Riverbank filtration in Cairo, Egypt—part I: installation of a new riverbank filtration site and first monitoring results

To cope with the increasing water demand in Cairo, the Holding Company for Water and Wastewater drilled 6 pumping wells to assess the applicability of riverbank filtration (RBF) for the waterworks in Embaba. Results from well drilling and subsequent monitoring of water levels and water quality were used to assess site conditions. Hydrogeology and surface water quality are typical for RBF sites. The aquifer is more than 60 m thick and has a hydraulic conductivity of 6 × 10⁻⁴ m/s. The Nile River is cutting through the upper clay cap that covers the aquifer and is hydraulically connected with the aquifer. Piezometric heads indicate a natural recharge of the aquifer by river water. Thus, the site seems to have high potential for water production. Water quality of the Nile River is feasible for natural treatment via RBF, TOC is < 5.5 mg/l, and NH₄⁺ is < 0.5 mg/l. Major challenges in Embaba arise from frequent riverbed clogging in front of the site as well as the appearance of Fe, Mn and NH₄⁺ in the produced bank filtrate with values slightly exceeding the Egyptian drinking water standards. Disinfection with chlorine oxidizes the dissolved Fe and Mn, causing undesired coloring of the treated bank filtrate. As there is no treatment step for Fe/Mn removal yet, pumping of the RBF wells was frequently stopped. The redox conditions at the site required further detailed investigations with emphasize on NH₄⁺ and Mn to find out if concentrations could be managed without additional treatment.