ARCHIVED REPORTS_1996_1 - Laserfiche WebLink

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II. Project Description Leachate Collection System 10 A leachate collection and removal system(LCRS),consisting of leachate collection trenches, collection pipes, and collection sumps, is required for all areas of the landfill footprint. The LCRS would be integrated into the base liner as shown conceptually in Figure IIS. The leachate collection trenches would receive liquids from the drainage system,as described above. The leachate collection trenches are designed with a perforated collection pipe surrounded by drainage gravel,acting as a secondary leachate collection area if a pipe should fail. The pipe would be at least six inches in diameter to allow for clean-out equipment or in 'on cameras. The drainage gravel around the collection pipe is wrapped in a geotextile filter to keep it separate from the drainage layer. The leachate collection trenches would be placed along the toe of the liner side slope sections and at approximately 300 foot intervals at the base of the landfill for the horizontal expansion. The minimum slope for the horizontal collection trenches is one percent. For the vertical expansion,collection trenches would be placed across the slope at 200 foot intervals and feed into a main collection trench at the base of the vertical expansion. The collection trenches would have a minimum slope of two percent and the main collection trench would have a minimum slope of 0.5 percent. The main collection trench has a milder slope because it would be located in a more stable subgrade,not in fill material. Stormwater run-off from the working face may contact refuse. This wastewater would be collected in a perimeter drainage system at the edge of the landfill and be directed to the perimeter leachate collection trenches. This would prevent overtopping of the perimeter berm. The leachate collection trenches and pipes would feed into collection sumps located at the low points of the landfill liner system. The leachate sump includes a geomembrane sump basin to allow submergence of the leachate discharge pump and free drainage of the collection trenches. It is recommended by the design engineers that the geomembrane sump basin be prefabricated and thoroughly tested for leakage prior to installation because of the potential problems due to the leachate pressure buildup required for pump efficiency. Field seams should be above the high leachate pump operation level. A series of leachate sumps as opposed to one sump are proposed for the Austin Road Landfill expansion. The reason is because of the minimal topographic relief at the site,the liner depth limit of 20 feet MSL,and the extensive area covered by the landfill. Several sumps result in higher operation and maintenance costs;however,they do provide for hydraulic isolation of specific landfill area for stormwater management or a failed ) sump basin. 11.12