24-MMP-A6 Mining and the Environment · May 2017
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, 2017-May. 3 hours duration, open book (any Casio or Sharp approved 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, prevention/treatment methods); Price, W.A., MEND Report 1.20.1, Prediction Manual for Drainage Chemistry from Sulphidic Geologic Materials (1997/2009) (acid-base accounting, NPR screening); Government of Canada, Metal and Diamond Mining Effluent Regulations (MDMER, the current name for the exam's "Metal Mining Effluent Regulations") under the Fisheries Act, s.36(3); Government of Canada, Canadian Environmental Protection Act (1999) and Impact Assessment Act (successor to the 2012 Canadian Environmental Assessment Act named in the exam); Species at Risk Act (2002); Ontario, Mining Act, R.S.O. 1990, and O.Reg. 153/04 (Records of Site Condition, under the Ontario Environmental Protection Act); Canadian Council of Ministers of the Environment (CCME), duty-to-consult and Indigenous engagement guidance for resource projects; Vick, S.G., Planning, Design, and Analysis of Tailings Dams (1990) (upstream/centerline/downstream construction, disposal practices); Canadian Dam Association (CDA), Dam Safety Guidelines (tailings impoundment construction); BC Ministry of Energy, Mines and Low Carbon Innovation, Health, Safety and Reclamation Code for Mines in British Columbia (current edition) (closure planning, revegetation, mine water management); ATSDR, Toxicological Profiles for arsenic and mercury.
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.
| Contaminant | Mining source & transport/fate | Toxicity concerns |
|---|---|---|
| Arsenic | Commonly hosted in arsenopyrite (FeAsS), often co-occurring with gold mineralization; released as sulphide oxidation (Question 3) proceeds, mobilizing arsenic into drainage predominantly under acidic, oxidizing conditions where it partitions between dissolved arsenate/arsenite species and adsorption onto iron oxyhydroxide precipitates – the same "yellow boy" solids from Reaction 3 – giving it complex, pH- and redox-dependent transport behaviour rather than simple conservative transport. | A recognized human carcinogen (skin, lung, bladder) via chronic ingestion or inhalation, causing skin lesions and peripheral vascular/neurological effects at lower chronic exposures; acutely and chronically toxic to aquatic organisms even at low concentrations, making it one of the most tightly regulated deleterious substances under the MDMER (Question 2). |
| Mercury (organic and inorganic) | Inorganic mercury can occur naturally in some ore bodies (particularly some gold and base-metal deposits) and historically was used directly in gold amalgamation processing (a legacy contamination source at many older sites); once released to a wetland, sediment or aquatic environment, inorganic mercury can be converted by anaerobic sulphate-reducing bacteria into organic methylmercury, which is far more bioavailable and mobile through the food web than the inorganic form. | Inorganic mercury exposure primarily affects the kidneys and, at high levels, the nervous system; methylmercury is a potent neurotoxin that bioaccumulates in fish tissue and biomagnifies up the food chain, making fish consumption (by wildlife, subsistence harvesters, and downstream communities) the dominant human exposure pathway of concern near a mine site with mercury-affected water bodies, rather than direct water contact. |
i. Three mine water control technologies (6 marks).
ii. Active vs. passive water treatment (6 marks). Active treatment (e.g. a lime/chemical precipitation plant, Question 3D) continuously doses reagent into collected contact water under mechanical/operator control to neutralize acidity and precipitate metals as a sludge that must be dewatered and disposed of; it requires substantial, ongoing energy input (pumping, mixing, reagent handling) and continuous operator/maintenance attention, generates an ongoing sludge disposal cost and liability, but achieves reliable, predictable, rapidly-adjustable treatment performance and can be scaled to handle variable flow and loading – making it well suited where discharge limits must be met with high confidence, such as near sensitive downstream fish habitat. Passive treatment (e.g. a constructed wetland or bioreactor, Question 3D) instead relies on natural or engineered biogeochemical processes (sulphate reduction, plant uptake, adsorption) with little to no external energy input and minimal day-to-day operator attention once established, lowering ongoing operating cost and reagent/sludge disposal burden substantially; however it needs periodic (rather than continuous) monitoring and maintenance to confirm the system has not become saturated or biologically exhausted, performs less predictably under variable or high loading, and – as noted in Question 3E – is markedly less effective in cold northern conditions. Both approaches still require ongoing water-quality monitoring against MDMER discharge limits, but active treatment's continuous instrumentation contrasts with passive treatment's more periodic sampling regime, since a passive system's performance changes gradually rather than being adjustable in real time.
