Stormwater quality is regulated at the federal level via the Clean Water Act, which contains an amendment (33 U.S.C. 1342) creating the National Pollutant Discharge Elimination System (NPDES) Storm Water Management Program, overseen by U.S. EPA. Oversight of stormwater quantity in Illinois is under the legal authority of local governments as authorized by the state (55 ILCS 5/5-1062). In undertaking GSI projects, it is important to be familiar with county and other local stormwater ordinances, including considerations such as design storm, detention requirements, and stormwater permitting requirements. Of 102 counties in Illinois, 16 have been granted authority from the state to manage stormwater to address urban flooding. Summaries and links to each county ordinance are provided below.
Illinois Stormwater Regulations
Boone County has the stormwater regulatory authority under Illinois state legislation (55 ILCS 5/5-1062.2). The county has developed a comprehensive stormwater management plan, but has not yet developed a stormwater ordinance.
The Metropolitan Water Reclamation District oversees Cook County’s Watershed Management Ordinance authorized by (70 ILCS 2605/1 et seq.). The Technical Guidance Manual includes design guidance for GSI, a design calculator, and a permit application. The design storm used for the stormwater conveyance system is the 100-year (1% annual chance) event (total precipitation over a 24-hour period that is expected to occur on average once every 100 years). The retention/detention requirement is for the first inch of runoff from impervious area to equal volume control storage.
The City of Chicago Department of Water Management has stormwater authority granted by Sections 2-106-040, 11-16-300, 18-29-110 and 11-18-110 of the Municipal Code.
DeKalb County’s stormwater ordinance and stormwater management plan are authorized by 55 ILCS 5/5-1062.2. The design storm used for the stormwater conveyance system design is the 10-year (10% annual chance) event, with a safe overflow pathway for the 100-year event required. The retention/detention requirements include 100-year, critical-duration storm events.
DuPage County’s Stormwater Ordinance is enabled by 55 ILCS 5/5-1062. The design storm used for the stormwater conveyance system is the 100-year (1% annual chance) event (total precipitation over a 24-hour period that is expected to occur on average once every 100 years). The retention/detention requirements include pre-development peak discharges in a 2-year, 24-hour, and 100-year event of critical duration up to a 24-hour duration.
Grundy County has stormwater regulatory authority under Illinois state legislation (55 ILCS 5/5-1062.2). The county has a stormwater ordinance.
The Kane County stormwater ordinance is enabled by 55 ILCS 5/5-1062. Accompanying this is the Stormwater Technical Manual and stormwater management and permitting are overseen by the Kane County Division of Environmental and Water Resources. The design storm used for the stormwater conveyance system is the 100-year (1% annual chance) event (total precipitation over a 24-hour period that is expected to occur on average once every 100 years). The retention/detention requirements include 0.1 cfs/acre detention + 0.75″ rainfall over impervious area of new development.
Kankakee County has stormwater regulatory authority under Illinois state legislation (55 ILCS 5/5-1062.2). The county has a stormwater ordinance and the Kankakee County Stormwater Technical Reference Manual. The design storm used for the stormwater conveyance system design is the 10-year (10% annual chance) event, with a safe overflow pathway for the 100-year event also required. The retention/detention requirements include 100-year, critical duration storm event.
The Kendall County stormwater management ordinance is enabled by 55 ILCS 5/5-1062 and includes a permit system. The design storm used for the stormwater conveyance system is the 100-year (1% annual chance) event (total precipitation over a 24-hour period that is expected to occur on average once every 100 years). The retention/detention requirements include the total precipitation over a 24-hour period that is expected to occur on average once every 100 years (100-year, 24-hour storm event).
The Lake County Watershed Development Ordinance is enabled by 55 ILCS 5/5-1062. The design storm used for the stormwater conveyance system design is the 10-year (10% annual chance) event, and the retention/detention requirements include: 0.04 cfs/acre for the 2-year, 24-hour event; and 0.15 cfs/acre for the 100- year, 24-hour event.
LaSalle County has stormwater regulatory authority under Illinois state legislation (55 ILCS 5/5-1062.2). The county has a Flood Damage Protection ordinance.
Madison County has stormwater regulatory authority under Illinois state legislation (55 ILCS 5/5-1062.2). The county has a stormwater program. The design storm used for the stormwater conveyance system is the 100-year (1% annual chance) event (total precipitation over a 24-hour period that is expected to occur on average once every 100 years). The retention/detention requirements include the total precipitation over a 24-hour period that is expected to occur on average once every 100 years (100-year, 24-hour storm event).
McHenry County has stormwater regulatory authority under Illinois state legislation (55 ILCS 5/5-1062.2). The county has a stormwater management ordinance. The design storm used for the stormwater conveyance system design is the 10-year (10% annual chance) event, and the retention/detention requirements include: 100-year, critical duration storm event.
Monroe County has stormwater regulatory authority under Illinois state legislation (55 ILCS 5/5-1062.2) and has stormwater regulations. The design storm used for the stormwater conveyance system is the 100-year (1% annual chance) event (total precipitation over a 24-hour period that is expected to occur on average once every 100 years). The retention/detention requirements include pre-development = post-development runoff.
Peoria County has stormwater regulatory authority under Illinois state legislation (55 ILCS 5/5-1062.3). Peoria has a stormwater ordinance, a permit system, and a stormwater utility. The design storm is 2-year and 25-year, and the retention/detention requirements include pre-development = post-development for
2-year and 25-year events.
St. Clair County has stormwater regulatory authority under Illinois state legislation (55 ILCS 5/5-1062.2) and has a stormwater ordinance. The design storm used for the stormwater conveyance system is the 2-year (50% annual chance) event. The retention/detention requirements include the 100-year (1% annual chance) event (total precipitation over a 24-hour period that is expected to occur on average once every 100 years).
The Will County Stormwater Management Ordinance is enabled by 55 ILCS 5/5-1062. The design storm used for the stormwater conveyance system is the 100-year (1% annual chance) event (total precipitation over a 24-hour period that is expected to occur on average once every 100 years).