Preliminary on the isotope hydrology investigations at the Nevada test site: Hydrologic resources management program; FY 1992--1993
A comprehensive isotope data base of the NTS groundwaters collected during FY 92-93 is presented with preliminary interpretations. Multiple samples were collected from over 30 sites on pumped wells and open-holes by wireline bailing. Field water level measurements indicate essentially a bimodal distribution separated by water levels at higher elevations (e.g. Pahute Mesa) from water levels of lower elevations (e.g. Yucca and Frenchman Flats). Down hole temperature measurements have confirmed anomalous temperature gradients in the eastern Yucca Flat area and on Pahute Mesa, where horizontal temperature gradients up to 0.33{degrees}F/100ft are found. Consistent with previous reports by others, the major ion geochemistry of the NTS groundwater are dominated by Na-K-HCO{sub 3} and Ca-Mg-HCO{sub 3} water types, where the Na-rich water appears to be related to dissolution in the volcanic tuffs and the Ca-rich water to the Paleozoic carbonates. Increases in dissolved Si also seems to be indicative of groundwater that resides in the volcanic tuffs. Processes controlling the Na/Ca ratios are complex and may include ion exchange reactions with clays, evaporative concentration in the vadose zone, and lithological heterogeneities in addition to simple differential dissolution between the volcanic tuffs and the Paleozoic carbonates. Apparent {sup 14}C ages range between 4000 and 38,000 years for groundwaters at the NTS. The uncertainty is large for exact age determinations at this time. The {sup 14}C abundance decreases with increased dissolved HCO{sub 3}, and {sup 13}C suggests dissolution of the ``dead`` Paleozoic carbonates significantly influence the ages, but more work is needed to investigate the influence of vadose zone carbonate.
- Research Organization:
- Lawrence Livermore National Lab., CA (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 145197
- Report Number(s):
- UCRL-ID--116122; ON: DE94011538
- Country of Publication:
- United States
- Language:
- English
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