The energy transition – from fossil fuels (oil, natural gas, coal) to sustainable energy (solar, wind, geothermal) – is being tackled at various different levels, both public and private. Geothermal energy from the shallow subsurface (< 500 m) plays an important role in this.

'Open' or 'closed' systems are increasingly being installed to provide (private) heating. This blog focuses on “closed” geothermal systems. In a recent Signal Report, the Dutch Human Environment and Transport Inspectorate (ILT) points out that drilling companies take insufficient account of the applicable requirements when installing closed geothermal energy systems, resulting in risks to the environment. The ILT calls for companies, environmental agencies, and municipalities to take an active role in preventing such risks.

Geothermal energy offers an alternative to Dutch households’ use of gas. It can be used, for example, to heat and cool buildings and homes in a sustainable manner. With effect from 1 July 2013, the Geothermal Energy Systems (Amendment) Decree (Bulletin of Acts, Orders, and Decrees (Stb. 2013, 112) amended a number of general administrative orders (AMBs) so as to facilitate the installation and operation of geothermal energy systems. The decree distinguishes between open and closed systems:

  • In open geothermal energy systems, extraction and infiltration wells are drilled via which groundwater is pumped up. After being used for heating or cooling, it is then returned to the subsurface. Pursuant to the Water Act (Waterwet), utilising an open geothermal energy system always requires an extraction permit issued by the relevant province;
  • closed systems do not involve extraction of groundwater, but a liquid (usually with added anti-freeze) is routed through the subsoil in closed pipes in order to extract heat or cold from it. Unlike an open geothermal energy, a closed geothermal energy system does not require an extraction permit. There is however a reporting obligation pursuant to the Discharge of Waste Water Outside Establishments Decree [Besluit lozen buiten inrichtingen] or the Activities (Environmental Management) Decree [Activiteitenbesluit milieubeheer].

Both systems are subject to different statutory requirements with regard to their construction and operation.

Since the beginning of the century, use of this energy source has increased considerably, partly in view of the domestic and international agreements and declarations of intent on phasing out the use of natural gas[1]. There is a target for the geothermal energy sector of about 8000 open and 150,000 closed systems by the year 2023[2]. This development is making increasing demands on the limited underground space from which Dutch drinking water is produced. For responsible and sustainable use of geothermal energy and to protect the drinking water supply from contamination, companies must take account of a number of requirements when installing such systems, for example:

  • The systems must not be located too close to one another, otherwise the energy yield will be lower
  • The boreholes must be properly sealed so that no contamination can occur
  • Drilling companies must not utilise environmentally harmful agents/materials during construction of such systems

Findings of ILT’s Signal Report
Provinces and municipalities (on behalf of the municipality often environmental agencies) are able to carry out preventive supervision by means of the aforementioned permit and reporting obligations. If supervision is performed appropriately, the risk of mixing different groundwater types and the spread of existing contamination can be controlled. The ILT also supervises construction of geothermal energy systems itself on the basis of reports of contraventions submitted to it by environmental agencies, municipalities and provinces.

In March 2021, the ILT published a 'Signal Report' (Signaalrapportage) in which it identified frequently occurring risks in construction of closed geothermal energy systems. The ILT finds that in the period from 2016 to 2020 compliance with the requirements for closed geothermal systems was poor. It finds that drilling companies take insufficient account of the requirements when constructing such systems. This results in unnecessary environmental risks and possible contamination of drinking water. Deviations from standards were found during some 75% of ILT inspections, half of them meaning that a risk to the soil could arise.

Drilling companies drill down an average of between 80 and 200 metres, thereby affecting soil layers that by their nature protect drinking water. The Soil Quality Decree [Besluit bodemkwaliteit] provides that construction of geothermal energy systems must not cause additional risks to the soil and groundwater. The ILT’s Signal Report describes four possible risks due to construction of closed geothermal energy systems and gives recommendations as to how these can be prevented:

a. Errors when sealing boreholes: When constructing closed systems, the clay layers that protect the deep groundwater must be restored properly after they have been drilled through. Failure to do so may entail a risk to groundwater quality. The current protocols do not stipulate sufficient requirements for the technical features of the sealant to be used, resulting in the use of substances to seal boreholes that are harmful to the environment. Environmental risks can be prevented by setting clear requirements as to which sealants are permitted.

b. Use of environmentally hazardous substances during operation: Harmful lubricants are sometimes used to prevent drilling rods – which are connected up by means of a screw connection – from jamming. The ILT advocates banning such environmentally harmful agents/materials and proposes that alternative environmentally friendly agents be used.

Attention points for closed systems
In its Signal Report, the ILT argues for companies to utilise correct working methods and for more stringent supervision of construction of closed geothermal energy systems by environmental agencies and municipalities. Mandatory utilisation of correct techniques and agents/materials can prevent drinking water supplies from being contaminated.

The ILT submitted the Signal Report to the State Secretary for Infrastructure and Water Management, Stientje van Veldhoven, on 24 March 2021. It was then submitted to the Dutch House of Representatives on 10 May 2021[3].

This blog was written with the help of our intern Selin Gönül.

[1] See for example the Climate Agreement and the Energy Agreement.

[2] Bloemendal, M., Kleinlugtenbelt, R., Valstar, J., van Asten , M., & Mars, J. F. (2020). Optimale ondergrondse inpassing van open bodemenergiesystemen. H2O: tijdschrift voor watervoorziening en waterbeheer, p. 9. See:

[3] Parliamentary Documents II, Government letter 'Signaalrapportage: Risico’s bij de aanleg van gesloten bodemenergiesystemen' [Signal Report: Risks in Construction of Geothermal energy Systems], 10 May 2021.

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