New Approaches In Hydrogeophysical Model Predictions: Case Studies From theP Reactor Area, Savannah River Site, South Carolina

The shallow subsurface of the earth is an extremely important geologic zone, one that yields much of our water resources, supports our agriculture and ecosystems, and influences our climate. Indeed, this zone also serves as the repository for most of our municipal, industrial, and governmental wastes and contaminants, intentional or otherwise. Many agencies and councils have recently described the urgent need to more fully develop tools and approaches that can be used to characterize, monitor, and investigate hydrogeological parameters and processes in the shallow subsurface at relevant spatial scales in a minimally invasive manner. Near-surface geophysical methods hold the potential to provide qualitative and quantitative information about subsurface hydrogeological parameters and/or processes. This research examines the advantages and challenges associated with the applicability, performance, and hydrogeological parameter estimation using surface and borehole ground penetrating radar (GPR), P-wave seismic reflection, and electrical resistivity tomography (ERT) data collected at a contaminant site located in the vicinity of the P Reactor at Savannah River Site, South Carolina. These near-surface geophysical methods provide information at different scales of resolution, making it difficult to model the heterogeneity of the shallow subsurface. However, this research demonstrates that the combined use of these methods, calibrated with cone penetrometer testing (CPT) data, can achieve the desired result, which is a more accurate geologic model. Historically, the P-waves have been the type of seismic waves used in near-surface seismic applications. However, this research validates that surface waves collected during high resolution seismic surveys can be useful to predict hydrogeological parameters and provide additional valuable information about the shallow subsurface. Finally, the application of geostatistical techniques demonstrates that the combination of geophysical data at different levels of resolution with conventional borehole data significantly improves the spatial predictions of hydrogeologic parameters (i.e. porosity) in heterogeneous media