(1) Beginning January 1, 1984, each city of the first class with firefighters participating in a retirement system shall contribute to the retirement system a sum equal to thirteen percent of each such participating firefighter's periodic salary. Such payment shall be credited to his or her employer account on a monthly basis. Each such account shall also be credited with regular interest. The city shall also contribute to the employer account of any firefighter employed by the city on January 1, 1984, an amount equal to the employee's contributions, without interest, that were made to the city prior to January 1, 1984, with such contribution to be made at the time the firefighter retires or terminates employment with the city. The city may contribute such amount before the firefighter's retirement or termination of employment or credit interest on such contribution.
(2) Each such city shall contribute any additional amounts necessary to fund retirement or other retirement plan benefits not provided by employee contributions or city contributions to the employer account required by subsection (1) of this section. Such additional contributions shall be accumulated in an unallocated employer account of the Firefighters Retirement System Fund and used to provide the benefits, if any, specified in sections 16-1027 and 16-1029 to 16-1031 which are not otherwise funded by the firefighter's retirement value. Funds needed to provide for a firefighter's benefits shall be transferred from the unallocated employer account when and as such funds are needed. All funds committed by the city to the funding of a firefighter pension system on January 1, 1984, that are not transferred to the firefighters employee accounts shall be transferred to the unallocated employer account.