7-13-2288. Interest rate on unpaid assessments. The installments of assessments remaining unpaid bear simple interest at an annual rate equal to:

(1) the sum of:

(a) the average interest rate payable on the outstanding bonds issued to finance the improvement in respect of which the special assessments are levied; plus

(b) additional interest at a rate to be determined by the board of directors, not exceeding 2% a year; or

(2) if bonds are not issued to finance the improvements, at an interest rate to be determined by the board of directors, but not to exceed 10% a year.