In order to erect an underground construction, it is necessary to drain its trench by pumping out groundwater. If information on hydrogeological data of the place and on the trench are available then it is possible to estimate, by using modelling, the necessary pumping rate and to compute lowering of groundwater head at the trench surroundings (depression cone) developed by the pumping. There ground dewatering happens that may cause subsidence of buildings and streets and to worsen life of plants. For this reason, the dewatering must be considerably minimized. It can be done by enclosing the trench by a watertight wall. In the town Riga, a many storied house will be built. It includes underground floors that can be created only in the drained trench. To find the wall depth and permeability, the detailed hydrogeological model (HM) has been built (size 400m×400m, 7 layers, plane approximation step 0.5m). To run HM, the commercial software Groundwater Vistas 6 was applied. The impact of the most probable failures of the wall was investigated. The original methodology of modelling has been applied. It may of interest for modelers dealing with finding of depression cones caused by groundwater withdrawals.