Birla Mount Gordon Mine

Birla Mount Gordon Mine

Report for Birla Mount Gordon Design Storage Allowance and Water Balance Assessment

April 2012

This Design Storage Allowance and Water Balance Assessment (“Report”):

1. has been prepared by GHD Pty Ltd (“GHD”) for Birla Mount Gordon (“BMG”);

2. may only be used and relied on by BMG;

3. must not be copied to, used by, or relied on by any person other than BMG without the prior written consent of GHD;

4. may only be used for the purpose of assessing the design storage allowance and site water balance (and must not be used for any other purpose).

GHD and its servants, employees and officers otherwise expressly disclaim responsibility to any person other than BMG arising from or in connection with this Report.

To the maximum extent permitted by law, all implied warranties and conditions in relation to the services provided by GHD and the Report are excluded unless they are expressly stated to apply in this Report.

The services undertaken by GHD in connection with preparing this Report:

were limited to those specifically detailed in Section 1.2 of this Report;

did not include items not mentioned in Section 1.2.

The opinions, conclusions and any recommendations in this Report are based on assumptions made by GHD when undertaking services and preparing the Report (“Assumptions”), including (but not limited to):

Those stated in Section 3 and Section 4.

GHD expressly disclaims responsibility for any error in, or omission from, this Report arising from or in connection with any of the Assumptions being incorrect.

Subject to the paragraphs in this section of the Report, the opinions, conclusions and any recommendations in this Report are based on conditions encountered and information reviewed at the time of preparation and may be relied on until 6 months, after which time, GHD expressly disclaims responsibility for any error in, or omission from, this Report arising from or in connection with those opinions, conclusions and any recommendations.

Birla Mount Gordon Design Storage Allowance and Water Balance Assessment

Contents

Executive Summary 1

1. Introduction 3

1.1 Overview 3 1.2 Objectives of Assessment 3

2. Data Collection 5

2.1 Overview 5 2.2 Environmental Data 5 2.3 Site Data 15 2.4 Raw Water Source 16 2.5 Seepage 16 2.6 Water Flow Diagram 16 2.7 Assumptions and Constraints 17

3. Design Storage Allowance Assessment 18

3.1 Overview 18 3.2 Criteria 18 3.3 Methodology 18 3.4 Additional Input Parameters 20 3.5 Existing Diversions 20 3.6 Storage Exclusions 20 3.7 Results 20 3.8 November 1st Storage Assessment 22

4. Water Balance Assessment 24

4.1 Overview 24 4.2 Model Development 24 4.3 Water Management 24 4.4 Assumptions 26 4.5 Results 27 4.6 Model Validation 28

5. Assessment Comparison 30

6. Conclusion 31


6.1 Overview 31 6.2 DSA Assessment 31 6.3 Water Balance Assessment 32 6.4 Assessment Comparison 32

Table Index Table 1 Report Cross-Reference to DERM Objectives 4 Table 2 Design Rainfall Data (NRW, now DERM) 7 Table 3 Monthly Evaporation Data 7 Table 4 AWBM Input Parameters 9 Table 5 Site Water Transfers 15 Table 6 DSA Rainfall Depths 20 Table 7 DSA Results Summary 21 Table 8 Estimated November 1st 2012 Available Storage 22 Table 9 Estimated DSA Results Summary 22 Table 10 Operational Order of Precedence to the Process

Ponds 25 Table 11 Esperanza TSF Decant Water Estimate 25 Table 12 Process Pond Water Supply Post Esperanza Pit

Water Level Reduction 27 Table 13 Collection Dam Overflows 28 Table 14 Assessment Input Parameter Comparison 30

Figure Index Figure 1 Rainfall Comparison 6 Figure 2 Schematic Representation of AWBM Model 11 Figure 3 Average Daily Streamflow for each Month 12 Figure 4 Total Annual Streamflow 13 Figure 5 Comparison between Rainfall and Streamflow 14 Figure 6 LPIII Distribution of 2 Month Wet Period Rainfall Data 19


Appendices A Site Locality Map B Catchment Plan C Storage Location Map D Storage Data Summary E Water Flow Diagram F DSA Results G GoldSim Model Layout H Overall Water Balance

1


Executive Summary

On November 4, 2011, Birla Mount Gordon was served with a notice from the Department of Environment and Resource Management to conduct or commission an environmental evaluation. GHD was subsequently commissioned by Birla Mount Gordon to undertake a water balance and Design Storage Allowance (DSA) assessment of the existing Birla Mount Gordon Mine. The assessment was undertaken in response to the water balance component (Section 6) of Department for the Environment and Resource Management s notice to conduct or commission an environmental evaluation.

The DSA assessment was undertaken incorporating the hydrologic events outlined in the Department for the Environment and Resource Managements notice to conduct or commission an environmental evaluation. The results of the DSA assessment are shown in Appendix F.

Based on the DSA assessment undertaken for storage volumes available as at March 2012, it was concluded that:

The Esperanza Tailings Storage Facility can accommodate most DSA scenarios with durations of 5 days or less;

The Mill Creek Dam can accommodate DSA scenarios with durations of 1 day or less;

The Process Ponds cannot accommodate any of the DSA scenarios assessed as the water levels are kept high for process purposes;

The Esperanza Pit can accommodate all DSA scenarios assessed; and

The total storage available can accommodate DSA scenarios with Average Recurrence Intervals (ARIs) of less than 50 years with 5 day durations and ARIs of less than 1,000 years with 1 day durations.

Based on the DSA assessment undertaken for estimated storage volumes available as at November 1st 2012, it was concluded that:

The Esperanza Tailings Storage Facility can accommodate all DSA scenarios with durations of 5 days or less;


The Process Ponds cannot accommodate any of the DSA scenarios assessed as the water level is kept high for process purposes;


The total storage available can accommodate DSA scenarios with ARIs of less than 1,000 years with 5 day durations and all ARIs with 1 day durations.

It should be noted that this assessment was undertaken using estimated storage volumes available as at November 1st 2012. The assessment should be updated nearer to November 1st 2012 using actual available storage volumes.

It is understood that an investigation is currently being undertaken by a 3rd party hydrogeologist into the plausibility of raising the Mandatory Reporting Level of the Esperanza Pit. Should the outcome of this investigation demonstrate the Mandatory Reporting Level could be raised, this would have a positive

2


impact on the storage capacity and thus the DSA assessment. It’s noted from the DSA scenarios run, that there is ample existing capacity in the pit.

The water balance assessment was undertaken incorporating historical daily rainfall data from 1910 to 2010 and the data collected and summarised in Section 2. The average annual water balance is shown in Appendix H.

Based on the water balance assessment undertaken it was concluded that:

The current site water balance results in a net deficit of water;

There was no discharge of water from the site over the duration assessed; and

Additional make-up water will be required to supply water to the process plant as shown in Table 12.

A comparison of the input parameters for each assessment was undertaken to highlight the variances. A summary of this assessment is shown in Table 14.

From Table 14 it can be seen that there are a number of significant variances between the two assessments undertaken. The variances are a result of the DSA assessment requiring inputs to be adopted in accordance with DERM’s guidelines, whereas the water balance assessment adopts inputs specific to the site. These variances have resulted in the water balance assessment showing no uncontrolled discharge from the site over the period assessed, whereas the DSA assessment resulted in uncontrolled discharge from most storages.

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1. Introduction

1.1 Overview The Birla Mount Gordon (BMG) mine is located approximately 120 km north of Mount Isa as shown in Appendix A. The operation consists of underground copper mining operations and a concentrator plant with a milling capacity to process up to 1.5 mtpa of ore, designed to produce copper in concentrate form. The mine utilises a number of on-site water storages to manage the flow of water throughout the site.

On November 4, 2011, BMG was served with a notice from the Department of Environment and Resource Management (DERM) to conduct or commission an environmental evaluation. GHD was subsequently commissioned by BMG to undertake a water balance and Design Storage Allowance (DSA) assessment of the existing BMG mine. The assessment was undertaken in response to the water balance component (Section 6) of DERM’s notice to conduct or commission an environmental evaluation.

1.2 Objectives of Assessment The objective of this assessment is to comply with the investigation requirements of Section 6 of DERM’s notice to conduct or commission an environmental evaluation as detailed below:

6. Determine the current water balance for the mine, which includes but not limited to:

a. The inflows and outflows for the source/s of contaminants identified in this investigation.

b. Modelling of the adequacy of the existing water management system at the mine during the storm events* listed below:

i. To prevent discharges of contaminants not in accordance with environmental authority MIN100489906; and

ii. To protect the environmental values of the receiving environment in accordance with the Australian and New Zealand Environment Conservation Council (ANZECC, 2000) methodology.

Modelling must be based on real weather data from a representative weather station for a minimum of 100 years where available and must be completed on a daily time step basis or high frequency.

* Storm events for requirement 6b include:

Design rainfall events for AEP 1 in 10, 1 in 25, 1 in 50, 1 in 100, 1 in 200, and 1 in 1,000 year for durations from 1 to 5 days.

2 month wet season AEP of 1 in 25, 1 in 100 and 1 in 200 year using the ‘ deciles method’ as outlined in the Site Water management Technical Guideline for Environmental Management of Exploration and Mining in Queensland (DME 1995).

c. Documentation for any water balance model that specifies the modelling input parameters and assumption used, including:

i. Calibration and validation; and

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ii. Assessment and comparison of relevant parameter values at the mine, as well as any external catchments or aquifers.

Table 1 cross-references the appropriate sections of this report to the objectives of DERM’s notice to conduct or commission an environmental evaluation.

Table 1 Report Cross-Reference to DERM Objectives

DERM Requirement Report Section

6a Storage data, pump data and water flow diagram as outlined in Section 2.

6bi, 6bii DSA assessment as outlined in Section 3, with the detailed results of the DSA assessment presented in Appendix F.

6ci Water balance assessment as outlined in Section 4, with runoff calibration presented in Section 2.2.4

6cii External catchment diversions as outlined in Section 3.5

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2. Data Collection

2.1 Overview Data was obtained from the following sources and reviewed for suitability for use:

Environmental Data:

– Daily rainfall (1910 – 2010) – SILO Drill Rainfall Data, DERM 2012;

– Design rainfall – BOM, 2012;

– Average monthly evaporation – Mount Isa Aero (Station No. 029127), BOM 2012; and

– Streamflow data (1971 – 2010) – Gunpowder Creek at Gunpowder (Gauge No. 913006A), BOM 2012.

Site Data:

– LiDar data– BMG, 2011;

– Catchment areas – BMG, 2011; and

– Site pump flows and storage volumes – BMG 2011/12.

A review of the data collected and used in the assessments is presented in the following sections.

2.2 Environmental Data Environmental data obtained for this assessment included:

Rainfall;

Evaporation; and

Streamflow.

The following sections discuss the environmental data.

2.2.1 Historical Rainfall

DERM SILO Drill rainfall data was obtained for the site location co-ordinates. SILO Drill rainfall data uses data from surrounding rainfall gauges to provide a complete rainfall set. A comparison between the SILO Drill data and a nearby rainfall gauge at Mammoth Mine (Gauge No. 29094) was undertaken for a period from 1971 to 2011. This period was chosen as no rainfall data existed for the Mammoth Mine station prior to 1971. The results of the comparison are shown in Figure 1.

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Figure 1 Rainfall Comparison

From Figure 1 it can be seen that the DERM SILO Drill rainfall data is consistent with the BOM Mammoth Mine rainfall data, except for the period from 1985 to 1991 where the BOM Mammoth Mine rainfall data is incomplete. This results in the differential in the total rainfall shown in Figure 1. Based on this comparison, the DERM SILO Drill rainfall data was adopted for this assessment.

2.2.2 Design Rainfall

Design rainfall depths were estimated using the Department of Natural Resources and Mines (NRW, now DERM) Rainfall program (2005) which is based on the Co-operative Research Centre Focussed Rainfall Growth Estimation (CRC FORGE) technique. CRC FORGE is a statistical (regional) analysis method that provides estimates of rare rainfall events at individual stations. The design rainfall data for Average Recurrence Intervals (ARIs) up to 2,000 years adopted for this assessment is shown in Table 2.

0

5000

10000

15000

20000

25000

1968 1973 1979 1984 1990 1995 2001 2006 2012

Cum

mul

ativ

e Ra

infa

ll (m

m)

DateMammoth Mine BOM BMG Silo DataDERM

7


Table 2 Design Rainfall Data (NRW, now DERM)

Duration

Rainfall Depth per ARI (mm)

5 10 20 25 50 100 200 500 1,000 2,000

15 min 22 25 29 33 34 39 44 52 58 64

30 min 32 37 43 49 51 58 66 77 86 96

1 hour 47 53 62 71 74 84 95 111 124 138

3 hour 65 76 90 103 108 124 140 164 183 203

6 hour 80 94 112 130 137 157 177 207 231 256

12 hour 98 117 141 163 173 198 225 262 293 324

18 hour 112 133 160 185 197 225 255 298 333 369

24 hour 123 146 175 203 215 246 279 325 363 403

48 hour 163 194 233 270 285 328 373 437 489 544

72 hour 184 218 261 303 321 368 418 488 545 604

96 hour 193 229 275 319 337 387 439 512 571 632

120 hour 202 239 287 332 352 403 457 532 593 656

2.2.3 Evaporation

Average monthly pan evaporation data from the Mount Isa Aero (Station No. 029127) was obtained from BOM to account for evaporation within the storages on the BMG site. The Mount Isa Aero was the closest climate station to the site containing evaporation data as there was no long term evaporation rate data available for the site. The Queensland Lake Evaporation Publication (Queensland Water Resources Commission, 1981) identifies the need to apply a pan factor to pan evaporation data. The pan factor accounts for the differences between the pan used to obtain the evaporation data and the use of the evaporation data for larger water bodies. These differences include depth and temperature of the water within the larger water body.

A pan factor of 0.9 was applied to the evaporation data in accordance with the Queensland Lake Evaporation. A summary of the evaporation data used for this assessment is shown in Table 3.

Table 3 Monthly Evaporation Data

Month Pan Evaporation (Mount Isa Aero, mm/day)

Modified Pan Evaporation (mm/day)

January 10 9.0

February 9.3 8.4

March 9.1 8.2

April 8.1 7.3

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Month Pan Evaporation (Mount Isa Aero, mm/day)

Modified Pan Evaporation (mm/day)

May 6.1 5.5

June 5.1 4.6

July 5.3 4.8

August 6.6 5.9

September 8.5 7.7

October 10.2 9.2

November 11.2 10.1

December 11.3 10.2

Total 100.8 90.7

2.2.4 Runoff

An assessment of the runoff from the catchments within the BMG site was undertaken to estimate how much of the site rainfall is reporting the site storages and to assist in the development of the water balance. The following section outlines how the Australian Water Balance Model (AWBM) was used to estimate the runoff from the catchments within the BMG site.

Background

Stream flows from the catchments in the study area were calculated using the widely used AWBM daily rainfall-runoff model (Boughton, 1993). The AWBM model is a catchment water balance model used to relate daily stream flow to daily rainfall and evaporation. The model represents the catchment using three surface stores to simulate partial areas of runoff. The water balance of each surface store is calculated independently of the others. The model calculates the water balance of each partial area at daily time steps. At each time step, rainfall is added to each of the three surface stores and evapotranspiration is subtracted from each store. If the value of water in the store exceeds the capacity of the store, the excess water becomes runoff. Part of this runoff becomes recharge of the base flow store if there is base flow in the stream.

The parameters used to define the AWBM are as follows:

Partial area fractions (A1, A2 and A3) represented by the three surface stores;

Surface store capacities (C1, C2 and C3) in millimetres;

Baseflow index (BFI – fraction of excess contributing to baseflow). Surface store recharge = (1-BFI) Excess. Baseflow store recharge = BFI Excess;

Daily base flow recession constant (Kb). Baseflow = (1 - Kb) Baseflow store;

Daily surface flow recession constant (Ks). Surface runoff = (1 - Ks) Surface routing store;

Total stream flow = Base flow + Surface runoff.

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Determination of the AWBM parameters requires calibration involving the comparison of simulated flows to stream flow records. Streamflow data from Gunpowder Creek was used to calibrate the AWBM to estimate the daily runoff from the catchments within the site.

A schematic representation of the AWBM model is shown in Figure 2.

Methodology

The following methodology was adopted to estimate the runoff from the catchments within the BMG site:

Develop a calibrated daily rainfall-runoff model for the Gunpowder Creek catchment. This is the closest catchment to the study area with long-term gauging data that has hydrological similarities to the BMG site catchment; and

Use the model parameters from the Gunpowder Creek calibrated model and apply them to the rainfall-runoff model for the BMG site using the available daily rainfall data.

Results

The AWBM was simulated over the period of data available (1971 to 2010). Through the methodology above, the AWBM input parameters were determined for the site. Table 4 summarise the AWBM input parameters.

Table 4 AWBM Input Parameters

Item Store 1 Store 2 Store 3

Capacity 40 80 150

Partial Area 0.1 0.7 0.2

Initial Store 2.5 30 45

Base Flow Index Daily Base Flow Recession Constant

Daily Surface Flow Recession Constant

0.7 0.5 0.8

To evaluate the model performance, a comparison was made between the average daily stream flow for each month and the total annual steamflow for both the AWBM and Gunpowder Creek gauged data. Figure 3 shows the average daily stream flow for each month while Figure 4 shows the total annual streamflow. The variation between the AWBM and Gunpowder Creek gauged data is also shown.

From Figure 3 and Figure 4 it can be seen that the general trend of the AWBM correlates with the gauged Gunpowder Creek streamflow. The variation between the AWBM and Gunpowder Creek gauged data is relatively constant on a daily basis, however varies over an annual basis. The variation seems to be exaggerated by the more extreme streamflow conditions, either high or low, suggesting a limitation in the estimation developed. If the input parameters were revised to achieve calibration with the extreme events, the correlation achieved with the more frequent events would be reduced.

In addition, the AWBM is based on a correlation between rainfall and runoff over time. The gauged streamflow data obtained from Gunpowder creek has an inconsistent correlation between rainfall and streamflow. A lack of correlation could be caused by localised storm events that do not occur over the rain gauge and therefore go unrecorded. Furthermore, inaccuracies in monitoring or missing data within

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runoff records would also effect the correlation. This is evident when the annual rainfall is added to Figure 4 as shown in Figure 5.

From Figure 5 it can be seen that in the years of 1993, 1998 and 2006 the annual gauged Gunpowder Creek streamflow does not correlate with the annual rainfall received, whereas the AWBM streamflow does.

Based on the trends shown and the correlation the AWBM achieves between rainfall and streamflow, the use of the AWBM for the water balance assessment is sufficient for the purposes of estimating the catchment runoff during average rainfall events. The overall agreement between simulated and recorded runoff (in terms of both temporal variation and magnitude of runoff) indicates that the AWBM is adequate for the purposes of simulating sequences of catchment runoff to meet the requirements of DERM’s notice to conduct or commission an environmental evaluation.

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Figure 2 Schematic Representation of AWBM Model

Source: Catchment Water Balance Modelling in Australia 1960 – 2004 by W. Boughton.

A1 A2 A3

C1C2

C3

P P P

E E E

EXCESS SURFACE RUNOFF= (1-BFI)*EXCESS

SS

BASEFLOWRECHARGE=BFI*EXCESS

BS

BASEFLOW= (1-K)*BS TOTAL

RUNOFF

SURFACERUNOFF= (1-KS)*SS

Parameters and State Variables:

P = PrecipitationE = Evaporation

C1-C3 = Surface Storage CapacitiesA1-A3 = Partial Areas Represented by Surface Storages

BFI = Baseflow IndexK = Daily Baseflow Recession Constant

BS = Current Volume in Baseflow StoreKS = Daily Surface Flow Recession ConstantSS = Current Volume in Surface Routing Store

A1 A2 A3

C1C2

C3

P P P

E E E


SS


BS


RUNOFF


A1 A2 A3

C1C2

C3

P P P

E E E


SS


BS


RUNOFF


Parameters and State Variables:

P = PrecipitationE = Evaporation

C1-C3 = Surface Storage CapacitiesA1-A3 = Partial Areas Represented by Surface Storages

BFI = Baseflow IndexK = Daily Baseflow Recession Constant

BS = Current Volume in Baseflow StoreKS = Daily Surface Flow Recession ConstantSS = Current Volume in Surface Routing Store

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Figure 3 Average Daily Streamflow for each Month

-800

-700

-600

-500

-400

-300

-200

-100

0

100

200

0

500

1000

1500

2000

2500

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

Stre

amflo

w (M

L)

Month

AWBM Gunpowder Model Variation from Gauged Data

Streamflow

Variance (ML)

13


Figure 4 Total Annual Streamflow

-400,000

-300,000

-200,000

-100,000

0

100,000

200,000

300,000

400,000

500,000

0

200000

400000

600000

800000

1000000

1200000

1970 1975 1980 1985 1990 1995 2000 2005 2010

Stre

amflo

w (M

L)

Year

AWBM Gunpowder Model Variation from Gauged

Streamflow

Variance (ML)

14


Figure 5 Comparison between Rainfall and Streamflow

0

200

400

600

800

1000

1200

0

200,000

400,000

600,000

800,000

1,000,000

1,200,000

1970 1975 1980 1985 1990 1995 2000 2005 2010

Stre

amflo

w (M

L)

Year

Gunpowder Streamflow AWBM Annual Rainfall

Rainfall (mm

)

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2.3 Site Data Site data obtained from BMG included:

Storage catchment areas;

Storage surface and base areas;

Storage volumes;

Forced Evaporation; and

Pump Rates.

The following sections review the site data obtained.

2.3.1 Catchment Plan

The official site catchment plan was supplied by BMG and is presented in Appendix B. The site catchment plan was used to determine the catchment area of each on site storage.

2.3.2 Storage Data

Available storage data was supplied by BMG. The location of each storage is shown in Appendix C. Storage data provided and used as part of this assessment is presented in Appendix D.

It is understood that other decommissioned and enclosed storages may exist throughout the site, however the storages associated with the DSA assessment were accounted for. In addition, if a storage is enclosed the effect of rainfall and evaporation is negligible, therefore only the pumped inflow and outflow would be required if those actions were taking place.

2.3.3 Forced Evaporation

High Capacity Evaporators (HCEs) are currently being operated during the dry season on site to increase the rate of evaporation. Through discussions with on-site personnel, the HCEs were found to operate at an efficiency of 50 percent.

2.3.4 Pump Rates

Water meter data was provided for various water transfers throughout the site covering a period from January to November 2011. Average flow rates were obtained from the flow data and it was assumed that these rates applied across the mine life. A summary of the average flow rates for the site water transfers adopted for this assessment is presented in Table 5.

Table 5 Site Water Transfers

Transfer From Transfer To Average Rate (m3/day)

Raw Water Process Plant 945

Raw Water Underground 389

Raw Water Raw Water Standpipe 80

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Transfer From Transfer To Average Rate (m3/day)

Raw Water Washbay 21

Underground Esperanza Pit 614

Process Ponds Process Plant 3,600

Process Ponds Dust Suppression 160 (wet season) or 320 (dry season)

Process Plant Esperanza Tailings Storage Facility (TSF)

3,600

Esperanza Pit Mill Creek Dam 194 (wet season only)

Esperanza Pit HCEs 2,570 (dry season only)

North Waste Rock Dump Sump (Seepage) Mill Creek Dam 36

Table 5 documents the extent of the transfer data provided for the purposes of this assessment, and therefore the model cannot account for any additional or ad-hoc transfers which may take place on an as-needed basis.

2.4 Raw Water Source Raw water is currently sourced from Lake Waggaboonya, located to the east of the site. The raw water is pumped to a header tank, from which raw water is supplied to:

The processing plant;

The raw water standpipe;

The washbay;

The lime slaker; and

The underground operation.

2.5 Seepage There is potential for seepage to occur at some of the storages located on the site. DERM’s notice to conduct or commission an environmental evaluation requires assessments of seepage at storage locations throughout the mine to be undertaken. This would result in seepage being collected through the use of interception sumps/trenches such as those to be implemented in the coming months. Based on the near future expectation of seepage being reduced on the site, the effect of seepage was deemed to not contribute to a loss of contained volume and therefore excluded from this assessment.

2.6 Water Flow Diagram Based on the data provided, a diagram was developed showing the flow of water throughout the site. The water flow diagram developed and used as the basis for these assessments is presented in Appendix E.

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2.7 Assumptions and Constraints The following assumptions and constraints applied to the data used for this assessment:

Historical rainfall data from 1910 to 2010 was use for the water balance assessment;

A pan factor of 0.9 was applied to the pan evaporation data obtained as detailed in Section 2.2.3. No allowance was made for the effect of water quality on the evaporation rate;

Streamflow calibration was performed using streamflow data from Gunpowder Creek for a period from 1971 to 2010 as shown in Section 2.2.4;

Catchment and storage data was provided by BMG; and

Average daily pump rates were adopted.

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3. Design Storage Allowance Assessment

3.1 Overview In accordance with DERM’s Manual for Assessing Hazard Categories and Hydraulic Performance of Dams (DERM, 2012), all regulated dams must as a minimum provide for a volume called a DSA. The DSA must be provided for at the first day of November for the coming wet season of every year the dam is in operation.

The following sections outline the DSA criteria adopted, the methodology used and the results of the assessment.

3.2 Criteria DERM’s notice to conduct or commission an environmental evaluation nominates a number of criteria for which to undertake the DSA assessment, including:

Design rainfall events for the 10 yr, 25 yr, 50 yr, 100 yr, 200 yr and 1,000 yr ARI design storm events for durations from 1 to 5 days; and

The 2 month wet season 25 yr, 100 yr and 200 yr events.

3.3 Methodology

3.3.1 Design Rainfall Events

The rainfall depths for the design rainfall event criteria were adopted as per Table 2.

3.3.2 2 Month Wet Season Events

The deciles method was used to estimate the DSA requirements for the 2 month wet season events in accordance with the DERM Guidelines for Assessing the Hazard Categories and Hydraulic Performance of Dams (DERM, 2012). The deciles method fits the available rainfall data to a Log Pearson III (LPIII) distribution to determine the rainfall depth of the required criteria. The LPIII distribution describes the probability of occurrence of a given event, which in this case is the predicted rainfall depth. The LPIII distribution of the wettest 2 month periods over the 100 years of available rainfall data is shown in Figure 6.

19


Figure 6 LPIII Distribution of 2 Month Wet Period Rainfall Data

100

1,000

10,000

Two

Mon

th R

ainf

all (

mm

)

Annual Exceedence Probability (%)

Best Fit

5% ile

Probability Axis Markers

99.9 99 90 0.111050

2 5 10 1001.1111.0101.001 1000

20


3.4 Additional Input Parameters The following additional input parameters were adopted as per DERM’s Guidelines for Assessing the Hazard Categories and Hydraulic Performance of Dams (DERM, 2012):

A runoff coefficient of 1;

The inclusion of process inputs and outputs to and from the storages where required as per the available pump data. If the outputs exceeded the inputs, a net input of zero was applied;

It is envisaged that during high rainfall events, water will be supplied to the process ponds from the Esperanza TSF only. No input to the process ponds by the Mill Creek Dam or the Esperanza Pit have been allowed for; and

The Esperanza TSF includes the inflow of solids.

It should be noted that no controlled discharge was allowed from the storages during the DSA scenarios as the assessment was based on assessing the current water management system’s ability to prevent discharges of contaminants not in accordance with Environmental Authority (EA) MIN100489906.

3.5 Existing Diversions There is an existing diversion dam located in the upper Esperanza catchment. The diversion dam was designed to permanently divert all flows within the upper Esperanza catchment, upstream of the diversion dam. The diversion dam catchment area was therefore not included in this assessment.

3.6 Storage Exclusions Through discussions with on-site personnel, four storages have been excluded from this assessment:

Retention Pond – The retention pond is understood to be an old name for the Mill Creek Dam. As this assessment already covers the Mill Creek Dam, the Retention Pond was excluded from this assessment; and

Evaporation Ponds 1, 2 and 3 – It is understood that there is no process input to the evaporation ponds from the BMG site. Therefore Evaporation Ponds 1, 2 and 3 were excluded from this assessment.

3.7 Results

3.7.1 DSA Rainfall Depths

Through undertaking the methodology outlined in Section 3.3, the rainfall depth for each DSA scenario assessed was determined as shown in Table 6.

Table 6 DSA Rainfall Depths

DSA Scenario Rainfall Depth (mm)

1 in 10, 1 day duration 146

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DSA Scenario Rainfall Depth (mm)










1 in 1,000, 1 day duration 363

1 in 1,000, 5 day duration 593

1 in 25, 2 month wet period 750

1 in 100, 2 month wet period 910

1 in 200, 2 month wet period 1,050

3.7.2 Current Storage Assessment

The DSA requirement for each scenario was assessed against the volume available within each storage as at March 2012. The results of this assessment are provided in detail in Appendix F, with a summary shown in Table 7. An assessment of the total storage available for the total DSA requirement was also undertaken.

Table 7 DSA Results Summary

Storage ID Non-Compliant DSA Scenarios as at March 2012

Esperanza TSF 1 in 1,000 year, 5 day duration; 1 in 25, 2 month wet period; 1 in 100, 2 month wet period and 1 in 200, 2 month wet period

Mill Creek Dam 1 in 25, 5 day duration; 1 in 50, 5 day duration; 1 in 100, 5 day duration; 1 in 200, 5 day duration; 1 in 1,000, 1 day duration; 1 in 1,000, 5 day duration; 1 in 25, 2 month wet period; 1 in 100, 2 month wet period; 1 in 200, 2 month wet period

Process Ponds All DSA scenarios assessed

Esperanza Pit None of the DSA scenarios assessed

Total 1 in 50, 5 day duration; 1 in 100, 5 day duration; 1 in 200, 5 day duration; 1 in 1,000, 1 day duration; 1 in 1,000, 5 day duration; 1 in 25, 2 month wet period;

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Storage ID Non-Compliant DSA Scenarios as at March 2012 1 in 100, 2 month wet period; 1 in 200, 2 month wet period

From Table 7 it can be seen that:

The Esperanza TSF can accommodate most DSA scenarios with durations of 5 days or less;




The total storage available can accommodate DSA scenarios with ARIs of less than 50 years with 5 day durations and ARIs of less than 1,000 years with 1 day durations.

3.8 November 1st Storage Assessment The DSA requirement for each scenario was assessed against the estimated volume available within each storage as at November 2012. The estimated volume available was based on data provided by BMG as summarised in Table 8.

Table 8 Estimated November 1st 2012 Available Storage

Storage ID Estimated 2012 Available Volume (m3)

Comment

Esperanza TSF 570,000 Same volume available as November 1st 2011

Mill Creek Dam 813,000 Same as current volume

Process Ponds 2,619 Same as current volume

Esperanza Pit 1,170,000 Reduction of 500 ML from current volume

The results of this assessment are provided in detail in Appendix F, with a summary shown in Table 9. An assessment of the total storage available for the total DSA requirement was also undertaken.

Table 9 Estimated DSA Results Summary

Storage ID Estimated Non-Compliant DSA Scenarios as at November 1st 2012

Esperanza TSF 1 in 100, 2 month wet period and 1 in 200, 2 month wet period

Mill Creek Dam 1 in 25, 5 day duration; 1 in 50, 5 day duration; 1 in 100, 5 day duration; 1 in 200, 5 day duration; 1 in 1,000, 1 day duration; 1 in 1,000, 5 day duration; 1 in 25, 2 month wet period; 1 in 100, 2 month wet period; 1 in 200, 2 month wet period

Process Ponds All DSA scenarios assessed

Esperanza Pit None of the DSA scenarios assessed

Total 1 in 1,000, 5 day duration; 1 in 25, 2 month wet period; 1 in 100, 2 month wet period; 1 in 200, 2 month wet period

23


From Table 9 it can be seen that:

The Esperanza TSF can accommodate all DSA scenarios with durations of 5 days or less;






24


4. Water Balance Assessment

4.1 Overview A water balance model was developed for the BMG site as per the requirement of Section 6c of DERM’s notice to conduct or commission an environmental evaluation. The following sections outline the model development, the water management strategy adopted and the results of the assessment.

4.2 Model Development The model used to represent the water balance was GoldSim Version 10.00 (GoldSim Technology 2009). Goldsim is a graphical object orientated program which simulates static or dynamic systems. It is similar to a spreadsheet but allows one to visually create and manipulate data and equations.

Simulation, in this context, is defined as a process of creating a model of an existing or proposed system (such as a mine water management system) in order to identify and understand the factors that control the system performance or predict (forecast) the future behaviour of the system.

The water balance modelling was completed using a daily time step. The assessment was undertaken for a period of rainfall from 1910 to 2010. The model layout is shown in Appendix G.

The water balance modelling adopted the input data collected from site as outlined in Section 2.

4.3 Water Management

4.3.1 Current Strategy

Prior to the diversion of the catchment area in the upper Esperanza, a significant volume of water entered the Esperanza Pit and caused it to exceed the Mandatory Reporting Level (MRL). As a result, the current water management strategy demonstrated through discussions with site personnel centres on the reduction of the water stored within the Esperanza Pit. This is achieved through the use of the HCEs within the Esperanza Pit along with treating and discharging Esperanza Pit water through the Mill Creek Dam during the wet season.

As the above are only temporary measures, they were added to the water balance assessment as methods of reducing water levels within the Esperanza Pit if the MRL was exceeded. If the water level is below the MRL, these water reduction strategies were not implemented. This means that the water level in the Esperanza Pit will only be effected by evaporation, rainfall and any process inflows unless the MRL is breached.

4.3.2 Process Ponds Operation

As shown in the water flow diagram (refer Appendix E), the process ponds are supplied with water from three main sources, namely:

Esperanza TSF Decant;

Esperanza Pit; and

Mill Creek Dam.

25


The operational order of precedence for the process ponds adopted for this assessment is shown in Table 10, in accordance with the advised site protocol.

Table 10 Operational Order of Precedence to the Process Ponds

Transfer From Transfer To Precedence Note

Esperanza TSF Decant Process Ponds 1 Only if decant water available

Esperanza Pit Process Ponds 2 Only if Esperanza Pit level is greater than the MRL

Mill Creek Dam Process Ponds 3 Only if water available

Alternate Source Process Ponds 4 Only if supply isn’t met by precedence’s 1, 2 or 3

4.3.3 Esperanza TSF Decant Estimation

It is understood that the slurry produced through production is pumped to the Esperanza TSF with a flow rate of water required as shown in Table 5. Of the slurry entering the Esperanza TSF, an estimation of the decant water available for reuse was made. This estimation, which was used for this assessment, is summarised in Table 11.

Table 11 Esperanza TSF Decant Water Estimate

Parameter Value Unit

Assumed Ore Density 2.7 t/m3

Settled Tailings Dry Density 1.2 t/m3

Percentage Solids in Tailings Slurry 50 %

Water Density 1 t/m3

Tailings Production 3,600 t/day

Slurry Production 7,200 t/day

Solids Volume in Tailings 1,333 m3/day

Water Usage for Slurry Production 3,600 m3/day

Total Slurry Flow to Esperanza TSF 4,933 m3/day

Settled Tailings Volume 3,000 m3/day

Water Released from Tailings (Decant) 1,933 m3/day

Percentage of Slurry Water Available for Reuse 54 %

26


4.3.4 Post Esperanza Pit Water Reduction

The current water management strategy results in a net reduction in water levels within the Esperanza Pit. As a result, the water level within the Esperanza Pit will likely return to below the MRL sometime in the foreseeable future. The recycled water from the Esperanza Pit will therefore only be transferred to the process ponds if the water level is greater than the MRL. The use of the HCEs will also only occur if the water level is greater than the MRL.

As a result, it is envisaged that an additional water source may be required to make up the processing plant demand. At this stage the source of the make-up water is not known, however the volume of make-up water required by the process plant was assessed.

It is understood that an investigation is currently being undertaken by a 3rd party hydrogeologist into the plausibility of raising the Mandatory Reporting Level of the Esperanza Pit. Should the outcome of this investigation demonstrate the Mandatory Reporting Level could be raised, this would have a positive impact on the storage capacity and thus the DSA assessment. It’s noted from the DSA scenarios run, that there is ample existing capacity in the pit.

4.4 Assumptions The following assumptions were made as part of this water balance assessment.

4.4.1 Model Development

A water management strategy post Esperanza Pit water reduction was adopted as per Section 4.3.4;

The process ponds operational order of precedence as shown in Table 10;

The Esperanza TSF decant water estimate as shown in Table 11;

The storage effect of the solids within the Esperanza TSF was not accounted for. This was due to the expected continuous raising of the Esperanza TSF as the solid volumes increased, keeping the available water volume relatively constant;

The Esperanza Pit storage level was initially set at the MRL to simulate the water level post Esperanza Pit water reduction. Transfer from the Esperanza Pit to the process ponds was only initiated if the water level is greater than the MRL. Alternate water was sourced if the water in the Esperanza Pit was below the MRL;

The process pond initial water level was set to produce no overflow;

All other initial storage water levels were set at the current water levels provided;

The wet season is defined as November to April, with the remaining months constituting the dry season;

The storage data is as shown in Appendix D;

The pump rates are as shown in Table 5;

Water quality data (in particular salinity level) was not considered as part of this assessment. It should be noted that the impacts of variable salinity on evaporation is not considered to alter the overall accuracy or outcome of the assessment undertaken;

27


Transfer rates were modelled using daily time steps. In reality at site, transfer rates are determined during the day on an “as needs basis” and may operate over periods smaller than a day. This would affect the water levels within storages at any time and therefore effect the storage evaporation; and

The water flows are as per the water flow diagram shown in Appendix E.

4.4.2 Environmental

Historical rainfall data from 1910 to 2010 was used for this assessment. The results obtained may differ from future climate patterns and does not account for the effects of climate change;

Evaporation varies within dams depending on the top water surface area; and

Evaporation is independent of rainfall.

4.5 Results

4.5.1 Annual Water Balance

The mean predicted values for each of the water transfers over the simulated period are provided in Appendix H. From the water balance undertaken it was determined that the site has an annual net reduction in water resulting in no discharge to Gunpowder Creek and the need for additional water to be sourced. Currently water is being discharged from site during the wet season as a result of the high water levels within the Esperanza Pit. Since the inclusion of the diversion dam in the upper Esperanza catchment, it is envisaged that once Esperanza Pit has returned to below MRL, there will be no discharge from the site.

4.5.2 Process Plant Recycled Water Demand

As shown in Table 10, recycled water can be supplied to the process plant by three main sources and one back-up source. After the water level in the Esperanza Pit is returned to the MRL or below, additional make-up water will be required as shown in Table 12.

Table 12 Process Pond Water Supply Post Esperanza Pit Water Level Reduction

Water Source Average Annual Flow (m3)

Supply

Esperanza TSF 478,653

Mill Creek Dam 167,451

Treated Esperanza Pit Water 57,795

Total 703,899

Demand

Dust Suppression 87,880

Evaporation 33,304

Process Plant 1,314,891

28


Water Source Average Annual Flow (m3)

Total 1,436,075

Make-up Required 732,176

4.5.3 Full Pit Water Reduction

The water balance assessment undertaken centred on only using the Esperanza Pit water for the process plant if the pit water level was greater than the MRL. If the Esperanza Pit water could be used in the process plant until there was no water available, there would be no requirement for make-up water until the Esperanza Pit was fully depleted. At this point, the average annual make-up requirement would be similar to that shown in Table 12.

4.5.4 Collection Dam Overflows

Both the North Waste Rock Dump Sump and the Hoover Dam are in place to collect seepage and return the water to Mill Creek Dam. In addition to the seepage, stormwater inflows will result in addition water to be pumped to Mill Creek Dam. For this assessment, the dams were allowed to overflow to provide information of the volume of water which will need to be managed. An assessment on the minimum, mean and maximum overflows from these dams has been undertaken with the results summarised in Table 13 summarises the results of this assessment.

Table 13 Collection Dam Overflows

Storage ID Minimum Annual Overflow (m3)

Mean Annual Overflow (m3)

Maximum Annual Overflow (m3)

North Waste Rock Dump Sump

204 12,893 94,186

Hoover Dam 0 8,592 28,452

4.6 Model Validation

4.6.1 Data

In order to assess the validity of the water balance model results, the reliability of the data source was investigated as the reliability of data is highly dependent on the data source. Both the site and environmental data sources outlined in Section 2.1 are considered reliable as they are either directly measurable by site personnel or supplied by reputable government agencies (ie. BOM). The water balance model results are therefore to be considered reliable. In addition, discussions held with on-site personnel confirmed the net deficit of water even without the current water management strategy in place.

4.6.2 Calibration

Calibration of the water balance model could be undertaken using the available data. Calibration would require the model to be assessed over an extended period of time utilising rainfall, runoff, transfer rates and storage level data. The difficulty associated with calibration is centred around the interaction

29


between rainfall and runoff as the size of the catchments will result in a variation in the rainfall throughout the site. Continuous assessment and updating of the model would be required as more data is collected.

4.6.3 Sensitivity

The most sensitive parameter adopted for this assessment is the runoff. If the runoff is significantly greater than what was estimated by the AWBM model, the volume of make-up water would be reduced along with the possibility of uncontrolled discharge from some of the on-site storages. If the runoff is significantly less than what was estimated by the AWBM model, the volume of make-up water would be increased. As the runoff was estimated based on available streamflow data, it is envisaged that the AWBM model is adequately estimating the runoff and the sensitivity is relatively low.

It should also be noted that the adoption of historical rainfall and evaporation data within the water balance model does not take into account the potential impacts of climate change and that this has not been accounted for.

30


5. Assessment Comparison

As discussed previously, two separate assessments were undertaken to satisfy DERM’s notice to conduct or commission an environmental evaluation. Through undertaken the assessments, it was evident that the estimate of the likelihood of uncontrolled discharge varied between the two. A comparison of the input parameters was undertaken to highlight the variances in the two assessments undertaken as shown in Table 14.

Table 14 Assessment Input Parameter Comparison

Input Parameter DSA Assessment Water Balance Assessment

Runoff Coefficient of 1 Varying coefficient depending on the calibrated AWBM model

Evaporation None Independent of rainfall

Solids input to Esperanza TSF Accounted for Not accounted for

Net inflow to a storage Cannot be less than zero Can be less than zero


31


6. Conclusion

6.1 Overview Two separate assessments were undertaken as part of this report to meet the requirements of Section 6 of DERM’s notice to conduct or commission an environmental evaluation, namely:

An assessment of the DSA required for a range of hydrologic events; and

A water balance assessment based on historical daily rainfall data.

6.2 DSA Assessment The DSA assessment was undertaken incorporating the hydrologic events outlined in DERM’s notice to conduct or commission an environmental evaluation. The results of the DSA assessment are shown in Appendix F.

Based on the DSA assessment undertaken for storage volumes available as at March 2012, it was concluded that:

The Esperanza TSF can accommodate most DSA scenarios with durations of 5 days or less;




The total storage available can accommodate DSA scenarios with ARIs of less than 50 years with 5 day durations and ARIs of less than 1,000 years with 1 day durations.

Based on the DSA assessment undertaken for estimated storage volumes available as at November 1st 2012, it was concluded that:

The Esperanza TSF can accommodate all DSA scenarios with durations of 5 days or less;





It is understood that an investigation is currently being undertaken by a 3rd party hydrogeologist into the plausibility of raising the Mandatory Reporting Level of the Esperanza Pit. Should the outcome of this investigation demonstrate the Mandatory Reporting Level could be raised, this would have a positive impact on the storage capacity and thus the DSA assessment. It’s noted from the DSA scenarios run, that there is ample existing capacity in the pit.


32


6.3 Water Balance Assessment The water balance assessment was undertaken incorporating historical daily rainfall data from 1910 to 2010 and the data collected and summarised in Section 2. The average annual water balance is shown in Appendix H.

Based on the water balance assessment undertaken it was concluded that:

The current site water balance results in a net deficit of water;

There was no discharge of water from the site over the duration assessed; and

Additional make-up water will be required to supply water to the process plant as shown in Table 12.

6.4 Assessment Comparison A comparison of the input parameters for each assessment was undertaken to highlight the variances. A summary of this assessment is shown in Table 14.


33


Appendix A

Site Locality Map

"

"

"

"

"

"

"

"

!(

Leichhardt River

Gregory

River

F iery C

ree

k

M ingera Creek

Dug

ald

Rive

r

Buckle y Rive

r

Gunpowder Creek

Corella

Riv

er

Temple

ton River

Archie

Cree

k

Yaringa Creek

Cloncurry River

Law n Hill C reek

Alexandra River

Sand

y Cre

ek

Middle Creek

O'S

hannassy

River

Musselbrook Creek

Dismal C

reek

Paroo

Cre

ek

Cartrige C

reek

M illar C

reek

Thornton River

Elizabeth CreekG

eorg

ina

Rive

r

Myally Cre ek

Inca Creek

Big

Toby Creek

Redba

nk C

reek

Mal bon River

Goonooma C reek

Emu Creek

Woo

roon

a Cree

k

Mistake Creek

Cam

eron RiverNottin

gham C

reek

Leic

hhar

dt R

iver

Dismal

Creek

Clon

curr

y Rive

r

MOUNT ISA CITY COUNCIL

CLONCURRY SHIRE COUNCIL

BURKE SHIRE COUNCIL

CARPENTARIA SHIRE COUNCIL

BOULIA SHIRE COUNCIL

Barkly Highway

Gregory Downs Camooweal Road

Wills Developmental Road

Gun

pow

der R

oad

Stock Route

Burk

e De

velo

pmen

tal R

oad

Burketown Road

Clo

n cur

ry D

ajar

ra R

oad

Sedan D

ip R

oad

Mount Isa D

uchess Road

Thor

n to n

i a Y

elv e

r tof t

Roa

d

Wills Developmental Road

Barkly Highway

Burke Developmental Road

Barkly

Gregory

Camooweal

Four Ways

Mount Isa

Gunpowder

Cloncurry

Three Rivers

Mt Gordon Mine

N:\AU\Toowoomba\Projects\42\16851\GIS\Maps\4216851_02.mxd

LEGEND

0 10 20 30 40

KilometresMap Projection: Universal Transverse Mercator

Horizontal Datum: Geocentric Datum of AustraliaGrid: Map Grid of Australia 1994, Zone 54 o

© 2012. Whilst every care has been taken to prepare this map, GHD, Navteq and Geoscience Australia make no representations or warranties about its accuracy, reliability, completeness or suitability for any particular purpose and cannot accept liability and responsibility of any kind(whether in contract, tort or otherwise) for any expenses, losses, damages and/or costs (including indirect or consequential damage) which are or may be incurred by any party as a result of the map being inaccurate, incomplete or unsuitable in any way and for any reason.

Birla Mt Gordon Pty LtdBirla Mount Gordon Water Management

Figure 1

Job NumberRevision A

42-16851

27 Mar 2012

Locality Map

Date

Data source: Navteq - Place Names, Highways, Major Roads, Local Government Boundaries (2011). Geoscience Australia - Major Waterways (2008). GHD - Mt Gordon Mine (2012). Created by: CM

85 Spence Street Cairns QLD 4870 Australia T 61 7 4044 2222 F 61 7 4044 2288 E [email protected] W www.ghd.com

1:1,000,000 @ A3

!( Mt Gordon Mine

" Place Names

Highways

Major Roads

Major Waterways

Local Government Boundaries

34


Appendix B

Catchment Plan

35


Appendix C

Storage Location Map

Ramp

Esperanza Pit

ProcessPonds

OldHeapLeach

RetentionPond

Mill Creek Dam

Upper Esperanza

Gunpowder Creek

North Waste Dump

Mammoth Waste DumpEvaporation

Pond 3

EvaporationPond 2

EvaporationPond 1

North WasteDump Sump

Tailings Storage Facility

Old Tailings Dam(Decomissioned)

Hoover Dam(North West Gully Dam)

327,000

327,000

328,000

328,000

329,000

329,000

7,820

,000

7,820

,000

7,821

,000

7,821

,000

7,822

,000

7,822

,000

N:\AU\Toowoomba\Projects\42\16851\GIS\Maps\4216851_01.mxd

LEGEND

0 100 200 300 400

Metres

Map Projection: Universal Transverse MercatorHorizontal Datum: Geocentric Datum of Australia

Grid: Map Grid of Australia 1994, Zone 54 o© 2012. Whilst every care has been taken to prepare this map, GHD makes no representations or warranties about its accuracy, reliability, completeness or suitability for any particular purpose and cannot accept liability and responsibility of any kind (whether in contract, tort orotherwise) for any expenses, losses, damages and/or costs (including indirect or consequential damage) which are or may be incurred by any party as a result of the map being inaccurate, incomplete or unsuitable in any way and for any reason.

Birla Mt Gordon Pty LtdBirla Mount Gordon Water Management

Figure 2

Job NumberRevision A

42-16851

27 Mar 2012

Site Layout

Date

Data source: Birla Mt Gordon - Imagery (2012). GHD - Place Names (2012). Created by: CM

85 Spence Street Cairns QLD 4870 Australia T 61 7 4044 2222 F 61 7 4044 2288 E [email protected] W www.ghd.com

1:10,000 @ A3

36


Appendix D

Storage Data Summary

Date : 13/04/2012

Job Number : 4216851

Revision : Draft

Prepared by: I Brown

ITEM DESCRIPTION OF ITEM VALUE UNIT SOURCE NOTES

Max Storage VolumeEsperanza TSF 649,000 m3 AWA Annual Regulated Dam Safety Review

2011Staged storage curve

Mill Creek Dam 1,400,000 m3 GHD Annual Review of Hazardous Dams, 2008

Raffinate Pond m3PLS Pond m3Bleed SX Pond m3Hoover Dam (North West Gully Dam) 20,000 m3 GHD Annual Review of Hazardous Dams,

2008 Esperanza Open Pit 6,342,000 m3 GHD Annual Review of Hazardous Dams,

2008 North Waste Dump Sump 4,500 m3 AWA Annual Regulated Dam Safety Review

2011

Max Storage HeightEsperanza TSF 55.0 m AWA Annual Regulated Dam Safety Review

2011maximum depth

Mill Creek Dam 20 m AWA Annual Regulated Dam Safety Review 2011

Raffinate Pond mPLS Pond mBleed SX Pond mHoover Dam (North West Gully Dam) 13.5 m GHD Annual Review of Hazardous Dams,

2008 Esperanza Open Pit 130 m GHD Annual Review of Hazardous Dams,

2008 Staged storage curve

North Waste Dump Sump 2 m

Storage Catchment AreaEsperanza TSF 45.8 ha Catchment PlanMill Creek Dam 263.2 ha Catchment Plan Upper Esperanza + Mid Esperanza + Lower Esperanza + Mill Ck Upper + Mammoth + Retention PondRaffinate Pond haPLS Pond haBleed SX Pond haHoover Dam (North West Gully Dam) 4.5 ha Catchment PlanEsperanza Open Pit 29.8 ha Catchment PlanNorth Waste Dump Sump 19.8 ha Catchment Plan

Storage Surface AreaEsperanza TSF 26.2 ha AWA Annual Regulated Dam Safety Review

2011maximum surface area

Mill Creek Dam 13.8 ha AWA Annual Regulated Dam Safety Review 2011

maximum surface area

Raffinate Pond haPLS Pond haBleed SX Pond haHoover Dam (North West Gully Dam) 1.4 ha AWA Annual Regulated Dam Safety Review

2011Esperanza Open Pit 10.4 ha AWA Annual Regulated Dam Safety Review

2011North Waste Dump Sump 0.5 ha AWA Annual Regulated Dam Safety Review

2011maximum surface area

Storage Base AreaEsperanza TSF 0.8 haMill Creek Dam 4.7 haRaffinate Pond haPLS Pond haBleed SX Pond haHoover Dam (North West Gully Dam) 0.1 haEsperanza Open Pit 3.3 haNorth Waste Dump Sump 0.2 ha

Storage MRLEsperanza TSF 0.6 m AWA Annual Regulated Dam Safety Review

2011 Depth below spillway level

Mill Creek Dam 0.5 m AWA Annual Regulated Dam Safety Review 2011

Depth below spillway level

Raffinate Pond - mPLS Pond - mBleed SX Pond - mHoover Dam (North West Gully Dam) - m GHD Annual Review of Hazardous Dams,

2008 Esperanza Open Pit 184.0 m AWA Annual Regulated Dam Safety Review

2011RL

Estimate only based on volume and depthProcess Ponds 1.0

Process Ponds

Process Ponds -

Process Ponds 6.2

Process Ponds 1.7

Water Balance and DSA AssessmentStorage Data

FOR

Birla Mount Gordon

Process Ponds 35,000 AWA Annual Regulated Dam Safety Review 2011

37


Appendix E

Water Flow Diagram

Note Birla Mount Gordon Job No 4216851

Water Flow Direction CLIENTS PEOPLE PERFORMANCE Water Balance Assessment Rev No 0

Overflow Flow Direction Water Flow Diagram Appendix ERunoff Flow Direction

Level 1, 85 Spence Street, Cairns QLD Australia T 617 4044 2222 F 617 4044 2288 E [email protected] W www.ghd.com.au

Process Ponds

Raw Water Tank

Underground

TSF

Esperanza Pit

North Waste DumpCatchment

Discharge to Gunpowder Creek

Process Plant

North Waste DumpRunoff

North Waste DumpSump

Mill Ck Dam

High Capacity Evaporators

Lake

Hoover Dam

Mill Creek Dam Catchment

Mill Creek DamRunoff

TSF Catchment

TSF Runoff

Esperanza Pit Catchment

Esperanza Pit Runoff

Water Treatment (Bat Cave)

Water Treatment (Thickner)

RW Standpipe Washbay

Standpipe (dust suppression)

Lime Slaker

Make-up Water

38


Appendix F

DSA Results

Date : 19/04/2012

Job Number : 4216851

Revision : Rev 0

Prepared by: I Brown

Storage ID Catchment Area + Storage Area (m2) DSA Criteria Rainfall Depth (mm) Rainfall Volume (m3) Process Input (m3) Process Output (m3) DSA Required (at November 1st) (m3) Total Volume (m3) Available Volume as at March

2012 Compliance at March 2012 Estimated Available Volume as at November 2012

Estimated Compliance at November 2012

1 in 10, 1 day duration 146 66,868 4,933 1,933 69,868 650,000 275,000 Yes 570,000 Yes1 in 10, 5 day duration 239 109,554 24,665 9,665 124,554 650,000 275,000 Yes 570,000 Yes1 in 25, 1 day duration 203 92,868 4,933 2,300 95,501 650,000 275,000 Yes 570,000 Yes1 in 25, 5 day duration 332 152,182 24,665 11,500 165,347 650,000 275,000 Yes 570,000 Yes1 in 50, 1 day duration 215 98,378 4,933 2,300 101,011 650,000 275,000 Yes 570,000 Yes1 in 50, 5 day duration 352 161,216 24,665 11,500 174,381 650,000 275,000 Yes 570,000 Yes

1 in 100, 1 day duration 246 112,714 4,933 2,300 115,347 650,000 275,000 Yes 570,000 Yes1 in 100, 5 day duration 403 184,620 24,665 11,500 197,785 650,000 275,000 Yes 570,000 Yes1 in 200, 1 day duration 279 127,736 4,933 2,300 130,369 650,000 275,000 Yes 570,000 Yes1 in 200, 5 day duration 457 209,260 24,665 11,500 222,425 650,000 275,000 Yes 570,000 Yes

1 in 1,000, 1 day duration 363 166,391 4,933 2,300 169,024 650,000 275,000 Yes 570,000 Yes1 in 1,000, 5 day duration 593 271,411 24,665 11,500 284,576 650,000 275,000 No 570,000 Yes

1 in 25, 2 month wet period 750 343,500 295,980 115,980 523,500 650,000 275,000 No 570,000 Yes1 in 100, 2 month wet period 910 416,780 295,980 115,980 596,780 650,000 275,000 No 570,000 No1 in 200, 2 month wet period 1,050 480,900 295,980 115,980 660,900 650,000 275,000 No 570,000 No

1 in 10, 1 day duration 146 384,272 194 0 384,466 1,400,000 813,000 Yes 813,000 Yes1 in 10, 5 day duration 239 629,574 970 0 630,544 1,400,000 813,000 Yes 813,000 Yes1 in 25, 1 day duration 203 533,686 194 0 533,880 1,400,000 813,000 Yes 813,000 Yes1 in 25, 5 day duration 332 874,548 970 0 875,518 1,400,000 813,000 No 813,000 No1 in 50, 1 day duration 215 565,354 194 0 565,548 1,400,000 813,000 Yes 813,000 Yes1 in 50, 5 day duration 352 926,464 970 0 927,434 1,400,000 813,000 No 813,000 No

1 in 100, 1 day duration 246 647,735 194 0 647,929 1,400,000 813,000 Yes 813,000 Yes1 in 100, 5 day duration 403 1,060,959 970 0 1,061,929 1,400,000 813,000 No 813,000 No1 in 200, 1 day duration 279 734,065 194 0 734,259 1,400,000 813,000 Yes 813,000 Yes1 in 200, 5 day duration 457 1,202,561 970 0 1,203,531 1,400,000 813,000 No 813,000 No

1 in 1,000, 1 day duration 363 956,206 194 0 956,400 1,400,000 813,000 No 813,000 No1 in 1,000, 5 day duration 593 1,559,723 970 0 1,560,693 1,400,000 813,000 No 813,000 No

1 in 25, 2 month wet period 750 1,974,000 11,640 0 1,985,640 1,400,000 813,000 No 813,000 No1 in 100, 2 month wet period 910 2,395,120 11,640 0 2,406,760 1,400,000 813,000 No 813,000 No1 in 200, 2 month wet period 1,050 2,763,600 11,640 0 2,775,240 1,400,000 813,000 No 813,000 No

1 in 10, 1 day duration 146 9,052 2,300 2,300 9,052 35,000 2,619 No 2,619 No1 in 10, 5 day duration 239 14,830 11,500 11,500 14,830 35,000 2,619 No 2,619 No1 in 25, 1 day duration 203 12,572 2,300 2,300 12,572 35,000 2,619 No 2,619 No1 in 25, 5 day duration 332 20,601 11,500 11,500 20,601 35,000 2,619 No 2,619 No1 in 50, 1 day duration 215 13,318 2,300 2,300 13,318 35,000 2,619 No 2,619 No1 in 50, 5 day duration 352 21,824 11,500 11,500 21,824 35,000 2,619 No 2,619 No

1 in 100, 1 day duration 246 15,258 2,300 2,300 15,258 35,000 2,619 No 2,619 No1 in 100, 5 day duration 403 24,992 11,500 11,500 24,992 35,000 2,619 No 2,619 No1 in 200, 1 day duration 279 17,292 2,300 2,300 17,292 35,000 2,619 No 2,619 No1 in 200, 5 day duration 457 28,328 11,500 11,500 28,328 35,000 2,619 No 2,619 No

1 in 1,000, 1 day duration 363 22,525 2,300 2,300 22,525 35,000 2,619 No 2,619 No1 in 1,000, 5 day duration 593 36,741 11,500 11,500 36,741 35,000 2,619 No 2,619 No

1 in 25, 2 month wet period 750 46,500 138,000 138,000 46,500 35,000 2,619 No 2,619 No1 in 100, 2 month wet period 910 56,420 138,000 138,000 56,420 35,000 2,619 No 2,619 No1 in 200, 2 month wet period 1,050 65,100 138,000 138,000 65,100 35,000 2,619 No 2,619 No

1 in 10, 1 day duration 146 43,508 614 194 43,928 5,701,000 670,000 Yes 1,170,000 Yes1 in 10, 5 day duration 239 71,282 3,070 970 73,382 5,701,000 670,000 Yes 1,170,000 Yes1 in 25, 1 day duration 203 60,425 614 194 60,845 5,701,000 670,000 Yes 1,170,000 Yes1 in 25, 5 day duration 332 99,018 3,070 970 101,118 5,701,000 670,000 Yes 1,170,000 Yes1 in 50, 1 day duration 215 64,010 614 194 64,430 5,701,000 670,000 Yes 1,170,000 Yes1 in 50, 5 day duration 352 104,896 3,070 970 106,996 5,701,000 670,000 Yes 1,170,000 Yes

1 in 100, 1 day duration 246 73,338 614 194 73,758 5,701,000 670,000 Yes 1,170,000 Yes1 in 100, 5 day duration 403 120,124 3,070 970 122,224 5,701,000 670,000 Yes 1,170,000 Yes1 in 200, 1 day duration 279 83,112 614 194 83,532 5,701,000 670,000 Yes 1,170,000 Yes1 in 200, 5 day duration 457 136,156 3,070 970 138,256 5,701,000 670,000 Yes 1,170,000 Yes

1 in 1,000, 1 day duration 363 108,263 614 194 108,683 5,701,000 670,000 Yes 1,170,000 Yes1 in 1,000, 5 day duration 593 176,595 3,070 970 178,695 5,701,000 670,000 Yes 1,170,000 Yes

1 in 25, 2 month wet period 750 223,500 24,560 7,760 240,300 5,701,000 670,000 Yes 1,170,000 Yes1 in 100, 2 month wet period 910 271,180 24,560 7,760 287,980 5,701,000 670,000 Yes 1,170,000 Yes1 in 200, 2 month wet period 1,050 312,900 24,560 7,760 329,700 5,701,000 670,000 Yes 1,170,000 Yes

1 in 10, 1 day duration 146 732,774 8,041 4,427 736,388 7,846,000 1,760,619 Yes 2,555,619 Yes1 in 10, 5 day duration 239 1,200,545 40,205 22,135 1,218,615 7,846,000 1,760,619 Yes 2,555,619 Yes1 in 25, 1 day duration 203 1,017,694 8,041 4,794 1,020,941 7,846,000 1,760,619 Yes 2,555,619 Yes1 in 25, 5 day duration 332 1,667,689 40,205 23,970 1,683,924 7,846,000 1,760,619 Yes 2,555,619 Yes1 in 50, 1 day duration 215 1,078,081 8,041 4,794 1,081,328 7,846,000 1,760,619 Yes 2,555,619 Yes1 in 50, 5 day duration 352 1,766,688 40,205 23,970 1,782,923 7,846,000 1,760,619 No 2,555,619 Yes

1 in 100, 1 day duration 246 1,235,176 8,041 4,794 1,238,423 7,846,000 1,760,619 Yes 2,555,619 Yes1 in 100, 5 day duration 403 2,023,159 40,205 23,970 2,039,394 7,846,000 1,760,619 No 2,555,619 Yes1 in 200, 1 day duration 279 1,399,799 8,041 4,794 1,403,046 7,846,000 1,760,619 Yes 2,555,619 Yes1 in 200, 5 day duration 457 2,293,181 40,205 23,970 2,309,416 7,846,000 1,760,619 No 2,555,619 Yes

1 in 1,000, 1 day duration 363 1,823,403 8,041 4,794 1,826,650 7,846,000 1,760,619 No 2,555,619 Yes1 in 1,000, 5 day duration 593 2,974,259 40,205 23,970 2,990,494 7,846,000 1,760,619 No 2,555,619 No

1 in 25, 2 month wet period 750 3,764,250 470,180 261,740 3,972,690 7,846,000 1,760,619 No 2,555,619 No1 in 100, 2 month wet period 910 4,567,290 470,180 261,740 4,775,730 7,846,000 1,760,619 No 2,555,619 No1 in 200, 2 month wet period 1,050 5,269,950 470,180 261,740 5,478,390 7,846,000 1,760,619 No 2,555,619 No

Water Balance and DSA AssessmentDERMs Notice DSA Assessments

FOR

Birla Mount Gordon

3,450,000Total

298,000

Esperanza TSF

Mill Creek Dam

Process Ponds

Esperanza Open Pit

62,000

458,000

2,632,000

39


Appendix G

GoldSim Model Layout


All units are m3/day CLIENTS PEOPLE PERFORMANCE Water Balance Assessment Rev No 0

GoldSim Model Layout Appendix H

Level 1, 85 Spence Street, Cairns QLD Australia T 617 4044 2222 F 617 4044 2288 E [email protected] W www.ghd.com.au

40


Appendix H

Overall Water Balance

29,220 7,670

8,662 0

12,889

13,140 345,159

12,889229,118

170,801

10,598

0 716,762

477,953

1,881

6,42562,946 4,173

62,946 57,660142,081

0 82,181


All units are m3/year CLIENTS PEOPLE PERFORMANCE Water Balance Assessment Rev No 0

Water Flow Direction Average Annual Water Balance Appendix HOverflow Flow DirectionRunoff Flow Direction Level 1, 85 Spence Street, Cairns QLD Australia T 617 4044 2222 F 617 4044 2288 E [email protected] W www.ghd.com.au

524,130

224,262

57,660

1,314,891 87,880

1,314,891

Process Ponds

Raw Water Tank

Underground

TSF

Esperanza Pit

North Waste DumpCatchment

Discharge to Gunpowder Creek

Process Plant

North Waste DumpRunoff

North Waste DumpSump

Mill Ck Dam

High Capacity Evaporators

Lake

Hoover Dam

Mill Creek Dam Catchment

Mill Creek DamRunoff

TSF Catchment

TSF Runoff

Esperanza Pit Catchment

Esperanza Pit Runoff

Water Treatment (Bat Cave)

Water Treatment (Thickner)

RW Standpipe Washbay

Standpipe (dust suppression)

Lime Slaker

Make-up Water

Seepage

42/16851/107344 Birla Mount Gordon Design Storage Allowance and Water Balance Assessment

GHD

1st Floor 85 Spence Street Cairns QLD 4870 PO Box 819 Cairns QLD 4870 Australia T: 07 4044 2222 F: 07 4044 2288 E: [email protected]

© GHD 2012

This document is and shall remain the property of GHD. The document may only be used for the purpose for which it was commissioned and in accordance with the Terms of Engagement for the commission. Unauthorised use of this document in any form whatsoever is prohibited.

Document Status

Rev No. Author

Reviewer Approved for Issue

Name Signature Name Signature Date

Draft I Brown 13/4/2012

0 I Brown P Sharry P Sharry * R Saunders R Saunders* 19/4/2012

Birla Mount Gordon Mine

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