<figure><img src="image_59.png" /><figcaption>**Fig. 1.56** Example of possible distribution of unpolluted excavation materials to the quarries nearest to the material extraction sites (the figures in black are the value in tonnes). The colours of the circles link a given extraction site to one or more quarries or backfilling sites. The figures in yellow show the quantity of materials that can be accepted by the quarries during the excavation. Swiss pathways are represented by a red dot, and French pathways by a yellow dot</figcaption></figure>

and in the absence of more detailed geochemical analyses, a working assumption of 30% of materials exhibiting natural geogenic variations appears to be the most reasonable.

As part of the FCC feasibility study, additional insights may be gained by examining recent projects related to the enlargement of certain LHC accelerator caverns (HL-LHC project). Underground excavations for this project indicated the presence of hydrocarbons in approximately 15% of the materials in France and nearly 50% in Switzerland. This difference is influenced not only by actual variations in subsurface conditions but also by differences in environmental regulations between the two countries.

Based on these initial inventories, presented in Sect. 1.6.6, a preliminary approach to the management of the excavated material was drawn up and used to assess the transportation costs from the extraction sites to the storage facilities and backfilling sites. The average transport distances are estimated to be 20 km in Switzerland and 40 km in France for uncontaminated materials and approximately 100 km in both countries for materials requiring specific treatment. This is because treatment facilities are generally located outside the Lake Geneva region, where the FCC will be installed.

Figure 1.56 presents the results obtained for uncontaminated materials. In this figure, the values displayed on black backgrounds indicate the quantities of material expected to be extracted per site, while the colours of the circles correspond to the quarries or backfilling sites designated for the disposal of outgoing materials. It should be noted that only quarries with a prefectoral permit valid beyond 2033 have been considered.

These scenarios will require updates, as the annual intake capacity of each site may be revised based on regional requirements. The extracted quantities are provided as an indication of each quarry’s backfill capacity. However, further studies will be necessary to assess the feasibility of this operation, and agreements with quarry operators should be established in due course.

Subject to updating and optimisation with respect to transportation, these studies show that it would be possible to find a pathway for all the materials excavated from the potential FCC project sites and provide an initial financial estimate which could be used as a basis to begin the optimisation process according to the ‘avoid, reduce, compensate’ principle.
The distribution of excavated materials should integrate the identified reuse cases as soon as the technical information on their feasibility becomes available. Therefore, the current distribution should be viewed as a preliminary benchmark assessment, expected to evolve positively as studies progress. Close collaboration between the FCC and the Host State authorities is essential to refine and better adapt the principles of the strategy of the excavation material management in alignment with the regional framework.

A subsequent project preparatory phase should include the development of a roadmap along the following points:

* Confirmation of the characteristics of the excavated material and correlation to the potential reuses via the analysis of the ongoing and future subsurface investigations;

* Study of the technical methods for the real-time analysis of the materials and their sorting according to their characteristics and potential reuse.

* Pilot projects on the potential reuse cases: on the example of the ongoing OpenSkyLab project for developing processes for using excavated materials for landscaping, other projects could be started for testing, for example, the possible reuse as construction or isolation materials. This study should include an evaluation of the environmental, economic and societal impact due to the potential injection on the market of the products based on excavated materials;

* Definition of the regulatory framework for the management of the excavated materials with the host States;

* Update of the regional treatment and disposal opportunities (e.g., availability of quarries, final deposits, treatment facilities) and related regulation;

* Study on the excavation material logistics (traceability, fluxes, conveyors etc.), including the evaluation of environmental and societal impacts and the potential limitations.

Certain activities can be carried out in parallel. Others must follow a sequential process, leading to the development of a preliminary excavation material management plan. Based on this plan, more concrete discussions can be initiated with the administrations of the Host States and the owners of potential final deposit and reuse sites.

# Chapter 2

## Territorial implementation

### 2.1 Introduction

To be able to take an informed decision for a future particle-collider based research infrastructure and to undergo the necessary project authorisation process with national authorities, a specific implementation scenario needs to be conceived. Such a geo-localised scenario must be well-balanced, considering the three main dimensions:

1. Scientific excellence.

2. Territorial compatibility.

3. Risks related to the implementation that affect cost and schedule.

While the exploratory phase of the FCC study between 2014 and 2018 [11] focused on the ‘in principle’ feasibility of the accelerator and the territorial boundary conditions, the studies between 2019 and 2024 included the development of a well-balanced project scenario considering the three above-cited dimensions.

This chapter summarises the methodology adopted to carry out this work as documented in [12], sheds light on the variants considered and the evolution towards a reference scenario. The resulting scenario presented serves as a reference to design the various elements of the future circular collider-based research infrastructure if the global science community decides to make such a facility their priority.

The reference scenario presented is the result of a total of 10 years study of a large variety of scientific, technical, cost, societal and environmental aspects. It represents an infrastructure with a circumference of approximately 91 km, including eight surface sites. It is conceived to be able to host two distinct particle colliders, a high intensity lepton collider first and a high energy hadron collider in subsequent phases. The second machine and its experiments profit significantly from the assets put in place for the first phase due to the residual asset value of that infrastructure, contributing to the overall sustainability of this long-term science programme. The iterative process that was used to develop the reference implementation scenario is summarised in the following sections.

The presence of a sufficiently large community of users committed to carrying out scientific research with the particle colliders for several decades is a prerequisite for justifying the construction of a research infrastructure of this scale. Scenarios involving a much smaller collider with a circumference of less than 90 km, would not allow the provision of a performance and a research programme that could attract a critical mass of scientists for a
sustained period of time. The doubling of the interaction regions from two to four reflects the aim of attracting as many scientists as possible to such an infrastructure. The size and the characteristics of the infrastructure also permit additional scientific activities with the injector and particle colliders, as is the case today at CERN with the LHC programme.

In terms of compatibility with the geological conditions that affect the construction risks and costs, only two types of configurations meet all requirements: an infrastructure with a circumference of between 89 and 91 km and eight surface sites, and a layout with a circumference of between 97 and 98 km and twelve surface sites. Concerning the availability of suitable surface site locations, however, layouts and placements suitable for scenarios involving a collider with a circumference well in excess of 91 km and comprising more than eight surface sites turned out to entail unacceptable risks concerning their implementation.

To date, only scenarios around 91 km circumference and eight surface sites seem capable of satisfying the following three requirements:

1. Good scientific performance of the particle collider and four experiment sites.

2. Compatibility with territorial constraints at the surface and the subsurface.

3. Understanding of the implementation conditions from cost and risk perspectives.

One of the scenarios named PA31 stands out from all of those iteratively developed following the ‘Avoid-reduce-compensate’ methodology [13] and analysed with a multi-criteria approach recommended for industrial installations [14, 15]. It has been further studied and optimised in depth involving bibliographic research, field work, and continuous discussions with the public administration services in both countries involved and with key stakeholders in the implementation area. In case of a decision to move forward with the implementation of a project, the conditions for this scenario will have to be further analysed, the scenario will have to be further improved, and detailed designs have to be developed before implementation can start.

Territorial constraints and legal frameworks in host countries and within the European Union are constantly evolving. Between 2014 and 2023, several layout and placement scenarios had to be ruled out due to these changes. The information contained in this document and the working hypothesis described here are therefore provisional. For the project to come to fruition, the validation and definitive freeze of a scenario securing the required surface areas and subsurface volumes should be done as soon as possible.

## 2.2 Methodology to develop a sustainable project

### 2.2.1 Approach

From the outset, the objective of the study was to draw up a scientific research infrastructure that reconciles, in an eco-design approach [16, 17], i) scientific excellence, ii) territorial compatibility and iii) consideration of acceptable risks associated with project implementation. A systematic process therefore had to be set up to develop scenarios through an iterative approach, taking these three essential aspects into account at all times. The eco-design approach adopts the ‘Avoid-Reduce-Compensate’ methodology (see Fig. 2.1), which takes into account both constraints and opportunities.

This process, which complies with the French Environmental Code, the Environmental Protection Act and the Swiss Federal Ordinance relating to the Environmental Impact Assessment Regulation, is perfectly in line with the desire and objective to arrive at a proposal based on a balanced scenario.

Ideally, all stakeholders are involved in the process from the outset. However, an iterative approach had to be taken given that in the beginning the placement of the infrastructure was not defined, the knowledge of evolving territorial conditions was incomplete, the possibilities of effectively involving stakeholders at all levels of society were limited, the knowledge of the technological choices to be made for periods longer than twenty years is evolving, and the availability of resources for conceptual studies and personnel at this very early stage is limited.

Despite these constraints, the international science community is committed to transparency and public participation. The aim is to obtain a “social licence to operate” [18] by developing a scientific peaceful endeavour in the context of a systematic and structured public participation process. To this end, the feasibility study phase laid the foundation for the implementation of an approach in line with the regulatory frameworks and the best practices in France and in Switzerland. The approach goes beyond informing the public, engaging affected stakeholders in the discussion of the various segments of the project and, as far as possible, involving them in design considerations that affect their territory. A consultation process will therefore be carried out in an equitable manner on both sides of the border, respecting the approaches and procedures specific to each country.

The scenario development process first used the bibliographic information available. It gradually integrated further aspects as they became relevant and stakeholders as they were identified. This is the case, for example, for the participation of local elected representatives (municipalities, intercommunal structures, departments, regions). Depending on the layout, the number of surface sites and their location, between twelve and twenty communes
<figure><img src="image_60.png" /><figcaption>**Fig. 2.2** The Plan-Do-Check-Act approach for environmental management, defined in standard NF EN ISO 14001, Sect. 0.4, page vii, is the basis for ‘eco-design’</figcaption></figure>

<figure><img src="image_61.png" /></figure>

were at any time directly concerned and had to be consulted. A further 30 or so municipalities could be indirectly affected, in terms of access needs or infrastructure connections, or simply because the tunnel passes under their territory. Other stakeholders will need to be added for the development of a detailed design scenario. These additional stakeholders include local infrastructure operators (e.g., water, canals or road networks), representatives of local authorities responsible for certain subjects (e.g., traffic and nature) and associations (hunting, fishing, tourism, environmental protection, heritage preservation, economic development, etc.). It is prudent to approach these representatives as soon as the likelihood of their community being affected in some way is sufficiently high, i.e., when a specific scenario and an intent for a project exist. In this way, their availability to be informed about the project vision can be taken into account, the relevant contacts can be designated and the limited availability of the study group members can be taken into account. This study has involved selected elected representatives of directly affected locations. A systematic involvement of a wider domain of stakeholders is potentially appropriate at a subsequent phase, when a project intent is formulated and when a reference scenario that permits a useful involvement exists.

The international standards applicable, NF EN ISO 14001 (environmental management [19]) and (for eco-design) NF EN ISO 14006 [16] (see Fig. 2.2) require an iterative approach.

This approach is also set out in greater detail in the good practices guidelines for environmental impact assessments, established by the French Ministry for the Ecological Transition, Biodiversity, Forests, Marine Affairs and Fisheries, and in the NF EN ISO 31000 [20] standard on risk management (page 8 of the ISO standard) (see Fig. 2.3).
**Fig. 2.3** Diagram from iterative impact study, French Ministry of Territorial Development and the Environment, 2001, p. 27, see footnote 6). Although this guide is from 2001 and specific regulations have changed, the principles described in the diagram are still valid and recommended for use today

<figure><img src="image_62.png" /><figcaption>**Table 2.1** Definition of the territorial sensitivity levels, representing constraints for determining the configuration and location. Each colour-coded level represents several data layers that can be shown on a map in a geographical information system (http://cern.ch/fcc-sensitivity-grid)</figcaption></figure>

<table><thead><tr><td>Level</td><td>Designation</td><td>Description</td></tr></thead><tbody><tr><td>4</td><td>Unacceptable</td><td>The level of constraint is such that the zone cannot be considered for a surface site. These zones are considered to be exclusion zones and should be avoided.</td></tr><tr><td>3</td><td>High</td><td>The zone is not recommended for the location of a surface site, but may be considered if it is decisive for the feasibility of the project, with additional reduction, compensation, or mitigation measures.</td></tr><tr><td>2</td><td>Acceptable</td><td>The zone is acceptable for the location of a surface site with appropriate reduction, compensation or mitigation measures.</td></tr><tr><td>1</td><td>Low</td><td>The zone can be considered for a surface site without further significant measures. Compensation may still be necessary.</td></tr></tbody></table>

### 2.2.2 Iterative process

The scenario development process is based on the iterative Plan-Do-Check-Act (PDCA) approach, and incorporates the Avoid-Reduce-Compensate (ERC) approach.

The process starts at a macroscopic level to identify the major constraints and opportunities. The constraints are recorded in a geographical information system (GIS) so that a map-based identification of areas to be avoided and areas in which a surface site or a subsurface passage would need to be limited can be rapidly identified. Such a system includes many data layers. Today, GIS-based Environmental Information System (EIS) for the FCC study comprises more than 120 layers that contain detailed information and are also used to build summary layers that are colour coded as shown in Table 2.1. The individual territorial sensitivity grid levels differ for French and Swiss territories [21]. They are based on national legal and regulatory constraints and concern particular regional and local constraints that are the result of exchanges with expert companies in the areas of environmental impact studies and project development as well as with public administration services. Typically, the constraints considered for the development of the future collider layout and placement scenario are highly conservative and sometimes exceed required legal and regulatory constraints in several domains to ensure that good territorial compatibility can be achieved by respecting known local and cultural heritage.

Scenarios were explicitly checked against such different interest zones, and a weighting took place whether to continue considering locations with known constraints or to discard the scenario due to its particular local high-value nature. The same strict constraint was applied to enlarged drinking water perimeters that were excluded as surface site locations, despite the fact that from a regulatory point of view, surface site constructions would be allowed in such zones.

This step permits the definition of entire classes for particle collider layout and placement candidates. Picking a representative candidate of a class permits the choices between the various configurations and locations under consideration to be progressively refined, introducing additional information obtained from the study of promising variants and discarding variants as soon as obstacles are detected. If a scenario is discarded, the main exclusion reasons are analysed and the entire class of scenarios is analysed with respect to those conditions. In many cases, this permits the elimination of an entire class of scenarios and the establishment of major exclusion criteria
<figure><img src="image_63.png" /><figcaption>**Fig. 2.4** As the layout and placement studies progress, additional information and stakeholders are included in the process to create a balanced scenario that meets the needs of all stakeholders</figcaption></figure>

and constraints at the macroscopic level. The approach helps to reduce the solution space and to avoid further consideration of unfeasible scenarios in the subsequent steps.

Scenarios that are considered potentially feasible are further analysed with more detailed information and further stakeholders are involved. The same elimination process as above is applied.

This approach leads to a gradual definition of exclusion criteria and zones, and to a selection of likely layouts and placements that can eventually be optimised.

With regard to the territorial analyses, the analysis process begins at a level that considers topography, bathymetry, geology, hydrography, protection zones and urban development. It then gradually expands to include additional aspects such as accessibility, transport, disturbances, potentially conflicting planned developments and the availability of technical and natural resources (e.g., electricity or water). It then incorporates additional elements, such as social factors, local preservation and development objectives, visibility, shared visibility, or disturbances for stakeholders affected directly (e.g., neighbours) and indirectly (e.g., communities affected by construction site traffic).

The scenario-building process requires a more detailed analysis phase, aimed at the direct participation of stakeholders and local players in order to draw up a scenario adapted to the specific plot of land, always taking into account the three main issues (science, territory, implementation) within the framework of the iteratively improving avoid-reduce-compensate project development approach.

With the choice of a reference scenario as a prerequisite for field studies, environmental impact assessment, and technical design work, also the dialogue with public stakeholders could be gradually defined and initiated. Considering the valuable accompaniment of the two CERN host states and their advice in engaging the public in territorial development projects, the study collaboration requested CERN to consult the French “Commission nationale du débat public (CNDP)” (english: National Commission for Public Debate) in 2024. A first analysis resulting in a list of recommendations were made public on 6 March 2025 [22]. Taking account of these recommendations and considering the transborder context of the particle collider scenario, it was decided to extend the collaboration with the CNDP and engage with the Swiss authorities to prepare subsequent public engagement processes in both Host States, should the international scientific collaboration express an intent to develop the study into a project and enter a preparatory phase.

Informal and formal processes engaging the public are ideally carried out as early as possible, and the French government reminds the principle and need of anticipation on various occasions. At the same time, care must be taken to time engagement appropriately. This approach aims at assuring that the project scenario can be adapted based on the involvement of stakeholders and having sufficient technical information at hand to inform he engaged stakeholders about the needs and constraints that govern the project and the environment in which it would eventually be embedded.

As new information is integrated into this iterative process, automated and cartographic research must be progressively completed, followed by manual research, interviews with people with good knowledge of the region, field visits and consultation with stakeholders (see Fig. 2.4).

### 2.2.3 Scenario assessment

To determine the value of a scenario, to assess if it should be further optimised or discarded and to be able to compare the merits of different scenarios among each other, a multi-criteria analysis scheme has been developed,
based on an approach presented by the French organisation Cerema in its guidelines for the environmental analysis of linear transport infrastructures [14]. This approach was completed using the UNIDO International Guidelines for Industrial Parks, published in November 2019 [15].

As required by the regulatory environmental authorisation frameworks in France and Switzerland, a development project is to be considered in broad terms, extending the analysis to various non-technical relevant aspects such as indirectly affected stakeholders; legal, regulatory, social and economic factors; networks (roads, railways, water, electricity, canals, public service and safety infrastructures); heritage sites; visual aspects; disturbances (noise, dust, light, smells, pollution) and potential benefits. As recommended in the Cerema guide, this approach was used to assess the relative merits of each variant, and contribute to the development of reduction, compensation, and support measures in an open and transparent process. In Switzerland, and more specifically in the canton of Geneva, a parallel can be drawn with the cantonal guide for the strategic environmental assessment tool (EES) [23]. When plans, programmes or projects (PPPs) are drawn up, the EES is sometimes used to ensure that environmental and human health issues are taken into account systematically and at an early stage, as defined in the Environmental Protection Act [24]. As such, it can be used as a decision-making tool, assessing the merits of different scenarios.

The multi-criteria analysis results use standardised qualitative indicators to compare the suitability of different scenarios. Its application during the scenario-building process makes it possible to quickly identify the types of scenarios that present significant advantages or disadvantages, and to determine whether the differences between the scenarios are major or minor. This approach also offers the advantage of clarifying which elements have the greatest or least influence on the value of the scenario, and thus guides the development of new types of scenarios. This approach is then used in the subsequent optimisation stages, for example with regard to moving shaft and surface sites to more suitable locations and taking into account the availability of existing infrastructures (e.g., roads, railways, water supply and treatment, electricity), urban planning documents (PLU, PLUi, PADD, SCoT, PDcn, PDcom) and synergies and opportunities (e.g., supply of residual heat, sharing of technical infrastructures, reduced transport distances).

The criteria list is made up of nine topics, each comprising several detailed criteria. These criteria cover the various themes that are relevant for an implementation. 32 environmental factors, the scenario configuration determining the performance for scientific research, implementation costs and risks were taken into account:

1. Land status

(a) Availability of plots

(b) Clearly defined ownership

(c) Plot price

(d) Acquisition time and expected difficulties in obtaining rights

(e) Plot development cost

2. Road connections

(a) Distance from transport, industrial and other infrastructures

(b) Distance from populated areas

3. Raw materials and services

(a) Availability of raw materials for construction and resources for operation

(b) Proximity to service providers

4. Physical characteristics

(a) Plot size and shape

(b) Topography

(c) Shaft depth

(d) Drainage and sanitation requirements for construction

(e) Surface soil condition

(f) Water resources

(g) Accessibility

(h) Subsurface conditions (physical)

(i) Subsurface conditions (regulatory)

5. Infrastructure

(a) Accessibility of electrical power

(b) Communication network

(c) Water for industrial use

(d) Drinking water

(e) Waste water discharge, rainwater collection, disposal and treatment points

(f) Temporary storage and processing areas during construction

6. Environmental and social factors

(a) Existing environmental constraints

(b) Fauna and flora
(c) Existence of construction constraints

(d) Adjacent constraints

(e) Disturbances

(f) Availability and accessibility of workforce

(g) Involvement of local authorities

(h) Support from civil society

7. Configuration

(a) Geometry

(b) Size

(c) Transfer lines

8. Implementation cost

9. Risks related to the implementation

For each scenario, six sets of criteria were evaluated individually for each of the surface site candidate locations for the surface sites in that scenario (land status, road connections, raw materials and services, physical characteristics, infrastructure, environmental and social factors) and three high-level criteria were considered for the overall scenario (configuration, costs, and risk).

Spreadsheets for each scenario were created to assign each criterion a qualitative score between -2 and +2, according to a pre-defined evaluation grid with standardised conditions. A score of '0' represents a neutral assessment of the indicator. For each high-level criterion, the scores of its sub-criteria were added together to provide an indicator for that criterion. The spreadsheet also shows the macro-criteria scores, and presents a final score for all criteria in the form of a percentage between 0 and 100. Lastly, the values of the criteria are synthesised to provide indicators for 1) scientific excellence, 2) territorial aspects and 3) appropriateness of project implementation. This approach not only makes it possible to quickly estimate the value of a scenario and compare it with others, but also to highlight criteria that are insufficiently known and require in-depth study.

Values were assigned for the qualitative indicators through a collaborative process by the multidisciplinary team, based on bibliographic and cartographic studies, database analysis, geographical information system queries, simulation and modelling. There were also field trips and field investigations; interviews to discuss the most suitable footprint with staff from the administrative departments of the two host states (e.g., DT, GESDEC, OCEV, OCAN, OCT in Switzerland; DDT 01 and DDT 74 in France); consultation with experts working in different technical fields (Cerema, Ecotec, HydroGéo, ILF, GADZ, particle accelerator designers working in many partner institutes, geologists employed in many partner universities); and feedback from local players during working meetings with municipalities, inter-communal entities, and elected representatives.

A disadvantage of this approach is that it simply adds up and averages all values. In some cases, there may be an obstacle related to territorial or scientific aspects or to project implementation. However, averaging means that a single low value will just lower the overall ranking but will not necessarily show the blocking point in the summary. The multi-criteria analysis was therefore complemented by an overall assessment of the scenario, which permitted the highlighting of the potential benefits of one scenario that make it particularly preferable to others or which indicate whether the scenario is difficult or not feasible. Thus, scenarios presenting obstacles continue to be analysed and recorded, but they are rejected even if the value of a thematic indicator (scientific performance, territorial compatibility or project implementation) is higher than the acceptable threshold value for that element. Examples of such situations include the strong probability of encountering geological features that would expose the project to an unacceptably high risk (karst, potentially conflicting water-bearing layers, crossing a major fault, presence of high-pressure aquifers), patrimony sites that represent incompatibilities with a technical installation, too dense residential zones, incompatibilities with local or regional development policies, a collider circumference that would not allow the scientific research programme to be conducted for technical reasons or would not allow its operation to be viable (for example, a collider circumference significantly smaller than 90 km). The ranking is highlighted in summary diagrams such as the one outlined as an example in Fig. 2.5. The illustration also shows the limitations of multi-criteria analysis: for example, two surface site locations in the PA0 scenario with twelve sites developed during the first exploratory phase are located in areas considered to be blocking points, but this is only visible in the individual sheet for each site. The three-column summary alone, however, does not show these exclusion criteria and must, therefore, be supplemented by a brief text description.

Territorial (T), implementation(I), and scientific (S) issues can, in fact, be easily visualised and compared thanks to this standardised qualitative approach. Figure 2.6 highlights the merits of the current scenario working hypothesis PA31, which makes it a preferred scenario for the detailed territorial and technical analysis. Such overviews also helped to understand that scenarios involving twelve sites do not meet the required conditions to undergo an in-depth study. The approach permitted further optimisation by understanding how the improvement on one site could potentially lower the performance of another and thus retain scenarios for further optimisation that improved all sites individually and the entire scenario as a whole.

With additional information becoming available, the assessment changes and therefore further optimisation of the scenario will be required until a decision to proceed with a construction project can be taken. The advantage of
<figure><img src="image_64.png" /></figure>

<table><caption>**Fig. 2.5** Example of a summary view of the multi-criteria analysis of an scenario (PA0-0.1). The scenario seems feasible, even if the territorial feasibility would be low. However, a closer look at each site reveals many blocking points</caption><thead><tr><th>PA0-0.1</th><th>PA</th><th>PB</th><th>PC</th><th>PD</th><th>PE</th><th>PF</th><th>PG</th><th>PH</th><th>PI</th><th>PJ</th><th>PK</th><th>PL</th><th>Tracé</th><th>Total</th></tr></thead><tbody><tr><th>FCC-ee</th><td>EXP</td><td></td><td></td><td>RF</td><td></td><td></td><td>EXP</td><td></td><td></td><td>RF</td><td></td><td></td><td></td><td>97,75 km</td></tr><tr><th>FCC-hh</th><td>EXP</td><td>EXP</td><td>Cryo</td><td></td><td>Cryo</td><td>Col</td><td></td><td>RF</td><td>Cryo</td><td>Col</td><td>Cryo</td><td></td><td>EXP</td><td></td></tr><tr><th>Site</th><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><th>Score</th><td>89</td><td>52</td><td>51</td><td>61</td><td>75</td><td>40</td><td>41</td><td>36</td><td>49</td><td>45</td><td>33</td><td>36</td><td>84</td><td>53</td></tr></tbody></table>

<figure><img src="image_65.png" /></figure>

<table><caption>**Fig. 2.6** Summary of the multi-criteria analysis of reference scenario PA31-4.0</caption><thead><tr><th>PA31-4.0</th><th>PA</th><th>PB</th><th>-</th><th>PD</th><th>-</th><th>PF</th><th>PG</th><th>PH</th><th>-</th><th>PJ</th><th>-</th><th>PL</th><th>Tracé</th><th>Total</th></tr></thead><tbody><tr><th>FCC-ee</th><td>EXP</td><td>Tec</td><td></td><td>Tec</td><td></td><td>Tec</td><td>EXP</td><td>RF</td><td></td><td>Tec</td><td></td><td>RF</td><td></td><td>90,6 km</td></tr><tr><th>FCC-hh</th><td>EXP</td><td>Cryo</td><td></td><td>EXP</td><td></td><td>Cryo</td><td>EXP</td><td>Cryo</td><td></td><td>EXP</td><td></td><td>Cryo</td><td></td><td>B</td></tr><tr><th>Site</th><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><th>Score</th><td>84</td><td>70</td><td>-</td><td>89</td><td>-</td><td>79</td><td>78</td><td>72</td><td>-</td><td>75</td><td>-</td><td>77</td><td>82</td><td>79</td></tr></tbody></table>

the systematic approach is that it permits the demonstration that there is a continuous improvement of the project scenario based on the growing understanding of the boundary conditions and the consideration of stakeholder input during an environmental evaluation and project authorisation process.

Around a hundred different scenarios have been developed and individually analysed (see Fig. 2.7). Eventually, the ten most promising scenarios (PA0-0.1, the scenario developed for the Conceptual Design Report, turned out to be not feasible and serves as a performance reference baseline only) have been retained for a review with experts from different project development domains. The scenarios were ranked using the VIKOR [25] quantitative method that was applied to the established multi-criteria analysis (see Fig. 2.8). The algorithm permits the evaluation of different multi-criteria factors with different units and scales and with different, potentially even conflicting, minimisation and maximisation goals. The following VIKOR criteria were set for the establishment of the ranking:
<figure><img src="image_66.png" /><figcaption>**Fig. 2.7** Around one hundred different layout scenarios were studied and individually analysed</figcaption></figure>

1. **Number of sites:** An eight-site configuration offers four interaction points for the lepton collider, compared with just two interaction points for the twelve-site configuration. Therefore, the goal was to minimise the number of sites with a weight contribution of 5%.

2. **Total length of curved sections:** A longer circumference length provides higher scientific performance or simpler design. Therefore, the goal was to maximise the circumference with a weight contribution of 5%.

3. **Territorial compatibility:** Territorial compatibility, ease of implementation and scientific performance are given equal weights of 30% each. Each of these three pillars must be maximised, and all three need to be balanced to ensure the feasibility of the scenario. The feasibility of each scenario can only be determined through detailed analysis.

4. **Compatibility of technical implementation and construction with geological constraints, configuration, and layout:** Maximise with a weight of 30%.
<table><caption>**Fig. 2.8** Multi-criteria analysis based ranking of the most promising implementation scenarios in 2022 with the performance of the gradual improvements of reference scenario class PA31</caption><thead><tr><th rowspan="2">#</th><th rowspan="2">Scenario</th><th rowspan="2">Number of sites</th><th rowspan="2">Arc length [km]</th><th rowspan="2">Total circumference [km]</th><th colspan="6">Results of multi-criteria analysis</th></tr><tr><th>T<sup>1)</sup></th><th>I<sup>2)</sup></th><th>S<sup>3)</sup></th><th>T<sup>1)</sup></th><th>I<sup>2)</sup></th><th>S<sup>3)</sup></th><th>Summary<sup>4)</sup></th><th>VIKOR<sup>5)</sup></th></tr></thead><tbody><tr><td>1</td><td>PA0-0.1</td><td>12</td><td>83.750</td><td>97.750</td><td>53</td><td>75</td><td>83</td><td>D</td><td>B</td><td>B</td><td>D</td><td>7</td></tr><tr><td>2</td><td>PB17-0.8</td><td>12</td><td>81.193</td><td>96.093</td><td>58</td><td>81</td><td>79</td><td>C</td><td>B</td><td>B</td><td>C</td><td>4</td></tr><tr><td>3</td><td>PB19-0.3</td><td>12</td><td>77.784</td><td>91.324</td><td>69</td><td>25</td><td>63</td><td>C</td><td>E</td><td>C</td><td>C</td><td>11</td></tr><tr><td>4</td><td>PA21-0.3</td><td>8</td><td>82.045</td><td>95.845</td><td>80</td><td>37</td><td>65</td><td>B</td><td>E</td><td>C</td><td>B</td><td>5</td></tr><tr><td>5</td><td>PA38-0.1*</td><td>12</td><td>75.228</td><td>89.228</td><td>57</td><td>81</td><td>67</td><td>C</td><td>B</td><td>C</td><td>C</td><td>9</td></tr><tr><td>6</td><td>PA33-0.13</td><td>8</td><td>79.377</td><td>93.377</td><td>50</td><td>81</td><td>83</td><td>D</td><td>B</td><td>B</td><td>D</td><td>8</td></tr><tr><td>7</td><td>PA35-0.6</td><td>8</td><td>78.637</td><td>92.637</td><td>54</td><td>75</td><td>83</td><td>D</td><td>B</td><td>B</td><td>C</td><td>6</td></tr><tr><td>8</td><td>PA37-0.3</td><td>8</td><td>80.823</td><td>94.823</td><td>54</td><td>62</td><td>53</td><td>D</td><td>C</td><td>D</td><td>D</td><td>10</td></tr><tr><td>9</td><td>PA31-1.0</td><td>8</td><td>76.932</td><td>91.172</td><td>74</td><td>87</td><td>80</td><td>B</td><td>A</td><td>B</td><td>B</td><td>3</td></tr><tr><td>10</td><td>PA31-3.0</td><td>8</td><td>76.929</td><td>90.658</td><td>76</td><td>87</td><td>78</td><td>B</td><td>A</td><td>B</td><td>B</td><td>2</td></tr><tr><td>11</td><td>PA31-4.0</td><td>8</td><td>76.929</td><td>90.658</td><td>78</td><td>87</td><td>78</td><td>B</td><td>A</td><td>B</td><td>B</td><td>1</td></tr></tbody><tfoot><tr><td colspan="12">1) Territorial compatibility, 2) Ease of project implementation, 3) Scientific performance, 4) Ranking according to multi-criteria analysis, 5) Value of multi-criteria analysis according to the VIKOR method.</td></tr><tr><td colspan="12">*) The total length of the curved sections is considered to be too short.</td></tr></tfoot></table>

**5. Scientific performance, taking into account the configuration and technical difficulties of the scenario:** Maximise with a weight of 30%.

The result was that the most promising scenario is an 8-site layout with a total circumference of the order of 91 km. This scenario gave sufficient residual margins for further optimisations. Meanwhile, all the other scenarios developed are no longer considered feasible, either because of the loss of site locations during the study years, because of unacceptable incompatibilities with territorial or geological conditions, or because their scientific performance is not sufficient to attract researchers from all over the world over the long term. Therefore, PA31 was considered for further detailed studies, in particular involving subsurface investigations and detailed field studies concerning environmental aspects. Optimisations lead to the versions 3.0 and 4.0 for which the performance is also displayed.

**2.3 Requirements and invariants**

**2.3.1 Science and technology motivated requirements**

*Layout* A set of parameters fundamental to particle accelerator design makes up the starting requirements for scenario development. The design parameters determining the overall size of the configuration cannot be chosen arbitrarily. These parameters include the geometry of the configuration (for example, a symmetry or periodicity of sectors involving a specific number of surface sites), the length of the basic curved cells, called 'arcs' (which repeat like the parts of a chain, to build the curved sectors), the number of arc accelerator cells to be repeated and the lengths of the various types of straight sections between the arcs. Figure 2.9 shows two basic configuration geometries used in configuration and layout studies. The first geometry (image on the left) serves as a starting point: it groups together three experiment sites in the upper part of the geometry. It offers greater freedom in terms
<figure><img src="image_67.png" /><figcaption>**Fig. 2.9** Two different collider layouts. The image on the left shows a configuration comprising twelve sites based on a geometry with mirror symmetry. The image on the right shows an eight-site configuration based on the repetition of a basic sector module. The arcs (blue) are separated by straight sections (green and red segments)</figcaption></figure>

of moving the various surface sites but requires twelve surface sites. The second geometry (image on the right) represents the current development: the four experiment sites are evenly distributed (top, right, bottom, left), and only eight surface sites are required. However, the freedom to move sites is less than with the first geometry.

The following requirements were initially set and had to be adapted during the development of a scenario that aimed at satisfying the territorial implementation constraints.

The initial simple mirror symmetry was discarded in favour of a 4 times repetition of a 90° sector, i.e., a four-fold symmetry. The initial configuration (12 sites) made it possible to group 3 experiment sites close to each other near the main CERN site, leading to shorter distances between surface sites and greater flexibility to lengthen and shorten the north and south sides. The current geometry (8 sites) enables a more regular design and thus facilitates performance optimisation processes. The lepton collider can also have four interaction points.

*Total circumference* The initial objective was to design a particle collider infrastructure with a circumference of around 100 km. A reduction of 10%, to a circumference of 90 km, is considered to be the lower acceptable limit, below which the performance obtained for scientific research would become too limited. The smaller the circumference, the smaller the radius of the curved sections and the more pronounced the curvature, resulting in greater energy losses, leading eventually to an unsustainable scenario from an energy efficiency perspective and the need for more powerful magnets for the hadron collider, which could then become technologically unattainable.

*Number of surface sites* The initial 12 sites were reduced to 8 sites with the advent of the four-fold symmetry layout. It proved too difficult to find a suitable layout scenario with 12 sites featuring intermediate access points compatible with the territorial constraints and risks involved in implementing the project. A scenario with eight sites offers less flexibility for the layout study since the fixed interaction sites are geographically opposed. Still, the number of necessary suitable locations to be found is lower.

*Number of interaction points* For the hadron collider, both geometries offer the possibility of four interaction points. However, only the four-fold symmetry layout provides the possibility of having four interaction points with the lepton collider. The 12-site scenario also proved difficult due to the need to combine experiments and injection at two points (PL and PB).

*Arc cell length* The hadron collider arc cell length drove the overall circumference of the layout. Initially, a cell length of 213.03 m was considered. It was eventually extended to 275.79 m. The total circumference depends on the multiples of that arc cell length and cannot, therefore, be arbitrarily chosen. In this case, the lepton collider adapts to the more stringent requirement of the hadron collider.
*Total number of arc cells* The size of the hadron collider curve can only be increased or decreased by inserting or removing an arc cell in each curve. The overall configuration must remain symmetrical. The initial 12 site layout required 4 sectors of 19 short cells and 4 sectors of 73 long cells. The current 8 site layout requires 8 sectors with 26 cells, i.e., a total of 208 cells. This requirement determines the total circumference of the infrastructure. In this case, the lepton collider adapts to the more stringent requirement of the hadron collider.

*Total arc length* The 12-site configuration featured four short arcs and four long arcs. The long arcs were too long to remain without intermediate access points for technical and personnel safety reasons. Therefore, an additional site had to be placed at the midway point, at a distance of around 8 to 10 km from each end. The 8-site layout no longer has this requirement. The total arc length should, however, permit safe operation and the possibility to evacuate personnel in case of emergency efficiently. The current distance between access sites of about 11.5 km is considered acceptable.

*Radio frequency system harmonics* The stability and performance of the radio-frequency system used to accelerate the subatomic particles depend on the circumference of the collider. It also concerns the transfer of particle beams from the existing SPS and LHC tunnels. For a 91 km long collider, 3 possibilities have been identified, which provide sufficient flexibility for the radiofrequency system design. A collider with a circumference of between 90.7 and 90.8 km is the best option. A length of 90.6 km is feasible but reduces the frequencies of the cavities in the radiofrequency system more than the others. In this case, the lepton collider adapts to the more stringent requirement of the hadron collider.

*Length of straight section at interaction points* At least 700 m are needed on either side of the interaction point to focus the collider beams to be able to achieve the high beam densities needed for high luminosities. The two colliders (lepton and hadron) have different space requirements for crossing the two beam lines, so the tunnel needs to be widened by around 10 m to a distance of 1400 m on either side of the interaction point.

*Length of straight section at radiofrequency locations* A distance of 2800 m between 2 straight sections was initially deemed adequate to accommodate the radiofrequency equipment that accelerates the beams. After various equipment integration studies, it was found that this value could be reduced. A distance of 2030 m is now considered the acceptable lower limit required for the systems and the integration of the ancillary equipment.

*Cooling water requirements* With the aim of conserving resources responsibly, ongoing studies have already helped to reduce requirements from an initial 4.9 million m³ per year to a range between 1.6 million m³ (Z mode) and 3.0 million m³ per year (tт mode). Further reductions can be expected due to the inclusion of the concept of heat reuse, taking into account technological developments and the development of water reuse synergies.

*Electricity requirements* Initial powering requirements of the lepton collider ranged between 1.2 and 2.0 TWh per year, depending on the operation mode. Gradual advances in the concept development reduced these values to a range between 1.0 and 1.77 TWh per year. Since the current scenario has four interaction points rather than two, further reductions are possible by limiting the radiofrequency power if a reduction of the annual integrated luminosity is acceptable for the scientific research programme. Further optimisations are to be expected from an adaptive operation concept and energy consumption reduction of systems that are powered down or set to an energy-saving mode when not required for operation and maintenance.

For the hadron collider, an initial annual energy consumption estimate was based on current superconducting magnet technology at very low cryogenic temperatures. This estimate has been revised by developing a design that works at higher cryogenic temperatures to allow significantly lower energy consumption. Leveraging a high-temperature superconducting magnet technology would allow the cryogenic operation temperature to be further increased. Together with adapting the operation plan and introducing an annual energy consumption ceiling, this would bring the annual energy consumption into the range of the lepton collider. However, a focused R&D programme is required to develop the technology. A window of opportunity in the range of more than 35 years is available to achieve this goal if a decision to proceed is taken.

*Space requirements of technical surface sites* The space requirements of the technical surface sites are determined by the technical infrastructures that both particle colliders will need. Although the lepton collider has significantly fewer requirements than the subsequent hadron collider, the surface sites must be able to host the additional equipment that will only be put in place for the second phase.

The minimum equipment required on each site comprises an electrical substation, power converters to drive the particle accelerator equipment for the sectors in both directions of that site, power amplifiers where there is a radiofrequency system, tunnel and cavern ventilation, raw water-based accelerator cooling systems, raw water
treatment systems, heat exchangers and refrigeration towers. Since the actual design of the particle accelerator is yet to come, it is challenging to estimate the space requirements for such systems. Therefore, the most advanced systems are used as a reference to estimate the space requirements.

In addition to the technical systems, space is required for temporary storage of the particle accelerator systems to be installed underground and for the handling of the technical systems at the surface. In the case of sites with a cryogenic refrigeration system, space is required to store the cryogens (liquid and gaseous helium as well as nitrogen). While the lepton collider will require only two sites with relevant cryogenic refrigeration systems for the radiofrequency systems, each site will host a cryogenic refrigeration plant for the hadron collider. Additional minor space requirements emerge from the roads on the site, such as the need to provide limited office space and storage of spare parts, cranes, and handling equipment.

The working hypothesis is that in the order of 100 technicians and engineers per day can be present during installation, major maintenance and upgrade interventions. During the operation phase, the presence of personnel is limited to the strict minimum, leveraging remote operation and intervention as much as possible. No permanent presence of personnel is planned during ordinary operations.

The current lepton collider net space requirements for construction elements on technical sites are: 2.2 ha for PB, 2 ha for PF, 4.4 ha for PH and 2.6 ha for PL. Additional space is required for the hadron collider cryogenic refrigeration plants and cryogen storage, as well as for additional technical equipment. Including the requirements for green buffers and landscape integration bring the requirements to about 3.5 ha to 4 ha for the technical sites PB, PF, PL. About 8 ha are required for PH due to the initial large cryogenic refrigeration system and the topographical challenges that call for a terrace-based landscape integration. The indicated space requirements do not include the requirements emerging from the need to accommodate the different topographical constraints, the need for green buffers and landscape integration. Hence, the specific local requirements are higher.

Subsequent architectural designs and landscape integration will aim to reduce land consumption as much as possible.

*Space requirements of experiment surface sites* In addition to the requirements of the technical sites, each experiment site also requires a pre-assembly hall for the experiment detector. To limit the surface space requirements, the working hypothesis is that the detector will be assembled underground. However, elements will need to be quality checked, pre-assembled and tested on the surface in a hall that measures about 1250 m². Sufficient space of about 1000 m² for handling of parts and a temporary buffer for magnets to be installed is also required.

An experiment site typically also hosts a data centre, workspace for a group of about 50 scientists and engineers, meeting rooms and a few offices, small workshops, a data centre and visitor facilities.

For the hadron collider, the largest detector part, a superconducting magnet coil, cannot be transported directly to the sites. It needs to be manufactured on-site. For this process, about 7500 m² are required in addition to each surface site. The space will remain untouched by construction during the first, lepton collider, phase, and it will be rewilded after the assembly and lowering of the magnet coil at the end of the hadron collider installation phase.

The working hypothesis is that up to 300 scientists, technicians, and engineers can be present per day during installation and major maintenance and upgrade interventions. During operation, only a small team of less than 20 people would be present on site. Additional personnel would be present to operate the visitor facilities.

The current lepton collider net space requirements for construction elements on scientific sites are listed below. 3 ha for site PA due to the possibility of leveraging the space of the existing LHC surface site Pt8. Including the temporary space required for the production of the superconducting magnet coil of the hadron collider experiment, the space requirement increases to about 4 ha. The sites PD, PH and PJ require about 4 ha for the lepton collider phase and 5 ha for the hadron collider phase. The space requirements indicated do not include the requirements emerging from the need to accommodate the different topographical constraints, the need for green buffers and landscape integration. Hence, the specific local requirements are higher.

Subsequent architectural designs and landscape integration will aim to reduce land consumption as much as possible.

### 2.3.2 Initial invariants

A set of invariants was established in the beginning to guide the development of an implementation scenario to ensure that a minimum set of criteria concerning scientific excellence, territorial compatibility and project risk control can be satisfied. They are a combination of avoidance and reduction constraints, goals and high-level requirements.

* Avoid karstic limestone formations, risks of high-pressure water penetration, known major faults and areas of seismic instability, as well as significant overburden.

* Place the underground structures in the molasse layer as much as possible.

* Provide a technically feasible connection to CERN's SPS underground infrastructure and, if possible, to the LHC infrastructure.
* Dig the tunnel to a sufficient depth below the lake bed to ensure stability and long-term low maintenance. The alignment can be optimised by identifying the minimum depth based on subsurface geophysical and geotechnical investigations for a preferred scenario. The current assumption is that the tunnel alignment crossing the Geneva lake is 100 m below the lake bed.

* Dig the tunnel deep enough under the Arve, Rhône and Usses rivers to guarantee the micro-stability required for precise alignment of the accelerator and to avoid adverse effects with any, potentially existing, surface constructions.

* Limit overburden under the Mandallaz, Fillière and Bornes zones (minimum depth to be defined by specific subsurface investigations).

* Avoid elevations above 750 m for surface sites to limit the depth of shafts and ensure good site accessibility.

* Aim for shaft depths of less than 250 m for scientific sites and 400 m for technical sites to avoid excessive challenges for the installation of the accelerator equipment and the experiment detectors.

* Avoid areas considered ‘exclusion zones’ in an established territorial sensitivity grid drawn up with contracted organisation Cerema, Direction Départementale du Territoire in France, collecting information from the Direction Régionale de l’Environnement, de l’Aménagement et du Logement and with contracted company Ecotec in Switzerland with additional information collected from the cantonal DT services. This grid lists environmental, spatial planning, zoning and strategic constraints, as well as public health and safety constraints with different relevance levels that lead to the definition of zones to be avoided and zones at surface and subsurface constructions will need to be limited if they cannot be avoided.

* Give preference to proximity to strategic project infrastructures (e.g., grid power lines, certain types of roads, autoroute stations, railway lines) and stay clear of certain other infrastructures (e.g., geothermal probes, gas pipelines, oil pipelines).

* Remain outside of town and village centres and hamlets to limit potential nuisances associated with the construction and operation activities.

* As far as possible, avoid areas subject to a set of less critical territorial constraints, and if avoidance is not possible, reduce surface areas in these zones.

* Respect the fact that it is not possible to individually displace the locations planned for scientific sites where particle beams cross and where the experiment detectors are located.

* Respect the limits for displacing technical sites along the straight sections of the ring within the lengths of those sections, according to the possibilities offered by the various technical systems required at the technical sites for the operation of the accelerators.

* Consider the constraint for positioning the shafts inside the ring to facilitate access to the transport zone in the tunnel.

* Limit the length to around 400 m for the horizontal connection tunnels from the technical sites to the shafts inside the ring. Building a longer tunnel is not out of the question, but it would entail additional costs and difficulties.

* If technically possible, limit the total occupied surface area of technical sites to 5 ha and the surface area of experiment sites to 8 ha. These areas include buffer zones, storage, and transport areas and take account of rewilding, reconstitution, replacement, or compensation measures. Wherever possible, seek synergies with existing infrastructures to reduce surface areas.

* Avoid areas with difficult topography (steep and potentially unstable slopes, unstable soils, areas at risk of flooding, discontinuous terrain).

* Ensure adequate road connections (7 m wide, 2 lanes, 20 m curvature radius, gradient well below 10%, minimum clearance height of 4.4 m, compatibility with heavy goods vehicles of 44 t to the main road network in accordance with article R312 of the French highway code).

* Maintain a minimum distance of 100 m between residential areas and sites. Depending on topographical conditions and the site's noise and visibility attenuation features, this distance can be as much as 250 to 300 m.

* Avoid protected agricultural areas unless they are essential to ensure technical feasibility.

* Avoid natural and historic heritage sites, avoiding shared visibility between the sites.

* Preserve the views and landscape protection zones as far as possible.

* Avoid rivers and streams (to avoid having to modify or stabilise riverbanks).

* Avoid wetlands and strictly protected areas.

* Avoid protected forests because of the need to clear them and preserve existing biodiversity and because of their inaccessibility and topography, unless these areas are essential to ensure feasibility. In the latter case, the land occupation should be limited.

* Give preference to areas in proximity to high-capacity power lines (225 kV and 400 kV).

* Look for opportunities with a connection or access to the autoroute system.

* Look for opportunities with a connection or access to the railway system.

* Consider the use of known brownfield sites for the installation of technical infrastructures that may be remote from the sites (e.g., electrical substations, pumping stations, cooling towers) and for the development of compensation areas.
* Look for scenarios that enable all surface sites to be reached within a reasonable time (30 minutes by car) from strategic service and supply points (e.g., CERN and CNRS/LAPP).

* Avoid creating new border crossings and do not consider sites that straddle the border.

* Avoid vineyards and areas with fruit trees.

* Give preference to public land over private land, undeveloped land over developed land, unused land, overused land (special agricultural uses such as vineyards and protected fruit crops) and brownfields.

### 2.3.3 General objectives

The multi-year study also led to the development of a number of objectives that would help make the project more territorially compatible. They have been taken into account in the evolution of scenarios and in the development of a preferred layout scenario that serves as a reference, which is presented in later sections of this document.

*Sustainable operation and maintenance* Ensure that the scenario can be operated and maintained sustainably. To achieve this, relevant technical facilities (high-tech workshops, offices) must be in proximity to the sites. Therefore, give preference to scenarios that take advantage of synergies with existing CERN sites and/or are close to the LAPP of CNRS/IN2P3.

*Protecting farmland* Limit the consumption of farmlands in both host states. Avoid protected agricultural areas, unless they are essential for feasibility.

*Road access to surface sites* To limit the need to build new roads and to avoid consuming land, surface sites must either be located directly on existing departmental roads or only require an improvement to existing access roads. If new roads are essential, then the requirements should be minimised.

*Disturbances* Limit direct disturbances for local inhabitants. Avoid proximity to residential areas, visibility, and shared visibility. Avoid locations on roads passing through residential areas. Avoid proximity to natural and historical heritage sites. Provide means of evacuating spoil by conveyor belt to avoid truck traffic where possible.

*Landscape integration* Aim to preserve views and landscape protection zones wherever possible. Specific studies by landscape architects are required for a preferred scenario during a subsequent design phase.

*Protection of water* Avoid water protection zones, rivers, and streams. Do not take in water from water-bearing layers, and avoid the use of drinking water for systems that require raw water. Avoid having to stabilise or modify riverbanks. Specific studies are required for a preferred scenario during a subsequent design phase.

*Forests* Respect protected forest zones and trees. Limit clearing forests or felling trees in both host countries to maintain biodiversity. Avoid high-quality forest zones whenever possible. Improve climate resilience by restoring impaired forests.

*Synergies* Give preference to locations that can create synergies with nearby private and public facilities and infrastructures. This includes, for instance, the availability of emergency rescue stations and fire brigades, hospitals, commercial and industrial development zones, food processing companies, infrastructures that support public works, electricity lines, major transport axes, autoroute service stations, train lines and school development projects. Identify the possibility of supplying residual heat within a 5 km radius, preferably to public facilities and major companies and residential housing. This is an approach that has already been put in place by CERN in Ferney-Voltaire and such an infrastructure serves as a demonstrator for the feasibility (see Fig. 2.10). Examples include, but are not limited to, milk processing companies (cheese production), hospitals and health service infrastructures, schools, fire brigades, prisons, offices, airports, train stations, and leisure facilities (pools and spas). Locating surface sites in the proximity of public services can lead to tangible added value for the region. For example, the significantly enlarged geographical extent triggered the need to develop an emergency intervention concept based on cooperation with regional fire departments and first-aid services. Other locations are particularly suited to foresee additional leisure activities around experiment surface sites that feature visitor centres. Additional services including exhibitions, restaurants, and meeting facilities have potential for indirect and induced economic value generation, but they need to be agreed with the local stakeholders to integrate with the local economic and tourism development strategies and plans.

*Reduced need for electrical infrastructure* To limit the effects and impacts of infrastructure development for electrical power, give preference to scenarios located near substations and high-capacity power lines.
<figure><img src="image_68.png" /><figcaption>**Fig. 2.10** CERN powered heat network under construction in Ferney-Voltaire, France</figcaption></figure>

**Excavated materials** Limit the annually excavated volume of materials excavated and reduce road transport whenever technically and economically feasible. Facilitate local reuse. The aim is to keep the volume of materials excavated annually to less than 10% of the volumes generated in each region (Auvergne-Rhône-Alpes in France: 24.2 Mt in 2021 [26], cantons of Geneva [27] and Vaud [28] in Switzerland: 3.071 Mt in 2022).

**Land use** The goal for the scenario development is to develop a scenario that keeps land consumption as low as possible by still meeting the needs of the required surface site installations. The scenario development process avoids protected agricultural spaces, keeps interactions with multiple private landowners for land plot acquisition low, as a multitude of negotiations and complicated ownership situations can significantly impact project implementation preparation and lead to unsatisfactory results for them. Consequently, prioritise the use of public land over private property and steer clear of areas with planned development projects and prefer non-protected agricultural spaces over protected ones.

The surface site candidate location in Switzerland is mainly located on publicly owned land. The surface site candidate locations in France concern mainly privately owned land plots, subject to the typical urbanistic planning evolution. After exchanges with municipalities to determine the territorial conditions and constraints of possible locations for surface sites, CERN asked the Prefect of the Auvergne-Rhône-Alpes region in France to set aside the land plots to assure their availability for field studies. This process and the orders signed by the Prefect of the region mitigate the risk of unanticipated use of the land plots for other territorial developments for the study time period, permitting a comprehensive and exhaustive investigation of the environmental conditions. As a result, the land considered for the surface sites will not compete with other emerging projects. The solution was made possible thanks to the support of France. It contributes to securing the studies while ensuring compliance with national legislative frameworks.

**Biodiversity and nature** Give preference to sites with low-quality nature characteristics. Through the ERC approach, preserve the elements of interest in terms of biodiversity and nature within the perimeter as much as possible. Study, together with design offices, the existing and projected conditions of the sites concerned, and carry out environmental, flora, and fauna surveys on the proposed site to identify valuable elements and the site's role in the ecological infrastructure. Propose appropriate restoration, replacement, and compensation measures based on the impacts identified by specialist consultants. Maintain or reinforce ecological infrastructure, particularly wildlife corridors.

The work on these voluntary goals was also considered during the development of the eco-design strategy and guidelines [29], which all project participants are required to consider during the subsequent design phase and which is also published in the report on the current state of the environment [30].
<figure><img src="image_69.png" /><figcaption>**Fig. 2.11** Zones in the scenario development perimeter classified as to be avoided ('red'). Note that this map does not consider numerous other exclusion criteria such as slopes and high altitudes (see also online at http://cern.ch/fcc-sensitivity-grid)</figcaption></figure>

## 2.4 Territorial constraints

### 2.4.1 Territorial sensitivity grid

The development of a territorial sensitivity grid with its four levels (unacceptable 'red', high 'orange', acceptable 'yellow', and low 'green') served as a starting point to integrate the territorial constraints into the implementation scenario development from the onset.

By applying the 'Avoid' approach, the analysis eliminated all the unacceptable zones to be avoided, shown in red (see Fig. 2.11), from the early development stages of the initial scenario at the macroscopic level. It should be emphasised that, in all cases, the scenario development process also aimed to avoid areas already developed if they were considered to be in active use (e.g., residences, farms, parking lots, industrial buildings and public infrastructures). Only brownfields or buildings that could be reliably described as unused (ruined houses, abandoned industrial warehouses, etc.) were examined on a case-by-case basis. In addition, for all the surface sites taken into consideration, choices have been made to avoid clearing protected forests, as well as avoiding the destruction of wetlands and hedgerows in agricultural areas.

Zones classified with high constraints, shown as 'orange' were generally avoided (see Fig. 2.12), but a more detailed manual analysis of the underlying rationale for this classification was always conducted to understand
<figure><img src="image_70.png" /><figcaption>**Fig. 2.12** Zones in the scenario development perimeter classified as to be avoided ('red') and with high constraints ('orange'). Note that this map does not consider numerous other exclusion criteria such as slopes and high altitudes (see also online at http://cern.ch/fcc-sensitivity-grid)</figcaption></figure>

whether and under what conditions such a zone might be considered for certain parts of the research infrastructure. This step required a more detailed study of the different layers of constraint that make up the overall layers. It also required additional information that the regional and local planning authorities of the two host states were best placed to provide (for example, the various offices of the Département du Territoire and the Infrastructure Department of the canton of Geneva, the DREAL, the DDT 74 and the DDT 01 in France).

In France, the law of 22 August 2021, on combating climate change and strengthening resilience to its effects set a target of zero net artificialisation of soils (also known as ZAN). The ZAN initiative is a target set for 2050. It calls on local authorities, municipalities, departments, and regions to reduce the rate of artificialisation and consumption of natural, agricultural, and forest areas by 50% by 2030, compared to the consumption rate measured between 2011 and 2020. A similar instrument for crop rotation areas in Switzerland, 'surfaces d'assolement' known as SDA exists.

The scenario development follows the regulatory frameworks in both host states regarding land use efficiency. This concerns in particular the consideration of the principle of “zéro artificialisation nette (ZAN)” (english: “zero net land take”) in France and the principle of the “Surfaces d’Assolement (SDA)” (english: crop rotation surfaces) in Switzerland. By considering these constraints in the “avoid-reduce-compensate” based development cycle, they support the development of projects that exhibit a high degree of territorial responsibility. The SDA
<figure><img src="image_71.png" /><figcaption>**Fig. 2.13** Examples of regional changes. Left: 17 ha of new exclusion zones in Ferney-Voltaire (Ain, France). Right: 790 ha of peatland inventory on the banks of the Rhône in France: in light red, previously orange zones that have become red zones</figcaption></figure>

imposed constraint was addressed by the development of an authorisation process for the territorial development of CERN at the federal level. Concerning ZAN it is noted that, on the recommendation of the prefect of the Auvergne-Rhône-Alpes region, the FCC segment on French territory is recognized among European and national large-scale projects (PENE) [31]. Consequently, the land areas potentially consumed by surface sites would be outside the regional quota, in accordance with the decree of May 31, 2024 [32], concerning the national pooling of the consumption of natural, agricultural, and forest spaces for projects of major general interest. However, this exclusion from the regional quota would not exempt the FCC from complying with the principles of land use efficiency and compensation. Through its transversal and eco-responsible approach, the study demonstrates its commitment in this area, thus affirming its intention to embed the project in a responsible and balanced dynamic.

Right from the start of the studies, it became clear that there were no areas with low constraints indicated with ‘green’ colour in the two host countries. The minimum number of constraints in both countries corresponds to the ‘yellow’ class, i.e., acceptable zones. In addition, Switzerland has special restrictions, imposed at the federal level, for a certain type of agricultural land, known as crop rotation areas (SDA), the best arable land in Switzerland. A federal sectoral plan sets a minimum surface area to be maintained per canton (distributed among the cantons by quota). The Confederation monitors the maintenance of the minimum SDA area. Under certain conditions, SDAs can be allocated to specific projects, provided that all stakeholders at the federal and cantonal levels agree and that the minimum is maintained. This constraint is high, but the SDA spaces have been classified as an ‘orange’ zone to leave the possibility of downgrading open and to provide an option for the development of a layout and placement scenario. Specific coordination at the federal and cantonal levels is nevertheless required to be able to release such land for a development project. SDA spaces will have to be compensated on a 1:1 basis by removing the topsoil and re-constructing the agricultural space on lower-quality plots or wastelands. Agricultural areas in the canton of Geneva outside the SDAs were classified as acceptable ‘yellow’ zones.

The initial classification of sensitivity layers is not fixed, but constantly changes as the territory evolves. Between 2014 and 2022, more than 1000 ha became ‘red’ exclusion zones (unacceptable constraints) in the Haute-Savoie department in France. In the canton of Geneva, around 100 ha have been affected by new restrictions and are now part of the exclusion zones, mainly due to stricter surface and groundwater protection rules resulting from improved knowledge of the subsurface. This led to the rejection of several candidate sites proposing a configuration and location initially considered as possible. These changes have made it even more difficult to continue developing scenarios, while at the same time highlighting the iterative aspect of the process.

Figure 2.13 shows two examples of these ‘lost spaces for layout scenarios’. The first concerns sectors of Ferney-Voltaire that are now intended for a development project (hospital project north of the D35, Route de Meyrin) and the classification of a sector as a compensation zone (south of the D35), which therefore cannot be compensated again. The second concerns a vast area north of the Rhône in France, which has been described as a ‘peatland inventory’.
<figure><img src="image_72.png" /><figcaption>**Fig. 2.14** After several years of analysing the subsurface conditions based on bibliographic data and modelling, the initial scenario development perimeter (yellow) had to be restricted (red) to assure compatibility with the known subsurface conditions</figcaption></figure>

## 2.4.2 Subsurface constraints

Subsurface constraints, such as unfavourable geology, major faults, presence of strategic aquifers, drinking water catchment areas and buffer zones, pipelines, power lines and gas mains, as well as reserved areas of public interest such as geothermal exploration zones or no-drilling zones due to superimposed aquifers or other information, were considered from the onset. Geological exclusion zones have been defined by the geological consulting firms GADZ and ILF and the University of Geneva to take full account of geological conditions. These partners also examined the geological and hydrological situation based on the following elements:

1. Fault lines representing a high risk of seismic activity and that could cause tunnelling challenges.

2. The interface between limestone and molasse.

3. Potential high-pressure water penetrations or karstic formations that would expose the project to an unacceptable risk.

As a result, between 2014 and 2020, the project's initial study perimeter had to be significantly narrowed (see Fig. 2.14) as additional knowledge was acquired and integrated into a 3D model of the subsurface. Figure 2.15 shows two example images from the 3D subsurface model that was established to support the analysis of the subsurface constraints, to identify zones that are definitely to be excluded, preferred locations for the subsurface
<figure><img src="image_73.png" /><figcaption>**Fig. 2.15** Example images from the 3D model (here molasse and cretaceous formations) used to determine the geological constraints</figcaption></figure>

structures, and to identify zones with particular challenges or insufficient data that require dedicated subsurface investigations.

Given the experience gained from the construction of the Large Electron Positron collider (LEP) underground structure and from the construction of underground transport structures in the region (e.g., the Vuache road tunnel), the risks of building a large tunnel and caverns, which could be unstable, move, collapse, or in which construction workers could be exposed to high-pressure water ingress that could lead to fatal accidents, are considered unacceptable and must be avoided. As far as possible, all underground structures should be located in the soft, stable molasse layer, which forms a reliable barrier against aquifers.

Although maps and modelling work have provided additional information, reliable data on the exact depth of interfaces between different geological layers in the Vuache and Jura zones is still lacking. The unavoidable limestone zones of Mandallaz have yet to be studied. Furthermore, little is known about conditions under the lake, as well as the Arve and the Rhône rivers. Since these conditions have a major impact on the cost and schedule of
<figure><img src="image_74.png" /><figcaption>**Fig. 2.16** Topography of the area. Red and orange colours indicate steep slopes</figcaption></figure>

the tunnel boring, more information about the subsurface in the key areas is being gathered with geophysical and geotechnical exploration between 2024 and 2025.

### 2.4.3 Topography, bathymetry, and other surface features

Information on topographical surface conditions has also been taken into account from the outset of the study. Steep slopes (Fig. 2.16) in excess of 30% presenting risks of unstable terrain and landslides are excluded, as are cliffs, narrow valleys, and canyon-type formations. Since the tunnel must be placed at a sufficient depth below the lake bed, elevations above 750 m are an obstacle due to the depth of the shafts and unacceptable overloading (Fig. 2.17). High elevations also lead to high overburdens, which can become challenging for tunnel boring activities, calling for more costly construction and slower progress.

The bathymetry of the lake must be taken into account to ensure that the tunnel can be placed sufficiently below the lake bed with as short a crossing as possible. Lake Geneva is more than 50 m deep beyond the Versoix-Corsier line (see Fig. 2.18). To avoid the tunnel becoming too deep over its entire footprint, it is necessary to stay below this line. Crossing the lake where it is narrow avoids areas of instability and minimises the risks associated with the
<figure><img src="image_75.png" /><figcaption>Fig. 2.17 Relief of the area. White and red colours indicate high elevations</figcaption></figure>

<figure><img src="image_76.png" /><figcaption>Fig. 2.18 Bathymetry of the Geneva lake</figcaption></figure>

presence of water. At the same time, other parts of the tunnel should not be located too deep under mountainous areas.

### 2.4.4 Scenario development flexibility

The initial outline surface and subsurface constraints and many more constraints that are documented in detail in a specific report [12] provided a starting point for a semi-automated search to determine approximate exclusion
<figure><img src="image_77.png" /><figcaption>**Fig. 2.19** Combination of subsurface and topographic constraints that lead to a ca. 300 m wide scenario development band and a diameter of about 28 km</figcaption></figure>

and candidate zones. However, zones marked in orange (undesirable zones) and yellow (acceptable zones), which at first glance appeared compatible with the location of a surface site, proved in various cases to be unacceptable due to restrictions that are not ‘encoded’ in the maps and publicly accessible documents which are available. This additional information was obtained in part by studying high-resolution maps, orthophotographs and data, by interviewing regional and local public administration services and local stakeholders, domain experts and by means of walking tours (visual inspection of the surrounding area).

Such additional constraints included, but were not limited to, the following: unfavourably shaped land areas (surface available too small, too narrow, non-monolithic or too irregularly shaped), presence of adjacent constraints (nature protection areas requiring buffer zones, natural hazard areas such as flood zones or unstable banks, residential areas, sensitive areas), limited access (no road or no possibility of creating one due to topographical conditions or other restrictions, rudimentary road unsuitable for regular traffic and unable to be upgraded to meet requirements), likely opposition or known conflicting development policies, known conflicting projects.

The constraints, together with the currently known geological and topographical conditions, limit the circumference of a future circular collider to less than 100 km. The layout studies conducted between 2017 and 2021 concluded that to obtain a circumference of over 90 km that would deliver good performance and therefore yield a research infrastructure of excellence, and given the various constraints that the configuration must simultaneously meet in different locations, the available layout for the ring is limited to a strip with a width progressively reduced from 3000 m to 300 m depending on the area concerned (see Fig. 2.19).

## 2.5 Initial variants

### 2.5.1 Introduction

This section provides the background which explains how the implementation scenario in the Franco-Swiss border region was developed. It explains why alternative scenarios to the west of the Jura were examined and then discarded in favour of scenarios to the east of the Jura. It reviews how the layout and placement considered during the exploratory phase of the FCC study (2014-2018) demonstrated the in-principle feasibility of a new, large-scale research infrastructure and how the specific scenario examined presented prohibitive obstacles in certain locations. Finally, it mentions the variant involving a linear collider, which was not selected for further studies.

The development of a scenario for the configuration in the Geneva region was based on the motivation of taking advantage of existing CERN infrastructures and assets built up over 70 years for a new project. The construction of a circular collider requires existing particle accelerators in operation with technical infrastructures that can serve as injectors; the availability of workspace, workshops, equipment, and skilled workforce; as well as favourable
<figure><img src="image_78.png" /><figcaption>**Fig. 2.20** Comparison of land areas and protection zones to the west and east of the Jura chain</figcaption></figure>

legal, administrative, and project management frameworks. It is, therefore, essential that the chosen layout remain within reasonable proximity to an existing CERN site.

In addition, the particle collider must have a circumference greater than 90 km to accommodate two different particle colliders in the future (an electron-positron collider and a hadron collider), each of which must deliver the performance required to carry out the desired scientific research programme. The immediate research zone would be located to the south of CERN’s Meyrin and Prévessin sites, away from the Jura mountains. Indeed, during the Large Electron Positron collider (LEP) construction phase, major obstacles were already encountered due to the presence of karstic formations and high-pressure water penetrations due to its proximity to the Jura mountains.

Nevertheless, as the next section highlights, an unbiased examination of the situation was conducted so as not to overlook any other possible scenario.

## 2.5.2 Scenarios west of the Jura

A study [33] examined a layout in the Bresse plain (Dolois region), to the west of the Jura Massif (see Fig. 2.20). These options had already been studied in 1997 and 2001 and were checked again between 2014 and 2019. The ring would have been located outside the Jurassic formations, at a depth of around 40 metres. Still, in any case, the infrastructure would have encroached on existing national and regional parks and vast nature conservation areas. In addition, the required link to CERN’s particle accelerator complex would have required a long tunnel of around 60 km for the transfer lines. This tunnel through the Jura mountain range would have passed through very unfavourable geological formations with significant overburden. Given that the distance between the Jura mountains and the Petite Montagne du Jura is less than 20 km, it is considered unfeasible to place a sufficiently large circular particle collider in this zone.

This variant was definitely dropped from further studies for the following reasons:

* A long tunnel for the beam transfer line through the Jura mountain range would pose too many difficulties, both from a civil engineering and a technical point of view. Construction times and overall costs would increase considerably, by at least 30%.

* This scenario would require deep access shafts in difficult-to-access mountainous regions of the Jura massif, which are largely nature conservation areas. The rock is highly unstable, and the penetration of high-pressure water is certain.

* The loose soil in the Bresse region would require stabilisation and protection measures. Hydrophilic gypsum swells considerably (ground movements of roughly one metre recorded in the Chienberg road tunnel), which is not compatible with large-scale cavern construction nor with the requirement for a highly stable tunnel. Maintenance costs would be much higher than on stable ground.
<figure><img src="image_79.png" /><figcaption>**Fig. 2.21** Racetrack layout scenario with two 11 km long straight sections, leading to a total circumference of 90 km</figcaption></figure>

* The installation would most likely interfere with nature protection constraints and cause significant disturbances to local residents during the construction phase.

* The space available between the Jura massif, its national park and the Petite Montagne du Jura area to the northwest is too small to accommodate a circular particle accelerator of sufficient size.

* There is no reasonable way of operating and maintaining the infrastructure from CERN or any other suitable partner organisation nearby.

### 2.5.3 Racetrack lakeside scenario

The conceptual feasibility investigations also comprised an analysis of the opportunities and constraints related to a racetrack layout with a lakeside placement of the particle collider ring that permits connecting the infrastructure to CERN’s particle accelerator complex [34].

The concept was based on having straight sections about 11 km long that could potentially also house a linear accelerator or collider. The motivation was to combine the possibilities of a linear electron-positron collider as a first stage with a circular hadron collider during a second stage. An alternative particle acceleration concept with linear accelerators for a first-stage circular electron-positron collider could also have been imagined.

The availability of long straight sections comes with advantages for the radiofrequency acceleration systems in terms of ample space and avoiding bending fields. A minimum crossing angle, 20 mrad in the case of CLIC, is required, however, in order to prevent collision debris passing through the opposite linear accelerator arm. Realistically, some bended beam delivery section would be required for dispersion suppression, collimation and chromatic corrections. Such a layout would lead to a racetrack with a total circumference of 90 km, permitting both, housing linear and circular accelerators (Fig. 2.21).

This layout comes, however, with some significant disadvantages: It only permits up to two experiments for the circular collider and also requires the inclusion of collimation, dumps, and beam transfer sections in the two straight sections.

When it comes to placement options (Fig. 2.22) for such a layout, numerous geological and environmental constraints are encountered: as with all circular scenarios, this one also needs to cross the Mandallaz limestone sector. Some shafts could be very deep in their nominal locations (Fig. 2.23), i.e., more than 500 m, however, with a systematic optimisation process it is likely that acceptable alternatives for displaced shafts can be found. In terms of traversal of the lake, the bathymetry starts to impose constraints with depths of 65 m, which would need to be carefully evaluated.

The strongest limitations stem from the highly challenging needs to integrate 12 surface sites in a highly urbanised area on one side and into a highly mountainous zone on the other side (Fig. 2.24). For instance, a site PJ in Switzerland would be in the fully protected Allondon river zone, where any construction activities on the surface and subsurface are strictly forbidden. It remains unclear where and how a feasible experiment site potentially covering up to 9 ha could be identified and rendered acceptable, considering that also major transport and electricity infrastructures would have to be created in this area which, is entirely natural. It is a highly protected nature zone. Site locations around PI in France in the close vicinity of the river Rhône face similar constraints. Locations for a site PK in the Prévessin sector in France would fall in highly urbanised areas. Site locations in PL in Versoix in Switzerland are in fully protected lake border areas with absolute bans for subsurface activities and in highly urbanised locations. Locations for site PB in Switzerland are in a large nature preservation zone, in particular the home for amphibians which are highly protected. Potential locations could most likely be identified using the Avoid-Reduce-Compensate sequence for other sites. In terms of cost, the scenario would lead
<figure><img src="image_80.png" /><figcaption>**Fig. 2.22** Placement option for a 90 km circular / 11 km linear racetrack scenario</figcaption></figure>

<figure><img src="image_81.png" /><figcaption>**Fig. 2.23** Example racetrack alignment scenario</figcaption></figure>

to significant increases for the circular collider scenario, since it is not optimised for a circular collider layout. The differences are in the order of 200 to 400 million CHF at least. Finally, the loss of at least 20% of arc sections directly leads to a corresponding loss in the maximum achievable energy or, in the case of a smaller radius in the curved sections, to significantly higher synchrotron radiation losses.

A racetrack layout is neither optimised for a linear collider nor a circular collider. It, therefore, creates additional complications and costs and leads to lower performance. The integration into the territory is extremely challenging and significantly more complicated than the finally adopted circular layout with eight surface sites. It will lead to higher environmental impacts and increased territorial development needs (e.g., access roads) and require more and deeper shafts. Therefore, further studies on this scenario have been discontinued.

### 2.5.4 Scenarios east of the Jura

For the zone to the east of the Jura, an initial large search perimeter was defined in 2014 based on the following geological conditions [35–37]:

* To ensure stability, the tunnel must cross Lake Geneva at a sufficient depth below the lake bed. Initial ideas of placing the tunnel in unstable ground (moraines, quaternary glacial deposits) or in a construction on the lake bed had to be rejected due to a) insufficient stability and b) the impossibility of creating suitable interfaces between the tunnel on either side of the lake and the construction in the lake.

* In order to be located at an acceptable depth below the lake bed and to remain as far as possible within the impermeable molasse layer, underground structures should be located at around 250 m above sea level, ideally avoiding crossing the limestone/molasse interfaces.

* A boundary line was drawn to the northwest (Jura zone) and to the west (Vuache zone) to ensure sufficient distance from high elevations leading to unacceptable overburdens, inaccessible and protected areas, unstable rocks, faults, seismically active zones, and unstable karstic formations where the penetration of high-pressure water is certain.
**Fig. 2.24** Example of the racetrack layout placement with the environmental constraints indicated. Site locations I, J, L and B are in highly constrained zones, rendering the identification of a feasible and societally acceptable scenario highly challenging. The lake depth at the crossing between L and A is about 65 metres deep

<figure><img src="image_82.png" /></figure>

* To the southwest, the Mandallaz mountainous zone forms a natural border. Its crossing cannot be avoided. Consequently, the preferred scenarios are those for which the overburden and crossing length are low.

* To the south, a boundary line has been drawn northwest of the Montagne des Frêtes nature reserve to avoid elevations above 750 m (unacceptable, as they would lead to excessively deep wells), inaccessible and topographically unacceptable zones, and protection zones to the south. This line crosses the Fillière valley at Thorens-Glières and spans the acceptable elevations of the Bornes plateau as far as La Roche-sur-Foron.

* To the east, a boundary line has been drawn to avoid mountainous zones and thus remain in the Arve River valley.

The perimeter obtained in this initial study turned out to be compatible with a circular infrastructure with a circumference of 90 to 100 km, and can meet geological, topographical, environmental and urban planning constraints (see Fig. 2.25). The maximum distance that can actually be used is 29 km from north to south and 30 km from west to east. The result is a zone capable of accommodating a circular collider with a circumference of up to 92 km for a configuration comprising eight sites or up to 98 km for a configuration comprising twelve sites.

## 2.6 Reference scenario

### 2.6.1 Introduction

Of the about 100 scenarios analysed [12], based mainly on bibliographical data and field visits, it was the PA31 scenario that seemed the most interesting to retain for further in-depth studies and optimisation. The trace of version 1.0 (PA31-1.0) stands out from the others. It proposes a balance between territorial placement, scientific performance that the particle collider and the four interaction regions can offer and technical feasibility in terms of manageable risks and costs. This working hypothesis, developed based on the Avoid-Reduce-Compensate (ERC) process described earlier, has made it possible to gain in-depth knowledge of the region, creating the basis for continuously improving the project considering territorial requirements and constraints as well as technological advances.

The scenario version 4.0 (PA31-4.0) shown in Fig. 2.26, presented in this chapter, is established as the reference scenario for a potential implementation project. It is the result of an optimisation process applied to the PA31-1.0 working hypothesis. It takes into account the progress made on design studies for the FCC-ee and FCC-hh colliders, infrastructure and civil engineering studies, as well as territorial information collected from local
<figure><img src="image_83.png" /><figcaption>**Fig. 2.25** Established study perimeter (red line). Exclusion zones and zones with too many difficulties for surface sites are indicated in red; favourable zones are indicated in blue</figcaption></figure>

<figure><img src="image_84.png" /><figcaption>**Fig. 2.26** The PA31-4.0 reference scenario that served as baseline for the subsurface investigations, the analysis of the state of the environment and studies concerning connected infrastructure projects. An interactive version can be consulted at https://cern.ch/fcc-overview</figcaption></figure>
<figure><img src="image_85.png" /><figcaption>**Fig. 2.27** The functions of the various sites in the PA31-4.0 scenario configuration</figcaption></figure>

stakeholders (concerned municipalities, departmental directorates of the territories and the Direction Régionale de l'Environnement, de l'Aménagement et du Logement in France and the services of the Canton of Geneva). There still exists room for minor adjustments for some technical surface sites and the disposition of the experiment site shafts.

The technical feasibility of the project based on the so-called PA31-4.0 reference scenario could be confirmed with the help of a diverse set of studies. However, it should be stressed that the territory and legal frameworks in France, Switzerland and Europe are constantly evolving. Since 2014, a number of surface site location candidates and scenario traces have no longer been feasible due to these evolutions. Therefore, the situation may further evolve and the conditions for implementing the reference scenario PA31-4.0 may also change. To ease the project authorisation process and to avoid potential interference with future developments and spatial planning, it is advisable to obtain the rights on the required land plots as soon as possible.

## 2.6.2 Scenario characteristics

The layout and functions of the PA31-4.0 reference scenario are shown in Fig. 2.27. The two shafts at the PA surface site (Ferney-Voltaire, France) were moved further north from the Route de Meyrin road to maintain a safe distance, to provide space for traffic on the surface site around the experiment assembly hall and shafts, and to protect against direct visibility. Moving the locations of sites PD and PJ further northward would be favourable, but is ruled out due to the presence of the departmental road at the northern limit of site PA. Moving them further eastward is also ruled out due to the presence of a compensation zone that is to be avoided and which will be turned into a fully functional wetland zone and natural habitat if the project is implemented. Such displacements would also move the surface site PG in Groisy and Charvonnex deeper into the forest and on a steep slope. Both are evolutions that are better avoided. The shafts at the PD surface site (Nangy, France) were rotated away from the autoroute to ensure compatibility with the RD 903 departmental road enlargement and integration with the A40 autoroute development project and to ensure the technical feasibility of creating a service shaft on the site without installing an additional cavern between the service and the experiment caverns. A move of site PA further southward is ruled out, as this would create incompatibility due to the presence of the A40 autoroute and the RD 903 road on the PD surface site, and topographical difficulties (steep slope) towards the D 1203 departmental road to Annecy on the PG site in Charvonnex.

The shifting and rotating of the scenario took into account the objective of placing the PG surface site in both the lower quality part of the forest affected and on the existing grassland plateau, where the soil turned out to be of poor quality for agriculture. In addition, the shafts should be kept away from the steep slope to the south to
<table><caption>**Table 2.2** Coordinates WGS84 of the theoretical beam interaction points for scientific sites</caption><thead><tr><th>Site</th><th>Location</th><th>Latitude</th><th>Longitude</th></tr></thead><tbody><tr><td>PA</td><td>Ferney-Voltaire, Ain, France</td><td>46.2480475° N</td><td>6.0986019° E</td></tr><tr><td>PD</td><td>Nangy, Haute-Savoie, France</td><td>46.1453657° N</td><td>6.3169260° E</td></tr><tr><td>PG</td><td>Charvonnex and Groisy, Haute-Savoie, France</td><td>45.9938019° N</td><td>6.1693009° E</td></tr><tr><td>PJ</td><td>Dingy-en-Vuache and Vulbens, Haute-Savoie, France</td><td>46.0962036° N</td><td>5.9513024° E</td></tr></tbody></table>

<table><caption>**Table 2.3** Coordinates WGS84 of the theoretical straight section midpoints for technical sites</caption><thead><tr><th>Site</th><th>Location</th><th>Latitude</th><th>Longitude</th></tr></thead><tbody><tr><td>PB</td><td>Presinge, Geneva, Switzerland</td><td>46.2271027° N</td><td>6.2374818° E</td></tr><tr><td>PF</td><td>Éteaux, Haute-Savoie, France</td><td>46.0490317° N</td><td>6.2865850° E</td></tr><tr><td>PH</td><td>Cercier and Marlioz, Haute-Savoie, France</td><td>46.0146646° N</td><td>6.0309816° E</td></tr><tr><td>PL</td><td>Challex, Ain, France</td><td>46.1926255° N</td><td>5.9810829° E</td></tr></tbody></table>

control construction risks and costs of building the shafts and buildings. It was not possible to move the shafts further away from the forest, towards the plateau, without creating a conflict for the PD experiment site (Nangy) with the autoroute, and for the PJ experiment site (Dingy-en-Vuache and Vulbens), due to the presence of a stream and topographical constraints. The PJ experiment site is therefore kept at a distance from the A 40 to the south, and from the creek and topographical constraints to the west. The wildlife corridor can be maintained. The placement of the PB technical site (Presinge, Switzerland) was optimised by taking into account maps concerning biodiversity and ecological indicators made available by cantonal services, and the results of a study of possible access routes carried out by a specialist firm in the canton of Geneva. The site would be located in Presinge, directly along the Route de Jussy road. A connection with the tunnel between the shaft and the service cavern, 98 m long, is required.

The working hypothesis of the location for the PF technical site is in Éteaux (France), directly adjacent to the RN 203 national road. It includes a connecting tunnel between the 400 m deep shaft and the service cavern at the collider tunnel. A variant further south is currently not considered since the creation of an inert waste deposit site (called I.S.D.I. in French) creates further constraints. However, in case the footprint of the main site is to be reduced, certain technical infrastructures that are limited to surface site constructions (e.g., ventilators, cooling towers, electrical substation) could be displaced to this area. The working hypothesis of the location for the PH technical site is across the border between the two communes Cercier and Marlioz (France), directly adjacent to the D 203 departmental road (Route de Choisy). Taking into account the analysis of fauna, flora and biodiversity, the state of the forest, topographical constraints and technical risks (gas pipeline north of the site), the site closely follows the Route de Choisy road to the north and stretches into the forest down a slope to the west. Should an adjustment become necessary, an alternative site location exists 900 m in clockwise direction directly at the D2 departmental road on a set of agricultural land plots. The significant displacement from the technical straight section mid-point would require the development of a design for the fitting and installation of the radiofrequency ancillary systems (cryogenic refrigeration, powering). The preferred location for the PL technical site (Challex, France) is on the nominal midpoint of the technical straight section to the east of the town, on a field and a plot of land containing two single-family homes. Another possible location, 600 m west of the nominal point, has been studied and discussed with the municipality. It is slightly less preferred due to the higher visibility from residential zones of the commune. This option is also characterised by additional technical challenges that would entail additional costs due to the need to build a shaft approximately 150 m outside the tunnel with additional civil engineering needs and more difficult access to the machine.

### 2.6.3 Scenario parameters

The geographical coordinates of the PA31-4.0 reference scenario resulting from this optimisation are shown in Table 2.2 for the scientific sites and in Table 2.3 for the technical sites.

Table 2.4 summarises the layout parameters of the particle colliders.

The functions of each surface site are shown in Table 2.5.

### 2.6.4 Multi-criteria performance of the reference scenario

Figure 2.8 shows the performance of a number of shortlisted scenarios that were studied in more detail before the PA31 scenario was chosen as a reference for further optimisation. Figure 2.28 shows the results of the multi-criteria
<table><caption>**Table 2.4** Layout parameters of the particle collider</caption><thead><tr><th>Parameter</th><th>Value</th><th>Comment</th></tr></thead><tbody><tr><td>Elevation of the tunnel under the PA site shaft</td><td>202 m above sea level</td><td>The elevation is subject to further optimisation after the availability of the geophysical and geotechnical investigations.</td></tr><tr><td>Length of straight sections at PA, PD, PG and PJ sites</td><td>1400 m</td><td>These sections feature tunnel enlargements. The ee and hh machines may have beam-optics dependent, different machine straight section lengths in these sectors.</td></tr><tr><td>Length of straight sections at PB, PF, PH and PL sites</td><td>2032 m</td><td>This is the minimum space required to ensure that all radiofrequency systems can reliably be fit. Subject to optimisation, not all available space may be used after optimisation.</td></tr><tr><td>East-west rotation of the collider around the PA site</td><td>10.97 degrees</td><td></td></tr><tr><td>Length of one hadron collider arc cell in the arcs</td><td>275.792 m</td><td></td></tr><tr><td>Number of cells in a curved section (arc) per octant</td><td>26</td><td></td></tr><tr><td>Total length of the arcs</td><td>78,684.476 m</td><td>The sum of the curved machine segments of the ee and hh machine may be different</td></tr><tr><td>Total circumference of footprint</td><td>90,658.745 m</td><td>The hh machine may be slightly shorter in the same tunnel (90,657.4 m)</td></tr></tbody></table>

<table><caption>**Table 2.5** Layout parameters of the particle collider</caption><thead><tr><th>Site</th><th>Function</th></tr></thead><tbody><tr><td>PA</td><td>Scientific site with one experiment, injecting the beam line from a linear accelerator at the CERN Prevessin site into the pre-accelerator (booster) located in the same tunnel as the collider.</td></tr><tr><td>PB</td><td>Technical site with injection of booster beam line into the collider, extraction of beam line from collider.</td></tr><tr><td>PD</td><td>Scientific site with one experiment.</td></tr><tr><td>PF</td><td>Technical site with betatron and momentum collimation.</td></tr><tr><td>PG</td><td>Scientific site with one experiment.</td></tr><tr><td>PH</td><td>Technical site with radiofrequency particle acceleration system for the collider.</td></tr><tr><td>PJ</td><td>Scientific site with one experiment.</td></tr><tr><td>PL</td><td>Technical site with radiofrequency particle acceleration system for the booster pre-accelerator.</td></tr></tbody></table>

analysis for this scenario in terms of territorial compatibility (T), implementation and risk management (I) and scientific value (S) for each site location and the entire trace.

### 2.6.5 Site PA

**Description of the site location** The main site is located in Ferney-Voltaire, Ain, France, south of the Route de Meyrin road, east of the Espace Candide shopping centre (see Fig. 2.29 and Fig. 2.30). The site would be connected to Point 8 of the LHC by the Chemin des Prés Jins, a public road. An extension to the south of LHC Point 8, already planned as part of the HL-LHC project, would make it possible to accommodate technical infrastructures to reduce the land take for the main site. The surface area of the site along the Route de Meyrin is 5.2 ha, and the surface area of the LHC Point 8 site extension is 2.7 ha.

**Known constraints** The site is located in a protected agricultural (Ap) zone, close to an environmental compensation zone classified as protected nature zone (Np). The water supply network passes close by Point 8 of the LHC. A gas pipeline runs along the boundary of the main surface site, before crossing the border between France and Switzerland. There is a network along the Route de Meyrin that supplies waste heat from LHC Point 8 to
<figure><img src="image_86.png" /><figcaption>**Fig. 2.28** Multi-criteria analysis percentage scores of each surface site location and the entire collider trace of scenario PA31-4.0. Note that site locations PC, PE, PI and PK do not exist in 8 site scenarios. Blue lines indicate the individual performance thresholds (green, yellow, orange, red). Green indicated bars exhibit a very good performance and yellow indicated locations correspond to a good performance)</figcaption></figure>

<figure><img src="image_87.png" /><figcaption>**Fig. 2.29** Aerial view of candidate location for surface site PA</figcaption></figure>
<figure><img src="image_88.png" /><figcaption>**Fig. 2.30** PA surface site location in Ferney-Voltaire, Ain, France. The hashed space in the south represents an annex that is an extension of the existing LHC P8 site</figcaption></figure>

dwellings and to the commercial zone (ZAC, mixed development zone). Good urban and landscape integration is necessary to preserve the view facing the Alps. Due to heavy traffic in the area, a concept must be developed together with the municipality's technical services for efficient site access. No dedicated access road is required, though.

*Synergies and territorial potentials* Waste heat from the particle collider cooling and the data centre can be recovered and supplied to the homes and business parks around the site, including the Geneva airport and industrial zone, building on the current heat supply network that has been put in place for the LHC programme. The existing but non-functional environmental compensation area can be turned into a fully functional natural habitat and wetland, providing substantially increased environmental quality in that area. Treated residual water from the cooling system can be used for this zone (the Poirier de l'Épine zone) and potentially for agricultural purposes close to the site. Synergy with LHC Point 8 would permit a substantial reduction of the footprint of the PA site. This requires good planning and sequencing of the new collider project with the HL-LHC programme. Synergy with the CERN site in Prévessin and the Bois-Tollot substation provides the electricity supply (existing 400 kV line to Prévessin and a dedicated 63 kV link from Prévessin to LHC Point 8). A visitor centre could be created in synergy with LHC Point 8 to exploit the location fully.

### 2.6.6 Site PB

*Description of the site location* The site lies in Presinge, canton of Geneva, Switzerland, to the south of the Nant du Paradis stream, on a field classified as a protected crop rotation area (in French: 'Surface d'Assolement' or in short SDA), bordering the Route de Jussy road (see Fig. 2.31 and Fig. 2.32). The surface area shown on the map indicates the site area covers 4.5 ha. The site is displaced south to the road, avoiding conflicts with nature protection zones and providing for improved access. An underground connection tunnel of about 100 m in length is required to connect to the service cavern that is located inside the collider tunnel.

*Known constraints* The prescribed protective distances between the Nant du Paradis creek that hosts an amphibian breeding area and the forest are respected. The environmental state analysis did not detect any interference with protected environments in the vicinity of the location, in particular the amphibian breeding site. The impact on the crop rotation area (SDA) should be kept to a minimum. The space consumed by SDA has to be compensated 1:1 by transporting the topsoil to another location that needs to be identified with the help of notified cantonal services. To blend in well with the surrounding landscape, the site needs to be as small and compact as possible and be ideally semi-underground. A study of the cooling system is necessary to reduce noise and visual disturbances. It is also necessary to develop a concept for reducing light pollution during the construction phase. The road access
<figure><img src="image_89.png" /><figcaption>**Fig. 2.31** Aerial view of candidate location for surface site PB</figcaption></figure>

<figure><img src="image_90.png" /><figcaption>**Fig. 2.32** PB surface site location in Presinge, canton of Geneva, Switzerland</figcaption></figure>
<figure><img src="image_91.png" /><figcaption>**Fig. 2.33** Aerial view of candidate location for surface site PD</figcaption></figure>

was studied by a specialised firm with in-depth knowledge of the sector. No new road needs to be constructed, but a junction would have to be created at the Route de Jussy. The detailed design and location of the recommended access option have to be validated by the notified bodies of the canton of Geneva once a construction project is proposed. A detailed technical access plan should be drawn up at a later stage for this purpose.

*Synergies and territorial potentials* According to the road access study carried out by the firm, direct access to the site from the Route de Jussy is technically feasible and preferable from the project perspective. This scenario would avoid the need to create a new access road. The green buffer zone around the site would reinforce and extend the natural environment in the vicinity of the Nant du Paradis watercourse. Surface sites that are semi-underground would not only improve the blending into the landscape but would also improve the overall ecological and biodiversity value of a non-agricultural habitat. The reinforcement of the local power grid, necessary for the construction phase, is seen as an opportunity to improve the infrastructure for the inhabitants of the entire area. Improved public transport, including cross-border transport as part of the FCC, also represents an opportunity for the area. Several opportunities exist, and demand for supplying heat recovered from the particle accelerator nearby, for example, with HEPIA and a new correctional institution slated for construction by 2030 on the Champ-Dollon prison site.

### 2.6.7 Site PD

*Description of the site location* The site is located in Nangy, Haute-Savoie, France (see Fig. 2.33 and Fig. 2.34) between the A40 autoroute and the RD903 departmental road on an agricultural field with zone ‘A’ classification in the local urban plan (in French: ‘PLU’). The surface area of the site is approximately 4.9 ha.
<figure><img src="image_92.png" /><figcaption>**Fig. 2.34** PD surface site location in Nangy, Haute-Savoie, France</figcaption></figure>

**Known constraints** The site is subject to space constraints to the west, east and south due to existing roads and plans to build a new connection between the roads. Road traffic is typically high, one reason for the road development project that is expected to integrate the departmental road with the autoroute. A study for the development of different access scenarios was carried out by a specialised firm. The scenarios were discussed with the Haute-Savoie department and with the mayor of the municipality. The commonly preferred scenario with the lowest impact is one that comprises a dedicated access road to the surface site. The access to the site would be via a roundabout, which would be built to the north at the D 1205 departmental road in Fillinges.

**Synergies and territorial potentials** The site is only accessible via the dedicated, approximately 250 m long access road. The site is not visible from residential areas, which facilitates its integration into the landscape. There are a number of possibilities for supplying residual heat from the cooling system, for example, to a nearby cheese factory, to an industrial and business park, to hotels, medical facilities, neighbouring communes such as Fillinges, Boringes, Scientrier, Contamine-sur-Arve and to the Alpes-Léman hospital complex. The heat can also be used for biogas production in the waste water treatment facility in Scientrier. Currently, a study is ongoing to source water from the waste water treatment facility ‘SRB’ in Scientrier for use in the accelerator cooling system. When the cleaned water is not used for the particle accelerator, it could be made available for agricultural and industrial purposes. A direct connection by conveyor belt to the autoroute during the construction phase has been studied. It would facilitate the removal and possibly also the supply of materials, thus largely avoiding the need for trucks. There are likely areas in the vicinity where excavated materials can be reused such as raised hedges, noise separation, covered trench creation, landfill and transport to quarries for rewilding purposes. To be able to develop a solid excavated materials management plan, these opportunities need to be identified with the help of local authorities and notified bodies (e.g., SAFER, DDT, DREAL).

### 2.6.8 Site PF

**Description of the site location** A technical surface site at the nominal point PF in La Roche-sur-Foron, Haute-Savoie, France (see Fig. 2.35 and Fig. 2.36) is not feasible because:

* The site would be in the middle of a hamlet of single-family homes.

* The presence of the Lavillat road in the direction of La Roche-sur-Foron is incompatible with the construction and installation of the accelerator site and equipment.

* The nominal point is located on high ground (755 m) leading to a shaft which is too deep and with an unfavourable topography.

* A slight movement of the ring inwards is ruled out due to the presence of steep slopes and the risk of landslides.
<figure><img src="image_93.png" /><figcaption>**Fig. 2.35** Aerial view of candidate location for surface site PF</figcaption></figure>

**Fig. 2.36** Nominal location of PF indicated with a spot on the collider trace. Two surface site candidate locations requiring horizontal access tunnels are indicated with black arrows

<figure><img src="image_94.png" /></figure>
<figure><img src="image_95.png" /><figcaption>**Fig. 2.37** PF surface site location in Éteaux, Haute-Savoie, France</figcaption></figure>

The preferred alternative selected for a technical surface site PF is a location in Éteaux, Haute-Savoie France (see Fig. 2.37), alongside the RD 1203 road, with a surface area of 4 ha. An underground connection tunnel is required between the shaft to be located in the indicated surface site perimeter and the service cavern at the inside of the collider tunnel.

If the surface site area needs to be reduced, made more compact or certain constructions cannot be made compatible with the required landscape integration, then an annex to the south of the site, alongside the autoroute in La Roche-sur-Foron can be envisaged. The land is on the perimeter of a newly constructed inert waste storage facility (in French: ‘I.S.D.I.’). Once the inert waste storage is full and no longer in use, it can host constructions that are limited to the surface such as ventilation systems, cooling towers and an electrical substation.

## Known constraints

**Main site in Éteaux** The shaft of the site and the accelerator tunnel are 558.5 m apart, depending on the position of the shaft. The wetlands to the east of the site must be maintained and could be integrated into the site. A certain distance must be maintained between the site and the hamlet to the east. As a result, there is little space left for the surface site, and the size of the site should be reduced. Work should be undertaken with the local authority and government agencies (DDT, DREAL) to define zones for recycling excavated materials in the vicinity of the site. The area available for the surface site is very limited (4 ha). It may, therefore, be necessary to relocate certain elements, such as an electrical substation or cooling towers, to the south option for the site in La Roche-sur-Foron or to another nearby location.

**Option of an annex in La Roche-sur-Foron** The technical site is located on the site of an inert waste storage facility (in France: ‘I.S.D.I.’), currently under construction, with the status of a facility classified for environmental protection (in France: ‘ICPE’), i.e., subject to particular construction, operation and monitoring constraints. Following an analysis carried out by civil engineering contractors, the location was found, in principle, to be compatible with the construction of a surface site. However, this choice would entail significant additional costs and additional technical difficulties. For example, it would be necessary to employ pillars for construction on inert waste dumps to assure the stability of the groundworks and the construction of the shaft. It would be necessary to create an access road 2.4 km long that crosses the existing railway line, and to build an underpass under the autoroute. Lastly, this option is located in the immediate vicinity of an environmental protection zone (in French: ‘ZNIEFF’), which is rich in biodiversity and includes a wildlife corridor that must be preserved. The available surface area is roughly the same as for the location in Éteaux (4.1 ha, versus 4.0 ha). However, if needed, the location could accommodate certain technical infrastructures that are compatible with inert waste deposits, such as an electrical substation or cooling towers. Further analysis will be carried out during the detailed technical design phase.
<figure><img src="image_96.png" /><figcaption>**Fig. 2.38** Aerial view of candidate location for surface site PG</figcaption></figure>

*Synergies and territorial potentials* For the location in Éteaux, it is possible to supply residual heat from the cooling system to public facilities and businesses in a radius up to 3 km. A zone that qualifies as wetland, but which today is not well preserved, can be rewilded, protected, and be well preserved together with the habitat in the vicinity of the Vuaz stream. Lastly, direct access from the main road is possible and would avoid the creation of a new access road. Electricity substations for the construction phase exist in the vicinity. If needed, a connection to the nearby autoroute service station could be implemented to facilitate the transport of excavated materials and the supply of construction materials.

### 2.6.9 Site PG

*Description of the site location* The experiment site PG lies to the north of the Route d'Annecy road on a plateau, crossing the border of the communes Charvonnex and Groisy, Haute-Savoie in France (see Fig. 2.38 and Fig. 2.39). The main site is partly in a forest and partly on grasslands. It is approximately 800 m south of the A410 autoroute area in Groisy. At this location, next to the autoroute service station, two smaller plots have been identified to host technical infrastructures that do not need to be close to the shaft. All plots are far from any dwellings. The area marked limits of the main site is 6.9 ha. However, only a fraction of that area would be constructed. Annexes of 1.9 ha and 1.7 ha for equipment storage, an electrical substation and cooling towers close to the autoroute are also indicated. An existing 800 m long, wide forest path has to be refurbished to serve as an access road to the main site.

*Known constraints* The forest is a classified wooded area (in France: ‘EBC’), heterogeneous, valued for its biodiversity in some parts. The use of the forest for the site will be reduced and limited to the part with the lowest quality in terms of its natural environment. Clearing will be compensated for by, for example, reforesting the
<figure><img src="image_97.png" /><figcaption>**Fig. 2.39** PG surface site location in Charvonnex and Groisy, Haute-Savoie, France. the main site intersects the collider alignment, shown in blue. The two plots at the autoroute in the north serve for equipment that does not need to be necessarily located in the immediate proximity of the shafts. The areas also serve for handover of incoming construction materials and the evacuation of excavated materials</figcaption></figure>

southern part of the plateau or existing brownfields in the forest. The site is on the edge of a steep slope towards the Route d'Annecy to the south, and must therefore remain on the top of the plateau. It is a quiet, natural area with exceptional views towards the Aravis mountain chain to the south. The location is exceptionally well suited to host a visiting facility with recreational facilities on the site. Measures will need to be taken to reduce noise and light pollution during the construction and operating phases.

*Synergies and territorial potentials* The possibility of reforestation compensates for the clearing of approximately 1.5 ha of forest. A forest road over flat land provides good access and makes it possible to create a route over approximately 800 m to the Groisy autoroute area and a wide road alongside the autoroute. Access to the autoroute during the construction phase for supplies and the removal of excavated materials has been studied and appears feasible. The use of a conveyor belt removes the need for trucks. There are two temporary storage areas for inert waste and other materials in the immediate vicinity of the site and the forest road. Annexes close to the autoroute could accommodate those elements most likely to generate disturbances, such as cooling towers and an electrical substation. The supply of residual heat from the cooling system appears to be possible. Several potential consumers have been identified in the vicinity, including public facilities (elementary school, middle school, fire station), a commercial zone and a veterinary clinic. There is also the possibility of creating a district heating network in Charvonnex and Groisy. The fire station can serve as a base for emergency services in the immediate vicinity of the site. Waste water from the cooling system could be used to feed the Fattes stream and wetlands in the forest. There is enough space on the site to build a visitor centre with recreational facilities that can be reached via the Groisy autoroute area or the Route d'Annecy. The site is located near Annecy, within easy reach for CNRS/LAPP staff. Sites for reusing excavated materials for agriculture and forestry have yet to be identified with the help of local authorities and notified government agencies (e.g., SAFER, DDT, DREAL).

### 2.6.10 Site PH

*Description of the site location* The technical site PH is located right along the D203 road in Cercier, Haute-Savoie in France (see Fig. 2.40 and Fig. 2.41). The site is located in the forest, straddling the municipalities of Cercier and Marlioz, stretching out to the west down a slope. It is far from dwellings and is not visible. It is in a nature setting. The defined area, located in an area with less biodiversity, is 8.2 ha.

*Known constraints* The environmental field investigations revealed that the part of the forested sector to the north of the site is of great value (rich biodiversity, natural environment). Therefore, use of the forest needs to be minimised and the specific locations of buildings and accesses in the forest need to be carefully developed during a subsequent design phase. The site will respect the buffer zone for the gas pipeline to the north. Considering
<figure><img src="image_98.png" /><figcaption>**Fig. 2.40** Aerial view of candidate location for surface site PH</figcaption></figure>

<figure><img src="image_99.png" /><figcaption>**Fig. 2.41** PH surface site location in Cercier and Marlioz, Haute-Savoie, France</figcaption></figure>
the quiet, natural setting, noise and light pollution must be given particular attention. A dwelling is located approximately 200 m to the south. There is no co-visibility between the site and the dwelling. Given the small size of the road, it is necessary to identify nearby reuse sites for excavated materials, so that they can be used in agriculture or for reforestation. Materials would mainly be transported away to the north or the west by conveyor belt to avoid road constraints. The location is well suited to host the radiofrequency system since a 400 kV grid line passes less than 2 km to the north. RTE, the national grid operator will have to take into account the need to supply electricity via buried cables when carrying out the study for the creation of a substation for access to the 400 kV line.

Should for any reason the site preferred location at the nominal point not be considered feasible, an alternative placement about 900 m in the clockwise direction of the collider has been identified as an alternative. This site is located on agricultural fields next to the D2 departmental road. It would be suitable as the location for the electrical substation in case of placement on the nominal point or when displaced since the electrical substation does not necessarily need to be in the immediate vicinity of the shaft.

*Synergies and territorial potentials* There is a great deal of interest in reusing water from the particle collider infrastructures for agricultural activities around the site (e.g., apple and pear trees). A water basin exists nearby, to the northeast. In case further, more detailed scenario developments are considered, a study will have to be carried out to find a way of integrating those opportunities with the site. It is advisable to work with local stakeholders to identify potential consumers of the residual heat, for instance, in the fruit and vegetable sector.

## 2.6.11 Site PJ

*Description of the site location* The experiment site PJ is located in a field on a slope to the north of the A40 autoroute and to the west of the Valleiry autoroute area, at the junction of the Chemin des Tattes and Chemin de Maigy roads across the communes of Dingy-en-Vuache and Vulbens, Haute-Savoie, France (see Fig. 2.42 and Fig. 2.43). To the west is a small stream. The site is far from any dwellings. The surface area of the site is 6.1 ha.

The site is accessible by the existing paved rural path Chemin des Tattes towards the north to Vulbens. This path has to be enlarged and refurbished.

*Known constraints* A wildlife corridor exists that needs to be respected in the development of the surface site. If possible, the corridor should be improved, as it currently functions poorly. An area with higher biodiversity in the middle of the site will have to be re-created at the border of the site in conjunction with the wildlife corridor. Site design will also have to take into account plans to improve soft mobility between Dingy-en-Vuache and Vulbens.

*Synergies and territorial potentials* The site is surrounded by numerous sloping farmlands. It will be necessary to work with local authorities and government notified bodies (e.g., SAFER, the agricultural chamber, DDT, DREAL) to determine where agricultural activities can benefit from the reuse of excavated materials. The site can also benefit from nearby developments to the south, over the same time frame (e.g., new national police station). It seems feasible to make residual heat available to public institutions and nearby business districts in Vulbens and Valleiry. In particular, it would be advisable to work with the department on integrating educational and training infrastructures with the surface site-related activities to generate local added value. The creation of a visitor centre would enable the development of high-quality, sustainable tourism. The connection to the Valleiry autoroute service area for removing materials and receiving supplies via the autoroute has been analysed and is feasible. To avoid trucks, a conveyor belt would be used to transport the materials to the autoroute area. Incoming materials could be transported via a temporary 700 m long road to the site. There is interest in developing synergies for the reuse of waste water to feed streams and for crop irrigation.

## 2.6.12 Site PL

*Description of the site location* The working hypothesis for the location of the technical site PL in Challex, Ain, France has been determined through various iterations with the municipality in 2023 and 2024. The reference site location at the nominal point can be seen in Fig. 2.44 and Fig. 2.45.

The site is at the nominal point in the middle of the technical straight section, near the border between France and Switzerland on an agricultural field. The perimeter includes two houses which would have to be integrated in the surface site project. The location still needs to be optimised in close cooperation with the municipality and architects. This option, located far from the village, requires the creation of an access road approximately 1.3 km long to the D89 departmental road. The route of this road will be developed by an expert company in close cooperation with the commune, respecting the existing environmental constraints. The area of the site is 5.5 ha. A large part of this space is foreseen for rewilding.
<figure><img src="image_100.png" /><figcaption>Fig. 2.42 Aerial view of candidate location for surface site PJ</figcaption></figure>

<figure><img src="image_101.png" /><figcaption>**Fig. 2.43** PJ surface site location in Dingy-en-Vuache and Vulbens, Haute-Savoie, France</figcaption></figure>
<figure><img src="image_102.png" /><figcaption>**Fig. 2.44** Aerial view of candidate location for surface site PL</figcaption></figure>

<figure><img src="image_103.png" /><figcaption>**Fig. 2.45** PL surface site options studies in Challex, Ain, France</figcaption></figure>
<figure><img src="image_104.png" /><figcaption>**Fig. 2.46** Alternative location for site PL in Challex, Ain, France. The plot is located on the outside of the collider tunnel, which calls for an underground connection tunnel and a more complicated access to the radiofrequency gallery and the collider tunnel for equipment installation and maintenance</figcaption></figure>

Should for any reason the implementation at the nominal point turn out to be unfeasible, an alternative location has been identified at a distance of 800 m in counter-clockwise direction along the straight section. This location would require the creation of an access shaft about 150 m outside the line of the collider and would therefore result in significantly higher costs (Fig. 2.46).

## Known constraints

*Option with location at nominal point* The proximity of the Franco-Swiss border, close to vineyards, presents a challenge, as there are no roads or other infrastructure. However, one remote dwelling in the vicinity would be affected by disturbances and would therefore have to be acquired. This plot would be integrated into the surface site and serve for rewilding and visibility protection. Access to the site through the village is ruled out. The roads are too narrow and the disturbance would be unacceptable. Building a new access route through the fields to the north of the village is complicated but feasible. The theoretical point is separated from the main roads (Route de Greny and Rue de la Craz) at the entrance to the municipality by natural areas. The forest to the north of Challex is a zone rich in biodiversity. On the Swiss side, the forest is a zone reserved for absolute protection (Ramsar site), the vineyards are protected, nature zones are protected, the village is a cultural heritage indexed zone and the slope is too steep for surface site construction. A suspected, temporary, shallow water table was added to the Swiss maps in 2023. If this is the case, it will be confirmed through ongoing geotechnical investigations. Technically, the creation of a shaft is feasible, even if there is a temporary water table in this location. In the present, the investigations will also determine its seasonal nature and the possibility of cross-border connections. The positioning of the shaft and the entire site can be optimised according to the results of these subsurface investigations. Following an analysis conducted with the local municipality, it has been determined that this location option is preferred.

*Option for the location 800 m east of nominal point (not selected)* A location 800 m east of the nominal point would not allow access inside the ring (see Fig. 2.46).

The site would be approximately 150 m from dwellings, 5 to 10 m lower than the municipality, on a gentle slope of approximately 3%. It would be visible from certain dwellings. The site would partially affect the protected natural area, but the impact would remain limited since it is currently a field, and the biological corridor passes further to the east of the site. It would be necessary to build an access road to the D89 (approx. 400 m long) or to the Rue de la Craz road (approx. 300 m long). This scenario was used as a basis for discussions with the municipality to find an alternative to the location at the nominal point.

A technically feasible solution for access from the outside of the ring, albeit at a higher cost, has been developed. The shaft would be located about 150 m outside the ring (see Fig. 2.47). The verification regarding its visibility from isolated dwellings on the outskirts of the municipality has shown that this location should not be prioritised.
<figure><img src="image_105.png" /><figcaption>**Fig. 2.47** Access to the main tunnel from the exterior via an underground connection. This approach is more complicated and induces additional costs</figcaption></figure>

*Synergies and territorial potentials* The proximity of the CERN sites (Prévessin in France and Meyrin in Switzerland) represents an exceptional opportunity to benefit from synergies for the installation, operation, maintenance and repair of equipment in the shortest possible time. The fields to the north of the municipality appear to be suitable for reusing excavated materials for agricultural purposes. There is no direct visibility from the village. The proximity of the former Collonges train station at a distance of 12 km via the de-commissioned railway tack represents an opportunity for removing materials and providing supplies, avoiding trucks as much as possible by using conveyor belts. A connection to the La Plaine train station in Switzerland would be technically possible, but would be subject to an agreement between France and Switzerland. It could also provide an opportunity for material removal via a combination of conveyor belts and railway systems. The improvement of the local power grid, necessary for the construction phase, would benefit the municipality and its residents. It would enable increased use of renewable energies and more robust vehicle recharging stations. Improving the public transport network, starting at the construction phase, can also be of benefit to residents of the municipality, who currently mainly use private vehicles on the D884 in France and travel to Meyrin and La Plaine in Switzerland. Challex has traditionally been home to employees of international organisations, many of whom work at CERN. Strengthening the infrastructure would therefore benefit both the community and the project. Residual heat from the particle collider could be used for heating individual and collective residences (e.g., the Les Cyclamens long-term care centre), as well as for the Val Thoiry commercial centre approximately 7 km away. Other nearby communities such as Greny, Saint-Jean-de-Gonville, Péron and La Plaine (Switzerland) could also benefit from this heat supply. The company Firmenich (perfumes and fragrances), based in La Plaine in Switzerland, could also benefit from this heat. Heat could also be used in innovative ways for fish farming, aquaponics, market gardening, and greenhouses.

### 2.6.13 Prévessin site

The aim of the placement studies for the injector facilities is to maximise the use of existing CERN infrastructures. Considering the strong territorial constraints that have been identified and documented throughout a 7-year period, the needs for electricity, raw water, a more than 1 km long space on the surface for a linear accelerator and associated workshops, offices and storage zones, the existing CERN Prévessin site emerged as the most suitable location for a working hypothesis. This site has the space to host the electron and positron sources, linear accelerators, damping rings and optional experimental facilities to leverage the powerful electron-positron injector as an additional scientific instrument that can be used even before the electron-positron collider enters operation. In addition, the site is at a reasonably close distance from the existing LHC surface site P8, which together with additional space in the immediate vicinity, forms the surface site PA. Hence, the implementation of the transfer line, also leveraging the existing SPS subsurface structures, leads to an advantageous configuration.
**Fig. 2.48** Sketch of the current working hypothesis for a linear-accelerator based injector that has a length of about 1.2 km. A definitive placement remains to be developed in the frame of a design phase, considering environmental, existing experimental facility, territorial development and engineering constraints

<figure><img src="image_106.png" /></figure>

Numerous technical infrastructures such as the existing 400 kV grid connection, water supply and treatment, offices, computing facilities, room for construction activities permit the efforts that are typically linked to territorial development for a new site to be kept within limits. At the current stage of conceptual development, the injector would have a total length of approximately 1.2 km. It could almost fit into the fenced space of the Prévessin site.

Common work with the authorities and further optimisation according to the ‘avoid-reduce-compensate’ approach will be performed so that any unavoidable territorial extension will be kept as small as possible and to assure that ultimately a suitable reference scenario for the injector placement can be identified.

Initial explorations have excluded the possibility of extending the site towards the north and east due to numerous nature, agriculture, and visibility constraints. The current, unfinished, working hypothesis shown in Fig. 2.48 is based on a placement between the ‘Lion’ creek and the North-Area beamline. The requirements and constraints of various technical concept elements, such as the exact size and shape of the damping ring, the widths and lengths of the accelerators and their integration, are today not yet at a level that permits freezing of the exact placement on the site. The analysis work carried out so far permitted, however, confirming the technical and territorial feasibility in principle and helped to identify the constraints to be considered for subsequent activities.

During a subsequent technical design phase, environmental analysis will guide the optimisation of the placement to ensure that natural constraints are respected, the required extension of the existing fenced domain is kept as small as reasonably possible, and that existing experimental facilities are not significantly impacted. A preliminary concept for the underground transfer line alignment avoids as much as possible conflicts with the projected construction areas on the surface. A definitive design will require more detailed environmental analysis, including geology and hydrogeology. The estimated efforts for these analysis and design activities are in the order of two to three years. They need to be integrated in the overall project environmental authorisation process.

### 2.6.14 Conclusion

Table 2.6 shows the status of the feasibility analysis for the surface site locations in scenario PA31-4.0. Technical feasibility was assessed using maps and data available to those working on the study and to contractors. The assessment was also based on fieldwork and environmental studies carried out by specialised companies, discussions with the relevant technical departments of the two host states, and with local elected officials (mayors, town councillors, departmental councillors, and regional councillors), who represent the citizens and act in their interests.

## 2.7 Territorial infrastructure needs

### 2.7.1 Introduction

To be able to construct, install and operate the particle-collider facility and its associated experiments, a number of different territorial infrastructures are required. The development of the implementation scenario put an emphasis
<table><caption>**Table 2.6** Status of technical feasibility assessment for surface sites of PA31 scenario</caption><thead><tr><th>Site</th><th>Location</th><th>Technical feasibility</th><th>Feasibility conditions</th></tr></thead><tbody><tr><td>PA</td><td>Ferney-Voltaire, Ain, France</td><td>Confirmed</td><td>Limit impact on the landscape, enhance the natural area and the existing compensation zone. Maximise synergy with LHC point 8. Compensate for the loss of agricultural space. Develop a visitor centre, for example, on the LHC Point 8 site. Develop synergies based on heat recovery with municipalities within a 10 km radius, including Swiss municipalities and the Geneva airport.</td></tr><tr><td>PB</td><td>Presinge, Geneva, Switzerland</td><td>Confirmed</td><td>Define the exact location of the site on the plot and initiate discussions with the municipality. Identify an area to compensate not only for the loss of agricultural but also natural space. Limit impact on the landscape. Take into account the sensitive location of the site in a natural setting. A detailed conceptual design of the road access is to be developed and approved by the Canton of Geneva. Reach an agreement to recycle excavated materials, preferably locally. Develop synergies based on heat recovery around the site with local stakeholders and authorities.</td></tr><tr><td>PD</td><td>Nangy, Haute-Savoie, France</td><td>Confirmed</td><td>There are no specific blocking points, but the major issues in this sector call for careful joint development of the site in coordination with local stakeholders. Limit the loss of agricultural space by working on a smaller surface site. Compensate for the loss of agricultural space. Maintain compatibility with the proposed connection between the RD903 and the A40. Estimated start of construction: first quarter of 2025. Develop a transport concept for the construction phase to limit impacts on a sector that is already overburdened. Develop synergies with the communities around the nearby hospital (CHAL), the Scientrier waste water treatment plant (STEP) and the industrial zone to the north.</td></tr><tr><td>PF</td><td>Éteaux, Haute-Savoie, France</td><td>Confirmed</td><td>The north option along the RD1203 was confirmed, provided that nearby wetlands are avoided. Limit the loss of agricultural space. For a potential southern extension option, a decision would be required before the start of phase 2 of the ISDI (inert waste storage facility) in La Roche-sur-Foron in 2027. This would allow earthworks to be carried out on the western part for a smaller site, rather than wait for a complete development for the ISDI. Otherwise, annexes would need to be constructed on top of the inert waste. An agreement must be reached with the ISDI operator and the landowners. The access layout should be developed for this option. Any economic loss suffered by the ISDI operator must be taken into account when developing synergies between the site and the operator. Develop synergies with local authorities in terms of site development with emergency services.</td></tr><tr><td>PG</td><td>Charvonnex and Groisy, Haute-Savoie, France</td><td>Confirmed</td><td>The site straddles the forest and the plateau, which includes unexploited grasslands. Two annexes close to the autoroute area will accommodate certain facilities (e.g., water cooling system, electrical substation) to avoid any disturbance to the wooded area. Plan a visitor centre to develop high-quality, sustainable tourism. Develop synergies with the municipalities of Groisy and Charvonnex to develop the site with neighbourhood services for on-site researchers and emergency services. The loss of woodland can be compensated by reforestation around the site. The layout of the existing access route to the north is suitable.</td></tr><tr><td>PH</td><td>Cercier and Marlioz, Haute-Savoie, France</td><td>Confirmed</td><td>Limit the site's footprint and remain within the wooded area to avoid impacts on the dwellings to the south of the site. Reduce the impact on natural habitats and biodiversity. Compensate for the impacts on woodland, habitat and biodiversity that cannot be avoided and reduced. Respect the easement for the gas pipeline near the site, and decide what distance to maintain between the pipeline and above-ground infrastructure. Consider a split or displaced site location along the straight section.</td></tr><tr><td>PJ</td><td>Dingy-en-Vuache and Vulbens, Haute-Savoie, France</td><td>Confirmed</td><td>Compensate for the loss of agricultural space. Preserve ecological corridors. Integrate the planned projects to develop soft mobility between Dingy-en-Vuache and Vulbens. Foresee a visitor centre to develop high-quality, sustainable tourism. Work with the municipalities to develop synergy for the site with regard to neighbourhood services for on-site researchers, emergency services and schools.</td></tr><tr><td>PL</td><td>Challex, Haute-Savoie, France</td><td>Confirmed</td><td>The location at the nominal point has been discussed with the municipality. Compensation for the loss of agricultural space. A joint optimisation of the site with the municipality is in progress.</td></tr></tbody></table>
<table><caption>**Table 2.6** (Continued)</caption><thead><tr><td>Site</td><td>Location</td><td>Technical feasibility</td><td>Feasibility conditions</td></tr></thead><tbody><tr><td>CERN</td><td>Prévessin and Saint-Genis Pouilly, Ain, France</td><td>Confirmed</td><td>The location of the injector at the existing CERN Prévessin site has been verified, and its technical feasibility has been confirmed in principle. Optimisation of the placement within the site remains to be done based once detailed technical requirements and invariants are available and the state of the environment has been analysed. Territorial development outside the fenced perimeter will be kept as low as reasonably possible. The alignment of the underground transfer line to site PA will be designed considering geology, hydrogeology and the project of constructed areas on the surface.</td></tr></tbody></table>

<figure><img src="image_107.png" /><figcaption>**Fig. 2.49** Noteworthy road, electricity, water treatment infrastructures, emergency services and border crossings in the vicinity of the surface sites indicated by red circles</figcaption></figure>

on leveraging existing infrastructures as much as possible (Fig. 2.49). The well-developed transport, electricity, and water networks in the region around CERN are one of the motivations to propose the facility in this region. The main infrastructures required and described in this section are: roads that provide access to the surface sites, autoroutes to evacuate excavated materials and to supply construction materials and equipment, railway lines to support possible excavated materials and construction materials transport, electricity for the construction phase, direct access to the French high-capacity power grid for the operation, and raw water for cooling purposes.

## 2.7.2 Road access

The road network is dense along the reference scenario footprint (see Fig. 2.50). For the site access roads, in order for two heavy goods vehicles to pass each other at reduced speed, a width of 5.50 m of roadway with two 0.50 m shoulders is required. Subject to environmental constraints, the lanes of reinforced roads or new roads may be smaller: widths of 4.00 m for the roadway and 0.50 m for the shoulders are acceptable if possibilities for passage in both directions are foreseen. This reduced section will require instructions to be given to the drivers of the vehicles concerned.

Several surface sites can profit from direct road access (PA, PD, PF, PH) and some others require minor reinforcement of existing road access (800 m of forest path to be paved for PG, 600 m of rural path to be paved
<figure><img src="image_108.png" /><figcaption>**Fig. 2.50** Overview of the road and railway transport network in the perimeter of the reference scenario</figcaption></figure>

for PJ). Site PD requires the creation of a 300 m long dedicated access. Site PL requires the creation of an approximately 1300 m long dedicated access. In total, less than 3 km of road have to be created. Figure 2.51 presents an overview of the road access concepts.

Road traffic analysis [38] has been carried out for all sites, and the feasibility of the construction was verified with this work. Technical designs for road accesses have been developed for sites PB, PD and PF to ensure the feasibility in areas that are subject to particular road traffic constraints linked in PB to visibility and road safety, in PD due to a major road enlargement and autoroute development project and in PF to ensure road safety. Detailed road access designs have now to be carried out for all sites for the development of a coherent design package that is required for environmental impact assessments and project authorisation.

### 2.7.3 Autoroute access

The study examined the feasibility of connections to the autoroute network for the removal of materials and the supply of equipment during the construction phase [39]. The possibility of obtaining autoroute connections, either directly, via conveyor belts or via temporary gravel paths during construction is a goal in the general interest, aimed at limiting the impact of the project, particularly during the construction phase. The specific technical choices will be made later, during the project development and preparation phase. To verify the technical, legal and financial feasibility of direct access to autoroutes, files with conceptual design plans and descriptions were compiled and submitted for review on 14 September, 2022 to the competent authority for granting concessions: the Direction générale des infrastructures, des transports et des mobilités (DGITM), Direction générale des infrastructures, des transports et des mobilités / Direction des mobilités routières / Sous-direction des financements innovants et du contrôle des concessions autoroutières / Chef du Bureau des services aux usagers et de la comodalité and the Direction générale des infrastructures, des transports et des mobilités / Direction des mobilités routières / Sous-direction des financements innovants et du contrôle des concessions autoroutières / Chef du Bureau du patrimoine et de l'aménagement.

The feasibility of four new connections to the autoroute network was analysed and confirmed to be in principle feasible (see Fig. 2.52) for the following sites:

1. PD site in Nangy (on the A40 autoroute),

2. PF site in Éteaux/La Roche-sur Foron (on the A410 autoroute),

3. PG site in Charvonnex/Groisy (on the A40 autoroute),
<figure><img src="image_109.png" /><figcaption>**Fig. 2.51** Overview of road access concepts for each individual surface site</figcaption></figure>

4. PJ site in Dingy-en-Vuache/Vulbens (on the A410 autoroute).

The conclusions of the interactions with the DGITM were as follows:

* The access concepts and loading/unloading areas provided are in principle acceptable.

* Adjustments will be needed, with the final decisions to be made with the autoroute operator in the project phase.
<figure><img src="image_110.png" /><figcaption>**Fig. 2.52** Location of the autoroute connections, which were studied using existing service and rest areas. Blue dots correspond to autoroute rest areas, magenta dots indicate autoroute service stations and green dots indicate toll stations</figcaption></figure>

* Detailed plans have to be developed and presented.

* The procedure for submitting an application in the future was specified.

* The proposed justifications, in the general interest, are acceptable;

* Entrances and exits will need to be equipped with detection devices to manage tolls.

### 2.7.4 Railway access

To reduce the need for truck traffic, to generate further opportunities to supply quality construction materials from further distances and to open possibilities to transport excavated materials to appropriate deposition sites and re-use locations in an environmentally friendly and high capacity way, railway access studies have been carried out by a qualified domain-expert company [40–48].

The current reference scenario was taken as a working hypothesis for analysing the opportunities and feasibilities concerning accessing the railway system via existing installations (goods loading and unloading facilities) and concerning the creation of new accesses (so-called ITE, ‘Installation Terminal Embranchée’ in French).

The studies used a multi-criteria analysis that considered the following indicators:

* Proximity of the surface site with a suitable railway track.

* Technical and administrative compatibility for access with the French and Swiss railway infrastructure.

* Presence of an existing service or ITE that could be leveraged.

* Feasibility of creating a transport connection between the site and the railway track access.

* Minimum space requirements for railway access and available space.

* Number of convoys required for evacuating all excavated materials.

* Capacity availability and limitations on each railway line analysed.
<figure><img src="image_111.png" /><figcaption>**Fig. 2.53** Minimum space requirements of a new railway access for goods transport</figcaption></figure>

<table><caption>**Table 2.7** Railway access opportunities for each surface site</caption><thead><tr><td>Site</td><td>Distance</td><td>Feasibility</td><td>Description</td></tr></thead><tbody><tr><td>PA</td><td>Less than 5 km</td><td>Unsure</td><td>Requires crossborder transport of materials</td></tr><tr><td>PB</td><td>Less than 5 km</td><td>Low</td><td>Requires crossborder transport of materials</td></tr><tr><td>PD</td><td>No opportunity within 10 km</td><td>Unfeasible</td><td></td></tr><tr><td>PF</td><td>Less than 1 km</td><td>Medium</td><td>Space and ISDI constraints</td></tr><tr><td>PG</td><td>Less than 2 km</td><td>Medium</td><td>Implementation constraints</td></tr><tr><td>PH</td><td>No opportunity within 10 km</td><td>Unfeasible</td><td></td></tr><tr><td>PJ</td><td>Less than 5 km</td><td>High</td><td></td></tr><tr><td>PL</td><td>Less than 10 km</td><td>High</td><td>Via existing, unused station at Collonges</td></tr></tbody></table>

It is important to keep in mind that each new railway access requires a space of about 400 m by 40 m, i.e., 1.6 ha of land (see Fig. 2.53).

The train line 890000 through Meyrin, Collonges, today provides the necessary free capacity. Line 902000 in Vulbens and line 897000 passing in Éteaux and in Groisy have only limited capacities.

The analysis (summarised in Table 2.7) revealed the following ‘in principle’ opportunities for railway access:

Based on the analysis, today, the most likely accesses to the railway system are the existing and unused train station in Collonges for site PL, new access north of Vulbens for site PJ and a new access west of Groisy for site PG. While the old train station of Collonges is 13 km from the surface site PL in Challex, a connection with a conveyor belt can be a suitable approach, avoiding truck traffic.

The feasibility in principle for the creation of access in La-Roche-sur-Foron on the site of an inert waste storage facility (I.S.D.I.) exists once that facility has been filled. However, the amounts of materials produced at site PF are limited compared to other sites, and the constraints due to the status of the facility (ICPE in France) and space limitations require a careful cost/benefit and administrative feasibility analysis in addition to the technical analysis.

The technical and administrative feasibility of railway access at Geneva Airport in Switzerland for site PA in France is subject to a specific analysis that will only be carried out in 2025. If it is technically feasible, an administrative challenge is to be addressed concerning the cross-border transport of materials in both directions: France to Switzerland for excavated materials and Switzerland to France for construction materials and equipment.

The creation of a new ITE requires about 10 years of planning, detailed development of the variants to be presented for authorisation, an economic demand study concerning use beyond the FCC construction phase, environmental impact assessment and the authorisation process. The implementation for use requires about 2 years.

If train access is to be used for the evacuation of materials and the supply of construction materials and equipment, a detailed design and common project together with the French and Swiss national railway network administration services would have to be started in a forward-looking way, starting in 2025.
### 2.7.5 Conveyor belt links

To reduce the need for temporary paths and truck traffic due to excavated materials and construction material-related transports between sites and autoroute accesses, example studies were performed to determine the feasibility of conveyor belt links [45, 49] by an expert company in the domain. Two sites have been selected for the case study: PJ (Vulbens and Dingy-en-Vuache, France) and PG (Charvonnex and Groisy, France). It is worth pointing out that the findings also apply to the other sites that were examined at a high level, but no technical designs have been developed. If a preparatory project phase is launched, detailed technical design variants for traces and conveyor technologies for a construction hypothesis have to be drawn up for all eight sites and submitted for authorisation in the frame of the project environmental authorisation process.

Conveyor belts would be operated with electricity with a capacity of 120 kW between the start and the end of the construction activities. Based on a speed of 2 to 2.5 m/sec and a width of 650 to at most 800 mm the following schedule has been established:

* 22 days per month.

* 226 days per year.

* Up to 8 hours per day.

* Operation between 08h00 in the morning and 18h00 in the evening.

* No operation during the night, weekends or holidays.

Various technologies for conveyor systems have been analysed, and their costs have been estimated for the two specific locations PG and PJ. Depending on the environmental conditions (topography, terrain, vegetation, urban constraints) different footprint and noise-limiting systems can be considered. In general, the choice is always determined by the goal to limit footprint and nuisances for the required capacities, limited by the available technical constraints. Public spaces would be leveraged whenever possible. New routes would be limited to 3 m width. The maintenance of new routes is limited: they are not permanent and the space used will be restored after use.

The feasibility of meeting the capacity requirements associated with a construction site that operates 2 tunnel boring machines (TBM) has been confirmed from a technical perspective and an environmental perspective. Noise levels are between 65 dB(A) directly at the conveyor and 47 dB(A) at a distance of 64 m with today's off-the-shelf technology. Example routes have been developed to confirm compatibility with the noise regulations in France for both study sites.

For site PJ, the conveyor can be created to the autoroute service station in Valleiry (distance 700 m) and/or to new railway access north of Vulbens (1565 m) outside any residential area. It has to cross the RD 1206 departmental road. Disturbances due to noise can be avoided in both cases.

For site PG, the conveyor can be created to the autoroute service area in Groisy (distance of about 800 m) and/or to new railway access at the north of the autoroute (925 m). The biggest challenge, although technically feasible (see Fig. 2.54) is the crossing of the A40 autoroute for a period of about 8 years. Residential areas are unlikely to be affected.

### 2.7.6 Electricity for the construction phase

For the supply of electricity during the construction phase, requests for hook-ups to local networks have to be made directly to the relevant national distributors (e.g., Enedis in France and SIG in Switzerland). According to information provided by company Herrenknecht, a leading TBM manufacturer, electricity requirements are around 3.7 MVA for a construction site using a single TBM and around 7.4 MVA for a construction site with two TBMs. The working hypothesis presented in Table 2.8 will be fine-tuned with the civil engineering companies during a subsequent design phase before the start of construction. This process will deliver the exact electrical power required during the construction phase. This will depend on the number and configuration of the TBMs around the ring and the specific machinery used. All that information will only be known with certainty shortly before the launch of the public works contracts. However, it has to be considered that planning, contracting, and implementing the local electricity connections for the construction phase will require several years and will need to be part of the overall environmental authorisation process.

### 2.7.7 Electricity for the operation phase

The FCC-ee scientific research programme is based on different collider operating modes (Z, WW, ZH, $t\bar{t}$ and an optional HH mode). Each mode uses a different equipment configuration. This equipment (acceleration systems by superconducting radiofrequency cavity, electrical energy conversion systems and cryogenic cooling systems) will be installed progressively during the maintenance and upgrade phases planned for these activities. One long shutdown (LS) is planned to install the radiofrequency systems for the $t\bar{t}$ and optional HH operation modes.
<figure><img src="image_112.png" /><figcaption>**Fig. 2.54** Example of a conveyor crossing a major road</figcaption></figure>

<table><caption>**Table 2.8** Working hypothesis for connection to local electricity networks during the construction phase</caption><thead><tr><td>Site</td><td>Location</td><td>Operator</td><td>Power</td></tr></thead><tbody><tr><td>PA</td><td>Ferney-Voltaire, France</td><td>Enedis</td><td>7.0 - 13.8 MVA (= 400 A at 20 kV)</td></tr><tr><td>PB</td><td>Presinge, France</td><td>SIG</td><td>3.0 - 7.0 MVA (= 200 A at 20 kV)</td></tr><tr><td>PD</td><td>Nangy, France</td><td>Enedis</td><td>7.0 - 13.8 MVA (= 400 A at 20 kV)</td></tr><tr><td>PF</td><td>Éteaux, France</td><td>Enedis</td><td>3.0 MVA (= 100 A at 20 kV)</td></tr><tr><td>PG</td><td>Charvonnex, France</td><td>Énergie et Services de Seyssel</td><td>13.8 MVA (= 400 A at 20 kV)</td></tr><tr><td>PH</td><td>Cercier, France</td><td>Enedis</td><td>3.0 MVA (= 100 A at 20 kV)</td></tr><tr><td>PJ</td><td>Vulbens, France</td><td>Enedis</td><td>13.8 MVA (= 400 A at 20 kV)</td></tr><tr><td>PL</td><td>Challex, France</td><td>Enedis</td><td>3.0 MVA (= 200 A at 20 kV)</td></tr></tbody></table>

Each configuration is characterised by different electrical power needs (see Table 2.9), which serve as the basis for average consumption estimates.

The collider operates on a yearly schedule, with a limited period of beamline operation for physics research. The programme also includes phases for equipment testing and start-up, machine performance optimisation and routine maintenance. Depending on the operating mode, electrical energy consumption varies from year to year.

At this stage of the study, it is only possible to provide approximate yearly consumption figures (see Fig. 2.55). The annual electricity consumption varies between 400 GWh/year for basic services that are in use also without beam operation and 1770 GWh/year for the tt operation phase. On average, the annual electricity consumption over the operation period is slightly above 1200 GWh/year. The capacities required to supply the particle collider with the required energy exist in France. However, a plan for a specific power purchasing agreement portfolio will have to be established, allowing ample preparation time before the energy is required to obtain favourable conditions and to contract a suitable energy mix with a low carbon footprint [50, 51].
<table><caption>**Table 2.9** Electrical power need estimations for the operation phase. Technical feasibility studies permitted reducing power requirements by almost 45% between 2020 (initial hypothesis) and 2024</caption><thead><tr><th>Mode</th><th>Beam energy</th><th>Operation</th><th>Initial capacity estimation</th><th>Current capacity estimation</th></tr></thead><tbody><tr><td>Z</td><td>45.5 GeV</td><td>4 years</td><td>65 MW - 240 MW</td><td>30 MW - 222 MW</td></tr><tr><td>WW</td><td>80 GeV</td><td>2 years</td><td>70 MW - 265 MW</td><td>33 MW - 247 MW</td></tr><tr><td>ZH</td><td>120 GeV</td><td>3 years</td><td>70 MW - 294 MW</td><td>34 MW - 273 MW</td></tr><tr><td>t<span style="text-decoration: overline;">t</span></td><td>175 GeV</td><td>5 years</td><td>80 MW - 350 MW</td><td>40 MW - 350 MW</td></tr><tr><td>HH</td><td>182.5 GeV</td><td>1 year</td><td>50 MW - 384 MW</td><td>41 MW - 357 MW</td></tr></tbody></table>

<figure><img src="image_113.png" /><figcaption>**Fig. 2.55** Annual electricity requirements of the collider and its technical infrastructure. The average annual consumption over the programme is indicated by a blue horizontal line</figcaption></figure>

Following the preliminary and exploratory studies, more detailed concepts to optimise the energy performance of the accelerator’s equipment and to improve operations based on information provided by electricity infrastructure operators and energy suppliers are required.

This approach will be based on the usual Avoid-Reduce-Compensate methodology.

* Avoid: the overriding goal is to limit consumption according to a cost-benefit analysis, which includes, for example: the research infrastructure layout of four experiments; limiting maximum annual power consumption, which will have impacts on luminosity and extending the duration of the research programme; and ensuring that systems do not consume energy when not in use.

* Reduce: this means to optimise system efficiency and reduce losses. This includes, for example, improving the efficiency of electrical energy conversion for radiofrequency, reducing losses in internal distribution and equipment, energy recovery and storage, smart consumption based on needs (e.g., for ventilation and cooling), and developing systems that can switch more easily and quickly between operating modes (standby or operating mode).

* Compensate: lastly, the goal of compensating is, on the one hand, to recover, store and supply renewable energy for society, and on the other hand, to develop synergies for the transition to energy from renewable sources, increase renewable energy capacity and cooperate internationally for the supply of renewable energy. Examples of compensation with direct economic benefits include the creation of energy communities and pooling for pre-financial-investment-decision support to build up renewable energy sources, use of waste heat in industrial processes (e.g., cheese production), for greenhouse operations, crop cultivation and the heating of public establishments such as hospitals, schools, and shopping centres.

All these measures will need to be improved over the fifteen years of the technical design and construction phases. They are an effective way of limiting electricity consumption and its impact.
With regard to the various phases of the collider maximum power requirements are only necessary during the tt operation phase, and during an optional phase at the end of the programme (hh) when all the radiofrequency equipment is installed. On average, during the scientific research phase, the FCC-ee would consume approximately 1.3 TWh per year. Over its entire lifetime, including shutdown periods and commissioning, its average electricity consumption would be around 1,3 TWh per year. To provide a context for the impact of this electrical energy consumption, it can be compared to the electricity consumption of a state-of-the-art data centre. For example, the Altoona (IA) data centre in the USA, owned by the Meta company, most known for the Facebook, Instagram and WhatsApp applications, has an annual consumption of 1.24 TWh [52]. The carbon footprint of this data centre is 532,158 tCO₂(eq) per year. This corresponds to about the carbon footprint of the entire FCC infrastructure construction. The consumption of all Meta company’s data centres is 15 TWh/year, i.e., a factor ten higher than the annual energy need of the FCC-ee. The total annual carbon footprint of all Meta’s data centres totals to about 5 million tons CO₂(eq).

The specific energy needs will only be known after the detailed technical development phase, so it will be possible to take advantage of technical advances and development to improve energy efficiency.

RTE, which was entrusted with the task of managing the electricity transmission grid in France<fnref n="1" /> through a public service contract dated 24 October 2005, which includes, among other things, the environmental integration of the grid (consultation, protection of landscapes and natural and urbanised environments) and safeguarding the public grid, is responsible for analysing the connection while taking into account technical choices; overseeing the hook-up process; and carrying out the necessary administrative procedures (connection agreement, grid access contract). RTE also carries out all works required to establish connections between surface site delivery points and the high capacity national electricity grid once the hook-up agreement has been signed.<fnref n="2" />

According to the results of the preliminary technical feasibility study carried out by RTE [53], which manages France’s electrical grid, the connection to the high-power electrical infrastructure calls for three supply points in France at this stage. A backup power supply point in Switzerland can be considered, but if required, its technical and administrative feasibility remains to be studied.

At this stage, the footprint of the reference scenario is crossed by various power lines, mainly 63 kV and 225 kV. Two 400 kV lines cross the PA31 footprint from west to east (see Fig. 2.56). The 400 kV lines pass close to the PL sites (Ain department in France) and the PF and PH sites (Haute-Savoie department, France). A major distribution station (Cornier) is located close to the PD and PF sites in France. Electricity needs are higher at the PL and PH sites, as these are designed to house the radiofrequency systems that accelerate particles in the collider.

Three supply points are currently envisaged to achieve a well-balanced electricity supply scenario: One in PL connecting to the nearby 400 kV line. One in PD connecting to the Cornier substation. One re-using the existing CERN grid connection in Bois Tollot (Ain, France). A detailed design study is required by RTE to determine the route and specificities of the new 400 kV connections. It may be advantageous to connect site PF instead of site PD to the 400 kV line, leveraging the proximity of the RTE distribution point in Cornier and thus avoiding the need to cross the Arve river. It is worth noting that the planning, authorisation, contracting and creation of grid power connections require substantial lead times. Ten years should be assumed for the entire process of one connection. In addition, for the entire particle collider project’s environmental authorisation process, the availability of environmental impact studies of the grid connections is required. Therefore, the detailed designs of the connections and their route variants based on the environmental constraints, technical feasibility and cost must be developed with high priority now, even if, ultimately, the connections are only required after the civil construction phase.

### 2.7.8 Raw water supply

The particle accelerators need raw water mainly to cool the magnets. Synchrotron radiation is the main source of heat in addition to numerous mechanical and electrical technical infrastructure components. All raw water can be taken from an existing raw water supply line provided by the local Swiss company Services Industriels de Genève (SIG) [54] that sources the water from Lake Geneva, as is the case with CERN today. No raw water will be consumed from drinking water reservoirs or subsurface water layers.

The technical solutions and equipment choices will not be known until shortly before the procurement of the technical infrastructures, mid-way through the subsurface construction phase, in order to take full advantage of

<footnote n="1">¹Decree no. 2005-1069 of 30 August 2005 approving the status of the company RTE EDF Transport: https://www.legifrance.gouv.fr/loda/id/JORFTEXT000000812363.</footnote>

<footnote n="2">²RTE, Instruction des demandes de raccordement, version 2, 17 Octobre 2019, https://www.services-rte.com/files/live/sites/services-rte/files/documentsLibrary/DTR%201.4.1%20Procedure%20Racc%20Conso%20L342-2%20v19%2010%2017_fr.</footnote>
**Fig. 2.56** Existing or planned electricity grids in France and Switzerland within the FCC perimeter. Sources: Public layer CAD element CONDUITE from SITG 2023 for Switzerland (https://sitg.ge.ch/donnees/cad-element-conduite), available for consultation and extraction for free use; for France, Open Data Réseaux Énergies (ODRE, https://opendata.reseaux-energies.fr)

<figure><img src="image_114.png" /><figcaption>**Table 2.10** Summary of the FCC raw water needs</figcaption></figure>

<table><caption>**Table 2.11** Summary of the annual raw water needs</caption><thead><tr><td>Mode</td><td>Annual raw water requirement</td><td>Years</td></tr></thead><tbody><tr><td>Z</td><td>1,604,861 m³</td><td>4</td></tr><tr><td>WW</td><td>1,928,943 m³</td><td>2</td></tr><tr><td>HZ</td><td>2,165,458 m³</td><td>3</td></tr><tr><td>L.S.</td><td>163,817 m³</td><td>1</td></tr><tr><td>t̅t̅</td><td>3,077,591 m³</td><td>5</td></tr></tbody></table>

<table><thead><tr><td>Item</td><td>Raw water need</td><td>Description</td></tr></thead><tbody><tr><td>SPS</td><td>944 m³</td><td>BA2, BA4, BA5, BE2</td></tr><tr><td>LHC</td><td>795,070 m³</td><td>LHC complex, LHC2, LHC3.2, LHC 3.3, LHC4, LHC5, LHC6, LHC7, LHC8</td></tr><tr><td>Meyrin, Prévessin</td><td>2,437,988 m³</td><td>Meyrin and Prévessin sites main supply, SPS BA1 and BA6, LHC1 safe supply, clubs, Globe</td></tr></tbody></table>

technical advances, including those in cooling system efficiency. Estimates of the maximum water requirements, based on consumption by CERN's existing accelerator cooling systems and on the current technical concept developments, have been established (see Table 2.10). These values are the result of a gradual development of a concept that permitted reducing the raw water requirements from a maximum initial amount of 5,000,000 m³ per year for tt operation to about 3,000,000 m³ per year. The current reference water capacity needs to assume the use of closed-circuit water cooling systems with evaporation towers. The raw water consumption stems from the need to make up for the evaporated water in the secondary circuits of the cooling towers at each surface site. For comparison, the raw water consumption at CERN in 2022 is summarised in Table 2.11.

Water for cooling purposes at CERN is today, mainly from Lake Geneva via the Services Industriels de Genève (SIG). It undergoes pre-treatment, including filtration, and is delivered through the existing supply network. The raw water supply scheme for the FCC builds on CERN's existing infrastructure, with a confirmed available capacity of 604 m³/h—equivalent to more than 5 million m³ per year—sufficient to meet the FCC's needs. This was established through exchanges with SIG in 2022 and reaffirmed in August 2023, when SIG confirmed the technical feasibility of the supply within the current contractual framework. Two options were identified: (i) constructing a
<table><caption>**Table 2.12** Water-saving potentials with the introduction of waste heat supply scenarios and use of treated waste water</caption><thead><tr><th>Mode</th><th>Conservative waste heat reuse</th><th>Realistic waste heat reuse</th><th>Treated waste water use</th></tr></thead><tbody><tr><td>Z</td><td>356,800 m³/year</td><td>476,800 m³/year</td><td>685,000-1,000,000 m³/year</td></tr><tr><td>WW</td><td>382,400 m³/year</td><td>523,200 m³/year</td><td>685,000-1,000,000 m³/year</td></tr><tr><td>HZ</td><td>409,600 m³/year</td><td>571,200 m³/year</td><td>685,000-1,000,000 m³/year</td></tr><tr><td>L.S.</td><td>96,000 m³/year</td><td>96,000 m³/year</td><td>685,000-1,000,000 m³/year</td></tr><tr><td>t̄</td><td>473,600 m³/year</td><td>678,400 m³/year</td><td>685,000-1,000,000 m³/year</td></tr></tbody></table>

new 200-metre connection with a 500 mm nominal diameter between the Tuileries-La Berne pipe and LHC Point 8 in Ferney-Voltaire (France), or (ii) upgrading two existing internal CERN pipelines.

To make the distribution of water along the entire length of the accelerator technically easier and economically more advantageous, two additional water supply points can be considered in France from the Arve and/or the Rhône rivers. To this end, a specific territorial study would be needed, which would have to integrate the quantitative management plans available for water resources (PGRE). Such water intakes would require the creation of water filtration and treatment plants.

In an effort to reduce further the water capacity needs, initial studies have been carried out to identify promising levers (see Table 2.12). First, the introduction of waste heat recovery and supply from the onset permits reducing the water intake needs significantly since less water needs to be evaporated if the heat is supplied to consumers. The conservative scenario indicates the water-saving potential without adaptation of the classical operation schedule. Some commercial consumers need heat throughout the year. It has to be pointed out that the realistic waste heat reuse indicated requires adaptation of the particle collider operation to the season during which heat is required. Even higher saving potentials than the ones indicated are possible, depending on the adaptation to seasonal territorial heat needs. Second, the adaptive operation of the cooling system and the evaporation towers using advanced supervisory control and potentially artificial intelligence would permit the reduction of consumption to the strict minimum required, compatible with the actual cooling needs. Third, the creation of an additional water intake next to site PD (Nangy, France) would ease the requirements on the overall system. Given that a dedicated water filtering and treatment facility would be required, an initial study aims to verify the use of waste water from the nearby Bellecombe/Scientrier waste water treatment plant (Syndicat des Eaux de Rocailles et Bellecombe). This installation discharges treated water at an average rate of about 550 m³/h into the Arve River. While in principle technically feasible and economically viable (the annual operation cost per m³ of water of a treatment plant required for the collider corresponds to the cost of a m³ of raw water purchased from a water supplier), studies are currently ongoing to estimate the effort to reduce the residual dissolved calcium carbonate (CaCO₃) and germs in the water to render it compatible with use in the industrial cooling system.

At this stage, from quantitative and commercial points of view, the reference scenario for water consumption is technically, financially, and territorially feasible, since water extraction and consumption represent quantities lower than CERN’s actual past consumption. The availability of a supply representing twice the total maximum requirement was confirmed in 2023.

### 2.7.9 Waste water management

Connections to the local sewage infrastructure are required at all sites for the management of drainage water in the subsurface structures, rainwater collected and treated water that is purged from the raw-water based cooling systems. The collected rainwater can also be reused on the sites for different project-related purposes and to maintain green spaces. Where possible, all collected water will be filtered and treated on-site before it is released into the environment. From a territorial perspective, this approach is preferred over centralized wastewater management since it is beneficial for sustaining existing creeks, wetlands, and biodiversity in rewilding projects developed in association with the surface sites. Only where the water does not qualify for free release would it be directed into the sewage system (e.g., due to a higher percentage of non-soluble residuals or during periods of heavy rain).

Alternatively, a central waste water management concept based on returning all waste water to a CERN site (e.g., LHC P8 and PA in Ferney-Voltaire) can be considered. For the management of the cooling water, a ‘zero liquid discharge’ (ZLD) approach can also be considered. ZLD requires the collection of solids from each surface site at regular intervals. A definitive choice of technology has yet to be taken and calls for a comprehensive, wider Cost-Benefit Analysis over the entire project period, covering investments and operational factors. Water treatment technology is advancing rapidly due to environmental and sustainability constraints. It is, therefore,
<figure><img src="image_115.png" /><figcaption>**Fig. 2.57** Fire-fighting and emergency services in the perimeter of the reference scenario</figcaption></figure>

wise to consult experienced companies and consider the various options in the frame of the environmental impact assessment before finalising the technology choice.

Waste water from human activities (toilets, sinks, offices, visitor centres, cafés and restaurants) will be directly evacuated via connections to the public waste water system. The design for the waste water network connections is to be developed in cooperation with local public administration services in a subsequent preparatory phase, involving companies’ experts in the domain. At this stage, the following configuration is envisaged for the local connections to the waste water networks:

* Site PA: Connection to the waste water network via the LHC Pt8 in France.

* Site PB: Connection to the local waste water network in Presinge, Switzerland.

* Site PD: Direct connection to the waste water treatment station ('STEP') SRB in Scientrier, France.

* Site PF: Connection to the local waste water network in Éteaux, France.

* Site PG: Connection to the local waste water network via the Groisy autoroute station. Alternatively, connection to the network in Charvonnex at the D1203 in France.

* Site PH: Creation of a new local waste water network to the nearest connection point at 250 to 300 m distance in France. The waste water treatment station (STEP) in the vicinity of the site is not capable of accepting all of the waste water from the site in the most demanding cases. Therefore, either the STEP needs to be reinforced for the collider project or the excess water needs to be re-directed via a waste water network in the tunnel to sites PG and PJ. Developing the strategy is part of a subsequent design phase.

* Site PJ: Connection to the local waste water network 500 m away in between Vulbens and Valleiry in France.

* Site PL: Connection to the local waste water network in Challex, France.
<table><caption>**Table 2.13** Selection of emergency services in the vicinity of surface sites</caption><thead><tr><th>Site</th><th>Distance</th><th>Location</th><th>Capacity</th><th>Service</th></tr></thead><tbody><tr><td>PA</td><td>1 km</td><td>Prévessin, France</td><td>66 persons</td><td>Departmental fire fighting station CIS Est-Gessien</td></tr><tr><td>PB</td><td>5.8 km</td><td>Chêne-Bougeries, Switzerland</td><td>30 persons</td><td>Cantonal fire fighting station</td></tr><tr><td>PD</td><td>0.3 km</td><td>Contamine-sur-Arve, France</td><td>n/a</td><td>Hospital, Centre Hospitalier Alpes-Léman</td></tr><tr><td>PD</td><td>9 km</td><td>Arenthon, France</td><td>11 persons</td><td>Fire fighting and first aid station</td></tr><tr><td>PD</td><td>12.1 km</td><td>Éteaux, France</td><td>68 persons</td><td>Regional fire fighting station</td></tr><tr><td>PF</td><td>3.2 km</td><td>Éteaux, France</td><td>68 persons</td><td>Regional fire fighting station</td></tr><tr><td>PG</td><td>2.3 km</td><td>Groisy, France</td><td>50 persons</td><td>Regional fire fighting station, emergency service</td></tr><tr><td>PH</td><td>10 km</td><td>Frangy, France</td><td>37 persons</td><td>Local fire fighting station</td></tr><tr><td>PH</td><td>14 km</td><td>Epagny, France</td><td>135 persons</td><td>Regional fire fighting station, emergency service</td></tr><tr><td>PH</td><td>1.3 km</td><td>Valleiry, France</td><td>26 persons</td><td>Regional fire fighting station, emergency service</td></tr><tr><td>PL</td><td>7.4 km</td><td>Thoiry, France</td><td>70 persons</td><td>Regional fire fighting station, emergency service</td></tr></tbody></table>

## 2.7.10 Emergency services

The analysis of the different implementation scenarios revealed that the continuation of the existing approach of serving surface sites of CERN's particle accelerators cannot be extended to the perimeter of the future particle collider without significant challenges. Although the surface sites are in the immediate vicinity of major road infrastructures, the distances and the traffic situation would call for intervention times, which would be too long if all sites had to be serviced from the CERN Meyrin site in Switzerland. Locating dedicated emergency service personnel on each of the surface sites is prohibitive from a financial point of view in terms of human resources and equipment, and would lead to challenges in the operational management of the facility. Subsequent analysis of a single dedicated support pole provides only limited improvements with respect to safety and emergency services. Therefore, a detailed geographical analysis was carried out to identify alternative approaches (see Fig. 2.57).

Apart from site PH, the surface sites of the reference implementation scenario are close to firefighting and emergency service stations (see Table 2.13). Some of them have recently been constructed. Therefore, the project scenario can consider making use of support for emergency and firefighting personnel at those stations, accompanied by regular common training and an emergency guidance centre at CERN. The strengthened collaboration of CERN with those services, the contribution of equipment, materials and training also leads to socio-economic benefits. These have been analysed and are part of the wider socio-economic impact assessment.

The build up of these resources and the transition to a new operation scheme require several years of preparation. The ten years of construction phase provide an adequate window of opportunity to launch this process, which requires agreements with the emergency and fire-fighting services.

## 2.7.11 Territorial aspects for the management of excavated materials

The management of excavated materials represents a socio-economic and project management challenge, beyond civil engineering considerations. The availability of suitable deposits for inert waste is decreasing, and corresponding deposit costs are increasing, with estimated final deposit costs between 385 million and 825 million euros depending on re-use potential [1].

The excavated volume of 6 million m³ consists mainly of molasse (95%) and moraines (3%). While limestone fractions are re-used within the project, the management strategy for the remainder focuses on:

1. Alleviating pressure on deposit sites,

2. Reducing transport requirements,

3. Optimising project costs,

4. Generating socio-economic benefits by pioneering innovative re-use solutions.

The molasse basin spans across Switzerland, Germany, Austria, and Hungary, making advances in re-use methods broadly relevant. Within the FCC Innovation Study (FCCIS), the international challenge *Mining the Future* [55] was launched to identify technically and economically viable re-use pathways on the 2030 timescale.

Depending on national regulations in France and Switzerland, 15–30% of the molasse may be classified as naturally polluted (e.g., hydrocarbons, nickel, zinc, chromium) and thus require controlled disposal. Clean fractions are primarily targeted for quarry refilling and land rehabilitation.