(a) The board of trustees shall appoint an actuary.
(b) The actuary shall perform duties in connection with advising the board concerning operation of the retirement system's funds.
(c) At least once every five years the actuary shall:
(1) make a general investigation of the mortality and service experience of the members and annuitants of the retirement system; and
(2) on the basis of the results of the investigation, recommend for adoption by the board tables and rates that are required.
(d) On the basis of rates and tables adopted by the board, the actuary shall:
(1) annually compute the normal contribution rate for each participating municipality;
(2) annually compute the prior service contribution rate for each participating municipality;
(3) compute the supplemental death benefits rate and the supplemental disability benefits rate for each participating municipality; and
(4) make an annual valuation of the assets and liabilities of the funds of the retirement system.