ARCHIVED REPORTS_1993_1 - Laserfiche WebLink

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H. Project Description Drainage System The drainage system consists of a drainage and operation layer. The drainage layer would provide drainage from the expansion area to the leachate collection trenches,described later in this section. The operation layer is above and protects the drainage layer. The drainage layer would consist of either a minimum 124nch thick layer of sand or gravel with a minimum permeability of 1 x 10-1 cm/sec or a geonet drainage layer providing similar performance. A geotextile filter would separate the drainage and operation layers and prevent soil fines from entering the drainage layer. The operation layer would be a minimum of 12 inches to protect the liner,if the drainage layer is sand or gravel. If a geonet drainage layer is used,the operation layer would be a minimum of 18 inches,to protect the geonet and liner. Leachate Collection System 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 11.5. 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 inspection 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. 11.11