Spatial variability in hydrologic properties of a volcanic tuff
- Oregon State Univ., Corvallis, OR (United States). Dept. of Civil Engineering
- Sandia National Labs., Albuquerque, NM (United States). Geoscience Assessment and Validation Dept.
- Raytheon Services Nevada, Mercury, NV (United States). Hydrologic Research Facility
- Geological Survey, Mercury, NV (United States). Hydrologic Research Facility
Spatial variability of hydrologic properties was quantified for a nonwelded-to-welded ash flow tuff at Yucca Mountain, Nevada, the potential site of a high-level, nuclear waste repository. Bulk density, porosity, saturated hydraulic conductivity, and sorptivity were measured on core specimens collected from outcrops on a grid that extended vertically through the entire unit thickness and horizontally 1.3 km in the direction of ash transport from the volcanic vent. A strong, geologically determined vertical trend in properties was apparent that correlated with visual trends in degree of welding observed in the outcrop. The trend was accurately described by simple regression models based on stratigraphic elevation. No significant horizontal trends in properties were detected along the length of the transect. The validity of the developed model was tested by comparing model predictions with measured porosity values from additional outcrop sections and boreholes that extended 3,000 m north, 1,500 m northeast, and 6,000 m south of the study area. The model accurately described vertical porosity variations except for locations very close to the source caldera, where the model underpredicted porosity in the upper half of the section. The presence of deterministic geologic trends, such as those demonstrated for an ash flow unit in this study, can simplify the collection of site characterization data and the development of site-scale models.
- Research Organization:
- Sandia National Laboratories (SNL), Albuquerque, NM, and Livermore, CA (United States)
- DOE Contract Number:
- AC04-76DP00789; AI08-78ET44802
- OSTI ID:
- 145531
- Journal Information:
- Ground Water, Vol. 32, Issue 5; Other Information: PBD: Sep-Oct 1994
- Country of Publication:
- United States
- Language:
- English
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