We investigate if a mean equivalent flow model can be defined to describe hydraulic head variations in a crystalline aquifer characterized by multiscale heterogeneity. We analyzed in particular the hydraulic response of a crystalline aquifer to pumping tests covering a large range of spatial and temporal scales. Pumping tests appear to be well designed to test the medium hydraulic properties and to track scaling effects, since the perturbation induced by pumping grows with time and samples increasingly large volumes. We tested well-test interpretation frameworks underpinned by equivalent media models that basically contain scaling information. Interpretations of drawdown time series, recorded in piezometers located at distances ranging from 2 to 400 m from the pumping well and of durations ranging from 5 to 90 days, show that the temporal evolutions of drawdown are well modeled by fractional flow models <Barker, 1988; Acuna and Yortsos, 1995>. Estimates of flow dimensions are consistent across the whole site and lie in the range <1.4--1.7>. To investigate the nature of diffusion, we defined a methodology based on the evolution of the characteristic time or amplitude of hydraulic head variations with the distance from the pumping well. For most of the piezometers, those aligned along the main fault, it is possible to define a scaling law for all piezometers with a unique set of parameters. The derived exponents imply that hydraulic head diffusion is anomalously slow, a characteristic that is taken into account only in the model of Acuna and Yortsos <1995>, based on diffusion in fractals.