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TMDL Goals for Bald Eagle Lake The Bald Eagle Lake TMDL indicates the lake is impaired for aquatic life/aquatic recreation. The pollutant that is creating this impairment is phosphorus. The TMDL has identified the current phosphorus budget and the required reductions to meet the in -lake phosphorus goal of forty (40) micrograms per liter. The TMDL has indicated a need for a ninety-one (91) percent reduction in internal phosphorus loading and a thirty-eight (38) percent reduction in external phosphorus loading to the lake from its watershed. Based on an extensive analysis of recently completed hydrologic and P8 modeling for the watershed, a summary of pertinent hydrologic and water quality information is provided below: • 3,523 acres of land within Hugo drain to Bald Eagle Lake • Under current conditions with existing BMPs, areas within Hugo create an annual phosphorus load of 756 pounds • If the phosphorus load is reduced by 38%, Hugo's share would correspond to a 287 pound reduction. This would correspond to the City having a projected allowable phosphorus load of 468 pounds. • The existing phosphorus load is generated with a corresponding runoff volume of 1,590 acre feet. • When the watershed is fully developed, it is estimated 1,971 acres of impervious surface will be present. This compares to the 1200 acres of impervious surface currently in place. • Based on fully developed conditions, if one inch of infiltration is provided from all impervious surfaces, and existing BMPs are in place the fully developed phosphorus load will be 668 pounds and have a corresponding runoff volume of 1,181 acre feet. • If full development takes place and only existing BMPs are utlized, the phosphorus load to Pether Lake would increase to 2,150 pounds per year (representing an increase of 1,398 pounds). • Without infiltration BMPs, the future runoff volume would be 4,338 acre feet. With one inch of infiltration, the volume would be reduced by 3,157 acre feet and result in a future runoff volume of 1,181 acre feet. • On average, modeling predicts 1.89 pounds of total phosphorus will be generated per acre of impervious surface and approximately one pound of phosphorus is contained in one acre foot of untreated stormwater runoff. • To meet the target watershed load reduction of 287 pounds, the TMDL has indicated that phosphorus concentration in water discharged to the lake could be reduced to have a maximum concentration of one hundred seventy seven (177) micrograms per liter, the runoff volume could be reduced by thirty-eight (38) percent, or a combination of the two could be utilized to achieve this goal. CIP for Storm Water Projects Within the City of Hugo City of Hugo, MN WSB Project No. 1687-85 Page 8