A presentation from the Nine Mile Creek Watershed District’s public hearing on July 15, 2020, about the proposed Rosland Park stormwater treatment project in Edina. It is presented by Janna Kieffer of Barr Engineering, the District’s engineer.

Lake Cornelia and Lake Edina regularly exceed the state phosphorus standard for shallow lakes, causing poor water clarity and blue-green algae blooms. A 2019 District study found the phosphorus comes from stormwater runoff, lake sediment, and the invasive curly-leaf pondweed. Work already under way included an alum treatment of Lake Cornelia in May 2020, herbicide treatment of curly-leaf pondweed by the City of Edina, and a study of carp and goldfish.

The proposed project would pump water from Swimming Pool Pond into a filtration vault on the north side of the Rosland Park parking lot, then send the cleaner water on to Lake Cornelia.

• The vault would be designed to fit in with the park, and divided into three chambers to test different filter materials.
• Pumping would lower water in Swimming Pool Pond and the connected Lake Otto to as much as about three and a half inches below the normal level. Computer modeling with 35 years of rainfall data shows how often levels would be lower than they are today.
• The system is expected to remove about 22 pounds of phosphorus a year. Construction was estimated at $744,000 (a range of $632,000 to $892,000), plus about $11,000 a year for maintenance. That works out to about $2,200 per pound of phosphorus removed, compared with a typical $5,000 to $10,000.
• The board would consider ordering the project in August 2020, with design that fall and construction in spring 2021.