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<br />amec'0 <br />July 20, 2010 <br />Mr. Timm Comer <br />Manager, Environmental Resources <br />Cripple Creek & Victor Gold Mining Co. <br />P.O. Box 191 <br />100 North Third Street <br />Victor, CO 80860 <br />Re: Proposed SLF Specification Changes <br />Dear Timm: <br />AMEC Earth and Environmental (AMEC) has prepared this letter proposing some modifications <br />to the Soil Liner Fill (SLF) specifications presented in Amendment No. 9. The current physical <br />specification for the SLF is: <br />Soil Liner Fill - processed materials as approved by MANAGER and CERTIFYING <br />ENGINEER, conforming to the following SPECIFICATION: <br />Hydraulic Conductivity: 1 X10-6cm/s maximum <br />Recent SLF samples from the current borrow source have had a fines content over 50 percent <br />(the current maximum limit). Per ASTM C117, C136, D1140, the fines content is determined as <br />the soil finer than the No. 200 sieve. By definition, soil finer than the No. 200 sieve define the <br />fraction of silt and clay size particles within the soil mass. Silts are fine-grained soils that are <br />generally non-plastic or have very low plasticity, while clays are colloidal particles of clay <br />minerals. The presence of clays are primarily responsible for imparting plasticity to the soil <br />mass. The presence of silts increases the fines content, but would have little effect on the <br />overall soil plasticity. To evaluate the SLF, a plot of fines content (soils finer than No. 200 sieve) <br />versus the Plastic Index (PI) is presented in Figure 1. As shown in Figure 1, the SLF has a <br />mean PI of about 25, with scattered points above and below this mean value. This observation <br />indicates that the increased fines content for the SLF is due to the presence silt not clay <br />particles. If the clay content had increased, the PI would also show an increase, the lack of <br />increase in the PI signifies the presence of silts rather than clays. This is a common trend that <br />has been observed in the CC&V area, and is due to the weathering profile and mineralogy of <br />the source rock for the soils (e.g. limited clay formation). <br />AMEC Earth & Environmental, Inc. <br />304 Inverness Way South, Suite 490 <br />Englewood, Colorado 80112 <br />Tel: (303) 433-0262 <br />Fax: (303) 433-0362 www.amec.com <br />MACINTOSH HD:USERS:JLUPO:D000MENTS:CC&V:SLF LETTER:SLF spec letter.doc <br />Plasticity Index: 10 minimum