An Overview Of The Inyo County Geophysical Program In The Death Valley Area

Abstract

Yucca Mountain, Nevada has been proposed as the site of the high-level nuclear waste repository for the United States. The repository concept uses the philosophy of multiple barriers, both engineered and natural, each of which impedes the movement of radionuclides into the accessible environment. The proposed repository would be in the unsaturated zone in Tertiary tuffaceous rocks. The principal transporting mechanism for radionuclides is moving ground water. Underlying the repository is an extensive Lower Carbonate Aquifer known to be highly permeable. Inyo County, as an affected unit of local government under the Nuclear Waste Policy Act, as amended, is concerned with the connections between the Lower Carbonate Aquifer underlying Yucca Mountain and the carbonate sources of waters in Inyo County, especially the Death Valley region. A primary concern of Inyo County is the potential connection between the carbonate aquifer beneath Yucca Mountain and the system of springs that discharge along the foot of the mountain ranges along the eastern wall of Death Valley. In February of 2000, a time domain electromagnetic induction (TEM) survey was conducted in Death Valley National Park, California. Fifteen TEM soundings were collected in Travertine, Texas, Nevares, and Grapevine Springs to determine the hydrogeologic controls influencing the location of the springs and to determine the subsurface extent of the Paleozoic carbonates exposed in the Funeral and Grapevine Mountains. The TEM data appears to have mapped a synclinal structure along the west side of the Funeral Mountains. The position of Travertine, Texas, and several other springs appears to be controlled by a fault along the western limb of the syncline. Nevares Spring appears to be controlled by a fault adjacent to the Funeral Mountains. We are currently completing a series of TEM, magnetics, gravity and magnetotelluric surveys of the east side of the Funeral Mountains. Surveys are being conducted in Sarcobatus Flat near Scotty’s Junction, the Armagosa Valley near Bat Mountain, and west of Death Valley Junction. The objective of the study in the Armagosa Valley is to map the structure of the carbonate aquifer to select locations for approximately three monitoring wells to be completed at depth of 1,000 to 4,000 feet. The surveys on the Sarcobatus flat and Death Valley Junction areas are to map the position and geometry of the valley fill deposits as support for a water right for the National Park Service. We are in the process of completing our analysis of the data and expect to have preliminary results to present. In FY2003, we intend to conduct gravity, magnetic and magnetotelluric surveys along the west side of the Funeral Mountains in the Furnace Creek area. The surveys will be used to interpret the complex geologic structure in this area and select the location for two deep monitoring wells to be completed in the carbonate aquifer. When completed, these surveys will provide a more complete picture of the structure of the carbonate aquifer in the area west of Yucca Mountain. The data will be used to support regional ground water models to predict ground water flow vectors in the region west of Yucca Mountain.