Tailings Dam Safety And Implementation Of Safety

Guidelines By A Tailings Dam Operator

Why are Dam Safety Programs Important?

Los Frailes Spain - 1998

Merriespruit South Africa - 1994

Dam Safety Program Implementation

• Guidelines provide templates and flow sheets for dam safety programs

• Operator must translate these into activities that can be carried out at the tailings management site to create an effective dam safety program

Dam Safety Program Development

• A good Dam Safety Program requires collaboration of a number of groups.

• Operators, designers and regulators must all provide input to the dam safety program

• Risk based approach can simplify the dam safety program:– Consider consequences of potential failure modes– Focus program on key failure modes

• Program must consider the “tailings management system” – not just the dam

• Program must be set up understanding that the system and risks will change over the mine life – recognize the changing conditions and changing risk

Roles and Responsibilities• Roles and responsibilities must be clearly

defined• The designer and the regulator do not control

the operation of the facility and are not involved in the day to day operation

• Therefore, everyone must understand that the owner/operator is ultimately responsible for the safe operation of the facility

• The Mine Manager must accept this responsibility and mandate that the dam safety program will be followed without exception.

Training• Best to have designer involved in training

– Present key aspects of the design, critical issues. Helps to focus site staff on the key issues

– Designer to have at least annual review of performance – field inspection and review of documentation

• All personnel that will be in vicinity of facility should be trained to identify conditions that could lead to failure

• All personnel should know how to report a potential problem

Inspections• Frequency of inspections and monitoring data collection

depends on the rate of system changes• Routine inspections on a weekly or monthly basis

– Frequency may change depending on the season– Daily to weekly during wet season or during snow melt– Monthly during dry season– By site personnel

• Engineering inspections on a semi-annual to annual basis– By designer

• Special inspections after significant events– By designer and site personnel following earthquakes and floods

• A dam safety review every 5 to 10 years– By independent engineer (not the designer)

Inspections

• Check lists for inspections– Don’t miss key information– Simplifies inspections – inspector can focus on the observations

• Inspection forms – Information is presented in a consistent format, changes in

system performance are more easily identified.

• Completing the checklist does not mean the inspection is complete

• Evaluation of the information collected is the important step – how is the performance of the facility changing and are these changes consistent with the expected performance

Typical Inspection Forms

FACILITY INSPECTION SUMMARY REPORT – FORM 1 PROJECT: _____________________

Sheet 1 of 1 All parts of this inspection form should be completed. Adverse conditions should be described and location stated. Additional information and relevant photographs should be attached. Inspecting Officer: Report No.: Inspection Date:

Inspecting Agency: (DD/MM/YR)

WEATHER: Temperature: oC Description:

Current Last 3 Days Other Comments: dry frost rain snow

FACILITIES INSPECTED: (A separate report sheet Form A or Form B to be prepared for each structure)

Structure Dam/Dyke Spillway/Flow Control Area I

Area II

Area III

Other

Review Officer: Review Agency: Date Reviewed: (DD/MM/YR) ACTION REQUIRED: none

VISUAL INSPECTION CHECKLIST PROJECT: ____________________________

The FIRST RULE of inspection is that CHANGED CONDITIONS ARE IMPORTANT. Below is a general checklist of items that one should keep in mind when examining the dams and spillways of the ___________________________. The list should be reviewed for each dam and spillway. DAM CRESTS Cracks running along the crest of a dam are evidence of slumping or slope instability. Cracks across the crest of dam are evidence of differential settlement. Settlement and particularly differential settlement is easy to see. Settlement is serious if the

freeboard is reduced. Freeboard is the vertical distance between dam crest elevation and the water level.

Trees should not be allowed to grow on a dam. Tree roots cause disturbance and tend to seek water. When the tree dies, the roots rot, leaving a pipe through a structure which can cause failure.

UPSTEAM SLOPE Rip-rap protects the surface of a dam from waves and flowing water. Deterioration of

erosion protection can lead to slope deterioration. Sloughing may be indicative of slope instability and/or inadequate erosion protection Depressions and sinkholes may be indicative of internal erosion (piping) of material

thorough the dam. If an upstream depression (sinkhole) is noted, you should check for signs of piping (dirty discharge) along the downstream toe of the dam.

Shoreline erosion adjacent to the upstream face of a dam should be noted, as this may require remediation and/or erosion protection.

Animal holes in a dam can create a “pipe” through the structure, and could cause an internal wash-out failure.

DOWNSTREAM SLOPE Soft zones and sand boils along the toe of a dam are evidence of a developing quick

condition, which can progress to piping and internal erosion and eventually lead to a wash-out failure.

Dirty, sediment laden seepage water is evidence of piping and internal erosion. Increased seepage rates and/or new areas of seepage are a sign that an adverse change has

taken place within a dam. Bulging on the lower part of a slope may be the result of slope instability, slumping, frost

deterioration and/or lateral spreading. It is essential to ensure that drains are free-flowing and not blocked with sediment or

precipitates, as this can adversely affect the stability of the dam. Animal holes in a dam can create a “pipe” through the structure, and could cause an internal

wash-out failure. SPILLWAYS Spillways should be free of obstructions and in good working order. The condition of

spillways are particularly important because plugging can cause an unwanted increase in water level and the possible overtopping of dam crests.

Erosion protection can be damaged during extreme flow events and should be repaired at the earliest opportunity to prevent further erosion.

Concrete deterioration is easy to see and should be noted and monitored.

Inspection Forms to Include Photographs

July 2005 June 2006

PHOTOGRAPH North Dam 1: View to the east along the downstream toe of the North Dam near the west abutment. Toe and face are in good condition. Small puddles of water in natural topographic depressions. Condition in 2006, including the size and location of water downstream of the dam, is similar to that observed in 2005 as shown by

comparison of the photographs.

Graphical Presentation of Monitoring Data Aids Interpretation

LOWER RIGHT ABUTMENT INSTRUMENTATION

3900

3920

3940

3960

3980

4000

4020

4040

4060

4080

25/J

an/0

0

24/M

ay/0

0

21/S

ep/0

0

19/J

an/0

1

19/M

ay/0

1

16/S

ep/0

1

14/J

an/0

2

14/M

ay/0

2

11/S

ep/0

2

9/Ja

n/03

9/M

ay/0

3

6/S

ep/0

3

4/Ja

n/04

3/M

ay/0

4

31/A

ug/0

4

29/D

ec/0

4

28/A

pr/0

5

26/A

ug/0

5

24/D

ec/0

5

23/A

pr/0

6

21/A

ug/0

6

19/D

ec/0

6

Time

Hea

d -

Po

nd

ele

v. (

m)

0

10

20

30

40

50

60

70

80

90

100

Pre

cip

itat

ion

(m

m)

P7 P9 P10 P11 P15 P16 P17 P18 Pond 24 Hour Precipitation

Key Learnings

• Training– Everyone involved with the tailings and water

management facility should be trained to identify and report conditions that could lead to failure.

– Training workshops involving the designer, the operators and the regulators are very effective. The operators need to understand what is important for dam safety, and why it is important.

Key Learnings

• Inspections and Data Collection– Continuity of personnel important– Human eye can identify small or subtle

changes in a structure– Filling out the inspection form is only the first

step. The inspection is not complete until the interpretation of performance is complete.

– There is a learning curve to understanding the performance of a dam

Key Learnings

• Review and analysis– Continuity of personnel important– There is a learning curve to understanding the

performance of a dam– Important to have independent review and verification

of the dam safety periodically

• Responsibility– The Mine or General Manager has the largest

influence on successful implementation of a dam safety program. Dam safety must rank equally with production.

General Comments• Visit mines with similar types of tailings management

systems– Discuss the dam safety program– Discuss the good and bad parts of your program so that both

can learn• Review case histories of dam failures

– Modern dam failures are well documented and the root cause of the failure is often identified in the investigation reports.

• Obtain current copies of dam safety guidelines– Guidelines are updated as the understanding of the mechanisms

of dam failures improves• With modern communication systems, news of a tailings

facility failure is known worldwide immediately and will affect the international mining community

Our goal: our tailings dams become an integral part of the environment post-closure

Feedback on the UNECE guidelines

• This document is a good starting point but to be useful to industry (dam operators) guidelines need to be specific

• There are a number of useful groups of documents already in use – such as the CDA Dam Safety Guidelines combined with the Mining Association of Canada guidelines for designing a tailings facility and for preparing operation, maintenance and surveillance manuals.

• It could be helpful to collaborate with some other agencies who have already developed regulations and guidelines for the safe operation of TMF’s such as ICOLD, CDA, or MAC.

An Operators perspective

• Operators require information on how to carry out the activities, frequencies of activities, selection of design criteria

• Some areas to be developed to make these guidelines relevant to operators are– how to assess risk – What factors of safety to use in construction– Details on preparation of operations manuals– Parameters such as return periods for inflow design floods– Seismic event parameters – Recommendations on planning tools to be used – such as water

management modelling tools

Deno Gold Mining Company, Kapan, Armenia

– Kapan - Located in SW Armenia

– Historical mining town

– Approx 250 years of mining

– 300km from Yerevan

– Two main deposits with numerous smaller deposits in the mines vicinity

DGMC - a little history• 2004 KOMPE mine bankrupted• 2004- Operated as DGMC • Dec 2005 Starter loan by EBRD initiated

upgrade existing equipment and environmental programmes

• 2005- WAI work with site staff to write EAP’s and proposed monitoring programmes

• 2006 Construction of Geghanush TMF• Sept 2006 Dundee bought 80% company,

began corporate responsibility programme

• April 2007 Begun environmental baseline study

• Sept 2007 7 fulltime environmental staff and 25 local consultants, ~ 15 international consultants

• End 2007 Commissioning of Geghanush

Artsvanik Dam• Small Tails Dam perched on very large Kadjeran TMF dam

structure• Designed in 2003 by Armenian design institute• Capacity 1.1 Million m3 Maximum dam height 20m• Regular inspections from RA inspectors• Regular inspections from International Tailings Dam Engineer• Continuous monitoring by site staff

– Dam movement (triangulation surveys)– Water quality and level– Peizometer water level checked daily– Rainfall data collected and weather station in use– Drilling crest of wall and analysis undertaken of materials

Procedures in place to stop production in heavy rainfall or if water level rises Operate with lowest possible phreatic water level to maximise capacity during rainfall events.

Geghanush Dam• New dam over existing historic dam – capacity 11.0 million m3

• Construction included front and rear dam walls, completion of diversion tunnel for river, gravity decant structures

• Plans and design were review by international tailings dam engineer and modified to include recommendations including finger drains

• Recycling water to process plant should decrease discharge significantly

• Same monitoring programme as Artsvanik to be implemented• Discharge water system is gravity decanted however backup

submersible pumps will be available for extreme rainfall events

Thank You