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~~ IqN-1^-1555 17:07 Lf~INERRLS (USR) INC. . ~ 6055643210 ~P.03 <br />January 12, 1995 -2- 943-2754 <br />Prior to cotlsauctioa, a beaton;rr amended soil was selected for crnuu-ucdon of nc~ clay liner. <br />A fiat grained gravel material available otrsiu (referred to as TypC N) wa, muted will 12% [o <br />1446 sodium bemm~ire (ohrained from American Colloid Cvmparry). The amhrded soil was <br />tuvtd for permeabilityy in the Golder soils laboratory in Lakewood. Colorado prior ro <br />construction. The raatcrial pctmeabdity was las than L x LP' cmisec. Afield perrneabiliry tes[ <br />was conducted ou a cL•[y linrr rest pad coastttrcttd a[ the sine. The permeability wac meaa[red <br />using a seated duublo ring infilTromc[cr in accordance with AS'1'M U 5()<I3. Tht permeability <br />was found to be less than 1 : !0'' cmisec. ConSrmacioa of the test pad permeability wav made <br />by Professor Craig 6enson, Ph.D. of the Utriversiry of Wisconsin. He obtaitxd and tested large <br />blvclt samples from the test pad and dre actual clay Cover layer over the wa~u nxk. <br />The clay layer drickness was reduced tiom 2a inches (as initially required by d1e DENR) w l8 <br />inches based on the demonstrated construmabiliry and low permeability of We beatouitr amended <br />soil. <br />IYcerrrto! Cover/Dr~r+ Dyer arrd Topsoil <br />A ttletmaJ coverldrain layer was placed on top of the compacted, bentoniu amended clay layer. <br />'Ibe dtertnal layer provides protection for the clay layer from free2iag a~ desiccation. The <br />thermal layer also gtovides a drainage medium for infiltration which reaches a through the <br />Topsoil. The thermal layer also acts az an extended root zone. The ducmal Layer wac <br />coactruetrd [o a thickness of a.5 feet. <br />The thermal laytr was covered by x ti irx:h llnckrreas of tvpsvil whi[-h wds dcsigtxd to st[ppon <br />vegetado~a. The thermal Payer and the topsoil wmbit[eci provide sttfficicnt thickness to protect <br />[be uodertyiag clay Sayer from frost penetration. <br />Rclicbllfry of the Cap <br />The closure cover for the Richmond Hill Mine was designed and constructed ro be a highly <br />reliable systrnt for limiring infiltration and promoting surface wa[er zuuoff iu a wutrulltti! <br />magnet. F~ttreme climatic camditioos were considered is the design and analyses inr;orporated <br />site specific material properties to provide realistic rebults. <br />The most important item in the closure cover is the clay layer. Protection of the clay layer from <br />erosion, root penetration, desiccation, and freezing were ail coasidtted during the design. <br />Thank you for the opportunity w be of service. Please call should you have any questions. <br />Sincerely, <br />GOLDER ASSOCIATES INC_ <br />~~~-~~. <br />Brian E. Simpson. P.E. <br />Senior Engineer <br />