Recently acquired mineralogic data from drill hole samples in Yucca Flat show that the tuff confining unit (TCU) can be subdivided into three mineralogic zones based on the relative abundances of primary and secondary mineral assemblages. These zones are (1) an upper zone characterized by the abundance of the zeolite mineral clinoptilolite with lesser amounts of felsic and clay minerals; (2) a middle zone with felsic minerals dominant over clinoptilolite and clay minerals; and (3) a basal argillic zone where clay minerals are dominant over felsic minerals and clinoptilolite. Interpretation of the mineralogic data, along with lithologic, stratigraphic, and geophysical data from approximately 500 drill holes, reveals a three-layer mineralogic model for the TCU that shows all three zones are extensive beneath Yucca Flat.The mineralogic model will be used to subdivide the TCU in the Yucca Flat hydrostratigraphic framework model, resulting in a more accurate and versatile framework model. In addition, the identification of the type, quantity, and distribution of minerals within each TCU layer will permit modelers to better predict the spatial distribution and extent of contaminant transport from underground tests in Yucca Flat, at both the level of the hydrologic source term and the corrective action unit.iv This page intentionally left blank.
This report is presented as a compilation of data and is intended to be used for future CAU-specific flow and transport models. 7.7.2 Projecf History This report is an account of work accomplished in late 1995 and early 1996, which was documented in a draft report distributed by IT Corporation (IT) for limited external review in April 1996 (IT, 1996a). Reviewers' comments have been addressed in this final report, but the scope and conclusions have not changed significantly fiom those presented in the IT draft publication. ' The hydrostratigraphic nomenclature used in this report follows that used for the UGTA Phase I regional groundwater modeling efforts (IT, 1996b). However, hydrogeologic characterization of the NTS area is a continuing process, and changes in the definitions of some hydrostratigraphic. units have occurred as a result of work conducted after publication of the draft report that forms the basis of this document (IT, 1996a). These changes have not been incorporated into this final report. Conclusions fiom the data presented in this fracture analysis report have, however, been assimilated into subsequent reports. For a more in-depth look at the hydrostratigraphy of the Pahute Mesa study area, the reader is directed to these recent works, which include Drellack and Prothro (1 997) and Prothro and Drellack (1 997). 1.2 Objecfives The objective of this study was to obtain information about fiactures in volcanic hydrogeologic and hydrostratigraphic units at Pahute Mesa to determine important hydrologic parameters for future CAU-specific flow and transport models. Critical fracture information gathered during this study included: ' Fracturedensity Aperture Orientation Secondary mineral coatings 1-3 7.3 Methodology 7.3. 7 Core Fracture Analysis A core fracture analysis was performed on conventional core samples from eight drill holes on or in the vicinity of Pahute Mesa. The drill holes were UE-18r, UE-18t, UE-lgx, UE-20bh #1, U-~OC, U E-~O C , UE-20e #1, and UE-20f. A summary of pertinent information about these wells is presented in Table 1-1. These drill holes were selected because cummulatively they provide representative core through five of the six hydrostratigraphic units (J3SUs) defined in the Phase I regional groundwater flow model, and they provide the opportunity to compare fractures in core to the BHTV and/or FMS borehole fracture logs. A total of 1,578 meters (m) (5,177 feet [a]) of core w k examined from December 1995 to February 1996 by geologists from Bechtel Nevada Corporation (BN), IT Corporation, Daniel B. Stephens and Associates, and GeoTrans, Inc. This study was conducted at the U. S. Geological Survey's (USGS) Geologic Data Center and Core Library in Mercury, Nevada. Typically, core was examined megascopically; however, lox-to 4Ox-zoom binocular microscopes were used routinely for more detailed examination. The fracture data collected during the fracture analysis as well as stratigraphic, lithologic, hydrogeologic, hydrostratigraphic, and geophysical information were entered into a ...
Understanding the nature of gas transport from an underground nuclear explosion (Une) is required for evaluating the ability to detect and interpret either on-site or atmospheric signatures of noble gas radionuclides resulting from the event. We performed a pressure and chemical tracer monitoring experiment at the site of an underground nuclear test that occurred in a tunnel in nevada to evaluate the possible modes of gas transport to the surface. the site represents a very well-contained, low gaspermeability end member for past Unes at the nevada national Security Site. However, there is very strong evidence that gases detected at the surface during a period of low atmospheric pressure resulted from fractures of extremely small aperture that are essentially invisible. our analyses also suggest that gases would have easily migrated to the top of the high-permeability collapse zone following the detonation minimizing the final distance required for migration along these narrow fractures to the surface. this indicates that on-site detection of gases emanating from such low-permeability sites is feasible while standoff detection of atmospheric plumes may also be possible at local distances for sufficiently high fracture densities. Finally, our results show that gas leakage into the atmosphere also occurred directly from the tunnel portal and should be monitored in future tunnel gas sampling experiments for the purpose of better understanding relative contributions to detection of radioxenon releases via both fracture network and tunnel transport.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.