The Metropolitan Water Reclamation District oversees all storm water improvements taking place within Cook County, Illinois (with the exception of the City of Chicago). On January 1, 2020, the Metropolitan Reclamation District of Greater Chicago (MWRDGC) will enact its new storm water ordinance, which will have dramatic impacts to future developments in Cook County. Changes to the ordinance will include:
1. An increase in the rainfall quantity used for detention modeling. The rainfall quantity used will increase from 7.58 inches to 8.57 inches (a 13% increase). This increase is based on new hydrologic data that was updated by the Illinois State Water Survey Prairie Research Institute in March 2019.
2. The MWRDGC allowable release rates will be reduced from 0.30 CFS per acre to 0.20 CFS per acre in some areas, representing a 33% decrease in allowable release rate. Please see the Watershed Planning Area Map for individual release rates for specific areas.
WHAT DOES THIS MEAN FOR FUTURE DEVELOPMENTS?
The implementation of these changes will increase development costs for projects within Cook County. We estimate that the new requirement could increase detention requirements by 20% to 25%.
HOW WILL A 25% INCREASE IN DETENTION VOLUME AFFECT DEVELOPMENT COSTS?
Most sites in Cook County have limited area for at grade detention ponds, therefore underground detention systems are usually required. A typical 3.5-acre development in Cook County will require approximately 1-acre foot of detention. The cost of a 1-acre foot underground detention system is $500,000.Therefore, after January 1, 2020, the detention cost of a typical 3.5-acre development will increase from $500,000 to $625,000.
WHAT CAN YOU DO?
If your project is recorded within the MWRD’s permit log system by December 31, 2019, the development will remain under the jurisdiction of the current ordinance. However, it is important to note that the local municipality must review and approve a project before a permit submittal can be made to the MWRD. In order to meet the deadline, we recommend that projects be submitted to the local municipality by September 1, 2019, to ensure enough time to review and approve the project and sign the MWRD permit applications.
If you have any questions or comments regarding this change, please feel free to contact Todd Abrams, PE, at 224-293-6333.