24-MMP-A6 Mining and the Environment · May 2016
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, 2016-May. 3 hours duration, open book (any non-communicating calculator permitted). SIX questions are printed on the paper; FIVE questions constitute a complete exam paper, and only the first five questions as they appear in the answer book are marked. Most questions require an essay-format answer; clarity and organization are explicitly assessed.
Reference texts: International Network for Acid Prevention (INAP), Global Acid Rock Drainage (GARD) Guide (ARD prediction, static and kinetic testing, sampling programs); Price, W.A., MEND Report 1.20.1, Prediction Manual for Drainage Chemistry from Sulphidic Geologic Materials (1997/2009) (acid-base accounting, sampling protocols); Government of Canada, Metal and Diamond Mining Effluent Regulations (MDMER, the current name for the exam's "MMER") under the Fisheries Act; Government of Canada, Impact Assessment Act (successor to the 2012 Canadian Environmental Assessment Act); BC Ministry of Energy, Mines and Low Carbon Innovation, Health, Safety and Reclamation Code for Mines in British Columbia (current edition) (closure planning, reclamation, waste dump erosion control); Canadian Dam Association (CDA), Dam Safety Guidelines (2013/2019 update) (tailings embankment design, dam safety inspections, failure modes); Global Industry Standard on Tailings Management (GISTM, 2020) (tailings governance and monitoring); Vick, S.G., Planning, Design, and Analysis of Tailings Dams (1990) (upstream/centerline/downstream embankment construction methods, beach hydraulic sorting); ATSDR, Toxicological Profiles for arsenic, polycyclic aromatic hydrocarbons, molybdenum and silica.
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.
| Substance | Transmission & effects |
|---|---|
| Arsenic | Mobilized primarily as a waterborne concern – arsenic commonly substitutes into or is adsorbed onto iron sulphide minerals (notably arsenopyrite, FeAsS) and is released into drainage as those sulphides oxidize under the same sulphide-oxidation (ARD) chemistry discussed in Question 1, making it a frequent co-contaminant of acidic mine drainage; secondary transport can also occur via wind-blown tailings/waste rock dust. Chronic ingestion or inhalation exposure is linked to skin lesions, peripheral vascular and neurological effects, and is a recognized human carcinogen (skin, lung, bladder), while in the aquatic environment it is acutely and chronically toxic to fish and invertebrates even at low concentrations. Arsenic is characteristically associated with orogenic/mesothermal gold deposits (arsenopyrite is a classic gold-pathfinder mineral), volcanogenic massive sulphide (VMS) deposits, and some porphyry systems. |
| Polycyclic aromatic hydrocarbons (PAHs) | Released mainly to air as combustion by-products from diesel equipment exhaust (haul trucks, generators, drill rigs) and from any on-site fuel or explosives handling/spillage, with secondary waterborne transport via runoff carrying settled particulate-bound PAHs into site drainage. Health effects include respiratory irritation and, for several specific PAH compounds (e.g. benzo[a]pyrene), recognized carcinogenicity following chronic exposure; in the aquatic environment PAHs bioaccumulate in sediment-dwelling organisms and can biomagnify up the food chain. PAHs are not geologically deposit-specific in the way the other three substances are – they are primarily an OPERATIONAL emission (fuel combustion, explosives residue) common to essentially any mine type rather than a signature of a particular ore deposit, though naturally-occurring PAHs can also be associated with coal and some organic-rich sedimentary units. |
| Molybdenum | Mobilized as a waterborne concern from the oxidative weathering of molybdenite (MoS2) in waste rock and tailings, entering drainage predominantly as the molybdate oxyanion (MoO42-), which – unlike most other mine-related metals – is MORE mobile at NEUTRAL to alkaline pH than under acidic conditions, making it a concern even from well-neutralized or non-acid-generating waste. Molybdenum is an essential trace nutrient for ruminant animals but becomes toxic at elevated intake (molybdenosis, inducing copper deficiency in cattle grazing on molybdenum-affected forage/water downstream of a site), so livestock and agricultural water-use pathways are the primary human/animal health concern rather than direct human toxicity, which is comparatively low. Molybdenum is characteristically associated with porphyry copper-molybdenum and porphyry molybdenum deposits. |
| Silica (crystalline, respirable) | An airborne occupational and ambient dust concern rather than a waterborne one – fine (respirable, <10 micron) crystalline silica dust is generated by drilling, blasting, crushing and hauling of silica-bearing rock (quartz-rich ore, waste rock or country rock) and becomes a health hazard when inhaled by site workers or, at lower concentration, nearby communities. Chronic inhalation causes silicosis (progressive, irreversible lung fibrosis) and is classified as a human lung carcinogen; it poses essentially no direct aquatic/environmental toxicity concern, distinguishing it from the other three substances in this question, which are predominantly waterborne. Because silica (quartz) is a near-ubiquitous rock-forming mineral, it is not associated with one specific deposit type the way arsenic or molybdenum are – the hazard is instead driven by host-rock quartz content and applies across virtually any hard-rock mining operation, with the highest-risk operations being those in high-silica country rock (e.g. many hard-rock gold, base-metal and industrial-mineral quartzite/silica-sand operations). |
Chemical dust suppressants / surface crusting agents (e.g. lignosulphonate, magnesium or calcium chloride, polymer emulsions, or bitumen-based products) are sprayed onto exposed waste dump or dry tailings beach surfaces to bind fine particles into a semi-rigid crust that resists wind entrainment. Their benefit is a long-lasting effect (weeks to months per application, far longer than water spraying) with relatively low ongoing water demand and equipment need, making them well suited to large, relatively inactive surfaces such as an inactive tailings beach or an old waste dump face awaiting final reclamation. Their drawbacks include material and application cost, the potential for some products (e.g. chloride-based salts) to alter surface water/leachate chemistry or vegetation establishment if over-applied, reduced effectiveness on actively-trafficked or actively-growing (advancing) surfaces where the crust is continually disturbed, and the need for reapplication after significant rainfall or freeze-thaw cycling breaks down the crust.
Progressive vegetative cover establishment on inactive waste dump slopes and reclaimed tailings surfaces provides a self-sustaining, low-maintenance dust control layer once established – root systems bind surface particles and above-ground biomass reduces wind velocity at the ground surface, and this simultaneously advances the site's progressive reclamation obligations (Question 3), giving a dual benefit unmatched by the other control methods. Its principal drawback is the establishment lag: vegetation takes one or more growing seasons to provide meaningful cover, requires suitable growth medium (often an engineered soil cover or growth-medium placement first) and irrigation/fertilization during establishment, is not viable on an ACTIVELY growing/trafficked waste dump face or an active tailings beach still receiving fresh discharge, and can fail on steep, unstable, or highly saline/acid-generating surfaces without significant surface preparation first.
