Oscillatory Hydraulic Tomography at the Field Scale: Boise Hydrogeophysical Research Site

Abstract:

The use of sinusoidal or periodic testing for field-scale tomography of aquifer parameters (conductivity / storativity) is a novel, minimally-invasive method for aquifer characterization between boreholes. Previous results have demonstrated the effectiveness of this method, which we name Oscillatory Hydraulic Tomography (OHT), through both numerical and laboratory experiments. However, implementation and analysis of field-scale OHT testing has not been achieved to-date, and thus the technique remains unproven for application in real-world aquifers. We present an evaluation of OHT at the field scale here through application at the Boise Hydrogeophysical Research Site (BHRS), a field-scale (~20m diameter x 20m thickness) research site. Through Bayesian inversion, we assess issues such as data quality impacts and resolution of obtained tomographic images. We discuss issues associated with both data collection and data processing, and based on our experiences suggest a workflow for OHT performance at other field sites. The advantages of OHT, relative to “traditional” hydraulic tomography with constant rate pumping tests, include the ability to test across a range of stimulation frequencies (obtaining increased heterogeneity information), very high signal-to-noise ratios. Additionally, we examine the impact of nonlinear effects – such as water table boundary conditions – and their impact on OHT analysis algorithms.