HR: 1340h
AN: H23A-1007    [Abstracts]
TI: Hydromechanical response characterization by integration of geophysical and hydrological data, San Lorenzo, California
AU: * Sneed, M
EM: micsneed@usgs.gov
AF: U.S. Geological Survey, 3020 St. Univ. Dr. E, Ste. 4004, Sacramento, CA 95819, United States
AU: Borchers, J W
EM: jborcher@usgs.gov
AF: U.S. Geological Survey, 6000 J St., Sacramento, CA 95819, United States
AU: Kayen, R E
EM: rkayen@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AU: Carkin, B A
EM: bcarkin@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AU: Ellett, K M
EM: kellett@usgs.gov
AF: U.S. Geological Survey, 6000 J St., Sacramento, CA 95819, United States
AU: Wheeler, G A
EM: gwheeler@usgs.gov
AF: U.S. Geological Survey, 6000 J St., Sacramento, CA 95819, United States
AU: Brocher, T M
EM: brocher@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AB: A deep (317 m) borehole constructed with 6 piezometers was drilled adjacent to a dual-stage extensometer (under construction) near the modern San Francisco Bay shore in San Lorenzo, California for the purpose of monitoring pore-fluid pressure changes that may result from a proposed aquifer storage and recovery (ASR) program. Continuous lithological and geophysical logging of the borehole along with discrete measurements of vertical hydraulic conductivity and of consolidation from selected core samples characterizes the distribution of properties controlling the aquifer-system response to stress. Characterizing the distribution of these properties will contribute details to the analysis of the bulk deformation measured by the extensometers. The lithologic and geophysical logs collected at the site generally indicate unconsolidated to partly consolidated continental and marine alluvial deposits consisting mostly of silt and clay, but include three coarse-sand and gravel layers totaling nearly 30 m between 155 and 198 m below land surface. A shear- and compressional-wave suspension log of the uppermost 30 m indicated the shear-wave velocity is 209 m/s, classifying it as a National Earthquake Hazards Reduction Program Class D site that can be expected to amplify strong ground motions by a factor of 2.4 for low (0.1 g) spectral accelerations. Pore-water chemistry (representing the water released from compaction if clay beds compact in response to ASR activities) was characterized and subsequently synthesized for use in saturated vertical hydraulic conductivity measurements; in general, the resulting vertical conductivity values decrease with depth and range from 0.0004 to 24 cm/d (geometric mean of 0.04 cm/d). Low overconsolidation ratios measured from consolidation tests reveal the sediments are normally consolidated; the compression indices indicate that the elastic and inelastic specific storage values generally decrease with depth and range from 1.8x10-5 to 1.9x10-4 m-1 and from 2.5x10-4 to 2.8x10-3 m-1, respectively. The property-distribution information derived from geophysical and hydrological data is valuable for characterization of the hydromechanical response from both natural and ASR-induced stresses, which will aid in understanding the composite depth-integrated measurements from nearby extensometers.
DE: 1822 Geomechanics
DE: 1829 Groundwater hydrology
DE: 1835 Hydrogeophysics
DE: 1859 Rocks: physical properties
DE: 5114 Permeability and porosity
SC: Hydrology [H]
MN: 2007 Fall Meeting