The Use Attainability Assessment (UAA) undertaken by the District and the City of Chanhassen in 2016 found that the majority of pollutant loading to Rice Marsh Lake is due to runoff within the watershed (44%), with internal loading accounting for an additional 35% of the pollutant load. The remaining load is from upstream water bodies or atmospheric deposition. Further, the UAA concluded that Rice Marsh Lake Subwatershed RM-12A was the largest contributor to external pollutant loading to Rice Marsh Lake. In the fall of 2018, Rice Marsh Lake was treated with Aluminum Sulfate (alum) to treat the internal loading. The Rice Marsh Lake Water Quality Improvement Project is now looking to address the external load from subwatershed RM-12A.
This project consisted of two manufactured treatment devices (MTDs) used in parallel, a rain garden, soil amendments and prairie restoration. These practices will result in the removal of approximately 1/3 of the load from the watershed - around 90 pounds of total phosphorus per year.
Construction began in fall 2021 with the installation of the MTDs and ancillary storm sewer improvements. Vegetative restoration occured in the spring of 2022.