S.C. Code § 9-1-1590
A disability beneficiary restored to active service at a salary less than his average final compensation shall not become a member of the System and his employer annuity shall be adjusted in accordance with the provisions of Section 9-1-1580.
Should a disability beneficiary under the age of sixty-five years be restored to active service and his compensation then, or at any time thereafter, be equal to or greater than his average final compensation at retirement, his retirement allowance shall cease and any election of an optional benefit shall become void and he shall again become a member of the System and contribute thereafter as provided in Section 9-1-1020. Any prior service certificate on the basis of which his service was computed at the time of his retirement shall be restored to full force and effect and, in addition, upon his subsequent retirement he shall be credited with all his service as a member. The average final compensation may be increased up to ten percent annually to adjust for inflation.
Should any other beneficiary who has been restored to active employment continue in service for a period of forty-eight consecutive months and his annual compensation be equal to or greater than seventy-five percent of his average final compensation at retirement, then he may elect to cease his retirement allowance and become a contributing member again and void his election of an optional benefit. Any prior service certificate on the basis of which his service was computed at the time of his retirement shall be restored to full force and effect and, in addition, upon his subsequent retirement he shall be credited with all his service as a member. Any such beneficiary may request the board to allow him to repay to the System all monies received by him as benefits during any periods subsequent to the date of his reentry into active service and make a contribution equal to the amount he would have contributed had he been a member during the period of his restoration to active service prior to his again becoming a member, together with the interest which would have been credited to the contributions on account of such period of restoration up to the date such contribution is made. Upon the completion of such payment, this period shall also be credited to him as membership service. In no event shall the retirement allowance payable upon subsequent retirement be less than the amount of his allowance previously payable plus any increases which would have been payable under Section 9-1-1810 had he not been restored to service.
S.C. Code § 9-1-1590
Section 9-1-1810, referenced in the third paragraph, was repealed by 2012 Act No. 278.