Constraining Hydrogeologic Models Using Geophysical Techniques: Case Study Fortymile Wash And Amargosa Desert, Southern Nevada

Fortymile Wash and the Amargosa Desert are located along the groundwater flow path from<br>Yucca Mountain, Nevada, site of a proposed high-level nuclear waste repository. Groundwater<br>flow models developed for .these regions are poorly constrained due to limited spatial information<br>on hydraulic head, hydraulic conductivity, and hydrostratigraphy. To overcome some of these<br>limitations, an integrated geophysical survey utilizing the time-domain electromagnetic method,<br>the induced polarization method, the Schlumberger resistivity method, and the magnetic method,<br>was used to map the spatial continuity of the hydrostratigraphy and watertable elevation between<br>point measurement locations in the region. Simultaneous inversion of the data from these surveys<br>identified several discontinuities that showed good correlation to stratigraphic units and<br>waterlevels identified at point measurement locations. In addition, several areas were identified<br>where units either thickened, terminated, or shallowed. The information obtained from these<br>surveys is currently being used to better constrain groundwater models for the region.