MUSE pilot area activities – RESULTS – #1 Ljubljana

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Eventful hydrogeological investigations

Mitja Janza (GeoZS), 25 March 2021

Goals and results of the field measurements

Aim of the hydrogeological investigations was to estimate the geothermal potential of the open-loop system that is planned for the heating of a primary school in Ljubljana. Retrofitting the school is part of the public-private partnership energy retrofit project of the City of Ljubljana. The planned capacity of the heat pump is 200 kW and will be primary source of heating (planned demand 340 MWh for heating and 95 MWh for domestic hot water). Required water flow rate for the heat pump is 15 l/s.

Research focused on the characterization of the aquifer and design of a well that will assure required pumping rate. To avoid risks of clogging and corrosion, the chemical composition of groundwater was analysed. The borehole logging (Fig. 1) showed favourable hydrogeological conditions which were later confirmed with pumping tests (Fig. 2). The temperature of the groundwater is around 13 oC and has very low Fe2+ and Mn content, therefore it is a suitable heat source for the planned heat pump.

The measurements conducted in the test site provided new data on the subsurface conditions, particularly on aquifer and groundwater properties, which will help in planning of new geothermal installations in the Ljubljana pilot area.

Fig. 1: Borehole cores (course and fine-grained sediments).
Fig. 2: Measurements of groundwater level, temperature and discharge during the step-drawdown pumping test.

Unexpected incident during drilling

During the drilling and cleaning of the well, muddy water appeared in the test site (left in Fig. 3) and was drained to the sewer system with the outflow to the open channel (right in Fig. 3). We have not been aware of this fact, until police came and stopped the drilling. Explanations and assurance that no harmful impacts on environment will be caused had to be given before we could continue the work. This case shows that hydrogeological explorations and the process of installing a geothermal system in urban areas have a big need for communication with the stakeholders and all potential impacts have to be considered, even harmless ones, because they might look suspicious to uniformed passers-by.

Fig. 3: Left – Water from the well at the test site. Right – Outflow of the muddy water from the test site into the open channel.

Find out more about the pilot area Ljubljana in our previous blog: Pilot area activities – #8 Hydrogeological and geothermal surveys in Ljubljana, Slovenia

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