Tracking down an elusive toxin

Tool: A hydrogeologist is attempting to develop a computer model to help find the source of a water contaminant and to determine how best to clean it up.

January 16, 2001|By Rona Kobell | Rona Kobell,SUN STAFF

Grant Anderson is used to quizzical looks when he tells people he does modeling for a living.

But the balding, bespectacled hydrogeologist isn't kidding. For five years, Anderson has been developing ground water models for the Army Corps of Engineers - complex, computer-generated formulas to determine the direction of water flow.

The ground water model he's customizing for Fort Meade has been in development for more than a year.

"It is a very imperfect tool," Anderson said. "But it is the best tool we have."

Officials at Fort Meade asked the corps to develop the ground water model after the military base was placed on the EPA's Superfund list of top cleanup priorities in 1998. The model was in its development when a 1999 sampling of a ground water monitoring well near the edge of the Army base turned up traces of carbon tetrachloride, a rarely used solvent once common in dry cleaning, auto-parts cleaning, fire extinguishers and insecticides.

High exposure to carbon tetrachloride can damage humans' livers, kidneys and central nervous systems. And though officials maintain that public health is not threatened and that the chemical has not seeped into drinking water, the discovery prompted Anderson to step up his efforts.

In the past two months, he's dove into the data, sifting through details such as monitoring well readings, water measurements and the consistency of raw materials on the base. In all, the model will examine 140,454 numerical elements-so data-intensive that he'll have to use a corps computer in Philadelphia to find enough memory for the final model. The hope is to glean potential sources for the solvent, as well as the best course for cleanup.

He gave the public its first glimpse of the model's features last week in a presentation to Fort Meade's Restoration Advisory Board, a citizen watchdog group that monitors the site's cleanup. The group has been concerned about the carbon tetrachloride since its October meeting, when Fort Meade officials first mentioned its discovery.

Fort Meade environmental engineer Jim Gebhardt joined Anderson in reminding the group that there are no quick answers to the carbon tetrachloride mystery.

The chemical's appearance is vexing to state and federal environmental officials because the well in which it was found is north of an old post landfill, in the opposite direction of ground water flow. For that reason, officials consider the landfill an unlikely source.

The same is true for the base's laundry facility. Its now-closed dry cleaner produced 400 pounds a month of perchloroethylene sludge waste in 1991, according to permits filed with the Maryland Department of the Environment. Perchloroethylene is a less toxic dry-cleaning byproduct than carbon tetrachloride, which Gebhardt said was never used at the laundry.

Such dead ends have left Gebhardt and others to pore over old maps in hopes of finding a long-shuttered business that used the solvent.

That could also be tricky. Carbon tetrachloride has had so many uses that Anderson has dubbed it "the solvent for all seasons." At the height of its popularity in the 1950s, few knew of its harmful effects. When it was time to dispose of it, Anderson said, "they would just say, `Go find a sandy area and pour it in the ground.'"

The chemical was found 110 feet into the Lower Patapsco Aquifer, the third water level of the four-level aquifer that supplies water to the area. Each water level is separated by a layer of clay and gravel. No chemical was found in higher layers used for drinking water.

Anderson said carbon tetrachloride sinks. A fracture in the clay the width of one human hair could allow pure carbon tetrachloride down great distances.

When he finishes the model in late spring, Anderson hopes it will include a three-dimensional graph of ground water flow as well as a list of the best spots for new monitoring wells and an assessment of how effective the existing wells are.

But it's not a magic bullet. It can't work backward to pinpoint the exact source, Anderson said. It will only give more hints of what possible sources could be and some of the best ways to clean the contamination.

The only thing it will say for sure, Anderson said, "is just how many questions there are."

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