(a) The District and each employee shall contribute to the defined benefit plan under § 1-626.05(1) the social security amounts mandated by federal law. (b) Each employee may voluntarily contribute to the deferred compensation plan under § 1-626.05(2) in amounts not exceeding the limits set by § 457 of the Internal Revenue Code. (c) The District shall contribute an amount equal to not less than 5% of the base salary of each employee participating in the defined contribution plan under § 1-626.05(3). The District contribution shall be made not less frequently than quarterly and shall be placed in the Section 401(a) Trust established by § 1-626.11. (d) In addition to the contribution under subsection (c) of this section, the District shall contribute no less than an additional .5% of a detention officer’s base salary to the Section 401(a) Trust established by § 1-626.11. The contribution shall be made not less frequently than quarterly.