The Prior Lake-Spring Lake Watershed District (PLSLWD) Board of Managers will make a final decision on the alum treatment of Spring Lake at their regular board meeting on October 8, 2013 at 6:00 pm at Prior Lake City Hall.
If the PLSLWD Board approves the treatment, an alum application will be applied to Spring Lake this fall. The treatment will cost approximately $450,000 and will be funded by the PLSLWD.
In 2011, the PLSLWD conducted a Total Maximum Daily Load (TMDL) study of Spring and Upper Prior Lakes. A TMDL study evaluates the maximum amount of a pollutant that a waterbody can receive and still meet state water quality standards. This study found that Spring Lake was impaired, or threatened, by excess phosphorus, and recommended that the phosphorus concentration should be reduced by about 85% in Spring Lake. The study also determined that approximately half of the phosphorus in Spring Lake comes from the surrounding land and streams that drain to the lake, and the other half is released internally from the bottom of Spring Lake.
In order to address the internal phosphorus concentrations, the PLSLWD is considering an alum treatment for Spring Lake. Aluminum Sulfate, or alum, is a nontoxic material that is commonly used in water treatment plants to clarify drinking water. In lakes, alum is used to lower the concentration of phosphorus in the water. The expected lifespan of the potential treatment of Spring Lake has been estimated at 15 to 30 years.
More than one approach is needed to reduce the phosphorus concentrations in Spring Lake. It will take a combination of land, stream, and in-lake practices to meet our water quality goals. By implementing best management practices, like installing raingardens, shoreline buffers, and working with the local community to reduce runoff from lawns and agricultural fields, we all can help lessen outside watershed sources of phosphorus caused by runoff.