Hydrogeological characterization of the South Oyster Bacterial Transport Site using geophysical data

A multidisciplinary research team has conducted a field-scale bacterial tra nsport study within an uncontaminated sandy Pleistocene aquifer near Oyster , Virginia. The overall goal of the project was to evaluate the importance of heterogeneities in controlling the field-scale transport of bacteria tha t are injected into the ground for remediation purposes. Geochemical, hydro logical, geological, and geophysical data were collected to characterize th e site prior to conducting chemical and bacterial injection experiments. In this paper we focus on results of a hydrogeological characterization effor t using geophysical data collected across a range of spatial scales. The ge ophysical data employed include surface ground-penetrating radar, radar cro ss-hole tomography, seismic cross-hole tomography, cone penetrometer, and b orehole electromagnetic flowmeter. These data were used to interpret the su bregional and local stratigraphy, to provide high-resolution hydraulic cond uctivity estimates, and to provide information about the log conductivity s patial correlation function. The information from geophysical data was used to guide and assist the field operations and to constrain the numerical ba cterial transport model. Although more field work of this nature is necessa ry to validate the usefulness and cost-effectiveness of including geophysic al data in the characterization effort, qualitative and quantitative compar isons between tomographically obtained flow and transport parameter estimat es with hydraulic well bore and bromide breakthrough measurements suggest t hat geophysical data can provide valuable, high-resolution information. Thi s information, traditionally only partially obtainable by performing extens ive and intrusive well bore sampling, may help to reduce the ambiguity asso ciated with hydrogeological heterogeneity that is often encountered when in terpreting field-scale bacterial transport data.