The two-dimensional models described above form a useful basis for understanding hydrogeology at Hays, but are limited tools for detailed prediction of contaminant migration. Two-dimensional approaches are generally sufficient for pro-active efforts such as WHPA delineation in pristine settings, but in areas such as Hays with pre-existing aquifer contamination, more detail and a 3-D view are needed. In order to evaluate potential 3-D effects of facies distributions on transport in the Hays valley aquifer, a 3-D hydrogeologic model was first developed based on lithologic logs. From this model, hydrologic flow and transport models were developed. An effort was made to utilize typical tools available to consultants and local government entities: the hydrogeologic model was developed using the Groundwater Modeling System (GMS), the hydrologic model was implemented using the finite difference program MODFLOW [McDonald and Harbaugh, 1988], transport and capture zones were determined using MODPATH [Pollock, 1994].