THE LOWER CARBONATE AQUIFER AS A BARRIER TO RADIONUCLIDETRANSPORT

摘要

Yucca Mountain is the site of the proposed high-level nuclear repository in the United States.rnUnderlying the repository at a depth of 4256 ft (1.3 km) is an extensive Lower PaleozoicrnCarbonate Aquifer known to be highly permeable. This paper presents the results of ourrninvestigation of the Carbonate Aquifer as a potential pathway for radionuclide transport to thernmajor Furnace Creek springs in Death Valley National Park. Our study culminated in arnMODFLOW groundwater model that simulates flow through the Funeral Mountains. Thernmodel is supported by our current program of: 1) monitoring well drilling on the northeastrnflank of the Southern Funeral Mountains, 2) surface and subsurface geologic mapping in thernarea, and 3) groundwater chemistry analysis from springs and wells in the area. One of thernmajor inputs to the modeling is a water budget analysis of the discharge from the FurnacernCreek spring system. Two bounding geologic hypotheses are proposed as contour maps of thernbase of the Carbonate Aquifer in the Southern Funeral Mountains: 1) a fault plane with arnshallow dip that projects a higher elevation for the base of the aquifer, and 2) a fault plane thatrnis more steeply dipping that projects a lower elevation base for the aquifer. The groundwaterrnmodeling suggests that both fault planes are feasible. The computed water table hasrnapproximately 300 feet of saturated carbonate rock above the higher elevation fault planernthrough the critical area—the so-called spillway. The more steeply dipping fault planernindicates a saturated thickness of more than 1000 feet through the critical area. The modelrnrecreates the flow of the various springs in Death Valley.