ARCHIVED REPORTS_2003_5 - Laserfiche WebLink

Home Browse Search

Base LCRS The base LCRS will be constructed of a 12-inch-thick layer of clean granular material with a minimum hydraulic conductivity of 0.1 cm/sec draining towards leachate collection pipe trenches. The particle size of the granular drainage material has been limited to a maximum of 3/8-inch to protect against puncture of the underlying geomembrane and the overlying geotextile filter fabric, and to a maximum of 3 percent of particles finer than the No.200 sieve to maintain its permeable nature. The granular drainage material is also specified to consist of well-rounded gravel (i.e., no crushed rock will be allowed) to protect the underlying geomembrane from puncture or tears. In addition, a protective geotextile cushion will be placed between the geomembrane and granular drainage material for added geoemembrane puncture resistance. If the granular drainage material appears more angular than desired by the Engineer and QA/QC Consultant, the Contractor will be required to demonstrate the suitability of the material by utilizing an on-site test area. The test will consist of placing a 1-foot thickness of granular drainage material on a 15-foot by 30-foot piece of 60-mil HDPE geomembrane and cushion geotextile using the same equipment and procedures as the Contractor is planning to use to place the granular drainage material in WMU FU-03. The QA/QC Consultant will then inspect and, if necessary, test the 60-mil HDPE geomembrane for damage and either accept or reject the angularity of the proposed granular drainage material. This testing was performed during construction of WMU D-95 and the proposed granular drainage material3 was found to be acceptable. The leachate collection trenches will contain 6-inch diameter SDR 11 perforated HDPE leachate collection pipes (see pipe sizing and loading calculations in Appendix B). The pipes will be placed within each leachate collection trench to increase the drainage capacity of the LCRS. Each pipe will be surrounded by coarse gravel wrapped with a nonwoven geotextile to prevent migration of fine 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 I inch with less than 15 percent of particles smaller than '/i 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 1/2-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-03 will drain to a permanent double-composite lined sump at the southern edge of WMU FU-03. The primary and secondary sumps are each lined with 60-mil HDPE geomembrane and GCL. The primary and secondary sumps are each 2-feet deep and sized to accommodate leachate from WMU FU-03. Within the primary and secondary sumps will be a perforated section of 18-inch diameter HDPE pipe surrounded by coarse gravel. The perforated 18- inch pipes will be connected to nonperforated 18-inch leachate riser pipes. The leachate riser pipes will extend from the primary and secondary sumps to the ground surface. Submersible pumps will be extended through the leachate riser pipes to the sumps for pumping out leachate. All leachate will be directed via a header pipe to the new Class II Leachate Impoundment WMU F-West, where it will be evaporated. 3 The granular drainage material for WMU D-95 had the same particle size and angularity requirements as is being specified for WMU FU-03. FORWARD LANDFILL WMU F-03 AND F-WEST DESIGN REPORT 5-4