The engineer shall inspect and require the work as it is being completed to be done in accordance with the plans, specifications, and contract for construction. Each month during the work, the engineer shall report to the drainage authority, in writing, showing the work completed since the previous report and all materials furnished under the contract.
The engineer shall issue with the monthly report a preliminary certificate for work done and approved or materials delivered. The certificate must contain the station numbers of the work covered by the certificate and the total value of all work done and the materials furnished according to the contract. For each ditch section, the certificate must show the actual volume, in cubic yards, of the excavation completed. For joint county drainage systems the certificate must also show the percentage of the total value to be paid by each county in the proportion fixed by the drainage authority order. Each certificate must show that a loss will not occur as a result of a partial payment. A duplicate of the certificate must be delivered to the auditor of each affected county.
The affected counties must pay the contractor, based on the certificate, 90 percent of the total value of work done and approved and 90 percent of the total value of material furnished and delivered. The materials may only be delivered as required in the course of construction and authorized by the engineer.