Beginning on July 1, 1991 and thereafter, each county board of education or electing charter school shall deposit in the member’s annuity account created pursuant to § 18-7B-9 of this code an amount equal to seven and one-half percent of all compensation paid to members of the defined contribution system in excess of that authorized for minimum salaries in §18A-4-2 and §§ 18A-4-8a of this code to the extent that the excess exceeds the amount distributed for salary equity to the county.