Revised October 13, 2014
The Prior Lake – Spring Lake Watershed District (PLSLWD) treated Spring Lake with Aluminum Sulfate (Alum) in October of 2013. The graphs below summarize sample results that have been taken since 2004, by the Three Rivers Park District. Two to Three samples are taken each month (during ice-free conditions), and the average monthly concentrations are displayed below (each graph represents one month). The red bar indicates the samples were taken after the Alum Treatment.
Water quality standards for Total Phosphorus on Spring Lake are currently held at 40 µg/L. However, the PLSLWD is submitting a request to the MPCA to raise the standard to 60 µg/L (which makes the standard less strict) based off of research that indicated Total Phosphorus on Spring Lake has never been as low as the current water quality standard. See 2013 Pre-settlement Water Quality and Algal Change in Spring Lake for a summary of this research, or 2013 Historical Water Quality and Ecological Change in Spring Lake for a full report.
So far, the results are very encouraging; however, the flood likely has impacted the results in June and July.