A hydrogeologic and geophysical investigation of a fault as a groundwater flow barrier in Reno, Nevada.

摘要

The Truckee Meadows area is an alluvium filled basin situated in the transition zone between the Sierra Nevada and the more moderate elevation of the Basin and Range Province. The Genoa Fault System (GFS) makes up the eastern boundary of a broad structural corridor between these two zones. The northern extension, called the Mt. Rose Fault Zone, of the main fault in the GFS has been mapped into the Reno, Nevada metropolitan area of the Truckee Meadows. Groundwater elevation differences across the projection of this fault suggest that it is a locally significant groundwater flow barrier in the basin. The Washoe Department of Water Resources is currently developing a groundwater flow and solute transport model to use as a management tool for addressing a widespread PCE contamination problem. Better definition characterization of the location, orientation, and the hydrogeologic properties of the fault are needed to reduce the model uncertainty in this part of the basin.;High resolution seismic reflection surveys allow for the potential identification and evaluation of the extension of the GFS fault trace in an area approximately 750 m to the north and 500 m to the east of the north end of the GFS as presently mapped. These geophysical surveys also constrain the geometry of the fault. Microtremor seismic surveys allow for a comparison of shallow shear velocities on opposite sides of the fault suggesting the possible location of the fault for evaluation by reflection imaging.;Predictive modeling done in advance of an aquifer test displayed drawdown not seen in the actual aquifer test. This result demonstrates the high productivity of the local aquifer and attests to the high degree of heterogeneity of the overall subsurface while highlighting the inadequacies of my conceptual model and the use of inappropriate hydraulic parameters in my model. While the drawdown curve in a monitoring well further in distance from the pumping well than the fault show immediate drawdown no apparent boundary effect is seen in the drawdown curve of the pumping well. Data from the aquifer test allow for the calculation of the hydraulic properties of the aquifer and provides some insight on the hydrogeologic characteristics of the inferred fault.