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.
| # | Statement | Answer | Explanation |
|---|---|---|---|
| a) | Subaqueous tailings disposal (to fresh water lakes or sea/ocean waters) is legal in Canada. | True | A natural water body can be listed as a Tailings Impoundment Area (TIA) on Schedule 2 of the Metal and Diamond Mining Effluent Regulations (MDMER) under the Fisheries Act, which is precisely the legal mechanism that permits deposit of tailings into a lake despite the general s.36 prohibition on depositing a deleterious substance into fish-frequented water – Canadian precedents include Island Copper's submarine tailings disposal and several lake TIAs. Listing requires a federal environmental (impact) assessment, fish habitat compensation and long-term monitoring, so it is legal but far from unconditional. |
| b) | Mineral and mining rights fall under the jurisdiction of the Federal Government. | False | Under ss. 92A and 109 of the Constitution Act, 1867, ownership, management and disposition of Crown minerals and non-renewable natural resources within a province are provincial powers; each province administers its own mineral tenure system, leases and mining permits. Federal jurisdiction is the exception (territories, federal Crown/reserve lands, uranium and offshore areas beyond provincial boundaries), not the rule. |
| c) | Tailings disposal to rivers is legal in Canada. | False | While a natural water body can in principle be listed as a TIA under MDMER Schedule 2, DFO and ECCC virtually never approve a flowing river for this purpose because a river cannot settle solids or attenuate contaminants the way a lake can, and continuous downstream fish habitat impact would be very difficult to justify or compensate; listed TIAs in Canada are essentially always lakes. Treated effluent meeting MDMER concentration limits can be discharged to a river, but that is a different act – disposing of raw tailings slurry to a river is not accepted practice. |
| d) | Mine sites in Canada are not allowed to discharge effluent to the environment. | False | The MDMER is a permission-with-limits regime, not a prohibition: a mine may discharge effluent (including from a listed TIA) to a fish-frequented water body provided it meets prescribed authorized concentration limits for substances such as arsenic, copper, lead, nickel, zinc, un-ionized ammonia, total suspended solids and radium-226, and undertakes an Environmental Effects Monitoring program. |
| e) | Progressive reclamation is a requirement under the Mining Act (or similar) in the jurisdiction (Province) in which you are writing this exam. | True | In British Columbia, the Mines Act and the Health, Safety and Reclamation Code for Mines require an approved Mine Plan and Reclamation Program before a permit is issued, and progressive reclamation – rehabilitating disturbed ground as mining advances rather than deferring everything to final closure – is an explicit permit condition, with security posted and periodically updated to cover the outstanding liability throughout the mine's life. |
| Term | Definition |
|---|---|
| Tailings | The fine-grained waste material remaining after valuable minerals have been separated from ore during milling/mineral processing (crushing, grinding, flotation or other concentration). Tailings are usually transported as a slurry and stored in an engineered surface impoundment, and typically retain most of the ore's original sulphide gangue – making tailings management the primary source of the acid rock drainage, seepage and dam-stability issues addressed throughout this exam. |
| Phreatic surface | The upper boundary of the zone of saturation within an embankment, tailings mass or soil slope – the locus of points where pore-water pressure equals atmospheric pressure. Below it, positive pore pressure drives seepage flow governed by Darcy's law, $q = -k\,\dfrac{dh}{dx}$; locating and controlling the phreatic surface (Question 4a) is the first step in any tailings dam stability analysis. |
| Plasticity index | The numerical range of water content over which a fine-grained soil behaves plastically: $PI = LL - PL$, where $LL$ is the liquid limit and $PL$ the plastic limit. For example, a tailings sample with $LL = 45\%$ and $PL = 22\%$ has $PI = 45 - 22 = 23\%$; a high PI indicates a highly plastic, compressible, low-permeability clay, while a PI near zero indicates a non-plastic silt or sand. |
| Liquid limit | The water content, expressed as a percentage of dry soil mass and determined by the standard Casagrande cup or fall-cone test, at which a fine-grained soil transitions from a plastic to a liquid consistency (effectively zero undrained shear strength). It is the upper bound used in the Atterberg-limits framework and, together with the plastic limit, defines the plasticity index above. |
| Creep | Slow, continuous, time-dependent shear deformation of soil, rock or tailings under a sustained stress that remains below the material's peak (failure) strength. It is the mechanism by which a tailings dam or pit slope can progressively lose stability over years without an obvious triggering event, and is tracked with inclinometers and slope-extensometer survey monitoring. |
| Subsidence | Downward (and sometimes lateral) deformation of the ground surface caused by collapse, caving or closure of underground mined voids, or by drainage/consolidation of unconsolidated overburden. It is the principal long-term ground-stability hazard that an underground mine's closure plan must characterize and, where necessary, control by backfilling, crown-pillar design or surface exclusion zones. |
| Financial surety for reclamation | A financial security instrument – a bond, letter of credit, cash deposit or trust fund – that a regulator requires an operator to post before and throughout mining, sized to cover the full estimated cost of reclamation and closure. It protects the public purse if the operator becomes insolvent before its closure obligations are complete, and is periodically re-estimated and updated as the mine plan and disturbed footprint change. |
