18-Env-A6 Solid Waste Engineering and Management · December 2016
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.
11.1 Four reasons to consider landfill mining. (i) Reclaim disposal airspace in an existing, otherwise-full cell to extend the site's operating life without new land acquisition; (ii) recover recyclable materials (ferrous/non-ferrous metals) and combustible fractions (RDF) that have economic value; (iii) recover degraded fines suitable for use as daily/intermediate cover soil, reducing the need for imported cover material; and (iv) remediate an older, unlined or poorly performing cell — excavation allows a modern composite liner and leachate/gas collection system to be installed beneath the reclaimed footprint, reducing long-term environmental liability.
11.2 Health and safety requirements. Personal protective equipment (respirators, cut-resistant gloves, steel-toe boots, high-visibility clothing) against dust, bioaerosols and sharps; continuous atmospheric monitoring for methane (explosive-limit alarms), hydrogen sulphide and oxygen deficiency in excavated pits/trenches; excavation shoring/sloping and confined-space entry procedures where trenches exceed regulatory depth; a site-specific health and safety plan addressing biological hazards (pathogens in decomposed waste) and hazardous-material discovery protocols (unexpected drums, asbestos); fire-watch and spark-control measures given methane presence; and worker vaccination/medical surveillance (e.g. tetanus, hepatitis) consistent with provincial OH&S requirements for waste-handling operations.
11.3 Work plan items. A landfill mining work plan should address: excavation sequencing and phasing (to maintain slope stability and minimize open-face exposure); screening and sorting process design (trommel screening to separate soil fines from recoverables, followed by magnetic/eddy-current/manual sorting); management of odour, dust and vector control during active excavation; leachate and stormwater management for the disturbed area; disposal or beneficial reuse pathways for each recovered fraction (metals to market, RDF to energy recovery, fines to cover material, residual to re-landfilling); regulatory approvals and any required environmental monitoring during the work; and a cost-benefit analysis comparing recovered material value plus reclaimed airspace value against excavation, processing and re-disposal cost.
