Domestic and industrial wastewater can be discharged or ready for reuse by means of wastewater treatment plant. The most common method for the treatment of urban wastewater is the biological treatment (second stage treatment) process. Due to the operation, maintenance and repair of biological wastewater treatment plants, there are many hazards in terms of environmental aspects as well as occupational health and safety. In determining the risks that may occur in wastewater treatment plants, it is necessary to determine the scope and size of the effects on the environment in addition to the effects on work and staff health. It is important to reassess and prioritize the risks taking into account the adverse environmental impacts of the hazards in these facilities. In occupational health and safety, the risk analysis of the environmental impact, as well as safety of the activities and employees, will be of benefit to both decision makers and managers. In this study, 22 risks were identified in the risk analysis at the biological wastewater treatment plant. These risks have been assessed by a 5x5 matrix of risk analysis method. In order to be taken into account in the environmental impact environmental dimension parameter is defined and has been established scale to consider the environmental impact. This allows considering the 22 risks again for risk analysis. It has been determined that the significance levels are changed from the risks detected except for the 2 identified risks. The order of importance of risks identified when the environmental dimension is added has changed. With this new evaluation, 7 risks priority orders have increased while 13 risks priority orders have decreased. The remaining 2 risks were not changed in priority order. These changes have shown that the environmental dimension is important for the risks identified in wastewater treatment plants.