A new $9.2 million seal should be in place by September 1993 for theclosed Michaelsville Landfill at Aberdeen Proving Ground to reduce pollution leaking into ground water.
The 20-acre landfill, which ison the Environmental Protection Agency's Superfund priority cleanup list, does not pose a threat to current area drinking water, and Armyengineers say its pollution levels measured at 33 monitoring wells appear to be declining.
The landfill was mostly used for domestic trash at the post from 1969 until its closure in 1980. But hazardous waste may have been dumped there also, the Army says.
The clay soil cover put on top of the dump a decade ago has eroded to the point where rainwater collectsand seeps into the landfill, becoming polluted from the trash and leaching into ground water.
Runoff from the seepage enters drainage ditches near the landfill that feed into a tributary of Romney Creek.
At a meeting Thursday, Army officials outlined APG's selected solution of the problem: using a plastic seal, covered with layers of compacted soil, sand, a fabric filter, topsoil and new grass, plus vents for underground gases.
The Army has rejected as ineffective simply re-covering the existing cap with new soil.
Excavating the entire landfill and disposing of the waste elsewhere would be too costly and create other pollution problems, said Neran Desai, project engineer.
The plastic membrane is the key to preventing seepage, Desai said, though he warned that "this cap is not a complete solution."
Underground water continues to pick up pollutants from the buried trash, he said. A ground water study should be completed in two years, he said, when an analysis would be made about the nature and extent ofthat pollution.
But the underground water flows could change course so that it no longer touches the refuse and avoids more polluted ground water, other engineers said.
Although several dozen people attended the meeting, none voiced opposition to the selected solution,which has been tentatively endorsed by the Maryland Department of the Environment.
Some even questioned why Michaelsville got on the Superfund priority list in 1989, given its relatively low level of pollution.
One reason is that APG moved quickly to set up monitoring wells that measured seeping pollutants, said Ken Stachiw, manager of cleaning up post disposal sites, while other potentially more threatening landfills had no monitoring.
Then, there was the possibility of hazardous waste and explosives being dumped in Michaelsville because of APG's testing mission. And the base's drinking water supply from Deer Creek was located nearby, Stachiw added.
Steve Hirsh, of the Environmental Protection Agency's Philadelphia office, noted that his agency tried to come up with a priority ranking for the entire proving ground, but that Michaelsville was the only landfill that had complete information for analysis. Pollutant levels slightly exceeded the cutoff point for making the EPA list.
All told, there are 360 solid waste dumps and handling sites scattered over the 72,500-acre military post.
The entire Edgewood area, with its burial grounds of explosives and old chemical warfare agents, is a Superfund site.
But Michaelsville is the only such priority cleanup site in the largerAberdeen area of the post.
Pollution of the ground water under Michaelsville landfill exceeds EPA safe drinking water standards. Benzene, pesticides, and heavy metals such as mercury, lead and chromium have been detected.
Polychlorinated biphenyls, or PCBs, were previously found in the aquifer but none were found in the last samples, Desai pointed out.
Water under the landfill flows southeast, away from the county's and APG's drinking water supplies.