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GLWMO MINUTES JANUARY 24, 2008 PAGE 7 Mr. Sobiech stated that the macrophyte survey showed a high density of curly leaf pondweed. This finding agrees with what lake management is seeing at the southern end of the lake and is the reason for the increase in phosphorous. It is impacting the water quality in the lake. The sediment core analysis shows the potential for Lake Owasso to have phosphorous from bottom sediments as low compared to other metro area lakes. Stark noted that there seems to be correspondence between the rates and deeper parts having more mobile phosphorous. Sobiech responded that in 2002, the MPCA completed a diatom study of 55 Minnesota lakes, including Lake Owasso. This study shows that historically the phosphorous content was 10 and 25 micrograms per liter, which is significantly better than where it is now. Last summer it was 33 and 31 micrograms per liter. It is safe to say the natural watershed at its best could expect approximately 20 micrograms per liter. Ferrington asked if there will be a raw data diatom report. Mr. Sobiech answered that the MPCA report can be made available to the Board. Stark asked if the MPCA diatom report fits the state's regional standards for phosphorous. Mr. Sobiech stated that the analysis shows that the area of development near the lake averages a concentration of 40 micrograms per liter with a range of 25 to 55. The data collected in this study agrees with that analysis. The actual watershed models the P8 computer program. Table 3 summarizes the total measured versus predicted pollutant loads for all events at each of the monitoring sites. Referring to footnote a of Table 3, during the entire summer of 2007, there were five events where enough data was collected to calibrate. The better site was West Owasso Boulevard which had eight storm events to calibrate. The first thing to look at in the models is to produce the right volume of runoff coming from the watershed which is compared to the monitoring data. Over time all three station models did well estimating volumes of runoff. The site used for Table 3 to estimate pollutants has not pond. That allowed calibration of the watershed parameters and not worry about treatment by BMP. From that calibration at that site, an estimate of depression storage was calculated to see how much water sits before runoff occurs. The other two locations indicated a pond infiltration rate. A lot of pond water levels are low. Infiltration and evaporation are occurring. Water levels have to fill before it gets to the lake. The outlet from Lake Owasso freezes during the winter, which is why the lake level stays above normal in winter.