2.1 Study Area
The MAR facility is located on the west coast of Belgium, close to the French-Belgium border (Fig. 1). The recharge pond is located on the dunes of the western Belgian coastal plain. The dune extends inland by 2 km to 2.5 km and has a surface elevation ranging from 6 mTAW to 35 mTAW (mTAW is the reference level corresponding to the mean low tide level, calculated as 2.36 m below mean sea level; mTAW is a standard Belgian reference). The mean thickness of the Quaternary phreatic aquifer under the entire region is 30m. The confining layer of this aquifer is a 100m thick clay layer, which is of the Eocene age and is considered impermeable in this study. The upper part of the aquifer consists of yellow Aeolian dune sands having considerable amounts of organic matter in it. A larger part of the aquifer is comprised of fine medium sand with occasional presence of silty and fine clayey sand lenses. The lower part of the aquifer consists of medium to coarse-medium sand pertaining to Eemian age (Vandenbohede, Van Houtte, & Lebbe, 2008b).
The WPC Torreele produces infiltration water from the effluent of the Wastewater Treatment plant of Wulpen (operated by Aquafin). This infiltration water is pumped to the St-André MAR facility through a 2.5 km long pipeline (Van Houtte & Verbauwhede, 2012) where it supplies an artificial infiltration pond (recharge method) with a surface area of 18,200 m2. The infiltration pond recharges an unconfined sandy dune aquifer (storage space) and water is then recovered from this aquifer using 137 wells (recovery facilities) which surround the pond. The recovered water is then used for municipal water supplies (end use) after aeration step, rapid sand filtration and UV disinfection (post-treatment) (Van Houtte & Verbauwhede, 2012). The schematic diagram of the processes involved in the St-André MAR facility are shown in fig. 2.
Fig. 1 Location of Wulpen wastewater treatment plant (WWTP), and St-André Managed Aquifer Recharge Facility
Fig. 2 Process of St-André Managed Aquifer Recharge Facility