Figure 17.9: Based on a series of 100 simulations of the subsurface, the uncertainty in the description of the subsurface geology can be defined. With this simple two unit model, a particular cell may always be of a specific material (best case). A particular location may also, half the time be one material, half the time be the other (worst case; either material type is equally likely). The uncertainty may also fall somewhere in between. Where the material type is always the same, risk is low. Where uncertainty is high, risk is high.