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DESIGN OBJECTIVES <br />The collection and conveyance of groundwater with high concentrations of iron <br />presents design challenges that can be difficult to overcome. The available gradient from the <br />seepage points to the point where the seepage must be delivered magnifies those <br />challenges. The proposed design assumes that precipitation of iron oxides will be a continual <br />problem, creating chronic conditions of sedimentation and potential clogging of pipes and <br />drains. 'The best methods for meeting those challenges are to first assume that amorphous <br />iron hydroxides will be a perpetual accumulation requiring maintenance and second to <br />provide multiple levels of redundancy to buy time while maintenance can be mobilized in the <br />event of a plug. Accordingly, we've adopted the following objectives for the design. <br />• Provide a means for positive collection of the seepage flow points that have been <br />observed to date <br />• Provide sufficient capabilities such that new seepage pathways, not yet developed or <br />visible, can also be effectively collected. <br />• Provide a means for flushing drains and collection pipes <br />• Provide redundancy, where practical, so that the functionality of each drain can be <br />covered by another drain if one becomes plugged or otherwise fails <br />• Address the fact that surface storm drainage flows through the area and needs to be <br />rerouted so that it doesn't comingle with the flows requiring collection <br />• To the extent possible, design for gravity flow conveyance <br />• Provide back-up pipelines from the seepage area to the seep water pipeline so that <br />the system will remain effective if the primary pipeline is plugged <br />• Provide equipment access corridors for maintenance of each of the components <br />• Provide the future capability for supplementing gravity flow conveyance with efficient <br />pumping, hopefully using solar powered pumps and equipment. <br />The design shown on the drawings is intended to meet those objectives. The <br />components of the design are described in detail in the next section. <br />Henderson Operations, Mill Site 9/7/10 <br />No. 3 Dam Seep Mitigation, Design Report Page 3