Characterizing well connectivity in fractured bedrock using periodic hydraulic tests

Harmonic hydraulic tomography experiments were conducted in a five-spot pattern well cluster completed in a single bedding plane fracture at the Altona Flat Rock site. Harmonic aquifer tests are performed by creating a periodic head disturbance in one well and observing the phase shift and attenuation of the head response in a monitoring well. If both discharge and pressure effects are known at the source well, transmissivity (T) and storativity (S) may be inverted independently from the frequency spectrum of head response. Harmonic tests are particularly effective in bedrock systems because the small storage capacity promotes propagation of the harmonic signal over larger distances compared with unconsolidated media, More importantly, the hydraulic diffusivity, T/S, measured in hydraulic tomography tests, has been shown to be a better predictor of hydraulic connectivity and solute transport than T alone. The harmonic tests hold potential, therefore, as a useful tool for predicting well connectivity.