In this study we investigated the hydrogeological problems of an open-pit brown coal mine in the Borsod coal basin with Processing Modflow software. The coal mine is located in the valley of the Sajó-river with high transmissivity overburden layer where the traditional dewatering solutions were not encouraging due to inrush risks and low cost-efficiency. A new way of barrier forming was found out and numerically simulated to prove the efficiency of the solution. Since there are several contaminated sites in the surroundings it was a key factor to assure that the new mine dewatering technique has only a negligible effect on the groundwater regime that undisturbs the known contaminant plumes nearby.