Well catchments estimation in heterogeneous aquifers with a stratified model

In natural formations the porous media heterogeneity influences the capture zone delimitation and considerable differences can result from the homogenous case. In the last decade several approaches were proposed to solve the problem, but generally they necessitate of the improbable knowledge of the aquifer’s statistical properties. In the note a method is proposed to delimitate wellhead protection areas in a bounded artesian aquifer where hydraulic conductivity is assumed as a spatially homogeneous random function. To give a probabilistic estimation of well catchments, we suggest that the 3-D aquifer can be suitably represented by a perfectly stratified model that is defined by the use of three parameters only: the expected value and the variance of the hydraulic log-conductivity, and the constant thickness of aquifer’s layers. While the log-conductivity expected value is derived from a standard pumping test, to define the variance and a proper number of layers, a multilevel tracer test has to be developed. To validate the proposed method pumping and tracer tests were developed in a fully 3-D synthetic aquifer and experimental results are processed to define the stratified model’s parameters. Isotropic and anisotropic conditions characterized by low and moderate hydraulic log-conductivity variance are investigated. In all cases the well catchment and time-related capture zones obtained by the suggested approach fit quite well the corresponding areas that can be recognized in the synthetic aquifer.