The recent global development in geotechnical and geophysical investigation methodologies has continued to improve the possibility of early identification of critical geohazards and mitigation of risks associated with construction of large underground projects. This is not only limited to highlighting the potential risks, but also minimizing the cost and time for construction by avoiding or mitigating unexpected risks. A case study is presented by a recent unprecedented tunneling project in the State of Qatar featuring a 4.5-8.5 meters diameter, 55 kilometers in length, with various deep shafts, pumping station, and outfall in the Al-Wakrah city. Following an extensive desk study from available geotechnical and geophysical data in the vicinity of the project area and from previous practical experience from similar projects, a thorough geotechnical and geophysical investigation campaign was planned and executed. The result of the comprehensive ground investigation gave a clear picture of expected geohazards and prospective mitigation measures to be taken during the construction of the works. The paper presents a description of the main identified geohazards, including the presence of chert bands, karstic areas, massive caverns, high permeability areas, and high aggressiveness ground conditions along with its implications and mitigation measures, to be taken into account in the next stages of the project. A similar approach can be adopted for future infrastructure projects to support the geotechnical risk assessment and to minimize the impact of construction activities on the environment.