Capping of the landfill will be progressive as landfill operations proceed across the site. There will be sections of the landfill the are closed and capped while other sections of the landfill are still operating. The landfill cap is a composite barrier system that is designed to limit water infiltration into the waste and leachate collection system and release of landfill gas to the atmosphere.
Prior to installation of the capping system on a section of the landfill, the waste and intermediate cover will be graded to bring the area to the elevations shown on the final design plans. The capping system will then be installed as shown in the figure below and will consist of the following layers:
The top cap system layers from bottom to top are as follows:
- 1.5 foot thick low permeability soil layer
- 40 mil (.040 inch) thick polyvinyl chloride (PVC) geomembrane layer
- 1.0 foot granular drainage layer
- 1.0 foot protective soil layer
- 6 inch top soil layer
- Vegetative cover
The side slope capping system will contain either a low permeability soil liner or PVC geomembrane as the barrier layer. The granular layer, protective soil layer, topsoil layer and vegetative cover will be the same construction as the top cap as referenced above.