Construction workers this week found a backpack filled with six hand grenades and other explosive devices in a county drainage ditch on Lakeview Avenue in Placentia.
Orange County bomb squad investigators detonated the hand grenades in a containment vessel, and the rest of the explosives were detonated in a larger open-air trailer, Jim Amormino of the Orange County Sheriff’s Department said.
The backpack containing the grenades, black powder, white powder, fuse igniters, blasting caps, grenade fuses and two canisters was found just on Lakeview between Orangethrope and La Palma avenues under a bridge, Amormino said.
Investigators later found “numerous” additional blasting caps near the backpack, which was significantly deteriorated, indicating it may have been in the ditch for quite a while, Amormino said.
The FBI was called in to help investigate “because of the sheer number of devices,” according to Amormino, who said it appeared someone deliberately buried the explosives.
Laura Eimiller of the FBI said no additional explosives were found and that investigators know of no terrorist threat related to the devices.
On Monday, Lakeview was closed between La Palma and Orangethorpe through much of the afternoon.
City News Service contributed to this article.