18-Env-A6 Solid Waste Engineering and Management · May 2017
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
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.); CCME, Guidance Document on Landfill Gas Management; ISO 14040/14044, Environmental Management — Life Cycle Assessment.
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.
(1) Landfill gas migration into the root zone — CH₄/CO₂ displacing oxygen around plant roots, and elevated soil temperature from the underlying decomposing waste, both stress or kill vegetation (see Q7). (2) Poor final-cover soil quality and depth — cover soil is often low in organic matter/nutrients and placed at a limited depth over a compacted, poorly-draining barrier layer, restricting root development and moisture availability. (3) Differential settlement — uneven settlement of the underlying refuse as it decomposes disrupts the cover surface and root zone, and can create ponding or erosion that further stresses newly-established vegetation.
These three factors compound rather than act independently: differential settlement (3) can crack or thin the cover soil (2) in localized low spots, which both concentrates any gas migration (1) at exactly those weak points and creates ponding that further degrades the soil's ability to support root growth — so a cover that starts marginal on one factor often fails faster than the sum of the three would suggest. Post-closure monitoring programs typically track all three together for this reason: gas-probe readings, cover-soil condition surveys, and settlement benchmarks are read on a coordinated schedule so that an emerging problem in one area (say, a settlement low spot) prompts a targeted check of the other two (gas concentration and soil condition) at that same location, rather than waiting for each to be flagged independently by a separate monitoring program. A post-closure care plan should name the specific inspection frequency and remediation trigger for each of the three factors, not just list them as generic future risks.
