Using seismic reflection to locate a tracer testing complex south of Yucca Mountain, Nye County, Nevada.

摘要

Tracer testing in the fractured volcanic aquifer near Yucca Mountain, and in the alluvial aquifer south of Yucca Mountain, Nevada has been conducted in the past to determine the flow and transport properties of groundwater in those geologic units. However, no tracer testing has been conducted across the alluvium/volcanic interface. This thesis documents the investigative process and subsequent analysis and interpretations used to identify a location suitable for installation of a tracer testing complex, near existing Nye County wells south of Yucca Mountain.;The work involved evaluation of existing geologic data, collection of wellbore seismic data, and a detailed surface seismic reflection survey. Borehole seismic data yielded useful information on alluvial P-wave velocities. Seismic reflection data were collected over a line of 4.5-km length, with a 10-m receiver and shot spacing. Reflection data were extensively processed to image the alluvium/volcanic interface. A location for installation of an alluvial/volcanic tracer testing complex was identified based on one of the reflectors imaged in the reflection survey; this site is located between existing Nye County monitoring wells, near an outcrop of Paintbrush Tuff.;Noise in the reflection data (due to some combination of seismic source signal attenuation, poor receiver-to-ground coupling, and anthropogenic sources) were sources of error that affected the final processed data set. In addition, in some areas low impedance contrast between geologic units caused an absence of reflections in the data, complicating the processing and interpretation. Forward seismic modeling was conducted using Seismic Un*x; however, geometry considerations prevented direct comparison of the modeled and processed data sets. Recommendations for additional work to address uncertainties identified during the course of this thesis work include: drilling additional boreholes to collect borehole seismic and geologic data; reprocessing a subset of the current seismic reflection data in the area chosen for a tracer complex; processing the existing reflection data set with refraction processing software; and conducting additional seismic reflection testing with different survey geometry.