Components Of A Modern Solid Waste Landfill's Environmental Containment System
Modern solid waste landfills in New York are designed with an environmental containment system that includes a final cover system and a double composite liner system which serve to protect the environment from contaminants which may be present in the solid waste. The landfill siting plan, which prevents the siting of landfills in environmentally sensitive areas, as well as on-site environmental monitoring systems, which monitor for any sign of groundwater contamination and for landfill gas, provide additional safeguards.
Final Cover System
The 12 inch thick soil barrier protection layer (or 18 inch thick, if using warm season vegetation) and the overlying six inches of vegetated topsoil protect the underlying geomembrane and promote evapotranspiration and runoff of precipitation.
A soil layer or geosynthetic drainage layer lies between the barrier protection layer and the composite barrier layer.
A 60 mil (0.06 in) thick (or 40 mil (0.04 in) thick, depending on the type of material used) geomembrane, along with the underlying GCL, form a composite barrier layer which prevents infiltrating rainwater from reaching the solid waste buried in the landfill and generating additional leachate.
Gas venting controls landfill gases generated by the decomposing waste mass.
The waste mass is contained between the final cover system and the double composite liner system. It may be greater than one-hundred and fifty feet thick.
Double Composite Liner System
The primary leachate collection and removal system consists of a series of drains and pipes within a layer of sand or gravel designed to collect all of the liquid leachate which has drained through the waste mass. A 80 mil (0.08 in) thick geomembrane underlies the leachate collection system. The 80 mil geomembrane is underlain by a GCL (a thin manufactured layer of very strong textiles and extremely low permeability clay) component to make the primary composite liner system.
The landfill's secondary leachate collection and removal system is a backup series of drains and pipes within a layer of sand or gravel and a geosynthetic drainage layer that are designed to collect any leachate which was not contained by the primary liner system. A 60 mil (0.06 in) thick geomembrane underlain by a 24 inch thick clay layer comprises the secondary composite liner system which acts as secondary containment for leachate.
All geomembranes in the liner systems and the final cover must be overlain with a geocushion to protect the geomembrane from overlying materials. All collected leachate is sent to a wastewater treatment plant.