Sec. 5. (a) The estimate of cost of the system required under section 4(4)(D) of this chapter may include all incidental, inspection, and engineering costs caused by the proposed construction. However, the estimate of the costs to be paid by special assessment may not include the following:
(1) Salaries and expenses of the necessary and regularly employed personnel of the engineering department of the county.
(2) Ordinary operating costs of the works board.
(b) If the works board determines that it is necessary to employ additional engineering services for construction of a particular system, the works board may include in the estimate of cost of the system required under section 4(4)(D) of this chapter the cost of the additional service actually performed in connection with the system.