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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />carried in the "first flush" of storm water across <br />the roofs and parking lots and this "first flush" <br />water will drain directly through the inverted <br />weirs being treated only for sediments, oils and <br />floatab1es. It therefore would appear that phos- <br />phate (phosphorus) removal and BOD (biochemical <br />oxygen demand) reduction will not be effectively <br />accomplished by this system. <br /> <br />To make this system effective for phosphorus and <br />BOD reduction, there are alternatives to include: <br /> <br />1. Increase the size of the sedimentation ponds <br />so retention of first flush water will be <br />continuous. This will probably involve <br />greater and deeper areas dedicated for that <br />purpose combined with adjustable water level <br />controls on the weirs. <br /> <br />2. Installation of aeration equipment to increase <br />oxygen content, and allow more rapid precipi- <br />tation of phosphorus through stimulation of <br />algae. This would be a secondary measure <br />with less effectiveness than the increased <br />retention. <br /> <br />Silver Lake has a water quality history typical of <br />many Metropolitan area lakes. 1974 values of total <br />phosphorus ranging from .033 to .106. This would <br />indicate that the lake in 1974 contained 40# to <br />128# of phosphorus in total quantity. Depending on <br />how effective the proposed treatment ponds really <br />are, the increased load of phosphorus due to the <br />action could range from 5.55# down to zero. <br /> <br />I <br />I <br /> <br />V-6 <br />