A federal lawsuit in Ohio, announced last month, also might add to the delay of a process ordered by international treaty and shadowed by terrorism.
The Army had planned to start destroying more than 1,200 tons of VX in October at the depot about 30 miles north of Terre Haute.
But the neutralization process doesn't yet meet the Army's environmental standard prohibiting more than 20 parts of VX per billion in the byproduct, known as hydrolysate.
VX is so deadly even a tiny amount of the thick, oily liquid can kill if it is inhaled or comes in contact with skin.
The Army also has ordered Parsons Engineering, the company hired to build and operate the Newport Chemical Depot, to install a sprinkler system that would include containment in case of fluid runoff. The system could take four to six months to design, install and test.
The depot is not expected to be ready before January at the earliest, said Jeff Brubaker, project manager for the Army.
Army plans call for the shipment of 300,000 gallons of the VX byproduct from the Newport depot to a facility in suburban Dayton, Ohio.
The Army plan called for the breakdown of hydrolysate into salts and other byproducts that would be treated in the Dayton sanitation treatment plant before being released into local waterways.
But a lawsuit filed by a citizen's group in Ohio has the Army considering construction of a tank farm for temporary storage of hydrolysate at Newport. In that case, the depot would not be able to start neutralizing VX before April, said Army spokeswoman Terry Arthur.
VX was scheduled to be destroyed by April 2007 under the Chemical Weapons Convention international treaty. Following the Sept. 11, 2001, terrorist attacks, Congress last year ordered the Army to destroy all stockpiled chemical weapons by 2004.
On Saturday, after years of preparation and legal challenges, the Army began destroying the another nerve agent, sarin, at a chemical weapons incinerator in Anniston, Ala. It was the first incinerator to go into operation near a residential area.