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18-Env-A6 Solid Waste Engineering and Management · December 2013

Question 9 of 16: Sanitary Landfill Cross Section

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

Notes on this paper

Reference texts: Tchobanoglous, Theisen & Vigil, Integrated Solid Waste Management: Engineering Principles and Management Issues; Freeze & Cherry, Groundwater (Darcy's Law, vadose zone); CCME, Guidance Document on Landfill Gas Management; EGBC/Engineers Canada 04-Env-A6/18-Env-A6 examination syllabus.

Question 9: Sanitary Landfill Cross Section (5 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Native subgrade soilComposite liner (compacted clay + geomembrane)Leachate collection / drainage layerLeachatesumpLift 1: compacted refuseLift 2: compacted refuseLift 3: compacted refuseDaily / intermediate soil cover (between lifts)Barrier + drainage layer (final cap)Topsoil + vegetationGas ventGroundwatermonitoring wellPerimeterbermAccess road / working face beyond →
Cross section of a modern sanitary landfill cell, from the composite liner system at the base through successive compacted refuse lifts to the final cover cap, with the ancillary leachate, gas and monitoring systems that a complete design must include.

From bottom to top, the cross section comprises: (1) the native subgrade soil, graded and proof-rolled to receive the liner; (2) a composite liner system (compacted clay plus a synthetic geomembrane) that provides the primary hydraulic barrier between refuse and native soil/groundwater; (3) a leachate collection and drainage layer directly above the liner, sloped to a network of perforated collection pipes that convey leachate to a collection sump for treatment or off-site disposal; (4) successive compacted refuse lifts (placed and compacted in thin layers by landfill compactor), each separated by a thin daily/intermediate soil cover that controls odour, vectors, blowing litter and fire risk during operation; (5) a vertical landfill gas vent/collection riser passing up through the waste mass to release or actively extract the methane-rich gas generated by anaerobic decomposition; (6) a multi-layer final cover (cap) system — a barrier/drainage layer to shed infiltrating precipitation away from the completed cell, topped with topsoil and vegetation to control erosion and support post-closure land use; (7) a perimeter berm containing the toe of the waste mass and separating the active cell from the surrounding access road; and (8) a groundwater monitoring well, screened in the native aquifer downgradient of the liner, used to detect any leachate breakthrough that the liner and collection system fail to intercept.