18-Env-A6 Solid Waste Engineering and Management · December 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.); Freeze & Cherry, Groundwater; CCME, Guidance Document on Landfill Gas Management; Canadian Environmental Protection Act, 1999.
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.
Methane in landfill gas poses three distinct classes of hazard. Fire and explosion: methane is flammable between roughly 5% and 15% by volume in air (its lower and upper explosive limits); LFG that migrates laterally through permeable soil or utility trenches into buildings, manholes or other confined spaces can accumulate within this explosive range, and documented incidents of structures built on or adjacent to old landfills exploding are the reason regulators set a perimeter action level (commonly 25% of the LEL at the property boundary, 100% LEL in structures). Asphyxiation: methane is a simple asphyxiant — in an enclosed or poorly ventilated space (gas-collection manholes, wellhead vaults, buried utility chambers) it displaces oxygen, creating an oxygen-deficient atmosphere that can incapacitate a worker with no warning odour of its own. Climate impact: uncontrolled LFG emission is a major contributor to a landfill's overall greenhouse-gas footprint, since methane's global-warming potential is roughly 25–28 times that of CO2 over a 100-year horizon, making fugitive LFG emissions a significant driver of the facility's contribution to climate change even though the gas itself dissipates quickly once released.
