It was closed in 1981, but soil tests in 1995 confirmed that oils, fuels and solvents, including traces of a metal degreaser, remained in the soil beneath the pit and had leached into the groundwater.
"This was one source for groundwater contamination. We're trying to take care of the sources first - to remove them and stop the ongoing process," said Marianne Merritt, environmental scientist with Letterkenny's Management Divison.
Using the "in-situ" method, workers in white protective clothing are injecting the ground with a solution of hydrogen peroxide and other nonhazardous compounds. They chemically break down the contaminants in the soil into carbon dioxide, oxygen and water.
"The chemistry is old but the process is new," said Jim Wilson, an employee with Geo-Cleanse of Newark, N.J., which patented the injection method four years ago.
The process requires no excavation, hauling or storing of contaminated soil, a costly process, said Ken Cowan, site manager from the Weston Company of West Chester, Pa., the main contractor for the project.
The hydrogen peroxide solution is injected every day for up to 12 hours through a series of vertical pipes placed at three different levels in the contaminated area, which covers an area 75 by 95 feet, Cowan said.
Now in its third week, the process is expected to be completed by Aug. 8, Cowan said.
The cost of cleaning this site with the injection process is $225,000, the cheapest method available, Merritt said.
The depot also is trucking about 1,500 cubic yards of soil contaminated with the degreasing solvent to a landfill in Detroit.
So far, the federal government has spent $77 million since 1980 on the depot's two cleanup projects under the Superfund program.
The total cost of cleaning up 2,500 acres at the depot is estimated at $290 million, Merritt said.
The cleanup is part of the transfer of 1,500 acres of the 19,600-acre Army base to Franklin County to create a multi-use business park.