Cal. Government Code § 20909

(a) A member who has at least five years of credited state service, may elect, by written notice filed with the board, to make contributions pursuant to this section and receive not less than one year, nor more than five years, in one-year increments, of additional retirement service credit in the retirement system. (b) A member may elect to receive this additional retirement service credit at any time prior to retirement by making the contributions as specified in Sections 21050 and 21052. A member may not elect additional retirement service credit under this section more than once. (c) For purposes of this section, “additional retirement service credit” means time that does not qualify as public service, military service, leave of absence, or any other time recognized for service credit by the retirement system. (d) Additional retirement service credit elected pursuant to this section may not be counted to meet the minimum qualifications for service or disability retirement or for health care benefits, or any other benefits based upon years of service credited to the member. (e) This section only applies to the following members: (1) A member while he or she is employed in state service at the time of the additional retirement service credit election. (2) A member of the system defined in Section 20324. (f) For purposes of this section, “state service” means service as defined in Section 20069. (g) This section shall apply only to an application to purchase additional retirement credit that was received by the system prior to January 1, 2013, that is subsequently approved by the system.