College of Natural Sciences - Seminar (PRO-SEM)

Geological characterization of aquifers is an important step in ground
water resource development and assessment as well as in understanding
the impact of ground water pollution. Traditionally, many wells are
drilled into a site to investigate the hydraulic properties and the
distribution of pollutants. These wells provide detailed information
about the subsurface conditions. However, this information is limited
in spatial extent to the region adjacent to the borehole.
Additionally, wells provide potential conduits for pollutants into
protected aquifers. Geophysics can extend the information from wells
to two- or three-dimensions. Furthermore, geophysical surveys can
reduce the number of wells necessary to characterize the subsurface,
thus reducing futher potential contamination and reducing costs due to
expensive drilling.

I will present two different investigative methods that use Ground
Penetrating Radar to characterize the upper 20 meters of a shallow,
unconfined aquifer. The site, the Boise Hydrogeophysical Research
Site, in Boise, Idaho consists of coarse grained alluvium deposited
along the Boise River. The site has been developed to study ground
water issues and contains 18 wells drilled to depths of about 20
meters to allow access for hydrological and geophysical studies.
First, I will provide background about the site and a goal for the
geophysical site characterization. I will show data and an
interpretation from a surface reflection survey. Reflection methods
provide detailed stratigraphic or structural images of the subsurface.
The second method, tomography, provides detailed images of the radar
velocity distribution in the subsurface. The radar velocities can then
be converted to other parameters more relevant to hydrological
studies. Hopefully, this talk will convince you of the important ways
geophysical surveys can contribute to geological studies of the
subsurface.