Section 25391 Of Article 4. Investigation And Penalties From California Public Utilities Code >> Division 10. >> Part 1. >> Chapter 5. >> Article 4.

. At least once in each four-year period after the establishment of the retirement system the board shall cause to be made an actuarial valuation of the assets and liabilities of the retirement fund, and upon the basis of such investigation and valuation shall make such revision or change of the rates of contribution, the periods and conditions of service, and amounts of retirement allowances as may be necessary.