10 -7

Peat and Pleistocene lacustrine deposits 68.0

Till

Lower Freshwater Molasse

199.0

Bohnerz Formation (pisolitic iron ores)

Quaderkalk/ Massenkalk

M3

M3

Mittlere Malmmergel Wohlgeschichtete Kalke to Glaukonit-Sandmergel

M2

538.8 Murchisonae Beds

M4

M4

451.2 Anceps Oolite to Wedelsandstein Formation

M2 406

MD1

MD1

D2

D2

342

O4

O4 O5

Opalinus Clay

? O6

652.0 692.3

Jurensis Marls to Psiloceras Beds

O5 O6

O7 ?

L1

O7 L1

K1

Rhät to Gipskeuper

K1

465 K2

K2

?

811.4

Lettenkohle Trigonodus Dolomite

MK2 406 MK1

MK2

MK1

Hauptmuschelkalk Anhydrite Group (with rock salt)

975.6 983.3 1007.0

Wellengebirge Buntsandstein

B1

B1

Basement (crystalline rocks, older than 300 Ma) Altitude: 404.3 m asl

Long-term monitoring (status: March 2001)

? uncertain (see Nagra 2002a)



)LJXUH. Lithological sequence in the Benken borehole and the measured hydraulic heads and hydraulic conductivities The host rock formation is overlain and underlain by further thicknesses (100 to 150 m) of clay-rich sediments, also with good isolation properties. Above and below these clay-rich formations, the sequenc