LAWRENCEVILLE — The $59 million Gwinnett County will collect next spring during a second billing of 2009 taxes could be set aside for employee pension liabilities, the county chief financial officer said.

Commissioners adopted a 2.28 mill property tax this week, causing a second billing since temporary tax bills were issued earlier this year.

Despite the fact that the money is part of the 2009 tax levy, CFO Aaron Bovos said the county considers those dollars 2010 revenues, since they won’t come in until after the March billing, and this year’s books will closed.

During a meeting of the Engage Gwinnett committee, he said the 13.25 total millage rate adopted will be key to balancing a 2010 spending plan, but county officials consider the incremental bills a “one-time revenue.”

“It is absolutely critical that we put (the money) to good use,” Bovos said.

While commissioners have to formally vote on how to spend the money, Bovos said his staff is considering a recommendation to use it to fund accrued liabilities for an employee pension plan.

Between the pension and medical benefits — which haven’t been offered to new employees since 2007 because of the expense — the county has about $300 million in liabilities that haven’t been funded, he said.

Currently, the county contributes 21 percent of each registered employee’s salary to the pension fund, but in three years, actuarial estimates show that will increase to 41 percent.

Bovos said using the increment for the liabilities will help offset those rising costs. An actuarial study is currently being conducted to determine the impact.