A sewer geyser is a series of ejecting air-water mixture eruptions through vertical shafts of drainage systems. In field observed geyser incidents, manhole covers were blown into the air and they were followed by ejecting air-water mixture eruptions that lasted for several seconds at a time. Trapped air in sewer systems during the transition between open channel flow to pressurized flow and its release processes are known to play an important role in causing sewer geysers. There is a lack of detailed three-dimensional numerical simulation of the sewer geyser phenomena using techniques that can capture air-water interactions. The present study attempts to fill this gap. A Finite Volume (FV) and three-dimensional computational fluid dynamics (3D-CFD) model was used and the simulation method was validated by numerically reproducing physical experiments on spring-type geysers and violent geysers. A qualitative assessment of the flow features present in the system during a violent geyser eruption was made and compared with the physical experiment. The flow was approximated using the Reynolds-Averaged Navier- Stokes (RANS) model and the air-water interface was modeled using the Volume of Fluids (VOF) method. The k — ε turbulence closure model was used. A numerical experiment was performed to identify the influence of the initially available air and water in a sewer system on the geyser formation.