Ground Water at Yucca Mountain How High Can It Rise? (1992) / Chapter Skim
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Executive Summary
Executive Summary
Pages 1-9
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for the permanent disposal of the high level radioactive wastes from civilian nuclear power plants. To select a site for an MODS, the DOE must study in detail the natural environment and the various natural processes to which a proposed deep geologic repository might be subject.
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Because the thesis was based primarily on the staff scientist's interpretation of geological occurrences and relationships in the field, the panel spent several days in the field led by scientists on both sides of the controversy, visiting and studying carefully those sites that were purported to reveal evidence for upwelling ground water. The panel regarded their task as not only evaluating the staff scientist's thesis, but also assessing the likelihood that the ground water
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Near-vertical veins of carbonates attributed by the proponents to deposition from upwelling ground water along faults, intersect the texturally similar surface deposits locally at Trench 14 and Busted
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the isotopic compositions of these springs being similar to rain water. Textural/Morphologic Evidence Comparison of features of an unequivocal carbonate spring deposit in the southern Basin and Range region, at Travertine Point near Death Valley, with features in Trench 14 Excavated across the Bow Ridge fault east of Yucca Mountain)
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CONCLUSION The panel concludes from the geologic features observed in the field and geochemical data that there is no evidence to support the assertion that the water table has risen periodically hundreds of meters from deep within the crust. In fact, the evidence strongly supports a surface-process origin from rainwater for the vein and surface parallel carbonate and carbonate-silica deposits throughout the Yucca Mountain area.
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However, until the DOE model assumptions are tested or better constrained by more complete hydrologic data, and the techniques for estimating recharge in the region better developed, the panel considers an increase in precipitation due to a climate change a possible means of raising the water table significantly. VoIcanic Intrusion In considering the long and complex volcanic history of the region, the possibility of a recurrence of the highly explosive volcanism of the Tertiary was dismissed because the subduction zone origin of the actively has been replaced by extensional tectonics that has resulted in the basaltic volcanism of more recent geologic time.
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Calculating the probabilities of occurrence of a dike intrusion close to Yucca Mountain results in a very small number, 10~ per year. Although there may be considerable uncertainty in the probability values, the panel considers that the small effect a basaltic dike intrusion would have on the water table and the low probability of a dike forming close to Yucca Mountain mean that volcanic intrusions can be discounted as potentially disruptive events with respect to water table stability.
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The panel recommends a comprehensive program of drilling, scientific testing and logging and core and fluid analysis in and close to this gradient. Paleozoic Carbonate Aquifer Results of regional elastic strain modeling to determine the water table response to earthquakes inclicated that information on the deep carbonate aquifer Is essential to more realistic modelling.
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Even among the geologists and geophysicists there seemed to be little integration of their individual spheres of knowledge and data. Because this important site characterization program is large and complex, strong scientific leadership must be provided to the participants and adequate attention must be paid to the continuing coordination and syntheses of scientific results.
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