S.C. Code Ann. § 59-101-610

A public institution of higher learning may spend federal and other nonstate appropriated sources of revenue to provide lump-sum bonuses at levels outlined in a plan approved by the governing body of the respective public institution of higher learning and according to guidelines established in the plan. The public institution of higher learning must maintain documentation to show that the use of federal funds for this purpose is in compliance with federal law. This payment is not a part of the employee's base salary and is not earnable compensation for purposes of employee and employer contributions to the respective retirement systems.