The steep dyke of the bauxite residue storage pond was constructed from slag, ash, fly ash. Its width is 25 meters and it was constructed directly on the soil. The underlying subsoil at 4-5 meters depth from the bottom of the dyke is made of a clayee sealing layer. In between the dyke bottom and the clayee layer an alternating sandy, silty formation is located.
The surface of the dyke shown on this photo indicates that the material of the dyke is not fully water sealing, there are signs of infiltrating water visible on it. The sandy, silty formation overlaying the clayee sealing layer is also permeable. The alkaline leachate from the the operating reservoir is able to infiltrate through it.
Therefore, the reservoir dams are not fully insulated/sealed. To prevent leakage of the alkaline lecahte into the environment, the red mud storage reservoirs were surrounded by an undergorund water sealing reactive barrier located at 10 meters distance from the reservoir dyke.