HR: 0800h
AN: H51A-0335    [Abstracts]
TI: Analysis of Responses From Hydraulic Testing of the Lower Carbonate Aquifer at Yucca Flat, Nevada Test Site, Nye County, Nevada
AU: * Bhark, E W
EM: ebhark@intera.com
AF: Stoller-Navarro Joint Venture/INTERA Incorporated, 7710 W. Cheyenne Ave., Las Vegas, NV 89129 United States
AU: Ruskauff, G
EM: gruskauff@intera.com
AF: Stoller-Navarro Joint Venture/INTERA Incorporated, 7710 W. Cheyenne Ave., Las Vegas, NV 89129 United States
AB: The Yucca Flat corrective action unit extends over an approximately 120 square-mile basin at the Nevada Test Site (NTS), southern Nevada, and was the site for over 650 historical underground nuclear tests. The lower carbonate aquifer (LCA), roughly 1,800 feet below ground surface at Yucca Flat and with a confined thickness of several thousand feet, is the primary aquifer for much of southern Nevada and underlies the full extent of Yucca Flat. Within the last decade, long-term (multiple-day) single- and multiple-well hydraulic tests have been performed to better define aquifer properties over larger scales. The LCA is highly heterogeneous, both laterally and vertically across Yucca Flat, reflecting differences in fracturing and fault density. As such, analysis of the recent testing data requires the consideration of heterogeneous hydraulic properties at multiple spatial scales. Three individual hydraulic tests are presented that portray the marked spatial variability of hydraulic properties related to both local fracturing and basin-scale faulting across Yucca Flat. Two ten-day single-well tests (wells ER-7-1, ER-6-2) and one ninety-day multiple-well test (well cluster ER-6-1) are considered. Interpretive and numerical analyses are based upon the log-log diagnostic plots of drawdown and recovery from pumping, utilizing both the head change and derivative. Heterogeneity is considered using the flow dimension, which represents a variable formation area of flow away from the well, and proves to be a fundamental analytical tool. All hydraulic parameter estimates, including flow dimension, are complete with a measure of uncertainty. The composite interpretation of all data results in a conceptual flow model representative of two spatially continuous scales. At the larger basin (km) scale, the data indicate a fracture- or high permeability strip-dominated flow regime created by fault-related features. Ubiquitous north-south trending faults throughout Yucca Flat appear to act as both (east-west) flow barriers, by juxtaposing permeable and non-permeable formations or otherwise breaking the feature connection, and (north-south) high-permeability conduits. At the local well (tens-of-meters) scale, the response data appear controlled by the local flow geometry within fault blocks. In general, the log-log diagnostics indicate a primary (linear) fracture-flow dominated system, which at intermediate times is fed by the secondary block conductivity (bilinear), until the volume of influence becomes sufficiently large that the flow system is effectively radial. The results are pertinent to basin- and regional-scale flow and transport, and also to hydraulic development of the LCA.
DE: 1828 Groundwater hydraulics
DE: 1829 Groundwater hydrology
DE: 1847 Modeling
DE: 1873 Uncertainty assessment (3275)
SC: Hydrology [H]
MN: Fall Meeting 2005