Question 7 of 18: Landfill Mining

Question 7: Landfill Mining (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.

Part (a) — 7.1 Four reasons to consider landfill mining. (1) Airspace recovery — excavating and screening an older cell reclaims void space for new waste placement, extending the site's remaining life without acquiring new land. (2) Materials and energy recovery — recovered ferrous and non-ferrous metals, and a combustible light fraction usable as refuse-derived fuel (RDF), have direct resale/revenue value. (3) Environmental remediation — mining removes or reduces a contamination source at a poorly engineered older site, cutting future leachate generation and LFG emissions and lowering long-term liability. (4) Land reclamation for redevelopment — once mined and remediated, the site can support a higher-value land use, which is often the primary economic driver in urban areas with rising land values.

Part (b) — 7.2 Health and safety requirements. Continuous atmospheric monitoring for methane (LEL), hydrogen sulfide and other trace VOCs; confined-space and atmospheric-hazard protocols wherever excavation exposes a void or trench; fire/explosion controls (no open ignition sources, spark-resistant equipment near methane readings); respiratory protection and cut-/puncture-resistant PPE against buried sharps and dust; biological-hazard precautions (leachate and pathogen exposure control, up-to-date tetanus immunization for site workers); excavation and slope-stability controls (benching/shoring per the applicable OH&S excavation regulation, since aged waste has unpredictable geotechnical properties); heavy-equipment traffic management; and worker training specifically on the hazards of buried hazardous or unknown waste.

Part (c) — 7.3 Work plan items. Site characterization (test pits/borings to establish waste depth, age, composition and moisture before mining begins); equipment selection and excavation/processing sequencing; the screening and separation process flow (trommel screening, magnetic and eddy-current separation, air classification); materials handling, temporary storage and stockpile area layout; a plan for residual material (re-landfilling or off-site disposal of the non-recoverable fraction); environmental controls during mining (dust suppression, odour control, leachate management from exposed waste); a production-rate schedule; the health and safety plan from Part (b); and the regulatory approvals/permitting needed to reopen and rework a closed or active cell.

Part (d) — 7.4 Equipment layout. The figure below shows the typical processing train: excavated waste is conveyed from the working face to a trommel screen, whose undersize (fines) is recovered as soil/cover material and whose oversize proceeds through a magnetic separator (ferrous metals), an eddy-current separator (non-ferrous/aluminum), and an air classifier that splits the remaining stream into a light combustible fraction (RDF) and a heavy residual fraction sent back for re-landfilling.