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British Geological Survey, Maclean Building, Crowmarsh Gifford, Wallingford OX10 8BB, UK
Large-diameter hand-dug wells are used to exploit the weathered zone aquifer of hard rock areas. A pumping test is described which is suitable for such dug wells. This test can be diagnostic of aquifer type and hydraulic properties.
Four techniques are described which can be used to interpret the pumping test. The first technique uses a digital model to simulate aquifer conditions and to reproduce changes in well water level observed during the test. Multi-layered conditions and partial penetration of the dug well can be simulated providing radial symmetry pertains. Two techniques are then described which require only manual calculation. In both these cases the aquifer is assumed to be single-layered but in one the aquifer is assumed to be confined and in the second it is unconfined. The fourth technique uses software developed for use on a personal computer. The software simulates a leaky aquifer and automatically determines the hydraulic parameters of the two layers of the leaky system using a least-squares technique. Finally, a week-long test is described which can be used to predict empirically the long-term behaviour of both dug and collector wells.
