Figure 1.2: For given drill logs defining information about gradual hydraulic conductivity changes (left illustrations), multiple interpretations of the distribution of material is possible. Hydraulic conductivity is often not directly measured, but is deduced from material characteristics, or calculated and averaged over a zone based on aquifer pump tests. When the modeler has to infer from the data a characteristic not directly defined by the data, the data is referred to as "soft," and is not exactly honored (There is uncertainty as to where the dividing lines are). This is why the hydraulic conductivity zones in each well do not exactly match. A similar process can be used to define variations in porosity (right illustrations), but for a particular realization, the distribution of porosity should be correlated to the distribution of hydraulic conductivity. In this case, a particular hydraulic conductivity realization can be used as "soft" data for evaluating the porosity.