Old riverbed keeps chemicals from entering Ohio River
DENVER -- A long-dry riverbed in northeastern Ohio is preventing a pool of chemical waste from infiltrating the Ohio River, geologists have found.
The finding may call into question the need to clean up similar chemical waste sites. It also indicates a previously unknown interaction between an underground aquifer and the nearby Ohio River.
Beneath sand and gravel on the grounds of Barium and Chemical Inc. in Steubenville, OH, lies an aquifer that contains chemicals such as nitrate and barium that the company dumped there when such dumping was still legal, before the 1980s. The company is now working with the United States Environmental Protection Agency to clean up the site, so that the chemicals wont enter the Ohio River -- which provides water to many local towns.
In 1992, the company asked Kevin Svitana, then an independent hydrology consultant, to study the site and determine how the cleanup should proceed. The site proved unusual, in that chemicals in the underground pool didnt flow into the river as he had expected.
Ever since, Svitana has tried to figure out why. He continued monitoring the pools strange behavior after becoming a doctoral student in geological sciences at Ohio State University in 2002.
Wednesday, at the Geological Society of America meeting in Denver, Svitana reported that he may have uncovered part of the answer: Ohio River water flowing into old troughs, or paleo-channels, beneath the former position of the river is forcing the pool to remain trapped within those channels and away from the present-day river.
The question now is, will the chemical pool stay in place, so that the company may use a natural attenuation approach to the cleanup? he said.
The river deposited sand and gravel above the aquifer more than 10,000 years ago, before the rivers path shifted almost a mile to the east, explained Svitana.
He found that the dry riverbed is still linked to the present-day Ohio River by old channels filled with sand and gravel that lie beneath the surface. Water flows between the buried aquifer and the present-day river in a kind of seesaw motion -- with the chemical pool caught in-between.
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 continued. As a result, this study clearly demonstrates the importance of the subsurface geology in affecting the speed and direction of groundwater flow.
Using a computer model, Svitana matched the shifts in the seesaw effect with rainfall and river rise in the area. He even determined that the raising and lowering of water levels in the shipping locks under a nearby bridge created waves that jostled the aquifer.
But over the course of this study, a flow from the river has always been balanced with a counterflow from the aquifer that keeps the chemicals in place.
Svitana wants to do more computer modeling to understand exactly what makes site capable of trapping the chemicals in this way. If the seesaw effect is not unique to the immediate area, it may help geologists understand other dumping sites along the river.
Krissek would like to see Svitanas studies repeated in similar settings to answer further questions.
For example, is there a critical buried channel size or depth, or a critical distance away from the major surface water source at which this rapid linkage to the groundwater system breaks down? Krissek asked.
Krissek has no connection to Barium and Chemicals, Inc. The company paid for the water monitoring equipment, and Svitana still does consulting work for the company during his breaks from the university.
Source: Eurekalert & othersLast reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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