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GENERAL45209
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Last modified
8/24/2016 8:14:06 PM
Creation date
11/23/2007 1:38:07 PM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
M1980244
IBM Index Class Name
General Documents
Doc Date
1/12/1995
Doc Name
PIT RACKFILL CLOSURE COVER SYSTEM DESCRIPTION RICHMONG HILL MINE LEAD SOUTH DAKOTA
From
GOLDER ASSOCIATES
To
LAC MINERAL USA INC
Media Type
D
Archive
No
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IRN-t 1995 17~U^ L~'II}JERHLS CUSRi INC. • E655B4~`_'1FJ F. u3 <br />r <br />7antiary 12, 1995 -2- 943-2754 <br />Prior to t:onstniction, a bentonire amended soil was selected for coustructiun of the clay liner. <br />A fine grained gravel material available on-site (referred oo as Type N) was [nixed with 129, [o <br />1496 sodium bemm~ite (ohrained from AIDericau Colloid Cumpany). The amended soil was <br />tesroed for pettneabiliry in the Golder soils laboratory in Lakewood. Colorado prior to <br />coastrucdon. The material permeability was less than l x lQ' cm/scc. Afield permeability [es[ <br />was conducted ou a e>ay liner test pad constructed at the site. The permeahihry was meanrred <br />using a sealed du~ble r_~ig lnfiltromcter in accordance w7Lh AS 1'M U SU93. The permeability <br />was found to be less than 1 x lQ'' cttt/sec. Confirmation of [he test pad perrneabihty was made <br />6y Professor Craig Benson, Ph.D. of the University of Wisconsin. He obtained and tested large <br />blink samples from the test pad and d[e azNa1 clay cover layer over the waste nnk. <br />The clay Layer thickness was reduced from 2a inches (as ittitially required b}' the DF1VR) w LS <br />inches based ten the demonstrated constnictabiliry and low lxnueability of the bentoirite ttmenderl <br />SOII. <br />Thermal Cover/Drran Layer artd Topsoil <br />A thermal cover/drain layer was placed un top of nc~ compacted, ben[onite amended clay layer. <br />The thermal layer provides prorecnoa for the clay- layer from freezing and desiccation. The <br />rberma! layer also provides a drainage medium for infiltration which reaches it tlriou¢h [he <br />topsoil. The [hefmal layer also acts as an extended too[ zone, The thermal layer was <br />wasrrucned [o a tlucltness of a.5 feet. <br />The thermal layer was coveied by a 6 iueh Uiickue~a of tupsuil which was designed to support <br />vegetation. The thermal Payer and the topsoil combined provide sufficient thickness to protect <br />the tttrderlying clay layer fiom frost penetrution. <br />Reliabfltry ojlhe Cap <br />The closure cover for the Richmond Hill Mine was designed and constructed w be a highly <br />reliable system for limiting infiltration and promoting surface water runuff ui a Cuuwllrd <br />manner. Ext[etne climatic condirious were considered in the design :utd analyses incorporated <br />site specific material properties to provide realistic resuhs. <br />The most important itt:ra in the closure cover is the clay layer. Protection of the clay layer from <br />erosion, too: penesation, desiccation, and free2mg wcte ail cvusrdcred during file desi~[. <br />Thanl; you tier the opportunity to be of service. Plisse call should you have any qucsnoas. <br />Sltlcercly, <br />GOLDER ASSOCLATES INC. <br />~~~ ~~~~ <br />Brian E. Simpson, P E. <br />Senior Engineer <br />
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