The Environmental Protection Agency is fencing off a gigantic and potentially dangerous slag heap in Midvale because of soil sampling conducted in May and June.

The problem is separate from lead and arsenic pollution that blew from the Sharon Steel plant onto neighborhood yards in Midvale. But these two toxic substances are found in high concentrations in the slag as well.Ominously, footprints at the site "indicate that children may have been playing in the area," said the EPA's Mike Zimmerman

The site has about 2 million tons of slag material left by a former lead and copper smelter. The facility operated from the late 1800s until 1958. The wastes have heavy loads of lead, arsenic, cadmium, copper, silver, chromium and zinc. A preliminary assessment - prepared for the EPA by the U.S. Public Health Service Agency for Toxic Substances and Disease Registry - recommends that the public be kept completely out of the site.

Zimmerman, on-scene coordinator for the project, cites "concern for the public health" as the reason for the recommendation.

"The contaminants of particular concern at the site are lead and arsenic," Zimmerman said. "Without the fence, trespassers could inhale particles in the air or ingest soil clinging to hands."

Fencing should be completed early in January 1991, Zimmerman said.