What is a Landfill Gas Cut-Off Trench?
It usually comprises a trench which is backfilled with single size stone, to allow landfill gas to vent (flow) upwards and not continue horizontally through the ground. A non gas-permeable membrane (usually HDPE (high density polyethylene) or LLDPE (Linear Low Density Polyethylene) is usually placed on the slope of the trench remote from the landfill. The depth of the trench and membrane must penetrate low enough into the ground to prevent the landfill gas flowing beneath the cut-off. It is usually extended downward to key into a low gas permeability soil or rock strata, or to 1 metre approximately below the lowest groundwater water level experienced at the location of the trench. Landfill Gas Cut-Off Trenches are normally passively vented (no extraction pumping takes place).
