N.D. Cent. Code § 61-35-85
Improvement bonds may be used in making payments on contracts for construction of the project for which the special assessment fund was created, or may be sold for cash at not less than ninety-eight percent of par and accrued interest, and the proceeds, less accrued interest, must be credited to the construction account of the fund and must be used exclusively to pay those contracts and construction costs. Any balance remaining in any construction account after completion of any project must be transferred to the sinking fund account of the assessment fund. The treasurer of the district shall pay special assessment bonds as they mature and are presented for payment out of the fund on which they are drawn and shall cancel the bonds when paid.
N.D.C.C. § 61-35-85