The available time series (four to eight years) of the groundwater chemistry in the ATES wells are investigated for seven ATES systems and compared with the time series of the ambient values in the used aquifer. For this study, an inventory was made of all monitoring wells in the used aquifer in a 10 km radius around each of the seven ATES systems.
The time series of the monitoring data for the different solutes in all ATES wells were analyzed using linear regression analysis to determine if the data series show significant BYL719 order trends. For that purpose, statistical hypothesis testing was conducted on the slope of the regression line. The null hypothesis of zero slope was evaluated at 5% significance level. The different studied aquifers (Fig. 2) are described below in chronological order. The Brussels Formation is an early Middle Eocene shallow marine sand deposit in central Belgium. The Brussels Sands occur Vemurafenib cost in a 40 km wide SSW-NNE oriented zone in
central Belgium. These sands fill an approximately 120 km long and 40 km wide embayment which ended in the north of the Province of Antwerp in the North Sea. The base of the sands is characterized by two central major SSW-NNE trending troughs and several minor troughs with the same orientation. The Brussels Sands consist of unconsolidated quartz sands with variable percentages of feldspar, flint, glauconite, lime and heavy minerals ( Gulinck and Hacquaert, Chlormezanone 1954). The groundwater in the aquifer is of CaHCO3 type
because of the presence of lime in the Brussels Sands and the layers above. At several locations the most shallow part of the aquifer has increased concentrations of nitrate, chloride and sulfate correlated with antropogenic activity ( Peeters, 2014). The Berchem Formation is an early Miocene shallow marine sand deposit in the north of Belgium. The Berchem Formation consists of green to black, fine to medium grained, often slightly clayey, very glauconiferous sand. The sand is rich in shells which appear dispersed in the sediment or concentrated in subhorizontal layers. At some locations however, the sand can be decalcified. The Diest Formation is deposited in the late Miocene during a large transgression. In erosive trenches, the deposit can be more than 100 m thick. The Diest Formation consists of gray-green to brownish glauconiferous coarse sands wherein sandstone layers often occur. The unit contains almost no fossils, except very local. The Kattendijk Formation is deposited in the early Pliocene. The Kattendijk Sands consist of dark gray to green-gray, fine to medium grained, slightly clayey glauconitic sand. Shells appear dispersed in the sand but also concentrated in one or more layers. The late Pliocene Mol Formation is a white coarse to medium grained sand deposit. It sometimes contains lignite and clay lenses. Locally the lower part is slightly glauconiferous ( Laga et al., 2001).