Question 20 of 20: Life Cycle Analysis of a Solid Waste Management Plan

Question 20: Life Cycle Analysis of a Solid Waste Management Plan (8 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.

The essential elements of a life cycle analysis (LCA) applied to a solid waste management (SWM) plan, following the standard ISO 14040 LCA framework: (1) goal and scope definition — state the functional unit (e.g. "management of 1 tonne of the community's MSW"), the system boundary (which stages are included: collection, transport, processing, disposal, and whether upstream material production and downstream avoided-burden credits are included), and the comparison being made (e.g. current system vs. an enhanced-diversion alternative); (2) life cycle inventory (LCI) — quantify the inputs (fuel, energy, materials) and outputs (air emissions including greenhouse gases, water emissions, solid residuals) for every stage within the boundary: collection/transport (fuel combustion), processing (MRF/composting/combustion energy and process emissions), and final disposal (landfill gas generation, leachate); (3) life cycle impact assessment (LCIA) — translate the inventory into impact categories relevant to SWM, most importantly global warming potential (CO₂-equivalent, dominated by landfill methane generation and any avoided-emissions credit from recycling/energy recovery), and secondarily resource depletion, acidification and human/eco-toxicity; (4) avoided-burden (system expansion) credits — recycling and waste-to-energy displace virgin material production and grid electricity respectively, and these avoided upstream burdens must be credited against the SWM system to avoid overstating its net impact; and (5) interpretation and sensitivity analysis — identify which assumptions (landfill gas capture efficiency, electricity grid emission factor used for displacement credit, transport distances) most influence the result, and test the conclusion's robustness against plausible ranges of each.

Stated assumptions (as the question explicitly requires): a 100-year global warming potential horizon (IPCC AR5/AR6 GWP₁₀₀ factors, methane ≈ 28–30× CO₂) is used to convert landfill methane to CO₂-equivalent; landfill gas collection efficiency is assumed at a stated value (e.g. 75%) since actual capture varies by cell age and cover integrity; the electricity grid emission factor used for any avoided-burden credit reflects the region actually served (a hydro-dominated grid yields a very different credit than a coal-dominated one); and transport distances are based on actual routing to existing or proposed facilities rather than a generic default.