Contribution of Recharge Along Regional Flow Paths to Discharge at Ash Meadows, Nevada Contribution of Recharge Along Regional Flow Paths to Discharge at Ash Meadows, Nevada

by Bushman, Michelle 1976-

Springs in the Ash Meadows, Nevada wetland area are discharging groundwater at a high volume that cannot be sustained by local, present-day precipitation and associated recharge. Previous groundwater flow models for this region have required groundwater to flow through complex geology for long distances (160km) through fractures that, in the current stress field, should be closed in many instances in the presumed flow direction.

This thesis examines several possible flow paths and evaluates each flow path using chemical and isotopic signatures in the water, as well as geologic and geophysical constraints, and determines that flow from beneath the Yucca Mountain area is the most viable source of groundwater for the springs at Ash Meadows. Isotopic signatures also indicate that recharge likely occurred during the last pluvial, a cooler, wetter period about 13,000 or more years ago, and that present-day water is discharging from storage.

Geophysical investigations show the relationship of a deep-seated crustal feature (the Gravity Fault) with shallow offset faults near the Ash Meadows springs. The damage zone of the Gravity Fault appears to provide a conduit for groundwater flow; the north-south fractures should have the greatest aperture under the current stress field, and the buried tufa mounds (revealed with ground penetrating radar data) indicate localized upwelling from a deeper regional water source.