Hydrochemical investigations in characterizing the unsaturated zone at Yucca Mountain, Nevada
- Geological Survey, Denver, CO (United States)
- Taipower Co., Taipei (Taiwan, Province of China)
- Univ. of Colorado, Boulder, CO (United States). Dept. of Civil, Environmental, and Architectural Engineering
Hydrochemical and isotopic investigations of ground water at Yucca Mountain, Nevada, site of a potential permanent national nuclear-waste repository, demonstrate that younger rocks are dominated by calcium-sulfate or calcium-chloride water and that older rocks contain sodium-carbonate or sodium-bicarbonate water. Furthermore, unsaturated-zone pore water has significantly larger concentrations of major ions and dissolved solids than does the saturated-zone water. Recharge of perched or saturated-zone water, therefore, requires rapid flow through fractures or permeable regions in the unsaturated zone to avoid mixing with the chemically concentrated water in the unsaturated zone. This conceptual model is consistent with observations of rapidly moved post-bomb (post-1954) tritium and chlorine-36 in the deep unsaturated zone at Yucca Mountain. Presence of post-bomb tritium in matrix water away from fracture zones further indicates that parts of the fast-flow water that moves through fractures have been diverted laterally into nonwelded units. Experimental data show that different lithologic units require specific water-extraction methods for stable-isotope analyses of hydrogen and oxygen to ensure accurate characterization. Vacuum-distillation and compression-extraction methods both can yield accurate data but must be used with specific lithologies. Column experiments demonstrate that percolating water can exchange with pore water of the core as well as water held in zeolite minerals in the core. Exchange rates range from days to months. Pore-water samples from core, therefore, reflect the most recently infiltrated water but do not reflect percolating water of the distant past.
- Research Organization:
- US Geological Survey, Denver, CO (United States)
- Sponsoring Organization:
- USDOE Assistant Secretary for Human Resources and Administration, Washington, DC (United States)
- DOE Contract Number:
- AI08-97NV12033
- OSTI ID:
- 677016
- Report Number(s):
- USGS/WRIR-98-4132; ON: DE99000507; TRN: 99:002283
- Resource Relation:
- Other Information: PBD: 1998
- Country of Publication:
- United States
- Language:
- English
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