The lack of freshwater supplies in the El-Dabaa area on the northern coast of Egypt is a challenge to development plans, particularly concerning the groundwater aquifer limits. Saltwater desalination is a reliable solution to water shortages. This study was conducted to assess the environmental impact of the abstraction operations from the groundwater in the Middle Miocene aquifer and the effect of the rejected brine resulting from the desalination plant on groundwater using numerical modeling. The calibrated transient model was used to predict the impacts of rejected water discharge. The forecasting scenario results indicate the decline of the aquifer's potentiometric surface to reach its maximum value of 1.4 m at well 3 within the study area by 2040. The radius of the affected area by drawdown is about 550 m, and the drawdown is generally decreased far away from the location of extraction wells (feeding wells). The salinity of the aquifer in the future scenario is affected by the rejected water inflow due to the high coefficient of permeability of the aquifer in the study area. The salinity increases to reach its maximum value of 40919 ppm at each reject well site and its maximum value of 37860 ppm at feed well 2 sites within the study area by the 2040 year. In contrast, most of the study area, mainly feed well 3, wasn't affected by rejected water. The radius of the affected area by salinity is about 700 m around the reject wells site by 2040.