MINE 480 ‐Mine Waste ManagementMINE 590Q – Advanced Mine Waste 

Management

Term 2 ‐ 2013Lecture 1, Part 2 – Water Dams and Tailings Management 

Facilities

Dirk van ZylNorman B. Keevil Institute of Mining Engineering

dvanzyl@mining.ubc.ca(604) 827‐3462

Outline

• Characteristics of water dams• Comparison between water dams and tailings management facilities

• Regulatory aspects• Codes of practice• Risk assessment and management

Characteristics of Water Dams• Contain water for one or more purposes:

– Hydro power– Irrigation– Water supply to cities

• Site selection and design can take a long time, very careful site investigations, etc.

• Construction is completed in a few years and water is then impounded

• First filling is a critical period• Expected life of facility 50+, 100+ years?• Maintenance on an ongoing basis as necessary

Water Dams vs. Tailings Management Facilities (TMF)

Water Dams• Design and construct over a 

relatively short period• Typically one designer and 

contractor• Construction completed 

before full operations• Life of structure 50+, 100+ 

years• Store clean water

TMF• Design and constructed 

over the life of the mine• Can have multiple designers 

and contractors• Construction ongoing 

during full operations• Life of structure is operating 

life of mine plus closure• Store water impacted by 

reagents and minerals

Regulatory Aspects

• Dam safety regulations established a long time before that for tailings management

• Dam safety regulations administered by a special branch of a jurisdiction dealing with all aspects of water, e.g. the Water Stewardship Division of the BC Ministry of Environment or the Sate Engineer’s office in many US States.

• Regulations focused on dam height and capacity, e.g. higher than 10 feet and storing more than 50 acre‐feet of water

Regulatory Aspects (2)

• In some jurisdictions a TMF is considered a dam and this can result in difficulties with interpretations:– The height of a TMF (measured from where?)– The amount of water stored (or the amount of slurry stored)

– What happens to the permit after closure (water cover vs. no water cover)?

Dam Safety Guidelines

• Canadian Dam Safety Association• Federal Emergency Management Association in the US

• International Commission on Large Dams –many useful publications

What is Risk?

• What can go wrong?• How can it go wrong?• What are the consequences?

Making it More Analytical

• Risk = hazard and pathway x consequences

• Risk = likelihood of occurrence x consequences

Example

• Evaluate the risk of an injury when crossing an ice packed road:– Define the “hazards”– Consider the pathway – how will the hazard result in a failure and how will that develop (the components of the failure)?

– Estimate the likelihood of the failure– What are the consequences of the failure?– How does that translate into risk?

Using Descriptive/Qualitative  Methods

Failure Modes and Effects Analysis (FMEA)

• Performed by a team of experts• Define the boundaries of the project

– Physical• Limit to area that will impact specific failures, e.g. a tailings impoundment with all associated facilities

– Temporal• Life cycle stage of facility, e.g. operations and closure

• Agree on the definitions of likelihood, consequences and confidence limits

• Identify the failure modes• Complete the FMEA matrix 

FMEA (2)

• Can perform the FMEA assuming only the availability failure mitigations in place

• Can also perform FMEA after further risk management, i.e. obtain the residual risk

Likelihood of Event Occurring

Level

RatingEstimated

Cost

Health & Safety Environmental Community Operational Security Legal Compliance

1 Insignificant> $1,000

First Aid Injury Nuisance value

No or very low environmental impact. Impact confined to small area.

Isolated complaint. No media inquiry.

Loss equivalent to 1 hour of production interruption. Routine wear and tear of screen panels at crusher requires change out.

Infractions: Violations of internal policies and procedures. No personal injury of property damage.

Minor technical/legal compliance issue unlikely to attract a regulatory response.

2 Minor> $10,000

Medical Treatment Injury Restricted Work Injury

Low environmental impact. Rapid cleanup by site staff and/or contractors. Impact contained to area currently impacted by operations.

Small numbers of sporadic complaints. Local media inquiries.

Loss equivalent to 6 hours of production interruption.Metal tooth on loader bucket comes loose while feeding crusher. Crusher plugged and tooth has to be cut out of crusher.

Minor Criminal Offences. Example: Trespassing, Theft under $5000.00, Minor Property Damage, etc.

Technical/legal compliance issue which may attract a low-level administrative response from regulator. Incident requires reporting in routine reports (e.g. monthly).

3 Moderate> $100,000

Single Lost Time Injury

Moderate environmental impact. Cleanup by site staff and/or contractors. Impact confined within lease boundary.

Serious rate of complaints, repeated complaints from the same area (clustering). Increased local media interest.

Loss equivalent to 12 hours of production interruption.The pressure oxidation vessel develops a small leak in the brick liner.

Appreciable property damage. Theft over $10,000.00 value. Low intensity civil unrest

Breach of regulation with possible prosecution and penalties. Continuing occurrences of minor breaches. Incident requires immediate (within 48 hours) notification.

4 Major> $1,000,000

Multiple Lost Time Injuries Admission to intensive care unit or equivalent. Serious, chronic, long term effects.

Major environmental impact. Considerable cleanup effort required using site and external resources. Impact may extend beyond the lease boundary.

Increasing rate of complaints, repeated complaints from the same area (clustering). Increased local/ national media interest.

Loss equivalent to 3-7 days of production interruption.A critical piece of environmental control equipment for gas cleaning at the roaster facility fails and requires replacement.Ground fall at the open pit closes of access road and buries equipment.

Significant property damage resulting in operational shut down. Significant Criminal offences committed against persons. High intensity civil unrest. High level fraud or embezzlement

Major breach of regulation resulting in investigation by regulator. Prosecution, penalties or other action likely.

5 Catastrophic>$10,000,000

Fatality(s) or permanent disability.

Severe environmental impact. Local species destruction and likely long recovery period. Extensive cleanup involving external resources. Impact on a regional scale.

High level of concern or interest from local community. National and/or international media interest.

Loss equivalent to more than a week of production interruption.Pressure oxidation vessel fails and depressurizes.Ground fall at an underground heading causes loss of entire heading.

Major criminal offences. Multiple fatalities. Forced evacuation of all personnel.

Serious breach of regulation resulting in investigation by regulator. Operation suspended, licenses revoked.

Consequence Matrix

Risk Matrix

Confidence Level Description

Low Do not have confidence in the estimate or ability to control during operations.

MediumHave some confidence in the estimate or

ability to control during operations, conceptual level analyses.

High

Have lots of confidence in the estimate or ability to control during operations, detailed analyses following a high

standard of care.

Level of Confidence

Probability of Failure

• For slope stability or other similar analyses where the results are expressed in a factor of safety (FS):

pf = P(FS<1)

Reliability

• Probability of Failure (pf) + Reliability (R) = 1

• Then:R = 1 – pf

Risk Assessment and Management for Water Dams

• Many case histories on successes and failures of water dams

• Statistical failure rate of water dams in the order of 1x10‐4 failures per dam year

• Dam Safety Risk Analysis

http://foboni.wordpress.com/2011/09/

Risk Management

• In principle: manage the components of the risk:– Manage the “hazard”– Manage the failure flow path, how it occurs– Manage the consequences

• Risk management for dams:– High quality site characterization and design– Use of review panel– Construction details– Instrumentation and monitoring– Regular maintenance 

Figure 4: Protection Zone Distances for Mining Near a Dam

Dam

No Mining PermittedTo Protect Dam

Minimum Offset Distance

3000 ft.

Maximum Offset Distance(All Conditions)

45°65°

Minimum Offset DistanceIncereases with Depth

Normal Mining Permitted

Mining Permitted Under Guidelinesfor Dam Offset Distance

2000 ft.Minimum Offset Distance

Dam

Impounded Surface Water

High Water Mark2000 ft.

No Mining PermittedTo Protect Dam

Minimum Offset Distance

3000 ft.

Maximum Offset Distance(All Conditions)

Minimum Offset DistanceIncereases with Depth

45° 65°

Mining Permitted UnderGuidelines for Dam Offset

Distance and ExtractionDepth

MinimumExtraction

Depth30t + 400 ft.

MaximumExtraction

Depth60t + 400 ft.

Mining Permitted Under Guidelinesfor Dam Offset Distance

No MiningPermitted

* t = Seam Thickness

Mining Permitted Under Guidelinesfor Extraction Depth

Extraction Depth from LowestElevation of Reservoir Floor

Figure 3: Protection Zone Distances for Mining Near a Dam and Under A Reservoir Rim and Foundation