Basic Terms and Knowledge: 24-MMP-A6 Mining and the Environment, May 2014, Q1

Question 1: Basic Terms and Knowledge (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.

True/False (2 marks each, 10 marks total)

True/false statements on Canadian mine-waste regulation
#	Statement	Answer	Explanation
a)	Subaqueous tailings disposal to fresh water lakes is allowable in Canada.	True	A natural lake 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 – 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. Listing requires a federal impact assessment, fish-habitat compensation and long-term monitoring, so it is legal but conditional and increasingly contested (Question 4b).
b)	Mineral and mining rights fall under federal jurisdiction.	False	Under ss. 92A and 109 of the Constitution Act, 1867, ownership, management and disposition of Crown minerals within a province are provincial powers; each province administers its own mineral tenure, leases and mining permits. Federal jurisdiction over minerals is the exception – the territories, federal/reserve lands, uranium and some offshore areas – not the general rule.
c)	Federal environmental approval is required for most mining projects in Canada.	False	A federal impact assessment under the Impact Assessment Act (successor to the 2012 Canadian Environmental Assessment Act) is triggered only when a project meets a prescribed capacity or physical threshold in the Physical Activities Regulations (e.g. a new metal mine above a stated ore-processing rate, or a tailings/waste-rock facility above a stated size). The majority of mining activity in Canada – exploration, most mine expansions and many smaller operations – proceeds through provincial environmental assessment and permitting alone, so federal review is the scale-triggered exception rather than the norm.
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 decant 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 (EEM) program.
e)	Progressive reclamation is a requirement under the Mining Act, or equivalent legislation, in your Province.	True	In British Columbia, the Mines Act and the Health, Safety and Reclamation Code 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 reclamation security posted and periodically updated to cover the outstanding liability.

Definitions (all eight terms defined; any five satisfy the mark scheme)

Definitions of mine-waste and geotechnical terms
Term	Definition
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; locating and controlling the phreatic surface (with internal drains, a wide beach, or a downstream toe drain) is the first step in any tailings dam stability analysis and directly governs the seepage outflow quantified in Question 6b.
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 (both from the Atterberg-limits framework, below). For example, a tailings sample with $LL = 38\%$ and $PL = 19\%$ has $PI = 38 - 19 = 19\%$; a high PI indicates a highly plastic, compressible, low-permeability clay, while a PI near zero indicates a non-plastic silt or sand more prone to liquefaction (Question 6a).
Atterberg limits	A set of standardized water-content boundaries – the shrinkage limit, plastic limit (PL) and liquid limit (LL) – that define the transitions of a fine-grained soil between solid, semi-solid, plastic and liquid consistency states as its water content increases. Determined by the Casagrande cup/fall-cone (LL) and thread-rolling (PL) tests, they are the standard classification framework for tailings and foundation soils and the basis of the plasticity index above.
Standard Proctor Compaction Test	A laboratory test (ASTM D698) that compacts soil into a mould in three layers, each struck with 25 blows of a 2.5 kg hammer dropped 305 mm, at a series of moisture contents, to determine the soil's maximum dry density and optimum moisture content. The result sets the target compaction specification (typically a percentage of maximum Proctor density) that embankment and cover-fill placement must achieve in the field.
Darcy's Law	The governing equation for laminar seepage flow through a porous medium: $q = -k\,\dfrac{dh}{dx}$, where $q$ is the specific discharge, $k$ the hydraulic conductivity of the material and $dh/dx$ the hydraulic gradient. It is the physical basis for calculating seepage quantity through or under a tailings embankment and for sizing underdrains and seepage-collection systems (Question 6b).
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.
Freeboard	The vertical distance between a tailings pond's normal operating water surface and the lowest point of the dam crest (or emergency spillway invert), providing an allowance for wave run-up, storm surge and inflow-design-flood routing so the reservoir cannot overtop the embankment (Question 6a) even during the governing flood event.
Probable maximum flood	The theoretical maximum flood that could occur at a given watershed, resulting from the most severe combination of meteorological and hydrologic conditions considered reasonably possible (probable maximum precipitation routed over an already-saturated, worst-case antecedent catchment). CDA guidelines require the PMF, or a defined fraction of it, as the design inflow flood for a tailings dam classed High, Very High or Extreme consequence, sizing both freeboard and spillway capacity.

Topic.

Key relations. $PI = LL - PL$ (Atterberg framework); Darcy's law $q = -k\,dh/dx$ (seepage/freeboard/PMF all trace back to controlling the phreatic surface and the inflow design flood); MDMER Schedule 2 as the legal mechanism converting a "prohibited deposit" into a listed, permitted Tailings Impoundment Area.

Why this works. Canada's federal structure splits authority by subject matter, not by industry: provinces own and manage the mineral resource itself, while the federal government retains narrow but powerful levers – fisheries habitat protection and nationally-significant project review above all – that apply to mining because mines discharge to water, disturb land and can be very large, not because mining itself is federally regulated. Every true/false item above turns on separating the ownership question (provincial, always) from the environmental-review/discharge question (federal, but only above a scale threshold or via the fisheries lever).

Common pitfall. Assuming every mine in Canada needs a federal environmental assessment, when in fact only large or high-risk projects meeting the Physical Activities Regulations thresholds trigger one – conflating "mining is a highly regulated industry" with "mining is federally regulated" is the exact trap item c) sets.

Source. Constitution Act, 1867, ss. 92A, 109; Impact Assessment Act and Physical Activities Regulations; Fisheries Act and MDMER; BC Health, Safety and Reclamation Code for Mines; BC Mines Act; Canadian Dam Association, Dam Safety Guidelines.

Question 1 of 6: Basic Terms and Knowledge

Question 1: Basic Terms and Knowledge (20 marks)

True/False (2 marks each, 10 marks total)

Definitions (all eight terms defined; any five satisfy the mark scheme)