Effect of ATES systems on the spreading of contaminants

Insight into spreading mechanisms

Using data from Vitens and the municipality of Utrecht, a model has been built to show how a point source has spread over most of the area in a period of ten years. One important spreading mechanism is recirculation: the extraction of the contaminants from an extraction source and their subsequent infiltration into another source. Contaminants can also ‘jump’ from one ATES system to another. ATES systems are of course situated outside of each other’s thermal spheres of influence, but since their hydrological spheres of influence are one and a half times bigger that their thermal spheres of influence, the systems can indeed exert an influence on each other . Furthermore, a short-circuit flow can occur between different sources, which accelerates the jumping. Through the combined impact of recirculation and the hydrological sphere of influence, a contaminant can jump from one aquifer thermal energy source to the source of another ATES system hundreds of meters away in a year and a half.

Ten times faster spreading

The presence of ATES systems in Utrecht’s city centre has, according to the model, accelerated the spreading by a factor of ten. This faster spreading caused by the city’s ATES systems only occurs in the area within which the systems influence each other hydrologically. Therefore, practically speaking, it has no effect on the quality of Vitens’s drinking water abstraction operations, since these are located far outside of Utrecht.

Area-specific approach to groundwater contamination

The insights gained can provide support and direction to the area-specific management of contaminated groundwater, and for the integration of ATES systems in spatial planning. Thus one could optimise the (further) spatial integration of ATES systems in line with the area-specific circumstances. The mixing and dilution of contaminants due to ATES systems can, for example, be influenced on the basis of weighted risks.