ABSTRACT: In 2004, the European Commision proposed development of the interconnected Trans-European High-Speed Rail-Network (TEN-T) by 2015. This network also includes Bratislava City. In line with this proposal, preparation work for implementation of the project related to rail connection between the TEN-T corridor and the M.R. Štefánik Airport and rail network in Bratislava has begun. The construction of the TEN-T corridor is a major project in Bratislava and the project includes assessment of the impact of the designed structure on groundwater as a significant element of the environment. This paper presents the results of the model assessment of the current state of groundwater regime and groundwater flow prior to construction of the TEN-T railway tunnel. It also explores expected changes in groundwater regime and flow after constructing the connection of the TEN-T railway corridor with the M.R. Štefánik Airport and Bratislava rail network. The TRIWACO model was used for simulation of the impact of the railway tunnel on groundwater. Results of modelling show expected changes in the groundwater regime due to the impact of this designed railway tunnel connection between the TEN-T corridor, the M.R. Štefánik Airport and the Bratislava rail network. Technical measures are proposed herein to minimize adverse effects of the TEN-T railway tunnel on the groundwater level regime, and also to contribute to an acceptable technical and environmental solution.