24-MMP-A6 Mining and the Environment · May 2014
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, 2014-May. 3 hours duration, open book, no 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, design flood/PMF); 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.
| Substance | Transmission & associated minerals | Human health effects |
|---|---|---|
| Polycyclic aromatic hydrocarbons (PAHs) | Released mainly from diesel combustion (haul trucks, generators) and blasting fumes, transmitted airborne on soot/particulates (inhalation) and waterborne adsorbed to sediment in runoff, where they bioaccumulate through the aquatic food chain. Not tied to a specific ore mineral – associated with combustion of fossil fuels/explosives generally, and with coal and bitumen-hosted (oil sands) deposits specifically. | Several PAHs (e.g. benzo[a]pyrene) are known or probable human carcinogens; chronic exposure is also linked to respiratory irritation and dermal effects. |
| Mercury | Naturally associated with some gold, silver and base-metal sulphide (Zn, Pb) deposits, and historically added directly in gold amalgamation; released to air by roasting/smelting volatilization and to water via tailings and effluent, then transported atmospherically and deposited into water bodies. | Anaerobic bacteria methylate deposited mercury to highly bioaccumulative methylmercury; chronic exposure (mainly via fish consumption) causes neurological damage, with fetal and childhood neurodevelopment most sensitive. |
| Lead | Associated with galena (PbS) in lead–zinc (and some silver) deposits; released as airborne dust from ore/concentrate handling and smelting, and leached to water from tailings and waste rock. | Accumulates in bone and soft tissue; causes neurological and developmental harm (cognitive/IQ effects, especially in children) and cardiovascular/renal effects, with no established safe exposure threshold. |
| Cyanide | Used as the lixiviant in gold (and some silver) cyanidation leaching – associated with that processing circuit rather than a host mineral; released mainly via process solution/tailings effluent (waterborne) and, as HCN gas volatilized from low-pH ponds, locally airborne. | Acutely toxic – inhibits cellular cytochrome oxidase, causing rapid hypoxia; free cyanide is also acutely toxic to fish at very low concentrations, the basis for the International Cyanide Management Code and MDMER effluent limits. |
Open pit haul roads – chemical dust palliative. A hygroscopic salt (magnesium or calcium chloride) or a bitumen/lignosulfonate binder is applied to the running surface of the haul road. It suppresses dust for weeks at a time rather than the hours a water application lasts, cutting water-truck fleet size and reducing freeze risk in winter operations, and it also reduces road maintenance from washboarding. Its drawbacks are that chloride salts are corrosive to vehicles and can leach to groundwater or surface water, requiring their own environmental controls, and effectiveness degrades with continued haul traffic and periodic regrading, so reapplication is required on a recurring schedule.
Waste dumps / tailings impoundments – progressive vegetative or physical cover. Inactive dump benches or a stabilized tailings beach are progressively capped with topsoil and revegetated, or covered with a coarse gravel/rock layer, as soon as that surface is no longer receiving fresh material. This is a durable, low-maintenance solution once established, and it does double duty as progressive reclamation (Question 1e) while also reducing surface-water infiltration, an ARD co-benefit (Question 3). Its main drawback is that it cannot be applied to an actively-growing surface still receiving fresh waste rock or tailings; vegetation establishment on nutrient-poor tailings can also be slow and may require soil amendment or irrigation to succeed, and a wind fence array (the alternative for an active tailings beach) only provides localized, partial control.
