Tests on Antietam Creek downstream from the plant have turned up traces of pesticides DDT and DDE. The EPA said it believes the source of that contamination is the former Central Chemical site.
Among the other toxic substances found by the EPA in on-site soil samples are lead, arsenic and the pesticides chlordane and dieldrin.
Central Chemical has owned the Hagerstown property since the late 1930s, according to company attorney Thomas Lynch of Frederick, Md.
He said the company produced agricultural fertilizers, "many of them under government contract," until it stopped operating as a production plant in the early 1980s.
Lynch said Central Chemical also produced pesticides at the plant from the late 1940s until 1965.
Workers have said that during that time, large quantities of DDT, Sevin and other pesticides were disposed of at the site.
A former worker told state environmental officials that during those years, workers dumped bags of crystallized copper sulfate, powdered chlordane, sulfur, arsenic, DDT, sulfuric and muriatic acid canisters and other substances into trenches and in a nearby water-filled quarry off Burhans Boulevard.
Central Chemical still owns the Mitchell Avenue plant, but has offices elsewhere in Hagerstown. The old plant is leased to Hagerstown Recycling and Trucking.
In January, the EPA sent letters to Central Chemical and 11 other companies telling them that if they don't agree to clean up contamination at the former site of Central Chemical's pesticide/fertilizer plant - to EPA standards - the federal government will put the site on the Superfund list, do it at taxpayers' expense, and then hand them the bill.
The companies are believed to be "potentially" liable for contaminating the site, according to the EPA.
The average cost of a Superfund site cleanup done by EPA contractors is $30 million, said the EPA's Yates.
"We have high criteria for the contractors we use, and we're limited in which contractors we can use by potential conflicts of interest," he said. "That means you cut down on the competition and the price goes up. We pay top dollar. That can be incentive for companies to do the cleanup themselves."
"Central Chemical intends to be and has been cooperative" with the state and the EPA, Lynch said.
Central Chemical wants to work with the 11 other companies named by the EPA as potentially liable for site contamination, he said.
"Depending on what kind of remedy is used by the EPA, cleanup could be very expensive," Lynch said. "Hopefully, some of these other entities (companies) will step forward and help."
The EPA will supervise the work regardless of who does it, Yates said.
Superfund Remedial Project Manager Lesley Brunker, who is handling the Central Chemical site, said cleanup work might not begin for 19 months.
Brunker said the next step will be for the EPA to send the 12 companies a "special notice" that opens the door for negotiations on site cleanup. Although the EPA can order firms to arrange and pay for cleanups, the agency prefers to work with them, she said.
Negotiations and further site assessment could take another 7 months, she said.
Brunker said the public will get a chance to inspect and comment on the EPA's proposed cleanup plan before it's put into action.