As reconstruction of Grange Avenue comes to a close, a number of people have asked questions about the wildflower covered medians in a portion of the project. Sections of the new pavement on the Grange Avenue project have been shaped to direct storm water toward the median and into the bio-retention swales. A series of 41 openings in the curb-line equally distributes the water in the filtering area via concrete flumes. After being collected in the swale, the water then percolates through large native wildflower covered beds comprised of layers of engineered soils, crushed stone and sand. The filtered water collects at the bottom of the swale and flows through a series of distribution pipes into Dale Creek.

This bio-filtration device is designed to remove silt and other pollutants from storm water runoff. It is an excavated area that is backfilled with crushed stone (for storage) and an engineered soil mix (consisting of sand, topsoil and compost) that is covered with a mulch layer and then planted with wildflowers. Storm water percolates through the mulch and engineered soil, where it is treated by a variety of physical, chemical and biological processes that trap pollutants and silt before infiltrating back into the native soil or overflowing into the storm sewer system.

The construction of the Grange Avenue bio-retention swales will help the Village of Greendale meet WDNR storm water permit compliance goals. The Village is proud to have participated in this beneficial Water Quality Initiative Project, with assistance from the Wisconsin Department of Transportation, the Wisconsin Department of Natural Resources, and the Milwaukee Metropolitan Sewerage District.


Graphic: Bio-Retention Swale