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'Ar. Bruce Humphries <br />April 12, 2000 <br />s.u., considerably lower than Dam No. 1 seepwater, which has a pH between 4 and a. <br />One theorv is that the design of the Dam No, 3 pumpback system is recvclinL Joky pH <br />seepwater through the dam. which has lowered the pH over time. The existing <br />seepwater collection ponds have tilled with eroded tailing or chemical precipitates from e-1 <br />the seepwater collection system. This limits the total system capacity and covers the ? <br />outlets of the existinga toe drain system which could result in a reduction of-the capacity z <br />of the toe drain svstem and increase die elevation of the phreauc surface within the slam W <br />during [ong periods of sustained tailing deposition. The pumpback pipeline has shoi?-n <br />evidence of buildup from chemical precipitation, limiting the capacity of the pumpback = <br />system. The collection ponds and return line are all outside of the tailing pond', natural <1 <br />containment so that loss of power, a failure of the pumps or the pumpback line. ar an <br />unexpected seepwater surge would likely result in a release outside of Henderson Q <br />Property. <br />Henderson plans to make significant changes to the existing system. The collection <br />ponds will be cleaned out and all residues from these ponds will be deposited info the <br />larger tailing basin. A channel will be constructed to direct the seepwater flow into rw() <br />parallel 10-inch diameter HDPE lines that will flow by gravity to the existing Dam NV <br />seepwater collection system. The collection ponds will be maintained to manage any <br />unusual tlow or problem with the delivery lines. <br />Henderson believes that combining the two seepwater sources in the Dam No, I <br />seepwater collection system will improve our ability to manage seepwater and reduce The <br />potential for a release of seepwater. As part of our Y?K efforts at Henderson. the Ute <br />Park Pump Station, which pumps the seepwater back into the water pool, has been <br />modified so that a diesel pump can be used to pump seepwater or process water. <br />Henderson leased a 455-hp diesel pump, rated at 5000 gpm. as Y3K coverage, and is <br />currently considering purchasing the pump. <br />Each of the HDPE lines will be capable of handling the normal seepwater flow from Dam <br />No. 3. The lines will be constructed to facilitate pigging or high pressure flushing, <br />allowing the lines to be cleaned regularly to avoid the buildup that plagues the current <br />system. Although these lines will be located outside of the containment of the tailing <br />basin, we believe that they are a dramatic improvement over the current system. These <br />lines will nut be subject to the pressures of pumping since the flow will be by gravity. <br />There will be no risk due to power or pump failure. In addition. Climax Molybdenttrn Co. <br />has had experience with parallel lines feeding influent to the water treatment plants at the <br />Henderson Mine and at the twit, Emmons Project and has found that the combination of <br />parallel lines and routine cleaning is very successful in improving the reliability of the <br />delivery system. Henderson proposes to clean these lines twice annually and conduct <br />leak down tests annually to connrm the svstem's integrity. Preliminary drawing D.i-1-01 <br />is attached.