The municipal waste landfill Barje (Ljubljana, Slovenia) is located in the northern edge of the Ljubljana Marshland, which is one of the deepest marshlands in Europe. The foundation ground consists about a 35 in thick layer of highly compressible soils, under which there are several separate gravel aquifers. The Upper aquifer is connected to the alluvial aquifer, which is also the main source of the drinking water for Ljubljana. Due to the consolidation in some parts of the landfill, settlements have already reached the height of 2 in or more. To improve the efficiency of bottom lining system, in 2000 a system of preparing the sub grade below the landfill was introduced with artificial sealing of the bottom with prior preloading. Since 1998 in the area of the landfill a vast geotechnical and hydrogeological monitoring system has been under construction. The 6 year time monitoring has showed extremely non-uniform settlements of soil, which is the consequence of the lenticular, heterogeneous geological composition. The ground water exhibits a clear influence of reduction conditions as a consequence of reduced soil permeability due to consolidation, due to the fact that large surfaces are covered by wastes, and due to impacts of seepage waters from the old part of the landfill. In the direct vicinity of the landfill the contents of chemical elements, such as Fe, Mn, NO2,NH4, As and others, are increased, which is typical of oxidation-reduction processes. Other parameters do not give evidence of spreading in the horizontal direction outside the landfill area. The findings of monitoring show that oxidation-reduction processes are the most important impact that the landfill exhibits to the subsoil, which means that in the future the main interventions will have to be based on the technology that allows control of these processes.
