Imaging the hydraulic properties of a contaminated alluvial aquifer perturbed with periodic signals
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PAPER
Imaging the hydraulic properties of a contaminated alluvial aquifer perturbed with periodic signals P. Fischer 1 & T. De Clercq 2,3 & A. Jardani 2 & L. Thannberger 3 & N. Massei 2 & M. Abbas 4 Received: 10 March 2020 / Accepted: 19 August 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Imaging characterization of a heterogeneous alluvial aquifer at a decametric scale is presented. The characterization relies on responses to oscillatory pumping tests led in two different wells and at two different periods of oscillation (5 and 10 min). These specific oscillatory responses are extracted from the hydraulic pressure values, measured in 13 boreholes during the pumping tests, through a data processing procedure. Then, a deterministic inversion process, led with a two-dimensional hydraulic properties model, aims to reproduce this set of oscillatory responses, in a frequency domain, by optimizing the distribution of the property values in the model. Two inversion processes are led separately with each set of responses corresponding to the two periods of oscillation used, and one joint inversion is led with the set of all responses together. The inversion results image the heterogeneities in the distribution of the field properties. The results suggest that longer periods of oscillation (in this case 10 min) permit characterization of larger areas around the pumping wells. In contrast, shorter periods (in this case 5 min) propagate more readily in the conductive zones near the pump and provide less information for the less conductive areas. Therefore, it appeared that performing a joint inversion, combining the information carried by the responses to both periods, provided more information on the heterogeneous distribution of the field properties and resulted in better constrained property maps than the ones obtained from separate inversions. Keywords Oscillatory pumping test . Periodic signal . Inverse modeling . Characterization . France
Introduction The assessment of subsurface hydraulic properties at field scale is a critical step for the selection and the implementation of an effective remediation protocol for contaminated aquifers. Generally, estimates of these properties (mainly transmissivity and storativity) are obtained from the analysis of measured hydraulic signals in response to extraction of water from a pumping well (Butler 2005; Batu 1998; Neuman and
* P. Fischer [email protected] 1
HydroSciences Montpellier, Univ. Montpellier, CNRS, IRD, Montpellier, France
2
Normandie Univ, UNIROUEN, UNICAEN, CNRS, M2C, 76000 Rouen, France
3
VALGO, 76650 Petit Couronne, France
4
School of Engineering, Lebanese International University, Beirut, Lebanon
Witherspoon 1972; Le Borgne et al. 2004; Li et al. 2008; Wen et al. 2010). The interpretation of pumping tests can be made with an analytical model of the groundwater flow equation, with the assumption of homogeneity, to deduce averaged values of these properties (Sanchez-Vila et al. 1999), or by using hydraulic tomogr
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