24-MMP-A6 Mining and the Environment · December 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Mining and Mineral Processing Engineering, 09-MMP-A6 Mining and the Environment, 2013-Dec. 3 hours duration, open book (any non-communicating calculator permitted). Six questions of equal value (20 marks each) constitute the bank; a candidate answers any FIVE. Most questions require an essay-format answer.
Reference texts: BC Ministry of Energy, Mines and Low Carbon Innovation, Health, Safety and Reclamation Code for Mines in British Columbia (current edition) (permitting, reclamation and closure planning requirements); Canadian Dam Association (CDA), Dam Safety Guidelines (2013/2019 update) (dam classification, embankment raising methods); Global Industry Standard on Tailings Management (GISTM, 2020) (tailings governance, upstream-construction restrictions); Price, W.A., MEND Report 1.20.1, Prediction Manual for Drainage Chemistry from Sulphidic Geologic Materials (1997/2009) (acid-base accounting, NPR screening criteria); International Network for Acid Prevention (INAP), Global Acid Rock Drainage (GARD) Guide (ARD prediction, prevention and treatment); Vick, S.G., Planning, Design, and Analysis of Tailings Dams, 2nd ed. (embankment construction methods, seepage control); Government of Canada, Metal and Diamond Mining Effluent Regulations (MDMER) under the Fisheries Act; Government of Canada, Impact Assessment Act (successor to the 2012 Canadian Environmental Assessment Act).
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.
Arsenic. Commonly hosted in arsenopyrite (FeAsS), and also in orpiment and realgar; it is transmitted as windblown dust from exposed ore, waste and tailings surfaces and, waterborne, through oxidative dissolution of these minerals into groundwater and surface water. Chronic ingestion or inhalation is linked to skin lesions, peripheral neuropathy and is a recognized human carcinogen (IARC Group 1, associated with skin, lung and bladder cancers), while acute high-dose exposure can be fatal. Environmentally, arsenic mobilized from mine waste is a major contributor to contaminated groundwater aquifers used for drinking water in a number of mining regions worldwide, and it can bioaccumulate in some aquatic organisms and sediments near a discharge point.
Mercury. Historically associated with cinnabar (HgS) ore, and also released as a trace contaminant from legacy gold-amalgamation processing and from coal combustion; it is transported as vapour through the atmosphere over very long distances and, in water, through methylation by anaerobic sediment bacteria into highly toxic, bioavailable methylmercury. Methylmercury bioaccumulates and biomagnifies up the aquatic food chain, so fish consumption is the dominant human exposure pathway; it is a potent neurotoxin with severe developmental effects on the fetus and young children (the historical Minamata disease precedent) and central nervous system effects in adults. Because of its atmospheric mobility, mercury is a transboundary contaminant – deposition can occur far from the original mining source.
Lead. Commonly hosted in galena (PbS), which frequently co-occurs with zinc in sphalerite-bearing Pb-Zn deposits; exposure is via dust inhalation and ingestion (contaminated soil and household dust) and, waterborne, via oxidative leaching from tailings and waste rock. It is a potent neurotoxin, with no known safe blood-lead threshold, causing measurable IQ and developmental deficits in children and affecting the kidneys, blood (anemia) and reproductive system in adults. Lead persists strongly in soils and sediments near historical smelters and tailings, does not readily degrade, and remains an environmental legacy issue for decades after mining ceases.
Silica. Crystalline silica (quartz) is not a metal but is the near-ubiquitous gangue mineral in virtually all hard-rock ore and waste, so it is present at essentially every mine site regardless of the commodity mined. The dominant exposure pathway is inhalation of respirable crystalline silica (RCS) dust generated by drilling, blasting, crushing and wind erosion of exposed waste and tailings surfaces; chronic inhalation causes silicosis, a progressive and irreversible lung fibrosis, and elevates the risk of lung cancer (IARC Group 1), COPD, and (per emerging evidence) autoimmune disease and tuberculosis susceptibility. Unlike the metals above, silica's principal impact is occupational/human-health rather than aquatic-ecotoxicological, since quartz is chemically near-inert in the environment; windblown silica-bearing dust is nonetheless also a broader visibility and community-nuisance issue (Question 6b).
Water spraying (fixed sprinklers or water trucks). Water applied directly to haul roads, waste dump faces or exposed tailings binds fine particles by surface tension and adds cohesion; it is low-capital, uses equipment and a water source usually already on site, and can be deployed immediately on any newly exposed surface. Its drawback is that the effect is short-lived – it must be reapplied frequently, especially in hot, dry or windy weather – it consumes water that must be accounted for in the site water balance (Question 5), and it is largely ineffective, or even counter-productive through ice formation, at the sub-zero temperatures common on Canadian sites for much of the year.
Chemical dust suppressants/binders (calcium or magnesium chloride, lignosulfonates, polymer emulsions). Sprayed onto haul roads or exposed surfaces, these form a longer-lasting crust or binding matrix, typically effective for weeks to months rather than hours, substantially reducing both water consumption and reapplication frequency; on haul roads they can double as a surface stabilizer that also reduces road-maintenance cost. Drawbacks include a higher per-application cost than plain water, the need for careful application-rate control to avoid over-application, and, for chloride-based products, a risk of salt loading to nearby soils and surface water if runoff is not managed.
Vegetative cover and mulch/tackifier stabilization (for inactive surfaces). Applying a mulch or tackifier and establishing vegetation on waste dump faces, tailings beaches or haul-road sections no longer in active use physically binds the surface with roots and organic matter, providing effective, low-maintenance, long-term dust control once established, and doubling as the first stage of progressive reclamation (Question 1e). The main drawback is the lead time and site conditions needed for establishment – a growth medium, seed mix suited to the climate and slope, and often an interim tackifier are required while vegetation takes hold, so it is not a rapid-response option and is unsuitable for any surface still receiving active traffic or fresh deposition.
