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Section V <br />Long Lake Alum Treatment <br />A. DESIGN CONSIDERATTONS <br />Aluminum sulfate (alum) will be applied, in a liquid form, near the surface of Long Lake. <br />The alum removes phosphorus from the water column by forming an aluminum phosphate <br />precipitate or by sorption of phosphorus on the surface of polymerized alum.inum hydroxide. <br />If sufficient alum is applied, the aluminum hydroxide floe that falls to the sediment continues <br />to sorb phosphorus from the water or to form aluminum phosphate precipitate. By allowing <br />a large dose of alum to reach the sediments, the phosphorus rich sediments supplying the <br />"internal loading" can be inactivated for potentially long periods of time improving the <br />trophic state of the lake. <br />Long Lalce is approximately 271 acres in size with approximately 220 acres where depths are <br />greater than four feet. It is proposed that only areas deeper than four feet be treated as long ­ <br />term deposition of alum is not practical in shallow areas and would likely be transported to <br />deeper parts of the lake by wave action and prop turbulence. <br />Alum treatment should be performed after the significant external loads of phosphorus have <br />been treated or reduced. Future deposition of high phosphorus concentration sediment could <br />cover over the alum on the lake bed wasting phosphorus binding capacity and allowing the <br />new sediments to exert a new internal loading into the lake. <br />Alum treatment will be performed at a time when water temperatures are above 42® F and <br />there are no severe algae blooms, preferably in the late spring or fall months.