Until 6 months after the effective date of this amendatory Act of the 101st General Assembly, any active participant in a fund established under this Article may transfer to that fund creditable service accumulated under Article 6 of this Code upon payment to the Article 4 fund, within 5 years after the date of application, of an amount equal to the difference between the amount of employee and employer contributions transferred to the Article 4 fund under Section 6-227.1 and the amounts determined by the Article 4 fund in accordance with this Section, plus interest on that difference at the actuarially assumed rate, compounded annually, from the date of service to the date of payment.
     The Article 4 fund must determine the firefighter’s payment required to establish creditable service under this Section by taking into account the appropriate actuarial assumptions, including without limitation the firefighter’s service, age, and salary history; the level of funding of the Article 4 fund; and any other factors that the Article 4 fund determines to be relevant. For this purpose, the firefighter’s required payment should result in no significant increase to the Article 4 fund’s unfunded actuarial accrued liability determined as of the most recent actuarial valuation, based on the same assumptions and methods used to develop and report the Article 4 fund’s actuarial accrued liability and actuarial value of assets under Statement No. 25 of Governmental Accounting Standards Board or any subsequent applicable Statement.