Depth and stratigraphy of Quaternary deposits – Preliminary site description – Laxemar subarea – version 1.2

This report concerns a study which was conducted for SKB. The conclusions and viewpoints presented in the report are those of the author and do not necessarily coincide with those of the client. Summary This report aims at describing the modelled Quaternary deposits (QD) depth according to six layers with different geological and hydrological properties in the Simpevarp regional model area. The program used in the modelling of QD depths is the GeoEditor, which is an ArcView3.3-extension. The input data used in the model consist of 102 boreholes and 328 observation points. As input is also a large number of observation points interpreted from geophysical investigations used; 1,087 points based on refraction seismic measurements (distributed in 31 profiles), 22 points from electrical soundings (VES) and 19,237 points from seismic and sediment echo sounding data. The outer part of the area has a low data density. Some of the used points are generally not very deep and do not describe the actual bedrock elevation. They do, however, describe the minimum QD depth at each location. A detailed topographical Digital Elevation Model (DEM), the maps of Quaternary deposits and outcrops were also used. The model is based on a three-layer-principle where each layer can be given similar properties. The uppermost layer, Z1, has been influenced by the impact from surface processes, e.g. roots and biological activity. The bottom layer, Z3, is characterized by contact with the bedrock and is corresponding to a till layer. The middle layer, Z2, is corresponding to a clay layer and assumed to have different hydraulic qualities than Z1 and Z3. Besides those layers, another three layers are also modelled; M1 corresponds to a peat layer, M2 answers to a glaciofluvial sediment layer and M3 corresponds to a layer with artificial fill. All layers can have thickness zero. The resulting model clearly shows the valleys with thicker depths of QD, surrounded by areas with thinner or no depths. The esker near Fårbo (Tunaåsen) is also distinctly marked in the southwestern area. The northern and central part of the model area are characterized by numerous bedrock outcrops. The maximum depth of QD in the model is about 50 m, and the average depth in this area is 2.1 m with outcrops included and 3.0 m with outcrops excluded. är 2,1 m med hällar inkluderade och 3,0 m beräknat utan hällar.