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<br />5.0 FILL MATERIALS <br />' 5.1 General <br />Fill materials shall 6e obtained from the mandatory <br />excavations and borrow areas as shown in the drawings or as <br />' directed by the Engineer. All fill materials shall be approved for <br />use prior to placement. <br />5,2 Leach Pad Base and Berms <br />The leach pad base and perimeter berms shall be constructed <br />with native soils. The material shall be a well graded gravelly <br />sand or gravel material. The maximum allowable particle size shall <br />be six inches. Oversized material shall 6e removed and placed as <br />slope protection along the outer perimeter of the pad. The upper <br />six to 12 inches of the pad base shall be alluvial gravelly sand <br />with a maximum particle size of three inches. <br />Alternate material may be used in the upper lift provided it <br />can be placed and compacted to provide a smooth surface suitable <br />for liner placement. The alternate material and final prepared <br />surface shall be approved by the Engineer prior to liner placement. <br />5.3 Leach Pad Soil Liner <br />The leach pad soil liner shall be constructed of fine-grained <br />native soils amended with powdered bentonite in a proportion <br />sufficient to meet the compacted permeability specification of 1 x <br />10-0 cm/sec or less (Appendix D). The native soils shall cl~issify <br />as silts, sandy silts, or very silty sands (USCS ML and SM) with a <br />maximum particle size of lJ2 inch. When amended with powdered <br />bentonite, the soils shall have a minimum plasticity index ~7f 10 <br />and a minimum liquid limit of 30. Mixing proportions and methods <br />for bentonite addition shall be determined by the Contractor and <br />approved by the Engineer, but shall meet the criteria stated above. <br />N-7 <br />