The VRWJPO and the City of Apple Valley continued their efforts to improve the Alimagnet Lake subwatershed. This project retrofits an existing stormwater pond, known locally as Sunset Pond, that drains to Alimagnet Lake with an iron-enhanced sand filter (IESF) bench, which will reduce the amount of phosphorus reaching the lake. Alimagnet Lake has too much of the nutrient phosphorus, which is often the key ingredient for excess algae growth. The project is near the southwest corner of McAndrews Road and 140th Street, within Apple Valley’s Sunset Park.

The project created an IESF bench along-side an existing stormwater pond and adjacent to Alimagnet Lake. The IESF bench was separated by a rock wall from the stormwater pond to keep out debris that might clog the filter. Stormwater ponds tend to capture particulate phosphorus tied to sediment that settles in them but remove very little dissolved phosphorus. Dissolved phosphorus moves with stormwater and ends up in Alimagnet Lake where it becomes available for plants, including algae which can make the water appear green. The iron material added in the IESF bench removes dissolved phosphorus as stormwater flows into the filter from the pond. This project prevents 12.4 pounds of phosphorus from reaching Alimagnet Lake each year.

The reduced phosphorus in the stormwater that is draining to the lake results not only in improved water quality in Alimagnet Lake, but also improved water quality in water bodies that Alimagnet Lake drains to, such as East Lake in Lakeville. The reduction in phosphorus aids in meeting State water quality standards and works toward removing Alimagnet Lake from the impaired waters list. The project also takes steps to restore water resources for public use.

This project was funded through a DNR – Clean Water Fund Grant and local in-kind and cash matches from the VRWJPO and the City of Apple Valley.