COMPLIANCE INFO_FINAL WMU FU-23 DESIGN RPT & CONCURRENCE LTRS

Home Browse Search

WMU FINAL WMU FU-23 DESIGN REPORT 2-18-23 5-4 particles from the overlying LCRS granular drainage material and to protect the underlying geomembrane. The minimum hydraulic conductivity of the coarse gravel will be 1.0 cm/sec. The coarse gravel will be washed, rounded, and have a maximum particle size of 1 inch with less than 15 percent of particles smaller than 1/2-inch, 5 percent finer than the No. 4 sieve, and 2 percent finer than the No. 200 sieve. The leachate collection pipe will be perforated at fourth-points, with 1/4-inch- diameter holes, spaced 6 inches on center. The granular drainage material of the base LCRS will be overlain by a sheet of nonwoven geotextile filter fabric. The geotextile functions as a filter to separate and prevent intrusion of fine materials from the overlying protective operations layer into the granular drainage material. This will allow the granular drainage material to retain its specified hydraulic conductivity by preventing clogging from piping of fines. Leachate in WMU FU-23 will drain to temporary sumps at the eastern edge of WMU FU-23. As WMUs to the east of WMU FU-23 are constructed, the LCRS pipes and trenches will be extended and will ultimately flow to permanent sumps on the eastern boundary of the site. The temporary sumps are composite lined and consist of a 4-ft deep pit with 3:1 side slopes. Within each sump will be a 5-foot diameter, perforated HDPE tank surrounded by coarse gravel. A lysimeter is included beneath each sump as shown on the Construction Drawings in Appendix A. Each tank will contain a submersible pump for pumping out leachate. All leachate will be directed to a Class II leachate impoundment, from where it will be evaporated. Leachate will be routed from the tanks via a piping system. The LCRS inspection requirement consists of 6-inch HDPE pipes on the north and south sides of WMU FU-23 that extend into the LCRS. A slug test can be performed by running liquid through these pipes and monitoring the flow rate into the sump. Specifications for the granular drainage material, coarse gravel, HDPE pipe and tanks, filter and cushion geotextile, and geocomposite drainage layers are included in Appendix C. Quality assurance testing of the LCRS materials is outlined in the CQA Manual (Appendix D). The testing includes particle size and hydraulic conductivity for the granular drainage material and coarse gravel and manufacturer's certification of material properties for the geotextile and GDN. Details of the composite liner and LCRS components are shown on the Construction Drawings in Appendix A. 5.3 Protective Operations Layer A protective operations layer will be placed above the LCRS to protect the LCRS, pipes, and composite liner from construction and operations traffic. The protective operations layer will consist of a minimum 12-inch-thick layer of generally sandy material excavated from onsite stockpiles with a permeability greater than 1 x 10-4 cm/sec at a confining stress of 4.5 psi. The maximum particle size of the sandy material will be limited to 1 inch to protect the underlying geotextile or GDN from puncture. Specifications for the protective operations layer are included under general earthwork (Appendix C).