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Zitholele Consulting

Reg. No. 2000/000392/07 PO Box 6002 Halfway House 1685, South Africa Building 1, Maxwell Office Park, Magwa Crescent West c/o Allandale Road & Maxwell Drive, Waterfall City, Midrand Tel + (27) 11 207 2060 Fax + (27) 86 674 6121 E-mail : [email protected]

Directors: S Pillay (Managing Director); N Rajasakran (Director); Dr AM Van Niekerk (Director)

DOCUMENT CONTROL SHEET

Project Title: Conceptual Engineering Design Report for the Continuous Ashing at Kendal Power Station

Project No: 12810

Document Ref. No: 12810-REP-ENG-001-Conceptual Design Report

DOCUMENT APPROVAL

ACTION FUNCTION NAME DATE SIGNATURE

Prepared Project Engineer N Rajasakran 25-08-2014

Reviewed Project Reviewer D Jansen van

Rensburg 25-08-2014

Approved Project Director S Pillay 25-08-2014

RECORD OF REVISIONS

Date Revision Author Comments

05-05-2014 0 N Rajasakran Concept Design Report Issued for Comments.

25-08-2014 1 J Heera Updated Concept Design Report Issued for Comments.

Zitholele Consulting

Reg. No. 2000/000392/07 PO Box 6002 Halfway House 1685, South Africa Building 1, Maxwell Office Park, Magwa Crescent West c/o Allandale Road & Maxwell Drive, Waterfall City, Midrand Tel + (27) 11 207 2060 Fax + (27) 86 674 6121 E-mail : [email protected]

Directors: S Pillay (Managing Director); N Rajasakran (Director); Dr AM Van Niekerk (Director)

REPORT ON

CONTINUOUS ASHING AT KENDAL POWER STATION

CONCEPTUAL ENGINEERING REPORT

Report No : 12810

Submitted to:

Eskom Holdings SOC Ltd

P O Box 1091 Johannesburg

2000

DISTRIBUTION:

2 Copies - Eskom Holdings SOC Ltd

1 Copy - Zitholele Consulting (Pty) Ltd – Library

05 September 2014 12810

05 September 2014 i 12810

ZITHOLELE CONSULTING

EXECUTIVE SUMMARY

Kendal power station was commissioned in the mid 1980’s, with a 40 year operating life. The initial

dry ash dump site was designed to have a capacity for the operating life with an eight year

contingency period. The life of the power station has since been upgraded to 60 years and with

some other contributing factors, such as the dry density and the load factor, the initial dry ash

dump is now under capacity. The power station is therefore expected to be decommissioned at

the end of 2053. This means that area to accommodate the additional ash generated during this

operational period will need to be extended. The area to the north of the existing facility will need

to be optimised in order to receive this ash. The Conceptual Engineering designs indicate that ash

may be accommodated here until early 2030 and thereafter an alternative site will need to be

licenced to receive ash up to the end of 2053. The supplementary site up to the end of 2053 is a

separate submission for Environmental Authorisation and is not addressed within this report.

Eskom has appointed Zitholele Consulting (Pty) Ltd (Zitholele) to start with the environmental

impact assessment (EIA) to extend the existing Kendal dry ash dump into the northerly direction.

Zitholele are also responsible for the conceptual engineering design for the options identified and

to recommend a preferred option. These engineering designs will be used to underpin and inform

the EIA.

The Conceptual Engineering Report discusses the following:

Continuation of the Ash Disposal Facility (ADF) with the extended footprint being lined in

compliance with DEA’s Norms and Standards as promulgated on 23 August 2013;

Design of pollution control dams and stormwater management infrastructure in compliance with

GN704

Diversion of a natural stream to accommodate the extended footprint of the ADF

Remedial works to an existing dam within Eskom’s property boundary but not part of their

water management system which addresses the mixing of flow from the final voids of the

adjacent mining operations.

Several options were considered for determining the go-forward option on the ADF and stormwater

management philosophy. The “piggyback” options described in both the determination of air space

on the ADF and stormwater management philosophy is not deemed feasible currently from a

mechanical perspective. This option was therefore not considered for implementation in this

report. Further investigation is currently underway here and will be reported on a separate project

that has been commissioned by Kendal Power Station.

Trade-off studies were conducted in order to determine the optimised go-forward scheme for the

continuation of the current Kendal Ash Dump and stormwater infrastructure. Environmental,

Technical and Financial aspects are considered in the trade-of studies when making the decision

on which option to proceed with to the next stage of design. Six options for the ADF layout and

nineteen options for the stormwater management philosophy were assessed. This was supported

by:

05 September 2014 ii 12810


Conceptual airspace modelling of each alternative;

A daily time-step water balance model over a 50 year period for run-off determination and PCD

sizing, as well as sizing of clean and dirty water conveyances. From the trade-off study,

Scenario 2 option 3B was identified at the preferred option

Conceptual development of dump infrastructure including surface drainage structures,

hydraulic structures, leachate and sub-surface drainage, lining and cover materials;

Cost estimation;

Trade-off study workshop.

From the trade-off study held the preferred option is identified as Option 2A, which is to divert the northern stream to get the maximum dump volume on the current site;

Option 2A provides a ashing capacity of 98 Mm3 at a density of 0.85t/m3

This provides a remaining life of 15 years from January 2015 until December 2029;

The preferred option as selected through the trade-off study analysis is based on a preliminary design. All fundamental aspects were addressed to inform the EIA study.

It is recommended to progress with the preferred option through a feasibility study and detailed design phase.

The requirements that are raised as issues and concerns through the EIA and stakeholder engagement process should be addressed during the feasibility and detailed design phase and the impacts should be mitigated through engineering solutions.

Based on the trade-off study work, it can be stated that the proposed facility extension is a feasible solution.

Following the workshops, it was proposed that Option 2A, for the ADF layout of diverting the

northern stream with no Piggy Backing, and Scenario 2 Option 3B, for the stormwater

management philosophy, be taken to the next stage of design. Scenario 2 being the scenario with

an optimum open ash area of 82 hectares, and Option 3B being the option where Dam 1 & 5 are

considered dirty, Dam 2, 3 and 4 are considered clean, dust suppression is done from Dam 5 to open ash

areas, irrigation is done from Dam 4 to rehabbed areas and irrigation is done from the existing Clean Water

Dam to the power station terrace. A Waste Management Licence (WML) and Water Use Licence

(WUL) need to be applied for the infrastructure and activities as described in the aforementioned

options.

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TABLE OF CONTENTS

SECTION PAGE

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

2 BASIS OF DESIGN ............................................................................................ 2 2.1 Assumptions and limitations............................................................................. 2 2.2 Ash characteristics ........................................................................................... 2

2.2.1 Grading and Specific gravity .............................................................. 2 2.2.2 Stability .............................................................................................. 3 2.2.3 Permeability ....................................................................................... 3

2.3 Annual tonnages .............................................................................................. 3 2.4 Capacity requirements ..................................................................................... 4 2.5 Dust suppression ............................................................................................. 4 2.6 Stormwater Management ................................................................................. 4 2.7 Stream Diversion ............................................................................................. 5

3 ADF OPTIONS MODELLED .............................................................................. 6 3.1 Description of options ...................................................................................... 6

3.1.1 Option 1A: Minimum volume .............................................................. 6 3.1.2 Option 1B & 1C: Minimum volume with staged (1B) or concurrent

piggybacking (1C) .............................................................................. 7 3.1.3 Option 2A: Maximum volume ............................................................. 8 3.1.4 Option 2B & 2C: Maximum volume with staged (2B) or concurrent

piggybacking (2C) .............................................................................. 9 3.2 Trade-off study for ADF Preferred Option ...................................................... 10 3.3 Approach to the trade-off study ...................................................................... 10 3.4 Trade-off study .............................................................................................. 12 3.5 Results of the trade-off study ......................................................................... 13

4 ADF CONCEPTUAL DESIGN .......................................................................... 14 4.1 Ash disposal .................................................................................................. 14

4.1.1 Option 1A &2A: Minimum & Maximum volume deposition strategy .. 15 4.1.2 Option 1B & 2B: Staged piggyback deposition strategy .................... 15 4.1.3 Option 1C & 2C: Concurrent piggyback deposition strategy ............. 16

4.2 Liner system .................................................................................................. 16 4.2.1 Liner System Installation .................................................................. 17 4.2.2 Leachate collection system .............................................................. 17 4.2.3 Sub-soil drainage system ................................................................. 18

4.3 Capping system ............................................................................................. 19 4.4 E-Dump ......................................................................................................... 20

5 STORMWATER MANAGEMENT PHILOSOPHY ............................................ 21 5.1 OBJECTIVES ................................................................................................ 21 5.2 EXISTING STORMWATER MANAGEMENT SYSTEM .................................. 21

5.2.1 Power Station Terrace ..................................................................... 22 5.2.1.1 Impacted Areas ................................................................................ 23 5.2.1.2 Clean Areas ..................................................................................... 23 5.2.2 Cross over plant ............................................................................... 24 5.2.3 Silt Traps .......................................................................................... 24 5.2.4 Dirty Water Dam............................................................................... 24 5.2.5 Emergency Dirty Water Dam ............................................................ 25 5.2.6 Clean Water Diversion Berm and Channel ....................................... 26 5.2.7 Clean Water Dam............................................................................. 26 5.2.8 Coal Stockyard Attenuation Basin .................................................... 26 5.2.9 E-dump Stormwater Management .................................................... 27 5.2.10 Pumps and Pipelines ....................................................................... 27

5.3 OBJECTIVES OF PROPOSED STORMWATER MANAGEMENT SYSTEM . 27

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5.4 MODELING APPROACH AND ASSUMPTIONS ............................................ 28 5.4.1 Rainfall data ..................................................................................... 28 5.4.2 Operating flows ................................................................................ 29 5.4.3 Description of catchment areas at ADF ............................................ 29 5.4.3.1 Open Ash Areas ............................................................................... 29 5.4.3.2 Rehabilitated Areas .......................................................................... 30 5.4.3.3 Transfer House F and Surrounding Areas ........................................ 30 5.4.3.4 Ash conveyor from E-dump .............................................................. 31 5.4.4 Stormwater runoff calculations ......................................................... 32

5.5 OPTIONS MODELLED .................................................................................. 34 5.6 MODELLING RESULTS ................................................................................ 35 5.7 TRADE-OFF ASSESSMENT ......................................................................... 36 5.8 PROPOSED INFRASTRUCTURE ................................................................. 39

5.8.1 Pollution Control Dams .................................................................... 39 5.8.2 Clean Water Dams ........................................................................... 41 5.8.3 Toe Paddocks .................................................................................. 44 5.8.4 Storage Reservoirs .......................................................................... 44 5.8.5 Conveyance infrastructure (pumps, pipelines and channels) ............ 44

5.9 1 IN 100 YEAR FLOODLINES ....................................................................... 45 5.9.1 Methodology .................................................................................... 45 5.9.2 Results ............................................................................................. 53

5.10 Suppression Abstraction Philosophy .............................................................. 58 5.11 Hydraulic Analysis ......................................................................................... 58

5.11.1 Sizing of “Clean” stormwater diversion drains and berms ................. 58 5.11.2 Sizing of “Dirty” stormwater conveyance drains ................................ 58

5.12 WATER BALANCE ........................................................................................ 60 5.13 OPERATIONAL REQUIREMENTS ................................................................ 60

5.13.1 Monitoring of Quality in Clean Water Dams ...................................... 61 5.13.2 Maintaining Open Ash Areas for Dust Suppression .......................... 61 5.13.3 Maintaining Silt Traps ....................................................................... 61

5.14 WAY FORWARD FOR STORMWATER MANAGEMENT .............................. 61 6 STREAM DIVERSION ...................................................................................... 62 7 PHASED APPROACH TO ADF ....................................................................... 63

7.1.1 Option 1A & 2A ................................................................................ 63 7.1.2 Option 1B & 2B ................................................................................ 63 7.1.3 Options 1C & 2C .............................................................................. 63

8 FARM DAM SYSTEM ....................................................................................... 64

9 OPERATION AND MAINTENANCE PLAN ...................................................... 66 9.1 Code requirements in terms of SABS 0286 .................................................... 66

10 DISCUSSION .................................................................................................... 67 11 RECOMMENDATION AND CONCLUSION ..................................................... 68

LIST OF FIGURES

Figure 1: Option 1A ............................................................................................................ 7

Figure 2: Option 1B & 1C ................................................................................................... 8

Figure 3: Option 2A ............................................................................................................ 9

Figure 4: Option 2B & 2C ................................................................................................. 10

Figure 5: Layout of conveyor system used to deposit ash ................................................ 14

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Figure 6: Typical Class C Landfill Barrier System............................................................. 17

Figure 7: Proposed Class C Barrier System ..................................................................... 17

Figure 8: Leachate collection system for Option 2A ......................................................... 18

Figure 9: Layout of the sub-soil drainage system ............................................................. 19

Figure 10: Section through rehabilitated ADF ................................................................... 19

Figure 11: Existing E-Dump ............................................................................................. 20

Figure 12: Current Stormwater System ............................................................................ 22

Figure 13 : Power Station Clean and Dirty Area Demarcation .......................................... 23

Figure 14: Concrete lined silt trap with adjustable overflow weir ....................................... 24

Figure 15: Dirty Water Dam with spillway in background .................................................. 25

Figure 16: Emergency Dirty Water Dam overflow channel ............................................... 26

Figure 17: Open Ash Area on ADF .................................................................................. 29

Figure 18: Rehabilitated Area on ADF .............................................................................. 30

Figure 19: Transfer House F ............................................................................................ 30

Figure 20: Stormwater Management at Transfer House F ................................................ 31

Figure 21: Maintenance at Low Point on Conveyor .......................................................... 31

Figure 22: Dirty Water Dam Levels for Simulation Period ................................................. 39

Figure 23: Emergency Dirty Water Dam Levels for Simulation Period .............................. 40

Figure 24: Proposed Dam 1 Levels for Simulation Period ................................................ 40


Figure 26: Existing Clean Water Dam Levels for Simulation Period ................................. 42




Figure 30: Positioning of Temporary Toe Paddocks ......................................................... 44

Figure 31: 1 in 100 Year Floodlines Pre- and Post-Development ..................................... 53

Figure 32: Resulting Longitudinal section of Three Dams Water Course .......................... 54

Figure 33: Cross Section of Diversion Channel ................................................................ 55

Figure 34 Resulting Longitudinal Section of Farm Dam Water Course, Pre-Development56

Figure 35: Resulting Longitudinal Section of Farm Dam Water Course, Post-Development57

Figure 36: Toe Line Drain ................................................................................................ 59

Figure 37: Outlet Drain ..................................................................................................... 59

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Figure 38: Proposed Stream Diversion ............................................................................ 62

Figure 39: Proposed changes at Farm Dam System ........................................................ 65

LIST OF TABLES

Table 1: Ash grading .......................................................................................................... 3

Table 2: Weightings for the options analysis workshop .................................................... 11

Table 3: Trade-off Study Workshop Delegates and Designations .................................... 12

Table 4: Results from the Trade-off matrix ....................................................................... 13

Table 5: Recorded rainfall statistics ................................................................................. 28

Table 6: Operating flows used in time-step model ............................................................ 29

Table 7: Catchment areas ................................................................................................ 32

Table 8: C values calculated according to catchment characteristics ............................... 33

Table 9: C values obtained from adjustment factors ......................................................... 34

Table 10: Options modelled ............................................................................................. 34

Table 11: Modelling results .............................................................................................. 36

Table 12: Option Analysis Criteria and Weighting ............................................................ 37

Table 13: Results of Trade-off Study Workshop ............................................................... 38

Table 14: Sub-Catchment Surface Areas ......................................................................... 45

Table 15: Resulting Time of Concentration for the sub-catchments ................................. 47

Table 16: Resulting Storm Depths, Storm Durations and Rainfall Intensities .................... 47

Table 17: Run-off Coefficients with regard to Surface Slope Classifications ..................... 48

Table 18: Run-off coefficients with regard to Permeability ................................................ 48

Table 19: Run-off coefficient with regard to Vegetation .................................................... 48

Table 20: Adjustment Factors for c1 with regard to Return Period: .................................. 49

Table 21: Resulting c-values ............................................................................................ 49

Table 22: Results of Hydrology Calculations .................................................................... 50

Table 23: Output from the Three Dams Water Course Pre-Development Model .............. 51

Table 24: Output from the Farm Dam Pre-Development Model ........................................ 52

Table 25: "Dirty" Water Channels Concept Design Parameters ....................................... 60

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LIST OF APPENDICES

Appendix A: Geotechnical Report

Appendix B: Waste Classification Report

Appendix C: Conceptual Engineering Drawings

Appendix D: Water Balance Diagram

Appendix E: Trade-off study matrix

Appendix F: Tech Memo Selection for barrier System

05 September 2014 1 12810


1 INTRODUCTION

Kendal power station was commissioned in the mid 1980’s, with a 40 year operating life. The initial

dry ash dump site was designed to have a capacity for the operating life with an eight year

contingency period. The life of the power station has since been upgraded to 60 years and with

some other contributing factors, such as the dry density and the load factor, the initial dry ash

dump is now under capacity. The power station is therefore expected to be decommissioned at

the end of 2053. This means that area to accommodate the additional ash generated during this

operational period will need to be extended. The area to the north of the existing facility will need

to be optimised in order to receive this ash. The Conceptual Engineering designs indicate that ash

may be accommodated here until early 2030 and thereafter an alternative site will need to be

licenced to receive ash up to the end of 2053. The supplementary site up to the end of 2053 is a

separate submission for Environmental Authorisation and is not addressed within this report.

Eskom has appointed Zitholele Consulting (Pty) Ltd (Zitholele) to start with the environmental

impact assessment (EIA) to extend the existing Kendal dry ash dump into the northerly direction.

Zitholele are also responsible for the conceptual engineering design for the options identified and

to recommend a preferred option. These engineering designs will be used to underpin and inform

the EIA.

05 September 2014 2 12810


2 BASIS OF DESIGN

2.1 Assumptions and limitations

The following assumptions were made in developing the conceptual designs presented herewith;

The requirements for the clean and dirty water systems stipulated in Regulation 704 and

Regulation 1560 of the National Water Act, 1998 will be adhered too;

The Pollution Control Dam (PCD) will be a Stormwater Dam; classified in terms of the National

Water Act, 1998 and will operate empty;

The life of the Power station was taken up to the year 2053 excluding final rehabilitation and

closure.

Ashing on an extended lined facility will start in July 2017; this timeline provides for

Authorisation, Further design, tender and construction project steps will be required to

commission the extended facility.

Conveyor system will move radially around existing pivot point and can extend to the required

dimension

The existing area of the ash facility that has been rehabilitated is seen as a final rehabilitation

and no other additional rehabilitation is needed except in the areas where the piggyback

options may be placed.

The Volume of ash per annum stays constant through the whole life of power station.

All volumes, remaining life and timelines are subject to the dump models that are produced.

2.2 Ash characteristics

2.2.1 Grading and Specific gravity

The fly ash varies from silty sand to silty clay using a triangular soil classification chart (US corps of

Engineers). The grading curve exhibits a uniform particle size distribution. According to ASTM

D422-63:

Clay sized particle is larger than 1 micrometre and smaller than 5 micrometre.

Silt sized particle is larger than 5 micrometre and smaller than 75 micrometre

Sand sized particle is larger than 75 micrometre and 425 micrometre

Thus using the above mentioned envelopes the grading of ash are as follows:

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Table 1: Ash grading

Particle size Weathered fly ash Median Fly ash

Clay-sized (%) 5-77 16 14

Silt sized (%) 23-83 60 59

Sand sized (%) 0-64 30 27

D50 (µm) 3-120 23 27.5

Specific Gravity (Gs) 2-2.2 2.2

Data used from : J.S. Mahlaba et al. Fuel 90 (2011)

2.2.2 Stability

The Stability of the final ash dump was not investigated in this phase as the already rehabilitated

slopes are at 1V:5H which has been assessed through an observational approach as stable

slopes. There is however a concern for the advancing ash face which is at angle of repose of

1V:1.2H. On the site visit held on 9 April 2013, some cracks have already formed close to the edge

of the ash disposal facility.

There are measures to mitigate the stability concerns of the ash face on the base liner; a textured

geomembrane can be used, this will increase the interface friction angle between the critical friction

interfaces. Other measures such as terracing the natural ground can also be considered. Further

investigations during the detailed design will have to be done to confirm the stability of the

advancing face when it is placed on the liner.

2.2.3 Permeability

The permeability is largely dependent on the density of the ash on the facility. A value of

11.5 m/year for medium dense ash was assumed. This is the mean of 3 m/y (dense ash) to

20 m/year (loose ash) (Brackley et al, 1987) (6.34*10-7 m/sec). This is required for calculating

seepage pool to the leachate collection system.

2.3 Annual tonnages

The indicated annual tonnage of ash placed on the ash disposal facility is 5500 kt/ annum. This

information is from a previous report (Report nr: 11613601-10981-2) in which Golder Associates

Africa did the development of an industry waste management plan for Eskom where all the waste

type and quantities of all the power stations were considered.

The density of the ash is 850kg/m3 and thus the annual airspace required for the continuous

ashing facility is approximately 6.5 Mm3/ annum. Based on this the remaining life for the continuous

ashing site is determined.

Refer to Eskom document number: 240-71273834 for coal quality used and Eskom Consistent

Data Set (CDS) – 36-623 for remaining life and coal burn plan utilised for coal consumption values.

05 September 2014 4 12810


2.4 Capacity requirements

The existing ash disposal facility was commissioned in the 1980’s for a 40 year life span and an 8

year contingency period. The operating life of the ash disposal facility has since then been

increased to 60 years and with a number of other design and material changes the existing dump

geometry is grossly under capacity.

The total additional capacity required for the ash disposal facility is 291 Mm3 from January 2015

until December 2058. With the current boundary and operating machinery limitations this capacity

will not be reached on the current site. The remaining area between the western and northern

streams does not have sufficient capacity to allow a new facility to be established. If the northern

stream is diverted, the continuous ash dump will only provide 98 Mm3 capacity, requiring a new

“30”year ADF of 193 Mm3. There are current investigations to identify a suitable site for the

remaining ash to be deposited. The size and commissioning date of this new site is dependent on

the Continuous ADF site capacity.

2.5 Dust suppression

The current approach is to use water from the three dam system (Dirty Water Dam, Emergency

Dirty Water Dam and Clean Water Dam) that is located on the Eastern side of the site and then via

irrigation, spray the exposed ash areas to minimise the mobilisation of the ash. Key operational

staff members in Eskom, are of the opinion that the current system is not fulfilling its intended

purpose and that the system will have to be modified so that the ash mobilisation is minimal.

There are a number of techniques and products that can be used such as:

Using a dust suppression chemical

Using a self-propelled spraying system; using pressure to propel itself forward

Upgrading the current system with better controls in place

50mm subsoil cover

The above mentioned options will have to be investigated further in the following phase of design

as there might be a lot of other innovative approaches that can be followed.

2.6 Stormwater Management

The management philosophy for the routing and capturing of stormwater is summarised as follows:

The separation of the runoff draining south-easterly towards the extended ash disposal facility

(i.e. from the area upslope of the ash dump) and runoff generated from within the footprint of

the extended ash dump;

The diversion of “clean” surface runoff generated from the upslope contributing catchments

away from the extended ash disposal facility, thereby isolating the ash dam as “dirty areas” in

accordance with the requirements GN 704 in terms of the National Water Act, 1998;

05 September 2014 5 12810


Containment of all “dirty” surface runoff generated from within the “dirty” catchment,

conveyance and discharge into a dedicated pollution control dam sized in accordance with the

requirements GN 704 in terms of the National Water Act, 1998.

The current and proposed stormwater management philosophy is discussed in depth in Section 1

of this report.

2.7 Stream Diversion

The current extent of the ash dump is bordered by one perennial stream to the east and one non-

perennial stream to the west. The stream to the East flows in a north-westerly direction whilst the

stream to the West flows northerly. The two (2) streams converge north of the existing ash dump.

Flood management philosophy is as follows;

Diversion of the stream forming the eastern border of the ash dump in a northerly direction.

The diversion channel will be sized to match the discharge capacity of the existing clean water

dam spillway upstream of the culvert system across the district road adjoining the R555 and R50

national roads, and the stormwater runoff to the east below the culverts. The stream diversion

design will be carried out in accordance with the provision of the water use licence.

05 September 2014 6 12810


3 ADF OPTIONS MODELLED

The Kendal Power Station Continuous Ashing project had to ensure the continued operations of

the Power Station when considering the options for the extended ashing facility. Any option that

involved the temporary stoppage of production was considered fatally flawed. The advancing face

of the current ashing operations is in a northerly direction and options were considered for this area

only as it did not involve major configuration changes of the conveyors and stackers. The vacant

area to the south of the existing ADF between the rehabilitated area and the National Road R545

was considered as being fatally flawed with respect to aforementioned conditions and was not

considered further as a feasible option.

Two broad options, and the respective sub-options, were considered in determining the air space

required for the extended facility. The broad options are as follows:

Option 1 Minimum Dump – The ADF is positioned between the two streams as previously

described.

Option 2 Maximum Dump – The positioning of the ADF requires the northern stream to be

diverted.

The sub-options for the above includes for a piggybacking option which may be done concurrently

with the current operations or done once the existing footprint is exhausted at the prevailing levels.

3.1 Description of options

3.1.1 Option 1A: Minimum volume

The minimum volume option stays within the original footprint area and is lined from the set

timeline of early 2017 as shown in the figure below. Physical parameters of the options are:

Total Footprint Area: 480 ha

Remaining dump volume: 32.5 Mm3

Remaining life: 5 years from January 2015

Maximum height: 60 m

05 September 2014 7 12810


Lined area: 114 ha

Figure 1: Option 1A

3.1.2 Option 1B & 1C: Minimum volume with staged (1B) or concurrent piggybacking

(1C)

These options are have the same footprint and piggyback area, the definitive difference is the way

in which they are constructed and the specific areas that were lined. The physical parameters of

these options are as follows:

Option 1B & 1C


Remaining dump volume: 47 Mm3



Only Option 1B

Lined area: 275 ha

The method of construction for this option is the footprint will first be totally completed before the

piggyback can be constructed the piggyback area will also be lined in this option.

Only Option 1C

Lined area: 114 ha

05 September 2014 8 12810


The method of construction for this option is the footprint area and the piggyback area will be

constructed concurrently by moving the conveyors back into the required position and not lining the

piggyback area.

Figure 2: Option 1B & 1C

3.1.3 Option 2A: Maximum volume

The maximum volume option falls outside the existing footprint and entails that the north eastern

stream be diverted up against the slope. The physical parameters are:


Remaining dump volume: 98 Mm3 from January 2015



Lined area:224 ha

05 September 2014 9 12810


Figure 3: Option 2A

3.1.4 Option 2B & 2C: Maximum volume with staged (2B) or concurrent piggybacking

(2C)

These options again have the same footprint and piggyback area as well as the stream

diversion.The most significant difference is the way in which they are constructed and the specific

areas that were lined. The physical parameters of these options are as follows:

Option 2B & 2C


Remaining dump volume: 114 Mm3



Only Option 2B

Lined area: 385 ha

The method of construction for this option is the footprint will first be totally completed before the

piggyback can be constructed the piggyback area will also be lined in this option.

05 September 2014 10 12810


Only Option 2C

Lined area: 224 ha

The method of construction for this option is the footprint area and the piggyback area will be

constructed concurrently by moving the conveyors back into the required position and not lining the

piggyback area.

Figure 4: Option 2B & 2C

3.2 Trade-off study for ADF Preferred Option

The objective of the trade-off study is to select a preferred option from those considered (refer 3.1),

with which to go forward to subsequent development stages of the project. Selection of an

alternative does not render it inflexible to improvement opportunities, but instead provides a broad

engineering framework for the development of the ash disposal facility.

3.3 Approach to the trade-off study

Six possible alternatives for the deposition of ash were conceptualised for consideration in the

trade-off study (refer 3.1).

Three broad criteria were selected for analysis of the options, namely:

Environmental influences;

Engineering aspects;

Financial considerations.

05 September 2014 11 12810


Each of these criteria was given a weighting in terms of perceived importance or influence on the

project. Each criterion was also subdivided into sub-categories which were deemed to be relevant

to the project. The table below shows the overall criteria and weighting matrix used for evaluating

and comparing the options:

Table 2: Weightings for the options analysis workshop

ENGINEERING ENVIRONMENTAL

CONSIDERATIONS

FINANCIAL

50% 30.0% 20%

Airspace won 15.0% Level of impact of the

footprint size

15.0% Lowest Cost in terms of R/m3

70%

Does the airspace

model provide

sufficient capacity to

reach the required

timeline of 2020

1.0% Impact on the 30 year

scheme

15.0% Least Total Capital Spent

30%

What is the

complexity of the

operations for the

Spreader and Stacker

20.0% Significance of

encroachment on

current land uses and

natural habitat (Zone

of Influence)

15.0%

What is the

complexity of the

phase construction

5.0% Influence of proximity

to water course

20.0%

Complexity of

disposal facility

geometry

12.0% Complexity of

disposal facility

geometry for closure

5.0%

What is the size and

complexity of the

leachate collection

system

5.0% Level of impact that

the proposed option

has on the ground

water system

20.0%

What is the

complexity of the

Stormwater

management system

on the dump

7.0% Visual impact

assessment of post

closure landform

5.0%

What is the

complexity of the

proposed Stormwater

management system

around the dump

5.0% Impact of exposed

ash body on air

quality

5.0%

05 September 2014 12 12810


What is the impact on

the proposed height

10.0%

What is the impact of

the required capping

system

10.0%

Impact on slope

erosion and resulting

sediment transport

10.0%

A trade-off study workshop was conducted on 9 May 2013 with the following representatives

present:

Table 3: Trade-off Study Workshop Delegates and Designations

ESKOM ZITHOLELE GOLDER

ASSOCIATES

NUT AIRSHED

Andre Kreuiter N Rajasakran D Hattingh Mina Cilliers Dr. Terri Bird

Tobile Bokee Virginia

Ramakuwela

C McLuckie

Eddie Setei Mathys Vosloo Dieli Mesoabi

Warren Kok Gerhard Coetzer

Jan-Dirk Brak Johan Jordaan

Andre Zinn

Francois Marias

Eddie van Wyk

Danie Brink

Warren Aken

3.4 Trade-off study

All delegates present participated in critically discussing each criteria and subcategory. The result

is that the ranking and rating matrix was modified and agreed to by the meeting.

Following the above process, each cell in the matrix was populated by robust debate between all

representatives and disciplines present. Financial criteria were not discussed at the trade-off

workshop because the workshop was seen as a qualitative workshop in where only the technical

feasibility and the environmental impacts were evaluated.

Financial comparison was conducted by analysing capital and closure costs associated with each

option and calculating the cost-benefit in terms of a rate – Rands paid per m3 airspace won or

R/m3. The total costs and the cost benefit rates were shown in the trade-off matrix and rated

accordingly. Costs were determined by measurements from the CADD models and using rates

obtained from previous work done on similar projects.

05 September 2014 13 12810


3.5 Results of the trade-off study

The trade-off study matrix is shown in Appendix E. The results are shown in the table below:

Table 4: Results from the Trade-off matrix

OPTION DESCRIPTION ENVIRONMENTAL ENGINEERING FINANCIAL TOTAL

Weighting

30.0% 50% 20% 100.0%

Option 1A Minimum dump 3.6 Fatally Flawed 0 FF

Option 1B Minimum dump and lined piggybacking (staged piggybacking)

3.25 2.23 1.3 2.35

Option 1C Minimum dump no lined piggyback concurrent piggybacking

2.9 2.61 4.3 3.04

Option 2A Maximum dump 1.75 3.85 4 3.25

Option 2B Maximum dump and lined piggybacking (staged piggybacking)

1.65 2.23 1.7 1.95

Option 2C Maximum dump no lined piggyback concurrent piggybacking

1.5 2.71 4.7 2.75

Option 1A is the preferred option for the environmental influences criteria; this result is a defensible

outcome, as this option has the smallest influence on the surrounding environment. Option 1A is

deemed fatally flawed in the engineering aspects criterion as it does not meet the timeline required.

Option 2A is the preferred option from an engineering perspective. The financial consideration was

based on the principal of the best return on investment; option 2C is the preferred option in this

case.

Taking all these considerations into account and looking at the criteria as a whole, Option 2A is the

preferred option and is recommended to be taken forward to the next phase of design.

05 September 2014 14 12810


4 ADF CONCEPTUAL DESIGN

4.1 Ash disposal

The ash is deposited onto the ash disposal facility by means of a conveyor system. The transfer

conveyors moves the ash from the power station to transfer house E, the emergency ash dump (E-

dump) is located just to the north of the transfer house and was initially designed to provide a

capacity of five days of ashing for emergencies such as maintenance to the overland conveyors

etc.

From transfer house E the ash is transported via the overland conveyors which cross a provincial

road and the north eastern stream to transfer house F. The extendable conveyors transfer the ash

from transfer house F to the shiftable conveyors. The extendable conveyors were initially designed

to extend in the direction of its current bearing as soon as the shiftable conveyors are

perpendicular to the extendable conveyors this method of deposition is called parallel shifting, but

this deposition strategy cannot be implemented due to the new boundary extents of the existing

area.

The shiftable conveyors are the stacker shiftable conveyor (Primary system) and the spreader

shiftable conveyor (Standby system). This is used to deposit the ash onto the ash disposal facility.

The current deposition strategy is to place ash only via radial shifting. In the figure below the layout

and naming for the conveyor system is shown.

Figure 5: Layout of conveyor system used to deposit ash

There are some limitations to these shiftable conveyor systems as the ash is only placed radially.

Some of the limitations are:

The maximum gradient the system can traverse is 1V:20H

As the conveyor cannot bend the advancing face as well as the final face position cannot have any kinks or bends as this meant that the conveyor had a bend in place

The maximum height the of the spreader system is approximately 45m and 62m for the stacker system

05 September 2014 15 12810


The spreader system can only place a front stack where the stacker system can place a front stack and back stack.

Shift intervals needs to be kept to a minimum, between 4-6 months per shift.

The estimated time it would take to get all the authorisation in place as well as providing detailed

designs, tender and construction would take up to September 2015, During this time the ash facility

still needs to continually ash and thus there is still a certain amount of ashing that will take place

while the authorisation is being considered on virgin ground which would then be impractical to line

the area. Refer to drawings 13615205-100-D-D100 and D102 for Options 1A,B and C and

13615205-100-D-D101 and D103 for options 2A,B and C for the section that will be lined.

The deposition strategies are explained in the sections below, the same philosophy was followed

for the various maximum and minimum options numbered A, B and C thus where the deposition

strategy explanations were combined

4.1.1 Option 1A &2A: Minimum & Maximum volume deposition strategy

The Minimum & Maximum volume options will be constructed in the same manner as currently

used. The ash is deposited radially while the stacker and spreader systems are pivoting around its

own fixed point on the extendable conveyors. The split that is designed for is 80:20 split which

means the stacker system is depositing 80% of the ash and the spreader only 20%.

This is currently not the case as the split is closer to 60:40 resulting in the front spreader system

running away from the stacker system. This is a major problem as this means that the backup

system will run its route a lot faster than anticipated with the result that the backup system will

become redundant because there is no designated area left to ash. This would have to be taken

into account in the following phases of design.

4.1.2 Option 1B & 2B: Staged piggyback deposition strategy

These options have the same final footprint as either option 1A or 2A but with another lift

constructed on the already placed ash called a piggyback. The deposition strategy for these

options is to first construct the initial dump which is again either 1A or 2A as described in the

previous section and then move the conveyor system back to where the piggyback section will

start and only then start constructing the piggyback section. It was assumed that the piggyback

would also be lined in these options.

There are some major limitations to this deposition strategy. If the initial option is first constructed

with both the spreader and stacker, the spreader would be on a level approximately 14m lower

than that of the stacker level. This means that as the stacker is moved back to the piggyback

starting point and that the spreader has run its route there is no means of depositing ash except at

the E-dump, which has only five days of storage. This is not sufficient capacity of the required

operation.

The stacker face next to the spreader needs to be shaped to an acceptable gradient so to be able

to pull the stacker shiftable conveyors up the slope. While the spreader is moved into position no

05 September 2014 16 12810


lining can be done as the spreader first needs to move across the area to be lined and ashing still

needs to take place, the spreader would have to be used and ash will be deposited on an unlined

area.

Once both the systems are in place the floor would have to be lined as that was the assumption for

these options. The lining of the piggyback area would have to happen concurrently with the

deposition as stopping the operations on the ash disposal facility is not an option. As the piggyback

liner is constructed the 300mm top soil cover layer placed on the initial option will become a

sacrificial layer as this topsoil is contaminated and other topsoil will be needed for the capping of

the system. These options are very complex and can be impractical to construct.

4.1.3 Option 1C & 2C: Concurrent piggyback deposition strategy

These options again have the same final footprint as either 1A and 2A and another lift the same as

described in the above section is constructed, the only differences are that the piggyback and initial

footprint will be constructed concurrently and that the piggyback area is not lined. It is impractical to

line the piggyback area if the initial footprint is not constructed first.

The stacker system will be moved back to the piggy back starting point while the spreader system

is used to deposit ash at its current position. When the stacker system is in place the spreader

system can be pulled back to the stacker shiftable conveyor position and extended to allow it to

place the full width of the initial frontstack.

Once both systems are in place ashing from both systems can be accommodated. Thus the

spreader will then deposit ash from the initial stacker position with the stacker system placing a

front stack and a back stack on the ash placed by the stacker.

This is a much easier deposition strategy and is fairly straight forward compared to the staged

piggyback strategy.

4.2 Liner system

A waste classification was carried out on the ash and it was classified as a Type 3 waste – low

hazard waste (Report no: JW030/13/D121-Rev3) which requires disposal on a landfill with a Class

C barrier system. A Class C barrier system entails the use of clay or a feasible alternative. Tests

were done on a Geosynthetic Clay Liner (GCL) to determine whether the GCL is compromised due

to cation exchange. The test proved inconclusive on the short term but was recommended not to

be used without doing long term testing. Due to time constraints, a Benonite Enriched Soil (BES)

is proposed as an alternative. Tests were done on similar projects and proved successful. Testing

is currently underway using in-situ soils from the ADF footprint.

05 September 2014 17 12810


Figure 6: Typical Class C Landfill Barrier System

Figure 7: Proposed Class C Barrier System

4.2.1 Liner System Installation

The construction timeline allowed for is twelve months; this includes the earthworks and liner

installation and will start approximately in July 2015 depending on the Environmental Authorisation

for the construction works. The liner system would be constructed with best practice in relation to

manufacturing, transport, storage and installation. The liner system will be installed according to

the manufacturer’s specifications where applicable.

4.2.2 Leachate collection system

As discussed in the liner system (section 4.2) the leachate collection layer is substituted with a

finger drain system. The finger drain system consists of perforated HDPE pipes110mm or 160mm

in diameter placed in 19mm washed stone and wrapped in a geotextile.

Filter sand Washed river sand

6mm Stone 19mm

Stone Leachate collection

drain Protection

geotextile

1.5mm Double

texture

geomembrane

*Clay layers

100mm Filter sand Excavatio

n line 19mm

Stone

Washed river

sand

6mm Stone

Filter sand Subsoil drain

Separation geotextile

05 September 2014 18 12810


The expected horizontal spacing of the drains is 20m. It is best practice to keep the pipes to a

reasonable length. This helps to avoid the severity of blockages if they occur. The finger drain

system has a herringbone layout and daylights into the dirty water drains on either side of the

footprint where it reports in the pollution control dam.

In Option 2A, B and C the leachate collection system of Cell 1 is constructed by having the

collector drains discharge into the dirty water channel every 400 metres. With Cell 2 the existing

stream bed is used as a drain and then has only two discharge points that daylight into the

channel. In the figure below the leachate collection system of Option 2A is shown:

Figure 8: Leachate collection system for Option 2A

4.2.3 Sub-soil drainage system

The subsoil drainage system is installed to prevent hydrostatic pressures on the liner system and

to convey clean ground water away from the site. The subsoil drain consists of a110mm or 160mm

perforated pipe enclosed in 19mm washed stone. The drains are at 20m horizontal spacing.

In Option 2A, B and C the subsoil drains are placed in a parallel layout for Cell 1, collecting the

perched ground water and conveyed to the outer perimeter of the access road outside the dirty

water footprint. Cell 2 has the same pipe system layout as the leachate collection; a main pipe is

placed in the existing river bed and feeder drains are connected to form the herringbone layout.

This option has only one outlet and special care needs to be taken to prevent blockages from

occurring. In the figure below the layout of Option 2A is given:

05 September 2014 19 12810


Figure 9: Layout of the sub-soil drainage system

4.3 Capping system

It is proposed that the current system of topsoiling and grassing be continued on the continuous

ashing site.

Figure 10: Section through rehabilitated ADF

Waste body

Soil saver

300mm Topsoil

Grass/hydroseed

Soil saver

05 September 2014 20 12810


4.4 E-Dump

The Emergency Dump or commonly known as E- Dump” is located between the Power Station and

the existing ash dump, on the Power Station terrace. The facility operates as an emergency

storage of ash if the spreaders or stacker at the dump is inoperable. Once the equipment is

operable, the ash is loaded onto the conveyor reporting to the ADF. Currently, this area is cleared

by means of trucking the ash to the ADF, which will be the emergency method of removal of the

ash in the event that the onloading conveyor is not available, in order to clear the emergency dump

area as quick as possible.

The current area comprises of a reinforced concrete surface bed with an area of approximately

5,500m². The facility includes for a silt-trap and stormwater impoundment facility, approximately

1,000m³ in capacity. The surface bed is currently unbunded. Currently less than 2 days ash

production may be accommodated on the surface bed.

It is proposed to increase the storage capacity of E-dump to accommodate 7 days ash production.

The total footprint area of the surface bed will increase to 31,141 m² and will accommodate a total

volume of 190,000 m3. The area will be bunded within a 1 metre high reinforce concrete wall. The

existing stormwater impoundment dam will not be upgraded. Water from the impoundment facility

will be used in that area for washwater and dust suppression Excess water from this area will

gravitate to the Dirty Water Dam.

The surface bed will be cast in 25 m2 panels, with expansion joints in between the panels. The

expansion joints will comprise of an expandable polypropylene filler and will be sealed off at the

surface with a two component polyurethane sealant. This will render the joint water tight. The

surface beds will be cast with a floor slope of 1 in 200 to facilitate the drainage of stormwater off

the beds.

It is proposed to use fibre reinforced concrete due to the ease of construction. The strength and

durability of the concrete and its functionality will not be compromised by this choice of material.

An access road around the facility will facilitate the removal of ash.

Figure 11: Existing E-Dump

Convey

or to

ADF

Conveyor from

Station

Silt traps

PCD

Emergency ash dump

05 September 2014 21 12810


5 STORMWATER MANAGEMENT PHILOSOPHY

Eskom is busy applying for an Environmental Authorisation to continue disposing of dry ash on

their existing facility located at Kendal Power Station. Conceptual engineering is undertaken at this

stage to underpin the Environmental Assessments. The following structures have been

conceptualised at this stage:

Continuation of ashing on the existing ashing facilities;

Pollution control dam(s) and canals to contain the dirty water runoff;

Stream diversions to facilitate the construction of the continuous ashing facility footprint.

The pollution control dams as indicated above will need to be designed in compliance with

Government Notice 704. More specifically, Clause 6 (d) of the regulation indicates that:

Design, construct, maintain and operate any dirty water system at the mine or activity so that it is

not likely to spill into any clean water system more than once in 50 years.

In order to achieve the above, a continuous model needs to be set-up to simulate the duration as

mentioned in the regulation in order to determine the performance of the proposed stormwater

impoundment infrastructure under normal operating conditions. Following the finalisation of the

model, the water balance may be derived for the facility once all proposed stormwater

infrastructure has been determined.

5.1 OBJECTIVES

In order to understand the stormwater management system and the relevance of each of the

proposed impoundment and conveyance structures, an integrated water balance needs to be

consulted.

This also informs the design of any facility that needs to comply with Government Notice 704.

Kendal Power Station does not have an integrated water balance therefore a conceptual water

balance is being proposed here for the stormwater management system.

5.2 EXISTING STORMWATER MANAGEMENT SYSTEM

Clean water and impacted water are separated within the power station terrace and handled

separately. The clean water reports to the Clean Water Dam and the impacted water reports to the

Dirty Water Dam via a water Crossover Plant and Silt Trap. Surface runoff within the catchment

draining naturally to the above Dirty Water Dams are diverted around it to the Clean Water Dam by

means of a berm, located to the north of the dams, and conveyed via a concrete channel located to

the south of the dams.

The Farm Dam, located to the west of the existing ashing facility, does not form part of Kendal

Power Station’s water balance and is therefore not included in this report.

05 September 2014 22 12810


The current stormwater management is summarised in Figure 12 below and is described in detail thereafter.

Figure 12: Current Stormwater System

The Layout of the current infrastructure is shown on Figure 2.

5.2.1 Power Station Terrace

The power station terrace is predominantly considered to be clean with most of the impacted water

coming from the process drains. Figure 2 below gives an overview of the clean and impacted areas

demarcation on the power station terrace.

05 September 2014 23 12810


Figure 13 : Power Station Clean and Dirty Area Demarcation

5.2.1.1 Impacted Areas

The impacted area within the power station terrace is located centrally, in the vicinity of the Boiler

and Turbine houses. An underground dirty water pipe system, located centrally within the plant,

conveys dirty wash water and some runoff to the cross-over plant, where the water is treated, the

sludge removed and then the treated water is conveyed to the dirty water dam.

The Coal Stockyard is also classified as an impacted area. Concrete channels constructed along

the boundary of the coal stock yard discharge storm water into an existing settling and attenuation

basin located at the coal stockyard. At the settling basin the solids settle out of suspension and the

liquid is then conveyed via a pipe to the Dirty Water Dam.

Stormwater runoff from the emergency dump is contained locally within a pollution control facility.

5.2.1.2 Clean Areas

Clean surface water runoff from the power station terrace is collected in an underground clean

water pipe system, located centrally within the plant, conveying clean storm water runoff to the

cross-over plant then to the Clean Water Dam. Clean storm water runoff that is not collected in the

central underground clean water pipe system is collected in concrete channels constructed along

the boundary of the plant. On the southern side of the plant the water collected in the channels is

discharged and is collected in the Clean Water Dam and on the northern side of the plant the clean

water is discharged into the surrounding veld area.

Clean Veld Discharge

Clean Area to Clean Water Dam

Dirty Area to Dirty Water Dam

05 September 2014 24 12810


Clean Stormwater runoff from the surrounding veld area on the southern side of the plant is caught

by an existing earth berm which directs the storm water runoff to a canal that conveys the water to

the clean water dam. This berm is not currently effective as it has been eroded over time and also

removed in areas for access.

5.2.2 Cross over plant

No information was available for the design capacity of this facility as well as the process flow. All

information contained within the attached Water balance is assumed based on the diameter of the

clarifiers. Percentage of sludge produced was assumed as approximately 2%.

5.2.3 Silt Traps

Before discharging into the Dirty Water Dam, silt is first settled out at the silt trap located in close

proximity to the dam. The silt trap is divided into two compartments to facilitate maintenance.

Each compartment is concrete lined. An adjustable weir controls the outflow from each

compartment to the Dirty Water Dam which is assumed to be designed to attenuate the outflow to

settle out the solids.

Figure 14: Concrete lined silt trap with adjustable overflow weir

No information was provided for this facility. Assumptions on functionality were based on the

footprint area of it.

5.2.4 Dirty Water Dam

The Dirty Water Dam is a licenced facility (DWA Licence No: 04/B20E/BCEG/1048) with an annual

waste throughput of 1,095 Mℓ. The approved size of the facility is not given in the licence.

According to the latest (June 2013) hydrographic survey conducted by Kendal Power Station, the

capacity of this dam was found to be 226,900 m3.

05 September 2014 25 12810


Impacted water is conveyed to the facility at an average rate of 35 ℓ/s via a 1500 mm diameter

concrete pipeline. The current licence for this facility does not require it to be lined. In-situ

weathered granite and felsite underlays the site and acts as a natural barrier.

The dam has an earth wall with a concrete weir spillway which overflows into the Emergency Dirty

Water Dam. A filter drain is located within the dam wall. Upstream and downstream faces of the

dam wall, constructed at slopes of 1:2.5 (v:h), are lined with rip-rap for erosion protection against

wave action. The base of the dam wall is keyed into the in-situ stiff residual material to prevent

against sliding.

Figure 15: Dirty Water Dam with spillway in background

5.2.5 Emergency Dirty Water Dam

The Emergency Dirty Water Dam is a licenced facility to receive a maximum of 55 Mℓ of impacted

water (duration not specified in the Water Use Licence) as an overflow from the Dirty Water Dam

when the Dirty Water Dam is full. The approved size of the facility is not given in the licence.

According to the latest (June 2013) hydrographic survey conducted by Kendal Power Station, the

capacity of this dam was found to be 83,242 m3.

Design and construction of the dam wall is as per the Dirty Water Dam. However, the overflow

spillway is a trapezoidal channel approximately 20 metres wide, lined with reno-mattresses. The

spillway discharges to the Clean Water Dam.

05 September 2014 26 12810


Figure 16: Emergency Dirty Water Dam overflow channel

5.2.6 Clean Water Diversion Berm and Channel

An earth berm was designed to divert clean stormwater run-off around the dirty water dams and

discharge it to a concrete lined channel which discharges to the Clean Water Dam. However, only

remnants of this berm remain due to erosion and removal to open vehicular accesses.

The concrete lined stream diversion trapezoidal channel, approximately 23 metres wide at the top,

discharges to the Clean Water Dam. In order to prevent erosion at the discharge point to the

Clean Water Dam, a still basin was constructed at the discharged end. This drains to the dam via

a reno-mattress lined chute.

5.2.7 Clean Water Dam

The Clean Water Dam is a licenced facility and is contained within the same licence as referenced

previously. Design and construction of the dam is the same as the Dirty Water and Emergency

Dirty Water Dams. It is licenced to have a storage capacity of 90 Mℓ. According to the latest (June

2013) hydrographic survey conducted by Kendal Power Station, the capacity of this dam was

found to be 87,262 m3. A concrete overflow spillway discharges to the natural watercourse.

5.2.8 Coal Stockyard Attenuation Basin

The coal stockyard is located to the south east of the power station terrace and covers an area of

approximately 48 hectares. This area comprises of the following infrastructure:

Coal stockpile

Concrete lined channels intercepting stormwater run-off and discharging it to the settling basin

Settling and attenuation basin with a combined capacity of 10 Mℓ

05 September 2014 27 12810


The surface runoff is conveyed via concrete lined open drains located to the west of the coal

stockyard. Two sets of drains, one running in a southern direction and the other northerly, drain to

an attenuation dam located centrally to the western boundary of the site.

Upstream of the attenuation basin is a settling basin. The settling basin is concrete lined and

facilitates the settlement of solids mobilised from the coal during the storm event. The combined

structure is not sized in compliance with the requirements of GN 704 and excess flow reports to the

Dirty Water Dam via a 1.2 metre diameter concrete pipe.

Mixing of water in the settling basin and attenuation basin is allowed in the current design. This will

need to be modified. Excess flow exits the facility via the settling basin. It is proposed that the

excess flow exits the facility via the attenuation basin.

5.2.9 E-dump Stormwater Management

“E- Dump” is located between the Power Station and the existing ash dump, on the Power Station

terrace. The facility operates as an emergency storage of ash if the spreaders or stacker at the

dump is inoperable. The current area comprises of a reinforced concrete surface bed with an area

of approximately 5,500m². The facility includes for a silt-trap and stormwater impoundment facility,

approximately 1,000m³ in capacity. The impoundment facility has not been designed to comply

with GN704 and will need to be addressed when the area is expanded.

5.2.10 Pumps and Pipelines

The pumps serving the Dirty Water Dam, Emergency Dam and Clean Water Dam are located

downstream of the Clean Water Dam. These pumps deliver water to the ash dump, for dust

suppression, and to the power station for wash water and ash conditioning. Ten (10) pumpsets are

provided for this of which four (4) are dedicated to the ash dump and the remainder to wash water

at the power station terrace. The combined flow to the ash dump is 60 ℓ/s on average and 80 ℓ/s

on average to the power station terrace.

Two dedicated sets of steel pipelines leave the pump station, a 150mm diameter in a westerly

direction to the ash dump and a 350mm diameter in a north-easterly direction to the power station

terrace. Currently, the latter pipeline is in the process of being replaced. Both pipelines, painted in

conspicuous colours as per the conditions of the WUL, are located above ground and fixed onto

concrete plinths.

5.3 OBJECTIVES OF PROPOSED STORMWATER MANAGEMENT SYSTEM

The new system will need to manage the stormwater run-off from the Ash Disposal Facility (ADF)

as well as manage the impacts that this has on the existing three dam system. All dams proposed

on this system will need to be in compliance with GN704. This will entail the following:

Confine any unpolluted water to a clean water system, away from any dirty area;

05 September 2014 28 12810


Design, construct, maintain and operate any clean water system so that it is unlikely to spill into

any dirty water system more than once in 50 years;

Collect the water arising within any dirty area, including seepage;

Design, construct and maintain all stormwater systems in such a manner as to guarantee the

serviceability of such conveyances for flows up to and including those arising as a result of the

maximum flood with and average period of recurrence on once in 50 years;

Design, construct, maintain and operate any dirty water system so that it is unlikely to spill into

any clean water system more than once in 50 years.

In order to determine the optimum solution for stormwater management around the extended ADF

to meet the above objectives, various possible options will need to be considered. These options

are modelled and trade-off against each other in order to find the “go-forward” option.

5.4 MODELING APPROACH AND ASSUMPTIONS

A fifty (50) year daily time-step model was built using Microsoft Excel for the different scenarios

and options as described in the subsequent sections of this report.

5.4.1 Rainfall data

The model takes into consideration daily recorded rainfall closest to the site under investigation.

An uninterrupted data set could not be found for Kendal so the one for Cologne in Mpumalanga

(Station No. 0478008_W) was used to make-up the required rainfall data. Cologne is located

approximately six (6) kilometres south-east of Kendal PS. Data for the period May 1963 to August

2000 was used from Cologne. Recorded data for Kendal PS was used for the period September

2000 to May 2013. The combined data set represents fifty (50) years of recorded rainfall.

The table below gives the statistics of the data set used.

Table 5: Recorded rainfall statistics

Recurrence Interval

(1 in)

1 Day Rainfall

Depth (Cologne)

1 Day Rainfall

Depth Range (mm)

No. of Occurrences

in Data Set

2 54 50 - 65 24

5 74 66 – 85 16

10 90 86 – 100 4

20 106 101 – 124 1

50 131* 125 - 135 1

* A rainfall value of 106mm was changed to 131mm to simulate the 50 year 24 hour rainfall depth

05 September 2014 29 12810


5.4.2 Operating flows

Table 6: Operating flows used in time-step model

Use Quality Description Ml/a m3/d

Process Waste Dirty Power station to

dirty water dam

4350 11918

Process Waste Clean Power station to

clean water dam

88 241

Washwater Dirty Dirty Water Dam to

SSC + Washwater

1570 4301

Ash Conditioning Dirty Dirty Water Dam to

Ash Conditioning

630 1726

5.4.3 Description of catchment areas at ADF

The connectivity of the catchment areas and the dams that they drain to are captured in the layout

drawings attached to the appendices. Brief descriptions are given below for each of the catchment

areas envisaged in the model.

5.4.3.1 Open Ash Areas

The open ash area is the most sensitive variable in the model. It was for this reason that different

Scenarios for this area were modelled. For all Scenarios, the open ash area is the area between

the toe of the standby stacker up to the crest of the main stacker. This run-off goes to the

proposed Dam 1.

Figure 17: Open Ash Area on ADF

OPEN ASH AREA

05 September 2014 30 12810


5.4.3.2 Rehabilitated Areas

The rehabilitated area is the top-soiled and grassed area which is behind the crest of the main

stacker. This run-off goes to Dams 2, 3 and 4.

Figure 18: Rehabilitated Area on ADF

5.4.3.3 Transfer House F and Surrounding Areas

The slab that the extendable conveyor is fixed to, from Transfer House F to the dump, is washed

on a daily basis. This water drains to two unlined earth dams located adjacent to Transfer House F

at the base of the embankment. This run-off is proposed to drain to Dam 5 in future which will be

located at a lower elevation on the existing stream. This stream is proposed to be diverted.

A portion of the rehabilitated area also drains to this area and mixes with the impacted run-off. It is

recommended to construct a diversion channel alongside the road at Transfer House F and divert

this clean run-off to Dam 4.

Figure 19: Transfer House F

REHABILITATED AREA

05 September 2014 31 12810


Figure 20: Stormwater Management at Transfer House F

5.4.3.4 Ash conveyor from E-dump

The conveyor route between E-dump and Transfer House F has its lowest point as it crosses the

national road. During abnormal conditioning of the ash, a slurry forms and drains to this point. It is

recommended that this area be concrete lined and a “V” drain be constructed from this point to

Dam 5, downstream of this point, to facilitate washing.

Figure 21: Maintenance at Low Point on Conveyor

DAMS HANDLING RUN-OFF

FROM TRANSFER HOUSE F

PROPOSED POSITION

OF CLEAN DAM 4 PROPOSED CUT-OFF DRAIN TO CHANNEL CLEAN

RUN-OFF AWAY FROM TRANSFER HOUSE F

TRANSFER HOUSE F

TRANSFER HOUSE F

E-DUMP

LOW POINT ON CONVEYOR AT

NATIONAL ROAD CROSSING

PROPOSED POSITION

OF DIRTY DAM 5 PROPOSED CHANNEL TO

FACILITATE CLEANING

AT CONVEYOR LOW

POINT

05 September 2014 32 12810


5.4.4 Stormwater runoff calculations

The steps for calculation of stormwater runoff volumes for areas and dams are given below.

Step 1: Catchment areas are calculated for each area and dam.

Table 7: Catchment areas

Catchment Hectares

Power Station Clean Area 75.5

Power Station Dirty Area 1.1

Coal Stockyard 48

Dirty Water Dam 15

Emergency Dirty Water Dam

5

Clean Water Dam 330

Dam 3 114

Dam 2 328

Dam 4 47

Dam 1 82

Dam 5 11

Step 2: The Run-off coefficient (C) for each catchment area is calculated. The c-values are

calculated as per the SANRAL Drainage Manual. Table 3.7 in the manual provides a description of

recommended values of C.

The recommended values are selected according to 3 characteristics of the catchment under

consideration. They are namely:-

a) Surface slope classification

b) Permeability classification

c) Vegetation classification

A C-value for each characteristic is selected and the sum of which is the overall C-value, known as

C1, for a particular catchment. C1 is then multiplied by adjustment factors for each return period, i.e.

2, 5, 10, 20, 50, 100 years. The return period for each storm event was determined using the

rainfall depth and comparing it against the one day depth as contained in Table 5. Table 3.8 in the

aforementioned Manual provides adjustment factors for the value of C1.

05 September 2014 33 12810


Table 8: C values calculated according to catchment characteristics

Catchment Area (m²)

Surface Slope Classification

Cs Permeability Classification

Cp Vegetation Classification

Cv C1

Power Station Clean Area

755 000 Flat Areas (3-10%)

0.08 Semi-permeable

0.16 Grasslands 0.21 0.45

Power Station Dirty Area

11 000 Flat Areas (3-10%)

0.08 Impermeable 0.26 No vegetation

0.28 0.62

Coal Stockyard

480 000 Hilly (10-30%)

0.16 Semi-permeable

0.16 No vegetation

0.28 0.6

Dirty Water Dam

150 000 Flat Areas (3-10%)

0.08 Permeable 0.08 Grasslands 0.21 0.37

Emergency Dirty Water Dam

50 000 Flat Areas (3-10%)


Clean Water Dam

3 300 000

Flat Areas (3-10%)


Dam 1 820 000 Flat Areas (3-10%)

0.08 Permeable 0.08 No vegetation

0.28 0.44

Dam 2 3 280 000

Flat Areas (3-10%)


0.28 0.44

Dam 3 1 140 000

Flat Areas (3-10%)


0.28 0.44

Dam 4 470 000 Flat Areas (3-10%)


0.28 0.44

Dam 5 110 000 Flat Areas (3-10%)


0.28 0.44

05 September 2014 34 12810


Table 9: C values obtained from adjustment factors

RP PS

Clean Area

PS Dirty Area

CSY Dirty

Water Dam

Emerg Dirty

Water Dam

Clean Water Dam

Dam 1

Dam 2

Dam 3

Dam 4

Dam 5

0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

1 0.21 0.23 0.26 0.18 0.18 0.18 0.23 0.23 0.19 0.19 0.19

2 0.23 0.31 0.30 0.19 0.19 0.19 0.26 0.26 0.22 0.22 0.22

5 0.25 0.34 0.33 0.20 0.20 0.20 0.28 0.28 0.24 0.24 0.24

10 0.27 0.37 0.36 0.22 0.22 0.22 0.30 0.30 0.26 0.26 0.26

20 0.30 0.42 0.40 0.25 0.25 0.25 0.33 0.33 0.29 0.29 0.29

50 0.37 0.51 0.50 0.31 0.31 0.31 0.40 0.40 0.37 0.37 0.37

100 0.45 0.62 0.60 0.37 0.37 0.37 0.48 0.48 0.44 0.44 0.44

Step 3: The adjusted C-values for Dam 1 is increased by 3.5% to take leachate into account. Only

half the facility will be line as this meets the requirements of the prevailing legislation therefore an

amount of 3.5 percent was utilised opposed to a norm of 7 percent.

Step 4: Rainfall, catchment area and C-values are multiplied to obtain a volume of runoff for each

area and dam.

5.5 OPTIONS MODELLED

Nineteen (19) Options under three (3) scenarios were modelled. The table below describes each

of the options.

Table 10: Options modelled

OPTIONS MODELLED

SCENARIO 1: Minimum open ash working area = 63 hectares

SCENARIO 2: Optimum open ash working area = 82 hectares

SCENARIO 3: Piggyback open ash working area = 98 hectares

OPTION 1 OPTION 2 OPTION 3 OPTION 4

• Status Quo

• Proposed system – Five (5) new dams.



• All dams considered to be dirty. Spills from Dams 2, 3, 4 & 5 over flow to Dam 1.

• Dam 1 & 5 considered dirty. Dam 2, 3 and 4 considered clean.

• Dam 1 & 5 considered dirty. Dam 2, 3 and 4 considered clean.

• Dust suppression from • Dust suppression from • Dust suppression from

05 September 2014 35 12810


Dam 1, DWD & EDWD. Dam 1, DWD & EDWD. Dam 1, DWD & EDWD.

• Spills from e-dump overflow to DWD.



• Upper catchment not bypassed. (Total catchment area = 330 hectares)

• Spills from Dam 5 over flow to Dam 1.

• Spills from Dam 5 over flow to Dam 1.

• No irrigation to rehabbed areas.

• Upper catchment not bypassed. (Total catchment area = 330 hectares)

• Upper catchment bypassed. (Total catchment area = 4 hectares)

• Irrigation from existing CWD to power station terrace. (20mm)

• Irrigation to rehabbed areas. (20mm)

• Irrigation to rehabbed areas. (20mm)

Dam capacities for Dams 2, 3 & 4 determined for 50 year storm event. Dam 2 = 166,000 m

3, Dam 3 =

57,000 m3, Dam 4 = 32,000

m3

Irrigation from existing CWD to power station terrace. (20mm)

Dam capacities for Dams 2, 3 & 4 sized to spill once in 50 years.

Resultant Dam 1 sized to GN704 to only spill once in 50 years.

Dam capacities for Dams 2, 3 & 4 sized to spill once in 50 years.



CWD becomes process dam, i.e. EDWD spills into CWD

OPTION 2a OPTION 3a OPTION 4a

EDWD spills into Dam 5, Dam 5 spills into Dam 1

EDWD spills into Dam 5, Dam 5 spills into Dam 1

CWD spills into Dam 5, Dam 5 spills into Dam 1

OPTION 2b OPTION 3b OPTION 4b

Water treatment plant at EDWD

Water treatment plant at EDWD

Water treatment plant at CWD

5.6 MODELLING RESULTS

The results of the modelling exercise are contained in Table 10 below.

05 September 2014 36 12810


Table 11: Modelling results

OPTIONS

2A 2B 3A 3B 4A 4B

SCEN

AR

IO 1

Dam 1 57,600,000 371,500 10,623,000 312,000 22,388,500 390,000

Dam 2 166,000 166,000 282,000 282,000 282,000 282,000

Dam 3 57,000 57,000 76,000 76,000 76,000 76,000

Dam 4 32,000 32,000 32,000 32,000 32,000 32,000

Dam 5 76,000 76,000 76,000 76,000 76,000 76,000

WTP(ML/d

)ay)

0 12.25 0 2.75 0 8.75

SCEN

AR

IO 2

Dam 1 17,368,623 371,500 120,000 120,000 297,000 120,000

Dam 2 166,000 166,000 257,000 257,000 257,000 257,000

Dam 3 57,000 57,000 76,000 76,000 76,000 76,000

Dam 4 32,000 32,000 32,000 32,000 32,000 32,000

Dam 5 76,000 76,000 76,000 76,000 76,000 76,000

WTP(ML/d

)ay)

0 9.25 0 0 0 1

SCEN

AR

IO 3

Dam 1 1,150,000 371,500 111,000 111,000 200,000 111,000

Dam 2 166,000 166,000 257,000 257,000 257,000 257,000

Dam 3 57,000 57,000 76,000 76,000 76,000 76,000

Dam 4 32,000 32,000 32,000 32,000 32,000 32,000

Dam 5 76,000 76,000 76,000 76,000 76,000 76,000

WTP(ML/d

)ay)

0 8.5 0 0 0 1

5.7 TRADE-OFF ASSESSMENT

The objective of the trade-off study is to select a preferred option from those considered in Section

5.5, with which to go forward to subsequent development stages of the project. Selection of an

alternative does not render it inflexible to improvement opportunities, but instead provides a broad

engineering framework for the development of the ash disposal facility. The nineteen (19) possible

alternatives for the stormwater management system around the ADF were conceptualised for

consideration in the trade-off study. Three broad criteria were selected for analysis of the options,

namely:

Environmental and social influences;

Engineering aspects;

Financial considerations.

The following approach was adopted:

Each of the above criteria was given a weighting in terms of perceived importance or

influence on the project.

05 September 2014 37 12810


Each criterion was also sub-divided into sub-categories which were deemed to be relevant

to the project. Table 12 below shows the overall criteria and weighting matrix used for

evaluating and comparing the options:

Table 12: Option Analysis Criteria and Weighting

Category Description Category Weight

Engineering (Overall Weight = 35%)

No and size of dams required 10.0%

What is the complexity of the proposed Stormwater management system

around the dump

7.5%

Ease of maintenance of stormwater management infrastructure 7.5%

Complexity of operational philosophy 12.5%

Experienced human resources to run facility (controlled release, water

treatment plant)

10.0%

Infrastructure requirements (more pipelines to divert spillages, erosion control

at multiple discharge points, etc.)

10.0%

Air space lost due to larger PCD requirements 12.5%

Management of excess water (dust suppression, irrigation and WTP

optimisation)

10.0%

Dam safety requirements due to higher dam walls 5.0%

Security risk to stormwater management equipment 5.0%

Construction and monitoring complexity to ensure clean and dirty water

separation

10.0%

Environmental (Overall Weight = 35%)

Encroachment on wetlands and floodlines 15.0%

Level of impact that the proposed option has on the surface water system 20.0%

Regulatory process risks 15.0%

Groundwater impacts 10.0%

Compliance with GN704 30.0%

Multiple points of discharge from dams to receiving waters 10.0%

Financial (Overall Weight = 30%)

Net Present Value (Rands) 100%

A workshop was convened with all stakeholders involved in this project. Delegates present at this

workshop participated in critically discussing each criteria and sub-category. The result is that the

ranking and rating matrix was modified and agreed to by the meeting.

Following the above process, each cell in the matrix was populated by robust debate between all

representatives and disciplines present. Financial criteria were not discussed at the trade-off

workshop because the workshop was seen as a qualitative workshop in where only the technical

feasibility and the environmental impacts were evaluated.

05 September 2014 38 12810


Financial comparison was conducted by analysing net present value of the capital costs associated

with each option. The total costs and the cost benefit rates were shown in the trade-off matrix and

rated accordingly. Costs were determined by measurements from the CAD models and using rates

obtained from previous work done on similar projects.

The summary of the results of the rating and ranking workshop are shown in Table 13. Full details

for all criteria are given in the appendices.

Table 13: Results of Trade-off Study Workshop

OPTION DESCRIPTION ENVIRONMENTAL CONSIDERATIONS

TECHNICAL FINANCIAL

Weighting 40.0% 30% 30% Score Rank

SCENARIO 0 STATUS QUO

0.00 0.00 5.00 0.00 14

SCEN

AR

IO 1

OPTION 2A 2.95 0.00 0.10 0.00 14

OPTION 2B 2.95 1.98 0.10 1.80 13

OPTION 3A 3.85 0.00 0.10 0.00 14

OPTION 3B 3.70 2.28 0.10 2.19 10

OPTION 4A 3.90 0.00 0.10 0.00 14

OPTION 4B 3.60 2.38 0.10 2.18 11

SCEN

AR

IO 2

OPTION 2A 3.10 0.00 0.10 0.00 14

OPTION 2B 2.95 2.63 0.10 2.00 12

OPTION 3A 4.30 3.53 4.93 4.26 4

OPTION 3B 4.30 3.53 4.98 4.27 3

OPTION 4A 4.20 2.80 4.35 3.83 6

OPTION 4B 3.90 2.88 0.10 2.45 9

SCEN

AR

IO 3

OPTION 2A 4.20 0.00 1.92 0.00 14

OPTION 2B 4.20 2.63 0.10 2.50 8

OPTION 3A 4.60 3.33 4.95 4.32 2

OPTION 3B 4.60 3.33 5.00 4.34 1

OPTION 4A 4.30 3.25 4.83 4.14 5

OPTION 4B 4.30 3.08 0.10 2.67 7

Option 3B, Scenario 3 is the preferred option following the technical, environmental and financial

scoring. However, this Scenario assumes that piggybacking is feasible. This has not been proven

as yet and cannot be considered at this stage. If proven feasible in future, the proposed

infrastructure will need to be sized adequately to accommodate the potential flows during this

Scenario. Since Scenario 3 is the best case scenario, it is proven that the infrastructure

implemented under the other Scenarios will accommodate flow generated under Scenario 3.

05 September 2014 39 12810


Taking all these considerations into account and looking at the criteria as a whole, Option 3B

Scenario 2 is the preferred option and is recommended to be taken forward to the next phase of

design.

5.8 PROPOSED INFRASTRUCTURE

Option 3B Scenario 2 is the preferred option following the Trade-off Assessment and will be taken

forward to the Conceptual Design Phase. The proposed infrastructure is detailed below. Layout

drawings of the proposed infrastructure for the options modelled as well as the preferred option are

attached to the appendices.

5.8.1 Pollution Control Dams

The two (2) existing pollution control dams, dirty water dam and emergency dirty water dam,

remain in place. Additional Dams 1 and 5 are proposed. The capacity of Dams 1 and 5 is 120 Mℓ

and 76 Mℓ (+ 2 days storage for dust suppression water) respectively. The performance (dam

levels) of these four pollution control dams for the fifty (50) year simulation period is shown on the

respective graphs below.

Figure 22: Dirty Water Dam Levels for Simulation Period

0%

20%

40%

60%

80%

100%

120%

16

-May

-63

16

-May

-66

16

-May

-69

16

-May

-72

16

-May

-75

16

-May

-78

16

-May

-81

16

-May

-84

16

-May

-87

16

-May

-90

16

-May

-93

16

-May

-96

16

-May

-99

16

-May

-02

16

-May

-05

16

-May

-08

16

-May

-11

Dam Level Dam Max Capacity

05 September 2014 40 12810


0%

20%

40%

60%

80%

100%

120%


Figure 23: Emergency Dirty Water Dam Levels for Simulation Period

Figure 24: Proposed Dam 1 Levels for Simulation Period

0%

20%

40%

60%

80%

100%

120%


05 September 2014 41 12810



5.8.2 Clean Water Dams

In addition to the existing Clean Water Dam, three (3) more dams are proposed for clean water

containment. These dams will be operated on a controlled release principle which is based on the

receiving water quality. It is not the intention to impound clean water if not required provided that

the discharge quality is acceptable. If the water in these dams are deemed impacted, it will be

irrigated onto the areas that it emanated from or utilised in the power station water balance if

possible.

The following are the proposed Clean Water Dams:

Dam 2 257 Mℓ

Dam 3 76 Mℓ

Dam 4 32 Mℓ + two day storage for irrigation water

The performance (dam levels) of these four (including the existing Clean Water Dam) clean water

dams for the fifty (50) year simulation period is shown on the respective graphs below

0%

20%

40%

60%

80%

100%

120%


05 September 2014 42 12810


0%

20%

40%

60%

80%

100%

120%

16

-May

-63

16

-May

-66

16

-May

-69

16

-May

-72

16

-May

-75

16

-May

-78

16

-May

-81

16

-May

-84

16

-May

-87

16

-May

-90

16

-May

-93

16

-May

-96

16

-May

-99

16

-May

-02

16

-May

-05

16

-May

-08

16

-May

-11


Figure 26: Existing Clean Water Dam Levels for Simulation Period


0%

20%

40%

60%

80%

100%

120%

16

-May

-63

16

-May

-66

16

-May

-69

16

-May

-72

16

-May

-75

16

-May

-78

16

-May

-81

16

-May

-84

16

-May

-87

16

-May

-90

16

-May

-93

16

-May

-96

16

-May

-99

16

-May

-02

16

-May

-05

16

-May

-08

16

-May

-11


05 September 2014 43 12810




0%

20%

40%

60%

80%

100%

120%


0%

20%

40%

60%

80%

100%

120%


05 September 2014 44 12810


5.8.3 Toe Paddocks

The slope available to facilitate self-cleansing velocities in the western dirty water channel

discharging to the pollution control Dam 1 could not be achieved. In order to prevent siltation within

the channels and reduce the required velocities, it is proposed that paddocks be constructed at the

toe of the advancing face to intercept run-off from the disposal facility and allow this to overflow to

the discharge channels. The temporary structures will facilitate siltation. It is envisaged that the

paddocks will be constructed from ash and will be located on top of the lined portion of the facility.

The paddocks will be covered over when dozing the side slope down to the final 1:5 slope for

rehabilitation of that section of the facility.

Figure 30: Positioning of Temporary Toe Paddocks

5.8.4 Storage Reservoirs

Apart from capturing runoff from its respective areas, dust suppression and irrigation water will be

stored in Dam 5 and Dam 4 respectively. It is proposed that additional two days storage be

allowed for in the capacity of these dams.

5.8.5 Conveyance infrastructure (pumps, pipelines and channels)

The proposed operational philosophy around stormwater management will involve the construction

of new infrastructure. Apart from the dams as mentioned in the previous sections of this report,

conveyance infrastructure will be required for the following reasons:

Conveyance of spills from one facility to the next;

Conveyance of dust suppression water from the relevant dams to the dedicated storage

reservoirs;

Conveyance of rehabilitated irrigation water from the relevant dams to the dedicated storage

reservoirs;

Dust suppression from storage reservoir to open ash area of the ADF;

Irrigation from storage reservoir to the rehabilitated area of the ADF;

Irrigation of the power station terrace grassed areas from the Clean Water Dam

CLEAN WATER CUT-OFF BERM

ACCESS ROAD

CHANNEL TO PCD

TEMPORARY TOE PADDOCK

CONSTRUCTED FROM ASH

ON TOP OF LINER

ADVANCING FACE OF ADF

REHABILITATED FACE OF ADF

ASH BODY

LINER UP TO DIRTY

WATER CHANNEL

05 September 2014 45 12810


5.9 1 IN 100 YEAR FLOODLINES

5.9.1 Methodology

Delineation of Catchment Areas

The 0.5m interval contours were obtained from the topographical survey. The contours and 1 in 50

000 topographical maps were studied to divide the area into smaller sub-catchments. Water

courses, streams and rivers were identified using the maps. Two separate water courses were

identified, namely the Three Dams Water Course and the Farm Dam Water Course. The surface

area of each sub-catchment was determined as well as the ground cover and the average slopes

and distances of overland flow and average slopes of water courses. The surface area of the sub-

catchments are shown in Table 14.

Table 14: Sub-Catchment Surface Areas

Water Course Sub-catchment Surface Area (ha)

Three Dam System A 436

Three Dam System B 408

Farm Dam System C 3 617

Flood Hydrology

The Rational Method as described in the document Drainage Manual, Sixth Edition (2013) as

published by SANRAL (South African National Roads Agency Limited) was used to determine the

magnitude of the 1 in 100 year floods.

The peak flow rate is calculated with the following formula:

Where Q = peak flow (m3/s)

c = run-off coefficient (dimensionless)

i = average rainfall intensity over the catchment (mm/hour)

A = effective area of catchment (km2)

3.6 = conversion factor

05 September 2014 46 12810


Rainfall data was obtained for the Cologne rainfall station (Number 0478008_W). The rainfall

record for this station is 97 years long. The rainfall station is located approximately 3.7km west of

Kendal Power Station. The Mean Annual Precipitation (MAP) was found to be 675 mm/year.

The Time of Concentration was determined for each sub-catchment in accordance with the

following formulas. Refer to Drainage Manual, Sixth Edition (2013):

For overland flow:

Where Tc = time of concentration (hours)

r = roughness coefficient = 0.4 for medium grass cover

L = length of the catchment from the boundary to where the flood needs to be

recorded (km)

S = slope of the catchment (m/m)

For defined water courses:

Where Tc = time of concentration (hours)

r = roughness coefficient = 0.4 for medium grass cover

L = length of the water course from the boundary to where the flood needs to be

recorded (km)

S = average slope of the catchment (m/m)

The total time of concentration is the sum of the time of concentration for overland flow plus the

time of concentration for water course flow, namely Tc1 plus Tc2. The time of concentration for

overland flow, flow in water courses and the total time of concentration is presented in Table 15.

05 September 2014 47 12810


Table 15: Resulting Time of Concentration for the sub-catchments

Water Course Sub-catchment Calculated time

of

concentration

for overland

flow (minutes)

Calculated time

of

concentration

for flow in a

water course

(minutes)

Total Time of

Concentration

(minutes)

Three Dam

System

A 7 22 29

Three Dam

System

A and B

together

7 66 73

Farm Dam

System

C 3 173 176

The storm duration is taken as the total time of concentration. The rainfall intensity is determined

from Figure 3.8 in the Drainage Manual, Sixth Edition (2013) as published by SANRAL.

The resulting storm depths, storm durations and rainfall intensities are shown in Table 16.

Table 16: Resulting Storm Depths, Storm Durations and Rainfall Intensities

Water Course Sub-catchment Storm Depth

(mm)

Storm Duration

(hours)

Rainfall

Intensity, i

(mm/hrs)

Three Dam

System

A 75 0.49 152

Three Dam

System

A and B

together

130 1.22 106

Farm Dam

System

C 160 2.93 55

The Run-off coefficient (c) for each sub-catchment must now be calculated.

The recommended values are selected according to 3 characteristics of the catchment under

consideration, namely:-

a) Surface slope classification

b) Permeability classification

c) Vegetation classification

05 September 2014 48 12810


The run-off coefficients with regard to surface slope classification are presented in Table 17.

Table 17: Run-off Coefficients with regard to Surface Slope Classifications

Description Run-off coefficient (cs) for rural

areas with an MAP between 600

and 900mm/year

Steep areas (slopes > 30%) 0.03

Hilly (10 to 30%) 0.08

Flat areas (3 to 10%) 0.16

Vleis and pans (slopes < 3%) 0.26

The run-off coefficients with regard to permeability are presented in Table 18.

Table 18: Run-off coefficients with regard to Permeability

Description Run-off coefficient (cp) for rural


and 900mm/year

Very permeable 0.04

Permeable 0.08

Semi-impermeable 0.16

Impermeable 0.26

The run-off coefficients with regard to vegetation classification are presented in Table 19.

Table 19: Run-off coefficient with regard to Vegetation

Description Run-off coefficient (cv) for rural


and 900mm/year

Thick bush and plantation 0.04

Light bush and farmlands 0.11

Grasslands 0.21

No vegetation 0.28

The overall c-value for a catchment, also known as the c1 is the sum of the c-values for the three

characteristics, as shown by the following equation:

Where c1 = Overall run-off coefficient for a catchment

05 September 2014 49 12810


cs = Run-off coefficient with regard to slope

cp = Run-off coefficient with regard to permeability

cv = Run-off coefficient with regard to vegetation

The overall run-off coefficient c1 is multiplied by an adjustment factor with regard to the return

period, as presented in Table 20:

Table 20: Adjustment Factors for c1 with regard to Return Period:

Return Period (years) 2 5 10 20 50 100

Factor (Ft) for steep

and impermeable

catchments

0.75 0.80 0.85 0.90 0.95 1.00

Factor (Ft) for flat and

permeable

catchments

0.50 0.55 0.60 0.67 0.83 1.00

The magnitude of the 1 in 100 year flood can now be determined for exact locations within the two

water courses. Generally, the larger a catchment area contributing to the run-off at a specific point,

the larger the magnitude of the flood at that point will be.

The resulting c-values are presented in Table 21.

Table 21: Resulting c-values

Description c-value

cs 0.26

cp 0.12

cv 0.16

c1 0.54

The magnitude of the 1 in 100 year flood can now be determined for exact locations within water

courses, streams and rivers.

The results of the hydrology calculations are presented in Table 22.

05 September 2014 50 12810


Table 22: Results of Hydrology Calculations

Water Course

Catchment or Sub-Catchment

Area (ha)

i (mm/hours)

c1-value Maximum 1 in 100 Year

Flood (m3/s)

Three Dam

System

A 436 152 0.54 99.3

Three Dam

System

A and B

together

408 106 0.54 134.4

Farm Dam

System

C 3 617 55 0.54 296.8

Hydraulic Simulation

The 0.5m interval contours were obtained from the topographical survey. The software Autodesk

Civil3D 2013 was used to extract longitudinal sections of the two water courses. Cross sections

were also extracted at intervals of approximately 250m. The length of typical cross sections was

approximately 1.2km.

The geometry was imported into the software HEC-RAS, a backwater model, which was developed

by the United States Army Corps of Engineers.

A Manning’s “n” hydraulic roughness value of 0.045 was assumed for all sections, which

corresponds to natural straight water courses.

Normal water flow depths were assumed for the upstream position and downstream position of the

river section. Normal flow depth here means the calculated water depth for a certain roughness, a

certain flow and a certain longitudinal slope. The software does the hydraulic calculations for each

cross section. The output from the software are flow depths, flow velocities, cross sectional area,

wetted perimeter etc. Four separate models were produced, namely:

Three Dam Water Course Pre-Development

Three Dam Water Course Post-Development

Farm Dam Water Course Pre-Development

Farm Dam Water Course Post-Development

The outputs from the Three Dams Water Course Pre-Development Model are presented in Table

23. An output longitudinal section of this model is presented in Figure 5-11.

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Table 23: Output from the Three Dams Water Course Pre-Development Model

River Station

(m)

Maximum Channel

Depth (m)

Velocity (m/s)

Cross Sectional

Area (m2)

Hydraulic Depth

(m)

5815.29 0.67 2.1 63.96 0.44

5692.63 0.86 0.82 164.91 0.67

5500.75 0.68 1.61 83.22 0.48

5264.58 1.19 0.93 144.28 0.72

4992.33 1.04 2.23 60.15 0.51

4714.41 1.66 1.44 93.22 1.12

4559.7 0.84 2.62 51.24 0.69

4380.86 1.99 0.61 221.22 1.61

4164.74 2.45 0.26 525.01 2.2

4084.26 2.44 0.21 632.53 2.29

4002.2 2.62 4.31 31.19 1.87

3916.36 4.82 0.14 948.05 3.57

3851.62 1.42 2.66 50.47 0.71

3775.49 3.14 0.24 561.42 2.48

3699.91 1.63 2.99 44.95 0.91

3628.32 6.86 0.25 540.42 3.19

3442.92 2.26 3.21 41.9 1.05

3333.43 1.75 3.84 35.03 0.76

3233.58 1.59 3.14 42.86 0.99

3133.43 1.88 4.21 31.92 0.96

3012.8 2.47 3.61 37.25 1.06

2901.17 2.16 3.1 43.36 1

2749.19 2 4.06 33.13 0.84

2564.16 1.13 2.75 48.81 0.77

2348.07 1.07 1.99 67.68 0.81

2142.4 1.32 2.38 56.5 0.63

1912.37 1.58 1.84 73.11 0.63

1698.17 1.11 1.8 74.66 0.77

1399.16 0.95 2.35 57.09 0.56

1000.06 0.86 1.31 102.35 0.64

742.81 0.99 1.08 124.55 0.7

501.76 0.8 1.98 67.88 0.49

222.11 0.89 1.1 122.2 0.63

0 1.63 1.84 72.86 0.34

A new diversion channel was designed for the Three Dams Water Course Post-Development

scenario. The new diversion channel will be lined with reno-mattresses and seeded with

indigenous grasses. The new diversion channel was designed to contain the 1 in 100 year flood

without overflowing. The minimum longitudinal slope of the new channel is 0.192% or 1 in 522

05 September 2014 52 12810


(m/m). A Manning’s “n” hydraulic roughness value of 0.035 was assumed for the new channel,

which corresponds to long grass growing in the diversion channel. The normal flow depth in the

channel was calculated to be 2.9 m, and the critical depth is 1.8m deep. Flow will therefore be sub-

critical. A cross section of the channel is presented in Figure 5-12.

The outputs from the Farm Dam Water Course Pre-Development Model are presented in Table 24.

An output longitudinal section of this model is presented in 5-13Error! Reference source not

ound..

Table 24: Output from the Farm Dam Pre-Development Model

River Station

(m)

Maximum Channel

Depth (m)

Velocity (m/s)

Cross Sectional

Area (m2)

Hydraulic Depth

(m)

5336.07 1.97 2.92 101.48 0.87

5005.81 2.68 5.91 50.23 1.22

4695.89 3.3 1.62 183.1 1.21

4343.33 3.11 1.94 152.6 1.08

4004.85 3.04 1.1 270.8 1.2

3740.42 1.83 1.72 172.86 0.91

3406.65 1.23 1.84 161.25 0.8

3149.75 2.09 1.68 176.47 1.59

2839.08 1.82 1.7 174.68 1.34

2550.1 3.2 0.37 792.46 2.34

2227.47 3.19 0.27 1104.32 2.95

1977.23 2.84 2.34 126.64 1.16

1802.67 3.01 0.21 1420.39 2.6

1556.71 3.01 0.25 1170.21 2.79

1331.24 3 0.2 1452.15 2.79

1164.38 1.4 2.14 138.79 0.45

946.45 1.06 1.48 201.2 0.71

624.74 1.88 0.79 374.08 0.84

441 1.11 1.57 189.17 0.45

176.53 0.8 0.89 335.31 0.66

0 2.26 1.99 148.9 0.39

The wall of the Farm Dam will be lowered by 3 m in elevation for the Post-Development scenario.

The post-development output longitudinal section of this model is presented in Figure 5-13.

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5.9.2 Results

The resulting 1 in 100 year floodlines are shown in Figure 5-10.

Figure 31: 1 in 100 Year Floodlines Pre- and Post-Development

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Figure 32: Resulting Longitudinal section of Three Dams Water Course

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Figure 33: Cross Section of Diversion Channel

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Figure 34 Resulting Longitudinal Section of Farm Dam Water Course, Pre-Development

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Figure 35: Resulting Longitudinal Section of Farm Dam Water Course, Post-Development

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5.10 Suppression Abstraction Philosophy

The Stormwater Management Philosophy proposed below is for the preferred option, Option 3B,

Scenario 2. Impacted (dirty) stormwater will be contained in four (4) pollution control dams,

namely:

1. Dirty Water Dam (existing)

2. Emergency Dirty Water Dam (existing)

3. Dam 1 (proposed)

4. Dam 5 (proposed)

The operating philosophies of these dams are interlinked with respect to abstraction of water for

dust suppression and will need to be managed effectively to ensure peak performance. The

relationship between these dams is as follows:

The Emergency Dirty Water Dam will need to always have 55 Mℓ available storage capacity

therefore it should be given priority for dust suppression to maintain this volume.

If the Emergency Dirty Water Dam has the available storage available, then water for dust

suppression will have to be abstracted from either the Dirty Water Dam or Dam 1 (proposed).

Water will be abstracted from the dam with the highest volume by percentage of its storage

capacity.

Dam 5 is used as a storage reservoir for dust suppression. Water from the three (3) other

pollution control dams are pumped here for dust suppression.

5.11 Hydraulic Analysis

5.11.1 Sizing of “Clean” stormwater diversion drains and berms

The topography of the area earmarked for the extension of the existing ash dump has a natural rolling terrain

in a north-westerly direction. Consequently, “clean” surface runoff can only be expected from the contributing

sub-catchments located to the east of the study area. This resultant runoff will be managed as part of the

river/stream diversion discussed in section 1 of this report.

The river diversion will be sized to convey the peak discharge generated during a 1:100yr storm event from

the contributing catchment downstream of the spillway and the clean water dam spillway capacity of

100m3/s. The spillway is used as a control point from the contributing catchments upstream.

5.11.2 Sizing of “Dirty” stormwater conveyance drains

Surface runoff generated from within the footprint of the extended ash dump will ultimately report into toe-

drains running northerly along the western toe line. This system comprises of two (2) types of drains (Toeline

drain & Outlet Drain) in series leading into the new PCDs shown in figure below.

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Figure 36: Toe Line Drain

Figure 37: Outlet Drain

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Preliminary design parameters for the “dirty” stormwater drains are indicated in Table 25:

Table 25: "Dirty" Water Channels Concept Design Parameters

Design

Parameter

“Dirty” Water Channel

Toe line

Drain (D1)

Outlet Drain

(O1)

Channel Type Trapezoidal Trapezoidal

Lining Type Concrete Concrete

Friction

Calculation

Method

Manning’s

Formula

Manning’s

Formula

Flow Rate

Q(m3/s)

33 46

Bed Slope S

(m/m)

0.005 0.005

Manning’s N

(s/m1/3

)

0.016 0.016

Velocity V(m/s) 4.1(to be

optimised at

detailed

design stage)

4.4(to be

optimised at

detailed

design stage)

Side Slopes

(m/m)

0.5 0.5

Bottom Width

(m)

2 2.5

Normal Depth

(m)

1.5 1.7

5.12 WATER BALANCE

The Water Balance for the preferred option is shown in Appendix D. Normal

operating levels for the dams, both existing and proposed, are shown on the

graphs in Section 5.8.

5.13 OPERATIONAL REQUIREMENTS

In sizing the proposed infrastructure, several assumptions were made for the

operational philosophy surrounding the ADF and its infrastructure. These

assumptions need to be realised during operation in order to ensure the

performance of the new infrastructure.

05 September 2014 61 12810


5.13.1 Monitoring of Quality in Clean Water Dams

The clean water dams, Dams 2, 3 and 4, have been sized not to spill more than

once in fifty years which takes into consideration irrigation onto the rehabilitated

areas. These dams will need to be monitored for water quality on a continuous

basis. If the water is deemed clean with respect to the discharge quality of the

receiving environment, then it may be released. However, if the quality does not

meet the discharge quality, then this water must be irrigated onto the rehabilitated

areas or utilised in the station water balance.

5.13.2 Maintaining Open Ash Areas for Dust Suppression

Option 3B Scenario 2 recommends an optimum open ash area of 82 hectares to

be maintained during operations, to balance the dirty water system using dust

suppression without the need for a Water Treatment Plant. The respective dams

have been sized accordingly. If significantly smaller areas are maintained, the

dams recommended is this report will be too small to ensure that we do not spill

more than once in fifty years from the pollution control dams.

5.13.3 Maintaining Silt Traps

The storage capacity of the proposed dams does not assume a continuous influx of

silt into it as it is equipped with a silt trap. If these silt traps are not maintained as

per their design requirements, the performance of the dams will be compromised.

The silt traps will be finalised during detailed design and the operations thereof

need to be communicated to the power station operators.

5.14 WAY FORWARD FOR STORMWATER MANAGEMENT

The trade-off study was conducted and finalised to inform the permitting process in

order to determine the optimised go-forward scheme for the implementation of

stormwater management infrastructure surrounding the extension of the current

Kendal Ash Dump. Option 3B Scenario 2 is the preferred option and conceptual

designs will need to be finalised for this.

It is also recommended that a Water Use Licence Application be made for the

water uses as described in this report.

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6 STREAM DIVERSION

The perennial stream located to the East of the existing ash dump currently runs

through the proposed footprint of Options 2A, 2B and 2C. Consequently, this

stream will be diverted to run northerly, parallel to the extended footprint of the ash

dump.

This stream serves as a receptor for discharge from the existing clean water dam

located up-slope. This dam serves as a primary source of flow for the stream. The

maximum discharge over the dam’s spillway is 100m3/s. The diversion channel will

be sized to cater for this flow, plus the runoff from the area below the spillway,

while incorporating an additional freeboard of 1m. A preliminary sizing has been

done; the bottom width of the stream diversion is 10m wide and a depth of 2m the

left and right side slopes are 1V:2.5 and 1V:3H respectively., on the lower left bank

side a berm is constructed to provide the 1m freeboard. In the figure below a

typical section is provided for the stream diversion. There are a number of aspects

listed below that needs to be investigated in the following phase of design to

provide an optimal solution for the stream diversion:

Investigating impact of stream diversion downstream of the stream diversion ,

Establishing similar vegetation in new stream

Erosion mitigation in initial stages

Probability of leachate of the existing facility migrating towards the stream

diversion

Design of this stream diversion channel will be carried out at a later stage of the

project, only a preliminary river section is provided in Figure 38

Figure 38: Proposed Stream Diversion

Berm constructed from suitable

excavated material

Reno-mattress lining

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7 PHASED APPROACH TO ADF

7.1.1 Option 1A & 2A

All the constraints where identified in terms of site boundaries, stream 100m lines

(Stream diversion lines for 2A) machinery and equipment used. Within these

options the maximum footprint was identified within these constrains. And a

maximum height was determined to be 60m.

For Option 1A the capacity of the site gives a remaining life of 5 years from

January 2015. This gives us time to 2019. If construction of the liner only finishes

at the end of 2015 the remaining life is only 4 years which means it would be

impractical to have phase development for this option

For Option 2A the capacity gives a remaining life of 15 years from January 2015.

This is triple the capacity of option 1A. It was assumed that the minimum cell life for

this option would be 5 years. Thus after construction there is only life for 11 years.

Thus a two cell approach is considered on which Cell 1 will have a life of six years

and Cell 2 a life of five years.

7.1.2 Option 1B & 2B

These options have the same footprints as option 1A and 2A therefore their

footprint cells will be the same. As the idea here is to do staged piggybacking the

piggybacked area is seen as another lined cell on its own. Option 2B has a

remaining life of 18 years which provides another three years of capacity. The

piggyback cell will only have a capacity of three years and will also involve moving

the suitable conveyor systems regularly if the piggyback is constructed solely

which can be an operational flaw.

7.1.3 Options 1C & 2C

These options again have the same footprint as option 1A and 2A, but due to the

piggyback section being constructed concurrently the piggyback area will not be

lined and the majority of it will be placed on the existing dump as the shiftable

conveyor system will be moved back and then covered with topsoil and grassed.

Option 1 C will have the same footprint cell and will thus have a capacity of 5

years, this means that 2 years for this option will be placed on the existing footprint

which will then be topsoiled and grassed.

Option 2C will also have the same footprint as Option 2A and thus have two

footprint cells with a capacity for 11 years. Thus 5 years of ashing will take place

on the existing ash dump and will then be topsoiled and grassed.

05 September 2014 64 12810


8 FARM DAM SYSTEM

To the west of the existing ADF, there exists a farm dam on Eskom’s property

which does not form part of the water management philosophy. The dam is

currently used by a farmer to irrigate two centre pivots, located on the footprint of

the proposed extension. His activities will cease once the ADF is extended and the

dam will no longer be required to serve its intended purpose. However, the dam

sustains a wetland located at the toe of the dam wall and will pose a significant

environmental impact if removed in its entirety. The wetland is sustained via

seepage through the dam wall, which was not designed or constructed to

acceptable engineering standards and poses a risk of failure.

The height of the dam wall poses a significant institutional challenge for Eskom as

the top water level reaches at times the level of the final open cast coal mine voids

located adjacent to the farm dam. This is not ideal as clean water flow enters the

final voids when the level in the dam is high, resulting in contamination of the clean

water in the dam. However, the mine may decant uncontrollably into the farm dam.

The latter should be addressed by the mining house as it is outside the control of

Eskom.

The farm dam is in-stream downstream of a diverted watercourse created by the

mine in order to undertake open cast mining on its original course.

The following work is proposed in order to make this system environmentally

acceptable:

New earth dam wall to be built to prevent overflow into mining voids and

vice-versa

Existing dam wall to be removed

Engineered seepage from the dam to downstream of wall taken into

consideration for wetland sustainability

Upstream approach channel and outlet channel to dam to be lined using

reno mattress – flat gradients

Channel designed for the 1:2 year stormflow velocities

It should be noted that a portion of the upstream approach channel falls within the

property of Side Minerals. This is portion 1 of Leeuwfontein 219 IR. Side Minerals

(or Shanduka Coal) are the mining right holders of the Lakeside and Stuart

Collieries which are no longer operational.

05 September 2014 65 12810


The proposed works are shown on the figure below.

Figure 39: Proposed changes at Farm Dam System

Reline stream diversion with

reno mattress

Lower dam wall to

below final void

decant level

Final voids

Reline dam outlet channel

with reno mattress

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9 OPERATION AND MAINTENANCE PLAN

There is currently an operational manual in place for the existing Kendal facility

which provides insight into all current activities on site.

9.1 Code requirements in terms of SABS 0286

The Following needs to be in accordance with SABS 0286

Management

Operational phase appointment

Facility audit

Hazard classification

Operating manual

Operation of the ash dump

Operation of silt trap/s and pollution control dam

Monitoring and maintenance requirements

Rehabilitation and environmental considerations

05 September 2014 67 12810


10 DISCUSSION

Trade-off studies were conducted in order to determine the optimised go-forward

scheme for the expansion of the current Kendal Ash Dump and stormwater

infrastructure. Six options for the ADF and nineteen options for the stormwater

management philosophy were assessed. This was supported by:

Conceptual airspace modelling of each alternative;

A daily time-step model over a 50 year period for run-off determination and

PCD sizing, as well as sizing of clean and dirty water conveyances;

Conceptual development of dump infrastructure including surface drainage

structures, hydraulic structures, leachate and sub-surface drainage, lining and

cover materials;

Cost estimation;

Trade-off study workshop.

From the trade-off study held the preferred layout option is identified as Option 2A and the preferred water balance option is identified as Scenario 2, Option 3B

Option 2A provides a ashing capacity of 98 Mm3 at a density of 0.85t/m3

This provides a remaining life of 15 years from January until 2029

The preferred option as selected through the trade-off study analysis is based on a preliminary design. All fundamental aspects were addressed to inform the EIA study.

It is recommended to progress with the preferred option through a basic and detailed design phase.

The requirements that are raised as issues and concerns through the EIA and stakeholder engagement process should be addressed during the basic and detailed design phase and the impacts should be mitigated through engineering solutions.

Based on the trade-off study work, it can be stated that the proposed facility extension is a feasible solution.

05 September 2014 68 12810


11 RECOMMENDATION AND CONCLUSION

Several options were considered for determining the go-forward option on the ADF

and stormwater management philosophy. The “piggyback” options described in

both the determination of air space on the ADF and stormwater management

philosophy are not deemed feasible currently from a mechanical perspective. This

option was therefore not considered for implementation in this report. Further

investigation is currently underway here and will be reported on a separate project

that has been commissioned by Kendal Power Station.

The go-forward option as proposed for the ADF layout is Option 2A and for the

stormwater management philosophy is Scenario 2 Option 3B. A Waste

Management Licence (WML) and Water Use Licence (WUL) need to be applied for

the infrastructure and activities as described in the aforementioned options.

ZITHOLELE CONSULTING (PTY) LTD

N Rajasakran Pr.Eng J Heera

Project Manager Project Reviewer


APPENDIX A

Geotechnical Report


APPENDIX B

Waste Classification Report


APPENDIX C

Conceptual Engineering Drawings


APPENDIX D

Water Balance Diagram


APPENDIX E

Trade-Off Study Matrix


APPENDIX F

Technical Memo: Selection of Barrier System

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