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81 5) BENNETT LAKE WATER QUALITY REPORT 82 Ryan Johnson, Environmental Specialist, introduced himself to the commission. Johnson provided 83 the definitions of two terms that would be used during his presentation on the Bennett Lake Water 84 Quality. The two terms are listed below: 85 Impaired: When a water body fails to meet standards set by the MPCA, it is listed as an impaired 86 on the MPCA 303(d) Impaired Waters List and a Total Maximum Daily Load (TMDL) study is 87 required 88 o Required by Section 303(d) of the Federal Clean Water Act 89 TMDL – Total Maximum Daily Load: Water quality study to determine allowable pollutant 90 loading from point and nonpoint sources determine allowable pollutant loading from point and 91 nonpoint sources to lakes/rivers so as to achieve the water quality standards. 92 o Approved by both the MPCA and the USEPA 93 94 The brief history and overview of Bennett Lake consist of the following details: 95 Drainage Area = ~780 acres 96 Primarily single family residential 97 Lake area = 25 acres 98 Maximum depth = 9 feet 99 During the 1940’s Bennett Lake area was only a wetland 100 101 Algae blooms happen during the summer months happen as a result of contaminants. One of the 102 main is Phosphorous. For Bennett Lake Phosphorous sources include: 103 External 104 o Stormwater runoff from hard (impervious) surfaces 105 o Soil erosion 106 o Pet/animal waste 107 o Leaves & grass clippings 108 o Fertilizers 109 o Point discharges 110 Internal 111 o Phosphorus can be stored in lake bottom sediments and released when oxygen levels are 112 low 113 o Bottom sediment can also be re suspended and bring phosphorus into the water column 114 o Carp can stir up lake sediments, causing turbidity and phosphorus release 115 o Macrophyte die off 116 117 Staff provided graphs showing the rates of Chlorophyll (1985-2019) Phosphorus (ug/l) (2003-2019) 118 and Secchi Disk Transparency (2003-2019) in Bennett Lake. 119 120 3 6