Laserfiche WebLink
Executive Sununary <br />Diagnostic and Feasibility Studies <br />This repon presents the results, implementation plan, and cost esumates tor the Dtagnostic <br />Feasibility Study on Long Lake in Hennepin County. The project was funded by the Minnehaha <br />Creek Watershed Distnct (MC^VD) and the Minnesota Polludon Control Agency (MPCA). <br />The diagnosdc study included a !Z-month water quality monitoring program and subsequent data <br />and land use assessments which characterized the sources of the water quality problems on the <br />lake, the feasibiUty study evaluates the various alternatives for water quality improvement and <br />finally, develops the implementation plan for the project. <br />Long Lake was found to be borderUne eutrophic-hypereutrophic with chronic occurrences of <br />blue-oreen algae blooms and low dissolved oxygen (DO) concentrations. Historical and current <br />monhoring data suggest that dte lake is phosphonts limited. The lake has a relatively shore <br />hydrologic residence time of approximately one year; thus, a reducaon ot the external an <br />internal phosphorus load to the lake was determined to be the necessary action to reduce the <br />blue-green algal bloom. Cutrentiy, the lake's phosphorus concentration is 114 micrograms per <br />Uter Otg/1); » goal of 53 ng'l established. This goal is to be reached after all <br />watershed improvements are implemented. <br />Reduction of the internal phosphorus loading will be accomplished by hypolimnetic aeration. <br />An additional benefit for the lake aeration is the improvement of the spore fishery. In order to <br />prevent excessive fish kills, DO levels must be maintained at 5 miUigrams per liter (mg/1) or <br />greater in the hypolimnion. It may not be necessary to have complete aeration of the <br />hypolimnion. However, a refuge of well oxygenated water would be required to improve the <br />fishery.