KRIEL ASH DAM ENVIRONMENTAL IMPACT ASSESSMENT …

AURECON

KRIEL ASH DAM ENVIRONMENTAL IMPACT ASSESSMENT

SITE SELECTION INPUTS

Report No.: JW71/10/A407 – Rev B

FINAL

July 2010

ACTION FUNCTION

Prepared Civil Engineer

Reviewed Director

Approved Director

RECORD OF REVISIONS AND ISSUES REGISTER

Date Revision

7 June 2010 A Draft

5 July 2010 B Final

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DOCUMENT APPROVAL RECORD

Report No.: JW71/10/A407 – Rev B

NAME DATE

SIGNATURE

Civil Engineer Anton Bain 4 June 2010

Danie Brink 6 June 2010

Danie Brink 6 June 2010


Description Issued to Issue Format

Draft M. Mangnall Electronic

Final M. Mangnall Electronic

T Bokwe Electronic

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Issue Format No.

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Electronic -

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SYNOPSIS Jones and Wagener was appointed by Aurecon to provide input into the Environmental Impact Assessment for a new ash dam at Kriel Power Station. The appointment includes input into a site selection study where alternative areas are identified and compared to one another. The site selection study aims to identify a preferred area upon which a conceptual design is subsequently carried out for the ash dam. This report documents the site selection study as it currently stands. The site selection process is iterative and the outcome of this study is twofold:- - A preliminary recommendation is made based on an evaluation of identified alternative

areas using information gathered at desktop level. - Additional recommendations are made for areas that must be investigated so that the site

selection process can be concluded. Note that in order to have carried out this site selection process a number of design aspects needed to be described and developed to a level that the suitability and major cost components that differ from area to area could be evaluated. Jones and Wagener carried out a feasibility level design for a new ash dam at Kriel in 2003. A number of options were considered based on an Ash Dam located on the backfilled open cast mine pit south east of the existing Ash Dam 3 (Kriel Colliery Pit 1). A number of alternative areas have been identified as part of this study. A search radius of 6km was used and later extended to 8km as all of the alternative areas to the original area are underlain by coal resources. Even within the 8km radius all alternative areas are still underlain by coal resources and the alternative areas to the original proposed are all also located on backfilled opencast mines. There is however a possibility that areas to the north east of the Power Station falling partially inside the 8km radius but predominantly outside the 8km radius may be underlain by coal that cannot be mined and may become viable alternatives to the original area. A simplistic selection matrix was applied to the open cast mines areas and the possible areas on natural ground as described above and it concluded that Area 16 is the preferred site. This preference is due to the current concerns of stability and groundwater impacts of development on backfilled pit areas. The excessive cost is however a major concern. The report concludes with a number of recommendations of which the investigation relating to the study of groundwater impacts and the collapse settlement of the spoils backfilled in the open cast pit are the most important. The most important investigation required for the areas situated on natural ground is to determine if the areas are underlain by minable coal resources and whether the sterilisation of the coal reserves can be economically justified. The report also recommends that Eskom re-evaluate and re-confirm the decision that development of the ash dams on coal resources be precluded from the selection process.

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AURECON KRIEL ASH DAM ENVIRONMENTAL IMPACT ASSESSMENT SITE SELECTION INPUTS REPORT NO: JW71/10/A407 – Rev B CONTENTS PAGE

1. INTRODUCTION 1

1.1 Background 1

1.2 Terms of Reference 1

2. GEOLOGY 1

2.1 General Description 1

2.2 Coal Resources 2

3. KEY DATA AND ASSUMPTIONS 4

3.1 Summary 4

3.2 Rate of Rise 4

3.3 Side Slope Profile 4

3.4 Slurry Density 5

3.5 Height and Footprint Areas 5

4. POTENTIAL AREAS 6

4.1 Constraints 6

4.2 Coal Sterilization 9

5. TECHNICAL ASPECTS 11

5.1 Groundwater 11

5.2 Foundations 14

6. SITE SELECTION 15

6.1 Area 10 15

6.2 Area 15 - South 17

6.3 Area 16 - North 19

6.4 Area 16 - Central 21

6.5 Comparison: Capacities and Areas 23

6.6 Comparison: Perimeter Lengths 23

6.7 Comparison: Distance from Plant and Relative Elevations 24

6.8 Comparison: Costs 25

6.9 Area Ranking 27

7. RECOMMENDATIONS 30

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List of Tables Table 1: Coal Resources ............................................................................................................ 3

Table 2: Key Data and Assumptions........................................................................................... 4

Table 3: Possible Areas, Coal Resources and Areas ............................................................... 10

Table 4-1: Seepage Rates ....................................................................................................... 13

Table 4: Area Capacities and Areas ......................................................................................... 23

Table 5: Area Perimeter Lengths .............................................................................................. 24

Table 6: Area Distances and Elevations ................................................................................... 24

Table 7: Delivery and Return infrastructure Costs .................................................................... 26

Table 8: Summary of Major Cost Items .................................................................................... 27

Table 9: Area Ranking Matrix ................................................................................................... 30

List of Figures Figure 1: Collieries Surrounding Kriel (Barker 2007) ................................................................... 3

Figure 2: Typical land uses as a function of slope steepness ..................................................... 5

Figure 3: 6km and 8km Search Radius Showing Identified Infrastructure ................................... 7

Figure 4: Potential Areas Showing 4-Seam Mined Areas and Future Resources........................ 8

Figure 5: Potential Areas showing all Coal Resources ............................................................... 9

Figure 6: Proposed Liner System ............................................................................................. 12

Figure 7: Liner Requirements (DWAF) ..................................................................................... 13

Figure 8: Area 10 Layout .......................................................................................................... 16

Figure 9: Area 15- South Layout ............................................................................................... 18

Figure 10: Area 16 North Layout .............................................................................................. 20

Figure 11: Area 16 Central Layout ............................................................................................ 22

Figure 11: Area 10 Previous Ash Backfill .................................................................................. 29

Jones & WagenerC o n s u l t i n g C i v i l E n g i n e e r s59 Bevan Road PO Box 1434 Rivonia 2128 South Afr ica

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TECHNICAL DIRECTORS: JA Kempe PrEng BSc(Eng) GDE MSAICE AIStructE CG Waygood PrEng BSc(Eng) MSAICE JR Shamrock PrEng MSc(Eng) MSAICE MIWM JE Glendinning PrSciNat MSc(Geochem)

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ASSOCIATES: BR Antrobus PrSciNat BS(Hons) MSAIEG MW Palmer MSc(Eng) AMSAICE AJ Bain BEng AMSAICE HR Aschenborn PrEng Hons Eng MSAICE PJJ Smit Hons BEng AMSAICE

R Puchner PrSciNat MSc(Geol) MSAIEG MAEG TG le Roux PrEng MEng MSAICE

CONSULTANTS: W Ellis PrEng CEng MIStructE FINANCIAL MANAGER: HC Neveling BCom MBL

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AURECON KRIEL ASH DAM ENVIRONMENTAL IMPACT ASSESSMENT SITE SELECTION INPUTS REPORT NO: JW71/10/A407 – Rev B

1. INTRODUCTION

1.1 Background

Kriel power station operates six 500MW units and was one of the first power stations to be supplied with coal from a fully mechanised coal mine (Kriel Colliery). The current ash dam complex is located 1,5km south of the station and consists of three compartments or dams.

An investigation carried out by Jones and Wagener in 2006 (JW127/06/A407) has shown that the existing ash dams at Kriel Power Station had, at that time, only approximately 5 years life remaining, up to July 2011. The study concluded that the most feasible option to provide additional deposition capacity is to construct a new ash dam, Dam 4, to the south east of Dam 3 over a portion of the backfilled north pit or Pit 1 of the Kriel Colliery. The major aspects that were highlighted that would need to be investigated in further detail before the area is developed included groundwater impacts and collapse settlement of the backfilled mine spoils.

1.2 Terms of Reference

Aurecon has been appointed by Eskom to carry out the Environmental Impact Assessment for the project and Aurecon has subsequently appointed Jones & Wagener to provide technical input.

The technical input includes a site selection process to evaluate alternative areas to the originally proposed area and to carry out a conceptual design on the most preferred area.

A search radius of 6km from the Power Station was set but was enlarged during the course of the study to 8km for reasons as described further on in this report.

2. GEOLOGY

2.1 General Description

Kriel power station lies within the Great Karoo Basin. The sediments of the Karoo basins were depoaread in fluvial floodplains and shallow shelves over a period of more than one hundred million years extending from the late Carboniferous (290million years ago) to the early Jurassic (190million years ago) prior to the separation of southern Africa from Gondwanaland. The dolerites that are such a prominent feature of the Karoo basin were intruded when sedimentation in the basin had virtually ceased after the outpouring of the

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Report JW71/10/A407 – Rev B

Final

Drakensberg basalt. The dark-coloured crystalline igneous dolerite dykes and sills intruded the Karoo sediments along planes of weakness in the older sedimentary rocks as the basalt cover prevented further extrusion of lava. In the area of interest, there are few dolerite intrusions, apart from a number of narrow sub-vertical dykes. None of the earlier investigations encountered any near surface dolerite.

The Karoo sediments that underlie Kriel are from the Vryheid Formation (Ecca Group). The sediments consist of sandstones and sub-ordinate gravels and mudrocks with economically exploitable coal seams. Over much of the Karoo basin the sedimentary rocks are horizontally bedded or have very gentle dips. Sandstones comprise a large proportion of the Karoo sediments and are generally closely intercalated with siltstones and shales/mudrocks. This results in the alternating arenaceous (sandy) and argillaceous (clayey) sediments that are characteristic of the Karoo Sequence.

Rocks within the main Karoo basin have been subjected to several cycles of erosion, which resulted in widespread planation. The great depths of weathering typically associated with the African surface are seldom preserved unless a surface pedocrete armour ("duri-crust") has remained to protect the weathered residue from erosion. Rock outcrops are rare in the area of interest and blanketing residual and transported soils generally mask the bedrock.

The mode of weathering is largely dependent on climatic conditions with disintegration prevalent in the dryer regions (N > 10) and decomposition in the wetter regions (N < 2). The Kriel area lies within the N < 2 classification and decomposition of the clay minerals can be expected where water is available.

2.2 Coal Resources

Kriel Power Station is centrally situated near the northern boundary of the Highveld Coalfield. The eastern part of the northern boundary is defined by pre-Karoo granite and felarea ridges. The northern boundary in the vicinity of Kriel Power Station constitutes a basin high where the Karoo sediments are shallow and ‘pinches’ out against the valley slopes of the pre-Karoo ridges.

The exploitable coal seams of the coalfield are well defined within the original 6km search radius and Kriel Colliery holds all the mining rights.

Beyond the 6km radius it is known that the exploitable coal seams extend to the west and somewhat to the south as part of Matla Colliery. Dorstfontein and Isibonelo are situated to the east and south east respectively and are currently being developed.

The mining rights of the area to the north east partly inside but predominantly outside the extended 8km search radius does not appear to be allocated to any existing collieries. This area is near the northern boundary of the Highveld Coalfield and it is possible that the coal in this area cannot be exploited due to weathering, baking due to lava intrusions (i.e. burnt coal) or possibly other factors that is not associated to geology. This must however be investigated and confirmed if these areas are considered in subsequent studies.

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Figure 1: Collieries Surrounding Kriel1

Kriel Colliery consists of three seams designated 2-Seam, 4-Seam and 5-Seam. 4-Seam is partly mined while Seam 5 and Seam 2 has not been mined but has been identified as future resources.

Table 1: Coal Resources

Seam Depth Thickness Type Status

2 70 2.5-5 Underground Future

Resource

4 60 5-5.5 Opencast and Underground

Currently being mined

5 30 1.5-2 Opencast and Underground

Future Resource

1 Barker’s Coalfield Map of South Africa, 2007

8km search radius

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3. KEY DATA AND ASSUMPTIONS

3.1 Summary

The capacity of the area was set by Eskom at 110 000 000 m3. This is in line with the input that was provided during the initial investigation. Some of the other parameters relating to the required capacity are carried forward from the initial investigation.

Table 2: Key Data and Assumptions

Capacity 110 000 00 m3

In-situ dry density of ash 0.9 ton/m3

Facility Life 26 years

Deposition rate 315 725 tpm

Slurry relative density 1.1 to 1.25 ton/m3

Rate of Rise 3 m/year

Height 50m to 80m

Sideslopes 1(horizontal):4(Vertical)

Footprint Area 250Ha to 320Ha

Note that the life of the facility is derived from an assumed in-situ density, the set capacity and an assumed deposition rate.

3.2 Rate of Rise

The limits that apply to the safe rate of rise of tailings dams are influenced by a number of factors including:-

- Strength characteristics of the tailings.

- Consolidation and drainage characteristics of the tailings.

- Environmental factors including drying by wind and sun.

- Drainage and drainage boundaries (i.e. a flow regime up, down and/or laterally outwards).

An assessment of the safe rate of rise is outside the scope of this report. A maximum rate of 3m/year is assumed here. A rate of rise of 3m/year is often achieved and sustained on ash tailings dams in South Africa constructed in an upstream direction by the ‘Daywall’ method. This assumption is considered conservative and the safe rate of rise may be higher.

3.3 Side Slope Profile

The new ash dam has been conceptualised with intermediate slopes at approximately 1(v):3(h). 7m wide horizontal benches are provided at 7m vertical intervals giving an overall slope of 1(v):4(h).

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This slope is:-

- Traversable by construction plant and compactors for specifically rehabilitation and closure.

- Considered flat enough to vegetate effectively, refer to Figure 2 below.

Figure 2: Typical land uses as a function of slope steepness

3.4 Slurry Density

The slurry density is also assumed and is typically what can be achieved by current sluicing methods employed by Eskom.

3.5 Height and Footprint Areas

The height of the facility, area, sideslopes and topography governs the area capacity and are interrelated.

The height and footprint areas are set as the most probable ranges that can be expected to provide the required capacity for the general topography of the area.

Typically, the final height of a facility will be governed by:-

- The limiting rate of rise.

- An assessment of the consequence of failure of a slope.

- Visual / environmental impact.

The actual stability of the wall usually does not govern the height of flat slopes as proposed here. The stability of flat slopes (i.e. that is substantially flatter than the angle of repose of granular material) is most often a function of the slope angle, material strength, and pore pressure regime. The consequence of failure in turn increases with height as the expected area downstream of the facility that is impacted increases and is a governing factor.

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In support of this, there is a number of tailings dams in South Africa that is more than 100m high and have stable outer walls. The limit on the maximum height that is set here is a practical height rather than a safe height.

Note

It was also assumed at this stage of the investigation that the facility will be developed as a tailings dam constructed using, the upstream method with a paddock or daywall system similar to the existing development. This was done so that the capacities of the various areas can be determined. A dry stacking operation will require a slightly larger area as the in-situ density is lower than for a hydraulic deposit. An in-situ density of 0.8 ton/m3 is probably realistic implying that a dry ash stack will need to be 13% larger than the hydraulically depoaread facility that is used for the site selection process in this report.

4. POTENTIAL AREAS

4.1 Constraints

A large number of potential areas were identified within the 6km search radius and the extended 8km radius. The borders of the areas are defined by features that will most probably be too expensive to be relocated.

- Tarred Roads.

- Perennial Streams.

- Primary power lines.

- Significant Pipelines.

- Urban development.

- Mine Shafts.

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Figure 3: 6km and 8km Search Radius Showing Identified Infrastructure

Note that some of these features can technically be relocated and can be accounted for if required for a specific area in a second round evaluation.

Infrastructure including farm houses, non-perennial streams and dirt roads was not accounted for to form the boundaries of the various areas.

In addition to the above, no potential area was identified that overlies Kriel Colliery 4-Seam coal resources, which are dedicated to Eskom. Some of the areas overlie mined out areas of 4-Seam and are not excluded from the selection process, as it is technically possible to construct a facility like an ash dam on such areas.

Perennial River

Power Lines

Main Roads and Dirt roads

Mine Shafts

Kriel Power Station

Canals

Komati Water Scheme Pipeline

Pipe Lines

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Figure 4: Potential Areas Showing 4-Seam Mined Areas and Future Resources

Area 1

Area 2

Area 4

Area 3

Area 5

Area 10

Area 6

Area 7

Area 8

Area 11

Area 14

Area 12

Area 15 S Area 13

Area 15 N

Area 16 S

Area 16 C

Area 16 N

Open cast mine

Kriel Power Station

Area 9

TYPICAL OUTLINES OF EXISTING MINING AREAS TYPICAL FUTURE MINING AREA

(Coal Resource)

8 Km

6 Km

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4.2 Coal Sterilization

A large number of the identified areas overlie coal in 2-Seam below and 5-Seam above 4-Seam. Some of the areas also overlie mined out Kriel Colliery 4-Seam areas that may also be developed further.

Figure 5: Potential Areas showing all Coal Resources

It appears that all areas within the 8km radius and even beyond the 8km radius overlie some form of coal resource. The exception is Area 10 and Area 15 (North and South), which overlie backfilled open cast mine pits.

It is also possible that Area 16 (North, Central and West) does not overly coal that can be mined. This must however be confirmed. Although Area 16 (Central and North) falls outside the 8km search radius it was included as it appears that it may be the only area within reasonable distance that is not underlain by exploitable coal resources.

Area 1

Area 2

Area 4

Area 3

Area 5

Area 10

Area 6

Area 7

Area 8

Area 11

Area 14

Area 12

Area 15 S Area 13

Area 15 N

Area 16 S

Area 16 C

Area 16 N

Open cast mine

Kriel Power Station

8 Km

Area 9

SEAM 5 OP

SEAM 5 UG

SEAM 2 – ALL UG

OUTLINE SEAM 4

6 Km

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The table below lists the potential areas and the status of the underground workings. The table also indicates if the area is potentially large enough to accommodate the capacity requirement that was set.

Table 3: Possible Areas, Coal Resources and Areas

SITE

Available Area

(m2)

Status of Coal Mine underlying area

Comments 2-Seam

Resource

Old 4-Seam Works 2-Seam

Resource UG OC

1 393 Kriel Kriel

2 306 Kriel Kriel Kriel

3 356 Kriel Kriel Kriel In Kriel Mine Plan

4 234 Kriel Kriel Kriel In Kriel Mine Plan if LoPP is extended

5 376 Kriel Kriel In Kriel Mine Plan

6 139 Kriel Kriel Area too small

7 160 Kriel Kriel Kriel Area too small

8 87 Kriel Kriel Kriel Area too small, part of current open cast

9 243 Kriel Kriel

10 359 Kriel

11 170 Matla Area too small



14 734 Matla

15 North 217 Kriel Area too small

15 South 282 Kriel

16 North 308 Unknown

16 Central 312 Unknown

16 South 181 Unknown Area too small

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Discussion

It was agreed with Eskom that areas overlying minable coal resources will not be considered.

Area 10, Area 15 South, Area 16 Central and Area 16 North are the only areas that are potentially large enough to accommodate the required capacity and do not overlie some form of coal resource and are the only areas considered further for selection..

The alternative areas can be divided into two groups:-

- Areas overlying backfilled mine spoils

- Areas overlying natural ground

The requirements and concerns related to these two area types vary significantly and are discussed below.

5. TECHNICAL ASPECTS

5.1 Groundwater

Areas overlying backfilled mine spoils

Seepage from the ash dam is likely to permeate through the existing topsoil and enter the pit backfill. With the high permeability of the backfill, the seepage water will spread rapidly through the pit and mix with the in-situ pit water. In time, even the water stored in the western void will be affected by the ash seepage water.

Power station ash is composed principally of alumina, silica, lime and iron oxides. Seepage from ash disposal areas contains high concentrations of dissolved salts and potentially elevated concentrations of certain trace elements including arsenic, boron, manganese, nickel, lead, selenium, molybdenum and fluoride. This composition of ash dam seepage poses a risk of contamination to soil and groundwater which it permeates.

The high pH of ash water makes for a favourable environment for the solution and mobilisation of complex trace metal compounds. However, exposure to the atmosphere, anaerobic microbial action or mixing ash water with acidic groundwater will generally lower the pH. Under neutral and acidic conditions the soluble metal complexes and carbonates will precipitate and increase the potential for pollution.

Although a precedent exists at Matla for the construction of an ash dam on spoils, the issue of potential groundwater contamination from the saturation of spoils will have to be addressed through a detailed groundwater study in order to satisfy the Department of Water Affairs and Forestry.

Collapse settlement may be possible on the spoils and is estimated with the existing information at hand to be in the order of 3m. This magnitude of settlement may cause a substantial differential movement of the foundations that no liner system will be able to accommodate. These areas can therefore not be lined and, if subsequent investigation proves that groundwater cannot be controlled sufficiently, may prove to be a fatal flaw.

It is however possible that the permeable spoils will act as a collection sump below the ash dam enabling one to abstract the groundwater if shown to be necessary in subsequent studies. The fact that one may be able to abstract groundwater effectively combined with an understanding of the impact resulting may serve as a basis not tro line the site.

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Note

As a mitigation measure the area may be developed as a dry-stacking operation where the impact on groundwater is significantly reduced as no water is introduced into the system other than infiltration, which in turn will be minimised as the dry ash will serve as a buffer zone where moisture will be stored during wet periods and extracted again by sun drying in dry periods.

Another mitigation measure that may prove viable is extraction and treatment of the groundwater.

Areas overlying natural ground

The area overlying natural ground can, in contrast to the above, be lined and it is assumed that this requirement will be confirmed with subsequent groundwater investigation. In addition, it is highly unlikely that the authorities will allow Eskom to develop a new ash dam on a Greenfields area without providing some form of liner system.

The type of liner system will be determined by the classification of the ash as a waste being either general or hazardous. For the sake of this report it has been assumed that a compoarea liner system with a drainage system above the liner will be sufficient. This liner system is a higher specification than the requirement for general waste and a lower specification than the requirement for hazardous waste.

Figure 6: Proposed Liner System

Ash placed here

Drainage Layer – 300mm River sand

2 x 150mm Compacted Clay

1.5mm Flexible Membrane Liner

In-Situ Soils

Bedrock

Compoarea Liner

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Figure 7: Liner Requirements2

Leakage Rates

The table below summarises the expected seepage rates for the facility with and without a liner. For the option without a liner the seepage rates were calculated using the permeability of the ash assumed to be 10-5cm/s and a typical 300Ha footprint while the options for the liner are quoted from the literature3. Note that it was assumed for the FML only option that a compoarea effect is obtained by the low permeability of the overlying tailings.

Table 5-1: Seepage Rates

DESCRIPTION

SEEPAGE DIFFUSION TOTAL

(litres/hectare/day)

No Liner 4000 - 4000

FML only (30m head) 85 - 300 300 385 - 685

Compoarea Liner (3m head) 11 - 60 100 111 - 160

Compoarea Liner (0.3m head) 1.5 - 7 1 2.5 – 8

2 DWAF, ‘Minimum Requirements for Waste Disposal – Edition 2’, 1998

1. 3 Geosynthetic Institute, GRI White Paper 15, GSI, 2009

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The table shows that a liner will reduce seepage significantly and illustrates the effect of the hydraulic head (i.e. pressure) above the liner on the total leakage rate and emphasises the importance of a properly sized underdrain.

5.2 Foundations

Areas overlying backfilled mine spoils

The major concern remains collapse settlements of the foundations. Matla Ash dam serves somewhat as a case study where an ash dam was placed over mine spoils. Matla however had the advantage that the toe of the outer wall slopes could be placed in its entirety on stable natural ground outside the pit boundaries.

This cannot be achieved at any of the Kriel areas that are under investigation and there are portions of the wall that will even physically cross the backfilled pit.

At present it has been assumed that a pre-built embankment will need to be constructed where the toe of the facility is founded on spoils (i.e. where the outerwall crosses the pit and is not on natural ground).

This embankment will allow one to observe the settlements and possibly induce collapse settlement before ash is depoaread. An additional benefit is that the spoils below the borrow area (i.e. where the embankment material has been excavated from) is over-consolidated and less initial settlement is expected. It is not possible to assess the extent of the pre-built embankment required before full scale tests are carried out on the preferred area. These full scale test embankments should form part of a second phase geotechnical investigation.

Areas overlying natural ground

Consideration of the foundation conditions will require area specific attention and falls outside the scope of this report.

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6. SITE SELECTION

A description of each area follows as well as a list of the advantages and disadvantages.

6.1 Area 10

The area overlies the backfilled open cast mined pit, Pit 1, with boundaries as follows:-

• East – Eastern portion of the backfilled Kriel Colliery open cast mined pit, Pit 1.

• South – Provincial Road R547 (Evander-Kriel).

• West – Existing active Matla Power Station Ash Dam.

• North – Existing Kriel Power Station Ash Dams 1, 2 and 3.

Advantages

• Relatively close to the Power Station with lower capital costs for delivery and return systems.

• Shorter crossing of backfilled area than Area 15S thereby reducing the extent of outer walls that is subject to an elevated stability risk and cost of mitigation.

• Brownfields area with limited future land use.

• Eskom owns surface rights to the area.

Disadvantages

• Situated over undermined areas with associated stability and groundwater concerns.

• Deposition over the eastern final void of Pit 1 that is open to the groundwater. Deposition of ash below the regional groundwater table may exacerbate the groundwater impact as the low pH groundwater may cause metals to leach from the ash.

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Figure 8: Area 10 Layout

Slurry delivery Line

Return Water Line

Crest Line

Toe Line

RWD

Area 10

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6.2 Area 15 - South

The area overlies the backfilled open cast mined Pit 23 with boundaries as follows:-

• East – Low point in backfilled pit.

• South – The adjacent backfilled open cast mined pit.

• West – Agricultural land.

• North – Provincial Road R547 (Evander-Kriel).

Advantages

• Relatively close to the Power Station with lower capital costs for delivery and return systems.

• Capacity for the life of the power station can probably be achieved avoiding deposition over any significant water filled areas open to the groundwater (i.e. final open cast mining voids). There is however a low point in the centre of the area that has standing water.

• Brownfields area with limited future land use.


Disadvantages

• Situated over undermined areas and groundwater impact is a concern.

• Situated near F- Block forming part of future operations of Kriel Colliery and safety in terms of operational interference may be a concern. F-Block services may also be impacted and may have to be re-routed.

• Length of outer wall crossing the backfilled spoils is longer than for Area 10. The cost of constructing the pre-built embankment will be more.

• East and south toe area overlies some coal resources. The impact on one another (sterilizing of coal vs. slope stability influence of mining underlying the toe) may be negligible due to low additional overburden pressures along the toe of the dam.

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Figure 9: Area 15- South Layout

RWD

Toe Line

Crest Line

Return Water Line


Area 15 S

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6.3 Area 16 - North

The area overlies natural ground with boundaries as follows:-

• East – Steenkool River.

• South – Partly used agricultural land and valley ridge.

• West – Agricultural land underlain by Kriel Colliery Coal fields.

• North – Partly used agricultural land and valley ridge.

Advantages

• Underlain by natural ground with no associated mine spoils instability concerns.

• Possibility exists that underlying coal cannot be exploited.


Disadvantages

• Relative to other areas far away from the Power Station with high costs for delivery and return infrastructure.

• Adjacent to the Steenkool River with a higher consequence of failure if ash runs down the river.

• Expensive liner system will probably be required by the authorities irrespective if the groundwater impact can be satisfactorily managed in a different manner.

• Disturbance of a Greenfields area partly used for agriculture.

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Figure 10: Area 16 North Layout

Area 16 N

RWD

Toe Line

Crest Line


Return Water Line

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6.4 Area 16 - Central

The area is a derivative of Area 16 North and is included as it is slightly closer to the Power Station. The area overlies natural ground with boundaries as follows:-

• East – Steenkool River

• South – Partly used agricultural land and valley ridge

• West – Agricultural land underlain by Kriel Colliery Coal fields.

• North – Partly used agricultural land and valley ridge

Advantages

• Underlain by natural ground with no associated mine spoils instability concerns.

• Closer to the Power Station than Area 16 North.

• Possibility that underlying coal cannot be exploited.


Disadvantages

• Adjacent to the Steenkool River with a higher impact or consequence of failure.

• Relative to other areas far away from the power station with high costs for delivery and return infrastructure.

• Expensive liner system will probably be required by the authorities irrespective if the groundwater impact can be satisfactorily managed in a different manner.

• Disturbance of a Greenfields Area partly used for agriculture.

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Final

Figure 11: Area 16 Central Layout

Area 16 C

Return water Line


RWD

Toe Line

Crest Line

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Final

6.5 Comparison: Capacities and Areas

A model was developed for each area as follows:-

- The maximum extremities of each area was used to develop a toeline from where a crestline was calculated at the set slopes of 1(h):4(v)

- The actual height at which the set capacity is achieved was determined from the height/capacity relationship.

- The rate of rise is checked at final elevation to ensure that it is not exceeded.

Table 2: Area Capacities and Areas

SITE LIFE

FINAL RoR

HEIGHT

A B B/A

AREA STORAGE VOLUME

LINER EFFICIENCY

(years) m m2 m3 m

10 26+ 1.7 71 359 110 000 000+ -

15 South 26+ 2.6 65 282 110 000 000+ -

16 North 26+ 2.2 70 308 110 000 000+ 35.7

16 Central 26+ 2.1 65 312 110 000 000+ 35.3

Discussion

The rate of rise of Area 10 is substantially lower than the 3m/year limit. This is due to the fact that the existing Ash Dam 3 comes back into service once the dams on Area 10 reach the crest of Ash Dam 3.

The final height of all the facilities is in excess of 60m while the actual rate of rise is less than 3m/year. This implies that the footprint areas can be reduced while still achieving the set capacity. This is particularly relevant for Area 16 as the cost of the facility is highly dependent upon the footprint area due to the fact that an expensive liner system will probably be required.

The liner efficiency is in essence the average height of the facility and provides an indication of how efficient the liner system is utilized. Differently put, how much ash one can stack on a unit area of liner.

6.6 Comparison: Perimeter Lengths

The toe length of the areas is of particular importance as a delivery line needs to be installed along the toe of the dam (around the whole dam).

The perimeter length of areas crossing the spoils is also of importance as the cost to construct the outer wall along these areas is substantially higher than on natural ground.

The perimeter length is also important for areas on backfilled spoils as drainage systems to ensure stability is placed along the outer walls. Lined areas have a continuous underdrainage system over the full area of the facility and not just along the perimeter and the additional cost for the perimeter drains are not significant.

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Final

Table 3: Area Perimeter Lengths

SITE PERIMETER LENGTH

Total on Spoils

km Km

10 8.7 0.9

15 South 6.8 1.7

16 North 7.0 0.0

16 Central 7.3 0.0

Discussion

The length of the toe lines of the various areas are similar with the exception of Area 10, which is longer. This is due to the fact that Ash Dam 3 comes into operation at a late stage of the area development and increases the available area and associated perimeter.

If one compare Area 10 to Area 15, the length of spoils that is crossed is significantly longer for Area 15 and the cost of the pre-loading will be substantially higher.

6.7 Comparison: Distance from Plant and Relative Elevations

The perimeter length is also important for areas on backfilled spoils as drainage systems to ensure stability is placed along the outer walls. Lined areas have a continuous underdrainage system over the full area of the facility and not just along the perimeter and the additional cost for the perimeter drains are not significant.

Table 4: Area Distances and Elevations

SITE

DISTANCE

FROM PLANT

DISTANCE TO PLANT

LEVELS

PLANT ASH DAM

CREST RWD

FLOOR

km km mamsl mamsl mamsl

10 5.5 6.3 1619 1618.5 1542.5

15 South 8.1 8.2 1619 1616 1545.5

16 North 11.1 11.7 1619 1615 1540.5

16 Central 10 10.2 1619 1610 1540.5

Discussion

All the areas are below the Power Station and the final crest level on each area rises approximately back to the level of the Power Station. The demand on the delivery infrastructure is therefore less and the demand on the return infrastructure is more.

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Final

6.8 Comparison: Costs

The purpose of this section is to highlight and compare major cost items that may influence the site selection process.

Liner Costs

As discussed earlier liner costs are only relevant for areas not situated on natural ground.

The unit cost of the liner system was derived from a residue deposit that is similar in nature to an ash dam that is currently being constructed at a neighbouring colliery. The cost takes account for the river sand, flexible membrane liner and the underlying clay and equates to R 2 million per Ha.

Assuming a typical footprint of 300Ha, the cost of a liner for a area on natural ground is in the order of R 600 million. The 300Ha footprint can be reduced by raising the final height of the facilities as discussed in Section 3.2. A 25% reduction is probably possible resulting in a significantly higher ash dam and a zone of influence (increased consequence of failure). This is considered an optimization and is not investigated further at this level of investigation.

Slurry Delivery and Return Water Costs

Of importance here is to note that the operational portion of the cost is significant and needs to be accounted for.

In order to derive these costs the delivery and return systems was provisionally sized based on:-

- Flow velocity of 2 to 2.5m/s for the delivery line, and

- Flow velocity of 1.0 to 1.5m/s for the return water line.

It is important to note that it has been assumed that the Power Station will need to sluice dry ash to slurry continuously and not in batches as is currently done. The required pipeline diameter is therefore set for a permanent constant flow. The return water line to the contrary was sized so that return pumping is done at certain periods only.

The resultant is a:-

Slurry Delivery Line : 450mm diameter.

Return Water Line : 450mm diameter.

It was also assumed that the existing slurry delivery system leading from the Power Station up to the highest point of the existing ash dam complex will be discarded and a new pump station at the Power Station and pipeline to the alternative areas will be required. This is due to the fact that the existing system consists of a pump and pipeline for 20% of the ash and a conveyor and sluice system at the existing ash dam for 80% of the ash. This system may be retained if Areas 10 or 15 are preferred as it leads towards them. If Area 16 is preferred it will most definitely be discarded as it leads in the oppoarea direction. Again, the consideration of whether the existing system needs to be retained is seen as an optimization exercise and is not investigated further.

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Final

The operational costs were taken as the electricity cost only. The unit rate for electricity supply was assumed to be 30c/kWh.

The cost for the pipeline was derived from commercially obtained costs and the pump stations were proportionally scaled from a 260l/s pump station that has recently been designed and priced.

Note: Treatment Cost

It was assumed that if water treatment is deemed necessary the volumes will be similar for ash dams on backfilled pits or on natural ground provided that the footprint areas are similar. The liner system will collect seepage and prevent it from entering the groundwater effectively making it available for treatment. For the backfilled pit options the seepage water that could possibly be collected by a liner system will have to be abstracted from the groundwater by pumping from the final void or from a set of boreholes around the site. If this is possible and what the impacts are on the environment are subject to the groundwater study required as described and recommended in this report.

Table 5: Delivery and Return infrastructure Costs

A. Capital Costs

Cost (x R 1 000 000)

ITEM DESCRIPTION

Area 10 Area 15 South

Area 16 North

Area 16 Central

1 450mm NB 6mm MS slurry delivery 44.6 51.5 62 59.6

2 Slurry delivery pump station 20 20 20 20

3 450mm NB 6mm MS return water 23.4 30.4 43.4 37.9

4 Return water pump station 10 10 10 10

Total 98 112 135.5 127.4

B. Operational Costs Cost (x R 1 000 000)

ITEM DESCRIPTION


Area 16 North

Area 16 Central

Electricity Cost

Slurry Line /year 0.6 0.7 1 0.8

Returnwater Line /year 0.8 0.8 1 0.9

1 Total Present Day Cost for 25 years 35 39.2 49.5 44

2 Present Value (10.6% discount rate) 12.1 13.6 17.2 15.2

C. Total

Cost (x R 1 000 000)

ITEM DESCRIPTION


Area 16 North

Area 16 Central

A+B1 Total Present Day Cost 133 151.2 184.9 171.4

A+C2 Present Day Value 110.2 125.6 152.6 142.7

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Final

Note

If a dry stacking operation is considered the cost of the conveyor belts will significantly influence the cost of the delivery system. The cost of a conveyor belt suitable to deliver the ash stream to area is estimated to be R 25 000/m vs. the 450NB pipeline of R 3700/m.

Combined Costs

The cost differences calculated above can be summed to provide an indication of the difference in cost for the various options.

Table 6: Summary of Major Cost Items

DESCRIPTION

Cost (x R 1 000 000)


Area 16 North

Area 16 Central

Delivery and Return Infrastructure Cost 110.2 125.6 152.6 142.7

Liner System 600 600

Pre-built embankments 40 70 0 0

Total 150.2 195.6 752.6 742.7

Note that a cost of the pre-built embankments of R 40 million for Area 10 and R 70 million for Area 15 was derived assuming 30m high embankment. The height of the embankment is probably conservative but needs to be investigated as part of the geotechnical investigation.

Discussion

The liner cost that will be required for the areas on natural ground is the major cost difference between the area types. It should be noted that the comparison can in principle not be made as the impact of groundwater and no liner may constitute a fatal flaw for the pit options.

6.9 Area Ranking

The various areas are ranked here to provide some form of structure to the site selection process. The ranking system and the weighing of the various components are and will always remain subjective. This ranking process should therefore only be seen as an input into the decision making process. The site selection process is also iterative and should be reviewed by all parties currently involved and should be repeated once consensus on the various weighing factors is achieved. This will probably only be possible once more information is gathered to understand the impacts.

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Final

As input to the selection matrix the:-

- The four areas are ranked from most favourable with an assigned value of 4 to least favourable with an assigned value of 1.

- The importance of the various objectives that is aimed to be achieved are weighed and assigned fractions of a total weight of 1.0. For the sake of this exercise the weighing factors for the objectives were assumed equal.

The objectives that are relevant here are:-

Minimization of Cost

The actual life cycle cost for each facility was not developed. The major cost components was however identified and used as input as set out in Table 6.

Stability Concerns

This objective takes account of the stability concerns associated with the open pit options due to the large settlements that is expected. The stability of the ash dam on natural ground should be acceptable provided that the dams are operated responsibly and most specifically limit the rate of rise as recommended in this report.

Minimization of Groundwater Impacts

It is assumed that the options on the mine spoils that will not be lined will impact on the groundwater while the impact of the facilities on natural ground is negligible due to the liner system provided.

The eastern void of Area 10 was previously backfilled with ash, which is probably contributing to the current groundwater impacts. It is therefore possible that an ash dam placed over this area ,specifically a dry stacking operation, may act as part of the remediation measures for this ash backfill. One may also argue that an ash dam will not change or introduce new constituents into the groundwater and that Area 10 could therefore be proven to have less of an impact than Area 15 (which does not have any ash backfill) during detailed investigations.

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Final

Figure 12: Area 10 Previous Ash Backfill

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Final

For the objectives Stability the two open pit areas were ranked the same and the two natural ground areas were ranked the same due to the fact that there is no distinction between the concerns the different area types have compared to one another.

Table 7: Area Ranking Matrix

OBJECTIVE STABILITY GROUNDWATER

IMPACTS COST SCORE

Weighing Factor 0.33 0.33 0.33

Area 10 1 2 4 2.3

Area 15 South 1 1 3 1.7

Area 16 North 4 4 1 3.0

Area 16 Central 4 4 2 3.3

Discussion

The ranking matrix shows that the development of Area 16 Central is the most favourable while Area 15 South is the least favourable.

This rankings system was used due to its simplicity and ease of use. Eskom may want to expand this matrix when more detailed information is available and the achievement of an objective can be assigned a score rather than an order of preference (i.e. a rank).

Area 16 falls outside the 8km search radius that was set as the battery limits for this project. Area 16 was however identified and included due to the fact that it appears to be the only alternative to Areas 10 and 15, which may prove to be fatally flawed if one cannot control the groundwater impacts.

7. RECOMMENDATIONS

Although the site selection process indicates that Area 16 Central is the preferred area it is recommended that a number of the investigations be carried out to conclude (i.e. confirm or alter) the site selection process outcome. The recommendations are listed in order of importance. - If an option that is situated on natural ground that does not overlie coal resources is to

be investigated further, the coal resources under Area 16 must be understood. - The groundwater impacts of the backfilled pit options must be investigated to

determine if the impacts can be satisfactorily managed or if the groundwater impact constitutes a fatal flaw.

- The groundwater impacts of the areas on natural ground must be investigated in support of the proposed liner option or as a motivation for a relaxation or increase of the requirements.


Final

- The geotechnical investigation needs to be carried out to improve the understanding of

the risk of settlement on the backfilled

to be defined to some degree of accuracy.

If the recommended investigations prove that the options on the are fatally flawed and the coal resources under investigate and determine the actual value of the coal lost due to resources.

Anton Bain B Eng for Jones & Wagener 4 July 2010 Document source: F:\Alljobs\A407-Eskom_Kriel_FAD4Document template: Report Geotech_tem_Rev1_Jan10.dotx

31

The geotechnical investigation needs to be carried out to improve the understanding of

the risk of settlement on the backfilled pit options and to enable the cost of mitigation

to be defined to some degree of accuracy.

If the recommended investigations prove that the options on the backfilled open cast pits are fatally flawed and the coal resources under Area 16 is minable investigate and determine the actual value of the coal lost due to area

Eskom_Kriel_FAD4\01_EIAUpdate\Report\A407ab_SiteSelection4_RevB.docxReport Geotech_tem_Rev1_Jan10.dotx

The geotechnical investigation needs to be carried out to improve the understanding of

pit options and to enable the cost of mitigation

backfilled open cast pits 16 is minable Eskom will have to

areas situated on coal

Danie Brink Pr Eng

A407ab_SiteSelection4_RevB.docx


Appendixes

AURECON

KRIEL ASH DAM ENVIRONMENTAL IMPACT ASSESSMENT

SITE SELECTION INPUTS

Report: JW71/10/A407 – Rev B

APPENDIX A

DESCRIPTION APPENDIX A - Table of Contents A.1 . . . A.2 . . .

KRIEL ASH DAM ENVIRONMENTAL IMPACT ASSESSMENT …

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