Homeowners have been finding military ordnance in their clamshell driveways in Delaware and Maryland for the last year.

So far, 318 pieces of ordnance have been recovered.

A clam dredging operation pulled them up about 20 miles off New Jersey. The clamshells were chopped up and widely distributed for cheap driveway fill throughout the Delmarva Peninsula.

One piece found in a driveway in the summer of 2004 was a 75 mm artillery shell from World War I, filled with mustard gas in solid form.

Three bomb disposal technicians from Dover Air Force Base dismantled the shell to see what was in it so investigators could better determine the hazards that all the discovered ordnance posed. The gas burned them. One was hospitalized with large pus-filled blisters on an arm and hand.

Newly released records reveal that the Army dumped at least 64 million pounds of chemical warfare agents in steel containers - as well as a minimum of 400,000 bombs and rockets and 500 tons of radioactive waste - off the country's shores in 26 ocean dump zones created from 1944 to 1970.

Rob Williams Jr. had no idea.

He's the Army Corps of Engineers' lead investigator into how Sea Watch International's clam dredging operation pulled up the sea-dumped mustard gas shell. He was shocked to learn that the Army used to throw weapons of mass destruction over the side of ships.

"When I first saw that, my jaw dropped," Williams said. "It made me not want to eat seafood anymore."

Poultry farmer Bill Layton ended up with 14 live French-made World War I-era grenades in his driveway in the summer of 2004. They had been in his driveway for eight months after he paid $600 for the clamshells to be delivered, officials said.

"That's what scares the hell out of me," Layton told the News Journal of Wilmington, Del. "We've been riding over them all winter."

Layton was lucky: None of the grenades was filled with chemicals.

At least two other chemical weapons had yet to be found.

In May, several months after Sea Watch International installed a metal detector at its processing plant, another unexploded 75 mm artillery shell was found in a pile of clamshells waiting to be chopped up for delivery.The shell was full of mustard gas but was disposed of safely.

No one was injured when a third mustard-filled shell was found at the plant Oct. 21 - nine days ago.

The continuing investigation found that grenades remained on the ocean floor where the clam dredging was done last year, Williams said.

The ordnance was found in about 130 feet of water. Scallop operations routinely dredge in more than 350 feet of water.

The dump is on no nautical charts. The Army has no record of chemical weapons being dumped that close to New Jersey.

The dump might have been created after World War I, when dumping often was in relatively shallow water.

The Army has never reviewed ocean dumping records from that era and doesn't know where those dumps might be, William Brankowitz said. He's a deputy project manager in the Army Chemical Materials Agency and a leading authority on the Army's chemical weapon dumping.

The Corps of Engineers is investigating whether it was part of a 1964 Army dumping operation that might not have disposed of everything in its intended deep-water burial. It was one of few known dump operations in which 75 mm shells were tossed into the Atlantic Ocean.

Surviving Army records show that in 1964 a barge dumped 1,700 75 mm artillery shells with mustard gas and tons of steel containers full of mustard gas and cyanogen chloride - which can cause convulsions, unconsciousness and death.

The chemical weapons were loaded onto the barge at Edgewood Arsenal in Maryland and pulled by another ship down the Chesapeake Bay, into the Atlantic Ocean and headed north.

The five-day operation was supposed to dump all its deadly load in deep water, Williams said the Army told him.

Army records show that the barge was unloaded off the Virginia-Maryland state line.

The records give no explanation why a barge headed there would go so far north, then south again to dump its load.

There is, however, a plausible explanation how some of those chemical weapons might not have reached their intended dump zone.

Along the way, a 1-ton steel container of mustard gas was found to be leaking, a little-known 1987 Army report indicates.

The barge was evacuated. The crew donned protective suits on an accompanying ship, then went back to the barge.

They decontaminated the deck with chlorine, which neutralizes mustard gas, and threw the leaking container and another contaminated container over the side.

Either other chemical weapons on deck were tossed overboard, as well - or the ship's captain said, " 'It's Friday,' or 'I don't want to go all the way out there. Throw it over,' " Williams guessed.