PUEBLO, Colo. (AP) — An Army facility in southern Colorado has temporarily stopped destroying obsolete chemical weapons because of liquid hazardous waste seeping from a storage tank.

Officials said Thursday the liquid is a byproduct of the destruction process at the Pueblo Chemical Depot and contains no chemical weapons. They say less than 8 ounces (237 milliliters) seeped out.

The seepage was discovered May 15. The cause is under investigation.

Destruction is expected to resume in mid-June.

The depot is eradicating a stockpile of 780,000 shells containing 2,500 U.S. tons (2,270 metric tons) of mustard agent. Since starting in 2016, the plant has eliminated 132,000 shells and 774 U.S. tons (702 metric tons) of mustard.

Mustard blisters skin, scars eyes and inflames airways. The U.S. is destroying it under a treaty banning chemical weapons.