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<br />location of the intake structure. The flow line from East Brush Creek <br /> <br />to the existing settling ponds would cost approximately $100,000 at to- <br /> <br />day's construction costs. By the time engineering contingencies and <br /> <br />increased costs are added to the'project the construction of a raw <br /> <br />water line to East Brush Creek would be approximately $180,000. An <br /> <br />economical analysis for the construction of this line is tabulated <br /> <br />on page 61 which follows the economical analysis of alternate three. <br /> <br />. <br /> <br />This alternate would not be recommended for the simple reason that <br /> <br />on JanuaryU30, 1970, the minimum daily discharge measured by the United <br /> <br />States Geological Survey was 1.2 cubic feet of water per second and in <br /> <br />Table VI we have shown that the maximum daily demand in 1991 may reach <br /> <br />as high as 1.4 cubic feet of water per second. <br /> <br />A third alternate for lessening the turbidity in the Brush Creek <br /> <br />0,- <br /> <br />waters would be to provide accelerated settling of the colloidal mater- <br /> <br />ial with chemically stimulated floculation and precipitation. Use of <br /> <br />coagulants has been tried a number of times in the past and has been <br /> <br />quite effective. However, with the diatomaceous-earth type water <br /> <br />treatment system, the addition of chemically accelerated settling is <br /> <br />not desirable as the floc carryover from any type of coagulant aug- <br /> <br />mented settling of water is removed by the filtering plant. In the <br /> <br />. <br /> <br />case of sand filters, the floc carryover is excellent since it creates <br /> <br />what the Germans call a "Schmutz-Decke". This acts quite the same as <br /> <br />the diatomaceous earth does in a precoat filter. The "Schmutz-Decke" <br /> <br />causes the sand filter to remove extremely fine solids from the water. <br /> <br />In the case of a diatomite filter, the "Schmutz-Decke" reacts on the dia- <br /> <br />tomite precoat, just like any other turbidity. This causes a very fast <br /> <br />pressure drop to develop across the precoat, causing the filter to back- <br /> <br />wash. Even though a number of plant operators and other water treatment <br /> <br />authorities doubt that this floc carryover would be a problem, the manu- <br /> <br />- 48 - <br />