2012-09-06_REVISION - M2008070 (18)

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Western Gravel E &P Waste Disposal Facility October 2011 CQA/QCP Page 2 of 19 Subgrade The earthen subgrade materials for the cells must be compact, stable and free of any gravels or bedrock fragments greater than 1 inch in size, sticks and roots. Final subgrade surface preparation must be completed with a smooth drum roller to form a smooth solid surface. Final surface subgrade must be observed and approved by the CQA Engineer prior to placement of the overlying liner materials. Leak Detection Clays The soils used for the clay collars at the downstream end of the leak collection pipes shall be cohesive soils consisting of the on -site clays having a Unified Soil Classification of CL. Cohesive soils used for construction of the required clay collars will be taken from on -site stockpiles or directly from excavation areas. All cohesive soils used in the leak detection system shall have a minimum liquid limit of 25, a minimum plasticity index of 10 and have at least 60 percent by weight passing the No. 200 sieve and have 100 percent passing the 1 -inch sieve. One sample per day will be collected and tested in the laboratory during placement of the clays. If the cohesive soils do not meet the Atterberg and grain size specifications outlined above, then a sample of the in -place soils will be obtained and tested for hydraulic conductivity. The cohesive soils used for clay collars will be placed in loose 9 inch maximum lifts and compacted to at least 95% of the maximum standard Proctor density at -3 to +3 percent of the optimum moisture content. Field compaction (moisture- density) tests shall be conducted on the clay collar materials by the CQA Engineer at a rate no less than one test per 100 cy of soil placed or at least once per day during the placement of these materials. The nuclear moisture - density (compaction) field testing methods used by the CQA Engineer during construction are presented in Table 1. Table 2 shows a list of the required field tests and testing frequencies for cohesive soils used in the construction of the clay collars. Table 3 shows the required laboratory tests and testing frequencies for the cohesive soils used in the clay collars. Leak Detection Sands The granular materials used in the leak detection system and placed around the slotted PVC collection pipes shall be clean, free draining sands having less than 3 percent by weight passing the No. 200 sieve. The sands shall be non - plastic and exhibit an in -place hydraulic conductivity equal to or greater than 1 x 10-2 centimeters /second. One sample will be collected prior to the construction of each cell from the borrow source and tested for grain size analyses and hydraulic conductivity. One sample per day will be collected by the CQA Engineer as the sands are placed and tested in the laboratory for grain size analyses. One hydraulic conductivity test will be conducted on the sands placed. Table 3 shows the required laboratory tests and testing frequencies for the sands used in the leak detection system prior to and during construction. Care shall be taken not to damage the liner materials and PVC pipe during the placement of the sands. The CQA Engineer shall observe the placement of the sands. There is no numerical compaction specification for the sands being placed as part of the leak detection system; however, placement and moderate compaction shall be conducted to the satisfaction of the CQA Engineer to prevent slumping around the pipe. Leachate Collection Gravels The granular materials used in the leachate collection system and placed in the floor of the cells and sumps shall be clean, free draining 1 '' /z" gravels having less than 3 percent by weight passing the No. 200 sieve. The gravels shall have 100 percent passing the 2 -inch sieve and a maximum of 5 percent passing the No. 4 sieve. The gravels shall exhibit an in -place hydraulic conductivity greater than 5 x 10 -2 centimeters /second. At least one sample per cell will be collected from borrow area/source and tested for grain size analyse and hydraulic conductivity. In addition, during construction samples will be collected by the CQA Engineer on a daily basis as the gravels are placed and tested in the laboratory for grain size NWCC INC.