What is strange is that normally a water source so close to a major river would flow directly into the river, and never in the opposite direction, Svitana said. But in this case, water flows in both directions. The good thing is that the chemicals never seem to reach the river, because of the opposite flow from the river toward the aquifer. The reason probably has something to do with the subsurface geology of the channels from the old riverbed.
Svitana knew something was odd during his first study of the site, when he inserted monitors in the ground to track the water flow. In one measurement, the water in the aquifer would be flowing in the wrong direction, away from the river. In the next measurement -- only days later -- it would be flowing toward the river again.
He began gathering data from the aquifer twice a week in 1999, and also monitored it continuously for one week in 2004, when the measurements showed that the water changed direction on a scale of hours instead of days.
Larry Krissek, associate professor of geological sciences at Ohio State and Svitanas advisor, said he was surprised to find that the seesaw shifted so quickly in response to a rainfall or a rise in water level in the river.
From my limited experience with groundwater, I knew that groundwater systems respond to surface conditions at timescales of weeks to months, but I didn't realize that the response time could be shortened to hours, Krissek said.
In this case, an important reason for that rapid response is the nature of the subsurface geology, particularly the presence of an old river channel filled with very permeable sands and gravels, he contin
Contact: Kevin Svitana
Ohio State University