Because PHAST requires that some data be assigned to elements and other data be assigned to nodes, some data sets used in PHAST will have a value for each element and others will have a value for each node. The initial water table in PHAST, which is a 2-D data set, is only defined for one layer of nodes in the model. The remaining data sets required by PHAST are 3-D. Geometrically, a MODFLOW cell is equivalent to a PHAST element.