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tiff~N-12-1995 17:0E, LR.IIJERHLS (USR) INC. • fA55643210 P.I0I2I <br />III IIIIIIIIIIIIIII~ <br />GOfdlf ASiOgO~L Y,G <br />200 Union BoWevort7. Su;te'S00 <br />~N.M~ou. eo us+t eo22e <br />TgVgpha~e j]0]) 980.OSW <br />for(30]I985~2080 <br />January 12, 1995 <br />IAC Minerals (USA) Inc. <br />Richmond Nill Minc <br />P.O. Box 892 <br />Lead, South Dakota 57754 <br />ATren[ion: Mr. Todd Ducx <br />999 <br />~l~ <br />Ai3~SOC12~~S <br />Our Ret'.: St43-?751 <br />RE: PTf BACI.~'ILL CLOSURE COVER SYSTEMDESCRIFTION, RICIiMOND ffiLL <br />MII~iE, LEAD, SOUTH DAkOTA <br />Dear Mr. Duex: <br />The Richmond Hill Minc, located near Lead. South Dakom, has utMcrrakcn a rcmcdiation action <br />m alleviate potential Acid Kline Drainage (AMD) from wazu rock and arras of nc~ pi[. The <br />waste rock was placed az backfdl is die inirv pit and a closure cover was placed over me wane <br />rock to limit ittfilQadon and promote surface water runoff. <br />The closure cover was designed as a geoMh~c~~Ty stable, mold-layered cap irrcorporating a low <br />permrabiliry layer [o limit infiltration of surface waters. The closure cover consisted of !hr <br />following layer;: <br />Corrrpacud FlIL <br />Waste rock was placed as backfill in dre pit. The wazoe rock waz placed 1n 3 foot [hick lifts azid <br />was cxnrrp~cteri widl a vibrawry roller ur with seveid paves of hauling eyuipmeni. Sela;t w:ulC <br />rock bari~ill, with a m~x;mum mm~;nal dimension of 4 inches, was placed u dte final layer of <br />compacted fill below dte closure cover. The Seiett maeerial enabled shaping and r:ontuuring of <br />the fill surface for cover coasauction. <br />Crushed Lsrnestune <br />After placement of the uppermost layer of wash rock, a 6 inch Jaya of crushed limestone, <br />obtained from oa-site sources, was placed. "Fhe crushed litmstone layer was designed to have <br />a calcium carbonate equivalence of 52:6. <br />Clay f~rrer <br />A clay liner was constructed about the crushed limestone layer. 'Ihe original design required <br />12 inches of on-site clay materials. ?hc on-Site clays lied pcrmcabilitics of less than 1 x 1Jt <br />cmisec. The design of du clay layer waz bassi ou infiltration modelling of the cover systczn. <br />?ha South DaYOra Department of Environment and Natural Rrxourc:es (DENR) reyuired drat the <br />clay liner be constructed ro a thickae.,s of 24 inches. <br />OFGICES IN aUSfRnrW CaNti)n, GERMaNV, NuNGarrv. R!~' Y. SwEOEN. JNREO ItINC-OOM, UNITED SUSES <br />