Components of A Modern Municipal Solid Waste Landfill's Environmental Containment System
The 24-inch thick soil barrier protection layer and the overlying six inches of vegetated topsoil protect the underlying geomembrane and promote evapotranspiration and runoff of precipitation.
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 low permeability clay layer, form a composite barrier cover system which prevents infiltrating rainwater from reaching the solid waste buried in the landfill and generating additional leachate.
The gas venting layer collects and controls landfill gases generated by the decomposing waste mass.
The waste mass may be greater than one-hundred and fifty feet thick.
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 60 mil thick geomembrane underlies the leachate collection system. On the bottom of the landfill, the 60 mil geomembrane is underlain by a clay layer or GCL (a thin manufactured layer of very strong textiles and extremely low permeability clay) component to make a composite liner. The collected leachate is sent to a wastewater treatment plant.
The landfill's secondary leachate collection and removal system is a backup series of drains and pipes within a layer of sand or gravel 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.
This design serves to protect the environment from contaminants which may be present in the municipal 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.