INDIANAPOLIS -- Activists said Friday they are joining with the Sierra Club to sue the Army over shipments of chemical waste from the destruction of a VX nerve agent stockpile in Indiana to Texas for incineration.

The Chemical Weapons Working Group, the Sierra Club and other groups on Thursday filed a notice of intent to sue that accuses the Army of hiring a contractor to ship waste that harbors more VX and toxic chemical compounds than the military says it contains.

"We can't sit by with a number of folks coming to us saying this material is dangerous to ship," Craig Williams, director of the Chemical Weapons Working Group, said in a Friday conference call with reporters.

He said several confidential sources have independently told his Berea, Ky.-based group that the caustic wastewater, called VX hydrolysate, created by the VX destruction contains more VX molecules than the Army has said it contains.

Mickey Morales, a spokesman for the Army Chemical Materials Agency, said the Army does not comment on pending litigation. But he said the disposal and shipment process had been reviewed by independent state and federal agencies, including the Centers for Disease Control and Prevention.

"We are committed to the safety of the public, the work force and protection of the environment," Morales said.

Earlier this month, the Army's onsite manager at the Newport Chemical Depot, Jeff Brubaker, said the VX hydrolysate contains no more than 20 parts per billion of VX. The Army has contended that the hydrolysate is no more dangerous than other hazardous wastes shipped each day across the nation.

The Army signed a $49 million contract with Veolia Environmental Services in early April to truck about 2 million gallons of VX hydrolysate from the Newport Chemical Depot in western Indiana to Port Arthur, Texas, for incineration.

Mick Harrison, an attorney for the groups, said he expects them to file a lawsuit in U.S. District Court in Indianapolis on Monday in a bid to halt those shipments.

The groups' notice also states that the Army has failed to notify communities affected by the shipment of the waste nearly 1,000 miles to a Veolia plant in Port Arthur.

"It's another sad chapter of Army mismanagement of chemical weapons disposal," said Ross Vincent, a senior policy advisor for the Sierra Club, a nonprofit group with 750,000 members nationwide.

"If the Army gets away with this in Indiana, they're very likely to try to replicate it."

Sara Morgan, who lives near the depot, said her group, Citizens Against Incineration at Newport, wants the Army to dispose of the VX hydrolysate onsite at the Newport Chemical Depot. Her group will be one of the plaintiffs in the suit.

"We don't want to ship our problem to somewhere else," she said.

The announcement of the notice of the intent to sue came one day after Army officials said they have destroyed 50 percent, or about 125,000 gallons, of the original stockpile of about 250,000 gallons of VX nerve agent at the depot, about 30 miles north of Terre Haute, Ind.

The Army produced its entire supply of VX at Newport in the 1960s. It is required by an international treaty to destroy the chemical weapon by 2012. Army contractor Parsons Technology Inc. began neutralizing the depot's VX in May 2005.

The Army's agreement with Veolia followed two failed deals with by Perma-Fix Environmental Services Inc., in Dayton, Ohio, and DuPont Co. in Deepwater, N.J. that were abandoned because of strong opposition.