Analysis of divergent flow tracer tests in fractured granite, near Oracle, Arizona

Abstract

A computer model is extended and applied to analyze divergent flow tracer test data from a field experiment near Oracle, Arizona. The model can accommodate a pulse, step increase, and an arbitrary distribution of injection concentration with respect to time. The model is tested against three analytical solutions and is subjected to sensitivity analyses. The model is free of numerical dispersion with proper grid spacing and location of the external boundary. Analysis of field data using the model involves a curve matching procedure. An equivalent radial flow field is used to account for non-radial flow conditions by adjusting the flow rate and the mass that enters the flow field. Application of the model to field data yields a longitudinal dispersivity of 5.08 meters and a product of effective porosity and thickness of 0.009 meters. Since the test was not conducted under strict flow conditions, the above results are considered tentative.