As an alternative to the terms of office specified in Section 31520. 1, the County of Contra Costa may, if the board of supervisors adopts a resolution, have terms of office which expire as follows:

Seat number 1, the treasurer, who serves on the board of retirement ex officio, and whose term of office on the retirement board expires with his or her term of office as treasurer.

Seats 2, 4, and 8 expire June 30, 1992, and every three years thereafter.

Seats 3, 5, and 9 expire June 30, 1993, and every three years thereafter.

Seats 6, 7, and alternate expire June 30, 1994, and every three years thereafter.