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. is r.y..'!.•Sz'•/�s� Y 8.��r .:.'r'�z•• . Commercial molybdenum production at Climax beg"in 1918, and the site win mined by <br /> underground methods until 1991,with daily production peaking at more than 51,000 tons per day <br /> in 1976(Vo nick 1996). Open pit mining commenced in 1977. Declining molybdenum prices <br /> \ Study Area !.y, i ''�., in the 1980's resulted in curtailment of operations. Production resumed for several months in 1985, <br /> 1989 and 1995;the mine has been an standby status since August, 1995. More than 470 million <br /> tons of ore have been mined to-dale,and current reserves stand at more than 145 million tons at <br /> 0.23 percent Mo. <br /> ".� Y'r � The large annual snowpack at the site and corresponding volume o(runoRduring the spring <br /> �'r �� '. , •-_^ makes water management an important task at Climax. The mine has a National Pollution <br /> - '1"ti •-x,� ` Discharge Elimination System PDES.�,.:•(, �� ,.r . �:' -� g y (N )permit,which allows discharge of water at the Out(all <br /> 001,located at the property line in the Tenmile drainage. Peak flow of water at the Outfall 001 <br /> !• ,.,M,� . `a t• ' during the high mnoRyear of 1995 was 152.000 gallons per minute. Discharges to Tenmile Creek <br /> t' must meet effluent limitations of the permit. <br /> 7"�'� t` 3 j � '� The oxidation of sulfide minerals (principally pyrite) associated with the molybdenum <br /> mineralization has led to the generation of acid drainage from the inactive and flooded <br /> �` ";` +•a r underground workings,the waste rock disposal facilities and the tailings impoundments. The • <br /> r'.''� !fI '{� effects of acid drainage are controlled by active water treatment,which is accomplished by lime <br /> `f: '4 "'�+ • �� 1/+ ' neutralization in a two-pond system involving two of the three tailings impoundments at the site <br /> L. •%l '. '" h," � (Terunile and Mayflower). Water treatment at Climax would be classified as*basic'according to <br /> the definition of Zinck et at.(1997). The effectiveness of the water treatment system is reflected <br /> in Climax's success in achieving the NPDES effluent limitations. <br /> .. _ y >i "' ' !' �.""— 'fi:• a Lime neutralization at Climax occurs in two stages. In the first stage milk of lime(Ca(OH),) <br /> is added to the water stream to raise pH l0 6, allowing precipitation of iron and aluminum <br /> ' a :;'�. . �;jr• hydroxide minerals in the pond on the Tenmile impoundment. Water is decanted from Tenmile <br /> �.a; i544 _ _ ...;� :•7I +• pond and routed to the 152-acre Mayflower pond,although the routing has recently been modified. <br /> Lime-treated water historically entered Mayflower from the east side of the pond,and resulted in <br /> accumulation of sludge and urueacled lime in a delta which extends from the shore of Mayflower <br /> o, _ :�. t —" +2 •' 1, out into the pond. This resulted in less efficient usage of lime and periodic short-circuiting of <br /> water as it entered the pond from the delta,since precipitated sludge had Iinfe time to settle before <br /> `°�1 %-'^"M"'" \•'„ water wits decanted from 6-riser,located on the west side of the d direct] opposite from the <br /> Pen Y PPo <br /> delta. <br /> {• 'F ?` ` r' '"f'--.a" u This practice w modified in 1995 to improve the efficiency of lime usage and promote better <br /> 1 y7 eL, N. .(L� <br /> - f + � _ I\ ;( � sludge settlement. Decant water from Tenmile is now delivered to the base of 3-dam(Tenmile <br /> P . y v:'- 1(((({ impoundment)where additional lime is added in a concrete mix box to raise the pH to I 1 prior to <br /> - discharge into the south end of Mayfower pond,where iron,aluminum,manganese and zinc • <br /> hydroxide compounds precipitate and settle. This configuration allows water to tmvel a reefer <br /> distance prior to being decanted through 6-riser,minimizing short-circuiting. Treated water is <br /> t M1 acidified with sulfuric acid prior to being discharged into Tenmile Creek. <br /> - The water treatment system provides challenges similar to those reported by Zinck et al.(1997) <br /> in their survey of eighteen Canadian water treatment systems. The pond'turns"twice annually in <br /> •t--� �:,. response to gravitational instability caused by thermal inversions,resulting in rapid pH changes <br /> and less efficient water beabnent. Short-circuiting of treated water,resulting in inefficient settling <br /> + - r•1 •;L of precipitated solids hssaccurred historically,although operational modifications described above <br /> •^ ;jxGin"' i; ` `" -{'� have minimized this problem. <br /> �• ,T <br /> 7 SLUDGE SAMPLING METHODOLOGY <br /> 0.4 0 0.4 0.8 N31e6 <br /> -=� Sludge samples were collected from four locations in Mayflower pond(Figure 2);7-dam,the delta, <br /> 6-riser and 5-darn. The 7-dam sample was taken at the point closest to where lime-]reeled water <br /> Figure I. Plan map of the Climax Mine showing the location of the Mayflower impoundment. enters Mayflower. The 5-dam sample was taken from the far(north)end of the pond where seep <br /> waters at the base of the dam are returned to the pond. Samples are composites from the near- <br /> 646 647 <br />