Geophysical Investigations at Toxics Program Study Sites
Task Contact: Jeffrey Lucius
The objectives of this project are to characterize shallow stratigraphy and vadoze and saturated zone hydrology, and to interpret and model geophysical measurements to provide quantitative hydrogeologic information.
In 2011, several EM data sets need to be processed and integrated with existing resistivity data to increase our understanding of the EM methods and to refine the initial geologic framework created in 2010. We will continue to include new core descriptions, Geoprobe property measurements, and improved spatial analysis in refinements of the geologic framework. We plan to renew our GPR and very-shallow seismic investigations. The GPR could be useful at the leading edge of the leachate front to understand potential pathways. The seismic work would help us refine our data collection and processing techniques, to provide depth to bedrock information between existing wells for hydrologic modeling, and possibly to predict hydrologic information. In addition, GPR, resistivity, and seismic data can be combined to produce a greater understanding of lithology and hydrogeologic properties than the methods used independently of each other.
Noman, OK Municipal Landfill
In April 2007 we renewed our investigations at the Norman, OK Municipal Landfill using 2-D multi-electrode electrical resistivity surveys, both galvanic and capacitive coupling, and EM induction surveys to determine depth to bedrock, variations in alluvium lithology, and vertical stratification and lateral extent of contaminants. In April 2008, we conducted additional 2-D resistivity surveys in order to produce more realistic cross sections and 3-D images of the near subsurface. In 2009, analyses and interpretations of the 2007 and 2008 resistivity data were completed.
- Electrical conductivity maps, developed from electromagnetic (EM) induction and dc resistivity measurements, showing lateral extent of ground water contamination around the landfill.
- Development of a seismic refraction survey method to explore the landfill itself.
- Multi-electrode DC resistivity survey, which helped to better characterize the alluvium and leachate plume.
- Creation of multiple databases from Geoprobe sediment conductivity logs and core descriptions.
Amargosa Desert Research Site (chemical and low-level radioactive waste storage facility)
For the Armagosa Desert Research Site (ADRS), NV waste storage facility, in 2008 a new, large trench was excavated at site. For 2009 work, this presents an opportunity to compare the exposed lithology to models of resistivity data previously collected adjacent to the trench.
- Conventional and multi-electrode dc resistivity surveys on and near the site have helped to better characterize the near-surface and deeper unconsolidated sediments for the hydrologic investigations.
- A seismic refraction survey was conducted near the SE corner of the site using three different sources. The data are still being processed and interpreted, but preliminary results possibly indicate a fault in the sediments.
- GPR data were collected in a dense grid and used to construct a GPR "volume" on part of the site. Additional studies of the soils themselves are needed to better interpret the reflectors seen in the data.
Bemidji, MN Oil Pipeline Spill Research Site
- Papers delivered presenting results of electrical and GPR investigations with respect to detectability of the crude oilcontaminated areas.
- Seventeen-fold GPR data collected near the south oil pool have been analyzed to determine 300 MHz antenna radiation patterns and to construct a GPR velocity profile, in order to determine the efficacy of multi-fold GPR data to directly detect oil contamination in the subsurface. The results were published in a MS thesis.
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