HR: 0800h
AN: H11C-0311    [Abstracts]
TI: Hydraulic Characterization using InSAR and Nuclear Devices
AU: * Halford, K J
EM: khalford@usgs.gov
AF: U.S. Geological Survey, 333 W. Nye Ln, Room 203, Carson City, NV 89706 United States
AU: Laczniak, R J
EM: rlaczni@usgs.gov
AF: U.S. Geological Survey, 160 N. Stephanie St., Henderson, nv 89074 United States
AU: Galloway, D
EM: dlgallow@usgs.gov
AF: U.S. Geological Survey, Modoc Hall, CSUS 3020 State University Drive East, Rm. 3005G, Sacramento, CA 95819 United States
AB: The tuff-pile unit, a series of air-fall tuffs, has been used extensively for nuclear testing at the Nevada Test Site. Confined water levels in the tuff-pile unit have been elevated more than 500 m because of nuclear testing beneath the water table. Measured water levels and land-surface subsidence suggest that the tuff-pile unit has been slowly depressurizing since nuclear detonations ceased in 1992. Spatial and temporal distributions of subsidence were estimated between 1992 and 2002 using Interferometric Synthetic Aperture Radar (InSAR) methods. Broad subsidence features over the tuff-pile unit are attributed to delayed-poroelastic deformation as pressurized fluids drain from the tuff-pile unit to the overlying water table and underlying carbonate aquifer. A hydraulic conductivity of 3x10$^{-6}$ m/d and a specific storage of 9x10$^{-6}$ m$^{-1}$ were estimated by fitting results from cross-sectional and three-dimensional MODFLOW models of the tuff-pile unit to measured water-levels and land-subsidence rates. The MODFLOW estimates are similar to a geometric mean hydraulic conductivity of 8x10$^{-6}$ m/d from 16 "slug-test" analyses of drilling recovery. Results from all methods support the delayed-poroelastic hypothesis.
DE: 3210 Modeling
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1894 Instruments and techniques
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting