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<br />Mr Erich J Bower <br />Climax Molybdenum Company <br />August 10, 2000 <br />Page 2 <br />Initial constriction of each darn consisted of clearing the foundation, installing a fioundation <br />drain system and constructing an earth till starter dam Tailing was deposited using header and <br />spigot deposition and water was removed from the resulting pond by a gravity decant sv teui <br />The basin in which tailing was deposited in Dam No 2 was bisected by a hill, subdividing the <br />decant pond. Two separate decant systems were required to remove water The south decant <br />system is aligned generally east and west direction along the south side of the impoundment <br />The north decant system and subject of this letter extends from the starter dam along; the north <br />side of the pond in an easterly direction for approximately 1600 feet. The decant line then turns <br />to the northeast for approximately 900 feet and then turns northwest and final IN, due north for a <br />distance of approximately 1100 feet. The Dam No. 2 north decant system has it total length of <br />almost 3600 linear Feet <br />The decant conduit consists of a 30-inch diameter reinforced concrete pipe founded on and <br />baektilled with compacted sands placed in a trench excavated into the glacial till foundation <br />soils Six decant towers were constructed at selected location along the north decant line and <br />were used to control the decant pond water elevation. Decanted water historically flowed by <br />gravity west toward Starter Da(n No. 2 <br />Tailing Dam No 2 was intended to be a temporary structure. Future tailing deposition in Tailing, <br />Dam No I was expected to inundated the dam and cover the impoundment. A third tailing dam <br />(Tailing Dam No 3) was constructed at the upper end of Tailing Pond No 2 in the late 1(nO's <br />Tailing Dam No. 3 was required once Tailing Dam No 2 reached a certain elevation Tailing <br />Dam No. 3 will eventually combine with Tailing Dam No I to form a single continuous dam <br />Tailing Dam No. 2 has been abandoned for about 15 years and recent tailing deposition has <br />almost completely covered the Tailing; Dam No. 2 crest and decant pond. <br />Tailing Dam No. 3 is similar in design to Tailing Dams No. 1 and No. 2. The embankment was <br />constructed on a prepared subgrade and foundation drains were excavated into the glacial till <br />subsoils. The starter dam was constructed of glacial till and tailing deposited using a header and <br />spigot system To our knowledge, no detailed records of Danz No. 3 construction are available <br />The Tailing Dam No 3 starter dam was constructed over the Tailing Dam No 2 North decant <br />system with the decant Tower 5N located at the downstream toe of the starter dam. It is our <br />understanding from discussions with the Climax staff that a partial or complete plug, was <br />installed in the Tailing Dam No 2 north decant line Ilowever, no records of the decant plug <br />construction or location are available <br />An inspection of Tailing Dam No. 3 in Fall of 1999 showed that seepage was discharging, from <br />Tower 5N at the rate of approximately 5 to 10 gallons per minute. This flow was in reverse of <br />normal gravity flow in the historic system, We recommended to Climax that the decant line <br />Tower 5N be plugged It is generally considered an undesirable practice to have an open conduit <br />through a <br />O <br />e-1 <br />1- <br />z <br />LU <br />V <br />Q <br />Q <br />J tNPMASfEiiWRC.7EC.T5+soaCR et dnc O&1C/JG(9 ?1 P),j)