Groundwater flow in the vicinity of two artificial recharge ponds in the Belgian coastal dunes

Since July 2002, tertiary treated wastewater has been artificially recharged through two infiltration ponds in the dunes of the Belgian western coastal plain. This has formed a lens of artificially recharged water in the dunes’ fresh water lens. Recharged water is recovered by extraction wells located around the ponds. Hydraulic aspects of the artificial recharge and extraction are described using field observations such as geophysical borehole loggings and a tracer test. Borehole logs indicate recharged water up to 20 m below surface, whereas the tracer test gives field data about the residence times of the recharged water. Furthermore, a detailed solute transport model was made of the area surrounding the ponds. Groundwater flow, capture zone, residence times and volume of recharged water in the aquifer are calculated. This shows that the residence time varies between 30 days and 5 years due to the complex flow pattern. The extracted water is a mix of waters with different residence times and natural groundwater, assuring a relatively stable water quality of the extracted water.