Supplemental Modeling and Analysis Report, Atlas Corporation Moab Mill, Moab, Utah

The purpose of this report is to provide additional numerical modeling and data evaluation for the Atlas tailings pile near Moab, Utah. A previous report (Tailings Pile Seepage Model: The Atlas Corporation Moab Mill, Moab, Utah, January 9, 1998) prepared for the Nuclear Regulatory Commission (NRC) by Oak Ridge National Laboratory/Grand Junction (ORNL/GJ) presented the results of steady-state modeling of water flow and subsequent discharge to the underlying groundwater system. At the request of the Fish and Wildlife Service (FWS), this model was expanded to evaluate the impact of drainage from the tailings pile in addition to recharge from precipitation in a transient mode simulation. In addition, the FWS requested transient simulations of contaminant transport in the alluvial aquifer. Subsequently, NRC requested an evaluation of additional hydrologic issues related to the results presented in the Tailings Pile Seepage Model (ORNL/GJ 1998a) and the Limited Groundwater Investigation (ORNL/GJ 1998b). Funding for the report was provided by the U.S. Department of Energy. The following section lists the individual tasks with subsequent sections providing the results. A map for the Atlas Moab Mill site is presented in Fig. 1.1