Journal Published Online: 12 July 2006
Volume 30, Issue 2

Falling-Head Permeability Tests in an Unconfined Sand Aquifer

CODEN: GTJODJ

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, Canada
Dallaire, V
Ecole Polytechnique, Department of Civil, Geological and Mining Engineering, Montreal, Quebec, Canada
Gagnon, F
Ecole Polytechnique, Department of Civil, Geological and Mining Engineering, Montreal, Quebec, Canada
Marcotte, D
Ecole Polytechnique, Department of Civil, Geological and Mining Engineering, Montreal, Quebec, Canada
Chouteau, M
Ecole Polytechnique, Department of Civil, Geological and Mining Engineering, Montreal, Quebec, Canada
Pages: 9
Price: $25.00
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Stock #: GTJ100067
ISSN: 0149-6115
DOI: 10.1520/GTJ100067