Does my city's stormwater ordinance preempt the state rule?

No. Indiana law sets a minimum statewide floor through IDEM's NPDES program. Local ordinances must equal or exceed state requirements but cannot weaken Rule 5 or MS4 obligations.

Do small construction projects need a permit?

Construction disturbing less than one acre and not part of a larger common plan is exempt from Rule 5 NPDES coverage, though local erosion control ordinances may still apply.

Indiana Stormwater Management Law: Statewide Environmental Rules Rules (2026)

Key Facts

Governing statute: IC 13-18-3
Construction Rule 5 trigger: 1 or more acres
MS4 minimum measures: Six required programs
Permit issuer: IDEM
Maximum daily penalty: Up to $25,000

Full Breakdown

Under IC 13-18-3 and Indiana Administrative Code Title 327 Article 15, IDEM issues general NPDES stormwater permits regulating municipal separate storm sewer systems (MS4s), construction sites disturbing one or more acres (Rule 5), and industrial activity (Rule 6). MS4 entities must implement six minimum control measures: public education, public involvement, illicit discharge detection and elimination, construction runoff control, post-construction stormwater management, and pollution prevention. Local stormwater ordinances must meet or exceed IDEM standards. Cities cannot reduce protections below the state floor, though they may add stricter local water-quality criteria.

Violations & Penalties

Discharging without an NPDES permit, failing to file Notice of Intent, or violating permit terms can trigger civil penalties up to $25,000 per day per violation under IC 13-30-4 and federal Clean Water Act enforcement.

Indiana NPDES Stormwater MS4 and Industrial Permits

Key Facts

Full Breakdown

Violations & Penalties

Frequently Asked Questions

Sources

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