Story highlights The lockdown is lifted shortly before 6 p.m., a spokeswoman says

The incident was at the expansive Savannah River Site in western South Carolina

Scans found possible "explosive residue" on a delivery truck, agency says

(CNN) Authorities triggered an emergency response on Monday -- including barring all incoming traffic -- at a South Carolina nuclear site because of what was described as "a potential security event."

The Savannah River Site, which is affiliated with the U.S. Department of Energy and National Nuclear Security Administration, announced the precautions via Facebook around 3:42 p.m.

About one and a half hours later, the site explained why: "Electronic and canine scans of a vendor delivery truck indicated a possibility of explosive residue on the truck."

That hit spurred authorities from South Carolina and Georgia to join the site's security contractor, Centerra, according to the Savannah River Site release.

The lockdown was lifted at 5:52 p.m., according to Savannah River Nuclear Solutions spokeswoman Lindsey MonBarren.

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