(a) The district shall pay the contract price of construction contracts only as provided in this section.
(b) The district will make progress payments under construction contracts monthly as the work proceeds, or at more frequent intervals as determined by the board or its designee, on estimates approved by the board or its designee.

(c) If requested by the district or district engineer, the contractor shall furnish a breakdown of the total contract price showing the amount included for each principal category of the work, in such detail as requested, to provide a basis for determining progress payments. In the preparation of estimates, the district engineer may authorize material delivered on the site and preparatory work done to be considered if the consideration is specifically authorized by the contract and if the contractor furnishes satisfactory evidence that he has acquired title to the material and that it will be utilized on the work covered by the contract.
(d) In making progress payments, 10 percent of the estimated amount shall be retained until final completion and acceptance of the contract work. However, if the board at any time after 50 percent of the work has been completed finds that satisfactory progress is being made, it may authorize any of the remaining progress payments to be made in full. Also, if the work is substantially complete, the board, if it finds the amount retained to be in excess of the amount adequate for the protection of the district, at its discretion may release to the contractor all or a portion of the excess amount. The district is not obligated to pay interest on amounts retained except as provided herein. The district shall not be obligated to pay any interest on the 10 percent retainage held on the first 50 percent of work completed. If the district holds any retainage on the remaining 50 percent of the work completed, the district shall pay interest on such retainage from the date the retainage is withheld to the date of payment to the contractor. The interest rate to be paid on such retainage shall be the rate of interest paid by the district’s depository bank on interest bearing accounts of similar amounts during the period of time interest accrues as provided herein.
(e) On completion and acceptance of each separate project, public work, or other division of the contract, on which the price is stated separately in the contract, payment may be made without retention of a percentage.