Indiana Code Title 36. Local Government § 36-9-38-32

Sec. 32. If the fees established under section 31 of this chapter produce net revenue in excess of reasonable costs of operation and maintenance, the excess revenue shall be used to pay part of the principal and interest on the bonds issued as the bonds mature.  To the extent that principal and interest is paid from the excess revenue, the assessments shall be reduced and canceled on a pro rata basis.