Characterization of the Hydrogeological Experimental Site of Poitiers (France) by stochastic well testing analysis

We assess the applicability and performance of the stochastic well testing methodology of Neuman et al. [Neuman, S.P., Guadagnini, A., Riva, M., 2004. Type-curve estimation of statistical heterogeneity. Water Resources Research 40, W04201. doi:10.1029/2003WR002405, Neuman, S.P., Blattstein, A., Riva, M., Tartakovsky, D.M., Guadagnini, A., Ptak, T., 2007. Type-curve interpretation of late-time pumping test data in randomly heterogeneous aquifers. Water Resources Research 43, W10421. doi:10.1029/2007WR005871] to provide a geostatistical characterization of the transmissivity distribution of a heterogeneous aquifer. We use cross-hole pumping test information (also referred to as interference testing) collected during two extensive and detailed experimental campaigns performed in 2004 and 2005 in a limestone aquifer constituting the Hydrogeological Experimental Site (HES) of Poitiers, France. The methodology we use is based on stochastic type-curves of mean drawdown and associated variance and is aimed at revisiting the results of routine pumping tests within a stochastic framework. It allows estimating the geometric mean, integral scale, and variance of local log-transmissivities on the basis of quasi-steady state head data when a randomly heterogeneous confined aquifer is pumped at a constant rate. The results are discussed by comparison against (a) previous deterministic analyses performed at the site using the same dataset and (b) information obtained by geostatistical analysis of existing geophysical data. The estimated values of integral scales and variance of log-transmissivity are viewed in light of multiscale theories which conceptualize the heterogeneity of porous and fractured systems as hierarchical random processes distributed across a multiplicity of scales. The scale dependence observed for the estimated variogram parameters of log-transmissivity at the HES site is consistent with the behavior of published worldwide data.