S.C. Code Ann. § 9-11-170
(3)
(4) Upon retirement, a member who has participated in the Supplemental Allowance Program will receive a supplemental allowance which shall be a monthly retirement allowance equal to the sum of (a) and (b) below:
(9) Each member participating in the Supplemental Allowance Program shall make monthly supplemental contributions equal to six percent of the portion of the monthly salary or compensation in excess of four hundred dollars received by him during his participation in the program.
In addition, each such member may irrevocably elect, within a period of one month following his date of participation, to contribute the amount which would have resulted had he, during each month of his credited service prior to his date of participation, made a contribution to the System equal to two percent of the portion of his rate of monthly salary or compensation in excess of four hundred dollars during the month immediately preceding his date of participation in the program and had such contributions been accumulated with interest at the rate of four percent per annum. If the member elects to make such additional voluntary contributions they shall be made within twelve months after his participation in the Supplemental Allowance Program commences, in such manner as the Board may deem reasonable.
(10) As of the employer's participation date and as of each July first thereafter the Board shall certify to each employer participating in the Supplemental Allowance Program the amount of employer supplemental contribution due the System. The amount of employer contribution payable during the first such period shall be equal to an estimate of the total amount of supplemental contributions that will be made by the participating members employed by that employer during the ensuing period up to the subsequent July first. However, the portion of such members' contributions which is in respect to service prior to the participation date shall be excluded from such estimate. The amount of employer contributions in any subsequent period shall be computed in a similar manner but the resulting amount shall be adjusted by the difference between the estimated amount of such member contributions and the amount of such contributions actually made. The estimate of the amount of contributions that will be made by the members during a period shall be based on the most recent payroll information available as of the date of the certification.
The participating employer shall make an additional level annual contribution for a period of ten years subsequent to its participation date. Such additional contributions shall, in total, be sufficient to liquidate an amount equal to the total contributions by its participating members with respect to their service prior to the employer's participation date. For the purpose of calculating this additional contribution an interest rate of four percent per annum shall be used.
Any forfeitures shall be used to reduce the contributions otherwise payable by a particular participating employer, and will not be applied to increase the benefits of any participating member.