The Free Surface dialog box is used to specify whether or not a free surface (water table) is used in the model. The Free Surface dialog box is displayed by selecting PHAST Options|Free Surface… If a free surface will be used, the user can choose to use the water table to define the initial head. If a free surface is not used or if the water table is not used to define the initial head, the "Initial_Head" data set is used to define the head at each node. If the free surface is used and the water table is used to define the initial head, the "Initial_Water_Table" data set is used to define the initial head.