DauniaCoalAppendixCMineLandformAndFinalVoidManagementPlan 2009

8/19/2019 DauniaCoalAppendixCMineLandformAndFinalVoidManagementPlan 2009

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DAUNIA MINE PROJECT EISSupplementary Report APPENDIX CMine and Final Void & Landform Management PlanBMA Coal Operations Pty Ltd

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

2 BACKGROUND ........................................................................................................... 4

2.1 Project Description ........................................................................................... 4

3

ENVIRONMENTAL CHARACTERISATION................................................................ 5

3.1 Pre-Mining Land Suitability and Use ................................................................ 5 3.2 Post Mining Landuse ........................................................................................ 5 3.3 Climate ............................................................................................................. 5 3.4 Background Surface Water Quality .................................................................. 6 3.5 Spoil Characteristics ......................................................................................... 6 3.6 Topsoil Quality & Resources ............................................................................ 7 3.7 Pit and Spoil Water Quality ............................................................................... 7 3.8 Geology ............................................................................................................ 8 3.9 Groundwater Resource .................................................................................... 8

4

FINAL LANDFORM PLANNING PROGRAM ............................................................ 10

4.1 Long Term Planning & Spoil Fit Investigations ...............................................10 4.2 Final Void Extent ............................................................................................ 10

4.2.1Initial Base Model................................................................................................10 4.2.2Mitigation Strategies ........................................................................................... 11

4.3 Proposed Residual Void Design Criteria ........................................................ 11

5 LONG TERM VOID WATER STORAGE AND QUALITY .........................................13

5.1 Factors Affecting Void Behaviour ................................................................... 13 5.2 Previous Studies ............................................................................................. 13 5.3 Daunia Void Water Balance and Salinity overview .........................................16

5.3.1Modelled Void Storage and Salinity Behaviour .................................................. 16

5.3.1.1

SKM MODFLOW & Void Hydrology Modelling .............................................. 17 5.4 Conclusions .................................................................................................... 24

6 GEOTECHNICAL STABILITY OF THE RESIDUAL VOID ........................................25

6.1 Introduction ..................................................................................................... 25 6.2 Relevant Studies ............................................................................................ 25

7 VOID CAPABILITY TO SUPPORT NATIVE FLORA & FAUNA ...............................26

7.1 Scenario Dependency ....................................................................................26 7.2 Residual Void Rehabilitation Performance Criteria ........................................27

8 REFERENCE AND INFORMATION DOCUMENTS ..................................................28


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LIST OF TABLES

Table 1 Long Term Climate Statistics BOM Moranbah ............................................................ 5 Table 2 Average Spoil Leach Test Salinity TDS in mg/L* ........................................................ 7 Table 3 Daunia Hydraulic Parameter and Storage Coefficients............................................. 18

Table 4 Summary of the 8 Daunia Climatic and Catchment Area Cases Runs ..................... 19

LIST OF FIGURES

Figure 1 Daunia Final Void – Deep Pit Water Level Scenarios ............................................. 20 Figure 2 Daunia Final Void – Shallow Pit Water Level Scenarios .......................................... 21 Figure 3 Daunia Final Void – Deep Pit Salinity Behaviour ..................................................... 22 Figure 4 Daunia Final Void – Shallow Pit Salinity Behaviour ................................................. 23

LIST OF ATTACHMENTS

Attachment 1 Daunia Mine Configuration At Closure – initial Base Case .............................. 29 Attachment 2 Daunia Mine Conceptual Rehabilitated Landform – Initial Base Case ............ 30

LINKAGE BETWEEN EPA SUBMISSION & REPORT CONTENT

Qld EPA Submission - IssueReportSection

Potential Impacts on Groundwater resources after mining

The EIS should provide a detailed, reasoned evidence based assessment of the potential for salinecontaminated water in the void to recharge groundwater. The EIS should detail what effects this recharge willhave on all aquifers including the alluvial aquifer.

3.8, 3.9, 5.1, 5.2,5.3, 5.4.

Size of Proposed Final Voids

The EIS should provide more detailed information on and illustrations of, the proposed size and shape of thefinal void.

4.1.4.2, 4.3 & Attachment 2.

Mine Planning and the size of the proposed final voids

The EIS should reassess the mine plan and consider alternative ways of extracting the resource that wouldleave a much smaller final void. Reasoned arguments should be presented for selecting a preferredalternative.

2.1, 4.1.4.2,4.3

Water Levels in Final Void

The EIS should provide more details on the equilibrium water levels in the final void in relation to theproposed final landform and illustrate the size of the residual lake during both drought and wet climaticconditions. The EIS should assess under what conditions if ever, including under Probable MaximumPrecipitation, water in the final void would discharge to the surrounding environment. If discharge from thefinal void occurs the EIS should address the potential impacts of the discharge.

5.1, 5.2, 5.3 &5.4

Final Void Water Quality and potential impacts on water resources

The EIS should model the water quality in final voids as a prelude to providing a reasoned evidence basedassessment of the potential impacts of hyper saline water in the void on both surface and ground waterresources.

5.1, 5.2, 5.3 &5.4

Rehabilitation of final landform and runoff into final voids

The EIS should provide details on the final landform and include figures that illustrate contours and includecross sections at appropriate intervals.

The EIS should also provide: Details on drainage and seepage control systems Measures to ensure stability of the waste dumps.

4.3, 6.1, 6.2, 7.1& 7.2.


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GLOSSARY OF TERMS

AHD Australian Height Datum

AOC Approximate Original Contour

BMA BHP Billiton Mitsubishi Alliance

CPP Coal Preparation Plant

EA Environmental Authority

Final Void The last mining pit and remainingramps.

EPA Environmental Protection Agency

EP Act Environmental Protection Act 1994

EMPlan Environmental Management Plan

Endwall The lengthwise extremities of thepit. (As opposed to the sideextremities which are the highwalland lowwall).

FRR Final Rehabilitation Report

Highwall The pit wall of un-mined land

LOA ‘Life of Asset’ Mine Planning

Lowwall The spoil placed immediatelyadjacent to the pit in the previouslymined strip and can rise to crest of

a prestrip dump.

Partings Overburden strata between coal

seams

Pre-stripping The operation to removeoverburden with truck and shovel

Rehabilitation Earthworks and revegetationtreatments

Rejects Coarse coal washery waste stream(non-coal material).

Residual Void A void remaining after mine siteclosure.

RO Runoff Coefficient

Salinity Generally refers to theconcentration of sodium chloride &other salts either in soil or water

Spoil Overburden after removal toexpose the coal seam

Tailings Fine coal washery waste.

Topsoil The upper layer of the soil profileremoved for reuse in rehabilitation.

TWL Top Water Level


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1 EXECUTIVE SUMMARY

The Daunia EIS has been submitted to the Queensland government and its EnvironmentalProtection Agency (EPA) has requested that the proponent BMA provide further informationon the treatment and performance of residual voids. These queries relate to the locationand size of the residual void, prospective rehabilitation treatments; possible interaction ofthe groundwater table with the residual void; long term water levels and the potential foroutflows; and the long term salinity of the void water. EPA states that the EIS shouldinclude a detailed reasoned evidence based assessment for the potential of saline water inthe void to recharge groundwater including the alluvial aquifer.

Thus the objective of this supplementary environmental impact study (SEIS) has been tofurther examine the possible hydrological behaviour of the residual void. The potentialinteraction with the regional ground water table, examine salinity behaviour and to propose

strategies for the rehabilitation of the future Daunia residual void. Areas of further researchand investigation during the mine operational period which may improve the outcomes forfinal void stability and potential uses are mentioned..

The EIS document provides a series of preliminary ‘snapshots’ of a feasible final landformat various points in time. Importantly it is noted that all of the mine void created to year 15has been completed backfilled to approximate original contour. Further, this supplementaryEIS document reports on the preliminary findings of longer term mine planning which isdeveloping options for reducing the residual void footprint. Preliminary results indicate thata reduced footprint of up to 75% of the base case footprint reported for year 21 in the mainEIS document can be achieved.

The treatment of final voids and the final configuration of highwalls and endwalls is an areaof considerable interest and largely unresolved from an industry viewpoint. Many open cutcoal mine operators intend to use a fence and bund scenario and EPA has approved thisvia Environmental and Integrated Environmental Authorities for many years.Notwithstanding this, the EPA via its policy determinations (such as Guideline18) indicatesa reluctance to accept relinquishment of mine leases which include voids that are left in anunsafe, unstable or unsustainable configuration. The proposed Daunia Mine conceptualresidual void includes considerable regrading to slopes of 17% percent or less, followed bytraditional topsoil and revegetation treatments above expected water level. This proposedtreatment for the Daunia residual void is substantially more conservative compared totypical EPA void compliance conditions as stipulated in many Environmental Authorities foropen cut mines in Queensland.

Once commissioned the Daunia Mine should remain an operational project well into theforeseeable future and the final configuration of the mine will ultimately depend on demandfor coal and other factors. However, in line with its commitments for reducing the footprint offinal voids, BMA will seek to infill voids with spoil, reject and tailings waste to the maximumextent practicable. Nonetheless at mine closure a void will remain and it is likely that mineplanning revisions which are routinely carried out during the life of any open cut coal miningoperation still will result in changes to the final void position, size and configuration. This isa normal situation with large opencut mine operations.

Daunia is not a developed mine, thus provision of quite specific geotechnical assessmentand hydrological performance of “the residual voids” will not be feasible for many years. Accordingly, much of the following information contained in this supplementary report is


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necessarily conceptual, however, where possible pertinent site data has been used. Furtherfor the purpose of predicting salinity levels and standing water levels in the residual void,quite conservative assumptions have been made.

This investigation includes contributions by Sinclair Knight Pty Ltd (SKM) and PW Baker & Associates Pty Ltd and has where appropriate drawn on the findings of several residualvoid investigations that BMA has completed and submitted to the EPA in mid 2008 as wellas the results of earlier studies sponsored by BHP in the early to mid 1990’s. Further asindicated above, BMA mine planning have provided initial results for reduced void footprintbased on recently commenced LOA plan revisions.

SKM have used MODFLOW Groundwater model to provide groundwatercontributions/behaviour and have developed an excel spreadsheet to integrate groundwaterand surface water contributions to provide conceptual void water level and salinityoutcomes. Initially the EIS conceptual void configuration was utilized as a base model withalternative scenarios then modelled to examine the prospects of quite different hydrologicaland salinity outcomes. Modelling by SKM and others show that it is possible to improve

void salinity outcomes.

Overall, the modelling undertaken by SKM demonstrates that the projected Dauniaregraded final void has very little potential to fill and spill, unless unusually large spoil areasreport to the void. Nonetheless, with a regraded void situation the void itself becomes aconsiderable catchment with the potential to store large quantities of water. As with thefindings of several other mine void studies undertaken in the Bowen Basin, increasedsalinity through time in the final void is likely unless strategies are implemented whichmodify the relationship between the regional water table and the mine void and itscontributing catchments.

These strategies which have been discussed in this supplementary EIS report include the

possibility of using greater backfill amounts to raise the predicted standing water level of thevoid above the regional water table level such that the groundwater gradient is reversed.This may also involve increasing or perhaps decreasing the catchment area above the voidto ensure that the long term water level and quality meets the performance requirement.

During the operational phase BMA Daunia is committed to undertake further investigation insupport of firming up residual void stability, hydrological behaviour and void rehabilitationstrategies. These studies/investigations include:

1. More detailed hydrological and geochemical research aimed at more accuratelypredicting long term void water levels and mechanisms that may be used to enablethe void to self regulate its salinity and not adversely impact on useful groundwater

reserves.

2. Groundwater investigation aimed primarily at understanding the behaviour of theregime in particular reference to the likely final position and configuration of the finalvoid so that the void’s potential to depress or recharge groundwater is more fullyunderstood and that the refined hydrological model accounts for groundwatermovements more comprehensively in determining long term storage and salinitylevels.

3. Ongoing spoil characterisation to determine the characteristics of spoilemplacements surrounding residual voids as well as physical measurements of spoilrunoff and leachate to refine the void salinity balance.


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4. Durable rock identification to ensure that sufficient material is available to for rockmulching steep long slopes into voids – in the event that improved outcomes forlandform stability, void hydrology and salinity are indicated.

5. Further investigation into erosion mitigation on long slopes which will be formedwhen highwalls and lowwalls are subjected to substantial regrade treatments.

6. Active liaison with the EPA so that the Regulator can understand the complex natureof the final void issues and provide more strategic advice on its requirements for therehabilitation outcome for large residual voids in Central Queensland. This will assistBMA as it develops strategies for mine closure which are consistent with theRegulators long term view and requirements.

7. The process of refining rehabilitation methods for spoil areas, including residualvoids and developing appropriate land use goals for land disturbed by mining is anongoing one as mining technology develops and mine plans change. Accordingly, inthe future, the treatments proposed for residual voids may change. Nonetheless,

BMA is committed to stable and sustainable outcomes for the Daunia residual void.

The desired outcome for the Daunia residual voids is that a stable landform eventuates andthat costs/liabilities to BMA are tolerable at closure. The final void and its configuration andits performance characteristics will be progressively refined during the operational life of theDaunia mine.


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2 BACKGROUND

2.1 PROJECT DESCRIPTIONEIS Section 3 Project Description provides a detailed description of the project. In summaryhowever, the Project will be an open cut coal mine using a conventional excavator andtruck fleet. Construction is expected to commence in 2009, with first coal in 2010.Exhaustion of the deposit is projected at approximately 21 years after mining commences.i.e. 2031.

The relatively shallow depth of cover makes the Daunia deposit ideal for open cut mining.The majority of the deposit is to be mined in a two seam operation of the Leichhardt andUpper Vermont Seams. The complex structural setting of the deposit is associated withfaults with throw greater than 5 m, which has allowed the deposit to be divided into a series

of mining areas or pits based on faulted blocks. These ‘pits’ define the direction of miningso that, to the extent possible, and consistent with reasonable mining practice, the mineadvances parallel to the strike of the faulting. This approach of defining ‘pits’ has been usedto develop a mining strip layout suitable for truck and excavator mining. This method istypically based on 100 m wide mining strip

Design parameters adopted for mine planning include:

100 m wide mining strips, nominally 500 m in length; out of pit spoil dump external face slopes of 1 (vertical) : 10 (horizontal), or 10%; out of pit spoil dump benches of 10 m width at 10 m intervals (lifts).

The depth to the top of the Leichhardt coal seam varies between about 40 m and 80 macross the deposit. Interburden between the Leichhardt and Upper Vermont seams result ina maximum pit depth of approximately 120 m to access the Upper Vermont seam, which isthe limit of economic coal.

Two box cut areas are planned (each along the eastern boundary of the resource). Spoilwill be carted to in pit and out of pit dumps. The dumps will be progressively shaped totheir final landform based on a maximum overall slope from dump crest to dump toe of 10per cent. The dumps will be topsoiled and revegetated either to native bushland or pasture.

At the completion of mining, voids will either be completely backfilled or rehabilitated with 1

in 6 (17 per cent) slopes and drainage protection, with rock armouring applied whererequired. The base of the rehabilitated final voids in the south will slope down to amaximum depth of 100 m below the existing surface level. Other voids will be eitherprogressively backfilled or backfilled at when mining operations stop.

The proposed post-mine land use for disturbed areas is a mosaic of self sustainingvegetation communities and grazing land using appropriate native tree, shrub and grassspecies, and improved pasture species as appropriate. Local plant species will be includedin the seed mix so as to restore elements of the pre-mining communities to the rehabilitatedassemblages. Note that the description of residual void treatment is superseded by thediscussion and findings in this further submission to the EPA.


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3 ENVIRONMENTAL CHARACTERISATION

3.1 PRE-MINING LAND SUITABILITY AND USEDetails for pre-mining land use and soils within mine lease areas have been described inthe Daunia EIS. Land within all of the Daunia project area has been used for beef cattlegrazing for many years. The area is under extensive buffel with some areas under nativegrass cover.

3.2 POST MINING LANDUSE

The current EIS preliminary mine plan shows that a residual void of approximately 390

hectares will be present by projected closure in 2031. Final use of the void area isproposed as bushland/pasture, whilst beneficial use of the void water will be dependent onthe actual treatment imposed on the residual void. Note that this submission includesamended advice on final void treatments, configuration and sizing, following furtherconsiderations by BMA and its consultants in which the results of preliminary LOA planningshow that it may be feasible to reduce this void footprint to less than 100 ha.

3.3 CLIMATE

The EIS provides a detailed description of the regional climate. The Daunia project islocated in the warm subtropics. The area exhibits moderate rainfall and high evaporationrates. The area experiences hot summers and warm winters with an average daily maxima

of 33.8oC in December and 23.6oC in July. Rainfall is highly variable between and withinseasons. Most rainfall (approx. 70%) occurs as intense storms and cyclonic rain in summer(December to March).

Overall, the annual rainfall is highly variable and droughts are common. As rainfall isgenerally concentrated in the cyclone season, temporary water surpluses can occuralthough evaporation rates are much higher than rainfall. Long term averaged monthly andannual precipitation and evaporation is shown below in Table 1.

Table 1 Long Term Climate Statistics BOM Moranbah

Month

TemperatureOC

Relative

Humidity %

Evap

(mm)

Wind

SpeedKm/Hr Rainfall (mm)

AverageMin

AverageMax

9am 3pm DAILY 3pm MedianHighestDaily

HighestMonthly

Jan 22.0 34.2 69 41 8.5 8.5 66.6 120.4 315.0

Feb 21.8 33.2 73 46 7.7 9.6 85.8 150.8 316.2

Mar 20.1 32.3 70 41 7.2 9.5 34.6 164.8 268.0

Apr 17.6 29.5 73 44 5.8 8.8 25.2 143.8 271.0

May 14.4 26.4 73 45 4.3 6.8 27.6 58.0 196.6

Jun 11.0 23.7 72 43 3.6 6.3 9.4 38.8 55.3

Jul 9.7 23.6 69 39 3.8 6.8 5.9 60.0 103.6

Aug 11.1 25.2 66 36 4.9 7.7 12.5 150.8 247.3

Sep 13.9 29.4 57 28 6.7 9.0 3.8 20.4 39.4

Oct 17.6 32.2 59 31 8.0 8.6 15.8 73.8 146.6


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MonthTemperatureOC

RelativeHumidity %

Evap(mm)

WindSpeedKm/Hr

Rainfall (mm)

Nov 19.5 33.0 61 35 8.6 8.8 69.4 85.6 220.3

Dec 21.1 33.8 65 40 8.7 8.5 82.6 116.6 318.2

Annual Av. 16.7 29.7 67 39 2,366 8.2 583.6 164.8 208.1

High rainfall events are common hence surface runoff can be substantial. Averageevaporation exceeds average rainfall 12 months of the year and the evaporation average isabout 4 times the annual rainfall. The long term average annual rainfall is 583.6mm fallingon an average of 55 rain days. Evaporation rates are high through the year, particularly soin the summer period. Annual evaporation is 2366mm. (Moranbah weather station), thusevaporation greatly exceeds precipitation, hence water stress is expected to be significantfactor in the performance of future rehabilitation of disturbed land, particularly on slopes orwhere topsoil thickness is limited and the under lying spoil may be compacted.

The above EIS climate information indicates that evaporative losses from the residual

Daunia void will be high and function as one of the prime determinants in establishing thelong term water level.

3.4 BACKGROUND SURFACE WATER QUALITY

Refer to the Daunia EIS Section 6, Surface Water Resources for details, but in summary;The mining areas are drained by two unnamed drainage paths. The unnamed drainagepaths were named Daunia and Daunia East for the purposes of the EIS assessment. Thetwo unnamed drainage paths are ephemeral and drain to the Isaac River.

The infrastructure area is drained by New Chum Creek. New Chum Creek flows south-westto its discharge point into the Isaac River. Few water samples measurements have beentaken to date, but overall waters arising from the site have low salinity, less than 200uS/cmRefer to EIS Table 6-15 Water Quality results from the field investigation. Low salinity isreflective of the low salinity soils of the area.

3.5 SPOIL CHARACTERISTICS

The chemical and physical characterisation of spoil surrounding and residual void will havea marked influence on residual void stability and water quality. The EIS document providescomprehensive information on overburden collected and analysed as part of the explorationprogram.

The Daunia EIS Appendix G Mineral Waste reports that Paste EC has been determined fora range of overburden and interburden samples at Daunia – the number of tests (199) andsite coverage is impressive.

Overall the paste pH’s are quite low as shown from data taken from EIS AppendicesMineral waste Table G5.

Min 51 us/cm.Median 739 us/cm

Mean 803 uS/cmMax 2, 520 us/cm with a desirable range reported as


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The leach tests show that spoil leachate is highly variable across the Bowen Basin, but thatsome spoils can express quite low salinity. As the Daunia mine operation has yet to bedeveloped, there is no monitoring data on spoil runoff quality; however, Daunia spoil salinityshould be reflective of the low salinity measured in overburden sampling. Further, the pH ofalmost all samples are strongly alkaline with a mean and median pH of 8.4 as reported inEIS Appendix G. Given these results, it is reasonable to conclude that surface runoff fromspoil areas will be alkaline and have quite low salinity. It follows that pit water accumulatingfrom surface runoff and spoil seepage generated from spoil is expected also be reflective ofthese characteristics, at least in the short term. Refer to Section 5 which discusses longerterm void salinity balance.

3.8 GEOLOGY

The Daunia EIS Section 7.1.2 Geology and Hydrogeology reports that the Project Site islocated in the northern part of the Bowen Basin containing principally fluvial and somemarine sediments. The Project Site lies near the western boundary of a sedimentarytrough known as the Taroom Trough, which was filled by a thick accumulation of mainly

terrestrial sediments during the Permo-Triassic period.

The Project Site occurs within a shallow basin structure immediately east of the New ChumFault, which separates Daunia from the Poitrel deposit to the west. The New Chum Faultmay influence groundwater levels and flow directions. However, it is reasonable to assumethat there is some hydraulic continuity between the coal seam aquifers across the depositsand that the groundwater levels and flow directions beneath Daunia are similar to Poitrel.

The coal deposits are contained in the Late Permian, Rangal Coal Measures (also knownas the Blackwater Group), which are approximately 100m thick. The Rangal Coal Measuresare underlain by the Fort Cooper Coal Measures and overlain by the Late Permian to EarlyTriassic Rewan Group.

The transition between the Rewan Group and the Rangal Coal Measures is difficult todefine and is often based on a change in colour, from green-grey of the Rewan sandstonesto blue-grey of the Rangal sandstones. Given the similar geological and hydrogeologicalproperties of the Rewan Group and the Rangal Coal Measures, these formations havebeen grouped together for the purpose of this assessment. In the southern half of theProject Site, Quaternary aged Alluvium overlies the Permo-Triassic sediments.

The Daunia deposit contains two coal seams of economic interest, the Leichhardt Seamand Upper Vermont Seams of the Rangal Coal Measures. The Leichhardt Seam (DL1) istypically 5 m thick and has a lower split (DL0) about 0.5 m thick located approximately 1 m

below DL1. The Upper Vermont Seam (DV4), located 10 m to 35 m below the LeichhardtSeam, is typically 3.5 m thick and splits to the north into upper and lower plies (DV2 andDV1 respectively) with up to 30 m of interburden.

3.9 GROUNDWATER RESOURCE

A detailed groundwater investigation based on monitoring water levels and qualities has notbeen undertaken for this EIS. However, a series of groundwater monitoring bores arebeing installed at the Daunia project at time of this report preparation. These bores willmonitored in a routine basis and will enable BMA to more comprehensively determine theextent and character of groundwater resources at the Daunia mine project and enable thecontinual refinement of the groundwater model for the Daunia mine.


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However, in the interim groundwater characteristics of the adjacent BMA Poitrel Mine are ofuse in developing a conceptual understanding of the Daunia situation. Groundwater studieswere completed for the adjacent Poitrel mining leases as part of the BMA Poitrel EIS in2004.

The Daunia Project EIS presents groundwater quality data available from four bores usedto collect data for the adjacent Poitrel EIS in 2004. The salinity (measured as totaldissolved solids) of groundwater in these bores ranges from 4,000 to 8,000 mg/L. Thiscorrelates to an electrical conductivity (EC) of approximately 7,000 to 14,000 uS/cm. Sincethe Project EIS was prepared, further background data has been analysed from operationalPoitrel groundwater monitoring bores that will be incorporated into the Project groundwatermonitoring network. Groundwater salinity from the Obs 1 bore (see EIS Appendix B fordetails on location) ranged from 3,160 to 5,800 uS/cm during monthly sampling events fromFebruary 2008 through to January 2009. There is a high degree of variability ingroundwater quality variability in the region. However, a conservative value has beenadopted for the preliminary Daunia final void modelling of 15,000 uS/cm.

The Daunia EIS section 7.2.2.2 Groundwater Quality – Post Mining reports that therehabilitated final void will collect and accumulate water only from groundwater ingress,direct rainfall into the void, and from overland surface flows from those slopes of the wastedump draining into the void. All other surface flows within the vicinity of the rehabilitatedfinal void will be diverted around the void. In general, as a consequence of evaporation, thesalinity level of the water in the rehabilitated final void is expected to rise over time. Therecould also be issues associated with oxidation of the coal seams and potential changes tothe groundwater chemistry, however any impacts are likely to be localised in the vicinity ofthe rehabilitated final void.

As indicated, this supplementary study discusses at a conceptual level how strategies might

be implemented which change the salinity and hydrological status of the residual void.


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4 FINAL LANDFORM PLANNING PROGRAM

4.1 LONG TERM PLANNING & SPOIL FIT INVESTIGATIONSThe greatest single challenge for provision of progressive rehabilitation into the futureinvolves effective planning of prestrip operations and spoil placement. This is wellrecognised by BMA and all of its operations are conducting substantial investigationsinvolving spoil fit, final landform and residual void treatment. Mine planning is an ongoingprocess and is progressively refined during the life of the operation. Changes in technology,operational costs and product demand require revisions to the mine plan, including the finallandform plan.

Long term mine feasibility planning for the Daunia project suggests that truck and shovelwill be the primary method for creating the final rehabilitation surface. The final landform

concept illustrated as Figure 3.1 in the EIS project description represents an outcome whichhas resulted from the initial mine plan schedule. Mine planning and schedulinghas focussed on the first 5-10 years of mining (all in the North), with only preliminary long-term planning having been completed for the Southern Pits

The planning which has been completed for the first 10 years shows that considerable voidbackfill is undertaken. For that matter, work to date shows that all of the final void created inthe first 15 years can be eliminated by progressive backfill. However, planning for the latteryears has yet to be optimized. Nonetheless, BMA recognises that the size and extent of thefinal void can be reduced by cost effective spoil placement programs in the latter years ofthe mine life and as already indicated, all BMA operations are currently in the process ofdeveloping spoil placement strategies which are aimed at cost effective reduction of thefinal void foot print. This is an extremely complex and time consuming task whichcommenced some two years ago and studies to date show that there are cost andenvironmental advantages available when final voids are progressively backfilled duringoperation. Mine planning for the Daunia Project is now also developing optimised longerterm mine plans which aim to reduce the final void footprint.

4.2 FINAL VOID EXTENT

4.2.1 Init ial Base Model

The initial final void base case is depicted in the EIS S3.1 Project description. As indicatedabove this void is reflective of the base mine plan which assumes that mining ceases atyear 21. Prior to year 15, mine planners have made a great effort in scheduling operationsto backfill almost all of the mine void to approximate original contour. However mitigationstrategies are not complete for the residual void beyond this time. The base case voidwithout mitigation in later years as outlined in the EIS document is approximately 9kilometres long. For the purpose of showing the conceptual rehabilitation treatment, a1V:6H grade has been imposed on all sides of the void.


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4.2.2 Mitigation Strategies

As previously discussed, optimization of the LOA mine plan is in the very early stages ofdevelopment, thus providing an accurate final landform plan in the immediate future is notpracticable. However, preliminary results indicate that the final residual void footprint can bereduced by up to 75% of the initial final void base case. Such reduction will reduce theresidual void footprint from the base case 390ha back to approximately 100 ha. This work isof a complex and time consuming nature. BMA practice is to review final landformobjectives and proposed outcomes annually as part of the it’s LOA monitoring and planningprocess or in those situations where a material change to the mine plan is required.

BMA will commit to providing the EPA with a conceptual final mine plan which will show thatas much as 50% of the residual void will have been backfilled by cessation of mining. Thevoid may be reduced further to 75% filled when the LOA process has been refined. As towhether the backfill will focus in the east or west residual void or parts of each will bedetermined as a consequence of the LOA planning and optimization work. This is underwaybut cannot reasonably be provided as part of this supplementary EIS submission, given the

lengthy time which is required to accurately determine the final void extent and locationthrough detailed mine planning.

4.3 PROPOSED RESIDUAL VOID DESIGN CRITERIA

BMA is committed to undertaking substantial treatments of residual voids at its proposedDaunia Mine to ensure that such areas are safe, stable and sustainable after cessation ofoperations.

In 2007 BMA Coal and its consultants commenced development of a set of generic designcriteria to assist its sites with the development of stable landforms. “Guideline for theDesign of Sustainable Mine Landforms”. See Appendix J of the Daunia SEIS. Thislandform guideline has been developed to help BMA mines implement closure planningprocesses aimed at the achievement of sustainable rehabilitated landforms on a costeffective basis.

The guideline acknowledges that rehabilitation of mine disturbed land is not simply anenvironmental task. The work is of a complex and expensive nature and satisfactoryoutcomes can only be available if closure planning is embraced at the corporate, sitemanagement and operational levels.

The BMA Sustainable Landform Guideline requires that planning, design and scheduling of

excavation and spoil placement should be aligned with a mine closure plan so that costeffective practices can be implemented during the operational phase of mining with a goalof substantially reduced rehabilitation expenditures at closure. This is the essential basis ofBMA closure / rehabilitation requirements.

These guidelines will be implemented for the Daunia Mining Operation and were used asbasis for initial long-term mine planning and short term design. The guideline provides aframework for ensuring that the mining and spoil placement program is aligned with theagreed final landform concept. It covers a range of issues which are pertinent to thisobjective including:

Embedding closure / landform requirements into the responsibilities and

accountabilities of all senior personnel. This is necessary as the ability of mines to


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5 LONG TERM VOID WATER STORAGE AND QUALITY

5.1 FACTORS AFFECTING VOID BEHAVIOURThe long term quality and quantity of water stored in residual voids is dependent on anumber of variables including:

1. Climate – particularly rainfall and evaporation.

2. Catchment areas reporting to the void

3. Extent of void regrade – regrading voids can substantially increase catchment area.

4. Topographical configuration of the final void and surrounding catchment spoil areas.

5. Effectiveness of rehabilitation in reducing surface and subsurface runoff into thevoids.

6. Rapidity of solubilisation of salts being transported by both surface and subsurfacedrainage to the voids.

7. Remaining amount of process and other water affected by the mine workingspumped into the voids.

8. The salinity and potentials of the void floor material.

9. The depth and manner of isolation of the coal seams below therehabilitated/backfilled void floor.

10. Presence of groundwater inflows and outflows from the voids.

5.2 PREVIOUS STUDIES

Predictive void investigations in Central Queensland have been undertaken from time totime since the mid 1990’s. The first major investigation was sponsored by BHP Coal PtyLtd in which PPK consultants (now Parsons Brinkerhoff) prepared a Spoil HydrologyLumped Parameter Model (SHLPM) for a number of voids at the BHP Coal operations(Now BMA). A daily water balance model was developed in an attempt to assess the long-term hydrological responses of final spoil-void systems in the Bowen Basin. The SHLPModel was designed for situations where containment of water reporting to the final void isrequired. (0.6 RO above water level and Pan Factor of 0.7 for low water level to 1.0 for

high-water level.

For the typical void scenario, the PPK modelling indicated that idealised voids would reacha steady state depth in about 40 years post closure. Work by P. Baker in 2003 usingOPSIM modelling at Oaky Creek Mine also demonstrated that voids have no potential tospill and are effectively dry most of the time when the catchment area to void area istypically 4:1 or less and where groundwater ingress is minimal. Much greater surface areato void ratios are required to cause a void spill situation.

Whilst it is recognised that in the absence of significant elevated groundwater table, there islittle likelihood of typical deep steep sided mining voids storing large quantities of water on apermanent basis, it is conceivable that voids which have large catchment areas and or


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which have been substantially regraded may have potential to spill in some circumstances.Thus the potential for rehabilitated voids to spill has been examined by SKM.

A long-term concern for residual voids in arid and semi arid areas is the potential for waterto become hyper-saline and perhaps seep into surrounding water tables. This has been

recognised for many years. For example, ACARP Project No. C7007 (Water Quality andDischarge Predictions for Final Void and Spoil Catchments) made a number of general /primary findings following completion of their field studies and void water quality modelling.In particular (S7.3 conceptual model of mine water flow) states that:

1. There is a correlation between TSS and TDS, thus water quality in final void will bereflective to some extent of the TSS of surface runoff.

2. In many situations most of the void water is derived by surface runoff.

3. The influence of subsurface flow through spoils might be limited because of low flowvolumes moving thru the spoil.

4. Preferred pathways may exist which may cause rapid movement of seepage water – e.g. along the base of the spoil piles. But preferred pathways may block over time.

5. Direct rainfall to the void introduces low concentration water.

6. Evaporation has the opposite effect.

7. A stable system with no salt build up will occur if groundwater inflows flows aregreater than evaporation.

8. In a closed system, the water accumulating in the void could come from any of thesources or paths described (groundwater/seepage/preferred pathways/incidentrain/surface runoff) but can only leave by evaporation. The water level is maintainedby evaporation and evaporation causes continuous deterioration of water quality

due to salinity build up.

Gilbert and Associates Pty Ltd conducted computer simulations for final void hydrologicalassessments in various final configurations at 6 BMA operated mines in the Bowen Basinregion of central Queensland in 2008. Final configurations included: Fence and Bund, 25%batter regrade and 10% batter regrade.

The simulations included inputs of historical rainfall and evaporation data for the region,information on salt concentrations and information on the geology, mining spoil andgroundwater conditions provided in various reports supplied to Gilbert & Associates by PWBaker and Assoc. Pty Ltd. The consultants utilized a version of the Australian WaterBalance Model (AWBM) developed by Boughton, W.C. (2004), to estimate the amount ofsurface water runoff entering pit voids using rainfall data, evaporation data and informationon the behaviour of various catchment types contributing water to the voids.

Seep/W was used to determine likely groundwater entry to and exits from the voids usinginformation supplied regarding the local geology and groundwater conditions, so far as thisinformation could be ascertained. Seep/W used the provided information together withinformation entered regarding water pressure or flow rates at the boundaries of the modelto compute flow rates of water across flux lines also drawn in the graphical representation.These flux lines were positioned to measure the rate water entered or left the pit void, aswell as the rate water travelled into the pit from expected salt sources such as coal seams.


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groundwater) occurred and, as expected, salt concentrations in the void continuedto increase throughout the simulations. Thus complete isolation of the void fromgroundwater transfer would likely produce an “evaporation pan” where salt levelscontinue to increase at a consistent rate until real world physical constrains limit theprocess.

5.3 DAUNIA VOID WATER BALANCE AND SALINITY OVERVIEW

As previously indicated the actual size and extent of the Daunia final void cannot bepredicted with confidence until Life of Asset Planning (LOA) has been completed, eventhen, changes in demand, economics and technology have potential to impact the LOA planand result in change to the location and size of the residual void as well as the extent ofimportant contributing catchments. This is consistent with the approach taken at all ofBMA’s operational mines. Nonetheless, the following generalisations regarding void waterquality can be made for the Daunia project based on the existing information:

Ground water monitoring from nearby local coal aquifers confirms that the water isquite saline. Small aquifers in shallow tertiary and quaternary paleo channels mightcontribute significant amounts of groundwater in wetter years. However, at this timethere is limited information on the potential ingress of groundwater to the Dauniapits.

During mine operations in Central Queensland pits depress groundwater levels andseepage of saline water into the pits is likely. But Evaporation rates are very highand for the main, the experience in the region is that pit water issues are negligibleduring operations. (Excluding storm events).

The overburden at the Daunia project has proved to be significantly non saline and

alkaline, thus the future spoil mass surrounding the future voids should also be nonsaline and alkaline. Catchment dams below spoil areas should also necessarilystore low salinity, alkaline water and as well flows of surface water to the pit fromspoil runoff should also be of low salinity.

Strata in close contact with coal e.g. coal basement strata are generally saline inthe Bowen Basin, thus direct contact with this material may cause elevated salinity;however this may be remedied by backfill with low salinity spoil at closure.

The general behaviour expectations as evidenced /indicated by studies undertaken at otherBMA mine sites are quite relevant to the Daunia project. The Daunia project is also locatedin a semi-arid climatic zone where the long term average annual evaporation greatly

exceeds average rainfall. Here the approximate long term average rainfall is 584mm andevaporation is 2,366 mm. Further, evaporation exceeds average rainfall 12 months of theyear. Thus as has been modelled at 6 other BMA mine sites, it is reasonable to concludethat without considerable backfill to raise the void water level above the standing groundwater table or providing a release mechanism to down stream surface waters, increasedsalinity in the void is reasonably anticipated.

5.3.1 Modelled Void Storage and Salinity Behaviour

Modelling post mining void storage and water quality behaviour to examine the potential forthe void to overtop in extreme events depends on an ability to determine the following keycharacteristics: surface flow and incident rainfall contributions and groundwater rechargerates (fluxes) to the void. Further to predict water quality, characterising the salinity of the


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spoil mass as well as predicting the effects of preferred flow paths and geochemicalprocesses within the spoil need to be undertaken. Conceptually these matters can bemodelled with only broad indications of likely behaviour. More detailed predictive modellingcannot be undertaken until the operational mine has firmed up on final mine landform andmaterials scheduling as well as an array of high quality environmental data have beencollected in sufficient intensity and over sufficient time to enable confident projections ofvoid and ground water behaviour to be made. This information is typically not available atthe time of an EIS, but is progressively collected over the operational life of a mine.

Such important longer term based data would include groundwater behaviour in monitoringbores established around the perimeter of operational and residual voids and in spoil areaswhich may have linkages to these voids as well as historic pit water data sufficient tounderstand the ranges and conditions of water levels and qualities and sources responsiblefor those contributions to the void.

5.3.1.1 SKM MODFLOW & Void Hydrology Modelling

From a purely water balance viewpoint, there is a reasonably high degree of confidencethat water level behaviour for voids including regraded or partially backfilled voids, can bepredicted using water balance models including daily step or annualised models.

Final void water and salt balance modelling has been undertaken by SKM consultants toinvestigate a range of final void configuration options to provide an indication of the likelybehaviour of residual voids at the Daunia Project. The study has involved:

• Hydrological assessment of the salt and water balance based on the preliminaryresidual void concept outlined in the EIS document Project Description using VisualMODFLOW Version 4.2 and Excel modelling techniques.

• Assessment of the long term behaviour of the void and its interaction with local andregional surface and groundwater resources as well as the sensitivity of predictedbehaviour to current unknowns;

• Formulation of recommendations for future investigations and research aimedultimately at developing an acceptable, low risk plan for the final void(s) at theproposed Daunia mine site.

MODFLOW Groundwater Modelling Predictive long term water balance scenarios within the final void were conducted using the

model developed for the purpose of identifying environmental impact during miningoperation (cf. EIS chapter 05). The model was built within MODFLOW ® software package.MODFLOW is a three-dimensional finite element software product for analysinggroundwater seepage and excess pore-water pressure dissipation problems within porousmaterials such as soil and rock. It allows analyses ranging from simple, saturated steady-state problems to sophisticated, saturated-unsaturated time-dependent problems.

The final void was simulated by attributing a high conductivity (k=9999m/day) to the cellscorresponding to the void. For these Cells, the specific yield (unconfined storageparameter) was set to 1.0 (i.e. the entire volume of the cell can be occupied by water).Refill material (Spoil Material) has a hydraulic conductivity set to 10m/day. All hydraulicparameters are summarised in the following Table 3.


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Table 3 Daunia Hydraulic Parameter and Storage Coefficients

G e o l o g i c a l

U n i t

M o d e l

L a y e r

K

m o d e l

K

S o u r c e s

S s m o d e l

( 1 / m )

S y m o d e l

S s / S y

S o u r c e s

Quaternary age Alluvium Unit

Layer 1 10 m/day

No known pumping tests havebeen conducted in the

Alluvium unit in the proximity ofthe site, and hence, measuredhydraulic conductivity valuesare not available. The range ofhydraulic conductivity valuesfor silty sands of between 1m/day and 90 m/day asreported by Freeze & Cherry(1979) has been adopted.

N/A 0.26

No known pumpingtests have beenconducted in the

Alluvium unit in theproximity of the site,and hence, storativityvalues are notavailable. The range ofstorativity values for amedium sand ofbetween 0.15 and 0.26as reported by Fetter(1994).

Sandstonecomponent ofthe Permian ageBlackwaterGroup

Layer 2,4,5and 6

0.1 m/day

No known pumping tests havebeen conducted in the

sandstone unit in the proximityof the site, and hence,measured K values are notavailable. The absence ofmoisture in these units duringdrilling (D. McManus,pers.comm., January 6, 2005)indicates the sandstone to belargely impermeable. Freeze &Cherry (1979) reports thehydraulic conductivity ofsandstone to range between0.00001 m/day and 1 m/day. Anumber of 0.1 m/day has beenassumed for the model after Ksensitivity analysis during

model calibration

5E-6 0.05

This aquifer wouldtypically be confinedwithin the groundwatermodel and thereforethe specific storagewas assumed to be0.000005.

Coal seamcomponent ofthe Permian ageBlackwaterGroup

Layer 3, 5 5 m/day

The representative and lowerlimit range of hydraulicconductivity results wassourced from BHP BillitonMitsubishi Alliance pump testsconducted on similar coalseams at Goonyella. Aconservative upper K valuewas selected from a range ofpump test results conducted inBlackwater.Selected exploration holes atPoitrel (nearby Daunia) weresubject to yield testing.Typically, yields of less than 2

L/s were measured. Yields aslow as 0.08 L/s and up to 15L/s were however recorded. Tothis end, the range of K valuesadopted from the pump testsconducted in Blackwater areconsidered to be a satisfactoryrepresentation of the yieldsmeasured at Poitrel.

5E-6 0.05

Typical storativity valuereported from BHPBilliton Mitsubishi

Alliance pump testsconducted on similarcoal seams at

Goonyella andBlackwater

Mine RefillSome cellsin layer2,3,4,5,6

10 m/day Assumed to be similar toalluvial material.

5E-6 0.26 Assumed to be similarto alluvial material.

VoidSome cellsin Layer 1& 2

9999m/day N/A 01


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Notes:

1. Conductivity (K) Property of a medium expressing the relative ease with which fluidscan pass through.

2. Specific Storage (Ss) is defined as the volume of water that a unit volume of aquiferreleases from storage under a unit decline in hydraulic head due to aquifercompaction and water expansion.

3. Specific Yield (Sy) is known as the storage term for an unconfined aquifer. It isdefined as the volume of water that an unconfined aquifer releases from storage perunit surface area per unit decline in the water table.

Results of this modelling were used to generate generalised relationships linkinggroundwater inflow/outflow functions to void water level. These relationships were thenincorporated into the overall surface water balance model of the conceptual Daunia void.See Section 5.4 for Conceptual Final void dimensions.

Void Hydrology and Salt Balance

The water and salt balance model was developed using Excel to simulates rainfall runoffinflows to the void from its catchment, evaporative losses from the void and groundwaterinflows and outflows derived from the generic groundwater flow modelling discussed above.

For the final mine pit void, the applied recharge was estimated from the historical rainfalltime series applying eight different scenarios with varying catchment area and climaticcondition. These scenarios are summarised in Table 4.

Table 4 Summary of the 8 Daunia Climatic and Catchment Area Cases Runs

Cases ClimateRainfallChange

CatchmentCase

Catchment Area (km )

Void Catchment

1a Historical Monthly Data 0% Minimum 3.88 0.8

1b Historical Monthly Data 0% Large 3.88 4.1

2a Climate Change - Dry Case = -30 % Rainfall -30% Minimum 3.88 0.8

2b Climate Change - Dry Case = -30 % Rainfall -30% Large 3.88 4.1

3aClimate Change - Median Case = -7.5 %Rainfall

-8% Minimum 3.88 0.8

3b

Climate Change - Median Case = -7.5 %

Rainfall -8% Large 3.88 4.1

4a Climate Change - Wet Case = +15 % Rainfall 15% Minimum 3.88 0.8

4b Climate Change - Wet Case = +15 % Rainfall 15% Large 3.88 4.1

In order to overcome model stability issues, the output of a model simulating one year afterthe end of mining operations has been used as initial conditions for all the eight cases runs.The one year model initial conditions were the water level output for “Daunia-Tr20 - bestestimate scenario” reflecting operational phase of the project between year 15 and 20.

The hydrology for the final void modelling was determined based on an annual runoffcoefficient. The annual volume of runoff was determined based on the runoff coefficient

and the catchment area. The runoff was generated for a range of scenarios to assess the


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impacts due to changes in catchment area and to capture the potential variation in rainfalldue to climate change. The scenarios considered are presented in table above.

Rainfall recorded and runoff calculations were supplied to be in included in the groundwatermodelling.

Two generalised scenarios with different catchments and climate influences have beenexamined including a deeper void scenario based on the initial Daunia base model and alsoa shallower void scenario.

Deeper Void Hydrology Scenario

The prelim conceptual void (base model) reported in the EIS assumed that the base of thereformed void was proximate to the base of the mined out lower coal seam atapproximately RL126M and that the batters of the void were established at 1V:6H. Theresults of this modelling are summarised in the following Figure 1. All cases show that anequilibrium level range is mostly reached within 10 – 20 years and the actual long term

levels are dependent with the adopted scenario.

Figure 1 Daunia Final Void – Deep Pit Water Level Scenarios

Case 2A is the wost case resulting from climate change induced drying and is reflective ofthe lowest yield situation, hence the long term average standing water level in the void islowest of the modelled scenarios T RL 159m MAHD. TWL of the void is approximate 200m AHD, hence remaining freeboard is considerable at approximately 40 metres.

Case 4B however represents the wettest case with the largest catchment. As expectedaverage void levels are considerably higher at RL 170mAHD approximately. Nonethelessavailable freeboard remains very substantial at approximately 30m.

Elevation of the pit lake surface for all studied cases

152

154

156

158

160

162

164

166

168

170

172

174

0 10 20 30 40 50 60 70 80 90 100

Time

(year

after

closure)

p i t l a k e s u r f a c e e l e v a t i o n ( m A H D )

Case 1A Case 1B Case 2A Case 2B Case 3A Case 3B Case 4A Case 4B


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As already stated this is the base scenario, there is clearly little or no prospect for the voidto spill. This is fully consistent with the results of similar but independently derivedmodelling undertaken a many of the existing BMA operations in central Queensland.

Modified Void – Shallow void hydrology scenario

This scenario has been developed to examine the probable changes in void hydrologicalbehaviour when considerable backfill into the void is undertaken to raise the mine pit floorfrom approximately RL126m AHD to RL160m AHD. That is the floor of the residual void israised by 34 metres to a level above the anticipated standing water level of the regionalground water table. The scenarios examined with this situation have been completed withthe historic rainfall (scenario 1 from the previous scenarios provided and with a reducedlake surface of 1.2 km2 for evaporation). Two versions of this shallow void scenario havebeen examined:

•

Scenario 1A-1 –minimum catchment case• Scenario 1B-1 – larger catchment case

Figure 2 provides an indication of long term water levels for the shallow void situation.

Figure 2 Daunia Final Void – Shallow Pit Water Level Scenarios

This shallow void scenario as expected shows that average water levels are higher than forthe deeper void situation, but that the maximum level for the large catchment scenario atRL 185 m AHD is still substantially below the crest of the void which is approximately RL200m AHD.

Calculations by SKM indicate that the void will not spill in a PMT event. Even if a spill werepossible, it is if feasible to manipulate external catchments by changes in spoil placementdesigns and programs as well as implementing surface drainage controls to prevent such aspill occurring.

Elevation of the pit lake surface for all studied cases

140

145

150

155

160

165

170

175

180

185

190

0 10 20 30 40 50 60 70 80 90 100

Time (year after closure)

p i t l a k e s u r f a c e e l e v a t i o n ( m A H D )

SC_1A‐1 SC_1B‐1


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6 GEOTECHNICAL STABILITY OF THE RESIDUAL VOID

6.1 INTRODUCTIONHighwall stability investigations are routinely carried out on an operational basis as part ofmine planning to ensure the safety of personnel and the security of the exposed coal.However, from a closure perspective, it is recognised that further specific investigationwould be required if the intention were to leave standing highwalls and endwalls.

Highwall and endwalls of mine pits in Central Queensland are often comprised ofdispersible, unconsolidated Tertiary material sitting above firmer consolidated Permiansediments. Endwalls usually exhibit greater instability than highwalls due to the exposedalignment of bedding and faulting planes. Some highwalls exhibit reasonable short tomedium term stability, others do not.

BMA does not propose to leave standing highwalls and enwalls at the Daunia project, butrather to backfill the final void to the most practicable and cost effective limit duringoperations and regrade the balance of the open void

6.2 RELEVANT STUDIES

Studies by ACARP researchers (Rehabilitation of Highwalls - ACARP Project C14048 -Final Report) based on inspections of several mines across the Bowen Basin concludedthat most of the highwalls in Tertiary and weathered overburden would not begeomechanically stable in the long term. These sedimentary materials are not strong

enough for the main to resist failures due to water incursion and failures due to physicalerosion damage. .

The stability of regraded spoils has been discussed by John Simmons by John SimmonsPty Ltd (Sherwood Geotechnical and Research Services) in several BMA residual voidinvestigation reports submitted to the EPA in mid 2008. This specialist geotechnicalconsultancy has considerable experience in evaluation of geotechnical conditions in BowenBasin mining formed over many years. The consultant noted in all instances that regradedslopes for final voids in the range of 10% - 25% are inherently "stable" overall and thatbased on typical short-term shear strengths and likely surface and groundwater scenarios,regrading to 25% would produce geotechnically stable landforms for lowwall spoil highwallsand endwalls with an outer surfacing of primarily Permian materials. Further that the

intervening final void might have a seasonally variable water ponding function, and thiswould be extremely unlikely to create conditions where geotechnical instability coulddevelop.

Thus considering the expert opinion of John Simmons Pty Ltd, from a geotechnicalperspective, the proposed regraded Daunia void batters which are nominally 1V:6H (17%)or flatter do not present significant risk of geotechnical failure events such as massslumping. Further, grades flatter than 25% are not likely to be affected by variable waterlevels in the final void. Local settlement is possible, but can only be gauged if and when itoccurs at a future time.


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7 VOID CAPABILITY TO SUPPORT NATIVE FLORA & FAUNA

7.1 SCENARIO DEPENDENCYThere are a number of scenarios that will cause marked differences in the capability of aresidual void to support flora and fauna.

• Intensive treatment such as backfilling will yield a similar environment to thebalance of the rehabilitated spoil areas. Fauna monitoring by WBM (WBM 1999 Assessment of Fauna Diversity in Rehabilitation) at nearby BMA Peak Downsmine demonstrates that a return of native fauna occurs in the rehabilitation, aswould be expected, given a variety of shrubs and trees and pasture cover havebeen established which can provide food and shelter for avifauna and

macropods.• Regrading lowwalls will provide safe access for fauna to temporary or permanent

water which may pond on the pit floor during rainfall. However, as discussed inearlier sections the usefulness of the water storage will be dependent on thenature of the interaction of the void with the regional ground water table andareas and types of contributing catchments.

• Also, provided the catchment area of the residual void exceeds a specified ratioit is possible that the water may be available on a permanent basis. Moreadvanced hydrological and geochemical modelling will be required in the future tosupport this strategy. Use of void to support specific uses such as aquatic faunafor aquaculture will require further investigation.

However with deep, steeply sloping voids in Central Queensland (and also reported inWestern Australia) the ability of voids as is to support significant life will depend on whetherthere is permanent water stored in the void and the ultimate salinity of the void water.

The oxygen flux of the void may also have important implications for the ability of the waterto sustain aquatic fauna. Measurements of some typical mine voids with standing highwallsin Central Queensland has shown that oxygen levels can diminish very rapidly as depthincreases, thus limiting use of the voids for aquaculture without active and costlyoxygenation. (Pers comm. – P. Baker, March 2008)

Decisions in the future will have to be made regarding mechanisms to maintain waterquality in final void at a useful level to support fauna or livestock. This may include a need

to utilize more backfill to reduce storage capacity or open up greater areas of catchment toimprove yield. Further the chemical and physical dynamics of the void water body requireinvestigation. For example, the development of a thermoclines and chemoclines may bedependent on a host of topographic and hydrological variables such as void depth, batterlength and slope, catchment area and yield, and perhaps groundwater incursion. Furtherstudies to better understand these issues need to be commissioned well before mineclosure should aquatic fauna habitat be considered as a viable post-closure option.


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8 REFERENCE AND INFORMATION DOCUMENTS

Daunia EIS and Appendices.

ACARP (Dec 2001) Project No C7007 – Water Quality and Discharge Predictions for FinalVoid and Spoil Catchments - Vol 1 & 2.

ACARP (1998) Post Mining Landscape Parameters for Erosion and Water Quality ControlProject.

ACARP Project C14048 Final Report Rehabilitation Of Highwalls, Nov 2006.

BMA (2008) Draft Sustainable Landform Guideline

BHP Billiton (2004) Closure Standard. HSEC.

Gilbert & Associates – Final Void Hydrological Assessments June 2008 - Gregory Crinum,Blackwater, Goonyella Riverside, Peak Downs, South Walker Creek and Saraji Mines.

John Simmons Pty Ltd (Geotechnical (Sherwood Geotechnical and Research Services)Final Void Stability Review – Peak Downs, Saraji, South Walker Creek, GoonyellaRiverside, Gregory Crinum and Blackwater mines.

PW Baker & Associates & Gilbert * Associates Residual Void Investigations A series ofreports for BMA Peak Downs, Norwich Park, Goonyella Riverside, Saraji, Gregory Crinum,South Walker Creek, & Blackwater Mine. June 2008.

SKM – Residual void hydrology and salinity balance models. March 2009.


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Dam 5

Dam 6

Dam 4

Dam 3

µLEGEND

Existing Railway

Proposed Mine Infrastructure

Internal Catchments

Mining Lease

))

DAUNIA COAL MINE

Attachment 2

FINAL LANDFORM

Data Source: Minserve

E 0 6 5 2

0 \ 1 8 0 0 S p a

t i a

l \ A r c

_ M X D \ F i g u r e s

\ F i g

_ A t t a c

h m e n

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P r o

p o s e

d_

M i n i n g

_ S e q u e n c e

_ F i n a

l L a n

d f o r m

_ v

2 . m

x d

P r o d

u c e

d :

1 9 / 3 / 2 0 0 9

Clean water drain alonglease boundary takingoff-lease run-off around Dam 4

DauniaCoalAppendixCMineLandformAndFinalVoidManagementPlan 2009

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