Vertical heterogeneities of hydraulic aquitard parameters: preliminary results from laboratory and in situ monitoring

A borehole is developed in a shallow multi-layered aquifer and used to derive the porosity, specific storage and hydraulic conductivity of the aquitard. Local values of hydrodynamical parameters are estimated from petrophysical analysis of core samples, and the empirical relationship between porosity and permeability. Vertical diffusivity is determined from the response of the aquitard to a loading cyclic signal using pressure records at different depths. Hydraulic conductivities deduced from the petrophysical analysis ranged from 10(8) to 10(10) m s(1) and are comparable with those of facies of marine/lacustrine clay observed in samples. The permeability values calculated based on diffusivity are within the range 10(9) to 10(11) m s(1) with a quasi-systematic bias of one order of magnitude. These values are average for a larger part of the aquitard and correspond to an integrated value. The methodology retained for the aquitard characterization is discussed with emphasis on the implications for the management of a complex aquifer system.