chnique called electrical resistivity. Current is passed through the soil using a car battery attached to two electrodes embedded in the soil. By using an array of 25 embedded electrodes, and by changing the locations of the current electrodes, voltages can then be measured at different electrodes in the array. Nearly 200 measurements are taken using a single array. "If you know the voltage and current, you can calculate the resistance," Schwartz said.

Different degrees of electrical resistance allows him to identify water, rock, soil, and voids to a depth of about 15 meters and create a model of the subsurface. Schwartz may also be able to determine the water's chemistry by the changes in electrical resistance measured in an aquifer. He explains that sitting or pooled water becomes saturated with minerals while fresh rainwater has a low dissolved mineral content. Fresh water conducts electricity poorly, compared to water loaded with minerals.

Depressions in the bedrock surface can also store contaminants. When rain and runoff pour water through caverns and fissures, the contaminants are flushed out of the depressions and into the aquifer.

Schwartz took advantage of Hurricane Ivan to measure a rapid change in water movement under a sinkhole. "I went out before the hurricane and ran two transects (measurements from lines of electrodes) as a control. I left the electrodes in place then made four measurements as the storm moved through and afterwards." He says he only actually got rained on once.

The resulting two-dimensional computer model showed the changes in water movement. "I saw that water was not sinking evenly or being taken up like a sponge, but that there are preferential flow paths."

Next, he will create a 3-D model by placing the electrodes in a grid, which will allow him to add the direction of water movement to his model. He combines the electrical resistivity measurements with a topographic map of the surface to
'"/>

Contact: Susan Trulove
strulove@vt.edu
540-231-5646
Virginia Tech
1-Nov-2004

Page: 1 2 3
Related biology news :

1. Study finds fecal microbes high in New Orleans sediments following Hurricanes Katrina and Rita
2. Urban sediments after Hurricanes Katrina, Rita contained high levels of contaminants
3. After the Hurricanes
4. Upcoming NJIT conference focuses on Hurricane Katrina, technology, more
5. Book released on Hurricane Isabels effect on Chesapeake Bay
6. Media alert: Special session on the impact of Hurricanes Katrina, Rita on crops, soils, environment
7. NASA sees 2004s Hurricane Charley slice a Florida island
8. An Eye on Katrina: Geoscience Perspectives on a Catastrophic Hurricane at GSA Next Week
9. Hurricane aftermath: Infectious disease threats from common, not exotic, diseases
10. DOEs Office of Science sets up program to aid scientists displaced by Hurricane Katrina
11. NIEHS launches website with information for assessing environmental hazards from Hurricane Katrina