AUGUSTA – More than 400 state social workers will be getting raises and a percentage of back wages dating from 1998 thanks to an arbitrator’s decision, which could cost the state $6 million.

Arbitrator John Alfano’s Oct. 4 decision boosts job grades for certain workers, mostly former caseworkers for agencies that have been combined into Maine’s newly merged Department of Health and Human Services.

The Maine State Employees Association, which represents state workers, notified workers who will benefit from the decision on Wednesday. Pay scales will rise by about 4.5 percent. Previous pay rates of $14.29 to $29.07 an hour will increase to $14.95 to $30.51 an hour, respectively.

“I’m ecstatic. It’s the biggest case I’ve ever heard of in Maine” for state employees, said Chuck Hillier, the union’s assistant negotiator.

Discussions between the state and union on the issue got under way in 2000. The agreement developed after the state sought to break the deadlock with the union, said state Finance Commissioner Rebecca Wyke.

The union estimated the cost of the increases and back pay at $6 million, but Wyke said the exact amount remains under review. The commissioner also said the Legislature likely will be asked to approve the funds through a supplemental budget request, so workers may have to wait until next year before they receive checks.

Current and former state employees who will receive payments as a result of the decision include adult-protective and adoption caseworkers throughout the state.