A service contract may be entered into only as approved by the Board of Public Works in accordance with this subtitle. Except as provided in subsection (c) of this section, the Board of Public Works may approve a service contract for a unit only if the Board receives a certification from the Department that: the service contract is exempt under § 13-404(b) of this subtitle; or the unit has complied with the requirements of § 13-404(c) of this subtitle. If the General Assembly authorizes or requires that certain services be performed by an independent contractor, the Board of Public Works may approve a service contract for those services without the certification required by subsection (b) of this section.