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Report Number: AISP/FBC/P12/10/02

19 June 2012

DRAFT DESIGN REPORT

FORBES COAL NEW DISCARD DUMP

Tellmore Masocha (B.Sc (Hons) Civil Eng)

AfriCan Innovative Solutions and Projects CC Draft Design Report

Forbes Coal Draft Design Report ii June 2012

Table of Contents

TABLE OF CONTENTS ........................................................................................................................................................................... II

1 INTRODUCTION ...................................................................................................................................... 1

1.1 AIM OF THIS REPORT .............................................................................................................................................................. 1

2 EXECUTIVE SUMMARY........................................................................................................................... 1

2.1 TAILINGS STORAGE FACILITY DESIGN CRITERIA ....................................................................................................... 1

2.2 RETURN WATER DAM CRITERIA ....................................................................................................................................... 2

2.3 CLIMATIC DATA ........................................................................................................................................................................ 2

2.4 DECANT SYSTEM....................................................................................................................................................................... 2

2.5 UNDER DRAINAGE .................................................................................................................................................................. 2

2.6 CLEAN AND DIRTY WATER SEPARATION CANALS ................................................................................................. 3

2.7 SOLUTION TRENCH ................................................................................................................................................................ 3

2.8 ACCESS ROAD ........................................................................................................................................................................... 3

3 BATTERY LIMITS AND CONSTRAINTS .............................................................................................. 3

3.1 SITE DESCRIPTION .................................................................................................................................................................... 3

3.2 CONSTRAINTS ........................................................................................................................................................................... 4

3.3 LEGISLATURE .............................................................................................................................................................................. 4

4 HYDROLOGICAL ASSESSMENT ........................................................................................................... 4

4.1 RAINFALL ...................................................................................................................................................................................... 4

5 GEOTECHNICAL INVESTIGATIONS .................................................................................................... 6

5.1 GROUND WATER ..................................................................................................................................................................... 6

5.2 CONSTRUCTION MATERIAL ............................................................................................................................................... 7

6 DISCARD DUMP DESIGN ........................................................................................................................ 7

6.1 COAL TAILINGS CHARACTERISTICS ................................................................................................................................ 7

6.2 DISCARD DUMP CAPACITY ANALYSIS ............................................................................................................................ 8

6.3 PUSH-UP STARTER WALLS ................................................................................................................................................. 10

6.4 UNDER DRAINAGE ............................................................................................................................................................... 11

6.5 SOLUTION TRENCH ............................................................................................................................................................. 11

6.6 ACCESS ROAD ........................................................................................................................................................................ 11

6.7 CLEAN AND DIRTY WATER SEPARATION CANALS .............................................................................................. 11

6.8 FENCING .................................................................................................................................................................................... 12


Forbes Coal Draft Design Report iii June 2012

7 RETURN WATER DAM DESIGN .......................................................................................................... 12

8 POLLUTION CONTROL MEASURES .................................................................................................. 15

9 STABILITY ANALYSIS ........................................................................................................................... 15

10 OPERATION ........................................................................................................................................ 16

10.1 SUPERVISION AND MONITORING ................................................................................................................................. 16

10.1.1 By the mine ............................................................................................................................................... 16

10.1.2 By the Operating Contractor .................................................................................................................... 16

10.1.3 Legal Appointments .................................................................................................................................. 16

10.1.4 The Professional Engineer ....................................................................................................................... 16

10.2 OPERATION PROCEDURES ................................................................................................................................................ 16

10.2.1 Slurry Ponds ............................................................................................................................................. 16

10.2.2 Return water dam ..................................................................................................................................... 16

10.2.3 Maintenance ............................................................................................................................................. 17

10.2.4 Inspection ................................................................................................................................................. 17

11 CONCLUSIONS AND RECOMMENDATIONS ............................................................................... 17

12 REFERENCES ....................................................................................................................................... 18

LIST OF ANNEXURES ................................................................................................................................... 19

ANNEXURE A: DRAWINGS ......................................................................................................................... 19


Forbes Coal Draft Design Report iv June 2012

LIST OF FIGURES

Figure 1: Magdalena Colliery average monthly rainfall ............................................................................................................................ 5

Figure 2: Magdalena Colliery monthly average maximum and minimum temperatures ................................................................ 6

Figure 3: Discard Dump design input .......................................................................................................................................................... 8

Figure 4: Discard Dump capacity assessment ........................................................................................................................................... 9

Figure 5: Discard Dump stage capacity graphs ...................................................................................................................................... 10

Figure 6: Return Water Dam 1 capacity analysis .................................................................................................................................. 13

Figure 7: Return Water Dam 2 capacity analysis .................................................................................................................................. 14


Forbes Coal Draft Design Report v June 2012

LIST OF TABLES

Table 1: Discard dump footprint centre coordinates ............................................................................................................................. 1

Table 2: Trapezoidal solution trench section ......................................................................................................................................... 11

Table 3: Pollution Controll Measures ...................................................................................................................................................... 15


Forbes Coal Draft Design Report 1 June 2012

1 INTRODUCTION

Forbes Coal (formerly Slater Coal) embarked on an expansion program of its operations on Mooidoorn Hoek Farm

No. 3722 near Dundee in KwaZulu Natal resulting in need for additional storage space to complement the existing coal

discard which is almost at the end of its life. African Innovative Solutions and Projects (AISP) CC was appointed by

Forbes Coal (Pty) Ltd to design the coal discard dump in April 2012.

1.1 Aim of this report

The purpose of this report is to provide an overview of the design criteria, design parameters used and the resulting

design process output that will affect the successful operation and subsequent closure of the facility in an

environmentally acceptable manner.

2 EXECUTIVE SUMMARY

This section summarises the design criteria of the coal slurry ponds and its associated storm water infrastructure.

The proposed footprint area is located on the following geographical centre coordinates:

Table 1: Discard dump footprint centre coordinates

Description Latitude (o ‘ “) Longitude (o ‘ “)

Centre of TSF 27o58’52.43” 30o11’45.29”

2.1 Tailings Storage Facility design criteria

The proposed discard dump foot print area is located within the mine’s property boundary. The proposed geometry

was influenced by the existence of underground mine workings to the east of the new discard dump stretching from

the north to the south. The design criteria are as follows:

� Type of facility: coal discard dump.

� Design life of mine estimated at: 22years.

� Tonnage production per year: 640 000t

� Assumed in-situ density: 1.469tm-3.

� Total tonnage in life of mine: 14 080 000t

� Total volume of residue: 9 584 751.5m3.



2.2 Return Water Dam criteria

The return water dam design was designed to adhere to the National Water Act and SANS 10286: 1998 regulations,

and therefore the criteria for the design of the same are as follows:

� Design return period: I:100year

� Design flood: 146.2mm

� Required volume: 14 500m3

� Freeboard: 0.8m

� Depth including freeboard: 4m

The return water dam is designed with a clay / HDPE composite liner in line with statutory requirements for surface

and ground water pollution control.

2.3 Climatic Data

Dundee receives an average of about 791.5mm of rain per year, with most rainfall occurring mainly during midsummer.

Monthly distribution of average daily maximum and minimum temperatures range from about 8°C in mid winter to

28°C in summer. Details of the rainfall and temperature variations of the area are dealt with in Section 0.

2.4 Decant System

It was envisaged that coal will be deposited in “dry” state and as such, no conventional decant system will be designed

for this project. However, momentary rising of the phreatic surface can be expected from seepage especially after a

prolonged low frequence storm. Supernatant water must then be drained off the top of the dump as soon as possible,

and to achieve this purpose, an “emergency type” pump budge will be utilised. The system must be sized to decant a 24

hour 1:100 year storm in not more than 72 hours (three days).

2.5 Under Drainage

Previous site studies have indicated that the water table is high and that there is need for pollution control measures to

ensure seepage does not come into contact with ground water under the impoundment. The topography of the site is

such that seepage flows downhill and an under-drainage system incorporated at the toe will capture all seepage; and

also help with consolidation necessary for strength gain and stability of the discard dump. The system will consist of

perforated or slotted geo-pipes just behind the starter push-up walls connected to out-falling solid pipes discharging

into the solution trench and then to the return water dam.



2.6 Clean and Dirty Water Separation Canals

To prevent storm water pollution, cut off trenches will be excavated in phases on the upstream of the facility to divert

“clean” storm water received on the upstream catchment to the stream without passing through the contaminated site.

The positions of the storm diversion trenches will be clearly marked on the detailed layouts.

2.7 Solution trench

The solution trench will be designed to contain flows resulting from the cumulative effects of the following:

(i) Seepage from under drains, plus

(ii) discard dump supernatant water resulting from a 1:100 year 24hour storm, plus

2.8 Access Road

Gravel “dirty” roads sufficiently network the site under any weather conditions. Since the envisaged method of

deposition is upstream mechanical tipping by truck, the impoundment has been designed with five mitre wide berms at

every five mitre vertical lift to enable access by tipper trucks at any point around the dam. Maintenance shall follow

procedures stipulated in the Operations Manual to ensure access under any weather conditions and at any time.

3 BATTERY LIMITS AND CONSTRAINTS

3.1 Site Description

The terms of reference for the design of the coal residue deposit at Mooidoornhoek Hoek Farm No. 3722 are to

design the discard dump within the existing statutory requirements promulgated under various South African Acts as

outlined in section a) and to be capable of satisfying the design criteria stipulated in section 2.1.

The proposed site for the discard dump was chosen by the client, however, best practice industry guidelines were

applied to optimise the selected area. Two options were provided and are presented in the attached layouts giving due

diligence to the following factors:

(i) Environmental considerations: to ensure the chosen area causes the least land degradation and pollution,

and that safety risks are minimised as far as is practical,

(ii) Mine planning: consideration was given to ensure no ore sterilisation or any encroachment of the facility

to future mining plans,

(iii) Economic considerations: all the options considered will be rigorously investigated and the most cost

effective choice recommended to the client.



3.2 Constraints

Constraints considered include the following:

a) Property boundary: the facility is to be wholly located within the property boundary of the mine which is

Mooidoorn Hoek Farm No. 3722,

b) Underground mine workings: there exist underground workings traversing the proposed extension area

ranging from as shallow as 25m below natural ground level to 50m. The Minerals Act and provisions of SANS

10286:1998 prohibits erection of a structure within 100m of underground workings without written

permission from the Minister;

c) An open pit the mine is using as a return water facility is in the middle of the proposed extension area

3.3 Legislature

The detailed design presented in this report was completed in accordance with the requirements of the following

legislation which pertains to the design, construction, operation and management of mine residue deposits:

• The National Water Act (Act 36 of 1968).

• The Minerals Act (Act 50 of 1991).

• Mineral and Petroleum Resources Development Act (Act 28 of 2002)

• The Mine Health and Safety Act (Act 29 of 1996).

• The Mines and Works Act (Act 45 of 1965).

• The Environmental Conservation Act (Act 100 of 1982).

• The Soils Conservation Act (Act 76 of 1969).

Additionally, the following documents were referenced;

• Department of Mineral and Energy (DME) guideline for the compilation of a mandatory code of practice for

mine residue (DME 16/3/2/5-A1)

• South African National Standards (SANS) Code of Practice for Mine Residue (SANS 10286:1998)

4 HYDROLOGICAL ASSESSMENT

The mine lies in the Buffalo Catchment Management area and is drainage region V32.

4.1 Rainfall

Dundee receives an average of about 791.5mm of rain per year, with most rainfall occurring mainly during midsummer.

Figure 1 shows the average rainfall values for the project site.



Figure 1: Magdalena Colliery average monthly rainfall

The monthly distribution of average daily maximum temperatures (Figure 2) shows that the average midday

temperatures for the project area range from 23°C in mid winter (which occurs in June or July) to 28°C in summer.

The region is the coldest during June and July when the mercury drops to 8°C on average during the night. Consult

Figure 2 for an indication of the monthly variation of average minimum daily temperatures.

145.60

112.10

76.00

44.10

14.80 12.80

5.60

18.60

36.60

86.10

108.80

130.40

-

20.00

40.00

60.00

80.00

100.00

120.00

140.00

160.00

January February March April May June July August September October November December

Average Rainfall (mm)

AVERAGE RAINFALL [mm]



Figure 2: Magdalena Colliery monthly average maximum and minimum temperatures

5 GEOTECHNICAL INVESTIGATIONS

Geotechnical data as used for this project was adopted from previous reports as contained in the following available

data:

� Technical Design Report - November 2008

� Code of practice – prepared 2008

� Annual Report 2010,

� Annual Report 2012,

� Survey in CSV format.

As an ongoing design and monitoring process, more samples will need to be taken for analysis now, to enable results

comparison and to allow adjustments in both the design and operation accordingly.

5.1 Ground water

Ground water is reported to have been encountered at depths below 6m, and is envisaged not to affect construction

or operation of both the storage and return water systems as both these are designed at a depth not exceeding 5m

below ground level.

28 28 28

26

25

23 23

24

26

27 27 27

17 17 17

14

10

9

8

10

12

14

16

17

0

5

10

15

20

25

30

January February March April May June July August September October November December

AVERAGE HIGH TEMPERATURE [oC]

AVERAGE LOW TEMPERATURE [oC]



5.2 Construction material

The ferricrete specified for the construction of both the slurry ponds’ and return water dam embankments was

reported to have been found in the western portion of the site. There is a reported transition from sandy hill-wash

soils at the top to silty-sand through clayey sand to firm/stiff silts and clays at depth around the site. From the

laboratory results, the clay has low to medium activity.

The suitability of the clay to use as a liner will need to be investigated further. Samples of both the clay and slurry from

the plant will be taken for determination of these geotechnical design parameters.

6 DISCARD DUMP DESIGN

6.1 Coal tailings characteristics

The following design input was used as researched and also as supplied by the client in some instances.



Figure 3: Discard Dump design input

6.2 Discard Dump capacity analysis

The survey data supplied by the client was modelled in the computer package AutoCAD Civil 3D. The stage capacity

graphs are included in Figure 4 and Error! Reference source not found. below for visual identification purposes.

It can be seen from the capacity analysis that the discard dump as modelled cannot sustain the full 22year life span but

just 63% (14years). However, area immediately east of the underground workings can be incorporated to balance the

shortfall of 8years.

Client: FORBES COAL

Project: NEW COAL DISCARD DUMP DESIGN

Description: CAPACITY DETERMINATION

Project No.: P12 - 10

Date: 23-Apr-12

Author: AiSP - TM

1.00 GENERAL INFORMATION

1.01 Name of Mine FORBES COAL

1.02 Postal Address of Mine

1.03 Telephone Number (Area code in Brackets)

1.04 Magisterial District

1.05 Dept of Mineral and Energy Affairs Region

1.06 Nearest Town Dundee

1.07 Distance to Town 22 km

1.08 Direction from Town North North-West

1.09 Name of person responsible for residue deposit to Minerals Act Regulations

1.10 Number of deposit

1.11 Common name of deposit Coal Discard

1.12 Name of closest river/stream to the deposit

2.00 DESIGN PARAMETERS

2.01 Reserves 14 080 000 t

2.02 Specific Gravity 2.65

2.03 Production Rate 53 333 tpm

2.04 % to tailings dam: 100%

2.05 Supply 640 000 t/year

2.06 Insitu Density 1.47 t/m3 - (average)

2.07 Lifetime 22.00 years

2.08 Side Slope (Overall) 1.00 vertical to

3.00 horizontal

2.09 Max Rate of Rise 4.50 m/year

2.10 Solids Concentration by Mass Cw 100.00 %

2.11 Mass flow rate Ms 73.06 t/h

2.12 Start of deposition 2012 year

2.13 Mean annual precipitation 791.5 mm/y

2.14 Mean annual evaporation 1670.5 mm/y

2.15 Evaporation correction factor 84% %

2.16 1 in 100 year 24 hr rainfall 146.2 mm

DISCARD DUMP DESIGN - INPUT



Figure 4: Discard Dump capacity assessment

Elevation

(masl)

Cumulative

Volume

(m3)

Incremental

Volume

(m3)

Surface

Area

(m2)

Surface

Area

(ha)

1255 - 0.00 - 0.00

1260 8 788.41 8788.4135 3 515.37 0.35

1265 74 860.76 66072.3435 22 913.57 2.29

1270 221 058.68 146197.9228 35 565.60 3.56

1275 415 584.88 194526.196 42 244.88 4.22

1280 632 370.11 216785.239 44 469.21 4.45

1285 901 955.59 269585.4793 63 364.98 6.34

1290 1 257 518.30 355562.708 78 860.11 7.89

1295 1 682 927.22 425408.9148 91 303.46 9.13

1300 2 198 219.04 515291.819 114 813.27 11.48

1305 2 788 204.77 589985.739 121 181.03 12.12

1310 3 392 739.11 604534.3363 120 632.71 12.06

1315 3 991 033.11 598294.001 118 684.89 11.87

1320 4 570 507.02 579473.9083 113 104.67 11.31

1325 5 120 537.19 550030.1715 106 907.40 10.69

1330 5 636 823.56 516286.3658 99 607.15 9.96

1335 5 986 090.29 349266.7288 40 099.54 4.01


Date: 23-Apr-12

Author: AiSP - TM

DAM CAPACITY

Client: FORBES COAL



1250

1260

1270

1280

1290

1300

1310

1320

1330

1340

- 1 000 000 2 000 000 3 000 000 4 000 000 5 000 000 6 000 000 7 000 000

Ele

vati

on

(mas

l)

Volume (m3)

Dam Capacity

1250

1260

1270

1280

1290

1300

1310

1320

1330

1340

- 20 000 40 000 60 000 80 000 100 000 120 000 140 000

Ele

vati

on

(m

asl)

Surface Area (m2)

Dam Surface Area



Figure 5: Discard Dump stage capacity graphs

6.3 Push-up starter walls

An initial box-cut of 750mm deep must be cut into the in-situ material over twice the width of the embankment crest

for anchorage. The clay material on the walls will be compacted to 98% Proctor Density within 2% of the optimum

moisture content. Care must be taken during compaction that the clay is compacted in layers not exceeding 200mm,

Under all circumstances, the optimum moisture content must be maintained as per specifications.

tons From To

years 2012 2026

t/m3


640 000

Deposition Rate

(tons/year)

Date

8 960 000

Tonnage Stored (106 tons)

Tim

e (years

)

STAGE / CAPACITY CURVES

1.469Assumed in-situ dry density:

Client:

Project:

FORBES COAL

Cre

st E

levation (m

asl)

NEW COAL DISCARD DUMP DESIGN

Tonnage Delivered (106 tons)

23-Apr-12

Rate of Rise (metres/year)


Tim

e (years

)

Rate of Rise (metres/year)

Cre

st E

levation (m

asl)

14Delivery period:

Outer wall side slopes: 1V:3H

Total tonnage delivered:

Date:

Author: AiSP - TM

1 260

1 270

1 280

1 290

1 300

1 310

1 320

1 330

1 340010203040

1 260

1 270

1 280

1 290

1 300

1 310

1 320

1 330

1 3400 2 4 6 8 10

0

2

4

6

8

10

12

14010203040 0

2

4

6

8

10

12

140 2 4 6 8 10



6.4 Under drainage

Internal under drainage is of vital importance to minimising of ground water pollution hence the environmental safety.

As such a reticulation of drains was provided on the inside toe of the push up starter wall right through the dam

perimeter. The under-drainage will facilitate the following:

• Collect leachate to the solution trench and then onto the return water dam,

• Minimise ground water pollution,

• Maintaining a low phreatic surface hence reduce pore pressure on the pond embankment walls especially the

downstream ones,

The drainage system comprises 110mm diameter perforated geo-pipes (Drainex) within the drainage catchment of each

basin connected to 110mm diameter solid imperforated pipes (Kabelflex). Leachate collected in these is discharged into

the solution trench which in turn discharges into the return water dam through a silt trap.

6.5 Solution trench

The solution trench was sized to carry the following:

(i) Drain flows, and

(ii) Supernatant water drainage.

Table 2: Trapezoidal solution trench section

Item Description Quantity

1 Side slope: 1v:?h 1.5

2 Bottom width 1000mm

3 Depth 1000mm

6.6 Access road

Access to the entire coal discard storage facility will be provided by means of a 4m wide gravel crest access roads at

each 10m vertical lift of the dump. The crest access was designed of gravel (G4 –G6) material readily available on site

and suitable for use as pavement material, and can with stand loads by any mine vehicular plant under any weather

conditions. Maintenance will follow specifications stipulated in the Operations Manual.

6.7 Clean and Dirty water separation canals

Storm water diversion canals will be constructed in phases so as to reduce the volume of storm water being handled at

any particular point in time. The clean and dirty water separation canals will be clearly marked on the detailed layouts.



6.8 Fencing

Allowance was made in the bills of approximate quantities to cater for fencing around the storage facility to prohibit

access by unauthorised people.

7 RETURN WATER DAM DESIGN

The return water dam was sized to contain flows as follows:

(i) A 24hour 1:100 year storm event onto the discard dump, and

(ii) Storm water caught within the return water dam.

Spillage will be permitted not more than once in 100years.

Due to the topography of the site, two return water dams were designed: one for a capacity of 8 000m3 and the other

for a capacity of 7 500m3. These volumes were modelled from the supplied survey data onto the available space using

AutoCAD Civil 3D to produce a layout as shown on the drawings. Capacity analysis was then conducted to establish if

the design requirements were fulfilled and the results are shown in Figure 6 and Figure 7.

Under normal operations, the volume of water in the return water dam will be kept not more than 4 000m3.

As discussed in 6.1, clay liner will be compacted to 98% Proctor Density at +/- 2% of the optimum moisture content,

and G4-G6 embankment at 98% MoD AASHTO at +/-2% of the optimum moisture content.



Figure 6: Return Water Dam 1 capacity analysis

RETURN WATER DAM 1 CAPACITY

Client: FORBES COAL




Date: 23-Apr-12

Author: AiSP - TM

Elevation

(masl)

Cumulative

Volume

(m3)

Incremental

Volume

(m3)

Surface

Area

(m2)

Surface Area

(ha)

1272.8 - 0.00 1 909.44 0.19

1273 393.09 393.089 2 021.45 0.20

1274 2 711.48 2318.39 2 615.33 0.26

1275 5 651.96 2940.4795 3 265.63 0.33

1276 9 270.94 3618.9795 3 972.33 0.40

1276.6 11 789.67 2518.728 4 423.43 0.44

1272.5

1273

1273.5

1274

1274.5

1275

1275.5

1276

1276.5

1277

- 1 000 2 000 3 000 4 000 5 000 6 000 7 000 8 000 9 000 10 000 11 000 12 000 13 000

Ele

vati

on

(mas

l)

Volume (m3)

Dam Capacity

1272.5

1273

1273.5

1274

1274.5

1275

1275.5

1276

1276.5

1277

1 500 2 000 2 500 3 000 3 500 4 000 4 500 5 000

Ele

vati

on

(m

asl)

Surface Area (m2)

Dam Surface Area



Figure 7: Return Water Dam 2 capacity analysis

RETURN WATER DAM 2 CAPACITY

Client: FORBES COAL




Date: 23-Apr-12

Author: AiSP - TM

Elevation

(masl)

Cumulative

Volume

(m3)

Incremental

Volume

(m3)

Surface

Area

(m2)

Surface Area

(ha)

1247 - 0.00 - 0.00

1248 250.27 250.2748 500.55 0.05

1249 1 388.16 1137.88155 1 775.21 0.18

1250 4 111.75 2723.58965 3 671.97 0.37

1251 9 019.35 4907.60475 6 143.24 0.61

1251.5 12 499.83 8388.088575 7 512.15 0.75

1246.5

1247

1247.5

1248

1248.5

1249

1249.5

1250

1250.5

1251

1251.5

1252

- 1 000 2 000 3 000 4 000 5 000 6 000 7 000 8 000 9 000 10 000 11 000 12 000 13 000 14 000

Ele

vati

on

(mas

l)

Volume (m3)

Dam Capacity

1246.5

1247

1247.5

1248

1248.5

1249

1249.5

1250

1250.5

1251

1251.5

1252

- 1 000 2 000 3 000 4 000 5 000 6 000 7 000 8 000

Ele

vatio

n (m

asl)

Surface Area (m2)

Dam Surface Area



8 POLLUTION CONTROL MEASURES

A synergistic effect can be achieved by combining different controls together. Inclusion of the features in the table

below is likely to give rise to the lowest pollution potential for the slurry ponds, taking not only the capital and

operating costs into account, but also the contingent liability associated with potential water contamination.

Table 3: Pollution Controll Measures

Control Type Description

Clean water diversion � The design will include clean water diversion systems for surface water

inflow from drainage systems within the natural catchment basins and

precipitation runoff. The clean water systems were sized to ensure it is

not likely to spill into any dirty water system more than once in 100 years

(SANS 10286:1998).

� Appropriate erosion protection and energy dissipation measures will be

included in the design (if necessary) for long-term closure requirements

Under-drainage and reuse of

contaminated water

� The design includes the implementation of an under drainage system to

collect seepage for re-use as process water.

� The return water dam was sized to contain seepage from the under

drainage systems and not to spill into any clean water system more than

once in 100 years (SANS 10286:1998).

9 STABILITY ANALYSIS

A conservative overall slope of 1v:3h (11.3o) known to produce factors of safety above 1.5 for similar slurry ponds

projects was adopted. The South African statutory required factor of safety is 1.3 hence the dam slopes are expected

to be stable.

The free draining nature of tailings is expected to cause a positive effect on consolidation and the strength gain of the

tailings hence enhanced stability. By induction, it is envisaged that the dam will be stable.

The heights of the dam walls average 2.5 above the natural ground level, which reduces the potential for failure.



10 OPERATION

10.1 Supervision and Monitoring

10.1.1 By the mine

In terms of South African legislation, the General Manager is ultimately responsible for the correct and safe operation

of the coal slurry dams. However, these responsibilities are delegated to competent persons within the Mine’s

management structure. A senior manager must be tasked with the duty to oversee the operation of the coal slurry

dams. He could be assisted by an experienced foreman who can monitor the operations on a daily basis.

10.1.2 By the Operating Contractor

The contractor must have an experienced and competent supervisor to manage the teams doing the deposition. The

distribution of the slurry must be uniformly maintained all round the dam.

10.1.3 Legal Appointments

All managerial and supervisory personnel are to be appointed in accordance with the provisions of the Minerals Act.

The duties at each level are to be clearly set out in a letter of appointment.

10.1.4 The Professional Engineer

The Mine shall appoint a professional engineer who will be required to inspect the coal slurry dams from time to time.

He shall satisfy himself that the facility is in a safe and stable condition. If not, he shall specify remedial action to be

implemented by the Mine.

10.2 Operation Procedures

10.2.1 Slurry Ponds

Once uniform deposition all around the coal slurry dam has been established, the following points are to be observed:

� The beach zone must be managed so that the pool will lie at the penstock inlet.

� No pools must be allowed to develop anywhere else in the basin.

10.2.2 Return water dam

This is to be operated such that it is kept virtually empty at all times thus maintaining sufficient capacity to store 1:100

year design storm run-off from the slurry dams without spilling. The pumps and return water pipeline must have

sufficient spare capacity to empty the dam within a reasonable period after a storm inflow.



10.2.3 Maintenance

The slurry dams, return water dam and the effluent trench must be inspected on a regular basis and deficiencies

rectified immediately. Items to watch out for and to be repaired according to standard practice are inter alia:

� Erosion gullies

� Pipe burst

� Rat holes

Other deficiencies observed and which must be reported to the Professional Engineer without delay are:

� Signs of seepage on the slopes

� Sloughing

� Movement or slips

� Blocked drain outlets

The Professional Engineer will determine the remedial measures to be implemented by the Mine to rectify the

deficiencies and to prevent a recurrence.

10.2.4 Inspection

Regular inspections shall be undertaken by the Professional Engineer, Coal Discard Manager, Coal Discard Foreman and

the Contractor in accordance with the Mine’s standard procedure.

11 CONCLUSIONS AND RECOMMENDATIONS

It is recommended that:

� The overall factors of safety at all the analyzed sections are above 1.3 indicating satisfactory conditions.

� Monthly monitoring of the technical data and hazard management system should be carried out.

� Under drain from selected waste rock or filter stone must be constructed to collect and direct rainwater

seepage that percolates through the discard facility, from the base areas to the solution trenches.

� Tonnages transported to the slurry dams must be recorded on a daily basis.

� Freeboard should be measured and evaluated against the statutory requirement and must be monitored.

� A code of practice and operating manual should be prepared to ensure that the facility is designed, operated

and rehabilitated in a responsible manner.

� Daily rainfall and evaporation must be recorded at the coal slurry dam.

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12 REFERENCES

1) Design Report: 2008.

2) A Guide to Tailings Dams and Impoundments, ICOLD, Bulletin 106, 1996.

3) Tailings Dams Design of Drainage, ICOLD, Bulletin 97, 1994.

4) Reference Number: DME 16/3/2/5_A1, Guideline for the compilation of a Mandatory Code of

Practice ,3 May 2000

5) SANS 0286: 1998, The South African Code of Practice – Mine Residue

6) The following South African Acts:

(i) The Minerals Act (Act 50 of 1991).

(ii) The Environmental Conservation Act (Act 100 of 1982).

(iii) The Mine Health and Safety Act (Act 29 of 1996).

(iv) The Mines and Works Act (Act 45 of 1965).

(v) The Soils Conservation Act (Act 76 of 1969).

(vi) The National Water Act (Act 36 of 1968).

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LIST OF ANNEXURES

20

ANNEXURE A: DRAWINGS

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