How Well the Perfect Layering Model Fits Natural Formations?

The paper discusses the validity of the perfect layering model in the definition of the well capture zone around pumping wells drilled in heterogeneous formations. The relevance of groundwater as source of water supply for both human consumption and agricultural use, makes necessary to set the limits of well head protection areas, whose definition cannot be done apart capture zone delineation. The schematization of the 3-D structure of the spatially random hydraulic conductivity in a simple set of layers each of them of constant properties simplifies noteworthy the computations, but its validity range has to be demonstrated. To reach this goal the travel time statistics in a 3-D heterogeneous domain are numerically achieved by considering different anisotropy conditions of the media. The comparison is posed in the case of a fully penetrating well pumping from an artesian aquifer characterized by a constant piezometric gradient. The results quantify the applicability of the perfect layering model by definition of the mean travel time upper limit for which the differences in the capture zone are negligible among formations with different anisotropy ratios.