After the requirements of this chapter have been satisfied and a contract and bond for any work for which a special assessment is to be levied have been approved by the water resource board, the board may direct special assessments to be levied for the payment of appropriate costs, and the secretary shall certify to the board the items of total cost to be paid by special assessments so far as the costs have been ascertained. The certificate must include the estimated construction cost under the terms of any contract for the project; a reasonable allowance for the cost of extra work that may be authorized under the plans and specifications; acquisition of right of way; engineering, fiscal agents’ and attorney’s fees for services in connection with the authorization and financing of the project; cost of publication of required notices; printing of improvement warrants; cost necessarily paid for damages caused by the improvement; interest during the construction period; and all expenses incurred in making the improvement and levy of assessments.

A contract that exceeds, by twenty percent or more, the estimated cost of the project as presented to and approved by the affected landowners is prohibited.