Leachate treatment is indispensable at landfills for the protection of water bodies. The Ihlenberg landfill began treating the leachate from the landfill as early as 1986. There are different methods to improve the water quality in order to allow a possible direct discharge into a water body. In the course of surface sealing measures at the Ihlenberg landfill and to avoid odor emissions, a new process for leachate treatment had to be designed. STEP conducted a study for this purpose in order to select a suitable process and also to carry out a design of the leachate basins. To determine the ideal process for the leachate treatment, the state-of-the-art, as well as an assessment of the future requirements for the leachate treatment, were included. This resulted in various concepts, which were further refined with additional criteria such as precipitation, open and sealed landfill areas, plant capacity, etc.