Officials at the Western Lake Superior Sanitary District on Wednesday said a hand grenade was discovered recently in a disposal bin at the district’s Materials Recovery Center off Rice Lake Road in Duluth.

The grenade was wrapped in plastic bubble wrap and found inside a tin that had been dumped into a large metal bin at the mixed-waste area of the recovery center that keeps recyclable and reusable material separated from what is headed to a landfill.

The bin was mostly empty and the tin was fished out for a closer inspection. The incident occurred Saturday.

The grenade “is believed to have been left for disposal only, not with intent to harm,’’ the WLSSD said Wednesday in a news release.

WLSSD staff moved customers quickly off site and closed the Materials Recovery Center for the remainder of the day. WLSSD coordinated with local authorities to transport the explosive device to a safe location.

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It's not the first time explosives have shown up at a WLSSD facility. Karen Anderson, WLSSD communications director, said dynamite has been found in vehicles of people dropping off materials at the household hazardous waste facility in Lincoln Park.

The WLSSD is asking residents who find explosive materials such as dynamite, TNT, blasting caps and loaders, military memorabilia or explosive chemicals in homes, barns and garages to leave the items alone, leave the area and immediately call 911. Do not transport explosive material.

WLSSD facilities do not provide disposal services for explosives and local authorities will provide assistance when contacted.