CONCORD -- Copper wire thieves have cost the city $700,000 in the past five years, with a $40,000 wire heist at City Hall the latest incident, officials said last week.

The theft of 1,100 feet of wiring from City Hall in July left a parking lot without lighting. It is the latest in a string of thefts that began in 2007 and surged from May to August 2011, when 25,000 feet of wiring was stolen from six city parks.

Another recent wire theft, from Ygnacio Valley Park, will cost $81,000, officials said.

In response, the city is replacing stolen or broken wire boxes with vandal-resistant ones that are welded shut, cemented underground with rebar and, in some cases, covered with a boulder.

"It takes some heavy-duty equipment to get these things out of the ground. It's been effective. The problem is it's expensive," said Director of Public Works Justin Ezell.

At $1,300 per box, Ezell said the city will not replace all its boxes, only broken or stolen ones. A park with streetlights could have 100 boxes, he said.

While the vandal-resistant boxes are helping, police said the wire theft problem still looms. Most of the private and public infrastructure in Concord was built when copper was cheap, so the wiring can be found in buildings throughout the city, said Sgt. Jeff Krieger, of the police department's financial crimes unit. It is also hard to trace stolen copper wiring because it is unmarked, and thieves usually cut the wires into multiple pieces, he said.

"It is a statewide epidemic," Krieger said. "The biggest problem we face is the targets are virtually everywhere."

In June, a countywide sting in Contra Costa uncovered metals stolen from BART, PG&E and other agencies at seven metal recyclers.

City officials are asking residents to call police at 925-671-3333 if they notice any suspicious people tampering with electrical boxes, especially during odd hours.

"There's so many eyes and ears out there that can help us stop this," said Ezell.

David DeBolt covers Concord and Clayton. Contact him at 925-943-8048. Follow him at Twitter.com/daviddebolt.