Evaluation of Media Effectiveness for Removal of Phosphorus and Other Pollutants in an Active, High-Volume Stormwater Filtration BMP

Nine Mile Creek Watershed District (NMCWD) and the City of Edina are constructing an active stormwater filtration BMP in Rosland Park to address external phosphorus loading to Lake Cornelia, an urban hypereutrophic lake. The BMP consists of an anthracite prefilter followed by three parallel media filters for dissolved phosphorus removal. Completion of the BMP is anticipated in the second quarter of 2022. The requirements of this treatment system were unique because it needed a small footprint but also to treat large volumes of water. The design solution was to site the BMP adjacent to Lake Cornelia to utilize the existing storage capacity and to use a filtration media that is highly permeable with the capacity to filter water on a regular basis.

This configuration and design differ from typical passive stormwater treatment systems that receive runoff on a per event basis, allowing for higher volumes of water to be treated. We are proposing to monitor the performance of this BMP and evaluate its ability to reduce external phosphorus loading to Lake Cornelia. This grant opportunity will allow NMCWD to thoroughly examine and share knowledge gained such that NMCWD and the broader stormwater community can evaluate the benefits of an active, high volume treatment system that has a small footprint and targets removal of nutrients that are unsettleable by traditional means.

Projected outcomes

  • A robust dataset comparing the phosphorus removal efficiencies and other performance criteria between three mixed media in an active stormwater filtration BMP.
  • A robust outreach plan to share key findings with stormwater practitioners regarding an innovative alternative to achieve phosphorus removal using a high-volume active filtration system.
  • Identification of a mixed media targeting dissolved phosphorus that could be applicable for active or passive filters that could provide a potential design benefit over existing designs.
  • An understanding of the design, engineering, operation, and maintenance considerations for an active stormwater filtration BMP.
  • Identification of a mixed media that is appropriate for use in a stormwater filtration BMP under consistent water inundation.