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18-Env-A6 Solid Waste Engineering and Management · May 2015

Question 11 of 12: Sanitary Landfill Cross Section

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

Notes on this paper

National Examination, May 2015 — 04-Env-A6 / 18-Env-A6, Solid Waste Engineering and Management. 3 hours duration, closed book, no calculator beyond an approved Casio/Sharp model, one letter-sized aid sheet permitted. All 12 questions constitute a complete paper (100 marks total).

Reference texts: Tchobanoglous, Theisen & Vigil, Integrated Solid Waste Management: Engineering Principles and Management Issues; Vesilind, Worrell & Reinhart, Solid Waste Engineering; Davis & Cornwell, Introduction to Environmental Engineering (6th ed.); Freeze & Cherry, Groundwater; CCME, Guidance Document on Landfill Gas Management; Canadian Environmental Protection Act, 1999.

Question 11: Sanitary Landfill Cross Section (10 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 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 and providing a secondary hydrogeologic barrier; (2) a composite liner system (compacted clay plus a synthetic geomembrane) forming the primary hydraulic barrier between refuse and native soil/groundwater; (3) a leachate collection and drainage layer immediately above the liner, sloped to a network of perforated collection pipes conveying leachate to a collection sump for treatment or off-site disposal; (4) successive compacted refuse lifts, placed and compacted in thin layers, each separated by a 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 shedding infiltrating precipitation away from the completed cell, topped with topsoil and vegetation for erosion control and 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/working face; 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.