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Third Pany Oversight 17 Water, Waste & Land, Inc. <br />San Luis Mine January 10, 1993 <br /> <br /> <br />1 <br />1 <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br />u <br />1 <br /> <br /> <br />30 through 42, and 49 through 52) received substantial heavy truck traffic during the delivery <br />and placement of the drainage layer/liner cover material. Therefore, representative in-situ dry <br />densities range from i 10 to 125 pcf and laboratory permeability samples should be w <br />compacted to within this range -- - - '"- `~-b~I <br />Figure 3 also demonstrates that although permeability values obtained from tests <br />conducted at relatively low (< 100 pcf) dry densities ISRK, 1993c and 1993s) are valid, they <br />do not accurately reflect the quantity of compactive effort being applied in the field as <br />observed by the engineer. <br />According to BMRI's Technical Revision No. 16 (BMRI, 1993s), permeability tests <br />indicated tailings coefficient values ranging from 1.9 x 10'6 to 5 x 10-' cm/:sec. WWL's <br />review of available permeability coefficient data are included in Figure 3. CPT values ranged <br />from 1.9 x 10-5 to 5.9 x 10-6 cm/sec and piezocone values ranged from 7.2 x 10-6 to 4.2 x <br />10'' cm/sec. The arithmetic and geometric means for the CPT data are also shown. <br />Therefore, a reasonable permeability coefficient for the tailings would be between 2 x 10 6 and <br />4 x 10-6 cm/sec. <br />4.5 DRAINAGE PIPE SPACING <br />In addition to the permeability of the drainage layer, drain spacing is critical to <br />controlling the height of head and minimizing the rate of seepage through the VLDPE liner. <br />DMG had expressed concerns after their initial site inspection that drains were oeing spaced <br />greater than the design value of 40 feet. During WWL's initial site visit, drain spacing <br />appeared to be adequate. Spacing was verified during construction oversight, .3s outlined in <br />Section 6.1. <br />1 <br />