Geologic character of tuffs in the unsaturated zone at Yucca Mountain, southern Nevada

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Authors:Scott, Robert B.; Spengler, Richard W.; Diehl, Sharon; Lappin, A. R.; Chornack, Michael P.
Author Affiliations:Primary:
U. S. Geol. Surv., Denver, CO, United States
Sandia Natl. Lab., United States
Fenix & Scisson, United States
Volume Title:Role of the unsaturated zone in radioactive and hazardous waste disposal
Volume Authors:Mercer, James W., editor; Rao, P. S. C.; Marine, I. Wendell
Source:p.289-335; Role of the unsaturated zone in radioactive and hazardous waste disposal, Philadelphia, PA, May 31-June 4, 1982, edited by James W. Mercer, P. S. C. Rao and I. Wendell Marine. Publisher: Ann Arbor Sci. Publ., Ann Arbor, MI, United States. ISBN: 0-250-40620-9
Publication Date:1983
Note:In English. 41 refs.; illus. incl. 2 tables, sects., geol. sketch maps
Summary:At Yucca Mountain, a potential site for a high-level nuclear waste repository on the Nevada Test Site in southern Nevada, evaluation of the geologic setting and rock physical properties, along with previous regional hydrologic studies, has provided background that can be used for construction of a preliminary conceptual hydrologic model of the unsaturated zone. The 500-m-thick unsaturated portion of Yucca Mountain consists of alternating layers of two contrasting types of tuff. One type consists of highly fractured, densely welded, relatively nonporous but highly transmissive ash-flow tuffs. The other type consists of relatively unfractured, nonwelded, highly porous but relatively nontransmissive, argillic and zeolitic bedded tuffs and ash-flow tuffs. Superimposed on this layering are two sets of faults and fractures; one strikes north-northwest (N. 15° W. to N. 40° W.) and dips steeply (60°-90°) westward; the other strikes north-northeast (N. 5° E. to N. 35° E.) and also dips steeply westward. The vast majority of recharge through the unsaturated zone is assumed to be vertical; the dominant migration may occur in fractures of densely welded tuffs and in the matrix of nonwelded tuff, but the mode of fluid flow in these unsaturated systems is undetermined. Limited lateral flow of recharge may occur at horizons where local perched water tables may exist above relatively nontransmissive zeolitized nonwelded tuffs. The pervasive north-northwest-striking fractures may control the direction of lateral flow of recharge, if any, in the unsaturated zone, and certainly that direction coincides closely with the observed southeasterly flow direction in the saturated zone under Yucca Mountain.—Modified book abstract.
Subjects:Ash-flow tuff; Cenozoic; Density; Distribution; Engineering geology; Faults; Fractures; Ground water; High-level waste; Hydrology; Igneous rocks; Interpretation; Miocene; Neogene; Normal faults; Paintbrush Tuff; Permeability; Physical properties; Pyroclastics; Radioactive waste; Site exploration; Strike-slip faults; Surveys; Tertiary; Textures; Theoretical models; Tiva Canyon Member; Topopah Spring Member; Tuff; Unsaturated zone; Volcanic rocks; Waste disposal; Welded tuff; Basin and Range Province; Great Basin; Nevada; Nevada Test Site; North America; Nye County Nevada; United States; Yucca Mountain; Fracture density; Materials, properties; Southern Nevada
Record ID:1984003230
Copyright Information:GeoRef, Copyright 2018 American Geosciences Institute.
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