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<br />LOW PERMEABILITY SOIL LINER <br /> <br />Once the tailings disposal area was excavated and shaped, one foot pf type 3 <br />material (sandy silts) was placed on the grade. During this stage ~f the <br />project, it was observed that most of the silt deposits on site had small <br />angular gravels within the gradation. The following procedure was used to <br />minimize the amount of gravels encountered at the silt to liner interface: <br />Silt material, containing small gravel particles, was placed on the <br />bottom 9 inches of the liner foundation layer. These materials were <br />moisture conditioned and compacted to the specified density of 95% of the <br />maximum Proctor density. This layer was then capped with very clean fine <br />grained silts from selected borrow sources. The clean fine grained silts <br />were rock raked and smooth drum compacted leaving a uniformly smooth <br />surface relatively free of small gravels which could damage the synthetic <br />liner materials. <br />From July 21, 1990 to December 9, 1990, 103 field tests for moisture content <br />and compaction were performed on the type 3 material liner. 53 of tihe samples <br />tested did not fall within the range specified for moisture con tent, and 9 of <br />the samples were compacted to less than 95% density. Permeability Nests of <br />compacted fill on the floor of the upper impoundment were performed 'in June of <br />1991. The highest value value for hydraulic conductivity obtained wys <br />3.1 X 10 -5CM/Sec, the area from which this sample was collected was <br />re-compacted, but apparently not re-tested. Other values for hydraulic <br />conductivity range from 1.2 X 10-6CM/Sec to 4.7 X 10-8CM/Sec. <br />SYNTHETIC LINER <br />Approximately 5.3 million square feet of synthetic materials were in talled in <br />the impoundment facilities during the Phase 1 construction. The bul~C of the <br />synthetic material was 40 mil VLDPE liner, with 60 mil HDPE liner in talled in <br />areas which will have continued exposure or potentially high hydraul~c heads. <br />The liner installation was divided into areas to facilitate the record keeping <br />for the quality control and quality assurance programs. <br />The bulk of the sheet seam welding was performed using double wedge fielders. <br />The air channels created by the double wedge welding machines were air tested <br />at approximately 31 psi. Leaks in the seams were isolated and cappe~. All <br />"T" joints were capped. Capping and repair joints were made using e trusion <br />welding techniques. A11 the extrusion welds were vacuum tested for t+ater <br />tightness. Destructive samples were cut from seams at approximately 500-foot <br />intervals and tested for specified integrity. <br />Destructive tests were conducted for shear strength of seams and for <br />resistance to peel failure. Destructive tests results for 460 samples were <br />submitted to the Division with 78 samples failing to meet peel test <br />specifications and 15 samples failing to meet shear specifications. These <br />failures were noted and marked for repairs on the seams in doubt. R$pairs <br />were made and vacuum tested prior to the acceptance of the panel. <br />-2- <br />