Is heat a contaminant?

Due to the great potential of geothermal energy systems to lower current greenhouse gas emissions
such systems and the thermal use of shallow groundwater are continuously increasing worldwide. In
Europe, for example, about 4 million tons of CO2 are annually saved by ground source heat pump
(GSHP) systems (Bayer et al. 2012). Hence, the increasing installations of shallow geothermal systems
put increasingly pressure on groundwater systems. Until now, appropriate criteria to control
geothermal groundwater use in national and international legislations are often still at a preliminary
state or even not existing. In 2000, for example, the European Union (EU) Water Framework
Directive (WFD) defined the release of heat into the groundwater as pollution. In contrast, the
cooling of groundwater for heating purposes, is not especially mentioned. Some of the national
legislations have far more reaching definitions. For example, in Germany, detrimental changes in
physical, chemical and biological characteristics have to be avoided. In Switzerland, the biocenosis of
groundwater should be in natural state. However, exact definitions of ‘detrimental changes’ and
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‘natural state’ is still absent. Hence, the current study provides an overview of the international legal
status of the use of shallow geothermal energy (Hähnlein et al. 2010), presents recent studies on
groundwater ecosystems, shows groundwater temperatures in Europe and presents a sustainable
policy for the thermal use of shallow geothermal energy (Hähnlein et al. 2013). In addition to shallow
geothermal systems, other anthropogenic heat sources could be identified by studying the spatially
distributed groundwater temperatures. Finally, the above question is answered and
recommendations are provided in context of the current discussions of all shareholders involved in
the use of shallow groundwater systems for drinking water and thermal applications.