Geology in the Vicinity of the TYBO and BENHAM Underground Nuclear Tests, Pahute Mesa, Nevada Test Site
Recent radiochemical evidence from groundwater characterization and monitoring wells in the vicinity of the TYBO and BENHAM underground nuclear tests in Area 20 of the Nevada Test Site, suggests that migration of radionuclides within groundwater beneath this portion of Area 20 may be more rapid than previously thought. In order to gain a better understanding of the hydrogeologic conditions in the TYBO-BENHAM area for more accurate flow and transport modeling, a reevaluation of the subsurface geologic environment in the vicinity of the two underground tests was conducted. Eight existing drill holes provided subsurface control for the area. These holes included groundwater characterization and monitoring wells, exploratory holes, and large-diameter emplacement holes used for underground nuclear weapons tests. Detailed and consistent geologic descriptions of these holes were produced by updating existing geologic descriptions with data from petrographic, chemical, and mineralogic analyses, and current stratigraphic concepts of the region. The updated descriptions, along with surface geologic data, were used to develop a detailed geologic model of the TYBO-BENHAM area. This model is represented by diagrams that correlate stratigraphic, lithologic, and alteration intervals between holes, and by isopach and structure maps and geologic cross sections. Regional data outside the TYBO-BENHAM area were included in the isopach and structure maps to better evaluate the geology of the TYBO-BENHAM area in a regional context. The geologic model was then evaluated with regard to groundwater flow and radionuclide migration to assess the model's implications for flow and transport modeling. Implications include: (1) confirmation of the general hydrogeology of the area described in previous studies; (2) the presence of two previously unrecognized buried faults that could act as zones of enhanced permeability within aquifers; and (3) secondary alteration within tuff confining units that is much more complex than previously described.
- Research Organization:
- Bechtel Nevada Corporation (US)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- AC08-96NV11718
- OSTI ID:
- 791565
- Report Number(s):
- DOE/NV/11718-305; TRN: US200206%%43
- Resource Relation:
- Other Information: PBD: 1 Dec 2001
- Country of Publication:
- United States
- Language:
- English
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TYBO/BENHAM: Model Analysis of Groundwater Flow and Radionuclide Migration from Underground Nuclear Tests in Southwestern Pahute Mesa, Nevada
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Related Subjects
BOREHOLES
GEOLOGIC MODELS
GEOLOGY
MONITORING
NEVADA TEST SITE
NUCLEAR WEAPONS
POSITIONING
RADIONUCLIDE MIGRATION
GROUND WATER
NUCLEAR EXPLOSIONS
UNDERGROUND EXPLOSIONS
HYDROLOGY
SITE CHARACTERIZATION
UGTA
OASIS VALLEY
ASH-FLOW TUFF
ALTERATION
CALICO HILLS FORMATION
GROUNDWATER FLOW