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

Key Facts

Statute: 415 ILCS 5/ Environmental Protection Act
Permit ILR10: Construction 1+ acre
Permit ILR40: MS4 municipalities
Agency: Illinois EPA
Plan required: SWPPP at construction sites

Full Breakdown

Under the Illinois Environmental Protection Act (415 ILCS 5/) and 35 Ill. Adm. Code 309, IEPA issues NPDES permits for stormwater discharges. Construction sites disturbing one or more acres must obtain ILR10 general permits and implement Stormwater Pollution Prevention Plans. MS4 communities require ILR40 permits with six minimum control measures. These federally driven obligations apply universally and cannot be waived by local governments, even where municipalities lack their own stormwater ordinances.

Violations & Penalties

Discharging sediment-laden runoff without an ILR10 permit, failing to implement SWPPP at construction sites, or unpermitted illicit discharges to storm sewers.

Frequently Asked Questions

When do I need a stormwater permit in Illinois?

Construction projects disturbing one or more acres must obtain an ILR10 NPDES general permit from Illinois EPA before ground disturbance begins, and implement a Stormwater Pollution Prevention Plan.

Can a city waive Illinois NPDES stormwater rules?

No. NPDES permits are federally delegated through Illinois EPA and apply uniformly statewide. Municipalities may add stricter rules but cannot waive permit conditions or federal Clean Water Act obligations.

What is an MS4 in Illinois?

A Municipal Separate Storm Sewer System. Operators in urbanized areas need an ILR40 permit and must implement six control measures, including public education, illicit discharge detection, and post-construction runoff control.

Illinois NPDES Stormwater Permit Statewide Requirements

Key Facts

Full Breakdown

Violations & Penalties

Frequently Asked Questions

Sources

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