The T5 Data Center proposed in Grayslake, Illinois poses a significant threat to the local environment, and particularly stands to impact local stormwater management, related to the removal of 16 acres of wetlands from the headwaters of the Mill Creek Watershed (a sub-watershed to the Des Plaines River Watershed).

Where wetlands provide ecosystem services by soaking up water like a sponge, filtering out chemicals, and providing unique habitat that cannot be efficiently replicated, hardscape environments provide none of those benefits. Developments at this scale fundamentally alter their watersheds by replacing wetlands,  vegetation, and permeable soil with impermeable surfaces like rooftops and pavement.

One acre of wetland can typically store between 1 million and 1.5 million gallons of floodwater, significantly reducing the load on municipal stormwater systems. The loss of this storage will result in predictable impacts on waterways in  downstream communities, including: heavier flows during storms, decreased baseflow, channel erosion and widening, degraded water quality, and increased flood risk.

Development in Lake County, IL that has the potential to impact stormwater resources is regulated by the Lake County Stormwater Management Commission. Their governing document, the Watershed Development Ordinance, outlines the minimum stormwater management requirements for Lake County developments. This document includes specific regulations for how wetland environments lost to development are mitigated/replaced. 

In most instances, the County requires that wetland mitigation occurs within the same primary watershed that has lost the wetlands. In the case of the Grayslake's T5 Data Center, mitigation would likely be required to occur within the Des Plaines River Watershed, which covers 44% of Lake County. From a County-wide perspective, this is a thoughtful requirement that does a lot of good. But depending on where mitigation occurs, there is a good chance it will do very little for the communities immediately downstream of the development that currently rely on existing stormwater management benefits from those 16 acres of wetlands. Communities with all or a portion of their municipal boundaries within the Mill Creek Watershed include Grayslake, Old Mill Creek, Gurnee, Lindenhurst, Third Lake, Round Lake Beach, Wadsworth, Libertyville, Round Lake Park, Hainesville, and unincorporated Lake County.

For this reason, we are calling for community support to require that this project exceed the County’s minimum requirements for wetland mitigation by requiring that the loss of these 16 wetland acres be mitigated locally, within the Mill Creek Watershed.

Join us in urging the relevant authorities to mandate that the T5 Data Center in Grayslake undertake wetland mitigation efforts within the Mill Creek Watershed, to ensure the downstream communities don’t lose the stormwater management benefits they currently receive from the 16 acres of wetlands planned for removal.

**For more information about the Mill Creek Watershed and locations downstream from Grayslake's T5 Data Center, see the 2014 "Mill Creek Watershed and Flood Mitigation Plan".