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24-MMP-A6 Mining and the Environment · December 2014

Question 3 of 6: Reclamation and Mine Closure

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

Notes on this paper

EGBC National Exam — Mining and Mineral Processing Engineering, 09-MMP-A6 Mining and the Environment, 2014-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, with only the first five questions appearing in the answer book marked. Most questions require an essay-format or point-form 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, tailings dam consequence categories, freeboard/PMF design basis, dam safety review and inspection intervals); Global Industry Standard on Tailings Management (GISTM, 2020) (tailings governance, design and closure principles); Price, W.A., MEND Report 1.20.1, Prediction Manual for Drainage Chemistry from Sulphidic Geologic Materials (1997/2009) (acid-base accounting, neutralizing potential ratio screening criteria); International Network for Acid Prevention (INAP), Global Acid Rock Drainage (GARD) Guide (ARD prediction, prevention and treatment across the mine lifecycle); Vick, S.G., Planning, Design, and Analysis of Tailings Dams, 2nd ed. (upstream/centreline/downstream embankment construction methods); 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); Mining Association of Canada, Towards Sustainable Mining Tailings Management Protocol; International Cyanide Management Institute, International Cyanide Management Code.

Question 3: Reclamation and Mine Closure (20 marks)

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.

a) Limiting pond water and reducing pore water pressure for tailings-surface reclamation

A fourth, complementary technique – relocating or progressively shrinking the active decant pond away from areas scheduled for near-term reclamation, or pumping the pond down with a reclaim/decant system – is often combined with the three methods above on real projects.

b) Underground mine closure – engineering investigations by hazard category

Underground mine closure plan: hazard categories and required engineering investigations
Hazard categoryEngineering investigation required
Mine entry points (portals, adits, shafts, raises)Engineer permanent closure of every opening – concrete bulkhead plugs, engineered caps, or bat-friendly gates where wildlife access must be preserved – sized to prevent public entry and structural collapse over the long term; inspect and stabilize collar structures before capping.
Mine working areas / ground stability & subsidenceLocate and characterize all old workings and crown pillars from mine records and survey; stope/pillar stability analysis; delineate surface subsidence risk zones; design backfilling, pillar reinforcement or surface exclusion zones where subsidence risk cannot be eliminated.
Mine gasCharacterize residual gas generation (methane, carbon monoxide, hydrogen sulphide, radon) from remaining broken rock, old workings and any residual organic material; assess whether passive venting, permanent sealing, or active ventilation is required at each opening; install gas-monitoring wells where a closed void could accumulate gas that migrates to surface or to adjacent occupied structures.
GroundwaterPredict post-closure water-table rebound and flooding rate of the underground workings; confirm the final discharge point(s) and design a passive or active (perpetual, if required) treatment system sized for the predicted long-term flow and chemistry; characterize residual acid-generating potential of exposed sulphide zones and assess whether controlled flooding (oxygen exclusion, Question 2b) is an effective long-term ARD control compared to perpetual treatment.
Surface waste rock piles and tailings facilityGeotechnical stability analysis of surface waste piles and the tailings dam; design erosion control and, where PAG material is present, a source-control cover (Question 2c); dam stability analysis, closure cover design and long-term seepage/water management (Questions 4 and 5).
Surface infrastructurePlan demolition and removal of buildings, plant and equipment; identify and remediate contaminated soils at fuel storage, assay laboratory and ore-handling areas; safely dispose of remaining hazardous materials, and reclaim haul roads no longer needed while retaining the minimum access required for long-term monitoring.
Long-term monitoring, maintenance and financial assuranceDesign a monitoring program (groundwater and surface water quality, subsidence markers, gas concentrations, structural integrity of bulkheads/plugs and dams) with defined trigger and contingency-action levels; produce and periodically update a full closure cost estimate covering every item above, held as financial surety per the mining licence requirement.