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Third Par[y Oversight 14 Wa[er, Waste & Land, Inc. <br />San Luis Mine January 10, 1993 <br />r <br /> <br /> <br />1 <br /> <br /> <br />1 <br /> <br />!~ <br />1 <br /> <br /> <br /> <br />u <br />r <br /> <br />1 <br />• Out-of-specification material to be removed and replaced with in-specification <br />material. <br />• In-specification material to be brought in and blended with the out-of-specification <br />material. <br />• In-specification material used to cover the out-of-specification rclaterial to a <br />sufficient depth to provide for acceptable drainage around these areas. <br />WWL considered each of these actions to be acceptable as they retained the original <br />intent of the design, but preferred the placement of additional material on top of the out-of- <br />specification material to avoid disturbing the synthetic liner. <br />4.3 PERMEABILITIES <br />Of the approximately 24 acres of drainage blanket/liner cover material placed before <br />the incorporation of the screening plant in the borrow area, only 0.75 acrrss contained <br />materials which were out of specification (too high a percentage of fines) (6~1RI, 1993s1. <br />WWL's opinion is that this area is small in comparison to the overall expansion arld would not <br />significantly affect the overall performance of the drainage blanket/liner cover. <br />The Design Report (SRK, 1993a) did not specify a permeability for *.he drainage ~"~~ ~</*"~ <br />c/'.~~s tPee <br />layer/liner cover material, however, results of field QA permeability tests condur:ted with the r <br />~~~E1f <br />BAT in-situ permeability testing system indicated that permeability values ranged from 1.6 x ~*~~;~~.xdf,` <br />10-8 cm/sec to 3.6 x 10 a cm/sec (SRK, 1993c). The BAT system is well suited for testing <br />materials possessing permeabilities less than 1 x 10'4 cm/sec. It appears that when the BAT <br />system is utilized to test materials within the permeability range of the drainage aver, results <br />can be misleading (SRK, 1993d). Therefore, the true permeability of the drainage layer was <br />unknown at the time of the initial document review and site visit. Preliminary laboratory <br />permeability tests for the drainage layer material were provided to WWI. during the <br />construction oversight phase. Table 4.1 summarizes laboratory and field permeability test <br />results from the tailings available at the time of the initial site visit. <br />Table 4.1 Summary of Measured Tailings Permeability Values <br />Information Source High fcm/sec) Low Icmisec) Averagelcm/sec) <br />Permit Application Amendment (SRK, <br />19891 2.5 x 10'S 5.0 x 10 ° 1.6 x 10'S <br />Design Report, Piezocone Data <br />(SRK, 1993a) 7.2 x 10'° 4.2 x 10'' 2.4 x 10'° <br />Construction Status Report, CPT' Data <br />(SRK, 1993c1 1.9 x 10'S 5.9 x 10'B 4.0 x 10'° <br />' CPT -Cone Penetrometer Test <br /> <br />