This innovative project cleans 20 million gallons of stormwater each year.
At 70 acres of mostly asphalt pavement and concrete surfaces, the Maplewood Mall was a major source of phosphorous runoff to nearby Kohlman Lake. Through a 4-year, multi-phase construction project, we installed a variety of features that now capture and filter 67 percent of rainwater at the mall, up from just 3 percent before the project.
The mall parking lot features innovative tree trenches, which use layers of angular granite to form a rock filter that slowly drains water into the local storm sewer. The main entrance is fitted with rain gardens, permeable pavers and a 5,700-gallon cistern that receives runoff from the mall roof. Interpretive signage and a conservation-themed mural draws attention to these improvements, and a large watershed map in the entry vestibule shows how water travels from the mall all the way to the Mississippi River.
The project received the Grand Award from the American Council of Engineering Companies, and it was named Project of the Year by the Minnesota Association of Watershed Districts.
Maplewood Mall Summary
Land & Water magazine article
Tree Trench Fact Sheet