Police in Union City are worried that a new rash of metal thefts could end up costing more than just money.

Thieves are now stealing grate that cover large storm drains

Without the grate, someone could fall into the gaping storm drain hole and the drop seven feet down.

Wayne Cruz of the Union City Public Works told KTVU that over the last several weeks, the city has been forced to replace as many as 15 of the 100-pound metal storm grates.

Cruz said the expense is only part of the problem.

"Hopefully nobody gets hurt, especially at night time," said Cruz. "You can't see [the hole] at night."

  Union City resident Ben Farmer agreed.

"It's pretty dangerous," said Farmer. "Some kid's going to fall in one of those, would be everybody's concern."

Cmdr. Ben Horner of the Union City Police Department said this was the first time he's seen metal storm drains being taken.

Horner said officers were on the lookout for this new kind of metal theft, with police putting the word out to local recycling yards.

Replacing each stolen grate costs the city more than $300. The thieves aren't likely to get more than a few dollars for them.

But safety was the main concern for police.

"Usually, the police get calls to rescue ducks out of these things. I don't want to get a call that we have rescue a child," said Commander Horner.

Police said another report of a stolen grate came in Wednesday.

Crews said they replace them as fast as possible. They've also started chaining them down to prevent more thefts