HR: 11:10h
AN: H32A-04    [Abstracts]
TI: Heterogeneous Vertical Hydraulic Conductivity in an Aquitard as Determined by Head Profiles and Pumping Tests
AU: * Hart, D J
EM: djhart@wisc.edu
AF: Wisconsin Geological and Natural History Survey, 3817 Mineral Point Road, Madison, WI 53705 United States
AU: Bradbury, K R
EM: krbradbu@wisc.edu
AF: Wisconsin Geological and Natural History Survey, 3817 Mineral Point Road, Madison, WI 53705 United States
AU: Cherry, J A
EM: cherryja@sciborg.uwaterloo.ca
AF: Department of Earth Sciences, University of Waterloo, Waterloo, ON ON N2L 3G1 Canada
AU: Gotkowitz, M G
EM: mbgotkow@wisc.edu
AF: Wisconsin Geological and Natural History Survey, 3817 Mineral Point Road, Madison, WI 53705 United States
AU: Parker, B L
EM: blparker@sciborg.uwaterloo.ca
AF: Department of Earth Sciences, University of Waterloo, Waterloo, ON ON N2L 3G1 Canada
AB: The vertical hydraulic conductivity (Kv) of aquitards is one of the most important parameters in groundwater flow systems but presents special challenges for estimation. It determines the role of the aquitard in a flow system and is a measure of the protection given by the aquitard to underlying aquifers. The properties of aquitards vary vertically and estimates of Kv should reflect this heterogeneity. Vertical head profiles in aquitards show this heterogeneity, and are probably the most important data to be collected in aquitard studies. The heads rarely vary in a linear fashion with depth as would be expected in a homogeneous medium. Instead, most head loss is either at the top or the bottom of the identified aquitard, suggesting that some portion of the aquitard has a much lower Kv than the rest. While this portion is the most effective part of the aquitard, the rest of the aquitard can still present a barrier to flow. We determined the Kv profile of a six-meter thick shaley aquitard, the Eau Claire Formation, by measuring head profiles in, above, and below the aquitard before and during a pumping test. The head profile before the pumping test was measured using three systems: a FLUTe^TM multi-level system with pressure transducers, a short interval straddle packer, and series of buried pressure transducers. All three measurements of heads gave similar profiles. The head decreased 1.5 meters in the upper five meters of the aquitard with most of the head drop, nine meters, occurring over the lower meter of the aquitard. The vertical component of gradient varied by a factor of 30. During the pumping test, the head profiles were measured with the FLUTe system and the buried pressure transducers. In general the two measurement systems agreed but significant differences occurred in the lowest conductivity part of the aquitard. The head profile measured by the FLUTe system showed variation similar to that in the rest of the aquitard while the head measured by the buried transducer varied little. We attribute this difference between the measuring systems to fouling of the buried transducer by the bentonite seal. The best estimate of the Kv profile was determined with a numerical model to match the observed transient response of the FLUTe system to pumping in a well 1000 meters distant. The model was inverted to arrive at the best fit vertical hydraulic conductivities for the aquitard. The discrete flow model allowed us to incorporate the vertical heterogeneity of the aquitard and showed an order of magnitude variation of Kv within the aquitard.
DE: 1828 Groundwater hydraulics
DE: 1894 Instruments and techniques: modeling
DE: 1895 Instruments and techniques: monitoring
SC: Hydrology [H]
MN: Fall Meeting 2005