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IAN-,.2-1595 1T•A6 L~IINEkALS [USA) INC. <br />t'.etdM ASSOr~ates hiG <br />20B 0rvon Bou19.OtC. Sw,e Sn0 <br />,nta..ooo. CO USA 80228 <br />Tglgp}~ong (30](980-0540 <br />Foi (3031 9E5-2080 <br />January 12, 1995 <br />LAC Minerals (USA) [nc- <br />Richmnnd Hill Mine <br />P.O. Box 892 <br />Lead, Sasth D~ko~ X7754 <br />Atuntion: Mr Todd Duex <br />• 6055Ua~?lU F. U? <br />III IIIIII'll llll'll <br />999 <br />~7~1~1 <br />Our Ref.: '1~3-27ba <br />RE: PiT BAC~'II.L CLOSURE COVER SYSTEM DESCRIPTION, RICHMOND HILL <br />MINE, LEAD, SOUTH DAKOTA <br />Dear Mr. Duez <br />The Richmond Hill Mine, located near Lead. South Dakota, has undcrrakcu a rcmcdianon ac[iou <br />to alleviate potential Acid Mine Draiuage (AMD) from wasu rock and areas of [bc pi[. Ttrc <br />waste rock was placed as backfill in dtc mine pit and a closure cover was placed over rbe waste <br />rock tv ltuut infiltration and promote surface water runoff. <br />The closure cover was designed as a geomchrtically stable, mule-layered cap incorporating a low <br />permeabihry layer to !taut infiltration oC surface waters. The cluaure cover conststed ui the <br />following (ayes: <br />Compacad Fit! <br />Waste rock was placed as backlit! in dre pit. The waste rock was placed iw 3 toot [tuck life and <br />was cutr,pactnd with a vibratory roller ur wtih several pasaes of hauling equipment. Sclcut waste <br />rock backfill, with a maximum nominal dimension of 4 inches, was placed as the final layer of <br />compacted fill below the closure cover. The select material enabled shaping :uul conrouring of <br />the fill surface for cover co,u¢uction <br />Crushed L.imesrone <br />Afrtr placement of the uppermost layer of waste rocd, a 6 inch layer o: crushed limestone. <br />obtained from on-site sources, aas placed. The crushed liatestone layer was designed to have <br />a ealciunt carbooa[e eyuivatence of SZ~. <br />Clay Cirrer <br />A clay liner was cons[ructed about the crushed limes one layer. The original design requ,red <br />12 iucbes of on-site clay ina¢rials. The ou-site clays had permcabiliucs of less than 1 x 1J' <br />crn/su. The des,gu of dte clay layer was base) ou infiltrituon tnodelliug of lho wver sys[eut. <br />The South Dakora Department of Environrneat and Natural Resource: (DENR) required tltat [he <br />clay liner be constructed w a thickae~s of 24 inches. <br />QfF[Q~S LN AUSt9QLIA CANA^A, GE4MAhV .iUNGAfiY, ITA!Y. SWEDEN. UNn'cD xINC-DOM. UNITED $TFTES <br />