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Third Pany Oversight 18 Water, Weste & Lend, Inc. <br />San Luis Mine June 9, 1994 <br />' Additionally, the in-situ moisture contents (significantly dry of optimum) may have <br />affected the BAT test results. It appears that when the BAT system was utilized to test <br />' materials within the permeability range and the moisture content of the drainage layer <br />material, the results were misleading (SRK, 1993d). <br />Preliminary laboratory permeability tests for the drainage layer material were provided <br />' to WWL during the construction oversight phase. Final laboratory test results were provided <br />in the Final Construction Report. Figure 3 contains all laboratory and field (BAT1 permeability <br />test results for the drainage layer/liner cover material, and all available tailings permeability <br />test results. A good correlation exists between dry density and laboratory permeability for <br />the drainage layer/liner cover material. This correlation can be expected for granwlar materials. <br />Although results obtained with the BAT (field test) system did not provide accurate <br />' permeability values (SRK, 1993c), the accompanying dry density test results collected at each <br />of the BAT locations and field notes concerning the compactive effort observeal at each test <br />location were valid and useful in determining suitable dry density values for laboratory testing. <br />As can be seen in Figure 3, the range of permeability values which can be expected for the <br />in-place drainage IayerAiner cover material is one to two orders of magnitude greater than the <br />mean tailings permeability. <br />5.4 FINAL CONSTRUCTION AND TESTING <br />' The specified frequency and type of QA test to be conducted on each of the materials <br />placed during construction, including density tests, was outlined in Appendix N of the original <br />112 Permit (BMRI, 1989). The 112 Permit specified that one density test was to be <br />conducted for every 2,000 cubic yards of material placed per work shift. An update or <br />change to these specifications was not found in subsequent designs, amendments, or <br />technical submittals ISRK, 1989, 1993a, 1993b, and BMRI, 1993s). Although density tests <br />appear to have been required for the drainage layer/liner cover material from the 1 12 Permit, <br />no density value was specified in the Design Report (SRK, 1993a) or Construction Status <br />Report ISRK, 1993c). WWL's opinion is that density testing of the drainage layer/liner cover <br />material was not necessary, and would have been useful only as a correlation trr permeability <br />test results. <br />DMG requested laboratory permeability testing frequency of 1 test per acre on the <br />drainage layer/liner cover material (DMG, 1993k1. Based on 2 feet of cover, that frequency <br />would be approximately 1 test per 3200 cubic yards. Results from 11 laboratory tests were <br />' provided in the Final Construction Report. <br />As seen from Figure 3, in-situ density values for Type 2 material ranged from 100.4 <br />' pounds per cubic foot (pcf) when placed with dozers tc 125.3 pcf for material placed with a <br />dozer and then exposed to construction traffic. Therefore, representative post-construction <br />in-situ dry densities should range from approximately 100 pcf for material placed on the <br />steeper portions of the expansion area to 125 pcf for material placed on portions of the <br />expansion area with flatter slopes where it was exposed to substantial construction traffic. <br />WWL's opinion is that during hauling and placement of Type 2 material a significant portion <br />of the expansion area with flatter slopes (approximately 50 percent of acres ~ through 23, <br />30 through 42, and 49 through 521 received substantial heavy truck traffic. <br /> <br />1 <br />