Mundelein Wastewater Treatment Plant - Wetland Mitigation

The Village of Mundelein Wastewater Treatment Plant (WWTP) is located adjacent to the Des Plaines River in Lake County, Illinois. Because of its proximity to the river, the WWTP property includes areas of wetland and 100-year floodplain. An expansion project required the Village to mitigate for causing impacts to the floodplain and surrounding area. Surrounded on three sides by private property and on one side by the river, the questions were where and how could the Village mitigate the impacts. Village staff had the vision to co-locate a new 1.5-acre wetland/prairie restoration area within the required compensatory stormwater storage area. The newly created wetland provides a natural best management practice for the cleansing of stormwater run-off before entering the Des Plaines River along with a habitat for wildlife.

Creating this new wetland area within an existing turf area that was designed to receive excess moisture only during the 100-year storm event would require the diversion of upland stormwater run-off that normally flowed through the site to the Des Plaines River, to the newly created wetland area. This required the construction of a cast-in-place concrete weir structure; installation of 30-inch storm sewer pipe, re-grading the proposed wetland bottom area to act as a meandering stream, installation of live wetland plugs, and seeding.

Prior to construction, the project had to be designed and permitted through the United States Army Corp of Engineers (ACOE). The Village/ACOE and SEC concurred that the new wetland area would naturally cleanse diverted stormwater runoff of sediment and chemicals by allowing it to percolate into the ground, evaporate into the air or be absorbed by the wetland plants.

With the start of construction, the project team now included the wetland contractor – Cooling Landscape Contractors, LLC (Cooling). Although the construction contract was awarded to Cooling in the spring, their experience with wetland projects along with the Village/SEC willingness to work cooperatively, allowed the delay of the start of construction to late summer in order to take advantage of the late summer/early fall planting season.  Cooling correctly staged the work and completed the project in approximately one month.