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20 <br /> EXECUTIVE SUMMARY <br /> (3) Greatest Risk <br /> Highest risks to attaining water quality management objectives for the reservoir are presented by: <br /> • Increased algal blooms associated with nutrient loading from future development. Summer algal blooms <br /> are already frequent in Cane Creek Reservoir. Most blooms are dominated by blue-green algae, including <br /> species associated with taste/odor problems and potential production of algal toxins. Increased residential <br /> development could worsen the problem(Figure E-3). <br /> 80 40% <br /> =L 60 <br /> r. <br /> 30% o <br /> -,. <br /> u <br /> � 40 o <br /> -S 20/o <br /> o <br /> � o <br /> 20 10% <br /> U c� <br /> w <br /> 0 /0 <br /> Undeveloped Cmmt Conditions /•25 Buildout FWl Buildout <br /> .P Concentration Algal Bloom Frequency <br /> Figure E-3. Projected Eutrophication Impacts under Current Protection Measures <br /> • High manganese cons caused by naturally occurring lake conditions, which result in undesirable <br /> aesthetic conditions in finished water. The intake raw water will contain problematic concentrations of <br /> manganese when OWASA must draw water from below the depth of the thermocline (a temperature <br /> barrier that separates surface from bottom waters in the summer)and occasionally at times when anoxic <br /> (devoid of oxygen).bottom water is mixed into the surface water. <br /> • Total organic cwbon levels,expected to remain high in the raw water supply because decaying vegetation <br /> and in-lake production are not amenable to control, which react to form harmful by-products during <br /> disinfection steps in the water supply treatment and distribution system. <br /> • Low dissolved oxygen concenamlon, reduced water clarity, and microbial pathogens also pose a moderate <br /> risk to attaining water quality objectives(See Chapter 2). <br /> E-5 <br />