Question 1 of 12: Definitions

Question 1: Definitions (5 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.

1.1 Darcy's Law — the empirical constitutive law for laminar flow of a fluid through a saturated porous medium, $Q = -KA\dfrac{dh}{dL}$, where $Q$ is the volumetric flow rate, $K$ the hydraulic conductivity of the medium, $A$ the cross-sectional flow area and $dh/dL$ the hydraulic gradient (head loss per unit flow length); the negative sign reflects flow moving in the direction of decreasing head. It is the governing relation for leachate seepage through a clay liner or native subgrade and for groundwater flow generally (see Question 5).

1.2 Pyrolysis — the thermal decomposition of organic material at elevated temperature (typically 400–800 °C) in the total or substantial absence of oxygen, yielding a solid char, a condensable liquid (pyrolysis oil/bio-oil) and a combustible syngas (H₂, CO, CH₄); it is distinct from incineration, which requires excess oxygen to fully oxidize the feed. Pyrolysis is used as a thermal-treatment/energy-recovery option for scrap tires, mixed plastics and, increasingly, the combustible fraction of MSW.

1.3 Vadose zone — the unsaturated zone of the subsurface extending from the ground surface down to the water table, in which pore spaces hold a mixture of air and water rather than being fully saturated. Infiltrating leachate must traverse the vadose zone before reaching the saturated zone/aquifer, and the travel time and attenuation (sorption, biodegradation) occurring in this zone are central to assessing a landfill's groundwater risk.

1.4 Landfill mining — the deliberate excavation, screening and reclamation of previously buried waste from an existing landfill cell, undertaken to recover recyclable/combustible materials (metals, RDF), reclaim disposal airspace and thereby extend the site's remaining life, remediate an older unlined or poorly performing cell, or recover degraded fines for use as daily/intermediate cover soil.

1.5 Vector control — the set of operational and design measures at a landfill or transfer facility (compaction and daily cover of exposed waste, litter fencing, site drainage, exclusion of standing water, integrated pest management) intended to prevent the harbourage, feeding and proliferation of disease-carrying vectors — rodents, flies, mosquitoes and scavenging birds (gulls) — that would otherwise pose a public-health nuisance to the surrounding community.