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CONCLUSIONS <br />The stated objectives for the design of the seepage collection system will be <br />substantially met by the proposed configuration shown on the drawings. Redundant <br />fixtures for collecting and conveying the seepage flow has been included. However, it is <br />expected that the system will be prone to sludge build-up because of the nature of <br />amorphous iron hydroxide precipitates. Accordingly, a disciplined schedule of <br />preventative maintenance will be implemented. The frequency of required cleaning will <br />not be known until the system is built and can be monitored. Over-scheduling <br />maintenance cleaning is initially planned until that frequency is known. If plugging <br />occurs and is allowed to back-up within the system it may be difficult to reestablish the <br />"clean" condition. <br />The effectiveness of the auto-siphon system will not be known with certainty until <br />the system has been operated for a year or more. The design will be reviewed and <br />monitored during that period to determine whether, 1) a small solar pump is needed to <br />lift the seepage from the boundary cutoff manhole to the siphon vault, and 2) the auto- <br />siphon system will not reliably deliver the seepage and must be replaced with an electric <br />pump system. <br />Henderson Operations, Mill Site 9/7/10 <br />No. 3 Dam Seep Mitigation, Design Report Page 8