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Drilling campaign explores subsurface for the Einstein Telescope

With drillings at eleven locations in the Belgian and Dutch search areas for the Einstein Telescope, and a number of so-called geophysical-seismic studies, the project office Einstein Telescope EMR aims to gain a better geological understanding of the subsoil this year.

Before the three vertices for the underground telescope are determined, potentially suitable sites can be mapped out based on information from drillings about the composition of the suburface. All eleven drilling locations are in the rural areas of the respective municipalities. There are four drillings in the Flemish Voeren, two in the Walloon municipalities of Plombières, two in the Dutch Limburg Vijlen, and further drillings in the Walloon Welkenraedt, Aubel, and in the Dutch Limburg Epen. The first drilling will start at the beginning of March in Hombourg (Plombières). Shortly thereafter, simultaneous drilling at the other locations will follow. The aim is that the last drilling will be completed in August.

Example of a drilling setup

Expertise

From the European tender for these drillings, the Swiss company Stump-BTE AG has emerged as the best from the tender. Stump, part of the Marti-Gruppe, is a company with extensive expertise in the field of special civil engineering and complex underground drillings. Excluding a few days for setting up and dismantling the drilling site, each drilling effectively lasts about 6 to 7 weeks. Soil samples are taken from the ground to a depth of an average of 275 meters. These so-called drill cores have a diameter of about 10 centimeters. The analysis of these cores should then reveal the composition and quality of the rock layers. The expertise of RWTH Aachen is used for this analysis.

Environmentally friendly aggregates

During the drilling campaign, four drilling machines are deployed simultaneously: two electric drill rigs and two diesel drill rigs. The latter two are mounted on a truck. At 6 drilling locations, both an electric drill setup and a diesel drill setup are used. At 3 locations only with a diesel setup and at the remaining two locations only with the electric drill. Electric drilling is most suitable for a location where a hard subsoil is encountered relatively quickly below the surface. The electric drill is powered by a very modern type of generator that has been available since last year and emits much less than regular generators.

The diesel drill setup is mounted on a truck. In order to be able to drill in more places at the same time, two of these drill rigs will soon be available, which are easy to move around in the search area. In all cases, the oxide gas released at this drilling rig is ‘captured’ and largely neutralized. For this purpose, the project office has hired a specialized company that has so-called NoNOx equipment that is coupled to this drilling rig. In fact, harmful oxide released during drilling is converted into nitrogen and water vapor, which are not harmful to nature.

Although this capturing (the so-called ‘mitigation’) is only necessary in the Vijlenerbos to prevent nitrogen from depositing directly on nature due to the Natura 2000 status of the area, the project office chooses to neutralize the released nitrogen at all drillings with the diesel setup. Project leader Guid Bartholomée: “We are not obliged to do so, except in the Vijlenerbos, but we choose to also capture nitrogen here. It costs a lot of money, but our vision is that we want to take optimum care of the landscape, nature, and environment. And as a cross-border project, that principle must apply to all countries.”

Permission

Discussions have taken place with private landowners, land users, the municipalities involved, and other authorities regarding the necessary permissions and exemptions. For example, an exemption for the silence area is required for the drilling location in the Dal van Vijlen. For the three locations in Dutch Limburg, a permit has been applied for because drilling is deeper than is currently possible according to the environmental regulation. This will be addressed during information meetings at the end of February.

Agreements have been made with, for example, Staatsbosbeheer and the Waterschap Limburg about the use of the locations they own. Agreements have also been made with the private owners of a drilling location regarding the duration, the manner, and the compensation for the drillings. Furthermore, discussions have taken place and information has been exchanged with organizations such as Natuurmonumenten, Limburgse Milieufederatie, local IVN branches, and Natuurpunt Vlaanderen.

Prior to the selection of the drilling locations, ecological scans and analyses of the locations and the environment were made. Parts of the preparations also include, among other things, an environmental scan, soil research, a sound scan, and a nature assessment.

Locations and dates of drilling campaign

(subject to change)

PlaceMunicipalityLocationPeriod
Hombourg (WA)PlombièresBounder4 March-11 April
Sint-Pieters-Voeren (FL)VoerenBrabant/Rullen27 March-6 May
Teuven (FL)VoerenKloosterhofstraat4 April-7 June
Gemmenich (WA)PlombièresRue de Terstraeten9 April-17 May
Obsinnich (FL)VoerenObsinnich near railway17 April-24 June
Aubel (south) (WA)AubelRte de Val Dieu / Bushaye25 April-8 August
Henri-Chapelle (WA)WelkenraedtNear Lekker road2 May-7 June
Epen (NL)Gulpen-WittemSchutterij grounds3 May-1 August
Dal van Vijlen (NL)VaalsGroeneweg13 May-19 July
Vijlenerbos (NL)VaalsCar park25 May-19 July
Sint-Pieters-Voeren (FL) (naboring)VoerenBrabant17 July-7 August
Note: WA = Wallonia / FL=Flanders / NL=Dutch Limburg

Planning

Project leader Guid Bartholomée indicates that work is being carried out with a tight schedule: “It is ambitious and based on our premise that drilling should not take longer than necessary. Not only to keep a grip on the costs but also to keep the environmental impact as brief as possible. Therefore, the drilling company also operates on Saturdays. Nonetheless, things can sometimes move faster, but once we are underway, we may need to adjust the schedule at a location because delays occur. This cannot be planned with 100 percent certainty in advance.”

Geophysical-seismic measurements

In addition to the drilling, seismic or ERT measurements are also planned. Where borehole measurements provide an accurate picture of the ground at the drilling site, the geophysical (ERT) measurements supplement this in the area between the drilling sites. The data from the eleven drillings form the calibration points for the geophysical measurements.
ERT stands for ‘Electric Resistivity Tomography’. This is an electrical resistance measurement that further maps the structure of the ground. A cable is manually laid along the entire length of a track. Then, every 50 meters, an electrode is attached to this cable by the researchers. These electrodes are comparable in size and shape to a tent peg. The researchers create a weak electric field in the ground for a short time. An electric resistance in the ground is then measured with a field computer. This provides an additional picture of the structure of the ground.

Example of an electric vehicle for seismic surveys


An additional method for seismic research is mobile measurement with a vehicle. Based on tests, the project office has chosen to do this with an electric vehicle, which ultimately delivers better and more reliable results. Additional advantages are that the electric vehicle is quiet and emits no exhaust gases.
Both methods of geophysical-seismic research are silent and are carried out during daytime normal working hours.

Communication and viewing opportunities

In the last two weeks of February, a total of seven information meetings for residents are planned in Plombières, Aubel, Gemmenich, Voeren, Vaals, and Epen, where the drilling campaign will also be further explained. Furthermore, it is intended to organize ‘viewing moments’ for each drilling location where interested parties can receive explanations about the work on-site.
As soon as information about dates/locations is available, it will be published in door-to-door newspapers appearing in the relevant municipalities and through municipal communication channels.

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