Indiana Code Title 13. Environment § 13-18-20-15

Sec. 15.  If a person does not remit an annual NPDES fee or an installment established by the department under IC 13-16-2 and any applicable delinquency charge to the department not more than ninety (90) days after the date the fee is assessed or not more than sixty (60) days after the date the installment is due, the department may revoke the person's NPDES permit.  However, before the department may revoke the permit:

the department must deliver a written notice to the person that describes what fees and delinquency charges are due and indicates that the department may revoke the person's permit for nonpayment after thirty (30) days.