HR: 1340h
AN: H23G-1688    [Abstracts]
TI: Analyzing pumped-well impeller logs to ascertain vertical hydraulic conductivity variations
AU: * Parker, A H
EM: a.parker@see.leeds.ac.uk
AF: School of Earth and Environment, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, United Kingdom
AU: West, J
AF: School of Earth and Environment, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, United Kingdom
AU: Odling, N E
AF: School of Earth and Environment, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, United Kingdom
AU: Bottrell, S H
AF: School of Earth and Environment, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, United Kingdom
AB: Horizontal variations in the hydraulic conductivity of aquifers are generally well characterized through simple pump test analyses. However, vertical variations are often poorly understood and misrepresented in the regional models used by regulatory bodies and water companies. Understanding these is key for predicting flow paths and hence the behavior of contaminants in the aquifer that might present a risk to public drinking water supplies. Traditionally, packer tests were used to characterize these variations, but they can be time consuming and costly to perform. However, other techniques have been developed which can quantify these variations, including impeller logging. This study aims to present new, more rigorous methods of analyzing impeller flow log data. Impeller logs were taken under pumped conditions in open wells in a chalk aquifer located in N. England. Theoretically, hydraulic conductivity can be obtained from the gradient in flow rate with depth. However, data are typically noisy due to turbulent flow and hole diameter variations with depth; so directly converting the flow rate gradient to hydraulic conductivity leads to rapid non-physical variation and negative hydraulic conductivity values. Correcting for hole diameter variations using caliper logs proved difficult due to phenomena such as jetting, whereby when the water enters a widening, it does not instantly slow down. In order to obtain more realistic hydraulic conductivity profiles, we firstly tried a data smoothing algorithm, but this approach distorted the data and still gave an unacceptable noise level. Instead, a layered modeling approach has been developed. A hydraulic conductivity profile consisting of a discrete number of uniform layers is constructed, and layer thicknesses and hydraulic conductivities are varied until a satisfactory fit to the observed flow log is achieved. Results from field sites on the confined Chalk aquifer of East Yorkshire in the United Kingdom showed good correlation to packer test analysis. The absence of significant ambient flows at this test site made the final analysis relatively simple. By testing boreholes across the aquifer a pattern of hydraulic conductivity variation with depth can be established, and compared to the proposed geological and climatic reasons for the variations' existence.
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 1835 Hydrogeophysics
DE: 1859 Rocks: physical properties
DE: 1895 Instruments and techniques: monitoring
SC: Hydrology [H]
MN: 2007 Fall Meeting