To improve the health of Normandale Lake, the District and City of Bloomington will conduct a lake-level drawdown, selective herbicide treatment, and alum treatment.
What’s happening now?
(July 31, 2018) Contractor Selected for Project
The District’s Board of Managers awarded a contract to Rachel Contracting to draw water levels down in Normandale Lake and construct a new, permanent outlet pipe in the lake. The lake drawdown is anticipated to begin no later than August 23rd. Once the the drawdown begins, you will slowly see water levels begin to drop in the lake.
Normandale Lake presently experiences high phosphorus concentrations in the summer (>60 µg/L) and potentially high phytoplankton amounts, both of which contribute to water quality concerns. The lake contains an abundance of curly-leaf pondweed, an aggressive invasive aquatic plant, which results in limited plant diversity. The low plant diversity in combination with low dissolved oxygen levels in the water column pose concerns for the lake’s aquatic communities. Excessive aquatic plants and filamentous algae in Normandale Lake cause late summer algal blooms, resulting in an occasionally strong hydrogen sulfide odor and impaired recreational use of the lake. The management options that will occur as part of this project will address these issues.
The project involves multiple steps to address concerns associated with a prevalence of curly-leaf pondweed in Normandale Lake and the release of phosphorus from lake-bottom sediments (internal loading).
A temporary pump and an existing bypass pipe will be used to draw the lake down in late-summer. At the same time, the District will install a larger bypass pipe to maintain the lake drawdown and decrease potential impacts of rainfall or snowmelt events during the drawdown period. The new pipe will be installed on the north side of the existing lake outlet structure. The pipe will extend into the deepest spot in Normandale Lake and convey water from the lake, under the embankment and directly into Nine Mile Creek downstream of the existing outlet. Once the larger pipe is installed, pumping will stop and the larger pipe will be used to maintain the drawdown. Following the drawdown, the lake will refill by mid-April.
A drawdown is one way to control curly-leaf pondweed, and to a lesser extent internal phosphorus release from sediment. Curly-leaf pondweed primarily reproduces through vegetative propagules called turions. Turions are produced in late spring, remain dormant in sediment through the summer, and germinate under cooler water conditions in the fall. However, a winter freeze of the lake sediment bed can kill the turions, thus stopping the curly-leaf pondweed’s reproductive cycle.
Chemical Treatment of Curly-leaf Pondweed
In the spring, once the lake has refilled after the drawdown, herbicide treatment with Endothall, a curly-leaf pondweed-selective herbicide, will occur. Endothall is most effective when applied in the spring when the water temperature is approximately 55-60oF. Endothall is applied from a treatment boat or barge.
In-lake Alum Treatment
When aluminum is applied to a lake as a solution of alum (aluminum sulfate), it forms an insoluble aluminum hydroxide floc that settles to the lake bottom. The aluminum binds with phosphorus in the sediment to prevent it from recycling back into the water column. Alum application will be conducted in the spring when the lake has refilled, at approximately the same time as Endothall treatment. Alum is applied from a treatment boat or barge. Conducting the alum treatment before aquatic plants are reestablished in the lake will allow the aluminum floc to reach the sediment more uniformly.
Two public meetings were held on May 15th and May 24th regarding the project, and a public hearing was held on June 12th.
Project Brochure: Normandale Water Quality Improvement Project Brochure (PDF)
The City of Bloomington and the NMCWD partnered to create two educational videos about the project.
Pack your bags, pondweed!
Upcoming water quality project to clean up Normandale Lake
The anticipated timeline is for the lake drawdown to begin in mid-August 2018 and for the lake to refill by the end of April 2019. The endothall and alum treatments would occur in spring 2019.
Lake users will notice low water levels in the lake from late summer to early spring. You will see boats on the lake in the spring doing work. After the lake refills, and the project is complete, a healthier plant population will grow in the lake.
The lake management practices considered as part of this project are part of a holistic approach to improving the water quality and ecological health of Normandale Lake. The practices are intended to reduce internal phosphorus loading, improve the native aquatic plant community, and increase the concentrations of dissolved oxygen in the water column, helping the lake’s fishery, reduce foul odors often produced during the summer months, and improve recreational use of the lake.
The District has recently expanded its emphasis on the role of ecological indicators (aquatic plants, phytoplankton, fish, etc.) in overall lake health, as well as the feedback mechanisms between these indicators. Several evaluation factors for holistic assessment of lake health, including water quality, aquatic communities, water quantity, wildlife habitat, and recreation are emphasized. While numerical goals exist for some of these factors (e.g., MPCA water quality standards), other ecological lake health factors will be assessed without strict numerical goals (e.g, health of the aquatic plant communities) before and after the project.
Contact Erica, Program and Project Manager, at 952-358-2276.
DID YOU KNOW?
The City of Bloomington and the NMCWD created Normandale Lake in 1979 for flood control. Since its creation, it has prevented significant flooding in Bloomington. More Information
Normandale Lake Project Updates
(July 31, 2018) Contractor Selected for Project
The District’s Board of Managers awarded a contract to Rachel Contracting to draw water levels down in Normandale Lake and construct a new, permanent outlet pipe in the lake. The lake drawdown is anticipated to begin no later than August 23rd. Once the the drawdown begins, you will slowly see water levels begin to drop in the lake. The lake will be substantially empty by mid-September, depending on rainfall during that time. A pool of water will remain on the west side of the lake. The District will close the bypass pipe in early March to allow the lake to refill by April. In addition, a temporary water control structure (weir) will be installed in the Nine Mile Creek channel just upstream of Normandale Lake to maintain normal water levels in the wetland area north of West 84th Street during the lake drawdown. The District will also install turtle fencing around the perimeter of the lake, allowing turtles to safely find new winter homes.
(June 20, 2018) Normandale Water Quality Improvement Project Ordered
On June 20, 2018, the NMCWD board of managers ordered the Normandale Water Quality Improvement Project.
(June 20, 2018) NMCWD Board decided Environmental Impact Statement (EIS) not necessary
The NMCWD Board of Managers issued a negative declaration that the preparation of an Environmental Impact Statement is not necessary.
(May 30, 2018) Environmental Assessment Worksheet (EAW) Comment Period Closed
The Nine Mile Creek Watershed District released a voluntary Environmental Assessment Worksheet (EAW) for the Normandale Lake Water Quality Improvement Project located in Bloomington, MN for review and comment. The project includes lake-level drawdown, herbicide treatment, alum treatment, possible aquatic plant harvesting and in-lake oxygenation. Written comments on the EAW were received through May 30, 2018.