Geological and geohydrological characterization of the Boom Clay and its overburden OPERA-PU-TNO411 Radioactive substances and ionizing radiation are used in medicine, industry, agriculture, research, education and electricity production. This generates radioactive waste. In the Netherlands, this waste is collected, treated and stored by COVRA (Centrale Organisatie Voor Radioactief Afval). After interim storage for a period of at least 100 years radioactive waste is intended for disposal. There is a world-wide scientific and technical consensus that geological disposal represents the safest long-term option for radioactive waste. Geological disposal is emplacement of radioactive waste in deep underground formations. The goal of geological disposal is long-term isolation of radioactive waste from our living environment in order to avoid exposure of future generations to ionising radiation from the waste. OPERA (OnderzoeksProgramma Eindberging Radioactief Afval) is the Dutch research programme on geological disposal of radioactive waste. Within OPERA, researchers of different organisations in different areas of expertise will cooperate on the initial, conditional Safety Cases for the host rocks Boom Clay and Zechstein rock salt. As the radioactive waste disposal process in the Netherlands is at an early, conceptual phase and the previous research programme has ended more than a decade ago, in OPERA a first preliminary or initial safety case will be developed to structure the research necessary for the eventual development of a repository in the Netherlands. The safety case is conditional since only the long-term safety of a generic repository will be assessed. OPERA is financed by the Dutch Ministry of Economic Affairs, Agriculture and Innovation and the public limited liability company Electriciteits- Produktiemaatschappij Zuid-Nederland (EPZ) and coordinated by COVRA. Further details on OPERA and its outcomes can be accessed at www.covra.nl. This report concerns a study conducted in the framework of OPERA. The conclusions and viewpoints presented in the report are those of the author(s). COVRA may draw modified conclusions, based on additional literature sources and expert opinions. A .pdf version of this document can be downloaded from www.covra.nl This report has been reviewed by: N. Vandenberghe (KU Leuven, Belgium) M.D.C. De Craen (SCK·CEN, Belgium) J. Grupa (NRG, Netherlands) OPERA-PU-TNO411 Title: Geological and geohydrological characterization of the Boom Clay and its overburden Authors: G.-J. Vis & J.M. Verweij Date of publication: March 2014 Keywords: Rupel Clay Member, depth, thickness, lithology, permeability OPERA-PU-TNO411 Page 2 of 86 Contents Summary ..................................................................................................1 Samenvatting .............................................................................................1 1. Introduction .........................................................................................2 1.1. Background ....................................................................................2 1.2. Objectives ......................................................................................2 1.3. Realization .....................................................................................2 1.4. Data quality and limitations of the work ..................................................4 1.5. What is the Boom Clay? ......................................................................7 1.5.1. Rupel Formation (NMRFC) ..............................................................7 1.5.2. Underlying and overlying deposits ....................................................9 2. Methods and assumptions ....................................................................... 12 2.1. Rupel Clay Member maps .................................................................. 12 2.1.1. Depth maps ............................................................................. 12 2.1.2. Thickness map ......................................................................... 14 2.1.3. Map accuracy and quality control ................................................... 14 2.2. Grain-size data .............................................................................. 20 2.2.1. Grain-size analyses .................................................................... 20 2.2.2. Uncertainties ........................................................................... 21 2.3. Well-log correlation ........................................................................ 22 2.4. Biostratigraphy .............................................................................. 22 2.5. Geohydrology ................................................................................ 22 2.5.1. Hydrogeological setting ............................................................... 22 2.5.2. Hydrodynamic setting ................................................................. 23 2.5.3. Porosity and permeability Rupel Clay Member .................................... 23 3. Results ............................................................................................. 27 3.1. Regional-scale geometry and overburden of the Rupel Clay Member ............... 27 3.1.1. Top and base ........................................................................... 27 3.1.2. Difference with previous CORA study ............................................... 27 3.1.3. Thickness ............................................................................... 27 3.1.4. Deeper than 400 m, thicker than 100 m ........................................... 28 3.2. Lithological characterization of the Rupel Clay Member .............................. 28 3.2.1. Lithological variability ................................................................ 28 3.2.2. Enhanced conceptual lithofacies model ............................................ 28 3.2.3. Focus on areas where deeper than 400 m, thicker than 100 m ................. 35 3.3. Regional scale geohydrological setting of the Rupel Clay Member .................. 39 3.3.1. Hydrodynamic setting ................................................................. 39 3.3.2. Hydrogeological setting ............................................................... 45 3.4. Geohydrological characterization of the Rupel Clay Member ........................ 49 4. Discussion .......................................................................................... 51 4.1. Stratigraphic interpretation ............................................................... 51 4.2. Geometry, distribution and lithology of focus areas ................................... 51 4.2.1. Roer Valley Graben .................................................................... 51 4.2.2. Zuiderzee Low ......................................................................... 56 4.2.3. North Netherlands ..................................................................... 56 4.2.4. Remaining onshore Netherlands ..................................................... 58 4.3. Integrity ...................................................................................... 58 4.3.1. Faults and seismicity .................................................................. 58 4.3.2. Salt domes .............................................................................. 59 4.3.3. Calcareous septaria ................................................................... 59 4.3.4. Sedimentation and bioturbation..................................................... 62 4.3.5. Boreholes ............................................................................... 62 4.4. Organic matter and hydrocarbons ........................................................ 62 4.4.1. Organic layers .......................................................................... 62 4.4.2. Hydrocarbons ........................................................................... 63 4.5. Geohydrology of focus areas .............................................................. 63 4.6. Data quality and limitations of the work ................................................ 64 5. Conclusions and knowledge gaps ............................................................... 65 5.1. Conclusions .................................................................................. 65 5.2. Knowledge gaps and recommendations for future work .............................. 66 References .............................................................................................. 68 Appendix 1 .............................................................................................. 74 Appendix 2 .............................................................................................. 77 Appendix 3 .............................................................................................. 80 Appendix 4 .............................................................................................. 84 OPERA-PU-TNO411 Page 4 of 86 Summary This desk-study presents the geological and geohydrological characteristics of a clay layer in the Dutch subsurface (Boom Clay, officially Rupel Clay Member). New depth and thickness maps show that the Rupel Clay Member is present in nearly the whole Dutch subsurface, up to a depth of ~1500 m. The thickness varies around a mean of 65 m. In the proposed disposal concept for OPERA, the repository depth is 500 meter with a clay thickness of 100 meter. Therefore for this study, a clay layer deeper