Project Number: SL-8
The BCWMC officially ordered this project at their meeting on September 19, 2019 after a public hearing. (There were no public comments regarding this project received during the hearing.) The federal grant for this project was approved and a grant agreement was executed in January 2020. A survey of aquatic plants and an herbicide treatment of curly-leaf pondweed will take place in spring 2020. Carp management in Sweeney Lake and Schaper Pond, including removing carp with baited box nets, will take place summer 2020. The first treatment with alum was applied fall 2020. A second alum treatment slated for fall 2022.
Estimated project costs are $568,080. Partial funding of $238,080 is proposed to come from the BCWMC’s Capital Improvement Program funds through 2020 and 2021 ad valorem property taxes collected by Hennepin County on property within the Bassett Creek Watershed. The remainder of project costs will be paid by a Federal Clean Water Act Section 319 grant awarded to the BCWMC through the Minnesota Pollution Control Agency.
This project will significantly reduce phosphorus, improve water quality, and support a balanced aquatic ecosystem in Sweeney Lake by performing an alum treatment and managing carp in Schaper Pond (just south of the lake) and/or in Sweeney Lake. Sweeney Lake is a 67-acre lake with a maximum depth of 25 feet and an average depth of 12 feet. The lake provides recreational value for fishing, boating, and swimming; and it harbors a variety of panfish, a limited game fishery, and an average plant community. The lake receives runoff from a 2,400-acre fully developed watershed with nearly all of the flow entering through the Sweeney Branch of Bassett Creek. The creek flows from the south and through Schaper Pond which is immediately upstream of Sweeney Lake. Despite numerous best management practices installed or implemented in the lake's watershed over the years, water quality in Sweeney Lake has not improved significantly. Regular monitoring from 1985 to the present indicates that total phosphorus concentrations exceeded the state standard of 40 ug/L 74% of the time. Further, the lake has a history of Harmful Algae Blooms, negatively impacting the lake’s recreational usability.
The combination of curly-leaf pondweed control in Sweeney Lake, carp management in Schaper Pond and Sweeney Lake, and an alum treatment in Sweeney Lake is expected to reduce total phosphorus by 350 pounds per year, effectively “flipping” this lake from a eutrophic, algae dominated system, to a healthy, clear water system that can fully support aquatic recreation and a balanced ecosystem for aquatic biota.
No further activity on the lake is planned for 2020. The first phase alum treatment was completed October 28th - November 5th with 37,700 gallons of alum and 18,000 gallons of sodium aluminate applied to Sweeney Lake in the north and south basins. Water quality and temperature was measured regularly to confirm that neutral pH was maintained throughout the application. The City of Golden Valley and the Hidden Lakes HOA assisted by accommodating equipment storage and lake access throughout the treatment. The second (and final) phase of alum treatment is scheduled for the fall of 2022.
Resolution 19-09 Ordering Project (Sept 19, 2019)
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