2012-09-06_REVISION - M2008070 (25)

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Design and Operations Plan October 24, 2011 Western Gravel E & P Waste Disposal Facility Page 23 of 51 a number of aggregates ranging from crusher fines (sands), to road base, and to 1 I/2 -inch screened gravels. The various aggregates are being stockpiled across the base of mined areas as mining operations progress from west to east and then south. The separation of materials during the mining operations will be beneficial for construction of the landfill cells. The topsoil materials being stockpiled will be used as the upper 6 -inch thick vegetative layer to be placed over final soil cover /cap that will be constructed during closure of the cells. Stockpiled clays will be used to construct embankment fills required to bring cell sidewalls to planned subgrade elevations, to line cell bottoms, used as daily and interim cover, and to construct final soil cover /cap during cell closure. Produced 1 %2 -inch screened gravels will be used as leachate collection gravels. A sieve /gradation analyses conducted on a sample of 1 %2 —inch screened gravels being produced and stockpiled at the site is provided in Appendix E. Screened fines (sands) will be used as protective soil cover materials to be placed over liner and drainage materials installed as part of the LCRS. 3.4.4 Liner System To provide environmental protection and prevent migration of potential leachate from the facility, the floor and inside slopes (sidewalls) of excavations/berms (cells) will be constructed using a double liner system. A 40 -mil smooth, high density polyethylene (HDPE) geomembrane shall be used as a secondary liner and will be installed over properly placed soils along the sidewalls and over compacted clays in the base of the cells. The primary liner will consist of a second layer of textured 60 -mil HDPE placed over the leak detection system (LDS). Liner materials positioned across the cell floor and sidewalls will be placed into anchor trenches constructed around the cell perimeter and above cell sidewalls. Forty- mil liner and geonet materials will be placed in an inside anchor trench and a 60 -mil liner will be placed in a separate anchor trench located outside of the first trench. Geomembrane to be used for secondary and primary liners shall meet the properties listed in the CQA/QCP provided in Appendix H. Construction and testing procedures to be followed during the placement of the liner materials are also provided in the CQA/QCP. The approximate limits of liner material placement and anchor trench locations are shown on Figure 5, Detail 5A. Liner and anchor trench details are provided on Figure 5, Detail 5B. Prior to constructing and placing the secondary 40 -mil HDPE liner, excavated areas shall be compacted and smoothed until the surface is free of any gravels or bedrock fragments greater than 1 -inch in size, sticks, roots, or other materials that could damage the liner. The subgrade will be constructed and tested /inspected in accordance with the CQA/QCP, prior to placement of secondary liner materials. The 60 -mil HDPE primary liner placed in the cell floor will be protected from abrasion/damage associated with the overlying leachate collection system gravels. A 16 -ounce (oz.), non -woven geotextile or 4 -inch thick layer of protective soil cover will be placed to protect the liner. A one -sided composite Geonet will be placed over the primary liner and along cell sidewalls to protect the liner material and aid leachate collection. The Geonet must be placed fabric side up. Protective materials placed over the primary liner shall meet properties listed in the CQA/QCP provided in Appendix H. Construction and testing procedures of these materials are provided in the CQA/QCP. Protective materials and underlying liner materials details are provided on Figure 5, Detail 5B and on Figure 6, Details 6B and 6C. 3.4.5 Leak Detection System (LDS) Because of the location and design, the LDS will allow an expedited corrective action in the event of potential cell leakage; thereby, minimizing migration of liquid from the facility. The LDS will be constructed between the primary and secondary liners of each cell in order to monitor potential leakage from the primary cell liner. In addition, discovered liquid can be collected, analyzed, and removed. The LDS will consist of a geocomposite drainage net (geonet) placed between the secondary and primary HDPE liners and NWCC, Inc.