Interpretation of chemical and isotopic data from boreholes in the unsaturated zone at Yucca Mountain, Nevada

Technical Report · Tue Dec 31 04:00:00 EST 1996

DOI:https://doi.org/10.2172/587921· OSTI ID:587921

Yang, I C; Rattray, G W ^[1]; Yu, P ^[2]

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1. Geological Survey, Denver, CO (United States)
2. Univ. of Colorado, Boulder, CO (United States)

Analyses of pore water from boreholes at Yucca Mountain indicate that unsaturated-zone pore water has significantly larger concentrations of chloride and dissolved solids than the saturated-zone water or perched-water bodies. Chemical compositions are of the calcium sulfate or calcium chloride types in the Paintbrush Group (Tiva Canyon, Yucca Mountain, Pah Canyon, and bedded tuffs), and sodium carbonate or bicarbonate type water in the Calico Hills Formation. Tritium profiles from boreholes at Yucca Mountain indicate tritium-concentration inversions (larger tritium concentrations are located below the smaller tritium concentration in a vertical profile) occur in many places. These inversions indicate preferential flow through fractures. Rock-gas compositions are similar to that of atmospheric air except that carbon dioxide concentrations are generally larger than those in the air. The delta carbon-13 values of gas are fairly constant from surface to 365.8 meters, indicating little interaction between the gas CO{sub 2} and caliche in the soil. Model calculations indicate that the gas transport in the unsaturated zone at Yucca Mountain agrees well with the gas-diffusion process. Tritium-modeling results indicate that the high tritium value of about 100 tritium units in the Calico Hills Formation of UZ-16 is within limits of a piston-flow model with a water residence time of 32 to 35 years. The large variations in tritium concentrations with narrow peaks imply piston flow or preferential fracture flow rather than matrix flow. In reality, the aqueous-phase flow in the unsaturated zone is between piston and well-mixed flows but is closer to a piston flow.

• Research Organization: Geological Survey, Denver, CO (United States)
• Sponsoring Organization: USDOE Office of Civilian Radioactive Waste Management, Washington, DC (United States); Geological Survey, Reston, VA (United States)
• DOE Contract Number: AI08-78ET44802
• OSTI ID: 587921
• Report Number(s): USGS/WRIR--96-4058; ON: DE98004729
• Country of Publication: United States
• Language: English

Related Subjects

05 NUCLEAR FUELS
ACID CARBONATES
CALCIUM CHLORIDES
CALCIUM SULFATES
CARBON DIOXIDE
ECOLOGICAL CONCENTRATION
EVALUATED DATA
EXPERIMENTAL DATA
GAS ANALYSIS
INTERSTITIAL WATER
ISOTOPE DATING
MATHEMATICAL MODELS
RADIOACTIVE WASTE DISPOSAL
SITE CHARACTERIZATION
SODIUM CARBONATES
TRITIUM
YUCCA MOUNTAIN