3D modelling and resistivity measurements for hydrogeological assessments in the northern part of Vombsänkan

Sammanfattning: The geology of Vombsänkan is characterized by a complex sequence of Quaternary deposits overlying the Paleozoic sedimentary bedrock. The area is 759 km2 and has recorded several ice advances followed by glacial retreats and ice melting. The glacial history of Vombsänkan, which is controlled by sequential geological events such as active ice-margin and stagnant ice, formation of dead ice as well as damming and subsequent drainage of glacial lakes and melting, has resulted in a diverse stratigraphy that is difficult to correlate across the entire basin. Abundant borehole data convey a recurring depositional pattern of the Quaternary deposits, which consist generally of till beds covered by glaciolacustrine and glaciofluvial deposits. The basin hosts several large aquifers with favourable hydrogeological properties. However, no detailed information in three dimensions exists on the hydrostratigraphic units and their properties. Lack of a 3D visualization of the northern part of Vombsänkan and an instruction for the application of Geoscene 3D in modelling of a complex geological setting such as Vombsänkan, emphasizes the importance of this thesis work. This study introduces a new 3D model of the northern part of Vombsänkan using Geoscene 3D. A simple hydrostratigraphic model is presented for the Vombverket water treatment plant, which demonstrates the presence of a thick glacial clay unit on top of the sedimentary bedrock. Locally, a till unit occurs between the sedimentary bedrock and the clay unit and the uppermost unit consists of 5–10 m of sand and gravel. Using Geoscene 3D, the approximate volume of the aquifer is estimated to 9.1–18.2 km3 for the confined aquifer within the sedimentary bedrock, and 1.3–2.6 km3 for the open aquifer within the overlying sand and gravel unit. The major flow directions are from the adjacent areas of higher elevation such as the Romeleåsen Horst in the Southwest and the Linderödsåsen Horst in the Northeast.