Water quality changes in the dunes of the western Belgian coastal plain due to artificial recharge of tertiary treated wastewater

Since July 2002, tertiary treated waste water has been used to artificially recharge the phreatic aquifer of the dunes in the Belgian western coastal plain. The purpose of this project is to develop a sustainable water source, and thereby minimize lowering of the water table while maintaining production capacity. The recharged water is extracted via production wells located south and north of two ponds used for the recharge. The uniqueness of this system is that the total dissolved solids in this recharge water is low (50 mg/L) in comparison with natural dune water (550 mg/L). In this paper, water quality of recharge water, groundwater between ponds and extraction wells, extracted water and dune water is analysed. The extraction water quality is determined by mixing of recharged water and dune water. Mineralisation of the recharge water occurs mainly by carbonate dissolution. Further O2 consumption, NO3- reduction and oxidation of Fe sulfide minerals are distinguished. At the beginning of 2007 clogging of the ponds began to occur and it was observed that extraction rates and temperature of the recharge water influenced the amount of water which could be recharged. Using Cl− data, it is confirmed that all the recharged water is recovered by the extraction wells. Finally, it is concluded that the quality of the extracted water does not change significantly as a function of time.