Deliveries from Deseret Chemical Depot, where the spray tanks are stored, are expected to resume this weekend after safety and compliance programs are reviewed, said Chuck Sprague, spokesman for the depot.

Workers had only pressure tested valves on the spray tank containers before they were transported to the disposal plant. Such testing to ensure that the seals are tight should have been completed after the containers arrived at the plant as well, officials said.

EG&G Defense Materials Inc., contractor for the plant used to destroy part of the nation's aging supply of chemical weapons, will conduct the environmental and safety review and determine if corrective action is necessary.

"As the compliance standards review is conducted, VX spray tanks currently inside the facility will continue to be processed until they have all been destroyed," said Sprague. "Other chemical operations will also continue during the review."

About 160 of the bulk agent containers have been processed at the disposal plant. More than 600 bulk containers are stored at the nearby Deseret Chemical Depot, about 40 miles southwest of Salt Lake City.

The spray tanks, each containing 1,356 pounds of VX, were designed to shower the nerve agent from aircraft onto battlefields. The agent, which remains toxic for several days, has an oily consistency that allows it to be sprayed onto plants before enemy troops march through an area.

VX is so powerful that a single drop on the skin can cause death within 15 minutes. The U.S. military never used chemical weapons in combat.

The Tooele County installation is one of nine sites in the United States where the nation's agent stockpile is stored and one of four U.S. facilities that is destroying chemical weapons.