Fig. 8. (a, b) Variation of the piezometric levels vs. time in the vicinity of the pumping well. (c, d) Variation of the electrical potentials vs. time in the vicinity of the pumping well. In both cases, the fit corresponds to a decreasing exponential function exp(–t/), where t is time and is a relaxation time (see main text). Note that the relaxation time is the same for both the electrical and the hydraulic signals in the vicinity of the pumping well (results from Exp. 1).