Appendix E - ERM€¦ · o Falling Head Permeability The laboratory test results for the discard...

Appendix E Design Report

Kangra Project

Design Report for New Maquasa East Coal Discard Dump

Report prepared for

Report prepared by

Guillaume de Swardt MSc (Eng), Pr Eng, Director

September 2014

Report no. GT-06/2014-Rev 1

Kangra Project New Maquasa East Coal Discard Dump September 2014

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CONTENTS

1 GENERAL .................................................................................................................................... 5 1.1 Introduction .......................................................................................................................... 5 1.2 Battery Limits ....................................................................................................................... 6 1.3 Exclusions .............................................................................................................................. 6

2 DESIGN CRITERIA AND ASSUMPTIONS ............................................................................. 7

3 GEOTECHNICAL CHARACTERISATION .......................................................................... 10

4 DESIGN ..................................................................................................................................... 11 4.1 Type of Facility ................................................................................................................... 11 4.2 Specialised Studies ............................................................................................................. 11 4.3 Safety Classification ........................................................................................................... 11 4.4 Storage Capacity ................................................................................................................ 13 4.5 Construction Method ......................................................................................................... 13 4.6 Design Components ........................................................................................................... 14

4.6.1 Site Preparation ......................................................................................................................................... 15 4.6.2 Access Control .......................................................................................................................................... 15 4.6.3 Clean Storm Water Diversion System ................................................................................................ 15 4.6.4 Runoff Control System ............................................................................................................................ 17 4.6.5 Starter Embankment ................................................................................................................................. 17 4.6.6 Under Drainage System ........................................................................................................................... 17 4.6.7 Liner Systems ............................................................................................................................................. 18 4.6.8 Cover System ............................................................................................................................................. 19 4.6.9 Pollution Control Dam ............................................................................................................................ 20 4.6.10 Borrow Sources ...................................................................................................................................... 22

5 STABILITY ANALYSIS ............................................................................................................ 24

6 ENVIRONMENTAL .................................................................................................................. 26 6.1 Risk Control Measures ....................................................................................................... 26 6.2 Closure Considerations ..................................................................................................... 26

7 QUALITY ASSURANCE ......................................................................................................... 27 7.1 Construction Phase ............................................................................................................ 27 7.2 Operation Phase ................................................................................................................. 27

8 BILL OF QUANTITIES ............................................................................................................ 28

9 RECOMMENDATIONS ........................................................................................................... 30

10 REFERENCES .......................................................................................................................... 31

APPENDIX A: DRAWINGS ....................................................................................................... 32

APPENDIX B: LABORATORY TEST RESULTS .................................................................... 33


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APPENDIX C: ILANDA REPORT ............................................................................................. 34


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TABLES

Table 1: Design Criteria and Assumptions ................................................................................................................... 7 Table 2: Laboratory Test Results ................................................................................................................................. 10 Table 3: Safety Classifications ........................................................................................................................................ 12 Table 4: Capacity Analysis Results ............................................................................................................................... 13 Table 5: Channel Sizing ................................................................................................................................................... 16 Table 6: Dirty Area used in Modelling ........................................................................................................................ 20 Table 7: Modelling Results ............................................................................................................................................. 21 Table 8: Borrow Sources ............................................................................................................................................... 23 Table 9: Shear Strength Properties .............................................................................................................................. 24 Table 10: Bill of Quantities – Discard Dump ............................................................................................................. 28 Table 11: Bill of Quantities – Pollution Control Dam ............................................................................................. 29

FIGURES

Figure 1-1: Location ........................................................................................................................................................... 5 Figure 4-1: Zone of Influence ........................................................................................................................................ 12 Figure 4-2: Storm Water Diversion Channels .......................................................................................................... 15 Figure 4-3: DD Liner System ......................................................................................................................................... 18 Figure 4-4: PCD Liner System ....................................................................................................................................... 19 Figure 4-5: Cover System ............................................................................................................................................... 20 Figure 5-1: FOS Overall Stability .................................................................................................................................. 25


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Disclaimer This report is protected by copyright vested in Geo Tail (Pty) Ltd. It may not be reproduced or transmitted in any form or by any means whatsoever to any person without the written permission of the copyright holder, Geo Tail.

The opinions expressed in this report have been based on the information supplied to Geo Tail (Pty) Ltd by the Client. The opinions in this report are provided in response to a specific request from the Client to do so. Geo Tail has exercised all due care in reviewing the supplied information. Whilst Geo Tail has compared key supplied data with expected values, the accuracy of the results and conclusions from the review are entirely reliant on the accuracy and completeness of the supplied data. Geo Tail does not accept responsibility for any errors or omissions in the supplied information and does not accept any consequential liability arising from commercial decisions or actions resulting from them. Opinions presented in this report apply to the site conditions and features, as they existed at the time of Geo Tail’s investigations, and those reasonably foreseeable. These opinions do not necessarily apply to conditions and features that may arise after the date of this report, about which Geo Tail had no prior knowledge nor had the opportunity to evaluate.


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1 GENERAL

1.1 Introduction

Geo Tail was appointed by GCS (Pty) Ltd to carry out the necessary activities and tasks, in accordance with the specified requirements and scope of work, to present a design report for the new Kangra Maquasa East Coal Discard Dump (DD) near Piet Retief in Mpumalanga.

Kangra Maquasa East is an existing colliery, located approximately 40 km west of Piet Retief and in close proximity to Heyshope Dam. The colliery’s location is shown in Figure 1-1.

Figure 1-1: Location

The purpose of the design report is to present the DD design, and in particular to:

• Document the design criteria and assumptions.

• Document the design concept for the DD.

• Undertake a capacity analysis and phased development plan for the design life of the DD.

• Undertake a water management plan for the DD.

• Document the environmental control measures.

• Undertake a side slope stability analysis for a critical section through the DD.

• Document the closure considerations.

• Prepare general arrangement drawings and typical sections.


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• Prepare a bill of quantities for the pre-deposition civil works.

• Document the recommendations for additional work.

1.2 Battery Limits

The battery limits for the DD design can be summarised as follows:

• Upstream: The haulage road to the discard dump is excluded.

• Footprint: All pre-deposition civil works are included.

• Downstream: The pollution control dam (PCD) is included but the return water pumping system is excluded.

1.3 Exclusions

The following items were specifically excluded from the Geo Tail scope of work:

• Servitudes for general infrastructure, including the haulage roads (by Kangra).

• The design for the PCD return water pumping system including all electrical and instrumentation designs (by Kangra).

• Topographical survey information in digital format (by GCS).

• Environmental baselines and other specialised studies (by GCS).

• The environmental classification of the coal discard material (by GCS).

• The hydrogeological investigation, including geochemistry (by GCS).

• The geotechnical investigation (by GCS).

• Meetings with public or legislative bodies and the preparation or submission of permit applications (by GCS).


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2 DESIGN CRITERIA AND ASSUMPTIONS

The following design criteria and assumptions were adopted for the design phase:

Table 1: Design Criteria and Assumptions

Item Description Value or Assumption Source

1 General

1.1 Topographical Survey Base date: March 2014 GCS

1.2 Residue Material Coal discard GCS

1.3 Legal Framework South Africa - benchmarking against good practice international standards Geo Tail

1.4

Authority Approvals and Permit Applications (including waste classification)

Excluded from Geo Tail scope of work GCS

1.5 Servitudes Haulage road, electricity and pipeline servitudes not included in Geo Tail scope of work

Kangra

1.6 Access Control (DD) Included in Geo Tail scope of work GCS

1.7 Site Selection

Sufficient candidate sites were identified in order to ensure the due consideration of potential alternatives. In identifying candidate sites, numerous economic, engineering, environmental, public and legal acceptance criteria were considered. These criteria interrelate, as there are always economic implications when candidate sites are sub-optimal in terms of environmental and/or legal acceptance criteria. Also, the public will usually not accept an environmentally unsuitable DD.

GCS

2 Solids Management

2.1 Deposition Rate 1.0 Mtpa GCS

2.2 Design Life 20 years GCS

2.3 Storage Capacity Required 20 Mt GCS

3 Water Management

3.1 Objectives

• Separate clean runoff from potentially contaminated runoff

• Prevent uncontrolled dirty surface water discharge to the environment.

Geo Tail


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3.2 Principles

• Divert clean storm water runoff away from the DD

• Minimise the storage of water (rainfall) on the DD

• Contain and/or re-use or treat the water emanating from the DD

Geo Tail

3.3 Water Balance A continuous daily time step water balance (Goldsim) iLanda

3.4 Climatic Data • MAP: 772 mm • MAE: 1 400 mm

iLanda

3.5 Design Storm 1 in 50 year, 24 hour storm event = 136 mm iLanda

3.6 Discharge to Environment

• The DD must comply with Government Notice 704 of the South African National Water Act, Act 36 of 1998.

• Water will be discharged from the DD to the environment, only, if the structural stability of the DD or PCD is compromised during emergency conditions.

Geo Tail

4 Structural Stability

4.1 Objective Create a safe and stable DD and minimise risk to human lives, health and property Geo Tail

4.2 Freeboard Target (minimum)

1 in 50-year, 24-hour storm volume plus 0.8 m dry freeboard (excluding decant return)

Geo Tail

4.3 Safety Classification SANS 0286:1998 method Geo Tail

4.4 Side Slope Stability

The minimum factor of safety for side slope stability under normal operating conditions (local and overall stability) will be: • Temporary side slopes = 1.30 • Permanent side slopes = 1.50

Geo Tail

4.5 Seismicity Low seismicity zone GCS

5 Environmental

5.1 Environmental Objectives

The design will be such that: • It remains fit for the intended purpose and

resists all external environmental influences that are reasonably likely to occur (sustainability).

• It conserves all resources as far as possible i.e. land area, water, airspace, topsoil, mineralization and energy.

• It minimises environmental impacts, where potentially possible.

Geo Tail


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5.2 Topsoil Management

• Topsoil is defined as unconsolidated soil with sufficient organic content and moisture retaining capacity to sustain vegetation growth. During stripping operations, topsoil will be stockpiled for future rehabilitation purposes. The topsoil stockpiles will be contoured so as to blend with the natural environment and will be stabilised with vegetation.

• The final closure requirements will determine the topsoil stripping and stockpile volumes. As far as possible, topsoil will be stockpiled within an economic radius of the proposed rehabilitation areas.

Geo Tail

5.3 Lining Requirements • DD: Lined • PCD: Lined

Geo Tail

5.4 Storm Water Management Objective

The objective is to separate clean and dirty water, ensuring that the two do not mix with a frequency of more than once in fifty years. Clean water runoff arising from the external catchment will therefore be prevented from flowing onto the DD and consequently becoming contaminated. In order to divert the flows from each portion of the catchment, cut-off trenches and diversion bund walls will be included in the design.

Geo Tail

5.5 Rehabilitation and Closure Objectives

• The minimum objectives for the closure and rehabilitation of the DD will be to prevent air and water pollution in accordance with the requirements of the relevant regulations and with good international practice.

• The intended end-use will take into consideration the prior land-use and the location with respect to current and potential future socio-economic development.

Geo Tail

5.6 Closure Plan

• The closure plan for the DD will be developed during the life of the facility. It is anticipated that the closure plan will be updated periodically before the preparation of the final closure plan.

• The purpose of preparing a closure plan is to ensure that the design, construction and operation procedures are compatible with the achievement of final closure and rehabilitation to acceptable environmental standards and at a reasonable cost.

• The closure plan will be prepared in accordance with “best practice” and the requirements of the environment.

GCS

5.7 Borrow Sources

• Construction material will be sourced from the DD basin, as well as the PCD basin.

• Filter materials will be imported from commercial sources.

Geo Tail


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3 GEOTECHNICAL CHARACTERISATION

A coal discard sample was submitted to “BM du Plessis Civil Engineering Laboratory” for testing. The laboratory test program included the following:

o Sieve analysis

o Specific Gravity (solids)

o Compaction

o Falling Head Permeability

The laboratory test results for the discard sample can be summarised as follows (see Appendix B for data sheets):

Table 2: Laboratory Test Results

Item Test Parameter Unit Value

1 Particle size distribution

< 63 mm % 100

< 53 mm % 97

< 37.5 mm % 79

< 26.5 mm % 57

< 19 mm % 44

< 13.2 mm % 33

< 9.5 mm % 26

< 6.7 mm % 17

< 4.75 mm % 13

< 2.36 mm % 10

< 1.18 mm % 7

< 0.75 mm % 2

2 Specific Gravity SG (solids) ratio 2.06

3 Permeability Average permeability m/s 3.7 x 10-6

4 MOD AASHTO moisture density relation Maximum dry density kg/m3 1 710

Optimum moisture content % 5.8


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4 DESIGN

4.1 Type of Facility

The DD will be developed as a three-compartment side hill type storage facility. The total DD footprint is approximately 65 ha with a final vertical height of approximately 34 m. The three-compartment layout allows for a modular implementation approach (Phases 1, 2 and 3) with the benefit of delaying capital expenditure.

The general layout drawings and typical sections for the DD (including PCD) are attached in Appendix A.

4.2 Specialised Studies

The findings and recommendations from the geotechnical and geohydrological investigations, undertaken by GCS, were incorporated into the design.

4.3 Safety Classification

The safety classification provides the basis for the implementation of differentiated safety management practices for specified stages of the life cycle of a residue storage facility. The practices prescribed for planning, design, operation and decommissioning may be differentiated on the basis of the safety classification for each specific storage facility. It therefore allows for the development of a management system that is tailored to suit the needs of the particular facility, rather than imposing a system on all facilities that, of necessity, must cater for the most severe hazards and risks.

This safety classification defines the potential consequences of a failure of the storage facility. It is important to note that a storage facility that may be classified as having a “high” hazard rating may not have an associated “high” risk. The risks (or the likelihood of adverse impacts – that is, probability of occurrence × consequence of occurrence) can be reduced and minimised through the implementation of risk management techniques.

The South African Code of Practice for Mine Residue (SANS 0286:1998) will be utilised for classification purposes. SANS 0286:1998 calls for a safety classification to differentiate between residue deposits of high, medium and low hazard rating on the basis of their potential to cause harm to life or property within the zone of influence. The classification should be based on the anticipated configuration of the storage facility at the end of its design life.

The hazard ratings for the DD can be summarised as follows (see zone of influence in Figure 4-1):


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Table 3: Safety Classifications

Item Description Zone of Influence

(Comments and Assumptions) Hazard Rating

1 Number of residents in zone of influence

Not aware of any residents within zone of influence

Low

2 Number of workers in zone of influence Only mine workers within zone of influence Low

3 Value of third party property in zone of influence Value of third party property not significant Low

4 Depth to under-ground mine workings

The DD footprint is not undermined Low

The above table indicates that the overall hazard rating is “Low”.

Figure 4-1: Zone of Influence


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4.4 Storage Capacity

The DD was three-dimensionally modelled for an accurate determination of the relationship between the height, area and capacity. The capacity analysis results are summarised in Table 4 below.

Table 4: Capacity Analysis Results

Item Description Unit Value

Phase 1 Phase 2 Phase 3

1 Assumed average dry density t/m3 1.8 1.8 1.8

2 Airspace available Mm3 4.1 4.1 3.0

3 Storage capacity available Mt 7.4 7.4 5.4

4 Design life year 7.4 7.4 5.4

5 Full supply level mamsl 1 371 1 376 1 376

6 Maximum vertical height m 34 33 32

7 Footprint ha 23.5 21.9 19.3

8 Final side slope area ha 13.1 9.0 8.2

9 Final top surface area ha 9.5 13.9 14.6

The above table indicates that there is sufficient storage capacity for the proposed coal discard production profile.

4.5 Construction Method

The construction method can be summarised as follows:

• The coal discard will be transported, placed and compacted mechanically as part of the mining operation (mining fleet). The discard will be placed in horizontal layers (bottom-up) following an approved performance compaction specification.

• On completion of the preparatory works, an access ramp should be created to form a platform from which dumping can take place. Simultaneous dumping from more than one platform can be considered in order to reduce the advance rate of a platform and to prevent potential damage to the HDPE geomembrane.

• The side slopes will be terraced and berm penstocks will be utilised to drain the permanent benches.


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• The final side slope geometry should include 10 m wide benches at 10 m vertical intervals.

• The benches should be cross-graded at 1(v):10(h) and a 0.5 m (minimum) high perimeter bund wall should be constructed. Berm penstocks should be extended to the final height of the DD. The longitudinal slope of the benches should be modified to achieve the required longitudinal fall to the berm penstocks.

• A perimeter bund wall should be implemented on the top surface. The top surface of each lift should be constructed to a 1(v):100(h) gradient that falls away from the perimeter bund wall in order to prevent overtopping at the side slopes (also an operational safety measure).

• The soil cover (including vegetation) should be constructed to a final side slope angle of 1(v):3(h), giving the DD an overall slope of 1(v):4(h). The soil cover should be constructed to an agreed performance specification.

• Survey control should be implemented to indicate the required limits for soil cover construction, as well as the required final as-built dimensions.

• The recommended compaction specification for the coal discard should be investigated further and confirmed during the operation phase. The following procedure should be implemented:

o The Design Engineer should approve the compaction specification and lift thickness before construction commences. The specification will be influenced by the size of the construction equipment. If necessary, a test fill program should be implemented prior to construction.

o Lift thickness should be measured.

o The density and moisture content of the compacted discard material should be determined directly by conventional methods and indirectly by observing settlement of the fill.

o Test pits should be excavated through the compacted layers to allow visual observation of lift thickness, particle size distribution and distribution of density.

o Inspection should form a critical part of the quality control plan. The inspector should ensure that the field-testing program establishes the methods required to achieve the required quality, then to ensure that the quality is being maintained and quantify means of rejecting substandard work.

o Records and data should be kept up to date (photographs, notes and visual observations are important).

o The Design Engineer reserves the right to re-execute tests and to re-specify the compaction requirements from time to time based on material variability, compactor type, moisture content etc.

4.6 Design Components

The design components associated with the pre-deposition civil works of the DD and PCD can be summarised as follows (see drawings attached in Appendix A):


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4.6.1 Site Preparation

The site preparation will include the following activities:

• Clear and grub footprint.

• Remove topsoil (approximately 400 mm thickness) and place it in dedicated stockpiles for future rehabilitation purposes. During the stripping operation, topsoil will be separated from trees and brush. The proposed topsoil stockpiles are located adjacent to the PCD and will have a maximum height of 3 m. The stockpiles will be graded to specific side slope angles, and will not be compacted during storage.

• Remove clay liner construction material from the DD and PCD basins.

• Reshape and rip and compact (to specification) the DD and PCD basins.

• Survey the final base surface.

4.6.2 Access Control

The boundary fencing will keep livestock out and will discourage people from gaining access to the DD and PCD. The haulage roads will provide access to all major components of the DD and PCD.

4.6.3 Clean Storm Water Diversion System

Geo Tail commissioned iLanda Water Services to prepare a hydraulic design for the storm water diversion system. The findings from the iLanda study is summarised below (the iLanda report is attached in Appendix C).

• Two channels are required, and are shown schematically in Figure 4-2. A local watershed runs generally east west through the southern portion of Phase 2. The two channels originate on this watershed. The North Channel runs generally northwards and the South Channel runs southwards before turning west and northwest around the southern perimeter of the DD. The external catchments associated with the channels are small.

Figure 4-2: Storm Water Diversion Channels


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• The storm water channels have been sized assuming unlined channels, and excavated into the natural ground. The material excavated from the channels should be placed in a berm on the downstream side of the channels. The channels should be kept free of long grass, shrubs and woody vegetation.

• The channels were sized to accommodate the required flood peaks (see Table 5 below). In order to keep channel depths practical to construct, the freeboard allowance within the channels are varied. Where freeboard within the channels is less than 0.3 m, the downstream berms will provide the additional freeboard. A minimum of 0.3 m freeboard is therefore available in the channels.

Table 5: Channel Sizing

Parameter Value

North Channel South Channel

Catchment size 32.9 ha 4.9 ha

50-year flood peak 4.7 m3/s 0.8 m3/s

Shape Trapezoidal Trapezoidal

Base width 1.0 m 1.0 m

Side slopes 1(v):1.5(h) 1(v):1.5(h)

Flow depth 0.83 m 0.48 m

Channel depth* 1.1 m 0.8 m

Max flow velocity** 3.7 m/s 2.7 m/s

Flow type at max velocity Supercritical Supercritical

* Note: Channel depths are based on the flattest downstream portion of the channel carrying the full design flow. ** Note: Flow velocities are based on the maximum longitudinal gradient.

• The portion of the North Channel adjacent to Phase 1 and downstream of this will require erosion protection. The flow regime is supercritical and design flow velocities are likely to exceed 3.5 m/s. The South Channel will require erosion protection once it turns west and northwest. Erosion protection could include the following liner systems:

o Concrete

o HDPE

o Grouted stone pitching

o Reno mattress

o Armorflex or similar technology


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4.6.4 Runoff Control System

A HDPE lined solution trench located along the downstream toe line of the starter embankment will collect run-off (utilising berm penstocks) from the side slopes of the DD from where it is then diverted to the PCD.

4.6.5 Starter Embankment

The homogeneous starter embankment will be constructed with the clayey sand material sourced from the DD and PCD basins. The technical specifications for the starter embankment can be summarised as follows:

• Box cut depth = 0.5 m

• Box cut base compaction standard = 100% Standard Proctor density

• Fill compaction standard = 100% Standard Proctor density at 0 to +2% of the optimum moisture content in layers not exceeding 200 mm loose

• Upstream side slope angle = 1(v):2.5(h)

• Downstream side slope angle = 1(v):2.5(h)

• Crest width = 5.0 m

4.6.6 Under Drainage System

The under drainage system is designed to collect seepage on top of the HDPE geomembrane and to achieve phreatic surface drawdown at the toe of the DD.

The under drainage system is strategically placed along the critical downstream toe line of the DD and includes the following:

• A filter drain (6 m wide toe drain)

• Non-perforated (High Density Polyethylene) HDPE drainage outlet pipes reporting to manholes

• A collector pipe (linking the manholes) that diverts the drainage flows to a downstream collection sump from where the seepage is diverted to the PCD

Generally, it is recommended that the filter materials should be cleaned and washed and the grading should comply with the following criteria:

o Auto stability criteria: D85 (filter) / D15 (filter) < 5

o Piping criteria: D15 (filter) / D85 (base) < 5

o Piping criteria: D50 (filter) / D50 (base) < 25

o Permeability criteria: D15 (filter) / D15 (base) > 4 and < 20

o Perforated pipe: D85 (filter) / Slot width > 1.5


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4.6.7 Liner Systems

The liner system for the DD generally complies with the Class C liner type in the waste classification regulations according to Government Notice R. 634 (Government Gazette No. 36784, 23/08/2013) pertaining to the National Environmental Management Waste Act (Act No. 59 of 2008) by the Department of Environmental Affairs.

The proposed liner system can be summarised as follows (see Figure 4-3):

• Layer D: This is a base preparation layer consisting of a compacted layer of reworked in-situ soils with a minimum thickness of 150 mm. The layer must be compacted to a minimum density of 95% Standard Proctor maximum dry density at a moisture content of 0 to +2% of the optimum moisture. The permeability of this layer should be lower than 1 x 10-9 m/s.

• Layer C: A 150 mm thick compacted clay layer. The layer must be compacted to a minimum density of 95% Standard Proctor maximum dry density at a moisture content of 0 to +2% of the optimum moisture content in layers not exceeding 200 mm loose. The permeability of this layer should be lower than 1 x 10-9 m/s.

• Layer B: A double textured 2 mm thick HDPE geomembrane, which must be laid in direct contact with the upper surface of compacted “Layer C”. As a result of the potential for mechanical damage when the discard is placed, this specification exceeds the Class C specification.

• Layer A: This is a cushion layer of approximately 500 mm thickness of fine to medium sandy or similar suitable material, which is placed immediately above the HDPE geomembrane to protect it from mechanical damage.

Figure 4-3: DD Liner System

The liner system for the PCD generally complies with the Class B liner type in the waste classification regulations according to Government Notice R. 634 (Government Gazette No. 36784, 23/08/2013) pertaining to the National Environmental Management Waste Act (Act No. 59 of 2008) by the Department of Environmental Affairs.


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The proposed liner system can be summarised as follows (see Figure 4-4):

• Layer C: This is a base preparation layer consisting of a compacted layer of reworked in-situ soils with a minimum thickness of 150 mm. The layer must be compacted to a minimum density of 95% Standard Proctor maximum dry density at a moisture content of 0 to +2% of the optimum moisture content. The permeability of this layer should be lower than 1 x 10-9 m/s.

• Layer B: A 450 mm thick compacted clay layer. The layer must be compacted to a minimum density of 95% Standard Proctor maximum dry density at a moisture content of 0 to +2% of the optimum moisture content in layers not exceeding 200 mm loose. The permeability of this layer should be lower than 1 x 10-9 m/s.

• Layer A: A 1.5 mm thick HDPE geomembrane, which must be laid in direct contact with the upper surface of compacted “Layer B”.

Figure 4-4: PCD Liner System

4.6.8 Cover System

The proposed cover specification is provided graphically in Figure 4-5. The figure has been copied from Figure A.8.12, Appendix A of the Minimum Requirements for Waste Disposal by Landfill (1998), and modified to reflect the proposed DD cover design. The proposed soil cover system can be summarised as follows:

• V layer: A 450 mm thick layer of selected material. The soil used should have a Plasticity Index (PI) of between 5 and 15 and a maximum particle size of 25 mm. The soil should be compacted to achieve an in situ permeability of 0.5 m per year, as measured using a double ring infiltrometer test. The compaction standard should be at least 85% of the maximum Standard Proctor dry density at +2% of optimum moisture content in layers not exceeding 200 mm loose.

• U Layer: A 200 mm thick layer of topsoil planted with local grasses and shrubs. The layer must be lightly compacted after spreading.


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Figure 4-5: Cover System

4.6.9 Pollution Control Dam

Geo Tail commissioned iLanda Water Services to size the PCD. The findings, conclusions and recommendations from the iLanda study is summarised below (the iLanda report is attached in Appendix C):

• The rehabilitation progress is a significant contributor to the sizing of the PCD. If the rehabilitation is truly concurrent, the PCD capacity will be minimised.

• The three phases of DD construction are similar in size. The principle of the modular approach is to size a PCD for a single phase of the DD. The PCD will therefore service an area equivalent to one phase of the DD being dirty. The largest of the three phases was selected to be slightly conservative. If the rehabilitation is truly concurrent, no more than one phase of the DD should be considered dirty at any point in time and the single PCD will be adequate during the entire life of the DD. If the rehabilitation lags the DD construction, a second and potentially a third PCD of the same size will be required, depending on how much the rehabilitation is lagging. As soon as the dirty area exceeds the area of the phase used in this modelling (see Table 6 below) a new PCD of the same size will be required. Up to three PCD’s will be required if no rehabilitation is done while the DD is constructed. This also has the benefit of delaying capital should a second and third PCD be required.

Table 6: Dirty Area used in Modelling

Parameter Value

DD dirty area (largest single compartment) 25.6 ha

Rehabilitated area 0 ha

Catchment paddocks 3.2 ha

Lined area not covered with discard 0 ha

Total Area 28.8 ha


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• Runoff from areas that are lined, prior to DD construction, should be managed so that it is clean and discharged to the environment. No runoff from lined surfaces has been accounted for. This runoff would significantly increase the required PCD capacity.

• Eight scenarios were simulated to comply with GN704 of the South African National Water Act. The scenarios provide a relationship between return pumping capacity and required PCD capacity. If no water is pumped from the PCD, it acts as an evaporation pond. If the PCD is emptied every day, the required capacity equals the volume generated by a 50-year design storm.

• Water that is pumped from the PCD (excluded the from the Geo Tail scope of work) is assumed to be:

o Managed elsewhere on the mine,

o Consumed in the process,

o Stored in another appropriate storage facility outside of the DD battery limits, or

o Treated to discharge standards and discharged to the environment.

• The water balance model consists of a mass-balance model that operates on a daily time step. The model is coded in GoldSim. The results of the simulations are summarised in Table 7. The results show the relationship between PCD capacity and return pumping capacity, to achieve compliance with GN704.

Table 7: Modelling Results

PCD Capacity (m3)

Required Return Water Pumping Capacity (m3/day)

1 450 000 0

100 000 200

75 000 500

50 000 1 100

40 000 2 200

30 000 6 300

20 000 16 200

17 400 17 400

* Note: This full pumping capacity should be used whenever possible. The PCD should be operated empty.

• The results indicate that:

o If no water is returned from the PCD, it acts as an evaporation dam. A 1.45 Mm3 PCD with an average depth of 2 m will be required to achieve compliance with GN704.


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o The more water that is pumped out of the PCD, the smaller the storage capacity required achieving compliance with GN704.

o If the PCD is emptied every day, the required storage capacity equals the volume generated by a 50-year design storm. This is 17 400 m3. This is the minimum PCD capacity that can achieve compliance with GN704.

• The maximum pump capacities will not always be required. Simulations show that the larger the pump capacity, the less frequent it will be used:

o The full pump capacity for the 100 000 m3 PCD (200 m3/day) will be used about 45% of the time (168 days a year on average).

o The full pump capacity for the 50 000 m3 PCD (1 100 m3/day) will be used about 4% of the time (15 days a year on average).

o The full pump capacity for the 20 000 m3 PCD (16 200 m3/day) will be used about 0.01% of the time (once every 25 years on average).

o The full pump capacity for the 17 400 m3 PCD (17 400 m3/day) will be used less than 0.005% of the time (once every 50 years on average).

For design purposes, it was decided to include a PCD with a capacity of 100 000 m3 in the design. The design specifications can be summarised as follows:

• Maximum water depth = 4.2 m

• Dry freeboard = 0.8 m

• Maximum embankment height = < 5 m

• Crest width = 5.0 m

• Upstream slope angle = 1(v):2.5(h)

• Downstream slope angle = 1(v):2.5(h)

• Box cut depth = varies

• Box cut base compaction standard = 95% Standard Proctor density

• Fill compaction standard = 100% Standard Proctor density at 0 to +2% of the optimum moisture content in layers not exceeding 200 mm loose

• Liner system = section 4.6.7 refers

4.6.10 Borrow Sources

Selected borrow material will be sourced as follows:


Page 23

Table 8: Borrow Sources

Design Component Material Type Borrow Source

Starter embankment Clayey sand Basin of DD and PCD

PCD embankment Clayey sand Basin of PCD

Filter drain materials Sand and Gravel From commercial sources

DD liner - Layer C Sandy clay Basin of DD

DD liner - Layer A Fine to medium sand Source not identified

DD cover - Layer V Sandy clay From basin of DD

DD cover - Layer U Topsoil From topsoil stockpiles

PCD liner – Layer B Sandy clay Basin of DD


Page 24

5 STABILITY ANALYSIS

A side slope stability analysis was undertaken for the final critical cross section through the DD, utilising the two-dimensional limit equilibrium computer programme SLIDE.

The side slope stability was assessed utilising block failure surfaces and the Bishop Simplified Method. SLIDE allows for the analysis of numerous potential failure surfaces and the identification of the critical surface with the lowest factor of safety against failure.

For the purpose of the stability analysis, a pore pressure parameter ru has been used, where (ru = pore pressure at a point / weight of overburden at that point) to represent the phreatic conditions. No excess water pressures have been assumed for any of the materials and it is assumed that the project area is in a region of low seismicity.

The material properties assumed for the stability analysis are summarised in Table 9. The values are based on previous experience with similar materials and laboratory testing.

Table 9: Shear Strength Properties

Material no. Material Type

Pore Pressure Parameter

(ru)

Unit Weight (kN/m3)

Cohesion (kPa)

Friction Angle (degrees)

1 Foundation 0.1 17 10 28

2 Starter embankment 0.1 19 15 30

3 Liner system 0.1 19 15 30

4 Coal discard 0.2 17 0 35

The stability analysis results (see Figure 5-1 below) indicate that the minimum overall factor of safety for side slope stability will be 2.2. This factor of safety is considered to be satisfactory for normal operating conditions. It however assumes that the management of the DD will be adequate and the need to monitor the identified critical parameters is essential.


Page 25

Figure 5-1: FOS Overall Stability


Page 26

6 ENVIRONMENTAL

6.1 Risk Control Measures

The environmental control measures can be summarised as follows:

• In the design, the total seepage flux (also oxygen) and, hence, the contaminant load will be minimised through:

o The lining of the DD and the PCD.

o Operating the DD with the minimum of water stored on the top surface at all times.

o Compacting the discard material.

o Implementing an engineered soil cover, as part of the rehabilitation plan.

• The under drainage flows will be diverted to the PCD through a closed system.

• The storm water diversion system will divert clean precipitation run-off from the external catchments.

• The side slopes will be terraced and the engineered benches will collect surface run-off and silt load.

• Catchment paddocks, located at ground level, will collect surface run-off and silt load from the side slopes. The run-off will be diverted to the PCD.

• Appropriate erosion protection and energy dissipation measures will be implemented for the open trenches, spillways etc.

• Monitoring boreholes will be installed upstream and downstream of the PCD and DD for leakage detection, ground water level and water quality monitoring purposes.

6.2 Closure Considerations

The high-level closure considerations can be summarised as follows:

• The required final side slope and top surface geometries will be achieved during the operation phase.

• The final top surfaces will either be divided into smaller compartments from where the runoff will be allowed to evaporate and/or the water will be allowed to discharge in a controlled manner to the environment (i.e. spillway/s).

• The side slopes and the final top surfaces will be covered with a vegetated engineered layer. The purpose of the cover is to stabilise the surface (erosion and dust generation) and to minimise the infiltration of water and oxygen.

• Emergency spillways will be included in the final closure design.

• The PCD will remain in place.

• Generally all surface structures (i.e. pumps, pipelines, power lines etc.) will be removed.


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7 QUALITY ASSURANCE

The quality assurance requirements can be summarised as follows:

7.1 Construction Phase

The DD and PCD will be constructed in accordance with technical specifications and construction drawings. This is essential to ensure that the DD and PCD functions according to the design intent. Suitably qualified personnel will carefully monitor (as a minimum) the following aspects during the construction phase:

• Box cut depths and foundation preparation requirements for the embankments and roads

• Excavation classification and stability

• Material selection, moisture conditioning and compaction for earthworks and clay liner

• Filter materials (quantity, specification and quality)

• HDPE liner installation

• Materials on site

• Concrete works (strength, reinforcement etc.)

• Survey measurement and control

7.2 Operation Phase

A system of management and monitoring of critical parameters will ensure that the DD and PCD is operated safely and efficiently, in accordance with good environmental practice and in a manner compatible with the final closure requirements. Some of the critical parameters to be monitored are listed below:

• Technical (i.e. settlement, phreatic levels, climatic data, side slope geometry, available storage capacity etc.)

• Process (i.e. particle size distribution, deposition rate etc.)

• Geotechnical properties of the discard material (i.e. compaction, shear strength, permeability etc.)

• Operational (i.e. freeboard, drain flow rates, return water pump rates etc.)

• Environmental (i.e. water quality, ground water levels etc.)

In addition, on-going maintenance and repairs will be required for all the design components to ensure that the design intent is met at all times.


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8 BILL OF QUANTITIES

The bills of quantities for the capital and closure phases of the Discard Dump and the Pollution Control Dam are summarized in the tables below:

Table 10: Bill of Quantities – Discard Dump

PHASE 1 PHASE 2 PHASE 31,0 ACCESS CONTROL1,1 Boundary fence Low specification m 4 800 0 01,2 Gates no 1 0 01,3 Warning signs @ 100m intervals no 48 0 02,0 SITE CLEARANCE2,1 Clear and grub All inclusive m2 360 000 310 000 270 0002,2 Top soil stripping 300mm depth m3 108 000 93 000 81 0002,3 Remove overburden dump m3 0 245 800 02,4 Remove topsoil dump m3 0 198 800 03,0 STORM WATER DIVERSION TRENCH

North Trench3,1 Trench excavation Soft excavation only m3 4 300 0 03,2 Compact trench base m2 4 300 0 03,3 Bund wall fill m3 4 300 0 03,4 Erosion protection Grouted stone pitching m2 3 100 0 0

South Trench3,5 Trench excavation Soft excavation only m3 2 400 0 03,6 Compact trench base m2 2 400 0 03,7 Bund wall fill m3 2 400 0 03,8 Erosion protection Grouted stone pitching m2 1 410 0 04,0 ACCESS ROADS4,1 Access road box cut 200mm depth below topsoil m3 11 860 0 04,2 Rip and compact base m2 59 300 0 04,3 Box cut fill 500mm depth to ngl m3 29 650 0 04,4 Access road fill Low spec gravel road - 300mm wearing course m3 17 790 0 04,5 Pipe culvert no 1 0 05,0 SOLUTION TRENCH5,1 General fill m3 2 300 1 700 1 5005,2 Trench excavation Soft excavation only m3 8 200 5 200 4 5005,3 Compact trench base m2 12 950 9 500 8 3005,4 Bund wall fill m3 8 200 5 200 4 5005,5 Anchor trench Excavate and backfill m3 1 500 1 100 9305,6 Surface preparation m3 22 900 16 700 14 6005,7 HDPE liner m2 22 900 16 700 14 6006,0 STARTER EMBANKMENT6,1 Box cut 300mm depth m3 11 520 8 490 7 7106,2 Rip and compact base m2 38 400 28 300 25 7006,3 Box cut fill m3 11 520 8 490 7 7106,4 Embankment fill 2 km free haul m3 71 600 52 500 49 4007,0 UNDER DRAINAGE SYSTEM7,1 Bund wall Compacted m3 620 550 7107,2 Anchor trench Excavate and backfill m3 420 360 4807,3 Geotextile A4 bidim m2 12 200 10 800 14 0007,4 Layer - 19mm stone Commercial source m3 1 010 890 1 1607,5 Layer - filter sand Commercial source m3 960 850 1 1007,6 Perforated drain piping 110 OD HDPE m 1 150 1 220 1 9207,7 Bends 90 degree no 11 7 117,8 Bends 45 degree no 11 7 117,9 End-pieces no 13 8 127,10 Concrete beams 300mm by 300mm by 500mm m3 0,5 0,3 0,57,11 Outlet pipe trench Excavate and backfill m3 290 130 2407,12 Non-perforated drain piping 110 OD DRAINEX m 290 130 2407,13 Puddle flanges 500mm by 500mm by 300mm m3 0,8 0,5 0,88,0 LINER SYSTEM8,1 Excavate clay material 150mm depth m3 33 195 32 865 28 9808,2 Rip and compact base 150mm depth m2 221 300 219 100 193 2008,3 Compacted clay liner 150mm thickness m3 33 195 32 865 28 9808,4 Surface preparation m3 266 200 238 900 212 9008,5 Anchor trench Excavate and backfill m3 700 670 6308,6 HDPE liner 2mm thickness m2 266 200 238 900 212 9008,7 Protection layer Sandy material - 500mm thickness m2 110 650 109 550 96 600

Item Description Qualifications UnitQuantity


Page 29

Table 11: Bill of Quantities – Pollution Control Dam

1 ACCESS CONTROLa Boundary fence High specification m 1 000b Gates 14 m wide double leaf gate no 1c Warning signs no 202 SITE CLEARANCEa Clear and grub All inclusive m2 52 000b Top soil stripping 300mm depth m2 15 6003 ACCESS ROADa Access road box cut 200mm depth below topsoil m3 880b Rip and compact base m2 4 400c Box cut fill 500mm depth to ngl m3 2 200d Access road fill 300mm wearing course m3 1 320e Pipe culvert no 14 COMPACTED EMBANKMENTSa Box cut 500mm depth m3 11 300b Rip and compact base m2 22 600c Box cut fill m3 11 300d Embankment fill m3 40 7005 BASIN & SPILLWAYSa Basin excavation m3 47 000b Rip and compact base and slopes m2 43 700c Spillway excavation m3 910d Compact spillway base m2 460e Erosion protection Stone pitching m2 460f Weir beams Mass concrete m3 66 PUMPSTATION PLATFORMa Box cut m3 Excludedb Rip and compact base m2 Excludedc Box cut fill m3 Excludedd Platform fill m3 Excluded7 LEAKAGE DETECTION SYSTEMa Trench excavation m3 1 700b Geotextile m2 1 750b HDPE 1,5mm thickness m2 1 750c Selected backfill m3 1 700e Perforated drain piping m 340f Non-perforated drain piping Geopipe 150mm diameter m 12g Bends 90 degree no 28 PUMP STATION INTAKE STRUCTURESa Excavation m3 140b Bell mouth no 2c HDPE Piping m 140d Valves no 2f Sump no 29 LINER SYSTEMa Excavate clay material 450mm depth m3 8 730b Rip and compact base 150mm depth m2 19 400c Compacted clay liner 450mm thickness m3 8 730d Surface preparation m3 33 300e Anchor trench Excavate and backfill m3 370f HDPE liner 1.5mm thickness m2 33 300

Item Description Technical Specification / Assumption Unit Quantity


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9 RECOMMENDATIONS

Key issues associated with any future advancement of the design have been identified in this report and are presented below:

• A full set of construction drawings and technical specifications should be prepared for implementation purposes.

• Borrow sources should be investigated for filter drain materials, as well as the DD cushion layer.

• The removal of the existing stockpiles/dumps located within the proposed footprint of the DD should be investigated further.

• A site-specific code of practice should be prepared for the DD.

• A risk monitoring, surveillance and audit system should be implemented for the operation and rehabilitation phases. Critical parameters should be monitored and analysed on a routine basis.

• A detailed closure plan should be developed during the life of the DD.


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10 REFERENCES

• South African Standards: Code of Practice, Mine Residue, SANS 0286: 1998

• Guidelines for Environmental Protection, Volume 1/1979 (Revised 1983 and 1995): The Engineering Design, Operation and Closure of Metalliferous, Diamond and Coal Residue Deposits, Chamber of Mines of South Africa, March 1996, and any Addenda published subsequently.

• Guidelines on the Safe Design and Operating Standards for Residue Storage - Department of Minerals and Energy (DME) Western Australia

• Guidelines on the Development of an Operating Manual for Residue Storage - Department of Minerals and Energy (DME) Western Australia

• A Guide to the Management of Residue Facilities - The Mining Association of Canada (MAC) - A Guide released in September 1998 by the MAC to encourage mining companies to practise safe and environmentally responsible management of Residue facilities through the development of customized, site-specific management systems.

• Guidelines for the compilation of a mandatory code of practice on mine Residue deposits - Ref. No. DME 16/3/2/5-A1. 30 November 2000, Department of Minerals and Energy, Republic of South Africa.

• Middleton, B.J. and Bailey, A.K. Water Resources of South Africa, 2005 study (WR2005), 2009. WRC Report No TT 382/08.

• Adamson, P.T., Southern African Storm Rainfall, Department of Environment Affairs, Technical Report TR102, Pretoria, 1981.

• Midgley, D.C., Pitman, W.V., Middleton, B.J. Surface Water Resources of South Africa, 1990. WRC Report No 298/2.1/94, Volume 2.

• ICOLD Bulletin 139, Improving Tailings Dam Safety, 2011.


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APPENDIX A: DRAWINGS


Page 33

APPENDIX B: LABORATORY TEST RESULTS


Page 34

APPENDIX C: ILANDA REPORT

Daily Average: m 3 /day (some flows expressed as m 3 /tonne) Rev 2Startup

Kkoemacau TSFWater balance1 compartment, unlined, 22.5% solids feed, 55% solids deposition

0

00

3.44 34,515 2.63 26,317 76%3.44 m3/t 2.63 m3/t

0.820 8,199 0.82 m3/t 0.64 6,407

0.64 m3/t132

577

1,263

8484

0.00

20

8 0

535

1,243

02,507

2,472

0.01 1020.01 m3/t 23

0 25

0

320 136

0.01 m3/t 0% return 3

0

Prepared by

Legend Note 1: Water is initially trapped in the pore spaces on the wet beach. This water is lost to dessication in the long term000 Flows represented in m3/tonne Note 2: Delta storage is the difference between the volumes at the start and end of the simulation.000 Dirty Flow (m3/day) Note 3: All returns are expressed as a percentge of the pre thickener water.000 Clean Flow (m3/day) General Note: These flows are rounded to zero decimal places for clarity. Consequently some flows may appear out of balance

Daily Average: m 3 /day Rev 2Startup

Kkoemacau TSFSummary water balance1 compartment, unlined, 22.5% solids feed, 55% solids deposition

3,0932,679

1243 Total inflow Total outflow

## 34,515 37,195 37,1953.44 m3/t

0.64 6,4070.64 m3/t

2.64 26,453 77%2.64 m3/t

0

Prepared by0

Legend Note 1: Water is initially trapped in the pore spaces on the wet beach. This water is lost to dessication in the long term000 Flows represented in m3/tonne Note 2: Delta storage is the difference between the volumes at the start and end of the simulation.000 Dirty Flow (m3/day) Note 3: All returns are expressed as a percentge of the pre thickener water.000 Clean Flow (m3/day) General Note: These flows are rounded to zero decimal places for clarity. Consequently some flows may appear out of balance

37,195 37,195Total Inflows Total Outflows

0 m3/t0

0

TSF complex

RainfallEvaporation

Seepage to GW

Return to Plant 3

Slurry water

TSFPool

Evaporation

Interstitial Storage 1

Natural catchmentRainfall

Seepage to GW

Evaporation

Rainfall

Wet Beach

Rainfall

Supernatant releaseSeepage to GW

Evaporation

Interstitial Storage 1

Dry Beach

InfiltrationInfiltration

Drain flow

pumped to pool

Pool Storage Change 2

Evaporation

Beach runoff

Rainfall

Slurry Water from Plant

Storage Changes 2

Spill to Environment

Return Water Dam

Evaporation

Seepage to GW

Return to Plant

Spill to Environment

Rainfall

Thickner Return to Plant 3

GEO TAIL PTY LTD

MINE RESIDUE CONSULTING SERVICES

LEOPARD COURT BUILDING

1 St. FLOOR, SOUTH WING,

c/o JEROME & KARIBA STREET,

LYNWOOD GLEN

TEL : +27 12 348 1051

FAX : +27 86 686 9023

EMAIL : [email protected] or [email protected]

Appendix E - ERM€¦ · o Falling Head Permeability The laboratory test results for the discard...

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