PUEBLO, Colo. – The Army’s plan to change the way it destroys some chemical weapons stored in Colorado has met one regulatory requirement, but other steps remain.

The Army said Friday a review concluded there would be no significant environmental impact from using closed detonation chambers to destroy problematic chemical weapons at the Pueblo Chemical Depot.

The depot is eradicating 780,000 shells filled with mustard agent under an international treaty banning chemical weapons. Most are being neutralized by an automated plant using water and bacteria, but the Army believes about 97,000 shells have interior rust that can interfere with the machinery.

The detonation chambers would use high heat to detonate or burn those shells and the mustard they contain.

The Army still needs approval from state and county officials to use the chambers.