The deep relationship between energy and water
The impact of ATES on groundwater quality
Aquifer thermal energy storage (ATES) makes use of the underground to store thermal energy. ATES is being increasingly used in non-residential and residential construction as well as in the greenhouse horticultural sector. Sometimes ATES systems are installed near areas where groundwater is abstracted for the production of drinking water. This raises the question about the possible effects of ATES systems on water quality. KWR, together with drinking water companies, researches this question within the framework of the water sector’s joint research programme (BTO). “The research has quantified the sensitivities, so that we can deal with the implementation of ATES systems,” says Eric van Griensven, Head of Sector, Corporate Market, at Brabant Water.
A key part of the research involves the monitoring of ATES systems at RIVM in Bilthoven and at the High Tech Campus Eindhoven. The measurements of these systems reveal the effects of ATES operation in the summers of 2010 and 2011. Van Griensven remembers his enthusiastic response to KWR’s research proposal. “Initially, we decided to conduct joint research with the provinces, the national government, companies and municipalities in the so-called ‘More with thermal energy’ project. But we missed the specialist water knowledge and critical capabilities of an entity such as KWR. That’s why the water companies and KWR have started a research project focusing on the interaction between drinking water and ATES.”
The monitoring results show that the quality of groundwater in the vicinity of ATES systems is influenced primarily by the mixing of deep and shallow groundwater of different quality. Shallow groundwater is frequently affected by human activities. The introduction of ATES systems accelerates the passage of this water to the deeper levels, where all the water was previously clean – that is, was unaffected by human activity. Moreover, the temperature of the ATES systems has an impact on the ground processes.
Laboratory experiments have been carried out to get a better understanding of the effects of temperature changes. The tests show that a temperature rise of up to 25ºC – the permissible range for approval of today’s ATES systems – various ground processes are affected. Substances that, at lower temperatures, are normally attached to the sediment become (perhaps temporarily) detached. Also, there is an acceleration in the mineralization of organic material. At 60ºC – thus above the “normal” ATES range – the microbiological population in the water changes, more organic material is flushed out, and other trace elements are detected in the water.
Delineating sensitivities and opportunities
Is this a setback for water companies that want to work with ATES systems or have to deal with them in their vicinity? “Not at all,” says Van Griensven. “Because our objective was to delineate the sensitivities, precisely to be able to work with them. Now we know exactly where the sensitivities are, how we can deal with them and where the opportunities lie. In the meantime our subsidiary, Hydreco, has 25 ATES installations operating at locations like town halls, businesses and housing complexes. And we anticipate more growth, because this is a sustainable technology and the subsurface in large parts of the Netherlands is well suited for it. We are also actively working on recovering heat from water mains, which is another sustainable technology with a future – in fact, it is one of the themes in the water sector’s new research programme.”
© 2017 KWR Watercycle Research Institute