(1) A member eligible to retire under RCW 41.37.210
may, at the time of filing a written application for retirement with the department, apply to the department to make a one-time purchase of up to five years of additional service credit.
(2) To purchase additional service credit under this section, a member shall pay the actuarial equivalent value of the resulting increase in the member's benefit.
(3) Subject to rules adopted by the department, a member purchasing additional service credit under this section may pay all or part of the cost with a lump sum payment, eligible rollover, direct rollover, or trustee-to-trustee transfer from an eligible retirement plan. The department shall adopt rules to ensure that all lump sum payments, rollovers, and transfers comply with the requirements of the internal revenue code and regulations adopted by the internal revenue service. The rules adopted by the department may condition the acceptance of a rollover or transfer from another plan on the receipt of information necessary to enable the department to determine the eligibility of any transferred funds for tax-free rollover treatment or other treatment under federal income tax law.
(4) Additional service credit purchased under this section is not membership service and shall be used exclusively to provide the member with a monthly annuity that is paid in addition to the member's retirement allowance.