County staff proposes simplified stormwater exemption method, tighter release-rate focus

McHenry County staff presented a draft overhaul to the county Stormwater Management Ordinance on a proposed simplified exemption method that would change how developers qualify for detention waivers and how allowable release rates are calculated. The proposal would align a bright-line threshold from 20,000 square feet to a half acre and allow a simplified exemption for up to a 10% increase in impervious area if downstream impacts remain within prescribed limits.

The draft replaces a narrow "no flood damage" test with a "minimal flood risk" standard and requires projects to maintain existing drainage patterns and discharge to a defined channel. "We're going to change the 20,000 square foot to a half acre," staff said during the presentation, noting that most other ordinance language uses acres. The simplified pathway uses standard downstream assumptions — for example, a…