Safe usage of post-flotation waste reservoirs (landfills) requires carrying periodical geodesic measurements in order to control their embankments' stability. This is particularly important if mining operations are performed under the landfill or in its neighbourhood. On the basis of the measurements results, various coefficients of the terrain deformation are determined and their values, together with the results of other observations, are used in order to evaluate the safety status of the facility further usage. The paper presents the results of experimental calculations, using satellite measurements of the landfill observation network fragment, including the middle zone of its embankments. 35 geometrical structures were selected in this zone, named "triangular rosettes". Vertices of relevant triangles are selected points the co-ordinates of which shall be determined with the satellite technology. Three annual cycles of GPS observations in the landfill controlled network were used in calculations, performed in 2004-2006. On the basis of the annual sets of point co-ordinates, periodical horizontal displacements of points making up the rosettes were determined. In turn, for the interior zone of each rosette, components of a two-dimensional deformation tensor were calculated, allowing for determining the values for horizontal extreme deformations and the directions of their occurrence in each rosette zone. Calculations were performed for three time periods: 2004-2005, 2005-2006 and 2004-2006. The results of evaluating the condition of horizontal deformations were presented against the background of mining operations performed in these time periods in the landfill region, as well as against the background of settlements in the analysed points in relevant annual periods obtained from classical observations, realised by precision levelling technology.