In response to increased flooding and water quality issues throughout the Chicagoland area, the Metropolitan Water Reclamation District of Greater Chicago (MWRDGC) spent nearly a decade developing new regulations for water storage and detention to find a balance between resource protection and new development in northern Illinois. The result of their labors is the new Watershed Maintenance Ordinance (WMO), effective May 1, 2014.
It’s no secret the ordinance tightens requirements, but the devil is in the details. We asked George Dreger, Technical Director at Eriksson Engineering Associates, Ltd. what changes will make the biggest impact, and what does it mean for our clients? Here’s what he told us.
For those with projects in suburban Cook County, the changes will have an effect on the overall cost and schedule, space required for detention and quality of water running off the site. On paper, the differences between the current Sewer Permit Ordinance and the new WMO are extensive, but there are a few key areas where projects will be affected moving forward.
The most predominant change with the new WMO addresses volume control or the first flush of rainwater leaving a site. In essence, with the new regulations, the MWRDGC is striving to capture and hold this water on the site longer so it might have the opportunity to infiltrate into the soil or evaporate before leaving the site.
With the new WMO, stormwater detention will be calculated in a new way using more current and stringent rainfall rates. Tied in closely with stormwater management, this means more land may need to be set aside or additional best management practices implemented to restrict the rate of rainfall leaving the site. The WMO regulations effective on May 1st will attempt to mimic current regulations, but we’ll see a further reduction in the release rate allowed in five years, resulting in a 50 percent overall change.
The WMO is also designed to improve water quality. To prevent water from carrying dust, oil or other matter from one site to another, the MWRDGC is encouraging the use of “green” mitigation practices and the protection of wetlands to assist in reducing release rates.
As these changes go into effect, it will be important to consider the size of the project site, as detention and erosion control will be required on more sites than in the past. A three-acre non-residential site, for example, will require detention with the new WMO when currently it requires no detention.
Projects currently underway, if submitted for permitting before May 1st, will not be required to meet the new WMO regulations. For projects following the inception of the new ordinance, there are still uncertainties surrounding the requirements they will need to follow depending on how the individual municipalities view the particular project’s progress. Regardless, moving forward, clients will need to carefully consider the size of their site, costs associated with stormwater requirements, the development timeline, and opportunities to incorporate best management practices.