Geo-Scientific Evidence to Support the I1 Isolation Function Related to Human Actions, As Part of the Safety and Feasibility Case 1 (SFC1)

EXTERNAL REPORT SCK•CEN-ER-186 12/MDC/P-39

Geo-scientific evidence to support the I1 isolation function related to human actions, as part of the Safety and Feasibility Case 1 (SFC1)

Mieke De Craen, Koen Beerten, Matej Gedeon and Katrijn Vandersteen

SCK•CEN Contract: CO-90-08-2214-00 NIRAS/ONDRAF contract: CCHO 2009-0940000 Research Plan Geosynthesis

July, 2012

SCK•CEN RDD & PAS Boeretang 200 BE-2400 Mol Belgium

EXTERNAL REPORT OF THE BELGIAN NUCLEAR RESEARCH CENTRE SCK•CEN-ER-186 12/MDC/P-39

Geo-scientific evidence to support the I1 isolation function related to human actions, as part of the Safety and Feasibility Case 1 (SFC1)

Mieke De Craen, Koen Beerten, Matej Gedeon and Katrijn Vandersteen

SCK•CEN Contract: CO-90-08-2214-00 NIRAS/ONDRAF contract: CCHO 2009-0940000 Research Plan Geosynthesis

July, 2012 Status: Unclassified ISSN 1782-2335

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Table of Contents

1 Introduction ...... 7 2 Safety functions and the development of safety statements ...... 10 3 The safety function 'Isolation' (I) ...... 11 4 Geo-scientific evidence to support the safety statement on 'reducing the likelihood of inadvertent human intrusion and human actions, and its possible consequences' (I1) ..... 12 4.1 The thickness of the overlying rock mass ...... 14 4.1.1 Current thickness of the rock mass overlying the Boom Clay ...... 14 4.1.2 Long-term evolution of the thickness of the overlying rock mass ...... 16 4.1.3 Main conclusions on the thickness of the overlying rock mass ...... 18 4.2 Natural resources in the Campine and associated human actions...... 19 4.2.1 Natural water resources ...... 20 4.2.2 Natural mineral resources ...... 26 4.2.3 Natural energy resources ...... 31 4.2.4 Use of deep geological layers ...... 42 4.2.5 Concessions and conflict of use ...... 50 4.2.6 Main conclusions on the natural resources in the Campine ...... 51 4.3 Consequences of human actions in the Campine ...... 53 4.3.1 Possible consequences of exploitation of natural water resources ...... 53 4.3.2 Possible consequences of exploitation of natural mineral resources ...... 56 4.3.3 Possible consequences of exploration and exploitation of natural energy resources ...... 56 4.3.4 Possible consequences of exploration and use of deep geological layers for gas storage ...... 58 4.3.5 Borehole drilling as most important type of inadvertent human intrusion ...... 59 4.3.6 Main conclusions on the possible consequences of human actions in the Campine ...... 68 5 References ...... 69

1 Introduction

The general safety objective of disposal as the final step of radioactive waste management is to protect human health and the environment, now and in the future, without imposing undue burdens on future generations. The generally adopted strategy for disposal to achieve this objective is to concentrate and confine the waste and to isolate it from man and the environment (IAEA, 2006). A safety case is a collection of arguments and evidence that demonstrates that a particular facility, part of a facility or an activity on a site is safe. Safety assessment is the process of using appropriate methods to analyse systematically the risk associated with the facility, and the ability of the site and the design of the facility to meet safety requirements (IAEA, 2011). The safety assessment methodology for geological disposal of radioactive waste is implemented through different safety functions (ONDRAF/NIRAS, 2009 a-b-c), i.e. functions that the disposal system should fulfil to achieve its general safety objective of providing long- term safety through concentration and confinement strategy. ONDRAF/NIRAS considers three main safety functions: engineered containment (C) preventing the dispersion of contaminants from the waste form as long as required, delay and attenuation of the releases (R) in order to retain the contaminants within the disposal system for as long as required, and isolation (I) of the waste from humans and the biosphere for as long as required. These three main safety functions are furthermore divided in several sub-functions, and for each of them, a set of safety statements is developed.

The isolation function I is determined by the geological environment, the occurrence of natural resources and associated possibility of human intrusions, the long-term geodynamic evolution of the geological system, and climate evolution. The sub-function I1 “Reduction of the likelihood of inadvertent human intrusion and of its possible consequences” is related to human actions, while the sub-function I2 “Ensuring stable conditions for the disposed waste and the system components” relies on the geological environment and its long-term evolution. In this report, we will focus on the geoscientific evidence to support the safety sub-function 'I1', i.e. 'reducing the likelihood of inadvertent human intrusion and of its possible consequences'.

There are many national and international references which describe the study of human impacts on repositories of radioactive waste (Bailey et al., 2011). The terms used for those impacts vary widely, e.g. human events, intrusion events, future human actions, human intrusion, inadvertent actions, etc. Some of them are similar and some are slightly different in their meaning. Unfortunately, the IAEA glossary does not provide definitions for human action, human intrusion, inadvertent action or other related terms (IAEA, 2007). Therefore, Baileys et al. (2011) gave an overview of several definitions. Based on these, the following definitions are used here: ‘Human actions’ is a general term that encompasses those actions that can influence the surface as well as the underground environment of the disposal system, e.g. alteration of the groundwater flow regime (Baileys et al., 2011) and those that can potentially alter the barriers or/and safety functions of the disposal system .’Human intrusion’ is a special case of human actions treated separately in safety assessment (ICRP 1998, NEA, 1995). A human intrusion affects the integrity of the disposal facility with direct disturbance and can potentially give 7

rise to radiological consequences (IAEA, 2011). A typical example is the drilling of a borehole through the waste emplacement area. By definition, an intrusion event bypasses the isolation function, and consequently could jeopardise other passive safety functions. In some extreme cases, it could even bring the waste in direct contact with the intruder and the nearby population if the waste material is brought to the surface. Only ‘inadvertent’ human intrusions are considered in geological safety assessment where either the repository or its barrier system are accidentally penetrated or their performance impaired, because the repository location is unknown, its purpose forgotten, or the consequences of the actions are unknown (NEA, 1995; ICRP, 1998). Deliberate intrusion into a repository are of the responsibility of the intruder and it is inherently impossible to limit their probability or their consequences. The elevated exposures from human intrusion is an inescapable consequence of the decision to concentrate waste in a discrete disposal facility rather than diluting or dispersing it (ICRP, 1998). The Boom Clay at the Mol-site is considered as the reference host formation and site for R&D related to a deep geological repository. The geological environment is considered in the entire Campine area, located in the provinces of Antwerp and Limburg, in NE-Belgium (i.e. Kempen, Figure 1). The occurrence of the Boom Clay (outcrop and subcrop) in NE-Belgium is shown in Figure 2. This study is part of the geosynthesis project which aims at compiling and integrating all geoscientific knowledge on the Boom Clay and its geological environment, and to effectively use this geoscientific information to support the Safety and Feasibility Case 1 (SFC1) for a deep geological repository designed for radioactive waste disposal. The geoscientific understanding of long-term geosphere barrier performance over time scales relevant to repository safety, by the assembly and synthesis of multi-disciplinary data, and by using multiple lines of evidence is therefore a major issue.

Kempen

Figure 1: Location of the reference site Mol in the Campine area in NE-Belgium (froom Google Earth, 2010)

Figure 2: Outcrop and subcrop of the Boom Clay in NE-Belgium, also showing depth to base relative to sea level and thickness (from SAFIR 2, ONDRAF/NIRAS, 2001). 9

2 Safety functions and the development of safety statements

The ONDRAF/NIRAS long-term safety strategy for the disposal of high level waste (ONDRAF/NIRAS, 2009a) is implemented through different safety functions, i.e. functions that the disposal system should fulfil to achieve its general safety objective of providing long- term safety through concentration and confinement strategy. ONDRAF/NIRAS considers three safety functions (De Preter, 2007): 1. Isolation (I) of the waste from humans and the biosphere for as long as required, by preventing direct access to the waste and by protecting the disposal system from the potentially detrimental processes occurring in the environment of the disposal system. 2. Delay and attenuation of the releases (R) in order to retain the contaminants for as long as required within the disposal system. 3. Engineered containment (C) consists of preventing as long as required the dispersion of contaminants from the waste forms and the escape of gaseous substances, by using one or several appropriate impermeable barriers. For each safety function, a set of safety statements is developed. Safety statements are developed in a top-down manner, starting from the most general (highest-level) statements and progressing to increasingly specific (lower-level) statements. Lower-level statements are generally statements about properties that the system should have, in order to satisfy higher- level statements. Safety statements generally begin as hypotheses (e.g. statements of the type "the repository and/or its components should ..." ), which may initially be tentative, and develop into increasingly well-substantiated claims (statements of the type "the repository and/or its components will or do ...") as the design is developed and optimised, and the evidence, arguments and analyses that support a statement are acquired or progressively developed. In order to guide these developments, the support that is judged to be available and required for the various statements is evaluated. In order to assess general, high-level statements regarding safety, more specific, lower-level statements that underpin them must first be evaluated. Thus the assessment of statements tends to be carried out bottom-up. The top level statements correspond with the safety functions a repository has to fulfil, namely to isolate the waste (I), to contain the waste during the thermal phase for heat-emitting waste (C), and to delay and attenuate the releases of radionuclides to the environment (R).

Note that the long-term safety assessment methodology for the geological disposal of radioactive waste (ONDRAF/NIRAS, 2009 b) is an ongoing process. The methodology will be further developed and refined to take into account the lessons learnt from its application and new developments. It is a 'living document' that is updated as necessary until the end of the SFC program. The geo-scientific evidence underbuilding the safety statements considered in this report may serve as a sound base to support the SFC1, regardless how the safety statements are formulated or structured within the safety statement tree in the future.

3 The safety function 'Isolation' (I)

The safety function 'Isolation' (I) considers isolation of the waste from humans and the biosphere for as long as required, by preventing direct access to the waste and by protecting the disposal system from potentially detrimental processes occurring in tthe environment of the disposal system (De Preter, 2007; ONDRAF/NIRAS, 2009 a-b-c). The isolation function is sub-divided in two sub-functions (Figure 3): • Reduction of the likelihood of inadvertent human intrusion and of its possible consequences (I1). This sub-function consists of limiting the likelihood of inadvertent human intrusion and, in case such intrusion does occur, of limiting its possible consequences in terms of radiological and chemical impact on humans and the environment. It should be noted thaat individual inadvertent intruderss cannot necessarily be protected or do not necessarily have to be protected to the same extent as the general public. So the consequences of human intrusion to be addressed arre those on people living near the disturbed repository annd further away (ICRP, 1998; IAEA, 2006). • Ensuring stable conditions for the disposed waste and the system components (I2). This sub-function consists of protecting the waste and the engineered barrier components of the disposal system from changes and perturbations occurring in the environment of the facility, such as climatic variations (i.e., freeze-thaw phenomena aand drying-wetting cycles), erosion, uplifting, seismic eevents or relatively rapid changes in chemical and physical conditions.

I The disposal system and its geological coverage isolate the waste for as long as required in such a way to minimize the probability and consequences of human intrusion and human actions, and to protect the waste and system components against internal and external geodynamic events and processes.

I1 The disposal system and its geological coverage isolate the waste to reduce thee likelihood and possible consequencees of inadvertent human intrusion and human actions.

I2 The disposal system and its geological coverage isolate the waste to create stable conditions for the disposed waste and the systtem components and to protect against internal and external geodynamic events and processes.

Figure 3: Schematic representation of the safetty function 'Isolation' and its two sub-ffunctions.

4 Geo-scientific evidence to support the safety statement on 'reducing the likelihood of inadvertent human intrusion and human actions, and its possible consequences' (I1)

In this chapter, geo-scientific evidence will be given to support the safety sub-function 'I1', i.e. 'reducing the likelihood of inadvertent human intrusion and human actions, and its possible consequences'. As this safety sub-function 'I1' is directly related to the human actions, the associated safety statements are coded as 'S IH' (Safety statement, Isolation, Human).

The safety statement S IH is currently defined as follows: "The disposal system and its geological coverage isolate the waste to reduce the likelihood of inadvertent human intrusion and human actions, and its possible consequences." It is further divided in lower-level statements considering the location of a repository site (far away from humans, and in a geological environment of limited economic interest), and the resilience of the system against consequences of human actions (see Figure 4).

The structure of this chapter is based on the current overall structure of the safety statements and will consider: • The thickness of the overlying rock mass (chapter 4.1) A future repository should be located deep enough to physically protect the repository from human actions (and vice versa). This means that the overlying rock mass should be sufficiently thick, and should remain sufficiently thick in view of the expected long-term evolution of the area (see De Craen et al., 2012). In preparation of the future siting, the current thickness of the overlying rock mass is discussed in this chapter, as well as the possible reduction of the thickness of the overlying rock mass. This may be due to the long-term natural evolution (mainly uplift and erosion, see De Craen et al., 2012), and/or due to human actions (mainly the exploitation of economically interesting layers at the surface and shallow sub-surface in the Campine). • Natural resources in the Campine and associated human actions (chapter 4.2) A future repository should be located in a geological environment of limited economic interest, to reduce the likelihood of human actions and inadvertent human intrusion in particular. In preparation of the future siting, an overview of the natural resources in the Campine is given, including natural water resources, natural mineral resources, natural energy resources, and some deep geological layers for particular use. For each of these resources, past and current human actions in the Campine (at the surface, shallow sub-surface, or in the deep underground) are discussed, and potential future exploration and exploitation sites are indicated. • Consequences of human actions in the Campine (chapter 4.3) Human activity in the Campine mainly relates to the exploration, exploitation, and use of deep geological layers. The consequences of these actions are evaluated, as they might jeopardise the performance of a future disposal system.

S IH 1.1 The overlying rock mass is (and remains) sufficiently thick to physically protect S IH 1.2.1 Natural water resources the repository from are present all over the Campine human actions, and should therefore be taken into hence significantly account during siting. S IH 1 The location decreasing the of the repository site likelihood of human reduces intrusions. S IH 1.2.2 Natural mineral resources as much as possible in the vicinity of the repository are the likelihood of limited: no exceptional mineral inadvertent resources such as ores are human intrusion present in the underground, and human actions. S IH 1.2 The repository is located clay and sand resources are in a deep geological restricted to the (sub-) surface. environment of limited economic S IH 1.2.3 Natural energy resources interest (except for in deep geological layers groundwater). (fossil fuels, geothermy) are adequately illustrated to be taken into account during siting.

n possible consequences. and human actions, its S IH 1.2.4 Deep geological layers ological the waste coverage isolate of interest for gas storage (natural gas storage, CO2 carbon capture and storage) are adequately illustrated to be taken into account durig siting.

S IH 2.1.1 Human actions considered are: eploration, S IH 2.1 exploitation, and use of Consequences of geological layers human actions do not jeopardise the S IH 2.1.2 Borehole drilling is performance of the S IH The disposal system and its ge system and its S IH The disposal S IH 2 The system considered to be buffers sufficiently system. the most realistic any potential inadvertent human intrusion. consequences of S IH 2.2 In case of inadvertent inadvertent human human actions. intrusion, the resilience of the

to reduce inadvertent the likelihood of human intrusio system is able to maintain its performance.

Figure 4: Schematic representation of the safety statement 'Reducing the likelihood of inadvertent human intrusion and human actions, and its possible consequences ', and its lower-level safety statements. (preliminary version, as the definitions and structure of the safety statements is still in discussion by ONDRAF/NIRAS).

4.1 The thickness of the overlying rock mass

Isolation of the repository system is a key function in the safety strategy of geological disposal of radioactive waste. In order to isolate the waste from human actions, a location has to be found 'sufficiently far away' from any human interest, taking into account current knowledge and practices. A future repository should thus be located in a suitable geological layer which is deep enough to physically protect the repository from human actions (to reduce the possibility of human intrusion). Similarly, the repository should be located deep enough to protect man and biosphere from the waste, and this for a long period of time. In Belgium, geological disposal in Boom Clay has progressively become the reference solution for the long-term management of category B&C wastes (ONDRAF/NIRAS, 1989, 2001, 2009a-b-c, 2011). Boom Clay is present in the Campine underground. With respect to the long-term safety, in particular the isolation function, the overlying rock mass should be sufficiently thick, and should remain sufficiently thick in view of the expected long-term evolution of the area within the next 1 Ma. Information on the depth of Boom Clay and the thickness of the overlying layers is found in general documents on the geology of the area, geological maps, the Databank Ondergrond Vlaanderen, … The long-term geological evolution is described in Beerten (2010) and De Craen et al. (2012).

4.1.1 Current thickness of the rock mass overlying the Boom Clay

Based on the available geological information, the depth of the top of the Boom Clay layer, and hence the thickness of the rock mass covering the Boom Clay, could be determined in the Campine underground. Based on the maps shown in Figure 5 and Figure 6, the following statement can be made:

1. The current thickness of the rock mass overlaying the Boom Clay is about 190 m at the Mol site, and thickening towards the north-northeast. Boom Clay is present in the Campine underground. At present, the top of the Boom Clay is located at a depth of about 190 m below the surface in Mol-Dessel (Mol-1 borehole, Wemaere et al., 2002), deepening towards the north-northeast, and reaching a depth of more than 300 m in the village of Ravels (Figure 5). In terms of ‘thickness of the overlying rock mass’, this corresponds to about 190 m of overburden at the Mol site, and increasing towards the north-northeast to a thickness of more than 300 m. The rock mass overlying Boom Clay mainly consists of Quaternary and Tertiary clays and sands. These clays and sands are exploited all over the Campine as natural resources for the ceramic industry, building industry, glass industry, … Exploitation is currently restricted to the upper few tens of meters, and only slightly reduces the thickness of the rock mass overlying the Boom Clay.

Figure 5: Isohyps map of the top of the Boom Clay relative to TAW, derived from isohyps maps of the base of overlying geological units (Vandersteen et al., in prep., based on data from Vancampenhout et al., 2008).

Figure 6: Isopach map of the thickness of the overlying rock mass of the Boom Clay, derived from the data provided by Vancampenhout et al., 2008 (and the figure above) and Albon (smoothed DTM).

4.1.2 Long-term evolution of the thickness of the overlying rock mass

Based on the available information on the current thickness of the geological layers overlying the Boom Clay, the current human actions, and the expected long-term evolution over the next 1 Ma, the following statements can be made:

1. Future human actions are not expected to significantly reduce the thickness of the rock mass covering the Boom Clay. Several types of human actions may occur in the rock mass covering the Boom Clay and may typically occur at the surface, in the shallow sub-surface or at greater depth. Surface activities typically relate to the exploitation of natural mineral resources in the Campine. Quaternary and Tertiary clays and sands are currently exploited all over the Campine as natural resources for the ceramic industry, building industry, glass industry, … Because of the availability, exploitations of mineral resources in the Campine are restricted to the surface or shallow sub-surface, although clays and sands are present in the Campine underground as well. At present, excavations are done in open pits which are generally a few tens of meters deep (generally about 25 m deep). Excavation down to the depth relevant for geological disposal is currently not existing in the area. Future excavation down to such a depth is not expected to be relevant as large reserves are present at the surface and in the shallow sub-surface, and as it is technically difficult and more expensive (Lie et al., 2011). Hence, the exploitation of these mineral resources in the Campine is not expected to significantly reduce the thickness of the rock mass covering the Boom Clay, and it will therefore not affect the isolation function. The exploitation of mineral resources at the surface and the shallow sub-surface in the Campine is therefore not considered as a relevant human action to be taken into account during siting (see also chapter 4.2.2 on natural mineral resources and 4.3.2 on the consequences of exploitation of natural resources). Shallow underground activities typically relate to geotechnical works and human constructions. These comprise foundations for surface structures, tunnelling, underground facilities for energy storage, or research laboratories, … The Tertiary sands overlying the clay layers are compacted (as clearly shown on the database of deep soundings maintained by Bestuur Geotechniek) and form therefore better foundation zones than the clays, so there is no need to penetrate from the sand into the clay. Foundations for surface structures are thus limited to the shallow sub-surface (<25 m), hence not significantly reducing the thickness of the coverage layers with respect to the safety function isolation. Deep tunnelling is unlikely in the Campine, because of the low urbanisation and the prohibitive depth to the clay. There is no technical reason to dig tunnels in the clay compared to the more shallow overlying sand. A successful example of tunnelling in sand is the HST line Antwerp - Amsterdam, starting from the Antwerp railway station. Human actions in the deeper underground may relate to borehole drilling or mining. Such human actions will not result in the reduction of the rock mass covering the Boom Clay, but the rock mass above Boom Clay (and Boom Clay as well) may be perturbed by boreholes and/or access shafts. For the consequences of borehole drilling, we refer to chapter 4.3.5.

2. Future natural processes, i.e. uplift and associated erosion, might reduce the thickness of the rock mass covering the Boom Clay by a few tens of meters within the next 1 Ma. The long-term geo-dynamic evolution of the Campine area is discussed in Beerten (2010) and summarised in De Craen et al. (2012). In general, it is expected that neo-tectonic movements and climate change are the major driving processes influencing the geomorphological evolution of the Campine. Neo-tectonics movement, in particular uplift and associated erosion processes may cause the removal of material of the Campine surface. Consequently, the thickness of the rock mass overlying Boom Clay may be reduced. A very conservative assumption, considering continuous uplift and erosion, with an uplift rate of 0.8 mm/year (maximal estimated uplift rate; Beerten, 2010), suggests that the top of the Boom Clay layer will reach the surface after about 2 Ma in the future; the repository after about 3 Ma in the future (see Figure 41 in De Craen et al., 2012). Within the considered time frame of 1 Ma, about 80 m of overburden might be removed at the maximum. However, in view of the past evolution, one continuous uplift phase lasting 1 Ma seems unlikely, so that the removal of 80 m of overburden is probably overestimated. Nevertheless, the removal of a few to several tens of meters of overburden is very likely, so that the thickness of the coverage layers will be reduced.

3. The Boom Clay in the Campine area is expected to remain at depth within the next 1 Ma, still covered by a considerable thick rock mass. As mentioned above, several tens of meters of overburden might be eroded in the future, so that the thickness of the coverage layers might be reduced. Nevertheless, it is expected that the Boom Clay in the Campine area will remain at depth, still covered by a considerable thick rock mass (De Craen et al., 2012). Human actions at the long-term are not expected to significantly change compared to today. Sands and clays are present in sufficient amount at the surface and shallow sub-surface. It is expected that there will be no need to exploit this from deeper locations. Hence, removal of overburden will not significantly reduce the thickness of the rock mass (current quarries are generally less than 25 m deep). Also with the combined effect of erosion processes (erosion of several tens of meters, with a maximum of 80 m within the next 1 Ma) and human actions (excavation down to a depth of 25-30 m), it is expected that the Boom Clay in the Campine area will remain at depth, still covered by a considerable thick rock mass.

4.1.3 Main conclusions on the thickness of the overlying rock mass

Boom Clay is present in the Campine underground. At the Mol site, the thickness of the overlying rock mass is about 190 m, and thickens towards the northeast, reaching a maximum of about 300 m in in the northernmost part of Belgium. Both natural processes and human actions may cause the removal of overburden on the long- term and hence reduce the thickness of the overlying rock mass. Natural processes, particularly neo-tectonic movements and climate change, are the major driving processes influencing the geomorphological evolution of the Campine. Future uplift and associated erosion processes in the Campine may reduce the thickness of the overlying rock mass by several tens of meters within the next 1 Ma (and 80 m at the maximum - very conservative assumption). Human actions related to the exploitation of natural mineral resources in the Campine are not expected to significantly reduce the thickness of the overburden. Currently, excavation in the Campine is restricted to the surface and shallow sub-surface (the upper 25 m). Excavations down to a depth relevant for geological disposal is not expected to occur in the future (large availability of mineral resources at the surface, drilling through aquifers, costs for deep excavations, …). In conclusion, it is expected that Boom Clay remains at depth within the next 1 Ma, and that a considerable thick rock mass will still cover Boom Clay in the Campine.

Uncertainties – open issues – knowledge gaps: Human actions at the long-term are not expected to significantly change compared to today, but human actions are unpredictable. On the relevant time scales, the combined effect of erosion processes and future human actions is difficult to predict.

4.2 Natural resources in the Campine and associated human actions

Isolation of the radioactive waste repository system is a key function in the safety strategy of geological disposal of radioactive waste. In order to isolate the waste from human actions, a location has to be found 'sufficiently far away' from known exploitable resources, taking into account current knowledge and practices. A future repository should thus be located in a geological environment of limited human interest, to reduce the likelihood of human actions, and inadvertent human intrusion in particular. A geological environment may be of economic interest because of the presence of natural resources1. In general, natural resources include water resources, mineral resources (ores, metallic minerals such as copper and iron, non-metallic minerals such as salt and gypsum, sediments such as clay and sand, and hard rocks), and energy resources (coal, oil, natural gas, uranium, geothermal). Besides natural resources, the use of deep geological layers for specific purposes may be economically interesting as well, e.g. heat and gas storage in natural geological reservoirs. A variety of natural resources occur in the Campine. Ground water resources are present all over the Campine and should be taken into account. Natural mineral resources such as clays and sands are present and mainly exploited in the (sub-) surface of the Campine. The Boom Clay itself, is also such a mineral resource and is presently extensively exploited in its outcropping zone in the Rupel area. Natural energy resources mainly occur in the deeper geological layers of the Campine underground (typically at a depth of 600-1000 m). Deep geological layers may furthermore be used for natural gas storage (typically at a depth < 600 m). Deep boreholes are generally well-prepared and preceded by detailed exploratory studies, but may still form a potential risk of human intrusion. In this chapter, an overview is given of the natural resources and geologically/economically interesting layers in the Campine underground. Information on natural resources in the Flanders is found in documents and databases provided by the Geological Survey of Belgium, the Vlaamse Gemeenschap – Dienst Natuurlijke Rijkdommen (ALBON), the Vlaamse Millieumaatschappij (VMM), and the Vlaamse Instelling voor Technologisch Onderzoek (VITO). A general overview of the natural resources in Flanders is given in Gullentops & Wouters (1996). New prospectives regarding geothermy and carbon capture and storage are discussed in Lagrou et al. (2002), Piessens & Dusar (2004), Laenen et al. (2006), Piessens (2011), Piessens et al. (2009, 2011), Dreesen & Laenen (2010), and others.

1 A natural resource is a concentration of naturally occurring solid, liquid or gaseous material in or on the Earth's crust in such form and amount that economic extraction of a commodity from the concentration is currently or potentially feasible (Jackson, 1997). 19

4.2.1 Natural water resources

Water resources are sources of water that are useful or potentially useful tto humans. Uses of water include agricultural, industrial, household, recreational and environmental activities. Natural water resources are widely present in north-eastern Belgium. In the Campine area, the Neogene aquifer system is one of the main water resources, giving continuous supply of good quality water. The thick cover of Tertiary and Quaternary sediments in north-eastern Belgium consists of a superposition of sandy and clayey layers, overlying Cretaceous sediments, that gently dip towards the north-east (see Figure 7). Hence there is a succession of sub-parallel aquifer units, which are separated from each other where argillaceous intercalations are large enough to form hydraulic or partial hydraulic barrieers. The aquifers deepen towards the north where they are confined, and outcrop in the south where they are recharged. The hydrogeological system is briefly described below, mainly based on SAFIR 2 (ONDRAF/NIRAS, 2001), as it forms tthe base of the discussion on the consequences of pumpinng in chapter 4.3.1.

Figure 7: Generalised block diagram of the Terrtiary and Cretaceous Formations in tthe Campine Basin (from SAFIR 2, ONDRAF/NIRAS, 2001).

The hydrogeological system in north-east Belgium can be subdivided in several main aquifer and aquitard units. The hydrogeological units were defined as a function of the hydraulic properties of the strata in general and of their lithological characteristics in particular, and they are based on hydrogeological subdivisions generally admitted in the literature (Gulinck, 1966; Laga, 1980). A brief description of each of the hydrogeological units is given hereafter. The extent of different post-Mesozoic aquifers in north-eastern Belgium is shown in Figure 8.

The Quaternary aquifer This first (i.e. youngest) unit is a group of more or less isolated perched aquifers consisting of Quaternary sediments. In northern Belgium, the Campine Complex contains water bearing layers of fine sands which are isolated from each other by the presence of argillaceous units. These perched aquifers are grouped into the 'Campine aquifer'. Other Quaternary aquifers include terrace deposits from the Rhine and Meuse (see Campine Plateau) and various alluvial deposits in the Meuse Valley. The waters of the Quaternary aquifer are particularly acidic and are hence not suitable for the production of drinking water, without treatment. This near-surface water is also highly prone to local pollution and varies in quality, greatly restricting its use as drinking water. The local extraction from this aquifer is negligible. Its value as a source of drinking water is very limited and concentrated mainly in the Maas terrace deposits.

The Pliocene aquifer The second regional aquifer is composed of the Mol, Brasschaat and Merksplas Sands, part of the Poederlee Sand, and sands of the Kasterlee Formation. Its name is associated with the presumed age of the Pliocene sand deposits. The waters of the Pliocene aquifer are generally highly acidic, with a pH below the standard used for drinking water. The production from this aquifer is limited.

The Lillo-Kasterlee aquitard The Pliocene aquifer is more or less isolated from the Miocene aquifer by the presence of clay in the Lillo Formation and its transition to the Kattendijk Formation to the west, and by a thin unit of diffuse and/or interstratified clay in the base of the Kasterlee Formation and/or the top of the Diest Formation. This semi-permeable hydraulic unit provides a partial differentiation of the hydraulic system into two adjacent aquifers, though without preventing slow communication between them.

The Miocene aquifer The third aquifer is the region's largest aquifer, comprising a small part of the Kasterlee Formation, the Kattendijk Formation, the Diest Formation, the Berchem Formation and the Bolderberg Formation. In some cases, the Voort Formation and the Eigenbilzen Formation are part of this aquifer as well. These latter two formations are in hydraulic contact with the sands above but are far less permeable. The aquifer's name is taken from the presumed age of the various units. Its thickness, which often exceeds 100 m, its excellent permeability, the low to moderate hardness of the groundwater and its low salinity make this aquifer very suitable for the supply of drinking water and for other uses. It is also the second largest source of groundwater at national level and the main source in Flanders. In NE-Belgium, about 75 % of the total amount of pumped water originates from this aquifer. Locally, the level of iron in the Diest Sand greatly exceeds the 200 µg/l limit and requires specific treatment (quality of drinking water, Ministerie van de Vlaamse Gemeenschap, 2003). 21

The Boom aquitard The Boom Clay plays a primordial role in the region's hydrogeological system. The Boom Clay separates the Neogene aquifer system (comprising the Miocene and Pliocene aquifers) from the underlying Eocene, Palaeocene and older aquifers. In the area around Diest and Averbode, the Miocene and Ledo-Paniselian-Brusselian aquifers are connected because of subsequent local post-Oligocene erosion of the Boom Clay. In the north-east, the splay faults of the Roer Valley Graben, which affect the Boom Clay, can also influence the hydraulic behaviour of the overlying aquifers, but the effect is not fully understood yet.

The Oligocene aquifer system The forth aquifer system lies immediately below the Boom Clay. It consists of the Berg Sand of the Bilzen Formation and the Ruisbroek Sands of the Zelzate Formation, which is in contact towards the east with the sandy/argillaceous and marly deposits of the Borgloon and Sint-Hubrecht-Hern Formations. This aquifer system is quite heterogeneous and shows generally low permeabilities. It is often referred to as the Ruisbroek-Berg aquifer because of the rather more permeable nature of these two formations in comparison to the other parts of the aquifer. In the Campine area, the Oligocene aquifer system is little exploited, mainly due to its low permeability and concomitant low yield, and its increased salinity towards the north-west of the region.

The Bartoon aquitard system

The succession of sands and clays of the Maldegem Formation, i.e. the Onderdijke Clay, the Buisputten Sand, the Zomergem Clay, the Onderdaele Sand followed by the Ursel Clay and Asse Clay, form a fairly massive aquitard system dividing the Oligocene aquifer system from the Ledo-Paniselian-Brusselian aquifer system. The Bartoon aquitard system wedges out towards the east, allowing direct contact between the Oligocene and Ledo-Paniselian- Brusselian aquifer systems.

The Ledo-Paniselian-Brusselian aquifer system The fifth aquifer system comprises the Wemmel Sands at the top, followed by the Lede Sands and the Brussel Sands which are more difficult to identify separately in northern and north- eastern Belgium. In the west, it also includes the sandy sediments of the Gent and Tielt Formations. Its extension is limited to the east of the Gete by the line running NNE through Tienen, Leopoldsburg and Lommel. In areas where this Ledo-Paniselian-Brusselian aquifer system occurs at shallow depth, it is often used for drinking water production. In the Campine, however, this aquifer is not often exploited due to its deeper location and rather poor hydraulic conductivity.

The Ypresian aquitard The argillaceous formations of the Ypresian form a hydraulic barrier at the base of the Ledo- Paniselian-Brusselian aquifer system.

The Landen aquifer The fine sand layers of the Landen Group that occur between clay strata, contain an aquifer that extends over quite a large area. It is found to the east of the Ledo-Paniselian-Brusselian aquifer system in outcrops and underneath the argillaceous-sandy Tongrian. This aquifer is unexploited due to its low yield and excessive salinity. 22

Underlying hydrogeological units A number of aquifer units may be idenntified beneath the Landen Group. They gradually assume the characteristics of rock formations with secondary permeabillity, e.g. the Heers marls, Maastrichtian Tuffeaux and Chalks, the Bundsandstein Sandsttoones found in the northeasst of the Campine, and other deep aquifers. The Maastrichtian was exploited locally for a fish hatchery, until recently.

Figure 8: Extent of different post-Mesozoic aquifers in north-eastern Belgium. Upper panel: aquifers above the Boom Clay. Lower panel: aquifers below the Boom Clay. (based on data from Vancampenhout et al., 2008).

As groundwater resources are present all over the Campine, the drilling of water wells, which form the most important category of boreholes in the Campine area (Liie et al., 2010), are spread over the entire area, with the exception of the north-east by reason oof depth (Figure 9). Most water wells in the Campine pump water from the Neogene aquifer system giving continuous supply of good quality water. Because of the availability of good quality water at moderate depth, deep pumping – from aquifers below Boom Clay – is currently rather exceptional. The Oligocene aquifer system is currently of little use, maiinly due to its high salinity, low yield and concomitant low permeability. The Ledo-Paniselian-Brusselian aquifer system, which is extensively pumped near its outcrop area, is an aquiffeer that is not often exploited in the Campine, due to its depth, its high salinity and its ratther poor hydraulic conductivity. Figure 9 also shows that the deepest boreholes are mostly of recent age. The technical conditions evolve so that it becomes easier to drill deeper. Lie et al. (2011) expect that this trend will continue but not indefinitely as it is opposed by the increasing levels of salinity observed in all aquifers with increasing depth.

Figure 9: Water wells in (marked with open dots) and througu h (marked with crossed dots) the Boom Clay showing northward shift with time. Water wells in Boom Clay generally represent weells equipped for water production from overlying Neogene aquiifers, but which touched the Boom Claay in order to reach a stratigraphic reference level (figure from Lie et al., 2011).

Figure 10 shows the pumping wells in the Antwerp Campine beneath tthe Boom Clay for licence holders between 1950 and 2011. The Oligocene aquifer and the Ledo-Paniselian- Brusselian aquifer are mostly exploited in the south of Antwerp, near the outcrop area of the Boom Clay. Further away from the outcrop area of the Boom Clay, a few pumping wells exist in the Ledo-Paniselian-Brusselian aquifer near the village of Geel. These pumping wells are still active today. Furthermore, a few pumping wells were drilled in the Cretaceous aquifer in Turnhout, Herentals and Dessel. In Turnhout and Herentals, water was pumped for

geothermal energy purposes (for the local swimming pool), while in Dessel, water was pumped by a local fish farmer. These pumping wells are no longer active today.

Figure 10: Pumping wells in the Campine beneath the Boom Clay according to the grroundwater licence database of the VMM. Licences between 1950 and 2011 are taken into account. Wells still active in 2011 are marked with black dots.

Based on the available information on natural water resources in the Caampine and related human activities, the following statements can be made: 1. Groundwater resources are present in the Campine underground. 2. Water wells form the most important category of boreholes in the Campine area. They are spread over the entire area with the exexception of the north-east by reasson of depth. 3. The Neogene aquifer system above the Boom Clay is the main source of groundwater in the Campine. Hence, most pumping wells remain at shallow or moderate depth, above Boom Clay. 4. The aquifers underneath the Boom Clay are mainly pumped at the southern border of the Campine Basin. In the Campine Basiin itself, good quality water is availabe at moderate depth, so that deep pumping from aquifers below Boom Clay iis currently rather exceptional. The future pumping of water from these deep aquifers cannot be excluded. 5. The consequences of human actions, i.e. drilling and pumping of water from various aquifers is discussed in S IH 2.1.1.

4.2.2 Natural mineral resources

Information on natural mineral resources in Flanders is mainly found in documents and databases provided by the Geological Survey of Belgium, and the Vlaamse Gemeenschap – Dienst Natuurlijke Rijkdommen (ALBON). A general overview of the natural resources in Flanders is given in Gullentops & Wouters (1996). Exceptional mineral resources such as ores do not occur in the Campine underground. Clay, sand and gravel are the most important mineral resources in the Campine. Clay and loam are, because of their plastic characteristics, the most important traditional resources for the ceramic industry (for construction of bricks, roof tiles, ceramic tiles, expanded clay, …). They are mainly composed of clay minerals which have very specific physical properties that can be explained by their structural build-up, their composition and grain-size. Their unique characteristics form the base of a wide variety of applications. In Flanders, thick clay deposits of Ypresian age are present in the Kortrijk Formation (Mont- Héribu Clay, Saint-Maur Clay, Moen Clay, Aalbeke Clay), the Tielt Formation (Kortemark clay/silt) and the Maldegem Formation (Asse Clay). From these, the most important clay deposit is formed by the Kortrijk Formation, which is outcropping in western Flanders where it has been extensively exploited in the past few decades. In the Campine, the Kortrijk Formation is present in the underground (approximately 350 meters beneath the surface in the Mol-Dessel region), and is much sandier here than in the west. Composition and depth make the Ypresian clays in the Campine uninteresting for economic purposes. Clay deposits of Oligocene age are known in the Borgloon Formation (Henis Clay) and Boom Formation (Boom Clay). The Henis Clay is outcropping and exploited near the southern border of the Campine. The Boom Clay is a thicker clay deposit, and is outcropping in two zones. Its western outcrop zone is bounded by the Scheldt estuary, and the Rupel and Demer rivers. The eastern outcrop zone is located in the Hageland and the Demer region in Limburg. The Boom Clay is extensively exploited for the building industry in the Rupel and Waasland region, where it occurs at the surface. In the Campine Boom Clay is not exploited, as it is present in the underground, deepening and thickening towards the north-northeast. In the Mol-Dessel region, the Boom Clay is present at a depth between approximately 190 and 290 meters beneath the surface, attaining a thickness of about 100 m. In the north, near the Dutch border, the top of the Boom Clay is at a depth of about 300 meters, and the clay layer is thicker than 150 m. Quaternary alluvial clays are found in the main river valleys of Flanders. Early Pleistocene estuarine clays, known as the Kempen Clays, are found in the northern Campine area where they generally are between 2 and 7 m thick. They are exploited in the northern Campine and used as resource for the ceramic industry. Figure 11 gives an overview of the locations of the main clay deposits in Belgium. In the Campine, the exploitation of the Kempen Clay in the north, and the alluvial clay of the Meuse river in the east are the most important. At the southern border of the Campine, the Boom Clay is extensively excavated in its outcropping zone along the Rupel river. Loam is mostly found in the southern parts of Flanders (Figure 12), as an aeolian deposit dating back to the last ice ages. In the Campine, loam deposits occasionally occur but these are considered unimportant.

Another important mineral resource in the Campine is sand. Depending on their quality, these sands are used as filler sands, building sands, or masonry sands. Silica sands constitute an important and very valuable sand deposit, which form the base of a thriving glass-making industry. A wide variety of Tertiary sands occur east of the Zenne river. Thick sand deposits of Eocene age are present in the Brussel Formation (Krakenberg, Neerijse, Diegem Sands) and the Lede Formation (Lede Sands). These sands are exploited for the building industry in outcrop zones in Brabant, south of the Campine. In the Campine, Eocene sands are present at depth (top at about 250 m in Zoersel, and 470 m in Weelde) and are not exploited. Oligocene sands are present in the Herne Formation (Neerrepen Sands), the Borgloon Formation (Kerkom Sands) and the Bilzen Formation (Berg sands). The sand layers are rather thin and locally excavated in the outcropping area. Miocene Sands are present in the Bolderberg Formation (Bolderberg Sands) and the Diest Formation (Diest Sands). The Bolderberg Sand is a fine and homogeneous sand of high quality, and reaches a thickness of about 40 m on the Campine plateau. A lot of small excavations existed in this region of the Campine, further extending to the Hageland where these sands are also occurring. The Bolderberg Sand is a valuable sand for various applications. In contrast, the use of the Diest Sands, containing up to 50 % of glauconite, is restricted to specific purposes. These sands are often used as filler sand for infrastructure purposes. Pliocene Sands in the Campine are present in the Kasterlee, Mol and Neeroeteren Formations. Especially the Mol Sands are very valuable, as they are almost pure quartz sands. They are used in refractory ceramic good (glass industry). The Neeroeteren Sands are coarse quartz sands, used for the production of concrete. Various Quaternary sand and gravel deposits are extracted in the Flemish Valley. In the Campine area, the most important Quaternary sand and gravel deposits are related to the Meuse (Winterslag Sand and Zutendaal Gravel on top of the Campine Plateau) and Rhine river (Lommel and Bocholt Sands). Especially the gravel deposit of eastern Flanders forms an important mineral resource. Two different types of gravel deposits are distinguished (LNE, 2010). The oldest terrace gravels were deposited ca. 0.7 Ma ago in a broad and undeep valley that today stands out as the Campine Plateau. They consist of relatively unclean and heterogeneous gravel deposits which occur above the current water table. They are extracted in dry open pit mines. The second series of gravel deposits occur in the current alluvial plain of the river Meuse (valley bottom gravels). They consist of very clean gravels which were partially reworked and deposited during the Late Pleistocene and Holocene. Only a limited amount of these gravels can be extracted through dry open pit mining. The majority is extracted from below the water table. The location of the main sand and gravel deposits in Belgium are shown in Figure 13 and Figure 14 respectively.

Figure 11: Location of the main clay deposits in Belgium. In the Campine, the exploittation of the Kempen Clay in the north, and the alluvial clay of the Meuse river in the east are the most immpportant. At the southern border of the Campine, the Boom Claay is extensively excavated in its outcropping zone along the Rupel river. (figure from Bouhenni & Delmoitiié, 2011; studyd commissioned by ONDRRAF/NIRAS in the frame of the near surface disposal of category A waste).

Figure 12: Location of the main loam deposits in Belgium, aeolian in origin, and generally occurring in the southern parts of Flanders. In the Campine, looam deposits occasionally occur but these are considered unimportant. (figure from Bouhenni & Delmoitié, 2011; study commissioned by ONNDRAF/NIRAS in the frame of the near surface disposal of category A waste).

Figure 13: Location of the main sand deposits in Belgium. In the Campine, exploitatiion of the Bolderberg Sand at the Campine plateau, the Lommel Sands, and the alluvial sand of the Meuse are the most important. (figure from Bouhenni & Delmoitié, 2011; study commissioned by ONDRAF/NIRAS in the frame of the near surface disposal of category A waste).

Figure 14: Location of the main grravel deposits in Belgium, typically occurring in easstern Limburg. (figure from Bouhenni & Delmoitié, 2011; studdy commissioned by ONDRAF/NIRASS in the frame of the near surface disposal of category A waste).

Based on the available phenomenological information on natural mineral resources and related human actions in the Campine, the following statements can be made:

1. There are no exceptional mineral resources, such as ores, known in the Campine. The geology of the Campine is well-known: the Campine is a sedimentary basin composed of a thick sequence of sedimentary clays and sands. No exceptional mineral resources such as ores were formed in this geological environment.

2. Clay, sand and gravel are the most important mineral resources in the Campine. Clay, sand and gravel are the most important mineral resources in the Campine. These mineral resources are widely used in the building and infrastructure sectors (Broothaers, 2003) and thus hold important economic potential.  Ypresian clays are present in the Campine underground. Ypresian clays are extensively exploited in the outcropping area, but not in the Campine.  Boom Clay is present in the Campine underground. Boom Clay is extensively exploited in the outcropping area, but not in the Campine.  Quaternary clays are present at the surface in the Campine, known as the Kempen Clays. They are exploited and used as resource for the ceramic industry.  Eocene and Oligocene sands are present in the Campine underground. They are exploited in the outcropping area south of the Campine, but not in the Campine itself.  Miocene sands are present in the Campine. Diest Sands are outcropping and locally exploited in the southern Campine. Bolderberg Sands are mainly present on top of the Campine plateau where they are exploited for their high quality and wide variety of applications.  Pliocene sands are present at the Campine surface and sub-surface (Kasterlee, Mol and Neeroeteren) and are locally exploited there.  Quaternary sands in the eastern Campine are related to the Meuse and Rhine deposits, and are locally exploited.  Quaternary gravel is present in the eastern Campine, and is exploited.

3. The natural mineral resources in the Campine are exploited by the open pit method. Because of the availability of these resources at the surface, exploitation is currently restricted to the surface although clay and sands are present in the Campine underground as well. In the past, every village had its own sand pit and clay or loam excavation for local use. However, there is a general tendency to minimize the number of extraction sites and maximize the production from single sites. The consequence of this generalized evolution is that quarries become larger and deeper, but fewer. Sand and clay pits are generally dug in or near the outcrop zone of the extracted raw material. Displacement towards the north following the structural slope of the sub-crop is facing handicaps: large amounts of overburden to be removed and temporarily stored, water pumping and control of water quality in the overlying aquifers, and mere size: environmental regulations require slopes that are well below limits of stability (down to 15° for wet quarrying) resulting in slope widths of about 550 m for a 150 m deep pit. Land requirements

for establishing deep pits are in the order of 4 km², making public acceptance unlikely. Dry quarrying would require draining of the Neogene aquifers, a mission impossible. The best chance for deep sand pits are related to the occurrence of the Kiezeloolith formation, which reaches 250 m thickness in northern Limburg and may be nearly entirely exploitable (Lie, 2011). Large wet sand extraction already exists near Lommel with pit depth below 50 m. A project for a large and deep (150 m) sand pit, supplying sand for the needs of the entire Flemish region, exists for the area north of Bree (‘t Hasselt) but meets fierce resistance from local inhabitants and creates conflicts of interest with the water production policy for this most productive aquifer of the Flemish region. In any case, the Kiezeloolith Formation is restricted to the Roer Valley Graben, thus outside the area of interest for deep repositories.

4. Natural mineral resources occur in sufficient amounts at the surface or shallow sub- surface, so that deep excavation is not necessary. From the above, it is clear that the exploitation of natural mineral resources in the Campine is currently restricted to the surface and shallow sub-surface. Deep excavation and exploitation is unlikely in view of the wide availability of these resources at the surface and shallow sub- surface. Excavation down to a depth relevant for geological disposal is thus currently not existing, and it is not expected in the future (difficult, more expensive, and large reserves are present at the surface and sub-surface).

4.2.3 Natural energy resources

General information on the presence and location of natural energy resources in the Campine is found on geological maps and in documents on the geology of the area. An overview of the natural resources (amongst which energy resources) is given in Gullentops & Wouters (1996). More specific information on the coal-exploration boreholes in the Campine is found in the Professional papers of the Belgian Geological Survey, such as Tys (1980), Dusar & Houlleberghs (1981), Dusar et al. (1986, 1987a, 1987b, 1998), Dusar & Langenaeker (1992), Langenaeker (1992) and others. Other papers on the presence of coal and coal bed methane generation in the Campine underground are presented by Grosjean (1949), Legrand (1960), Kimpe (1961), Van Doorselaer (1983), Goddeeris (1982), Dreesen et al. (1995), Dreesen (1993), Dusar (1987), Langenaeker (2000), Lie et al. (2011), Wenselaers et al. (1996), Laenen & Hildenbrand (2005), and others. Documents on geothermy and its potential in Flanders are presented by Vandenberghe & Bouckaert, (1980), Berckmans & Vandenberghe (1998), Vandenberghe & Fock (1989), Vandenberghe (1990), Dreesen and Laenen (2010), and others.

4.2.3.1 Fossil fuels Fossil fuels are formed by the anaerobic decomposition of buried organic matter, and are typically several millions of years old. Organic matter in recent and ancient sediments is a reflection of the original organic input and subsequent processes of diagenesis and metamorphism. Peat originates from the accumulation of partially decayed vegetation matter. The formation of lignite or brown coal from peat requires burial, absence of air, and time. The

further conversion to bituminous coal in general requires more time, but also increases in temperature and pressure, and are entirely physical and chemical processess (Tucker, 1991). Oil and gas originate from a diverse group of rocks, i.e. fine grained organic-rich sediments. Diagenesis of the organic matter begins very early at shallow burial depth, and substantial quantities of methane can be produced through bacterial fermentation.. Burial diagenesis further leads to the production of kerogen, the type depending on the nature of the organic input. Burial to temperatures of 50-80 °C causes thermocatalytic reactions in the kerogen, and types-I and –II cycloalkanes and alkanes are generated, two of the main constituents of crude oil. Whhen this process takes place, the source rock is said to be mature. Oil generation takes place at temperatures around 70-100°C; in areas of average geothermall gradient this is at depths of 2-3.5 km (the so-called 'oil window'). With increasing temperature, more and more oil is generated until a maximum is reached, and then the quantity decreases and an increasing amount of gas is formed (Tucker, 1991). Peat, lignite, coal, oil and gas are all fossil fuels: important energy sources all over the world.

In the Campine, fossil fuels have been explored and exploited in the past. Below, an overview is given, and the potential of future fossil fuel exploitation in the Campine iis evaluated.

Peat or turf, originated from the accumulation of partially decayed vegetational remains, is a fossil fuel, and has been an important energy resource in the past. In the northern Campine, the water shed divide from Essen to Postel was very wet and swampy duee to the combination of a very flat relief and the presence of impermeable clay, and provided important amounts of peat. Since the 13th century, peat has been harvested in this region as an iimportant source of fuel. The last exploitation in the area around Postel dates from the latest seeventies (Gullentops and Wouters, 1996). Exploitation of remaining peat is not considered to be relevant in the frame of geological disposal of radioactive waste, because of its occurrence at the surface.

Lignite or brown coal is a soft brown fossil fuel with characteristics that put it somewhere between coal and peat. Two lignite layers occur in the Pliocene Mol Sands (Figure 15). In the 20st century, lignite was extensively exploited in the area of Mol. However, to the east of the Rauw fault, the lignite layers occur at a greater depth and were therefore not exploited. Exploitation of remaining lignite is not considered to be relevant in the frame of geological disposal of radioactive waste, because of its occurrence in the shallow sub--surface.

Figure 15: Lignite layers in the vicinity of Mol (figure from Gullentops and Wouters,, 1996). 32

Coal is a readily combustible black or brownish-black fossil fuel, normallly occurring in rock strata in layers (coal beds) or veins (coal seems), and containing more than 50 weight % and more than 70 volume % of carbonaceouus material including inherent moiisture, formed from compaction and induration of variously alltered plant remains similar to those in peat (Jackson, 1997). Coal has been discovered in the Caampine underground by A. Dumoont in 1901.

The origin of coal in the Campine: geological background The coal in the Campine underground originated some 310 Ma ago during the Westphalian (Upper Carboniferous). At that time, the configuration of land and sea was considerably different than today. The Campine region was located south of the eqquator, and a warm tropical climate prevailed and resulted in the growth of a rich vegetation. Subsequent fires and floodings hindered the growth of vegetation and resulted in the sedimentation of sand and clay layers, followed again by new periods of vegetation growth. This cycle was repeated several times. Vegetation growth and sedimentation occurred at the same rate as the subsidence of the Campine Basin, so that a thick sequence of organic maatter and sediments was formed. Increasing temperatures and pressures resulted in the compaction and gradual change from peat to lignite to coal. This ccoalification process was largely ffinalised by the end of the Carboniferous.

Figure 16: Simplified pre-Cretaceous geological map of the Campine Basin with indiication of the most important faults (from Gullentops & Laga, 1996).

A sequence with a thickness up to 3000 m has been preserved locally in the Campine Basin, with an average coal content of 3 %, divided over several coal beds. These coal beds occur about every 15 m, with a thickness of about 120 cm for the exploitable beds. At the end of the Carboniferous, the Variscan orogeny reached its maximum and the favourable conditions resulting in coal formation in the Campine Basin disappeared, as the delta plain evolved to a lower and upper alluvial plain. The Campine Basin was not directly affected by the orogeny (no folding), but was faulted intensely. Later on, the Carboniferous coal beds in the eastern Campine have been buried and covered by a thick sequence of Permian, Triassic and Jurassic sediments. These Permo-Trias-Jurassic sediments form the first sequence of sediments covering the Campine coal beds (Figure 16). By the end of the Jurassic, sedimentation was interrupted by the Kimmeridgian orogeny. Uplift of the Brabant Massif resulted in the monoclinic inclination of the layers in the Campine Basin, dipping towards the north-northeast. Furthermore, erosion removed the majority of the Permo-Trias-Jurassic sediments, except in the north-eastern part of the Campine Basin. Uplift of the Brabant Massif lasted till the end of the Cretaceous. A new period of sedimentation then started. Cretaceous and Tertiary sediments form the second sedimentary sequence of layers covering the Campine coal beds, and may reach a thickness of 300 to 700 m.

Exploitation of coal in the Campine The discovery of coal significantly changed the economic, social and demographic evolution of the province of Limburg in the eastern Campine during the 20st century. Due to its particular good quality, the coal of the eastern Campine underground gained a lot of interest. In this region, mature coal of high quality was found at mining depth, so that exploitation was started in 7 mines along the Beringen-Maasmechelen axis. Further towards the north, coal of similar quality was buried too deep, so technically more difficult to reach and therefore economically not intersting. Potential future mining areas are located north of the Beringen- Maasmechelen axis and concerns less mature coal (see Figure 18). The area west (Olen- Meerhout) and south (Genk) of the historical mining region contains few but undeep and regular coal seams that are much easier to exploit. Coal beds in the central (e.g., Mol), northern and northeastern Campine area are too deep and thus economically not interesting to be mined given the present-day technological state-of-the-art. Because of the thickness of the coverage layers (about 800 m), deep shafts were needed to reach the coal in the Campine underground. Furthermore, the occurrence of coal in about 1 m thick coal beds separated by sedimentary layers of a few meters thick, and extensively faulted (see schematic representation in Figure 17), did not facilitate exploitation. Nevertheless, about 440 x 106 tons of coal have been extracted. Due to economic reasons, all coal mines were abandoned between 1987 and 1992. A reserve of more than 4 billion tons of potentially exploitable coal has been identified in the underground of the eastern Campine by the 'Kempense Steenkolenmijen' and the Geological Survey of Belgium (Gullentops & Wouters, 1996; Langenaeker, 2000). Figure 18 shows the un-mined and mined coal in the eastern Campine.

Figure 17: Schematic representation of the exploitation of coal in Eisden (figure from Gullentops and Wouters, 1996).

Coal concessions are located in the easterrn Campine; coal outside this regiion is considered to be uninnteresting for exploitation, taking into account the current technological opportunities. Hence there is still a large zone of interest for geological disposal of radioactive waste outside the coal concession area.

Figure 18: Coal concessions in the eastern Campine (figure from ALBON). Unmined coal (red areas) and mined coal (green areas), completed by areas of more than 250M m3/km2 coalbed methane from VITO simulation (hatched blue areas). 35

Coal bed methane is a natural gas (CH4 methane), adsorbed into the solid matrix of coal. It is often extracted from the coal, as it is an interesting source of energy. In the Campine, the presence of methane associated with coal is well-known from the mining activities (so-called 'mine gas'). In the beginning, this gas was considered as 'waste', but soon the economic value of it was realised. Around 1950, methane was captured and used as source of energy as well. By the end of the 20st century, studies were performed in order to evaluate the potential for coal bed methane extraction or CO2-enhanced coal bed methane recovery, taking into account the evolving technology in gas captation (Wenselaer et al., 1996; Dusar et al., 1999; Dreesen et al., 2000; Van Tongeren et al., 2000). The total coal-bed methane gas-in-place reserves in the Campine Basin of Belgian Limburg 3 3 amount to 132 billion m of CH4. Of these reserves, only 53 to 79 billion m are considered likely to be economically recoverable (Dreesen et al., 2000). Conventional coal-bed methane production could be cost efficient in the Campine Basin today, however, the economic feasibility for CO2-enhanced coal-bed methane production is still questionable (Laenen & Van Tongeren, 2010). On 2011-04-29, the LRM (Limburgse Reconversie Maatschappij) and the Australian energy group Dart Energy Limited set-up an agreement to exploit coalbed methane in Limburg in the future (http://www.deredactie.be/permalink/1.1013328). If the pilot project, which runs over the next three years, is proven to be successful, large-scale exploitation of coal bed methane will start from 2015 onwards.

Oil and gas are fossil fuels, and important sources of energy world-wide. The geological structure of the Campine Basin, however, is not very interesting from an oil and gas exploration point of view. Indeed, more than 200 'dry' wells have been drilled until present. Nevertheless, it is believed that declaring it free of oil and gas is somewhat premature (Langenaeker, 2000), since the majority of wells has been drilled for purposes of coal exploration, geothermal energy or gas storage, for which other parts of the basin are interesting, especially where the Palaeozoic basement is at relatively shallow depths.

Hydrocarbons are natural organic compounds, gaseous, liquid or solid, consisting solely of hydrogen and carbon (Jackson, 1997). Hydrocarbons are found in oil and gas, but since they are mobile, they can be found far away from their source rock. Hydrocarbons are typical fossil fuels and are an important source of energy all over the world. In Belgium, research was performed on the Palaeozoic rocks in order to find potential sources and/or reservoirs of hydrocarbons. Source rocks of hydrocarbons are definitely present in the Flemish underground and in the continental shelf (flat?), but the presence of hydrocarbons themselves is not excluded, neither proven. The presence of hydrocarbons in the Campine Palaeozoic is thought to be 'not unlikely', since hydrocarbons have been found in the British East Midlands, which is geologically very comparable to the Campine Basin.

Based on the available geoscientific information on natural energy resources in the Campine and related human activity, the following statements can be: 1. The exploitation of remaining peat and lignite in the Campine is not considered to be relevant in the frame of geological disposal of radioactive waste, because of it occurrence at the surface. 2. Coal of particular good quality has been extensively exploited in the eastern Campine during the past century. A reserve of more than 4 billion tons of potentially exploitable coal is still present in the underground of the eastern Campine. Elsewhere in the Campine, coal is present in the underground as well, but it is currently considered to be economically unintersting for exploitation, taking into account its burial depth and the current technological posibilities and associated economic results.

3. Coal bed methane is a natural gas (CH4 methane), adsorbed into the solid matrix of coal. The total coal-bed methane gas-in-place reserves in the Campine Basin amount to 132 3 billion m of CH4. Of these reserves, about 50 % is considered likely to be economically recoverable (Dreesen et al., 2000). Conventional coal-bed methane production could be cost efficient in the Campine Basin today, however, the economic feasibility for CO2- enhanced coal-bed methane production is still questionable (Laenen & Van Tongeren, 2010). A pilot project, which runs over the next three years, should provide more insight in the feasiblilty of coal bed methane extraction in the Campine. 4. The geological structure of the Campine Basin is not very interesting from an oil and gas exploration point of view. Therefore, oil and gas exploration and exploitation is not considered to be relevant in the frame of the geological disposal of radioactive waste. 5. Hydrocarbons are found in oil and gas, but since they are mobile, they can be found far away from their source rock. The presence of hydrocarbons in the Campine Palaeozoic is thought to be 'not unlikely', but is not proven, neither excluded.

4.2.3.2 Geothermy Geothermy refers to the natural heat of the interior of the earth. Part of the heat is related to the heat of the molten nucleus of the earth and the associated heat release and flux towards the surface. This deep heat flux is not homogeneously distributed within the earth, and the 'warmer' zones are generally associated with important rift systems. Besides the deep heat flux, radioactive decay within the earth's crust also generates important amounts of heat. Both process, i.e. cooling of the earth's nucleus and radioactive decay, are very slow processes. The rate of change of temperature in the earth with depth (the geothermal gradient) differs from place to place depending on the heat flow in the region and the thermal conductivity of the rocks (Jackson, 1997). The average geothermal gradient in the earth's crust approximates 25-30°C per km of depth. Geothermy is a natural energy resource. It is used in different ways and for different purposes. Shallow-depth geothermy is generally for direct use of geothermal water, for example for the heating and cooling of buildings, while deep geothermy is generally for indirect use as steam and hot water are used for electricity generation. In contrast to fossil fuels, geothermy is a 'renewable' energy resource. The increasing demand of energy, and the shrinking availability of fossil fuels, increases the search for alternative energy resources. In this frame, geothermy may be an alternative, ànd 37

renewable, energy resource. Recently, the potential of geothermy in Belgium (Berckmans and Vandenberghe, 1998) and particularly in Flanders (Dreesen and Laenen, 2010) has been evaluated. From these studies, it is concluded that the Campine is an area of interest with regard to geothermy.

Different exploitation forms of geothermy and its applications exist (based on Dreesen and Laenen, 2010): Shallow-depth geothermy is the use of the internal heat of the earth at shallow depth. It is generally for direct use of geothermal water, for example for the heating and cooling of buildings. Two exploitation forms exist:  Cold-heat storage: open system; boreholes typically 50-150 m deep; applied for direct use in offices, hospitals, shopping centres, industrial buildings and in agriculture.  Shallow-depth geothermal probes: closed system; boreholes up to 300 m deep; applied for the heating of individual buildings. Deep geothermy is the use of the internal heat of the earth from deep (hydro-)geological sources. Deeper sources generally provide higher temperatures. Natural heat from deep geothermy may be directly used, or indirectly for electricity generation. Several exploitation forms exist:  Hydrothermal systems: open system; exploitation from deep aquifers typically 2-3 km deep (an aquifer at 2 km depth has an average temperature of 60-80 °C); applied for direct use in living districts, industrial areas, or agriculture. Note that the decrease in temperature due to the exploitation is relatively quickly restored.  Enhanced geothermal systems (also called Hot-Dry-Rock, Hot-Wet-Rock, or Hot- Fractured-Rock systems): open system; induced fracturing of fine porous media to enhance circulation of water between two sources; typically up to a few km deep; both heat and steam production are possible due to the high temperatures; applied as industrial steam, for heating networks and the generation of electricity.  Deep geothermal probes: closed system (lower capacity and rendability); typically 2-3 km deep; applied at locations where knowledge of the underground is poor or where boundary conditions of the geothermal reservoir are not adequate enough.

In the frame of a study on the use and potential of geothermal energy in Belgium, Berckmans & Vandenberghe (1998) presented a set of temperature maps for the Belgian underground. The maps resulted from the interpolation of temperatures measured in 60 boreholes all over the area. Figure 19 shows the temperature map of Belgium at a depth of 1000 m. It is shown that the old Caledonian Massifs are relatively cold. The warmer areas correspond to the sedimentary basins. In Flanders, this corresponds to the Campine Basin. Such temperature maps enable to evaluate the application of geothermy in a certain area. In Flanders, the average geothermal gradient is 30°C/km. For pumping water of 25°C (the lower limit for application of geothermy), a depth of 500 m is necessary. In Flanders, geothermal reservoirs at such a depth are present in western Flanders and in the Campine. For applications requiring water at 40°C or more, a geothermal reservoir at depths of 1000 m or more is required. The presence of such geothermal reservoirs in Flanders is limited to the

deep sedimentary basins in the north and the south of the Brabant Massif. For Flanders, this corresponds to the Campine Basin. Possible geothermal reservoirs in thee Campine Basin are related tto the Cretaceous, Bundsandstein (Lower Triassic), Silesian sandstones (Upper Carboniferous, mainly Neeroeteren sandstones), and Dinantian limestones (Lower Carboniferreous) (Figure 20; Laenen, 2009; Dreesen & Laenen, 2010).. The geothermal potential of these reservoirs was calculated by Berckmans & Vandenberghe (1998). These calculations gave an idea of the total energy content of the potential reservoirs, but provide no information on the extractable energy content, or the potential of the reservoir to restore (the so-called 'renewable' energy). Therefore, the heat flux was ccalculated (Laenen, 2009; Dreesen & Laenen, 2010). It was concluded that the overall heatt flux is low, albeit slightly higher in the northern Campine and near the graben structure in the east (Figure 21). Regeneration of an exploited geothermal reservoir will therefore be low. This should be taken into account when considering exploitation of deep geothermal reservoiirs in the Campine. Moreover, exploitation of deep geothermy is still a very costly issue. In the region of interest for geological disposal of radioactive wastte, Cretaceous and Carboniferous rocks are present (Figure 20). They are located far below Boom Clay.

Figure 19: Temperature map of Belgium at a depth of 1000 m (Dreesen & Laenen, 2010; study perfomed for ALBON in the frame of the VLAKO reference task). The geothermal target areaa is indicated in pale red.

Figure 20: Location of potential geeothermal reservoirs in Belgium, mainly located in the Campine Basin (Dreesen & Laenen, 2010; study perfomed for ALBON in the frame of the VLAKO reference task).

Figure 21: Local heat flux in Flanders, deduced from temperature measurements in ddeep boreholes (Laenen, 2009). 40

Shallow-depth geothermy is currently of increasing interest in Flanders. The obtained energy can be used for the heating and cooling of builings. In the Campine, shallow-depth geothermy (cold-heat storage type) is applied in e.g. the hospital in Turnhout. A first deep geothermal project in the Campine, performed in 1978 in the region of Hoogstraten failed because the considered reservoir was not encountered during the drilling (Dreesen & Laenen, 2010). In 1983, a new deep geothermal project was started in the region Beerse-Merksplas (Dreesen & Laenen, 2010). The production test showed that the productivity was lower than expected. Some modifications were made, but because of the low productivity and the high financial costs of an effective production, the rendability of the installation is currently questioned. No other deep geothermal reservoirs are exploited yet. One reason is the high financial cost of the traditional applications of geothermy, especially since the heat flux in Flanders is very low. Hence, the regeneration potential of a geothermal reservoir will be very slow as well. Both heat flux and regeneration potential are therefore important issues in the evaluation of geothermal reservoir candidates. Non-traditional applications of geothermy, such as the 'enhanced geothermal systems' are possible – at least in principle – in the whole of Flanders, but appear even more expensive. Research on the potential of geothermy in Flanders is continuing. Recently, VITO did a seismic campaign in the area of Mol for studying the underground and potential geothermal reservoirs (VITO persbericht 2011/02/09). Of particular interest is a future pilot study on the potential of the pumping of naturally heated water from a depth of 2.5 to 3.5 km inside the earth (M. Brootaers & B. Laenen, pers. comm). If this seems to be successfull, the application of geothermy for household and industrial heating, and the generation of electricity will be tested. This study will be performed on the Balmatt site in Mol. The outcome of this pilot study will probably have a large influence on the future application of geothermy in Flanders. With respect to the increasing energy demand and the decreasing availability of fossil fuels, the use of geothermy in the future seems very likely. Its possible impact on a geological repository for the disposal of radioactive waste should therefore be evaluated with respect to the safety and feasibility case 1. Note that geothermy is not subject to concession legislation. A drilling permit based on environmental impact assessment (MER) allows setting up a geothermal project. Exploitation and application of geothermy will not directly influence the performance of a geological repository system in the area. Borehole drilling may form a potential risk of human intrusion in a future repository system. However, it is believed that borehole drilling will be preceded by exploration campaigns such as seismic campaigns allowing to identify repositories at depth, thereby minimizing the risk of human intrusion as much as possible.

Based on the available phenomenological information on natural energy resources in the Campine and related human activity, the following statements can be made:

1. The Campine is an area of interest with regard to geothermy. 2. Possible geothermal reservoirs in the Campine Basin are related to the Cretaceous, Bundsandstein (Lower Triassic), Silesian sandstones (Upper Carboniferous, mainly Neeroeteren sandstones), and Dinantian limestones (Lower Carbonifereous) (Laenen, 2009; Dreesen & Laenen, 2010). These layers occur in the deep underground in the

Campine. As deep drillings are required, they may form a potential risk for perturbing Boom Clay or a future repository. 3. Regeneration of an exploited geothermal reservoir will be low, as the overall heat flux in the Campine area is low, albeit slightly higher in the northern Campine and near the graben structure in the east. 4. A pilot study on the potential of the pumping of naturally heated water from a depth of 2.5 to 3.5 km inside the earth is planned by VITO in the near future. If the pumping seems to be possible, the application of geothermy for household and industrial heating and the generation of electricity will be tested. The outcome of this pilot study will probably have a large influence on the future application of geothermy in Flanders.

4.2.4 Use of deep geological layers

Several deep geological layers may be interesting reservoirs for the storage of gas: for the temporal storage of natural gas for later consumption, or for the long-term storage of CO2 to decrease the contribution of fossil fuel emissions to global warming. Also in the Campine area, there is an increasing interest of man in deep geological layers for the storage of gas. General information is found in documents on the geology of the area and in geological maps. Specific information on natural gas storage in the Campine is found is Laenen et al. (2004), Total E&P UK (2007), Amantini et al. (2009), FLUXYS website, and others. Specific information on Carbon Capture and Storage in Belgium is found in Lagrou et al. (2002), Piessens & Dusar (2004), Bertier et al. (2006), Laenen et al. (2006), Piessens (2011), Laenen & Van Tongeren (2010), Piessens et al. (2009, 2011), Welkenhuysen et al. (2011), and others. Natural gas can be stored for an indefinite period of time in natural gas storage facilities for later consumption. Gas is injected into storage during periods of low demand and withdrawn from storage during periods of peak demand. The most important type of gas storage is in underground reservoirs, either in depleted gas reservoirs, salt domes, or in aquifer reservoirs. With regard to the geological structure of the Belgian subsoil, there are not many opportunities for natural gas storage in Belgium. However, a suitable reservoir is present in the Visean limestones of the Campine underground. Geologically, the Campine area is characterised by the presence of dome-shaped structures in the Visean limestones (Lower Carboniferous). The best documented structures are the Heibaart dome between the villages Loenhout and Rijkevorsel, and the antiform at Poederlee (Figure 22). Both explored domes are late Visean algal to crypto-algal reef mounds that developed on a shallow carbonate platform. Wells within this part of the basin reveal a general trend from restricted marine facies in the west, over reefs towards fore-reef facies in the east (Bless et al., 1976; Muchez et al., 1991). In all wells from the western half of the basin, the transition between the Lower and the Upper Carboniferous is abrupt and the top of the limestone sequence is karstified. A totally different picture emerges from the eastern part of the Campine basin. Here, the early and middle Visean platform carbonates are replaced by thick turbidic limestone sequences characteristic of slope-settings during the late Visean. Moreover, the Visean-Silesian transition appears to be gradual and uninterrupted without signs of late Visean palaeo- karstification (Bless et al., 1976). From this geologic framework it is deduced that reef

mounds similar to those found at Heibaart and Poederlee may be presenntt in the unexplored areas in the western part of the Campine basin (Laenen et al., 2004).

Figure 22: Isochron map for the top of the Visean limestones in the northwestern part of the Campine Basin (from Laenen et al., 2004; modified after Dreesen et al., 1987)

The underground gas storage facility at Loenhout (Campine region, provinncce of Antwerp) was developed in an aquifer system and was put in operation by FLUXYS (formely known as DISTRIGAZ) in 1985. Gas is stored in the Visean karstic limestones of the Heibaart dome structure. The reservoir consists of fissured and karstified rockmass developed into a thight and compact carbonated rock matrix. The original carbonate massif has been subjected to erosion and dissolved by rainwater during its emersion between tthe Visean and Namurian. The result is an aquifer reservoir consisting of a complex network of dissolved volumes, partlly filled with both calcitic and shaley materials (Amantini et al., 2009). The reservoir characteristics of the carbonate matrix are very poor (porosity of 1-3 % and extremely poor peermeability), but the effective porosity is created by the karstification which provides an enhanced effective permeability of between 40-50 mD (1 darcy = 10−12m2), locally up to opeen vugs and caverns (Total E&P UK, 2007). The top of the porous limestone reservoir lies att 1080 m below sea level; its final split point is situated at 1295 m (Amantini et al., 2009; Laenen et al., 2004). It is covered with an impermeable layer - guaranteeing good closure of the reservoir - composed of a thick cover of Namurian shales. Additional sealing is provided by the overlying Westphalian coal seams, which would capture escaping CO2 (Laenen et all., 2004). Due to the absence of Permian, Triassic and Jurassic formations, an unconformity separates the marly 43

and chalky Cretaceous formations and the Lower Carboniferous reservoir and its caprock. The 300 m thick Cretaceous layers are overlaaid by an alternation of 650 m of clay and sand layers of Tertiary and Quaternary ages. In 2007, FLUXYS started to expand the uunderground storage capacity at itts Loenhout facility by 15 % over a fouur-year period. In 2010, the workable storage volume increased from 650 to 675 million cubic metres. In addition, the flexibility in operating the sttorage facility were boosted by increasing send-out capacity from 500,000 to 625,000 cubic metres per hour and injection capacity from 250,000 to 325,000 cubic metres per hour. At present, the working storage volume at Loenhout is 700 million normal cubic metres of nattural gas (from the FLUXYS website: http://www.fluxys.com/en/Services/Storage/Storage.aspx). For its activities, FLUXYS currently has a production concession for its fafacility at Loenhout, and a much larger exploration concession over the central Antwerp Campine, recently confirmed for a 30 year period (Figure 23).

Figure 23: Map showing the production and exploration concessions of FLUXYS (figure from ALBON).

Research for gas storage in deep geological layers continues. In collaboration with the Flemish Institute for Technological Research (VITO) and the Limburg Investment Company (LRM), FLUXYS is looking for potential sites for underground gas storage in the Campine region, this time in the northeast of the province of Limburg (in the rift zone, B. Laenen, personal communication). The limited available data in this area indicated the presence of porous sandstone bodies with possibly suitable properties for large-scale gas storage. Seismic research performed in 2008 indicated the presence of suitable structures. In order to confirm the characteristics of the subsoil and to analyse possible storage structures, further exploratory drilling is needed. Up till now, this drilling is not yet performed. Besides the temporal storage of natural gas for later consumption, deep geological layers may also be used for the long-term storage of CO2. Carbon capture and storage (CCS), alternatively referred to as carbon capture and sequestration, is a means of mitigating the contribution of fossil fuel emissions to global warming. The process is based on capturing CO2 from large point sources, such as fossil fuel power plants, transporting it to the storage site, and storing it in such a way that it does not enter the atmosphere. Although CO2 has been injected into geological formations for various purposes, the long term storage of CO2 is a relatively new concept.

For geological storage of CO2, three types of formations are suitable: depleted oil and gas reservoirs, deep saline aquifers, and coal seams and (coal) mines. For the storage of CO2 in a liquid or supercritical phase, CO2 is commonly stored in formations below 800 m depth. Based on the lower density of CO2 compared to water, a sealed cap rock is required on top of the CO2 storage reservoir. Additional trapping results from capillary forces, dissolution in formation water and mineral precipitation. In coal sequences, adsorption is an essential trapping mechanism. The possibilities of carbon capture and storage in Belgium are currently studied and summarised by Piessens et al. (2008) and Piessens et al. (2011).

Potential reservoirs for CO2 storage in Belgium are poorly explored. The main criteria for reservoir selection and evaluation are reservoir properties, sealing, depth and the occurrence of trapping structures. Deep saline aquifers and coal sequences are considered as potential geological reservoirs for CO2 storage in Belgium (Figure 24, Welkenhuysen et al., 2011). In Flanders, the Campine region offers a variety of potential CO2 storage sites. Based on the currently available data (geological maps and layer models of the Belgian sub- surface), four stratigraphic intervals were selected as potential reservoir formations within the Campine Basin (Laenen et al., 2004; Piessens et al., 2008; Welkenhuysen et al., 2011): the Upper Cretaceous to Palaeocene carbonates, the Lower Triassic sandstones of the Bundsandstein Formation, the Upper Carboniferous sandstones, particularly the Neeroeteren Formation, and the Lower Carboniferous carbonates. Cenozoic aquifer formations were not considered because they are located at a depth less than 800 m. Cretaceous to Palaeocene sequences in Flanders are restricted to two geological regions: the Campine Basin and the Roer Valley Graben (Figure 24A). In the Campine, the Cretaceous sequence gradually dips and deepens towards the north. In the Antwerp Campine area, Cretaceous strata are present at a depth of 600 to 800 m, with a thickness up to 300 m. In the Meer borehole, the northernmost deep borehole in Belgium, Cretaceous layers were reached at a depth of 808 m, and were 378 m thick (Piessens et al., 2008). In the Roer Valley Graben, the top of the Cretaceous is present at a depth below 800 m. In the Molenbeersel borehole, the top of the Cretaceous is present at 1220 m depth, with a thickness of only 60 m. This reduced thickness is due to inversion of the Roer Valley Graben (uplifting of a block) during the Late Cretaceous. 45

Permian to Lower Triassic strata are present in the north-eastern Campiinne and in the Roer Valley Graben. The total preserved thickness attains 550 m in the Campiinne Basin and about 1500 m in the Roer Valley Graben. The rock sequence of interest is tthe Lower Triassic Buntsandstein Formation. Its occurrence iis shown in Figure 24B.

Figure 24: Location of the storagee opportunities in Belgium. A: the Houthem and Maastricht calcarenites (Cretaceous to Palaeocene porous carbonates); B: the Buntsandstein sandstones and the northern and southern Dinantian carbonates; C: the northern and southern coal sequences and deep coal miningn areas; D: the Neeroeteren sandstones and northern and southern Devonian carbonates (from Welkenhuyu sen et al., 2011).

Westphalian strata are present in the subsurface of a large part of the Campine. The Westphalian sequence contains coal layers (Figure 24C). The top of the seqquence is located at a depth of about 500 m in the south, to more than 1000 m in the northeeast of the Campine Basin. Its thickness may be more than 2000 m. Towards the east, in the Roer Valley Graben, the thickness of the Westphalian strata is unknown as they are buried to a depth of more than 2500 m. The Westphalian sediments were deposited during a period of gradual regression, evolving from a marine-influenced to a continental environment. A transition from marine pro-delta, lower and upper delta plain, to lower and upper alluvial plain can be recognised (Langenaeker & Dusar, 1992; Dreesen et al., 1995). This transition culminated in the deposition of thick fluvial sandstone bodies, known as the Neeroeteren Formation, in a braided river system during the Late Westphalian (Wouters et al., 1989). In the northeast of 46

the Campine Basin and in the Roer Valley Graben, the Upper Westphaliian D sandstones of the Neeeroeteren Formation have been preserved (Figure 24D). Lower Carboniferous or Dinantian strata are present in the western part of the Campine underground (Figure 24B). The top is located at a depth of 1000 m to more than 2000 m. Towards the southern border of the basin, the depth decreases to 300 m. The thickness of the Lower Carboniferous layers varies between 350 and 750 m in the western part of the basin, and 800 to more than 1200 m in the easteern part. In Table 1, the reservoir characteristics of each of these aquifers is evaluated, and an assessment is made of the storage potential of each reservoir (Piessens et all., 2008).

Table 1: Summary of the CO2 storage characteristics of the four stratigrraphic intervvals that qualify for aquifer storage of CO2 in Flanders (from Piessens et al., 2008).

The relatively limited surface of the taarget area and the lack of sufficiiently large, closed structures (traps) make the Cretaceous carbonate aquifer a less importtant target for CO2 storage in the Campine. The reservoir units are restricted to the uppeermost part of the sequence (Houtem and Maastricht formations), and the storage potential is limited due to the relatively shallow depth of the potential reservoirs.

The Lower Triassic Buntsandstein appears to be promisisng for storage of CO2. It occurs at sufficient depth within the Roer Valley Graben, and contains thick, porous and permeable sandstone bodies that can be good reservoirs. It is furthermore covered by Upper Triassic to Jurassic sediments forming an adequate seal. Trapping structures may be present. The storage potential of individual reservoirs may be in the range of 15 to 40 Mton of CO2. Sandstones of the Neeroeteren Formation provide sufficient porosity and permeability for storage of CO2. However, the reservoir is not always sealed and is nott always present at sufficient depth. The requirements on depth and salinity may be met iin the Roer Valley

Graben, but the presence of the Neeroeteren Formation and its reservoir prrooperties in that area remain to be proven. Karstified horizons within the Carboniferous Limestone Group provide sufficient porosity and permeability for the storage of CO2. The CO2 can be trapped in dome structures, covered by a seal of Namurian shales. The storage pottential of the limestone sequence however is limited due to the low accessible pore volume and the limited thickness of the pay zone. The storage potential of individual traps is estimated to be small.

Besides aquifers, storage in coal also qualifies for CO2 storage. Unmined coal sequences have a relatively large capacity, but the low permeability will pose technical difficulties. Abandoned coal mines have a very high injectivity, but pressure and sealling issues will first have to be solved. So, CO2 storage in coal could deliver substantial capacity when technical difficulties are overcome (Welkenhuysen et al., 2011). Interesting to note is that CO2 storage in coal may be combined with coal bed methane extraction (ECBM, see also natural energy resources, Laenen et al., 2004). With the current knowledge, Piessens et al. (2008) conclude that the Buntsandstein and the Dinantian reservoirs appear the most prommiising for geological CO2 storage in the Campine. In Figure 255, the potential reservoirs for geollogical CO2 storage in Belgium are shown, together with the expected economic value of these reservoirs (from Piessenss, 2011).

Figure 25: The geological map of Belgium overlain with the outline of potential reservoirs that can be used for carbon geological storage. The blue to red colours indicate the probability that the reservoirs will prove to be economic. (from Piessens, 2011). 48

Based on the available information on the use and the potential use of deep geological layers in the Campine and related human activity, the following statements can be made:

1. In the Campine, several deep geological layers may be interesting reservoirs for the storage of gas. Temporal storage of natural gas is already ongoing in Visean limestones in the Campine underground between the villages of Loenhout and Rijkevorsel. A larger area in the province of Antwerp is currently explored for enlarging the underground storage facility of natural gas, and new explorations are started in the province of Limburg as well. In order to decrease the contribution of fossil fuel emissions to global warming, studies are started to investigate the potential of long-term storage of CO2 in deep aquifers and coal. With the current knowledge, the Buntsandstein and the Dinantian reservoirs appear the most promising for geological CO2 storage in the Campine.

2. The storage of gas in deep geological layers is not expected to significantly change the properties of Boom Clay and its geological environment. Due to the injection of gas, the geochemical conditions in the reservoir rock may change, especially in the case of CO2 injection. CO2-water-rock interactions are highly reservoir specific and cannot easily be generalised (Holloway, 1997). Bertier et al. (2006) evaluated possible CO2-water-rock interactions induced by CO2 injection in three sandstone aquifers in the Campine. It was concluded that dissolution/precipitation reactions of carbonates and Al- silicates due to CO2-water-rock interactions will have a significant effect on the reservoir properties. Reservoir rocks are sealed by the overlaying low-permeable geological layers (i.e. cap rocks). Gas migration through these layers will occur, but diffusion rates are typically very slow (similar to diffusion rates in low-permeable clays used for the geological disposal of radioactive waste). As the reservoirs and low-permeable cap rocks, are located far below Boom Clay, it is expected that the storage of gas in deep geological layers will have no effect on the properties of Boom Clay and its geological environment.

3. As the drilling of boreholes is required, human intrusion by borehole drilling through the repository system forms the major risk for a geological repository. In order to be able to store gas in the deep geological reservoir, boreholes need to be drilled to reach the deep geological layer. The major risk for a geological repository is human intrusion by borehole drilling through the repository system.

4. See also S IH 2.1 on the consequences of exploitation and use of geological layers.

4.2.5 Concessions and conflict of use

In the Campine, exploration and production concessions exist for coal mining and for gas storage: the Campine coal mine concessiion (Limburgse Reconversie Maatschappij), the Gas storage and exploration concession (Fluxys) (Lie et al., 2011). The location of these concessions are shown in Figure 26. Geothermy projects do not need an application for a concession. The legal situation of concesssions is however not clear. Both federal and Flemish concessions exists. ONDRAF/NIRAS is currently studying the legal aspects and the new decree of the Flemish Community. As in the Campine, various geological layers are of economic interest (eitther for exploitation or use), the conflict of use should be evaluated and taken into accountt during siting. The Campine Basin forms an important geo-energy area in Belgium and has attracted interest for coal, hydrocarbons, geothermics, gas storage, coal bed methane, CO2 storage (Lie et al., 2011). It is evident that conflicts of interest will arise among these subjjects, but also with potential nuclear waste disposal in the overlying Tertiary clay formation. In view of the ever rising energy demand and prices it is not unlikely that more intensive exploration campaigns and possible production centres will spread all over the Campine basiinn, jeopardising the possibilities for locating suitable sites for nuclear waste repositories. Despite the exploitation and use of geological layers in the Campine, a (large) area in the west of Mol-Dessel exists with limited human activity in the Campine underground at present (see Lie et al., 2011). This is of course the present-day situation, and the evolution of human actions is unpredictable.

Figure 26: Map showing existing E&P concessions for gas storage, unmined coal (red areas) and mined coal (green areas), completed by areas of more than 250Mio m3/km2 coalbed methane from VITO simulation (hatched blue areas) (from ALBON). 50

4.2.6 Main conclusions on the natural resources in the Campine

Natural water resources are present all over the Campine and should therefore be taken into account. Groundwater is mainly pumped from the Neogene aquifer system above Boom Clay, and most wells remain at shallow depth so that they do not form a potential risk for penetrating a geological repository in Boom Clay. The aquifers underneath the Boom Clay are mainly pumped near the outcrop area, at the southern border of the Campine Basin, but generally not in the Campine Basin itself. Note however that, within the past 100 years, the amount of water wells tends to increase, deepen and shift towards the north with time. It is not known how this evolution will continue in the future. Natural mineral resources in the Campine are mainly Quaternary and Tertiary clay, sand and gravel. Because of the availability of these resources at the surface and sub-surface of the Campine, exploitation is generally located near the outcrop zone, and restricted to the upper 25 m of the surface or shallow sub-surface. It is not expected that exploitations down to a depth relevant for geological disposal will occur in the future. Exceptional mineral resources such as ores do not occur in the Campine underground. With regard to the geological setting and the long-term evolution it is not excepted that new mineral ores at depth will be formed in the next 1 Ma. The Campine is an interesting area with respect to natural energy resources. Coal of particular good quality is present in the Campine underground in deep Carboniferous layers. The coal has been extensively exploited in the eastern Campine during the past century but all coal mines are currently abandoned. Future mining activity in the eastern Campine area is not expected to occur, although considerable coal reserves are still present. Elsewhere in the Campine, coal is present in the underground as well, but it is currently considered to be economically uninteresting for exploitation, taking into account the current technological situation. The extraction of the associated coal-bed methane, however, is taken into consideration and can therefore not be ruled out for the future. Small amounts of peat and lignite are present in the Campine, but they are not considered to be relevant in the frame of geological disposal of radioactive waste, because of their occurrence at the surface. The presence of oil and gas is not considered to be relevant in view of the geological structure of the Campine Basin, and the presence of hydrocarbons in the Campine Palaeozoic is thought to be 'not unlikely', but is not proven, neither excluded. Geothermal energy is another natural energy resource of increasing interest in the Campine. Possible geothermal reservoirs are related to the Cretaceous, Bundsandstein (Lower Triassic), Silesian sandstones (Upper Carboniferous, mainly Neeroeteren sandstones), and Dinantian limestones (Lower Carbonifereous), which all occur in the deep underground in the Campine. Studies on geothermal energy extraction and its potential in Flanders, particularly in the northern Campine, are currently on-going. There is an increasing interest in the use of deep geological layers for gas storage. In the Campine, several deep geological layers may be interesting reservoirs for the temporary storage of natural gas for later consumption, or for the long-term storage of CO2 to decrease the contribution of fossil fuel emissions to global warming. Natural gas storage requires specific geological conditions with regard to structure, host rock and cap rock, and already occurs in deep Visean (Lower Carboniferous) limestones in the vicinity of Loenhout. Other locations are currently explored for additional gas storage in the Campine underground. Also 51

the possibility of carbon capture and storage in the Campine underground is currently studied. The use of deep geological reservoirs requires the drilling of deep boreholes. In this way, human intrusion by borehole drilling may form a major risk for a geological repository in the Campine underground. Exploration and production concessions in the Campine exist for coal mining and for gas storage: the Campine coal mine concession (Limburgse Reconversie Maatschappij), the Gas storage and exploration concession (Fluxys). Geothermy projects do not need an application for a concession. The legal situation of both federal and Flemish concessions is however not very clear. As in the Campine, various geological layers are of economic interest (either for exploitation or use), the conflict of use should be evaluated and taken into account during siting. The Campine Basin forms an important geo-energy area in Belgium and has attracted interest for coal and coal bed methane extraction, geothermy, and gas storage. It is evident that conflicts of interest will arise among these subjects, but also with potential nuclear waste disposal in the overlying Tertiary clay formation. In view of the ever rising energy demand and prices it is not unlikely that more intensive exploration campaigns and possible production centres will spread all over the Campine basin, jeopardising the possibilities for locating suitable sites for nuclear waste repositories. Despite the exploitation and use of geological layers in the Campine, a (large) area in the west of Mol-Dessel exists with limited human activity in the Campine underground at present (see Lie et al., 2011). This is of course the present-day situation, and there is no scientific basis for predicting future human actions.

Uncertainties – open issues – knowledge gaps:

• Potential of the Campine underground with respect to future human interest • Evolution of human interest in deep aquifers, evolution of pumping technology and pumping activity (amount and depth of boreholes, pumping rate, … ) • Future interest in coal and coal bed methane extraction, and future interest in geothermy • Future evolution of the human interest in gas storage in deep geological reservoirs.

4.3 Consequences of human actions in the Campine

In the case of inadvertent human actions, a future repository system should be able to significantly buffer the consequences of human actions. In this chapter, the consequences of human actions are evaluated. The human actions considered are related to the exploration of the Campine underground, the exploitation of natural water/mineral/energy resources, and the use of deep geological layers for gas storage described in the previous chapters. These human actions may interfere with the safety concept of the geological repository system. It is therefore of utmost importance to evaluate the possible consequences of these human actions with respect to the safety functions of a geological repository system for the disposal of radioactive waste. In what follows, the consequences of human actions are evaluated according to the various types of interest.

4.3.1 Possible consequences of exploitation of natural water resources

Groundwater resources in the Campine are studied for several reasons: (1) drilling for water (boreholes, pumping wells, …) may form a risk of human intrusion, (2) pumping of water may cause a large zone of interference (pumping cone), influencing hydraulic pressure heads, and hence the hydraulic gradient over the Boom Clay, (3) water is an important agent of radionuclide migration. Water may be exploited for various aspects of human use: for human consumption (drinking water), and for industrial and agricultural uses. In Belgium, the responsibility for the drinking water supply is assigned to the regions. Drinking water in Flanders is currently distributed by the VMW, seven intercommunal companies and seven municipal companies. Approximately 51 % of the drinking water is derived from surface water and 49 % from groundwater. The main drinking water companies in the Campine are the VMW in the province of Limburg, and the PIDPA in the province of Antwerp. In the Campine area, the majority of the groundwater supply originates from the Neogene aquifer system giving continuous supply of good quality water. The Oligocene aquifer system is not often used for water supply because of its low yield and low permeability, and the saline nature of the water especially in the north-west of the area. The Ledo-Paniselan- Brusselian aquifer system is not often used either, predominantly because of its large depth in this area, and the continuous availability of water from the Neogene aquifer system. Pumping of water has consequences on the groundwater levels in the hydrogeological system. In order to monitor the groundwater levels of the various aquifers, a groundwater monitoring network in the regional groundwater system of north-east Belgium was established 30 years ago in the framework of the Belgian radioactive waste disposal programme, and is still in use today (Labat, 2011). The last decade, the Flemish administration VMM considerably expanded the monitoring network. Monthly groundwater level measurements have been collected in numerous piezometers in north-eastern Belgium. The results for the Mol site are shown in Figure 27. The upper aquifer system in north-eastern Belgium hosts the largest groundwater reserve of Flanders and it is intensively exploited by industry and waterworks. However, the water extraction is compensated by the substantial recharge of this aquifer. The piezometric record

in the upper aquifer system shows a strong influence of the surface hydrollogy as the seasonal variations are reflected in the groundwater level (Figure 27). Such influence is not visible in the lower aquifer system beneath the Boom Clay. The aquifers in the loower aquifer system have been exploited by industries for more than 50 years at locations where these aquifers occur at shallow depth. Although the pumping rates are smaller than in the upper aquifer system, the water extraction exceeds the slow recharge resulting in a connttinuous decrease of groundwater levels (Gedeon et al., 2011).

Figure 27: Groundwater levels (GWL, in m abbove sea level) at the Mol site in the aquifers above and below the Boom Clay. Despite water exploitation, the aquifer above the Boom Clay shhows a strong influence of surface hhydrology as the seasonal variations are reflected in the groundwater level. In contrast, the aquifers below the Boom Clay are influenced byb overexploitation, as the water extraction exceeds the slow recharge, resultingn in a continuous decrease of groundwater levels (Gedeon et al.., 2011).

An important consequence of excessive pumping in the aquifers located below the Boom Clay, iss the increase in the hydraulic gradient over the Boom Clay with time (Figure 28). The estimated hydraulic gradient at the Mol site increases in time from about 0.015 in the beginning of the eighties to about 0.04 in spring 2010. This increase is caused by the decreasing groundwater level in the Oligocene aquifer system caused by tthe overexploitation of the Oligocene and the Ledo-Paniseliann-Brusselian aquifer systems. Noote that the seasonal influence is significantly smaller (magnitude about 0.01) than the influence of the pumping. The long-term evolution of the pumping is unpredictable. Possibly physicaal limits of the water exploitation exist, but the quantitative estimation of such limits is diffificult to make. The Flemish administration VMM has set up a detailed monitoring network and it can be expected that VMM will intervene through their licence policy when the decrease of groundwater levels in the Oligocene and the Ledo-Paniselian-Brusselian aquifer systems further continues. In case pumping continues as it is today, the gradient over the Boom Clay is expected to further increase, although the magnitude of such increase is difficult to eestimate. Figure 29 shows a logarithmic extrapolation of the current trend at piezometer 15 in Mol until 2040. In this case, the projected hydraulic gradient is 0.1. Several calculations haave shown that the change in hydraulic gradient across Boom Clay does not significantly modify the diffusion controlled transport in Boom Clay (Gedeon & Wemaere, 2009; Liu, in prep.).

Figure 28: Groundwater level measurements (A) in the Miocene aquifer (above the Boom Clay) and the Lower Rupelian (below the Boom Clay) and the estimated hyh draulic gradient (B) at tthe SCK•CEN piezometer site 15.

0.1 0.009 0.008 0.007 0.006 0.005

0.04 ln(y) =910-5 x - 6.9

Hydraulic gradient [-] R2 = 0.92 0.003 0.002 0.001 1980 1990 2000 2010 2020 2030 2040 Date Figure 29: Extrapolated hydraulic gradient until year 2040 yields the maximum hydrraulic gradient value of 0.1.

As a conclusion, it can be said that the pumping of water from the various aquifers around Boom Clay will have no significant consequences on a geological reposittory in Boom Clay. Even if the hydraulic gradient over the Boom Clay increases due to excessive pumping of the lower aquifers, transport of radionuclides trough the Boom Clay willl remain diffusion- dominated, and hence the safety function R2 'limited water flow' is guarantteed.

4.3.2 Possible consequences of exploitation of natural mineral resources

Natural mineral resources in the Campine are studied, as they may increase the interest of man, and hence increase human actions or even human intrusions. Because of the availability of the natural mineral resources at the surface, exploitation is currently restricted to the upper 25 m of the surface, although clay and sands are present in the Campine underground as well. Future excavation down to a depth relevant for geological disposal is not expected to occur as it is difficult, more expensive, and large reserves are present at the surface and in the sub-surface. Future excavation of natural mineral resources in the Campine is therefore expected to have no significant direct consequences for a geological repository in Boom Clay.

4.3.3 Possible consequences of exploration and exploitation of natural energy resources

Natural energy resources in the Campine are studied, as they may increase the interest of man, and hence increase human actions or even human intrusions. The major consequences of exploration are related to borehole drilling. The drilling of deep boreholes may form a major risk of inadvertent human intrusion, as the borehole may penetrate the disposal system. If this happens, the I-function 'isolation' will be affected, and a preferential pathway for radionuclide migration may be created, affecting the safety function R 'delay and attenuation of the releases'. For the drilling of boreholes, the use of a liner should also be considered as well. In the case that a liner is used, the borehole will be isolated from the waste, whereas in the case that no liner is used, the sealing capacity (convergance of the clay) will determine the isolation function. For the exploitation of natural energy resources, different consequences can be envisaged, related to the drilling of boreholes, the excavation of deep access shafts, and the removal of relatively large volumes of material at depth. Coal bed methane extraction, hydrocarbon extraction, and extraction of geothermal energy essentially require the drilling of boreholes. The major risk of inadvertent human intrusion is formed by a borehole penetrating the repository system. If this happens, the I-function 'isolation' will be affected, and a preferential pathway for radionuclide migration might be created, affecting the safety function R 'delay and attenuation of the releases'. Note however that this type of drillings are generally well prepared and often preceded by desk study.

The presently existing coal concessions are located in the eastern Campine, leaving a large zone of potential interest for geological disposal of radioactive waste outside the coal concession area. However, in the Mol-Dessel area, coal is present in the underground as well, but it is currently considered to be uninteresting for exploitation, taking into account the current technological opportunities. Technology and economics will change in the future, and hence the future exploitation of the remaining coal in the Campine underground cannot be completely ruled out. In the case of future coal exploitation elsewhere in the Campine, there might be some consequences with respect to the presence of a repository in Boom Clay.

Firstly, deep mining activity requires deep access shafts to reach the coaal beds. These will crosscut Boom Clay. It seems however very unlikely that access shafts (or more likely the freezing tubes preceding the excavation of an access shaft) would crosscut a geological repository, completely destroying all safety functions. This is because the exploitation of coal is always preceded by an exploration campaign, often including seismiccs and desk studies. Hence the location of a geological reposiitory will definitely be noticed. Itt is more likely that freezing tubes or access shafts occur in the vicinity of a repository system (so not crosscutting the disposal system, but creating a large hole in the neighbourhood). In this case, the hydraulic properties may be affected as a hydraulic gradient will be created towards the shafts, with the latter acting as a preferential pathway for radionuclide migration. This may influence the safety function R2 'limited water flow'. Furthermore, in casee of a small distance between the repository and the shaft, the I-function 'isolation' may be influencede . Note however, that the properties of the liner may decrease (or prevent) the impact on the safety functions. Secondly, mining activity is associated with the removal of large amounts of coal in the underground. In the past century, about 440 x 106 m3 coal (or about 680 x 106 m3 coal + rock) has been exploited from the Campine coal Basin. Removal of such large amounts of coal caused the 'collapse' and associated sinking/subsidence of the overburden, resulting in large depressions at the surface (Figure 30). The radius of the disturbed zone at the surface is much larger than at depth i.e. the radius of the subsided area is equal to the depth of the exploited coal beds. The range of subsidence is diirectly related to the thickness of the exploited coal bed. Comparison of topographical maps created during the past century with recent investigations performed by VLAKO has shown that significant depressions have been formed within the past 50 years above the old coal mines in the easstern Campine area (VLAKO, 2011). Gullentops and Wouters (1996) reported values of more than 8 m in the eastern Campine (Figure 31). A Persistent Scatterer Interferometry (PSI) based study committted by ONDRAF/NIRAS is currently ongoing at the Geological Survey of Belgium. In the frame of this study, aiming at quantifying the present day ground motioons (i.e., the last 20 years) in the area of interest for geological disposal, some results suggestt that the previously subsidising coal districts are now uplifting (up to +1.9cm/year; Declerq et al., 2012). This is explained by the increasing groundwater pressure recharge in the abandoned cole mines.

Figure 30: Schematic representation of possiblle consequences of coal exploitation in tthe Campine underground. The removal of large amounts of coal may result in the sinking/subsideence of the overburden, and a change in the hyh drological regime as the position of the groundwater table relative to the surface may channge (modified after Gullenntops & Wouters, 1996).

Figure 31: Iso-lines showing the depressions above the coal mines in the eastern Campine (Gullentops & Wouters, 1996)

If coal beds are exploited in the future elsewhere in the Campine, similar features might occur. The sinking may cause flexures in the layers overlying the coal bedds, and perhaps even faulting may occur (see Figure 30). In the case that the Boom Clay will be affected in such a way, it is expected that the plastic behaviour of the clay will enhance ssealing, so that the safety functions will not be significantly affected.

4.3.4 Possible consequences of exploration and use of deep geological layers for gas storage

Exploration and the use of deep geological layers for gas storage mainly requires the drilling of deep boreholes. Consequences of the drilling of boreholes are already discussed in the previouus chapter. Long-term gas storage may also be associated with gas migration (in case of bad sealing), and gas-water-rock interactions. Due to the injection of gas, the geochemical conditions in the reservoir rock may chhange, especially in the case of CO2 injection. CO2- water-rock interactions are highly resservoir specific and cannot eassily be generalised (Holloway, 1997). Bertier et al. (20066) evaluated possible CO2-wateer-rock interactions induced by CO2 injection in three sandstones aquifers in the Campine. It was concluded that dissolution/precipitation reactions of carbonates and Al-silicates due to CO2-water-rock interactions will have a significant effect on the reservoir properties. Since these reservoirs are sealed by overlaying low-permeable geological layers, and furthermoree located far below Boom Clay, it is expected that the storage of gas in deep geological layerss will have no effect on the geological environment in generaal, the properties of Boom Clay in particular, and the performance of a future repository system in Boom Clay.

4.3.5 Borehole drilling as most important type of inadvertent human intrusion

Human actions in the Campine underground, possibly affecting Boom Clay, are mainly related to the exploration of the deep underground, and the exploitation and use of deep geological layers for various reasons. Although these human actions are generally well- prepared, the risk of human intrusion is thought to be real, and hence inadvertent human intrusion cannot be excluded. In whatt follows, an overview is given of the drilling activity in the Campine and its evolution during the last century (based on the study performed in the frame of the geosynthesis project by Lie et al., 2011).

• Increasing number of boreholes with time Increasing drilling activity can be observed with time (Figure 32). The year 1900 represents the start of the coal exploration, the year 1930 the start of the economic recession and large government infrastructural programs, the year 1960 the start of geologicaal exploration wells, the year 1990 the start of progressive regionalization of Belgium. The lattter period may not contain all relevant boreholes, as obligatioon of notification no longer exists in Flanders. Hence many boreholes are introduced in the boreehole-database with delay, or even not at all.

Figure 32: Graphical representation of number of boreholes drilled per year (Lie et al., 2011).

• Decreasing number of boreholes with depth The nummber of boreholes in relation to their final depth is presented in Figure 33. The majority of boreholes is drilled within the upper 300 m, and the amount of boreholes decreases with increasing depth.

Figure 33: Graphical representation of the number of boreholes in relation to their ffiinal depth (Lie et al., 2011)

• Drilling activity in the Campine for diifferent purposes Drilling activity in the Campine is done for a variety of reasons (Figure 34): mainly water wells, and recently also wells for piezometric monitoring are drilled, but also geotechnical wells, geological reconnaissance boreholes, gas storage wells, geothermall wells, and other – undefinned– boreholes. In absolute numbers (Figure 34 above) all categories other than water wells are dwarfed by this single category. It is evident that water production is the fore most reason for borehole drilling. It is likely that this will not be different in the future. In the relative representation (Figure 34 below), some categories are not representative because of the low numbers, e.g. geothermal wells (TH), while others are on the increase, e.g. piezometric monitoring wells (PM) reflecting the growing impact of environmental regulation, or are under-represented for the post 1990 group, e.g. water wells (WW) for reasons of slow release of data, or gas storage wells (GAS) because tthey are no longer

registered. Truly remarkable is the great expansion of geological reconnaissance boreholes (VK) during the period 1960-1990 followed by a marked drop in general drilling activities after 1990, coinciding with the interruptiion in drilling programmes by thee Geological Survey of Belgium and the increased emphasis on monitoring or strictly applied drilling (from Lie et al., 2011).

Figure 34: Purpose of drilling according to thee year of drilling. Above: Absolute representation. Below: Relative representation. (from Lie et al., 2011).

• Depth distribution of boreholes often related to the purpose of drilling The depth distribution of the various types of boreholes is shown in Figure 35.  Geotechnical wells (GEO) are restricted to the shallow subsurface, and generally do not reach a depth of 100 m.  Water wells (WW) – the majoritty of boreholes in the Campine – and piezometric monitoring wells (PM) mainly occur in the shallow subsurface. The number of booreholes is highest at shallow depth (>1500 boreholes at depths between 40-99 m), and further decreasing with depth (1106 boreholes at depths between 100-149 m; 575 booreholes at depths between 150-199 m, ….; see Lie et al., 2011). Below a depth of 300 m, water wells and piezometric wells are less frequent. From a hydrogeological point of view, this means that the majority of water wells and piezometriic wells are drilled within the Neogene aquifer. Only few wells reach the deeper aquifers.  Geological reconnaissance boreholes are drilled down to various depptths, often to several 100's of meters deep, or sometimes more than 1000 m deep.  Gas storage wells and geothermal wells reach depths of more than 1000 m.

Figure 35: Number of boreholes according to the purpose of drilling in function of drilling depth. Most boreholes have a depth between 0 and 249 meters. This is very clear in the category of groundwater wells (WW) and piezometric monitoring wells (PM). Geotechnical (GEO) drilling mostly does not reach 100 m. Geological reconnaissance boreholes (VK) show all depth values, while drilling for gaas storage (GAS) and geothermmy (TH) mostly shows a depth of moree than 1000 m.

• Geographical spread of drilling activities in the Campine Water wells form the most important category of boreholes and are spread all over the Campine area (Figure 36, Lie et al., 2010). These wells generally represent wells equipped for water production from the Neogene aquifer system, but often reached the top of Boom Clay in order to reach a stratigraphic reference level. There is an obvious shift towards the north with time. Water wells for deep aquifer pumping are mostly of recent age. In the northeast, there is a zone where the drilling of water wells is absent, probably because of the large amount of water above, and the fact that the deeper aquifers are too deep to reach, and also too saline. A rather recent phenomenon is the drilling of monitoring wells. After some problems in the first half of the twentieth century, government and water companies realised that good monitoring is a must, so a network of monitoring wells was created. These boreholes are relatively well spread over the Campine area (Figure 37). Environmental considerations will probably tend to maintain the high number of wells drilled. Their depth, however, will remain linked to the depth of drilling for water production itself, so that depth increase will also be limited by salinity thresholds for drinking water (Lie et al., 2011). Geotechnical boreholes are related to infrastructural works and are generally not deeper than 40 m. Some deeper boreholes are concentrated around Antwerp and its harbour (Figure 38). Geological reconnaissance boreholes were very important for prospection of exploitable coal beds, hence most of them are situated in the eastern part of the Campine and were drilled around the year 1900 in the area of the Campine Collieries and between 1982-1986 in the prospection area north of the Campine Collieries (Figure 39). However, there are many and diverse reasons to drill geological reconnaissance boreholes, hence this category of boreholes is spread over the whole Campine area. Note that some reconnaissance boreholes were drilled in the frame of our own research on geological disposal. They are therefore not considered as potential risks of inadvertent human intrusion. Wells for gas storage are imposed by a production concession, and are concentrated near the village of Loenhout.

Figure 36: Geographic location of water wells in and through Boom Clay. Water wellls in Boom Clay generally represent wells equipped for water production from overlying Neogene aquifers, but which touched tthe Boom Claay in order to reach a stratigraphic reference level. Water wells are spread all over the Camppine and clearly show a shift towards the north with time (figure from Lie ett al., 2011)

Figure 37: Geographic location of piezometric monitoring wells in and through the Boom Clay. Piezometric monitoring wells are a recent phenomenon, mostly resulting from a reconnaissance program for all useful aquifers, and therefore much more evenly spread over the Campine area than the water wells (figure from Lie et al., 2011).

Figure 38: Geographic location ofgf eotechnical wells in and through Boom Clay. Geotechnical boreholes form a geeographically restricted group (figure from Lie et al., 2011).

Figure 39: Geographic location of reconnaissance wells in and through Boom Clay, showing a strong concentration near the most accessible coal deposits (figura from Lie et al., 2011).

• Potential risk of boreholes cutting through Boom Clay at repository depth Based on the available data on drilling activities in the Campine area, Liie et al. (2011) has drawn a map on which all boreholes (with a final depth > 40 m) are inndicated, making a distinction between boreholes not reachinng Boom Clay, boreholes reaching or ending within Boom Clay, and boreholes cutting through Boom Clay. The map is shown in Figure 40.

Figure 40: Boreholes (with a final depth > 40 m) not reachingn Boom Clay (yellow), boreholes reaching or ending within Boom Clay (red), and boreholes cutting througu h Boom Clay (blue), (from Lie et al., 2011).

It can be concluded that:  Boreholes cutting through Boom Claay are mainly located near the outcrop area. As this area is not considered for geological disposal of radioactive waste, the drilling of boreholes through Boom Clay in the outcrop area is not considered as a potentiall risk of inadvertent human intrusion.  North of the outcrop area, where Boom Clay is present at depth, most boreholes do not cut through the clay layer, although there are some exceptions (see next bullet). In this area, the majority of the drilling activity is related to the drilling of water, geenerally restricted to depths within the Neogene aquifer. Many of these boreholes do not reaach the Boom Clay (Figure 40, yellow dots), while a significant number does reach the top of the clay layer (Figure 40, red dots). However, the drilling of this type of boreholes iis not considered to form a potential risk for penetrating Boom Clay at repository depth.  It is clear that in the region where Boom Clay is deep enough to consider geological disposal of radioactive waste, only few boreholes cut through the clay layer (Figure 41). Some of these boreholes are water wells or piezometric monitoring wells reaching the deeper aquifers. A cluster of deep boreholes related to the gas storage at Loenhout can be observed. Deep geological reconnaissance boreholes are spread over the Campine area, 66

and concentrated in the Campine coal basin. The future drilling of deep geological reconnaissance boreholes may be done for a variety of reasons and hence spread all over the Campine. Reconnaissance boreholes for our own research are not coonsidered to form a potential risk for inadvertent human intrusion as future drilling of this ttype of boreholes is unlikely once the repository is a fact. Taking into account the current intterest in gas storage and the potential for geothermal energy exploitation, drilling activities in the Campine for these purposes will definitely increase in the future. Drilling of such deep boreholes in the Campine may form a potential risk of inadvertent human intrusion in a future repository system in Boom Clay. However, it is believed that borehole drilling for the latter purposes will be preceded by well-prepared exploration campaigns (e.g. seismic campaigns), so that the risk of inadvertent human intrusion will be significantly reduced.

Figure 41: Detailed map of the Campine, with indication of boreholes crosscutting the Boom Clay, and the aim of drilling (figure from Lie et al., 2011).

4.3.6 Main conclusions on the possible consequences of human actions in the Campine

The pumping of water from the various aquifers around Boom Clay is expected to have no significant consequences on the performance of a geological repository in Boom Clay. Most pumping wells remain at shallow or moderate depth, not cross-cutting Boom Clay at a depth relevant for the geological disposal of radioactive waste. Increasing interest in the deeper aquifers in the Campine area is possible, although the increasing salt content strongly limits possible applications of the water pumped from these aquifers. Excessive pumping from the aquifers underneath the Boom Clay might increase the hydraulic gradient over the Boom Clay, but it is expected that transport of radionuclides trough the Boom Clay will remain diffusion-controlled, and hence the safety function R2 'limited water flow' is guaranteed. Excavation of natural mineral resources in the Campine is expected to have no significant consequences on the performance of a geological repository in Boom Clay, because of their availability at the surface and shallow sub-surface. Future excavation of the remaining coal in the Campine underground seems unlikely in view of the present perspectives, although future human actions are unpredictable. Deep mining activity will be associated with the removal of large amounts of coal in the underground, causing the 'collapse' and associated sinking/subsidence of the overburden, resulting in large depressions at the surface. In case future mining activity might occur, it is expected to continue in the eastern Campine and not in the area representative for the geological disposal of radioactive waste more towards the north-west. In case that the mining activity should occur in the vicinity of a geological disposal system, the mining activity (and associated collapse) might affect the geological stability of the area (and hence the I2 safety function isolation), and might cause significant changes in the hydrology of the area, possibly influencing the R2 safety function (limited water flow). Also the location of the access shafts might influence the safety functions of a geological repository. If access shafts are built in the vicinity of a repository, the hydrogeological context might change, as a hydraulic gradient might be created towards the shafts. Moreover, the shafts might act as a preferential pathway for radionuclide migration. This may influence the R2 safety function 'limited water flow'. Furthermore, the distance between the repository and the shaft may have an impact on the I1 safety function 'isolation'. Exploration, exploitation of many natural energy resources (coal bed methane extraction, hydrocarbon extraction, and extraction of geothermal energy), and the use of deep geological layers for gas storage essentialy requires the drilling of deep boreholes. The major risk of inadvertent human intrusion is formed by a borehole penetrating the repository system. If this happens, this inadvertent human intrusion might have consequences on the I1 safety function 'isolation', and on the R2 safety function 'limited water flow' as a preferential pathway for radionuclide migration might be created. Note however that such drillings are generally well prepared and often preceded by desk study, minimalizing the risk of inadvertent human intrusion. Furthermore, the presence of a lining and the convergence of the clay will strongly limit the impact of a borehole drilled through the repository.

5 References

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