Geophysical Investigations at Toxics Program Study Sites

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.

Noman, OK Municipal Landfill
Armagosa Desert Research Site
Bemidji, MN Pipeline Spill Research Site

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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, we plan to publish our analysis and interpretations of the FY 2007 and FY 2008 resistivity data, and to develop a 3-D site conductivity model that includes GEOSED data. In addition, we plan to continue our multidiscipline investigation to better characterize the alluvium and leachate plume using resistivity measurements, EM induction, and data from boreholes and Geoprobe sampling. In particular, we propose to jointly interpret co-located geo-hydrologic borehole and Geoprobe data and surface geophysical data with the goal of transforming the measured geophysical properties into hydrogeologic properties. This work will build on the previous investigations of others to define hydrostratigraphic units at the site.

Recent Accomplishments

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.

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.

Recent Accomplishments

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 be 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

Accomplishments

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. Additional work with this data is still being performed.

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