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Section 5 <br />Alternative 1: No Federal Action/No project <br />Under Alternative 1, the project would not be implemented. There would riot be <br />any injection wells constructed in Centennial Park and there would be any need <br />to back flush well water into Centennial Lake or into the Greenville Banning Flood <br />Control Channel. There would be no change to existing flood risks at Centennial <br />Lake or at the Greenville Banning Flood Control Channel. <br />Alternative 2: Proposed Project <br />Under the Proposed Project, water from the Centennial Park injection wells is <br />proposed to be back flushed into the Centennial Lake or into the Greenville <br />Banning Flood Control Channel. Typically, the back flushing operations would <br />occur weekly or every two weeks and could discharge up to 70,000 gallons of <br />well water per minute into Centennial Lake. If a single well back flush occurs the <br />water level in the lake would rise 0.3 inches, Assuming a worst case condition <br />that all four wells were back flushed in one day, a total of 280,000 gallons of <br />water would be discharged into Centennial Lake, The water level in the lake <br />would rise 1.2 inches. Typically, Centennial) Lake maintains 2-3 inches of <br />freeboard in the lake elevation before spilling into an overflow structure that <br />drains into the Greenville Banning Flood Control Channel. Therefore, typically <br />during dry periods the back flushing would not cause the water elevation in <br />Centennial Lake to spill over into the Greenville Banning Flood Control Channel <br />or topple over and cause localized flooding in Centennial Park, In the event there <br />is not sufficient freeboard during dry periods, OCWD would have the flexibility to <br />back flush the wells into the Greenville Banning Flood Control Channel. <br />Assuming a worst case condition that all four wells are back flushed into the <br />Greenville Banningi Flood Control Channel, a total of 7.8 cfs of well water would <br />be discharged into the channel. During dry periods this amount of well water <br />would be an incidental contribution and would not result in significant adverse <br />impacts to the flood control capacity of the Greenville Banning Flood Control <br />Channel, <br />During wet periods and based the intensity of storm conditions there could be the <br />potential that the back flushed water from the injection wells could reduce the <br />flood control capacity of the Greenville Banning Flood Control Channel, OCWD <br />would be required to obtain an encroachment permit from the County of Orange <br />to discharge the back flushed well water into the Greenville Banning Flood <br />Control Channel. Thee encroachment permit would provide conditions to ensure <br />that adequate coordination occurs between the County of Orange and OCWD <br />during storm events to minimize flood risks. With the implementation of Mitigation <br />Measure HWQ-1 potential flood risks along the Greenville Banning Flood Control <br />Chanel would be reduced to a less than significant level. <br />roject Final EIR 5-125 <br />Mid Basin Centennial Park �19&fiAp <br />