HR: 10:55h
AN: H32A-03    [Abstracts]
TI: Estimating Recharge Through a 7-40 m Thick Layer of Fine-Grained Residuum Using Tritium/Helium and CFCs
AU: * McKay, L D
EM: lmckay@utk.edu
AF: The University of Tennessee, Department of Earth and Planetary Sciences, 1412 Circle Drive, Knoxville, TN 37996 United States
AU: Vulava, V M
EM: vulava@utk.edu
AF: The University of Tennessee, Department of Earth and Planetary Sciences, 1412 Circle Drive, Knoxville, TN 37996 United States
AU: Schultz, B
EM: Bryan.Schultz@tetratech.com
AF: Tetra Tech Inc., 800 Oak Ridge Turnpike, Oak Ridge, TN 37830 United States
AU: Bogle, F
EM: Frank.Bogle@tetratech.com
AF: Tetra Tech Inc., 800 Oak Ridge Turnpike, Oak Ridge, TN 37830 United States
AU: Solomon, D K
EM: ksolomon@mines.utah.edu
AF: The University of Utah, Department of Geology and Geophysics, Salt Lake City, UT 84112 United States
AB: A study is underway to compare methods of estimating recharge through residuum derived from weathering of carbonate rocks in southeastern Tennessee. This type of residuum is typically very fine-grained (up to 90% smaller than 2 microns), but can also contain substantial macroporosity due to roots, fractures, chert layers and saprorelicts. In many cases there are also sinkholes or swallets, which can divert runoff directly into the underlying aquifer without passing through the residuum. As a result of the heterogeneity and the potential for bypass flow, there is a great deal of uncertainty about the amount of recharge that occurs through these clay-rich "aquitards" and the degree of protection they provide to aquifers from sources of near-surface contamination. Recharge rates are being estimated for a field site in southeastern Tennessee using conventional Darcy flux calculations based on hydraulic conductivity and hydraulic gradient measurements and using the environmental tracers tritium, helium-3 and CFCs. Recharge estimates from the Darcy flux calculations vary widely because of the large range in hydraulic conductivity values (7×10^-9 to 2×10^-5 m/s) and lack of data on seasonal variations in vertical hydraulic gradient. Samples were collected from 15 wells at the site and are currently being analyzed for tritium, helium-3 and CFCs. We expect these to yield more reliable estimates of recharge through the residuum than the Darcy calculations, because tracer concentrations are indicative of transport from the water table to the monitoring point, and hence "integrate" the influence of spatial or temporal variations in hydraulic conductivity and hydraulic gradient.
DE: 1829 Groundwater hydrology
DE: 1830 Groundwater/surface water interaction
DE: 1832 Groundwater transport
DE: 1875 Vadose zone
DE: 4924 Geochemical tracers
SC: Hydrology [H]
MN: Fall Meeting 2005