North Wilmes Lake Alum Treatment Facility

Challenge

The South Washington Watershed District (SWWD) identified North Wilmes Lake in Woodbury, Minnesota, as a priority site for phosphorus reduction, targeting a reduction of 153 pounds per year to improve water quality within the lake and the broader watershed. A previous study determined that an alum treatment facility would be the most cost-effective solution for reducing phosphorus levels. The challenge was not only technical—designing a facility that would function effectively—but also spatial and aesthetic. The facility needed to be constructed within a public park, requiring sensitivity to community use and environmental stewardship.

Solution

HR Green was selected to lead the project through every phase—from alternatives analysis to final design and construction services. HR Green designed an innovative stormwater treatment facility that pumps water from the lake’s influent channel into a chemical dosing station, where alum is introduced to bind with phosphorus. The treated water then flows into a constructed settling pond before returning to the lake, significantly reducing phosphorus levels. The facility’s design carefully integrated low-impact lighting, native landscaping, and a permeable driveway to minimize disruption to the surrounding park space. A recreational trail through the site was preserved, and educational signage will help the public understand the facility’s environmental benefits.

Benefit

By improving water quality in North Wilmes Lake, the facility enhances both ecological health and community enjoyment of the area. Given the lake’s high turnover rate, it contributes to maintaining water quality in downstream lakes. The project leverages municipal partnerships to establish a new option for regional stormwater treatment in Minnesota.