The first step in setting up a SEEP2D simulation is to construct a 2D finite element mesh. This can be accomplished using the Map -> 2D Mesh command in the Map module.
SEEP2D only supports meshes composed entirely of linear elements (three node triangles and four node quadrilaterals). The mesh should not contain quadratic elements (six node triangles and eight node quadrilaterals).
Related Links:
Building a SEEP2D Simulation
Creating 2D Meshes
Map -> 2D Mesh