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