Toxics Geophysics Project

Geophysical Investigations at Toxics Program Study Sites

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Task Objectives

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.

Task Statement of Work

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. In Fiscal Year 2008, we plan to finish interpretation and publication of the Fisal Year 2007 results. In Spring 2008, we plan to conduct 3-D resistivity surveys in order to produce more realistic cross-sectional and 3-D images of the near subsurface, including, for example, depth to bedrock, variations in alluvium lithology, and vertical stratification and lateral extent of contaminants. The work in Fiscal Year 2007 verified that the electrical and electromagnetic methods can detect and map the leachate. However, additional investigation is required to detect the leachate at lower concentrations and to map contaminant pathways.

In 2008, a new, large trench is scheduled for excavation at the Armagosa Desert Research Site (ADRS), NV waste storage facility. This presents an opportunity to collected GPR and resistivity data near the trench, and to compare inversions of the data to the exposed lithologies. A site visit is tentatively planned for spring 2008.

Past Accomplishments with the Toxics Program

This project began in the mid 1980's and has involved numerous scientific investigations at multiple field sites. The most recent accomplishments at the current active field sites are listed below.

Norman, OK Municipal Landfill

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.

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. Additional work with this data is still being performed.

Amargosa Desert Research Site (chemical and low-level radioactive waste storage facility)

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.

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