USGS Groundwater Information: Branch of Geophysics
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Mapping Aquifer Heterogeneity: Integrated Analysis of Electrical-Resistance Tomography, Tracer Tests, and Hydraulic Data at the Massachusetts Military Reservation, Cape Cod, Massachusetts
As part of OGW Branch of Geophysics (BG) geophysical monitoring research through the USGS Toxic Substances Hydrology Program, electrical-resistivity tomography (ERT) surveys of saline tracer tests in porous media were conducted on the Massachusetts Military Reservation (MMR), Cape Cod, Massachusetts. This is an ongoing project, building on research that was conducted in FY2001.
Accurate characterization of flow and solute transport in groundwater systems is a critical problem in hydrology. Given the large volume of data required to develop an accurate model of subsurface flow and the cost of direct sampling, the use of geophysical methods can contribute significantly to information about the subsurface.
In this experiment, ERT is being explored as a tool to create detailed maps of subsurface flow paths and flow barriers. In addition, systematic procedures for delineating hydraulic conductivity through integrated analysis of multiple data types (including ERT, borehole electromagnetic induction, hydraulic head, tracer concentration, and tracer test travel times) are being tested to provide images of aquifer properties. The goal of the field experiments in FY2002 was to collect data to help constrain three-dimensional flow and transport models of the area.
Field data were collected at MMR during the summer of 2002. ERT was employed in conjunction with a weak doublet saline tracer test. Data were collected in six "planes" parallel and perpendicular to tracer migration via four ERT source and receiver corner-point wells.
The field research is only one aspect of this project, which was conducted in collaboration with researchers from the Geological and Environmental Sciences Department of the Stanford University School of Earth Sciences. Prior to the field experiments, extensive computer analysis and modeling of initial data collected in FY2001 were conducted at Stanford in order to determine the most appropriate field design for research during the summer of FY2002.
Upon conclusion of the field experiments, integration and analysis of the geophysical, hydraulic, and tracer data will be accomplished through geostatistical simulation based on models of ERT and of flow and transport. The product of the project will be a set of conditional hydraulic conductivity realizations conditioned to known histograms, variograms, head data, tracer concentrations and travel times, and soft geophysical data.
This work was funded by the National Science Foundation and the U.S. Environmental Protection Agency, with support from the USGS Toxic Substances Hydrology Program.
This research was conducted by Kamini Singha (Stanford University School of Earth Sciences) with assistance from OGW BG staff.
Singha, K., Binley, A.M., Lane, J.W., Jr., and Gorelick, S.M., 2003, Electrical imaging of tracer migration at the Massachusetts Military Reservation, Cape Cod, in Symposium on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP), April 6-10, 2003, San Antonio, Texas, Proceedings: Denver, Colorado, Environmental and Engineering Geophysics Society, CD-ROM, 11 p.
View the online photo gallery from this project.
For more information about USGS Toxics Substances Hydrology Program research on Cape Cod, see the Toxic Substances Hydrology Program Cape Cod Research Site web site.