BOSTON -- The high-pitched noise coming from gas leak detector Bob Ackley's meter is a bad signal.

"OK, that's in the explosive range," Ackely says after finding a high level gas leak on Route 9 in Wellesley, Mass. "It's an immediate hazard. This manhole cover could blow off at any time."

Team 5 Investigates reported Tuesday how it took less than an hour to find four hazardous leaks on Rt. 9 that had to be reported immediately. These are the same gas lines that lead to homes and businesses in the suburbs and the city.

"Do you think the gas companies are doing everything possible to guarantee that customers are safe?" Team 5's Sean Kelly asked Mark McDonald, president of the New England Gas Workers Association. "Unfortunately no," McDonald said. "With tens of thousands of gas leaks out there, I can't say that's the case."

McDonald estimates there are at least 25,000 leaks in Massachusetts that need to be repaired. Team 5 found one leak at a busy Dorchester intersection that showed a 10 percent reading, an especially dangerous hazard. "It's pretty bad," McDonald said. "A 10 percent reading in our industry is the worst reading." "What would it have taken to have an explosion in that area that day?" Kelly asked. "An ignition source, a spark," McDonald said.

Some of thousands of leaks have gone unrepaired for months. National Grid says that's because they're in busy areas. The company said it eliminated all immediate hazards using vents as a temporary fix until it completes repairs.

State Representative Lori Ehrlich wants them to hurry up. She introduced legislation that would give deadlines for gas companies to fix all leaks. "It's only a matter of time before some of these leaks become fatalities," Ehrlich said.

Officials with National Grid told Team 5 they believe the number of gas leaks in the system calls for a robust gas main replacement program and they have tripled their capital investment to replace their leak prone infrastructure.