Adopting the MWRDGC Watershed Management Ordinance (WMO)

Back in 2013, EEA shared some changes to the WMO effective October 4, 2014 and possible project implications. As we mentioned, although this ordinance has the potential to improve regional flooding and reduce water pollution, it could also result in increased project costs. Before May 1, 2015 there was still an opportunity to permit projects under the old ordinance to avoid increasing project costs, pending municipal acceptance. Since that window closed, now all projects falling within the MWRD jurisdiction are required to adhere to the WMO.

The Criteria: Who is impacted and how does your project stack up?

The MWRD is a government agency that oversees the treatment of wastewater and stormwater management in Cook County. The WMO provides requirements and regulations for stormwater management.

Detention considerations:

  • Projects located in suburban Cook County (including combined sewer areas)
  • Multi-family or non-residential projects—Property size exceeding three acres
  • Single-family residential project—Property size exceeding five acres
  • Proposed improvements disturb (consume) more than 0.5 acres

Volume Control (Best Management Practices) Considerations:

  • Projects located in suburban Cook County (including combined sewer areas)
  • Multi-family or non-residential projects— Property developments larger than 0.5 acres except those that contain an area where there are improvements are less than 0.1 acres in size
  • Single-family project – Property size exceeding one acre

We have to do that? We never did before”

So what revisions did we find most surprising? Generally, changes involving volume control, detention and wetland delineations near developments. Below are the ten most impactful changes you should be aware of:

  • An MWRD permit is required prior to any mass grading or foundation installation
  • Disturbance area is a criterion  for MWRD permitting. The permit is no longer dependent upon sanitary sewers or prior permits
  • Stormwater detention is required in combined sewer areas
  • Volume control (infiltration) is required on developed or redeveloped properties more than 0.5 acres
  • Volume control is required in both separate and combined sewer areas
  • Volume control is required for all new pavement/building areas, regardless if it is replacing an existing hard surface area
  • There must be elevation separation between groundwater elevation and the bottom of the volume control system in combined and separate sewer areas
  • Infiltration is required regardless of soil types- clay soil is not an exception
  • Soil testing may be required to determine the permeability of the soils
  • The MWRD now has jurisdiction over erosion and sediment control measures
  • The detention requirement will automatically become even more restrictive in approximately three years

How we can help navigate these changes

EEA has permitted dozens of projects under the WMO. Our team has helped clients use the nuances of the ordinance to make key design decisions that meet the requirements in cost-effective and innovative ways, while incorporating green infrastructure. The following is a sampling of recommendations on how to best utilize the ordinance:

  • 25% reduction in volume control with every 5% reduction in imperviousness
  • Synthetic turf athletic fields are not considered impervious
  • Reduce or eliminate additional detention where minimal changes affect an existing basin
  • Eliminate the need for conveyance of off-site flow by incorporating it into site stormwater facilities at a net reduction in cost
  • Eliminate an increase in detention for on-site flow that cannot be captured by offsetting it with equivalent upstream areas

EEA is a resource in guiding consultants and owners through the intricacies of the WMO. For more information, please contact us at or at (847) 223-4804.