HR: 1340h
AN: H33B-0468    [Abstracts]
TI: Properties of Flow Zones in Fractured Rock
AU: * Salve, R
EM: R\_Salve@lbl.gov
AF: Lawrence Berkeley National Lab., MS 14R0108 One Cyclotron Road, Berkeley, CA 94720 United States
AB: Observations over the last 25 years from various field studies suggest that preferential flow is common in soils and rocks. Despite this realization, very little is known about the large-scale properties (e.g., structure, distribution, continuity) of such flow regimes. This information is important for predictive models, but it remains elusive, mainly because of the difficulties involved in characterizing flow that has substantial spatial (both vertical and horizontal) and temporal variability. To better understand preferential flow in fractured rock, we carried out an in situ field experiment in the Topopah Spring tuff found in Exploratory Studies Facility at Yucca Mountain, Nevada. This experiment involved the release of ~22 m3 of ponded water (at a pressure head of ~0.04 m) over a period of 7 months, directly onto a 12 m2 infiltration plot. As water was released, changes in moisture content were monitored along horizontal boreholes located in the formation ~19-22 m below. Distinct flow zones, with significant differences in flow velocity, size, and extent of lateral movement, intercepted the 6-9 m long monitoring boreholes. Further, in some flow zones saturation levels persisted for the time period in which water was released, while in others there were periodic fluctuations. There was also evidence of water being diverted above the ceiling of a cavity in the immediate vicinity of the monitoring boreholes. Observations from this field experiment suggested that inconsistencies exist in present conceptual models of flow in fractured rock. Particularly, these observations suggest that isolated conduits within the fractured rock formation encompass a large number of fractures to form preferential flow paths that persist if there is a continuous supply of water. It appears that in fractured welded tuffs, the propensity for vertical dispersion and fracture-matrix interactions may be significantly greater than suggested by existing conceptual models. These observations indicate that refinements in the understanding of flow and transport in fractured, welded rock may be realized through additional field investigations conducted at spatial scales of tens of meters. This work was supported by the Director, Office of Civilian Radioactive Waste Management, U.S. Department of Energy, through Memorandum Purchase Order EA9013MC5X between Bechtel SAIC Company, LLC, and the Ernest Orlando Lawrence Berkeley National Laboratory (Berkeley Lab). The support is provided to Berkeley Lab through the U.S. Department of Energy Contract No. DE-AC03-76SF00098.
DE: 1832 Groundwater transport
DE: 1875 Unsaturated zone
DE: 1894 Instruments and techniques
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting