S.C. Code Ann. § 9-17-50
< [Effective until July 1, 2002, this section reads as follows:] >
Any person electing to participate in the optional program under this chapter is ineligible for membership in the South Carolina Retirement System so long as he is employed in a position for which the optional retirement program is available. In the event an optional program participant assumes a position in public service for which the optional program is not available, he must at that time begin membership in the South Carolina Retirement System.