Sustainable construction is a comprehensive process of balancing the natural and built environment by applying sustainable development concepts. The golden triangle of time, cost and quality in construction must also assess risks from a sustainable perspective and consider the environmental dimension of the project. However, proper risk assessment for green sustainability is challenging, resulting in project management under uncertain conditions. This research focuses on improving the assessment of critical risk factors associated with construction activities using a Monte Carlo simulation-based approach. The AHP methodology is applied to prioritise environmental impact indicators and the EMC approach is used to calculate the impacts of expected outcomes. Preliminary results show that air, water and soil pollution, water consumption and solid waste are the most critical indicators. Equipment failure significantly affected the duration and increase of environmental impacts. Evidence suggests that attention should be paid to sustainability risk factors during construction activities, for example, the unavailability of materials had the most significant impact on the cost of the construction phase. Inadequate control of sustainability risk factors can lead to poor performance and difficult decisions in a construction project.