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Mr Erich ! Bower <br />Climax Molybdenum Company <br />August 10, 2000 <br />Page 2 <br />Initial construction of each dam consisted of clearing the foundation, installing a foundation <br />drain system and constructing an earth fill starter dart Tailing was deposited using header and <br />spigot deposition and water was removed from the resulting pond by a gravity decant sv.tem <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 darn 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 finally due north for a <br />distance of approximately 1100 feet. The Dam No. 2 north decant system has a 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 />backfilled 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 Dam 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 1970'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 1 to form a single continuous dam <br />Tailing Darn No. 2 has been abandoned for about 15 years and recent tailing deposition has <br />almost completely covered the Tailing Dana No. 2 crest and decant pond. <br />Tailing Darn 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 Dam 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 SN 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. however, 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 />J t 4STERTRC gosh144ca OO'1 i c3 11 PM) <br />