Volume 30, Issue 2 (March 2007)

    Falling-Head Permeability Tests in an Unconfined Sand Aquifer

    (Received 22 February 2006; accepted 19 June 2006)

    Published Online: 2006

    CODEN: GTJOAD

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    Abstract

    This paper examines the reliability of hydraulic conductivity estimates, k, obtained using equations of Hvorslev (1951) or Bouwer and Rice (1976) for falling-head tests in monitoring wells (MWs) having short screens at the bottom of an unconfined sand aquifer. Two issues are examined. First, the equations come from the theory of steady-state flow whereas a variable-head test means transient flow with a changing water table position. This first problem was investigated using a finite element analysis, taking into account the sand capillary retention curve and its saturated-unsaturated permeability. The main result was that the equations can still be used for variable-head tests. The effects of specific storage (elastic deformation of the solid matrix in saturated conditions) and delayed gravity drainage (frequently schematized by a specific yield) can be neglected for these tests. The second issue is how partial clogging or fine particle washing against the screen can influence the k value. This practical problem was investigated by using a surge block to develop MWs and then performing successive permeability tests to assess the effects of development. Before development, the tests provided k values in the range 1 to 12×10-2 cm/s, the average being equal to 2/3 of the large-scale k value obtained using a pumping test under steady-state condition. After development, the tests provided k values that were increased by 50% on average, and thus their mean value became almost equal to the pumping test k value.


    Author Information:

    Chapuis, RP
    Ecole Polytechnique, Department of Civil, Geological and Mining Engineering, Montreal, Quebec

    Dallaire, V
    Ecole Polytechnique, Department of Civil, Geological and Mining Engineering, Montreal, Quebec

    Gagnon, F
    Ecole Polytechnique, Department of Civil, Geological and Mining Engineering, Montreal, Quebec

    Marcotte, D
    Ecole Polytechnique, Department of Civil, Geological and Mining Engineering, Montreal, Quebec

    Chouteau, M
    Ecole Polytechnique, Department of Civil, Geological and Mining Engineering, Montreal, Quebec


    Stock #: GTJ100067

    ISSN: 0149-6115

    DOI: 10.1520/GTJ100067

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    Author
    Title Falling-Head Permeability Tests in an Unconfined Sand Aquifer
    Symposium , 0000-00-00
    Committee D18