The MODPATH pane is on the MODFLOW Features tab of the Object Properties dialog box.
There are two types of data specified on this pane: IFACE and the Initial particle placement.
When a boundary condition is used to represent a flux through the edge of the model IFACE is used to specify the cell face through which the flux occurs. For example, you might use the well package on the edge of the model domain to represent a constant flux boundary at the edge of the model. There are several choices and the diagram next to the choices illustrates how they apply. If the specified edge is not a boundary of the model, the flux will be treated as an internal source or sink regardless of the value of IFACE.
The user may also choose to specify the Initial particle placement with an object. The user may choose among several different patterns of particles and that pattern will be used to specify in each cell enclosed or intersected by the object. The diagram illustrates how the particles will be placed in each cell. The user can also specify release times for the particles. The release times are specified relative to the reference time. (For steady-state simulations, the reference time is the beginning of the model. For transient simulations, it is the user-specified reference time.) For backward particle tracking, the reference time would typically be set to the end of the model and the release time would be set to zero.
The Object choice for the placement of particles is not illustrated. For it, the particles will be placed at the location of the object. The Object choice is only available for point objects with one Z formula.
