A hazardous waste landfill cell is bounded above and below by two independently engineered multi-layer barrier systems — a composite BOTTOM LINER with leachate collection beneath the waste, and a low-permeability FINAL COVER (cap) with gas management above it — each built from bottom (waste side) to top (or vice versa) as a stack of purpose-built layers rather than a single material.
Cross section A: composite bottom liner (compacted clay + HDPE geomembrane + geotextile cushion) beneath a granular leachate collection layer with a perforated collection pipe sloped to a sump, all resting on a graded native subgrade.
Cross section B: final cover system over the completed waste mass — gas venting/collection layer, low-permeability barrier (compacted clay or geomembrane), drainage layer, vegetative support soil, topsoil and vegetation, with a vertical gas vent penetrating the cap.
Both systems share the same governing principle — a low-permeability barrier flanked by a drainage/collection layer — applied in mirrored order: the bottom liner keeps leachate IN (collecting it before it can reach groundwater), while the final cover keeps water OUT (shedding infiltration before it can reach the waste and generate more leachate) while still venting the landfill gas the waste continues to generate.
