Water and Environment

Transcription

1 Water and Environment WEST CREEK WATER SUPPLY GROUNDWATER MODELLING Prepared for Toro Energy Ltd Date of Issue 30 June 2010 Our Reference 1134/C/104a As part of Aquaterra s commitment to the environment this PDF has been designed for double sided printing and includes blank pages as part of the document.

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3 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING Prepared for Toro Energy Ltd Date of Issue 30 June 2010 Our Reference 1134/C/104a

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5 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING Date Revision Description Revision A 30/06/2010 Draft Name Position Signature Date Originator Iain Marshall Senior Hydrogeologist 30/06/2010 Alan Woodward Principal Hydrogeologist 30/06/2010 Reviewer Kathryn Rozlapa Principal Modeller 30/06/2010 Jeff Jolly Principal Hydrogeologist 30/06/2010 Location Address Issuing Office Perth Suite 4, 125 Melville Parade, Como WA 6152 Tel Fax Our Reference 1134/C/104a

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7 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING EXECUTIVE SUMMARY EXECUTIVE SUMMARY Toro Energy s (Toro) Lake Way and Centipede uranium deposits are located along the edge of the Lake Way playa, just south of the town of Wiluna, in the Murchison region of Western Australia s Mid West. Toro propose to process approximately 2Mt of ore per annum over a project life of 10 years. It is estimated that ~0.70GL/year of moderate salinity water (TDS < 3,000mg/L) will be required to process the ore. This study evaluates the feasibility of sourcing this process water from the West Creek groundwater system, located to the east of Wiluna. This report presents the following: A review of the existing environment and hydrogeological conditions of the West Creek area. Details of the development of a 3 layer regional-scale Modflow/Surfact groundwater model to assess the long-term yield potential of the shallow calcrete aquifer system that extends along the West Creek, in terms of its potential to meet the water demand of Toro s Wiluna Uranium Project, both in terms of the water quantity and quality requirements. The model is also used to assess the supply potential of the existing West Creek production bores and to determine the optimal borefield configuration required to maximise abstraction from the aquifer within various prescribed water level drawdown constraints. Results of the modelling. Borefield development costs. The following conclusions are reached from the work undertaken: Water quality within the calcrete aquifer in the study area is marginal at best with respect to the Wiluna Uranium Project water quality constraints. Water quality within the deeper silty/clayey sediments underlying the calcrete aquifer is unlikely to meet Toro s water quality constraints. The modelling indicates that the current West Creek Borefield (installed in the calcrete aquifer) comprising bores P18, P22, P61 and P62 is unlikely to satisfy Toro s water demand of 0.7GL/year for a project life of ten years. The modelling indicates that a reconfiguration of the existing West Creek Borefield (comprising P18, P26, P62, P70 and P21) is unlikely supply the required 0.7GL/year for ten years. The modelling indicates that an expanded West Creek Borefield installed in the calcrete aquifer may meet the Projects water requirements (0.7GL/year) for 8 to 9 years, before declining to ~0.66GL in the tenth year. The final water quality of the blend of an expanded West Creek Borefield will not be known until further hydrogeological data is collected. Operation of the Apex Southern Borefield at significant rates is likely to have a deleterious effect on the operation of the West Creek borefield. The capital costs of developing a 0.7GL/year capacity water supply scheme to pipe water from the West Creek Borefield to the Centipede and Lake Way mines, as well the mine village, is estimated at $12.1M. Our Reference 1134/C/104a

8 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING EXECUTIVE SUMMARY A number of recommendations are presented in this report, these are summarised as follows: A further hydrogeological investigation of the study area should be undertaken. If the above investigation provides favourable results, a more intensive investigation (including the installation of new production bores and the refurbishment of existing bores) be undertaken. The groundwater model developed for this study should be updated if the above investigations provide favourable results. The updated model should be used to generate new abstraction predictions. It should be noted that the modelling results are based on the current model geometry, which has in turn been developed from the current limited hydrogeological dataset, and it assumes average rainfall conditions. The limitations of the modelling work reported here are presented in Section 4.8. Our Reference 1134/C/104a

9 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING INTRODUCTION CONTENTS 1 INTRODUCTION BACKGROUND SCOPE OF WORK EXISTING ENVIRONMENT CLIMATE TOPOGRAPHY GEOLOGY HYDROGEOLOGY MINE WATER REQUIREMENTS DEVELOPMENT AND UTILISATION OF THE WEST CREEK GROUNDWATER RESOURCE WEST CREEK BOREFIELD APEX SOUTHERN BOREFIELD CONCEPTUAL HYDROGEOLOGY PREAMBLE DATA REVIEW DATA SOURCES OUTCOME OF THE DATA REVIEW CALCRETE AQUIFER GEOMETRY WATER LEVELS AND GROUNDWATER FLOW GROUNDWATER RECHARGE AND EVAPOTRANSPIRATION KEY AQUIFER PARAMETERS ALLUVIUM ALLUVIUM GEOMETRY WATER LEVELS AND GROUNDWATER FLOW GROUNDWATER RECHARGE AND EVAPOTRANSPIRATION KEY AQUIFER PARAMETERS BASAL CLAYS AND SILT FRACTURED ROCK (BEDROCK) MINE WATER SUPPLY BOREFIELD OPTIONS EXISTING BORES RECOMMENDATIONS FROM PREVIOUS STUDIES POSSIBLE NEW DEVELOPMENTS GROUNDWATER MODEL MODELLING OBJECTIVES Our Reference 1134/C/104a Page i

10 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING INTRODUCTION 4.2 MODEL SETUP MODEL GRID AND EXTENT MODEL GEOMETRY GROUNDWATER INFLOW AND OUTFLOW GROUNDWATER THROUGHFLOW RAINFALL RECHARGE EVAPOTRANSPIRATION GROUNDWATER ABSTRACTION MODEL CALIBRATION PREAMBLE STEADY-STATE CALIBRATION TRANSIENT CALIBRATION MODEL PREDICTIONS SETUP PREDICTION RESULTS SENSITIVITY ANALYSIS GROUNDWATER RECOVERY MODEL LIMITATIONS ABSTRACTION ESTIMATES RECHARGE AQUIFER CHARACTERISTICS AND CALIBRATION TO TRANSIENT DATA DISCUSSION WATER SUPPLY OPTIONS PREDICTED DRAWDOWNS WEST CREEK BOREFIELD DEVELOPMENT COSTS BORE CONSTRUCTION AND TESTING COSTS PUMP, PIPELINE AND POWER SUPPLY CAPITAL COSTS CONCLUSIONS RECOMMENDATIONS REFERENCES Page ii Our Reference 1134/C/104a

11 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING INTRODUCTION TABLES Table 1.1: Technical and operational information for the West Creek production bores Table 1.2: Chemistry of Groundwater from the West Creek Production Bores Table 1.3: Groundwater chemistry of the production bores in the Apex Southern Borefield Table 2.1: Hydraulic Characteristics of the calcrete aquifer in the West Creek Borefield Table 4.1: Corner Coordinates of the Model Domain Table 4.2: Model Layers Table 4.3: Adopted Recharge Values Table 4.4: Calculated and Adopted Steady-State Calibration Heads for West Creek Borefield.. 52 Table 4.5: Steady State Predicted Water Balance (m 3 /day) Table 4.6: Transient Calibration Model Specific Yield and Storage Coefficient Values Table 4.7: Transient Calibration Model Cumulative Mass Balance (m 3 ) Table 4.8: Borefield Prediction Scenarios Table 4.9: Summary of Results for Modelled Scenarios Table 4.10: Sensitivity runs Table 5.1: Areas of drawdown- Scenarios 6, 8 and Table 6.1: West Creek Borefield Development Costs Table 6.2: Pumping, pipeline and genset power supply capital costs to Centipede Table 6.3: Pumping, pipeline and HV power supply capital costs to Centipede Table 6.4: Pumping, pipeline and power supply capital costs to Lake Way FIGURES Figure 1.1: Locality plan of the West Creek Groundwater Unit... 3 Figure 1.2: Simplified Geological Map... 7 Figure 1.3: Location of West Creek and Apex Southern Borefields Figure 1.4: Water level fluctuations in the West Creek Borefield versus [A] Monthly Rainfall and [B] Abstraction Figure 1.5: Groundwater salinity variations in the West Creek Borefield Figure 1.6: Apex Southern Borefield- Groundwater level fluctuations versus abstraction Figure 4.1: Model Grid and Boundary Conditions Figure 4.2: Aquifer Parameter Distribution Layer Figure 4.3: Aquifer Parameter Distribution Layer Figure 4.4: Aquifer Parameter Distribution Layer Figure 4.5: North-East to South-West Cross-Sections Figure 4.6: North-West to South-East Cross-Section Figure 4.7: Modflow Evapotranspiration Package Schematic Figure 4.8: Evapotranspiration Distribution Our Reference 1134/C/104a Page iii

12 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING INTRODUCTION Figure 4.9: Pumping and Monitoring Bore Locations Figure 4.10: Measured versus Modelled Water Levels Figure 4.11: Measured versus Modelled Water Levels and Predicted Steady-State Water Level Contours Figure 4.12: Modelled Recharge Distribution Figure 4.13: Apex Southern Borefield Calibration Hydrographs Figure 4.14: West Creek Borefield Calibration Hydrographs Figure 4.15: Modelled Borefield Configuration Figure 4.16: Total Abstraction for Modelled Borefield Scenarios Figure 4.17: Scenario 6- Predicted Watertable after 10 Years Figure 4.18: Scenario 8- Predicted Watertable after 10 Years Figure 4.19: Scenario 9- Predicted Watertable after 10 Years Figure 4.20: Scenario 6- Predicted Drawdown after 10 Years Figure 4.21: Scenario 8- Predicted Drawdown after 10 Years Figure 4.22: Scenario 9- Predicted Drawdown after 10 Years Figure 4.23: Predicted Abstraction Rates- Sensitivity Runs for Scenario Figure 4.24: Water Levels for Model Cell Containing Bore P62- Scenario 6 and Recovery Run. 95 APPENDICES Appendix A Appendix B Appendix C ACTUAL AREAL EVAPOTRANSPIRATION MAP STEADY-STATE CALIBRATION GROUNDWATER ELEVATIONS PREDICTION MODEL ABSTRACTION VOLUMES Page iv Our Reference 1134/C/104a

13 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING INTRODUCTION 1 INTRODUCTION 1.1 BACKGROUND Toro Energy s (Toro) Lake Way and Centipede uranium deposits are located along the edge of the Lake Way playa, just south of the town of Wiluna, in the Murchison region of Western Australia s Mid West (Figure 1.1). Wiluna is located 750km northeast of Perth and lies along the Goldfields Highway, which connects Wiluna to Leinster (170km to the south-southeast) and to Meekatharra (130km to the west). The nearest regional centre to Wiluna is Kalgoorlie, which is located 500km to the south-southeast of the town. The Lake Way uranium deposit is located ~15km southeast of Wiluna on the northern shore of the Lake Way playa and lies within exploration licence E53/1132. Toro are currently apply for a mining lease, M53/1090, to cover this deposit. The Centipede deposit is located along the western margin of Lake Way, approximately 30km south-southeast of Wiluna and falls within mining lease M53/224. The uranium mineralisation, consisting mainly of carnotite, is hosted within sheet-like superficial calcrete deposits and associated fluviatile-deltaic sequence of sediments, ranging from thin clay layers to clean coarse sand and gravel. The Lake Way uranium deposit was discovered in 1972 by Delhi and Vam during exploration for base metals in the Wiluna area. Delhi undertook exploration and initial feasibility work prior to their acquisition by CSR in The Centipede deposit was discovered in 1977 and CSR acquired the mineral rights to it in The following year Australia adopted the Three Mines Policy which resulted in the cessation of uranium prospecting. However, the recent reversal of this policy and reconsideration of the national energy policy has resulted in renewed interest in uranium mining across Australia. During 2006, Toro Energy (then Nova Energy) completed a conceptual mining study that confirmed the technical and economic viability of the Lake Way and Centipede Uranium Project. Preliminary estimates placed the combined resources of both deposits at ~20.2 million tonnes (Mt) of U 3 O 8 (triuranium octaoxide) with an average grade of 0.06% The ore-body generally extends form just below the shallow watertable to a maximum depth of 12 metres below ground level (m.bgl). Toro propose to process approximately 2Mt of ore per annum over a project life of 10 years, with the Centipede and Lake Way deposits to be mined over years 1 to 6 and 7 to 10, respectively. It is estimated that ~0.70GL/year of moderate salinity water (TDS < 3,000mg/L) will be required to process the ore. Toro Energy propose to rehabilitate and upgrade a disused borefield at West Creek, located on Miscellaneous Lease L53/150, some 18km WNW and 30km NNW from proposed processing plant at Lake Way and Centipede mines, respectively, as the primary water supply for the project. This report details the development of a groundwater model to assess the long-term yield potential of the shallow calcrete aquifer system that extends along the West Creek, in terms of it s potential to meet the water demand of Toro s Wiluna Uranium Project, both in terms of the water quantity and quality requirements. The model is also used to assess the supply potential of the existing West Creek production bores and to determine the optimal borefield configuration required to maximise abstraction from the aquifer within various prescribed waterlevel drawdown constraints. 1.2 SCOPE OF WORK In late February 2010, Aquaterra were appointed by Toro Energy (PO TOEP028), to conduct studies to characterise the surface hydrology and groundwater conditions at the Lake Way and Centipede uranium deposits, to allow for the development of an environmentally acceptable water management plan for the Wiluna Uranium Project. Aquaterra s scope of work also included assessing the potential of the West Creek Borefield to meet the Project s water requirements of 0.70GL/year. In addition, Toro require information on the likely magnitude and extent of the potential cone of water level drawdown that would develop as a result of abstraction from the West Creek Borefield. In terms of assessing the supply potential of the West Creek borefield, Aquaterra (2010) proposed that the following tasks be undertaken: Our Reference 1134/C/104a Page 1

14 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING INTRODUCTION A desktop study to collate all of the available information and to develop a conceptual model of the aquifer system. Construction of a numerical flow model based on the conceptual aquifer, model calibration, and scenario analysis, to cover a number of potential borefield development options, i.e. using the existing production bores and additional bores. The model will be used to evaluate if and how a given borefield configuration could abstract the required water demand, within potential water level drawdown constraints that may be imposed by the Department of Water (DoW). Preparation of a report that describes the background hydrogeology, the conceptual hydrogeological model, the design, setup and calibration of the numerical flow model, as well as the results and recommendations for implementation. A preliminary design and costing for the reticulation system / engineering required to deliver the water to the Centipede mine would also be supplied. Page 2 Our Reference 1134/C/104a

15 LOCALITY PLAN OF THE WEST CREEK GROUNDWATER UNIT FIGURE 1.1 f:\jobs\1134\c\600_report\figures\fig 1.1_locality plan of the west creek groundwater unit.doc

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17 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING INTRODUCTION 1.3 EXISTING ENVIRONMENT CLIMATE The Study area has a semi-arid climate which is characterised by low rainfall and large temperature variations. The closest Commonwealth Bureau of Meteorology (BoM) weather station to the project area is located at Wiluna. The mean annual rainfall is approximately 257mm, but may vary widely from in excess of 700mm to less than 50mm. The highest and most reliable rainfall falls between May and August. Intense tropical cyclone related rainfall events may occur between December and April. Cyclone Bobby is a significant recent example, when in the order of 250mm of rainfall was recorded at Wiluna (in a 9 day period from 19 to 27 February 1995). The mean annual maximum and minimum temperatures for Wiluna are 29 and 14.2 C, respectively. Potential evaporation is approximately 2400mm/year and exceeds rainfall in all months (Water and Rivers Commission, 1999). Actual areal evapotranspiration is estimated to be between 200 and 300mm/year (BoM, 2010) TOPOGRAPHY The study area is largely an alluvial plain and is relatively flat, with a typical elevation of ~500mRL. The area slopes towards the south-east, towards Lake Way with a gradient of about 6x10-4 m/m (Geoscience Australia, 2003). Zones of bedrock outcrop form low-relief hills and largely compartmentalise the study area from adjoining catchments (Geological Survey of Western Australia, 1999) as follows: North and north-west: the Finlayson Range, with an elevation of up to about 600mRL. South and south-west: a range of hills incorporating Mt Wilkinson, with an elevation of up to about 600mRL. East: a range of hills passing to the east of Wiluna town. Hydrology The study area is drained by the south-easterly flowing, ephemeral West Creek and its tributaries, which discharge into the northern edge of the Lake Way salt lake. The Cockarrow and Freshwater tributaries drain the floodplains to the north and south of the West Creek. The extensive Yandil and Paroo catchments, located to the northwest of the area, drain through a narrow valley in the Finlayson Range into the West Creek system. The West Creek catchment is ~32km long and extends over an area of 647km 2. Lake Way is a large playa which is ~36km long and ~10km wide, with a surface area of some 245km 2. Lake Way forms the drainage basin for an 11,000km 2 catchment GEOLOGY The geological map (Sheet SG5109, Geological Survey of Western Australia, 1999) indicates that the study area is largely encircled by bedrock outcrop (Figure 1.2): Northern and north-western periphery of the study area- the bedrock comprises of the Finlayson Member of the Yerrida Group, described as a quartz arenite with subordinate siltstone. Southern periphery of the study area- Archean granitoids (Yilgarn Craton). Eastern periphery of the study area is dominated by metamorphosed Archaean felsic volcanic and volcaniclastic sedimentary rocks (Yilgarn Craton). The geological map of the area also indicates the following surficial geology in the study area is indicated: Sheetwash deposits (comprising of clay, silt and sand) are reported to cover most of the study area. In areas shown to be watercourses, alluvium is indicated. Our Reference 1134/C/104a Page 5

18 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING INTRODUCTION Calcrete outcrops along the upstream reaches of the West Creek River in the narrow valley passing through the Finlayson Range in the north of the study area. A well developed, relatively extensive delta-shaped body of calcrete extends from the West Creek Borefield to the edge of Lake Way. Exploration drilling in the vicinity of the borefield area indicates that the calcrete is approximately 5 to 20m thick, and that it extends further northwards beneath the soil cover. In summary, the study area is mostly covered by alluvial sheetwash sediments, with calcrete zones developed along the main drainage system, all underlain by a number of consolidated Archaean and Proterozoic units. Page 6 Our Reference 1134/C/104a

19 LOCATION MAP 225,000 me 210,000 me 195,000 me DERBY NEWMAN Project KALGOORLIE 7,065,000 mn PERTH ALBANY LEGEND 7,050,000 mn Yerrida Basin Study Area/ West Creek Groundwater Unit Qa Quaternary Alluvium Czb Ephemeral Lake and Dune Deposits Cza Sheetwash Deposits Czk Calcrete Bubble Well Member: stromatolitic chert and chert breccia Pyjb Pyjf Finlayson Member: quartz arenite and subordinate siltstone Agf Undifferentiated Granites As Metasediments/ Metavolcanics Af Metamorphosed Felsics Yilgan Craton Ag Metamorphosed Mafics Ab DATA SOURCES: 1:250K Scale State Topographicl Map % 7,035,000 mn Kilometers Scale: GDA 1994 Zone 51 FIGURE 1.2 SIMPLIFIED GEOLOGICAL MAP Location: F:\Jobs\1134\C\GIS\Vector\MapInfo\Figure 1.2.wor AUTHOR: IM REPORT NO:... DRAWN: MS REVISION:... DATE: 22/06/2010 JOB NO: 1134C

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21 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING INTRODUCTION HYDROGEOLOGY Within the Northern Goldfields area, groundwater is reported to occur within the following aquifer units (Waters and River Commission, 1999): Alluvium. Shallow aquifers with a watertable less than 5m below the ground. The salinity of these aquifers is reported to range from 1,000 to 4,000mg/L on the flanks of palaeo-drainage systems, with higher values encountered along the downstream sections of the drainage system. The hydraulic conductivity of the alluvium aquifers is generally low, with values of less than 2.5m/d. Bore yields vary from 50 to 600m 3 /day, with higher yields being from unconsolidated clayey basaltic gravels. Calcrete. Calcrete forms local high-yielding aquifers due to secondary porosity and high permeabilities. Calcrete generally occurs in the lower portions of the drainage system where the watertable is shallow (generally less than 5m below surface). Saturated thicknesses generally range from 5 to 10m. The salinity of groundwater in calcrete is frequently brackish to saline, however can be fresher where they are recharged directly from rainfall, or when inundation occurs. Potential bore yields are reported to range from 100 to 4,400m 3 /day. Palaeochannel sand. Tertiary-aged palaeochannel sand aquifers are inferred to be continuous along the major drainage systems throughout the northern Goldfields. However, their continuity is poorly understood and the permeable sand horizons may be absent where palaeochannels transgress greenstone belts. These aquifers are the most important aquifer in the region, providing significant groundwater supplies. The aquifer is up to 1km wide, and up to 40m thick in the main channels, reducing to several hundred metres wide in the tributaries. The sand is confined beneath as much as 80m of structureless kaolinitic clay, although in tributaries the confining layer often contains silt and several sandy horizons. Most of the water within the palaeochannel aquifer is reported to be hypersaline, although fresh to brackish zones may occur in drainage tributaries. Fractured rock. Fractured rock aquifers comprise greenstones, granitoids and minor intrusives, where permeability and secondary porosity have been produced by fracturing. These hydraulic characteristics are directly related to the fracture intensity, with lithology having limited control. 1.4 MINE WATER REQUIREMENTS Toro proposes to start construction of the Wiluna Uranium Project in 2012, with commercial production of uranium commencing in 2013, and are currently considering two methods for processing of the uranium ore at the Centipede and Lake Way deposits, namely: Option 1: involves crushing and screening of the ore followed by alkaline heap-leaching with ion exchange uranium recovery. Option 2: involves crushing and grinding of the ore followed by agitated alkaline leaching and direct precipitation of uranium. Currently, Option 1 is the preferred method for processing of the ore to produce a uranium oxide concentrate via direct precipitation of sodium di-uranate (SDU). Toro has estimated the process water requirements at 0.70GL/year (~1920m 3 /day or 22L/s) for a project life of 10 years. For the purposes of this study, Aquaterra have increased the water requirements by 10% (0.77GL/a) to allow for auxiliary water uses, i.e. village consumption, dust suppression etc. It is understood that the water required for this processing option should ideally have a chloride and sulphate concentration of less than 1,000mg/L (pers. comm., D. Kenny, 18 February 2010), which generally corresponds to a TDS content of less than 3,000mg/L (Aquaterra, 2007a). Recently, Toro (2010) have revised their estimates of the water requirements for processing Options 1 and 2 to up to 0.8 and 2.5GL/a, respectively. Toro propose to construct a water treatment plant to produce 768m 3 /day (8.9L/s) of demineralised water for steam generation, as well as a reverse-osmosis plant to produce ~120m 3 /day (1.4L/s) of potable water (<1,000mg/L TDS) for product washing and for camp/plant amenities (Toro, 2010). Our Reference 1134/C/104a Page 9

22 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING INTRODUCTION 1.5 DEVELOPMENT AND UTILISATION OF THE WEST CREEK GROUNDWATER RESOURCE Two large-scale abstraction schemes have been developed and operated in the West Creek Groundwater Unit since 1986, namely: The West Creek or Wiluna (Gold Mine) South Borefield. The Apex (Wiluna Gold Mine) Southern Borefield. The development and operation of these borefields are discussed below WEST CREEK BOREFIELD Australian Groundwater Consultants (AGC) (1985) describes the RAB drilling of early exploration holes, P9 to P16, in the calcrete aquifer along the West Creek drainage system. During March to May 1986 further exploration drilling took place in the area and production bores P18, P22 and P26 were installed and pump-tested (Figure 1.3). According to AGC (1986), bores P26 and P32 tap clayey sands of a palaeochannel aquifer that underlies the calcrete aquifer. The water quality of the palaeochannel aquifer is highly saline, with measured salinity levels in bore P32 of 140,000mg/L TDS (AGT, 1986). Production Bore and Operational Specifications The West Creek Borefield consists of six production bores, P18, P22, P26, P61, P62 and P70. The construction and operational details for these bores are summarised in Table 1.1. Bores P26 and P70 were maintained as standby production holes (Figure 1.3). In 1987, Argent Exploration Services recommended commissioning bores P18, P22, P61 and P62 at a combined pumping rate of 1,789m 3 /day or 20.7L/s (0.65GL/year). Resource Investigations (1991) increased the combined pumping rate from the four production holes to 1,900m 3 /day or 22.0L/s (0.694GL/year), after reviewing three years of operational information. KH Morgan (2006a) estimated that, based on historical abstraction records and work they completed, production bores P18, P26, P61, P62 and P70 should be able to sustain a yield of ~2,400m 3 /day or 27.7L/s (0.875GL/year). Table 1.1: Technical and operational information for the West Creek production bores Bore Number [Date Drilled] Cased depth (m) Slotted Interval (m.bgl) Base of Aquifer (m.bgl) Original SWL A (m.bgl) SWL 12-Jun- 07 (m.bgl) Available Drawdown (m)* Recommended Pumping Rates (L/s) P18 [Mar 1986] P22 [Mar 1986] (14 B ) C, 3.2 A (14 B ) C, 4.9 A P26 [Apr 1986] & B C P61 [Nov 1986] P62 [Nov 1986] C, 3.5 A C, 10.4 A P70 [Sep 1988] Note: A Resource Investigations (1991). B Relates to upper calcrete aquifer. C Argent Exploration Services (1987). * Available drawdown 66% of saturated thickness of aquifer (Resource Investigations, 1991). Resource Investigations (1991) provided estimates of available drawdown in each production bore (Table 1.1), based upon their experience with similar calcrete aquifers in the Eastern Goldfields, which indicated that once waterlevel drawdowns declines below 66% of the saturated Page 10 Our Reference 1134/C/104a

23 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING INTRODUCTION thickness of the aquifer, waterlevels begin to drop more rapidly and bore yields begin to diminish. Groundwater Abstraction Chevron Exploration Corporation (CEC) commissioned the West Creek Borefield in April 1987 and it served as the primary mine water supply to their Mt Wilkinson Gold Mine up until April In May 1989, EON Metals NL (EON) took over operation of the borefield to supply their Matilda Gold Project and operated the borefield up until November However, detailed production and water quality records for this period are not available (Aquaterra, 2007a). EON was licensed (License No ) to abstract 0.55GL/year (1,507m 3 /day or 17.4L/s). Subsequently, Asarco and later Wiluna Gold Mines, operated the borefield up until March 1997, whereafter there is no record of the borefield being utilised. Monthly production information is only available for November 1988 through to January 1991, as well as from April 1993 to March 1997 (Figure 1.4). The following summary of pumping from the borefield is compiled from the above detailed monthly information and other more generalised estimates of borefield abstraction: April 1987 to April 1989: average borefield production varied between 1,100 and 1,200m 3 /day (~0.432GL/a) to supply Mt Wilkinson Mine. Resource Investigation (1989) report that 411,823 m 3 was abstracted from the borefield over the period April 1988 to April May 1989 to January 1991: the average borefield production varied between 767 (8.9L/s) and 1,904 m 3 /day (22.0L/s). Approximately 0.446GL was abstracted over the 12 months ending in January 1991 (Resource Investigations, 1991). January 1991 to March 1994: No information is available for this period, but waterlevel records indicate that the borefield was pumped at ~1900 m 3 /day up until July Furthermore, it would appear that only standby production bore P26 was pumped between late 1992 and August 1993 (Figure 1.4). April 1994 to March 1996: apparently only 44m 3 of groundwater was abstracted from production P62 (Aquaterra, 2007a). April 1996 to March 1997: approximately 1,185 m 3 of groundwater was pumped from the borefield, which is only 17% of the authorised abstraction of 0.7GL permitted under License (KH Morgan & Associates, 1997). The water was abstracted from production bores P22 and P62. This licence expired at the end of December Our Reference 1134/C/104a Page 11

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25 DERBY 240,000 me 225,000 me 210,000 me 195,000 me LOCATION MAP NEWMAN Project KALGOORLIE PERTH 7,065,000 mn ALBANY NO1 WELL LEGEND Study Area/ West Creek Groundwater Unit NO 408 Existing West Creek Production Bores COCKARROW WELL Notional Production Bores Apex Southern Production Bores Monitoring Bores HAYES WELL Processing Plant RAILWAY WELL Mine Village Pipeline 7,050,000 mn N5 SB1 N4 P26 P70 P22 N2 RED HILL WELL GARDEN (GOVT NO16) WELL P18 BUTCHER WELL P61 N1 P62 N8 LANAGAN BORE NO383 CRITCHES BORE FRESHWATER WELL XP5 XP3 P32 WARD WELL LW12 GARDEN WELL HADJI WELL LAKE WAY DEPOSIT DATA SOURCES: 1:250K Scale State Topographicl Map GOLD TOOTH WELL NO 388 TRENNAMANS WELL P31 DEEP BORE 7,035,000 mn XP4 XP2 XP1 WARD NO1 WELL DIORITE WELL MILLIE WELL MINE VILLAGE % DEEP MILL WELL LINDEN BORE Kilometers Scale: GDA 1994 Zone 51 CENTIPEDE DEPOSIT Location: F:\Jobs\1134\C\GIS\Vector\MapInfo\Figure 1.3.wor FIGURE 1.3 LOCATION OF WEST CREEK AND APEX SOUTHERN BOREFIELDS AUTHOR: IM REPORT NO:... DRAWN: MS REVISION:... DATE: 22/06/2010 JOB NO: 1134C

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27 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING INTRODUCTION Groundwater Quality The groundwater quality in the calcrete aquifer system is generally brackish, with measured salinities ranging between 2,000 to 3,500 mg/l TDS. The available groundwater chemistry for the production bores is summarised in Table 1.2, where it is evident that: In terms of Toro s process water requirements, the groundwater quality is marginal, with TDS and chloride concentrations generally exceeding 3,000 and 1,000mg/L, respectively. The sulphate content of the groundwater is below the 1,000mg/L constraint level. In general, the groundwater salinity in the borefield increases downstream from the most north-westerly production bore, P26 (2,344mg/L TDS), to the most south-easterly hole P62 (TDS 3,100mg/L TDS). Further southwards, towards Lake Way, the TDS of groundwater in the Apex Southern Borefield (Section 1.5.2) increases to ~4,500mg/L. The quality of the groundwater in the low permeability sand units of the underlying palaeochannel aquifer is hypersaline, i.e. the TDS of groundwater in P32 is 134,550mg/L. The nitrate levels of the water in the calcrete aquifer often exceeds the Australian Drinking Water (2004) health limits, and should be treated if it is to be used for domestic consumption. The salinity of the groundwater in the shallow calcrete aquifer shows short-term variations associated with significant rainfall recharge events. Figure 1.5 shows the TDS of groundwater from production bores P18 and P22 rising by 2,200 and 3,800mg/L, respectively, over a period of 9 months following the February 1995 flood event (cyclone Bobby ), when 250mm of rain fell in the area. This may be due to flushing of salt from unsaturated zones of the soil/aquifer profile. Our Reference 1134/C/104a Page 15

28 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING INTRODUCTION Table 1.2: Chemistry of Groundwater from the West Creek Production Bores Bore No. Sample Period Statistic ph TDS (mg/l) Na (mg/l) Ca (mg/l) Mg (mg/l) K (mg/l) Cl (mg/l) HC0 3 (mg/l) SO 4 (mg/l) NO 3 (mg/l) F (mg/l) Si (mg/l) P18 Apr 96 Jan 10 Number Mean 7.6 2, , Std Dev Min/Max 7.2/7.8 2,300/3, /700 83/130 91/190 56/90 730/1, / /560 52/95-32/77 P22 Apr 96 Jan 10 Number Mean 7.6 3, , Std Dev Min/Max 7.1/8.1 3,215/4, / / /230 85/98 1,175/1, / /890 47/75-33/85 P26 Apr 96 Jan 10 Number Mean 7.6 2, Std Dev Min/Max 7.3/7.9 1,900/2, / / /165 49/65 790/ / /410 47/ /75 P61 Jan 10 1 sample 5.8 4, , P62 Jul 96 1 sample 7.6 3, , P32 May-86 1 sample ,550 36, ,230 3,160 64, , Australian Drinking Water Guideline (2004) A A N/S N/S N/S A N/S N/S Notes: A No guideline, as not considered necessary. N/S Not supplied. 500 Exceeds Australian drinking water health limit (Underlined). 500 Exceeds Toro s processed water quality requirements for alkaline heap-leach treatment (Boldfaced). Page 16 Our Reference 1134/C/104a

29 WATER LEVEL FLUCTUATIONS IN THE WEST CREEK BOREFIELD VERUS [A] MONTHLY RAINFALL AND [B] ABSTRACTION FIGURE 1.4 document2

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31 GROUNDWATER SALINITY VARIATIONS IN THE WEST CREEK BOREFIELD FIGURE 1.5 document1

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33 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING INTRODUCTION APEX SOUTHERN BOREFIELD The Apex (Wiluna Gold Mine) Southern Borefield is located 9.5km south of Wiluna town (Figure 1.1) and taps the shallow calcrete aquifer in this area, some 4.5km downstream of production bore P62 in the West Creek Borefield. The borefield comprises five production bores, XP1 to XP5, which provided water to the Wiluna Gold Mine up until early The borefield is currently not being utilised by Apex Gold. The bore construction details and hydrogeological logs could not be located. There is also no information available on the sustainability of the borefield, although the borefield was licensed to abstract up to a maximum of 1.13GL/year. The borefield layout is shown in Figure 1.3. Groundwater Abstraction Monthly groundwater abstraction information is only available for the following two operational periods (Figure 1.6): January 1987 to April 1991: Over this period ~1.563GL of groundwater was abstracted from the five production bores. Approximately 76% of this water was pumped from bores XP2, XP4 and XP5. During this time abstraction rates varied between and 0.572GL/year. April 2005 to March 2007: Total abstraction from the borefield over the periods April 2005 to March 2006 and April 2006 to March 2007 was 7.86GL and 7.43GL, respectively. Groundwater Quality The groundwater abstracted from production bores in the Apex Southern Borefield is brackish, with TDS concentrations averaging between 4,000 to 5,000mg/L (Table 1.3). Our Reference 1134/C/104a Page 21

34 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING INTRODUCTION Table 1.3: Groundwater chemistry of the production bores in the Apex Southern Borefield Bore No. Sample Period Statistic ph TDS (mg/l) Na (mg/l) Ca (mg/l) Mg (mg/l) K (mg/l) Cl (mg/l) HC0 3 (mg/l) SO 4 (mg/l) NO 3 (mg/l) F (mg/l) Si (mg/l) XP1 Jul 94 Jun 06 Number Mean / Std Dev / / /19 250/56 121/ / / /128 30/7 1.5/0.8 66/26 Min /Max 7.4/ / / / /150 81/ / / / /39 0.7/3.4 1/88 XP2 May 94 - Dec 05 Number Mean 7.8/ / / /16 189/24 99/ / /31 867/97 30/8 1.6/0.9 68/22 Min 7.2/ / / / /230 76/ / / / /46 1.0/3.8 32/90 XP3 May 94 - Jun 06 Number Mean / Std Dev 7.8/ / / /13 229/20 122/ / /128 28/10 1.7/0.6 65/28 Min 7.2/ / / / /280 89/ / / /1300 6/46 1.2/3.3 2/94 XP4 May 94 - Jun 06 Number Mean / Std Dev / / /13 225/48 118/ / / /210 26/9 1.9/0.7 64/29 Min 7.2/ / / / /400 88/ / / / /46 1.4/3.7 2/96 XP5 May 94 - Jun 06 Number Mean / Std Dev 7.7/ / / /12 216/20 124/ / /53 944/82 35/9 1.9/0.8 62/30 Australian Drinking Water Guideline (2004) Min 7.2/ / / / /250 94/ / / / /47 1.3/3.7 2/ A A N/S N/S N/S A N/S N/S Notes: A No guideline, as not considered necessary. N/S Not supplied. 500 Exceeds Australian drinking water health limit (Underlined). 500 Exceeds Toro s processed water quality requirements for alkaline heap-leach treatment (Boldfaced). Page 22 Our Reference 1134/C/104a

35 APEX SOUTHERN BOREFIELD GROUNDWATER LEVEL FLUCTUATIONS VERSUS ABSTRACTION FIGURE 1.6 document3

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37 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING CONCEPTUAL HYDROGEOLOGY 2 CONCEPTUAL HYDROGEOLOGY 2.1 PREAMBLE The conceptual hydrogeology for the modelled area, outlined below, is based on the integration of all available information. The conceptual hydrogeology represents a simplified understanding of the geometry, hydraulic characteristics and flow dynamics of the aquifer systems, and provides the technical foundation for the compilation of the numerical flow model. 2.2 DATA REVIEW DATA SOURCES In addition to the documents cited in Section 1, a number of other data sources were reviewed to increase our understanding of the extent and thicknesses of the geological/hydrogeological units in the study area. These data include the following: Water and Rivers Commission, Groundwater Resources of the Northern Goldfields, Western Australia. Report HG2. Geological Survey of Western Australia, 2001.Explanatory notes. Geological sheet SG51-09, Wiluna (2 nd Edition). Published digital 1/100,000 and 1/250,000 geological and topocadastral map-sheets. Hydrogeological and water supply reports prepared by consultants. Available LANDSAT satellite imagery and the 90m resolution SRTM digital elevation model. Electronic data supplied to Aquaterra by the Department of Water on 9 th March Lithological logs of mineral exploration holes, hi-resolution aerial-photographs, digital geophysical and LIDAR elevation data supplied by Toro. Waterlevel and groundwater quality data supplied by Toro OUTCOME OF THE DATA REVIEW In terms of potential water resources, the calcrete aquifer represents a significant source of fresh to marginally brackish water in the study area. Published data (Water and Rivers Commission, 1999) indicates that calcrete aquifers in the area to the south of Wiluna may store up to 190GL of water, of which 5GL/year is renewable. Examination of the data suggests that a significant palaeochannel groundwater source does not underlie the calcrete aquifer present within the study area. Further discussion of the geological units in the study area is presented below. 2.3 CALCRETE AQUIFER GEOMETRY Following the review of available data, Aquaterra consider that it is plausible that the calcrete extends as an aquifer (with variable width) along the full length of West Creek drainage system. In the north-west of the study area the calcrete is estimated to be approximately 1km wide, broadening to ~4km in the south-east. Aquaterra s interpretation of the thickness of the calcrete aquifer is mainly based on hydrogeological information available from on a limited number of exploration bores drilled to establish the West Creek Borefield (Australian Groundwater Consultants, 1986 and 1987). This information indicates the presence of an extensive body of calcrete that extends from between 0 to 5m below surface to maximum recorded depths of 20 to 25m below surface. Groundwater levels in this area range between 3 and 7m below surface, providing an average saturated thickness of 10 to 15m and a maximum saturated thickness of ~20m. The calcrete is assumed to thin towards the north, with an estimated thickness ranging from 5 to 10m. In the southern portion of the study area the calcrete is interpreted as being ~10 to 15m thick, increasing in thickness towards Lake way in the south-east. Our Reference 1134/C/104a Page 25

38 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING CONCEPTUAL HYDROGEOLOGY Extensive alluvial sediments, which are predominantly clayey, with occasional sand horizons, occur adjacent to and extend beneath the calcrete deposits. The main calcrete aquifer in the vicinity of the West Creek Borefield is underlain by a clay-rich unit. According to AGC (1986), production bores P26 and P32 intercepted water in clay-rich sand horizons which form part of a palaeochannel deposit that underlies the calcrete aquifer. They reported that P32 intercepted only 3m of calcrete at 2m, but intersected clayey sands at depths of 85-93m and m, before penetrating the meta-basalt bedrock at 102m. Subsequent, airlift testing showed that the sands have a relatively low permeability and therefore a lower yield potential than the overlying calcrete. The authors, however, believe that it is plausible that the logged sequence of silty sand and clay represents highly sheared, deeply weathered and decomposed, volcaniclastic sedimentary rocks associated with the north-west trending Erawalla Fault system that passes directly below the West Creek Borefield. The above interpreted calcrete thicknesses are consistent with published data in Water and Rivers Commission (1999) which indicates that the thickness of calcrete aquifers in the area is highly variable, up to 30m thick with an estimated average of 5m WATER LEVELS AND GROUNDWATER FLOW Groundwater data from existing reports and supplied by the Department of Water were examined. Aquifer responses to pumping from the calcrete can be can be observed within the dataset (Section 1.5.1). Based on this data, interpreted static waterlevels in the calcrete aquifer are ~4m below ground surface. Groundwater elevations confirm that flow within the calcrete is essentially from the north-west to the south-east of the study area, where it discharges at Lake Way. Essentially Lake Way is considered to act as drain, acting to remove groundwater from the system via evaporation. Based on the geometry of the outcropping Finlayson Member sandstone in the north-east of the study area, there would appear to be limited opportunity for groundwater inflow into the study area from the north-west via the calcrete. It is possible that during high rainfall events that greater flow takes through the calcrete at this locality. However, on a long-term average this is not expected to provide significant inflows into the catchment GROUNDWATER RECHARGE AND EVAPOTRANSPIRATION Direct groundwater recharge to the calcrete aquifer would be expected to occur in response to rainfall events. Published data suggests that recharge directly from rainfall or via infiltration of runoff in areas of out cropping calcrete would constitute at least 1%, possibly as much as 5% of total rainfall. Rainfall events in excess of 50mm would generate significant runoff that would rapidly inundate the calcrete via solution cavities (Water and Rivers Commission, 1999). Rockwater (1978) estimated rainfall recharge rates of % of MAP (228mm/a) for the alluvial aquifers developed along the Negrara and Kukabubba Creeks to the north of Wiluna. Indirect recharge of the calcrete aquifer would also be expected to take place via lateral inflow from the flanking alluvial sediments. Induced recharge would occur in response to groundwater abstraction from the calcrete and would be subject to a time lag as groundwater flowed from neighbouring less permeable sediments into the calcrete. Australian Groundwater Consultants (1986) found that localised recharge of the West Creek aquifer system is only likely to occur following significant runoff events and that historical records reveal several extended periods of five years or more without any significant runoff producing rainfall events. Evapotranspiration would be expected to occur where groundwater levels are shallow, perhaps within 2-3m of the ground surface KEY AQUIFER PARAMETERS The hydraulic conductivity of the calcrete aquifer is expected to be variable, due to the likely presence of solution cavities and the entrapment of fine grained clasts within the aquifer. Page 26 Our Reference 1134/C/104a

39 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING CONCEPTUAL HYDROGEOLOGY AGC (1986) present the results of pump-testing on production bores P18, P22 and P26 that tap the calcrete aquifer in the West Creek borefield, which provided transmissivity and specific yield values in the range of 135 to 350m 2 /day (average 250m 2 /day) and 3 to 8% (average 5%), respectively. The hydraulic parameters as determined from test-pumping of the West Creek production bores are summarised in Table 2.1. The specific yield of calcrete is reported to be highly variable due to its karstic nature, ranging from 5 to 25%. Specific yields are reported to be highest around the watertable and generally decreases with depth. Groundwater storage estimates presented in Water and Rivers Commission (1999) were based on 10%, this value being derived from pumping tests around Wiluna. Table 2.1: Hydraulic Characteristics of the calcrete aquifer in the West Creek Borefield Bore No. Static Water Level (m.bgl) Pumptest Yield (L/s) Transmissivity (m 2/ day) [Recovery] Storativity Recommended Production Yield (L/s) Aquifer / Comments P [135] Calcrete, 42hr test in April 86, max. drawdown of 4.5m. P P Calcrete, 50hr test in April 86, max. drawdown of 1.59m hr test in April 86, max. drawdown of 5.3m. Deep Clayey Sands T = m 2 /d P [682] Calcrete. Duration Test 4080min, Max. Drawdown = 14.53m. P [950] Source: Argent (1987) and AGC (1986) 2.4 ALLUVIUM Calcrete. Duration Test 4080min, Max. Drawdown = 2.38m ALLUVIUM GEOMETRY Laterally the alluvium is constrained by the presence of the calcrete aquifer through the central part of the study area, and the bedrock on the periphery. Based our experience of similar settings, we have assumed that, where present, the alluvium is approximately 5m thick over the majority of the area, with the thickness being increased where appropriate, to tie-in with the calcrete thickness. It is likely that a lateral transition zone exists between the calcrete and the alluvium, where finer grained sediments are interlayered with the calcrete WATER LEVELS AND GROUNDWATER FLOW The data indicates that groundwater levels in the alluvium to the east of the West Creek are approximately 4 to 9m below ground surface. It is likely that groundwater within the alluvium drains towards the calcrete aquifer in the centre of the study area and ultimately discharges to Lake Way GROUNDWATER RECHARGE AND EVAPOTRANSPIRATION Groundwater within the alluvium is recharged from irregular and episodic rainfall events. Published data suggests that the alluvium receives between 0.09 and 1% of total rainfall as recharge (Water and Rivers Commission, 1999). It is possible that enhanced recharge occurs in the alluvium along the flanks of outcropping bedrock, however we have no data to confirm or quantify this recharge mechanism. Our Reference 1134/C/104a Page 27

40 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING CONCEPTUAL HYDROGEOLOGY Evapotranspiration would be expected to occur where groundwater levels are shallow, perhaps within 2-3m of the ground surface KEY AQUIFER PARAMETERS Published data for alluvial aquifers in the northern Goldfields indicate low permeability values for these units. Data from the Albion Downs borefield provides hydraulic conductivity values of less than 2.5m/d. Bore yields from alluvium aquifers in the region are reported to range from 50 to 600m 3 /day, indicating variable permeability (Water and Rivers Commission, 1999). An average specific yield of 0.05 was proposed by the Water and Rivers Commission (1999) as an appropriate value for water resource calculations, however other data suggests that a value of 0.1 is may be more appropriate (Geological Survey of WA, 1992). 2.5 BASAL CLAYS AND SILT In general, the calcrete aquifer is underlain by a layer of clay-rich sediments with thin intercalations of sand or occasional silty gravel layers. This clayey horizon is also present below the calcrete at the Centipede and Lake Way deposits. The thickness of this horizon is highly variable and is assumed to vary between 5 to 10m. Little or no information is available on the hydraulic properties of this horizon which, where present, acts as an aquitard. AGC (1986) report a transmissivity of 13m 2 /day for a clayey sand layer intercepted between 85 and 102m in bore P32 (i.e. hydraulic conductivity ~ 0.77m/d). They report transmissivity values of 30 to 80m 2 /day for a 13m thick unit of interbedded fine sand and clayey sand intercepted at 20m in production bore P26 (i.e. K-values of 2.3 to 6.0m/d). 2.6 FRACTURED ROCK (BEDROCK) Permeability in fractured bedrock aquifers in the study area is believed to be largely derived from secondary porosity derived from structural features, although the Finlayson Member may have a primary porosity component. Literature reviewed indicates that the local geological structure is the dominant feature controlling the occurrence and flow of groundwater in fractured rocks; the lithology is considered to have only limited influence in this respect. Fractured rock aquifers are recharged infrequently by rainfall and ephemeral drainages into open fractures and weathered zones. Higher recharge rates may occur where elevated laterite occur (Water and Rivers Commission, 1999). Aquaterra anticipate the bulk hydraulic conductivity and storativity values to be low for fractured rock aquifers in the study area. Hydraulic conductivity and specific yield values would be expected to be in the region of 0.01m/day and respectively. Groundwater flow within fractured rocks would discharge to either overlying unconsolidated units, or as throughflow to Lake Way. In either case it is assumed that groundwater flow through fractured rock aquifer system within the study area would represent a small proportion of the overall water budget. Page 28 Our Reference 1134/C/104a

41 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING MINE WATER SUPPLY BOREFIELD OPTIONS 3 MINE WATER SUPPLY BOREFIELD OPTIONS 3.1 EXISTING BORES Two borefields currently exist in the Study area: West Creek Borefield, comprising of production bores P18, P22, P26, P61, P62 and P70 (Section 1.5.1). The Apex Southern Borefield, which is currently inactive. This borefield comprises production bores XP1 to XP5 (Section 1.5.2). The locations of these borefield and individual production bores are shown in Figures 1.1 and 1.3, respectively. As indicated in Section 1.5, previous studies have recommended that the West Creek Borefield can be operated at a rate of between GL/year. The data available also suggests that the water quality from this borefield is marginally acceptable, in terms of Toro s requirements. Data for the Apex Southern Borefield indicates that water quality closer to Lake Way is too saline to be considered for Toro s purposes. On this basis, Aquaterra consider that Toro would need to source water from the existing, or a reconfigured, West Creek Borefield only. 3.2 RECOMMENDATIONS FROM PREVIOUS STUDIES Sanders (1972, in Rockwater, 1978) recommends the exploring the narrow band of outcropping calcrete along the upper reaches of the West Creek, just south of the Bubble Well, which has a salinity of 2500mg/L TDS. Currently we have little information concerning the hydrogeology of the far north-western portion of the Study Area. It is possible that good groundwater prospects exist in this area, however, given the current data gaps we believe that this option represents a strategy with a higher risk. 3.3 POSSIBLE NEW DEVELOPMENTS Aquaterra considered that one potential approach to meet Toro s bulk water volume and water quality requirements, was to spread the required abstraction over areas of the calcrete aquifer where we have the highest level of existing data. Given the low rainfall for the area, combined with an anticipated low throughflow, we would expect such an approach to essentially provide abstraction volumes via the withdrawal groundwater from storage. The thin saturated thickness of the aquifer would necessitate the distribution of production bores across as wide an area as possible, to limit drawdown to an acceptable level. Unfortunately, the increasing salinity as one moves downstream in the catchment places a limit as to how far abstraction bores could be developed towards Lake Way. Given the above, Aquaterra currently considers that a distributed borefield, located in the general area of the existing West Creek Borefield presents the most promising water supply prospect for the Wiluna Uranium Project.. Our Reference 1134/C/104a Page 29

42 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING GROUNDWATER MODEL 4 GROUNDWATER MODEL 4.1 MODELLING OBJECTIVES The main objective of the modelling study was to develop a numerical groundwater flow model to assess the feasibility of a proposed water supply borefield for Toro s Wiluna Uranium Project. The anticipated water demand for ore processing and handling and mining operations is estimated to be up to 0.7GL/year for the 10 year life of the project. The calibrated numerical groundwater model was used to determine sustainable abstraction rates and to evaluate potential impacts of a borefield drawing groundwater from the shallow calcrete aquifer for the life of the project. A regional numerical groundwater model was developed to assess the water supply potential and impacts of the proposed borefield abstraction on the calcrete aquifer. The extent of the model domain also makes it suitable to assess interaction with future groundwater development in the calcrete aquifer if required. The key features of the numerical groundwater model are discussed in detail in the following sections, and may be summarised as follows: Groundwater recharge from incident rainfall. Groundwater evapotranspiration from phreatophytic vegetation and near surface water tables. Groundwater inflow from the upstream catchment and groundwater outflow to the Lake Way playa system. Groundwater pumping from the proposed water supply borefield. 4.2 MODEL SETUP MODEL GRID AND EXTENT The numerical groundwater modelling package Modflow-Surfact (Version 3.0, Hydrogeologic, Inc. 1996) was used to develop the model operating under the Groundwater Vistas graphical user interface (Version 5.40, Rumbaugh and Rumbaugh, ). Modflow-Surfact is one of the industry s leading groundwater flow modelling packages and was chosen for its ability to simulate a shallow water table aquifer with potential for desaturation and re-saturation. The upper right-hand corner of the model is positioned approximately 18km NNW of Wiluna, and extends 40km to the west and 45km north (Figure 4.1). The model grid was rotated 42 degrees anti-clockwise from the MGA grid to align the model grid with the inferred preferential flow direction in the calcrete aquifer. The corner coordinates of the model are shown in Table 4.1. Table 4.1: Corner Coordinates of the Model Domain Easting* (m) Northing* (m) Top left Top right Bottom left Bottom right Notes: *- Indicates GDA 94 Zone 51 A uniform model cell size 500m by 500m was employed. The model grid comprises 3 layers, 64 rows, and 82 columns, resulting in a total of 15,744 cells with 7,875 active cells (Figure 4.1). Page 30 Our Reference 1134/C/104a

43 Vincent Bore Constant Head Inflow (522 mrl) Hadji Well LEGEND No Flow Boundary Grid Constant Head (CH) MODEL GRID AND BOUNDARY CONDITIONSFIGURE 4.1 F:\Jobs\ Fig 1.1.srf

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45 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING GROUNDWATER MODEL MODEL GEOMETRY Model layer elevations were set to follow surface topography or aquifer/aquitard geometry within the model boundary consistent with available data (bore logs and regional geological information) as detailed in Table 4.2. Layer 1 represents the calcrete, surrounding calcrete/alluvium transition, alluvium and fractured bedrock. Three hydraulic zones are represented in the calcrete aquifer consistent with: A decrease in the permeability of the calcrete aquifer as a result of increased silt/clay content with distance away from the groundwater discharge zone at Lake Way. Monitoring data associated with groundwater pumping from the calcrete from the Apex Southern Borefield (bores XP1 to XP5) and the West Creek Borefield (P18, P22, P62, etc) suggests varying responses to pumping that may be described by varying aquifer transmissivity. This is discussed further in Section Surrounding the calcrete aquifer is a transition zone of interbedded alluvium/calcrete, with alluvium adjoining the transition zone. Layer 2 represents a smaller deeper-seated area of calcrete in the northern extremities of the model, a silty/clay unit underlying the calcrete aquifer and fractured bedrock surrounding the calcrete. Layer 3 represents the underlying and surrounding fractured rock. The hydrogeological units represented in each layer are illustrated in Figures 4.2 to 4.4. Cross sectional views of the hydrogeological units modelled are shown in Figures 4.5 and 4.6. Table 4.2: Model Layers Layer 1 (Top of Model) Hydrogeological Units Elevation of Ground Surface Calcrete (3 zones) Calcrete/Alluvium Transition Alluvium Layer Geometry Top of active cells in layer follows surface topography based on Shuttle Radar Topography Mission (SRTM) elevation data (90m resolution), and/or LIDAR survey data supplied by Toro. Calcrete thicknesses consistent with available data to a maximum thickness of 20m (in the vicinity of bores P26, P18, P70, P61 and P62), 15m adjacent to Lake Way, with a minimum thickness of approximately 5m. Generally assigned a thickness of 5 to 10 m to provide a smooth hydraulic transition to the adjacent calcrete and alluvial areas. Thickness increases to approximately 13m in some localised areas. Generally assigned a thickness of 5m with a maximum of up to 10m in some localised areas. Fractured Rock Assigned a thickness of approximately 5m. 2 Silt/clay Calcrete Generally assigned a thickness of 5m, increasing to approximately 12.5m below the main body of the calcrete aquifer. Assigned to a limited area in north-east of Layer 2. Approximate thickness of 5m. Fractured Rock Assigned a nominal thickness of approximately 5m. 3 (Base of Model) Fractured Rock Assigned a thickness of between 70 and 190 m with the base of the model set at an elevation of 400m RL. Our Reference 1134/C/104a Page 33

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47 Northing (m) Easting (m) LEGEND Eastern Alluvium Kh/Kv (m/d) 1/0.1 S/Sy /0.2 Western Alluvium 1/ /0.2 Calcrete/Alluvium Transition 2/ /0.05 Northern Calcrete 2/ /0.05 Middle Calcrete 12.5/ /0.1 Southern Calcrete 25/ /0.1 Fractured Bedrock 0.005/ /0.001 No Flow Cells Projection: MGA94 Z51 AQUIFER PARAMETER DISTRIBUTION: LAYER 1 FIGURE 4.2 F:\Jobs\1134\C\600_Report\Figures\104a Figures\Fig 4.2.srf

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49 Northing (m) Easting (m) LEGEND Fractured Bedrock Kh/Kv (m/d) 0.005/ S/Sy /0.001 Clay/Silt 0.5/ /0.001 Northern Calcrete 2/ /0.05 No Flow Cells Projection: MGA94 Z51 AQUIFER PARAMETER DISTRIBUTION: LAYER 2 FIGURE 4.3 F:\Jobs\1134\C\600_Report\Figures\104a Figures\Fig 4.3.srf

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51 Northing (m) Easting (m) LEGEND Kh/Kv (m/d) S/Sy Bedrock 0.005/ /0.001 No Flow Cells Projection: MGA94 Z51 AQUIFER PARAMETER DISTRIBUTION: LAYER 3 FIGURE 4.4 F:\Jobs\1134\C\600_Report\Figures\104a Figures\Fig 4.4.srf

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53 W A A' E A' Northing (m) B' B B' A B Easting (m) Projection: MGA94 Z51 Key as per Figures 4.2 and 4.3 Note: Vertical Exaggeration Not to Scale. SCHEMATIC CROSS-SECTIONS: NORTH-EAST TO SOUTH-WEST FIGURE 4.5 F:\Jobs\1134\C\600_Report\Figures\104a Figures\Fig 4.5.srf

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55 A Northing (m) A' Easting (m) A' A S N Note: Vertical Exaggeration Not to Scale. Key as per Figures 4.2 and 4.3 Projection: MGA94 Z51 NORTH-WEST TO SOUTH-EAST CROSS-SECTION FIGURE 4.6 F:\Jobs\1134\C\600_Report\Figures\104a Figures\Fig 4.6.srf

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57 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING GROUNDWATER MODEL 4.3 GROUNDWATER INFLOW AND OUTFLOW GROUNDWATER THROUGHFLOW The general direction of groundwater flow within the calcrete in the study area is from the north-west towards Lake Way in the south-east. Groundwater flow from the alluvial units in the periphery of the Study area flows to Lake Way via the calcrete. Two fixed-head boundaries simulate groundwater flow into and out of the model domain as outlined below: Groundwater inflow from the northwest of the model domain is simulated by a fixed head boundary set at an elevation of 522mRL. This elevation value is consistent with a groundwater elevation based on monitoring data supplied by DoW for Vincents Bore. Groundwater outflow from the south-west of the model domain is simulated by a fixedhead boundary set at an elevation of 489mRL. The elevation of this boundary was based on monitoring data for bore LW12 (490mRL). This value is consistent with groundwater elevations in the Hadji Bore estimated from DoW gauging data. The location of the above bores and the assigned fixed-head boundaries are shown in Figure RAINFALL RECHARGE In addition to the inflow boundary described in Section 4.3.1, inflow into the modelled groundwater system is also provided via rainfall recharge, assigned as a proportion of rainfall recorded at Wiluna town. Recharge is incorporated in the model using the Recharge (RCH) package. The average annual rainfall recorded at the Wiluna monitoring station (since recording began in 1899) is around 257mm/year. Rainfall recharge applied in the model was calculated as a percentage of average measured monthly rainfall rates for the following units: Calcrete (3 recharge Zones). Calcrete/Alluvium Transition Zone. Fractured Rock. Alluvium (2 recharge Zones). The areal distribution of rainfall recharge assigned to the calibrated model is discussed in detail in Section EVAPOTRANSPIRATION Evapotranspiration (ET) is a collective term for the transfer of water, as water vapour, to the atmosphere from both vegetated and un-vegetated land surfaces (BoM). The Actual Areal Evapotranspiration 1 for the Wiluna area is between 200 and 300mm/year (Bureau of Meterorology, 2010). Evapotranspiration is implemented in the groundwater model using the Evapotranspiration (EVT) package in Modflow Surfact. Modflow-Surfact uses a linear depth dependent relationship such that if aquifer water levels are at or above a specified evapotranspiration surface, ET occurs at the maximum specified rate. If the aquifer water level falls below the specified ET surface, the ET rate decreases linearly to zero as the predicted water level reaches an elevation equal to the ET surface minus the extinction depth. The ET rate is also set to zero whenever the aquifer water level is below the elevation equal to the ET surface minus the extinction depth. This is illustrated schematically in Figure 4.7. An ET rate of 5x10-5 m/day was set for all active cells within the model, with the exception of cells where a fixed boundary had been defined (Figure 4.8). An extinction depth of 3m was set 1 Defined as by BoM as: ET that actually takes place, under the condition of existing water supply, from an area so large that the effects of any upwind boundary transitions are negligible and local variations are integrated to an areal average. For example, this represents the evapotranspiration which would occur over a large area of land under existing (mean) rainfall conditions. Our Reference 1134/C/104a Page 45

58 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING GROUNDWATER MODEL in all cells where the ET package was operative. ET was only applied to the top layer of the model, with the extinction surface assigned consistent with ground surface GROUNDWATER ABSTRACTION Groundwater abstraction from existing production bores tapping the calcrete aquifer was simulated using the Well (WEL) package in Modflow-Surfact. Available monitoring data suggest that abstraction from the calcrete aquifer commenced in April 1987 utilising production bores P18, P22, P61 and P61. Evidently, the Apex Southern Borefield was commissioned in the mid (Section 1.5.2). The location of the pumping bores in relation to the model layout is shown in Figure 4.9. Page 46 Our Reference 1134/C/104a

59 GROUND SURFACE / ET SURFACE h EVAPOTRANSPIRATION RATE EXTINCTION DEPTH WATER TABLE ALLUVIUM h - Predcited Water Table hc ET SURFACE ELEVATION EXTINCTION DEPTH 0 ETmax EVAPOTRANSPIRATION RATE MODFLOW EVAPOTRANSPIRATION PACKAGE SCHEMATIC FIGURE 4.7 F:\Jobs\1134\C\600_Report\Figures\104a Figures\Fig4.7.srf

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61 Northing (m) Easting (m) LEGEND ET Rate (m/d) 5e-005 Extinction Depth (m) No Flow Cells Projection: MGA94 Z51 EVAPOTRANSPIRATION DISTRIBUTION FIGURE 4.8 F:\Jobs\1134\C\600_Report\Figures\104a Figures\Fig 4.8.srf

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63 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING GROUNDWATER MODEL 4.4 MODEL CALIBRATION PREAMBLE Model calibration or history matching is a process of demonstrating that a groundwater model can replicate historical monitoring data. The calibration data set includes water levels and groundwater abstraction information over the period October 1986 to September A total of 37 measured water levels across the modelled area were available for steady state calibration. These water levels were derived from both the DoW and Toro, and were selected on the basis that they reflected pre-development conditions. For the transient calibration, an dataset of water level and abstraction information was available for the West Creek Borefield extending from November 1988 to March In the case of the Apex Southern Borefield, monthly water level and abstraction records were available for two periods extending from January 1987 to April 1991 and April 2005 to March 2007 (Section 1.5.2). Monitoring data is not available for all locations over the entire calibration period, however all available/appropriate data was incorporated into the calibration dataset. During model calibration, aquifer parameters, the proportion of rainfall recharge and the level of the fixed head boundaries were adjusted within realistic limits until a reasonable match between measured and predicted groundwater levels was produced. The calibration process involved numerous iterations and refinements for both the steady state and transient models, with feedback between the two models. These refinements were required to address some of the uncertainties related to hydrogeological conceptualisation of the aquifer systems STEADY-STATE CALIBRATION The steady state (or long-term average ) calibration provides: A distribution of water levels across the model domain that reflects the groundwater conditions prior to any development. Initial groundwater conditions for the transient calibration. Quantification of the groundwater flow through the model domain, under average conditions prior to any groundwater development. Groundwater conditions in the study area are dynamic in nature and often respond to extreme cyclonic rainfall events. As a result, groundwater levels may vary significantly over a year, or from year to year. The steady state calibration makes no attempt to model seasonal variations and provides an estimate of the groundwater flow regime under average rainfall conditions prior to any borefield development. Measured and modelled steady state water levels are presented in Figure The Scaled Root Mean Squared Error (SRMS or RMS error divided by the range of measured water levels) is 13.6% which is slightly higher than the accepted 10% error for green fields catchments and 5% for developed catchments (MDBC, 2001). Figures 4.10 and 4.11 show that there is a mismatch between the measured and predicted water levels at Diorite Well and Deep Bore. All of the other bores are likely to provide water levels related to the upper alluvium or calcrete aquifer, which it is probable that the water levels in these two bores are associated with bedrock aquifers only. We note that if these two data points are removed from the SRMS calculation, the resulting error is reduced to 8.4%. Predicted steady state groundwater contours and measured spot heights are presented in Figure Our Reference 1134/C/104a Page 51

64 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING GROUNDWATER MODEL Table 4.3: Adopted Recharge Values Unit Recharge as % of Rainfall Adopted Steady-State Recharge (m/d) Fractured Rock E-08 Southern Calcrete E-06 Eastern Alluvium E-07 Western Alluvium E-07 Calcrete/Alluvium Transition E-06 Northern Calcrete E-06 Middle Calcrete E-06 The percentage of rainfall apportioned to recharge for the alluvium and calcrete are consistent with those values cited in the literature (see Section 2). The distribution of recharge within the model is shown in Figure The calculated steady-state calibration heads and the corresponding observation data are provided in Table B2 of Appendix B. A summary of these data for the West Creek Borefield is presented in Table 4.4. Table 4.4: Calculated and Adopted Steady-State Calibration Heads for West Creek Borefield Calibration Bore Calculated Head (m RL) Adopted Steady-State Calibration Head (m RL) Error (m) P P P P P P P Notes: Table 5.5 is an abridged version of data supplied in Table B1, Appendix B. The predicted steady state water balance is presented in Table 4.5. Table 4.5: Steady State Predicted Water Balance (m 3 /day) In Out Constant Head Recharge Evapotranspiration Total Based on the data presented in Table 4.5, recharge accounts for almost all of water inflows into the model domain, with outflows dominated by flow to Lake Way and evapotranspiration. Page 52 Our Reference 1134/C/104a

65 NO1 WELL RAILWAY WELL NO 408 COCKARROW WELL HAYES WELL Northing (m) NO 388 LANAGAN BORE NO383 CRITCHES BORE RED HILL WELL DIORITE WELL WARD NO1 WELL P26 FRESHWATER WELL P70 P18 P22 P61 P62 MILLIE MILLIE WELL P31 XP1XP2XP3XP4XP5 P32 GOLD TOOTH WELL GARDEN (GOVT BUTCHER NO16) WELL WELL WARD WELL GARDEN WELL TRENNAMANS WELL HADJI WELL LW LINDEN BORE DEEP BORE DEEP MILL WELL Easting (m) LEGEND No Flow Cells Constant Head (CH) Observation Bores (Existing) Pumping Bores (Existing) Projection: MGA94 Z51 PUMPING AND MONITORING BORE LOCATIONS FIGURE 4.9 F:\Jobs\1134\C\600_Report\Figures\104a Figures\Fig 4.9.srf

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67 LINDEN_BORE NO_ DEEP_BORE P32_CHEVRON 530 DIORITE_WELL Modelled Head (m) WARD_NO_1_WELL NO1_WELL DEEP_MILL_WELL RED_HILL_WELL RAILWAY_WELL LANAGAN_BORE COCKARROW_WELL P26_CHEVRON BUBBLE_WELL SRMS Error = 13.6% SRMS Error = 8.4% without Diorite Well & Deep Bore MILLIE_MILLIE_WELL TRENNAMANS_WELL HAYES_WELL P22_CHEVRON P62_Chevron WARD_WELL NO_383_CRITCHES_BORE P18_CHEVRON GOLD_TOOTH_WELL P61_Chevron GARDEN_(GOVT_NO_16)_WELD NO_408 P31_CHEVRON XP3XP2 XP1 XP4 XP5 GARDEN_WELL FRESHWATER_WELL LW12 P70_Chevron Measured Head (m) MEASURED VERSUS MODELLED WATER LEVELS FIGURE 4.10 \\aquaterra.com.au\data\at1\jobs\1134\c\600_report\figures\104a Figures\[Fig 4.10 C_S069_WestCreek.xls]Figure 4.10

68

69 LEGEND Northing (m) No Flow Cells Constant Head (CH) Measured Waterlevel Modelled Waterlevel Predicted Waterlevel Contours Calcrete Extent Projection: MGA94 Z51 Easting (m) MEASURED VERSUS MODELLED WATER LEVELS AND PREDICTED STEADY-STATE WATER LEVEL CONTOURS FIGURE 4.11 F:\Jobs\1134\C\600_Report\Figures\104a Figures\Fig 4.11.srf

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71 Northing (m) Easting (m) LEGEND Western Alluvium Percentage Recharge (m/day) 5.94E-07 Eastern Alluvium E-07 Calcrete Alluvium Transition Northern Calcrete E E-06 Middle Calcrete E-06 Southern Calcrete E-06 Fractured Bedrock E-08 No Flow Cells Projection: MGA94 Z51 MODELLED RECHARGE DISTRIBUTION FIGURE 4.12 F:\Jobs\1134\C\600_Report\Figures\104a Figures\Fig 4.12.srf

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73 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING GROUNDWATER MODEL TRANSIENT CALIBRATION Calibration to transient or time varying conditions was completed for the groundwater model for the period October 1986 to November This period was chosen as it included abstraction from both the West Creek Borefield and the Apex Southern Borefield. The locations of the West Creek and Wiluna South Borefield are shown in Figure 1.1. The transient calibration was run using a monthly stress period (period over which all stresses remain constant) for the entire calibration period. Other assumptions of the transient calibrations are as follows: Initial heads from the steady-state calibration. Rainfall recharge is varied monthly and assigned at the same proportions as the steady state calibration. Groundwater pumping is varied monthly. Historical abstraction data was sourced from both consultant reports and the DoW database. The available dataset required some interpretation due to the following factors: The apparent lumping of several months of abstraction data into a single month. Possible typographical errors. Missing abstraction information, for example, observed water levels in bore P70 show a decline of ~4m between January 1991 and October 1993 (Figure 1.4), however, no abstraction was recorded. Calibrated aquifer parameters, including both unconfined and confined storage coefficients are presented in Table 4.6 and shown in Figures 4.2 to 4.4. Aquifer parameters are consistent with available data and as with the steady state calibration, no hydrogeological features that cannot be justified on the basis of current hydrogeological understanding have been included to force or improve model calibration. Table 4.6: Transient Calibration Model Specific Yield and Storage Coefficient Values Horizontal Hydraulic Conductivity (m/d) Vertical Hydraulic Conductivity (m/d) Storage Coefficient Specific Yield Bedrock e Southern Calcrete Eastern Alluvium Western Alluvium Calcrete/Alluvium Transition Northern Calcrete Middle Calcrete Clay/Silt e The locations of monitoring bores used for transient model calibration are shown in Figure 4.9. Calibration hydrographs for the Apex Southern Borefield are shown in Figure Measured groundwater levels in the Apex Southern Borefield (bores XP1 to XP5) are well matched with groundwater elevations are generally within 2m of the observed values. It is noted however that when abstraction rates from the Apex Southern Borefield increase, the match between measured and modelled water levels is not as good. The reliability of pumping data is such that this impact cannot be addressed further with the currently available information. Calibration hydrographs for the West Creek Borefield bores (P18, P22, P61 and P62) are shown in Figure Measured groundwater levels are also generally well matched. Bores P26 and P70 showed little response to pumping which is not predicted by the model. The reason for this Our Reference 1134/C/104a Page 61

74 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING GROUNDWATER MODEL mismatch is unclear and as with the Apex Southern Borefield the abstraction records available are not sufficient to determine if the mismatch is due to data validity or localised hydrogeological features in the vicinity of bores P26 and P70 that result in no measurable response to pumping from bores P18, P22, P61 and P62. Page 62 Our Reference 1134/C/104a

75 XP1 APEX SOUTHERN BOREFIELD CALIBRATION HYDROGRAPHS FIGURE 4.13 \\aquaterra.com.au\data\at1\jobs\1134\c\600_report\figures\104a Figures\[Fig 4.13 and 4.14_ hydrographs.xls]fig 4.13 Water Level (mahd) Oct-86 Oct-87 Sep-88 Sep-89 Sep-90 Sep-91 Sep-92 Sep-93 Sep-94 Sep-95 Sep-96 Sep-97 Sep-98 Sep-99 Sep-00 Sep-01 Sep-02 Sep-03 Sep-04 Sep-05 Sep-06 Sep-07 Sep-08 Sep-09 Oct-86 Oct-87 Sep-88 Sep-89 Sep-90 Sep-91 Sep-92 Sep-93 Sep-94 Sep-95 Sep-96 Sep-97 Sep-98 Sep-99 Sep-00 Sep-01 Sep-02 Sep-03 Sep-04 Sep-05 Sep-06 Sep-07 Sep-08 Observed Modelled XP Water Level (mahd) XP XP4 Water Level (mahd) Oct-86 Oct-87 Sep-88 Sep-89 Sep-90 Sep-91 Sep-92 Sep-93 Sep-94 Sep-95 Sep-96 Sep-97 Sep-98 Sep-99 Sep-00 Sep-01 Sep-02 Sep-03 Sep-04 Sep-05 Sep-06 Sep-07 Sep-08 Sep-09 Oct-86 Oct-87 Sep-88 Sep-89 Sep-90 Sep-91 Sep-92 Sep-93 Sep-94 Sep-95 Sep-96 Sep-97 Sep-98 Sep-99 Sep-00 Sep-01 Sep-02 Sep-03 Sep-04 Sep-05 Sep-06 Sep-07 Sep-08 Sep-09 Water Level (mahd) XP5 Water Level (mahd) Oct-86 Oct-87 Sep-88 Sep-89 Sep-90 Sep-91 Sep-92 Sep-93 Sep-94 Sep-95 Sep-96 Sep-97 Sep-98 Sep-99 Sep-00 Sep-01 Sep-02 Sep-03 Sep-04 Sep-05 Sep-06 Sep-07 Sep-08 Sep-09

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77 P Sep-09 Oct-86 Oct-87 Sep-88 Sep-89 Sep-90 Sep-91 Sep-92 Sep-93 Sep-94 Sep-95 Sep-96 Sep-97 Sep-98 Sep-99 Sep-00 Sep-01 Sep-02 Sep-03 Sep-04 Sep-05 Sep-06 Sep-07 Sep-08 Sep-09 Water Level (mahd) 506 P Sep-09 Oct-86 Oct-87 Sep-88 Sep-89 Sep-90 Sep-91 Sep-92 Sep-93 Sep-94 Sep-95 Sep-96 Sep-97 Sep-98 Sep-99 Sep-00 Sep-01 Sep-02 Sep-03 Sep-04 Sep-05 Sep-06 Sep-07 Sep-08 Sep-09 Water Level (mahd) P26 WEST CREEK BOREFIELD CALIBRATION HYDROGRAPHS FIGURE 4.14 \\aquaterra.com.au\data\at1\jobs\1134\c\600_report\figures\104a Figures\[Fig 4.13 and 4.14_ hydrographs.xls]fig 4.14 Water Level (mahd) Oct-86 Oct-87 Sep-88 Sep-89 Sep-90 Sep-91 Sep-92 Sep-93 Sep-94 Sep-95 Sep-96 Sep-97 Sep-98 Sep-99 Sep-00 Sep-01 Sep-02 Sep-03 Sep-04 Sep-05 Sep-06 Sep-07 Sep P P Water Level (mahd) Oct-86 Oct-87 Sep-88 Sep-89 Sep-90 Sep-91 Sep-92 Sep-93 Sep-94 Sep-95 Sep-96 Sep-97 Sep-98 Sep-99 Sep-00 Sep-01 Sep-02 Sep-03 Sep-04 Sep-05 Sep-06 Sep-07 Sep-08 Sep-09 Oct-86 Oct-87 Sep-88 Sep-89 Sep-90 Sep-91 Sep-92 Sep-93 Sep-94 Sep-95 Sep-96 Sep-97 Sep-98 Sep-99 Sep-00 Sep-01 Sep-02 Sep-03 Sep-04 Sep-05 Sep-06 Sep-07 Sep-08 Sep-09 Water Level (mahd) P18 Water Level (mahd) Oct-86 Oct-87 Sep-88 Sep-89 Sep-90 Sep-91 Sep-92 Sep-93 Sep-94 Sep-95 Sep-96 Sep-97 Sep-98 Sep-99 Sep-00 Sep-01 Sep-02 Sep-03 Sep-04 Sep-05 Sep-06 Sep-07 Sep-08 Observed Modelled

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79 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING GROUNDWATER MODEL Mass Balance The cumulative water balance for the Transient Calibration Model (October 1986 to November 2009) is presented in Table 4.7. Table 4.7: Transient Calibration Model Cumulative Mass Balance (m 3 ) In Out Storage 10,028,500 8,564,200 Constant Head 213,600 5,732,200 Recharge 12,084,500 0 Evapotranspiration 0 4,243,000 Wells 0 3,789,500 Total 22,326,600 22,328,900 The following is noted with respect to the Transient Calibration Model: The total cumulative mass balance error was 2,325m 3 or 0.01%. The mass balance error within individual time steps ranged from -3% and 3%, however, most errors were significantly lower. The total abstraction from the model was 3,789,455m 3, this agrees well with the volume in the input file of 3,789,451m 3. Groundwater elevations in the abstraction bores remained above the base of layer 1 during the entire simulation. Based on the above and the hydrographs presented in Figure 4.13 and Figure 4.14, the Transient Calibration Model was considered acceptable. 4.5 MODEL PREDICTIONS SETUP The calibrated model was used to assess the potential for groundwater abstraction from the calcrete aquifer to supply the project water demand. A number of borefield configurations were simulated including one scenario with pumping from both the West Creek Borefield and the Apex Southern Borefield at the same time. The location of the two borefields is shown in Figure 4.15 Predictive modelling was completed using two different operating constraints. The operating constraints assumed either maintenance of 75% or 60% of the saturated aquifer thickness, to allow set pumping rates to be maintained and to maintain an acceptable habitat for stygofauna. For the 75% case this corresponds to an aquifer drawdown of around 3 metres, with 4 metres for the 60% case. Maximum assigned pumping rates are assigned consistent with historical performance and available bore hydraulic information. These constraints and scenario configurations are presented in Table 4.8. Our Reference 1134/C/104a Page 67

80 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING GROUNDWATER MODEL Table 4.8: Borefield Prediction Scenarios Scenario % of Calcrete Saturated Thickness Maintained* Maximum Total Abstraction (m 3 /day)@ Existing Production Bore Locations and (Individual Pumping Rates # ) Notional Production Bore Locations (Individual Pumping Rates) P18 (311) P22 (519) P61 (286) P62 (977.5) P18 (311) P22 (519) P61 (286) P62 (978) P18 (303) P26 (286) P62 (917) P70 (303) P21 (286) P18 (303) P26 (286) P62 (917) P70 (303) P21 (286) P18 (173) P62 (397) P70 (233) P26 (259) P18 (173) P62 (397) P70 (233) P26 (259) P18 (173) P62 (397) P70 (233) P26 (259) P18 (173) P62 (397) P70 (233) P26 (259) nil nil nil nil N1 (216) N2 (173) N4(216) N5 (151) N8 (216) N1 (216) N2 (173) N4(216) N5 (151) N8 (216) N1 (216) N2 (173) N4(216) N5 (151) N8 (216) N1 (216) N2 (173) N4(216) N5 (151) N8 (216) (excludes Apex Southern Borefield- XP1 to XP5) P18 (173) P62 (397) P70 (233) P26 (259) XP1 (495)^ XP2 (389)^ XP3 (163)^ XP4 (478)^ XP5 (215)^ N1 (216) N2 (173) N4(216) N5 (151) N8 (216) Notes: *- Indicates saturation in cells containing simulation wells. ^- Indicates assumes abstraction by another party (not Toro) # -indicates existing bore location only. New boreholes may be required. Pumping rates in m 3 Indicates simulated maximum abstraction rate set in FWL4 fracture well package. Rates will decrease as the FWL4 Pumping Level is reached Page 68 Our Reference 1134/C/104a

81 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING GROUNDWATER MODEL In addition to the constraints outlined in Table 4.8, model predictions assumed: A total prediction period of 10 years, consistent with the demand period. The model was run using a monthly stress period. Initial water levels derived from the end of the transient calibration. Recharge was assigned consistent with the distribution of the Transient Calibration model assuming average monthly rainfall data (BoM 30 year average ) for Wiluna. Abstraction was simulated using the Fracture Well Package (FWL) of Modflow-Surfact. This package simulates pumping at a maximum specific rate until a minimum groundwater level or operational constraint is reached. The minimum groundwater elevation is set consistent with the operating constraints to maintain either a 60% or 75% saturated thickness of the aquifer as outlined in Table 4.8. The FWL package decreases the assigned pumping rate once water levels approach the assigned water level constraint and allows the pumping rate to increase if water levels increase. No other groundwater abstraction or development within the model domain. Our Reference 1134/C/104a Page 69

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83 N5 Northing (m) N4 P26 P70 N2 N1 P21 P18 P22 P61 P62 N8 XP1 XP2 XP3XP4XP Easting (m) LEGEND No Flow Cells Model Grid Projection: MGA94 Z51 Simulated Prediction Well MODELLED BOREFIELD LOCATION FIGURE 4.15 F:\Jobs\1134\C\600_Report\Figures\104a Figures\Fig 4.15.srf

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85 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING GROUNDWATER MODEL PREDICTION RESULTS Predicted pumping rates (m 3 /day) for Scenarios 1 to 9 over the 10 year prediction period are shown in Table 4.9, Figure 4.16 and Appendix C. The predictions results suggest that for all Scenarios considered, water demand cannot be met by the modelled borefields. The results of Scenario 6 (which assumes an expanded West Creek Borefield is implemented with a 40% permissible drawdown) predicts the delivery of approximately 1820m 3 /day (6.6GL/year) after ten years of borefield operation. Table 4.9: Summary of Results for Modelled Scenarios Scenario Scenario Description % of Saturated Thickness Maintained* Maximum Total Borefield Abstraction Rate (m 3 /day)* Total Borefield Abstraction Rate after 10 Years (m 3 /day) 1 Original borefield Original borefield Revised original borefield Revised original borefield Expanded borefield Expanded borefield Expanded borefield No recharge 8 Expanded borefield No recharge Expanded borefield with XP1 to XP5 operating (total excludes pumping from Apex Southern Borefield XP1 to XP5) Notes: *- Indicates simulated maximum abstraction rate set in FWL4 fracture well package. Rates will decrease as the FWL4 Pumping Constraint Level is reached. Predicted Watertable and Drawdowns Predicted watertable contours at an elapsed time of 10 years for Scenarios 6, 8 and 9 are presented in Figures 4.17 to Predicted drawdown contours at an elapsed time of 10 years for Scenarios 6, 8 and 9 are presented in Figures 4.20 to Our Reference 1134/C/104a Page 73

86

87 Pumping Rate (m 3 /d) Scenario 1 Scenario 2 Scenario 3 Scenario 4 Scenario 5 Scenario 6 Scenario 7 Scenario 8 0 Scenario Elapsed Time (years) TOTAL ABSTRACTION FOR MODELLED BOREFIELD SCENARIOS FIGURE 4.16 \\aquaterra.com.au\data\at1\jobs\1134\c\600_report\figures\104a Figures\[Doc 102b Consolidated FWL output.xls]figure 4.16

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89 Northing (m) N4 N5 P26 P70P18 N2 N1 P62 N Easting (m) LEGEND No Flow Cells Constant Head (CH) 525 Water Level Contours Pumping Bores Calcrete Extent Projection: MGA94 Z51 SCENARIO 6 - PREDICTED WATERTABLE AFTER 10 YEARS FIGURE 4.17 F:\Jobs\1134\C\600_Report\Figures\104a Figures\Fig 4.17.srf

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91 Northing (m) N4 N5 P26 P70P18 N2 N1 P62 N Easting (m) LEGEND No Flow Cells Constant Head (CH) 525 Water Level Contours Pumping Bores Calcrete Extent Projection: MGA94 Z51 SCENARIO 8 - PREDICTED WATERTABLE AFTER 10 YEARS FIGURE 4.18 F:\Jobs\1134\C\600_Report\Figures\104a Figures\Fig 4.18.srf

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93 Northing (m) N4 N5 P26 P70P18 N2 N1 P62 N8 XP1 XP2 XP3 XP4 XP Easting (m) LEGEND No Flow Cells Constant Head (CH) 525 Water Level Contours Pumping Bores Calcrete Extent Projection: MGA94 Z51 SCENARIO 9 - PREDICTED WATERTABLE AFTER 10 YEARS FIGURE 4.19 F:\Jobs\1134\C\600_Report\Figures\104a Figures\Fig 4.19.srf

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95 Northing (m) N4 N5 P26 P70P18 N2 N1 P62 N Easting (m) LEGEND No Flow Cells Constant Head (CH) 525 Drawdown Contours Pumping Bores Calcrete Extent Projection: MGA94 Z51 SCENARIO 6 - PREDICTED DRAWDOWN AFTER 10 YEARS FIGURE 4.20 F:\Jobs\1134\C\600_Report\Figures\104a Figures

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97 Northing (m) N4 N5 P26 P70P18 N2 N1 P62 N Easting (m) LEGEND No Flow Cells Constant Head (CH) 525 Drawdown Contours Pumping Bores Calcrete Extent Projection: MGA94 Z51 SCENARIO 8 - PREDICTED DRAWDOWN AFTER 10 YEARS FIGURE 4.21 F:\Jobs\1134\C\600_Report\Figures\104a Figures\Fig 4.21.srf

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99 Northing (m) N4 N5 P26 P70P18 N2 N1 P62 N8 XP1 XP2 XP3 XP4 XP Easting (m) LEGEND No Flow Cells Constant Head (CH) 525 Drawdown Contours Pumping Bores Calcrete Extent Projection: MGA94 Z51 SCENARIO 9 - PREDICTED DRAWDOWN AFTER 10 YEARS FIGURE 4.22 F:\Jobs\1134\C\600_Report\Figures\104a Figures\Fig 4.22.srf

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101 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING GROUNDWATER MODEL 4.6 SENSITIVITY ANALYSIS In any modelling exercise, uncertainties always remain in the adopted parameters. A sensitivity analysis was performed to assess the potential effect of parameter variability, on the predicted groundwater fluxes. The sensitivity analysis can be used to identify critical factors and provide some confidence limits about the predictions. The parameter values for the sensitivity analysis were selected to provide further conservatism in the predictions. The following sensitivity runs were completed assuming the operational constraints and pumping configuration of Scenario 6 (the case which shows the highest sustainable borefield yield): Sensitivity Run 1 assumed reduced hydraulic conductivity of the three calcrete units. Sensitivity Run 2 assumed reduced specific yield of the three calcrete units. Sensitivity Run 3 assumed reduced specific yield of the two alluvium units. The aquifer parameters associated with the sensitivity runs are summarised in Table Table 4.10: Sensitivity runs Aquifer Parameter Model Units Base Case* Sensitivity Run 1 Sensitivity Run 2 Sensitivity Run 3 Hydraulic Conductivity (m/d) Calcrete/Alluvium Transition Northern Calcrete Middle Calcrete Southern Calcrete Specific Yield Calcrete/Alluvium Transition Northern Calcrete Specific Yield Middle Calcrete Southern Calcrete Eastern and Western Alluvium Notes: *- Indicates Scenario 6. Parameters changed for specific sensitivity runs are shown in bold type. The sensitivity analysis indicates the following: Sensitivity Run 1- predicts that abstraction from the West Creek Borefield would decrease below 1,920m 3 /day (0.7GL/year) after 5 to 6 years. After ten years the total abstraction from the borefield would decline to ~1,450m 3 /day (5.3GL/year). Sensitivity Run 2- predicts that abstraction from the West Creek Borefield would decrease below 1,920m 3 /day (0.7GL/year) after 4 to 5 years. After ten years the total abstraction from the borefield would drop to ~1,200m 3 /day (4.38GL/year). Sensitivity Run 3- predicts that abstraction from the West Creek Borefield would decrease below 1,920m 3 /day (0.7GL/year) after 8 to 9 years. After ten years the total abstraction from the borefield would drop to ~1,800m 3 /day (6.6GL/year). Figures 4.23 shows the results of the three sensitivity runs, together with those from Scenario 6 for comparison. Our Reference 1134/C/104a Page 89

102

103 Abstraction Rate (m 3 /day) Scenario Sensitivity Run 1 (Calcrete Hydraulic Conductivity Reduced) Sensitivity Run 2 (Calcrete Specific Yield Reduced) Sensitivity Run 2 (Alluvium Specific Yield Reduced) Years PREDICTED ABSTRACTION RATES- SENSITIVITY RUNS FOR SCENARIO 6 FIGURE 4.23

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105 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING GROUNDWATER MODEL The results for Sensitivity Run 3 are very similar to those obtained for Scenario 6, indicating that the model is not particularly sensitive to the specific yield of the surrounding alluvial aquifer. Conversely, and as would be expected, the model is sensitive to both hydraulic conductivity and specific yield of the calcrete aquifer. In particular, the model seems to be very sensitive to reductions in specific yield; this would be expected in a situation where much of the water abstracted from the calcrete aquifer is derived from water released from storage. 4.7 GROUNDWATER RECOVERY Once water supply pumping from the calcrete aquifer ceases, after the projected demand period of ten years, groundwater levels will slowly recover to close to pre-development levels where a balance exists between groundwater inflow (from recharge) and outflow (to Lake Way and via evapotranspiration). The groundwater flow model was used to predict the time taken for groundwater levels to return to pre-development levels. The prediction assumed: Initial conditions from the end of Scenario 6 (i.e. after ten years of groundwater abstraction). Average rainfall recharge conditions. A recovery prediction period of fifty years. Predicted water levels for P62, over the ten year supply period and the subsequent fifty year recovery period are shown in Figure Predicted water levels suggest that the majority of groundwater recovery closer to 2.5 metres, is completed twenty years after water supply pumping ceases. A further 1.5 metres of recovery is predicted after a further forty years. Our Reference 1134/C/104a Page 93

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107 Water Levels for Model Cell Containing Bore P62- Scenario 6 and Recovery Run Predicted Water Level (mrl) Water Level Recovey Water Level (Abstraction Scenario 6) Steady-State (Pre-Pumping) Water Level Prediction Elapsed Time (years) WATER LEVELS FOR MODEL CELL CONTAINING BORE P62- SCENARIO 6 AND RECOVERY RUN FIGURE 4.24 F:\Jobs\1134\C\600_Report\Figures\104a Figures\[Fig 4.24 Doc 110a Results for C_P016 and C_C01 (recovery).xls]figure 4.24

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109 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING GROUNDWATER MODEL 4.8 MODEL LIMITATIONS All of the work carried out has been undertaken at a Pre-Feasibility level of understanding. As a result, there are areas within and surrounding the West Creek area which are not fully understood at this time, in hydrogeological terms. To date these areas have been represented with the available information from the site or from other similar areas. However, to improve model reliability we recommend that the following areas are investigated or addressed and the relevant changes are subsequently made to the conceptual model and the groundwater model ABSTRACTION ESTIMATES To date the groundwater model has been used to predict groundwater abstraction that can be expected based on our current hydrogeological understanding. It is recommended that further hydrogeological testing is completed and the relevant data used to upgrade abstraction predictions to provide greater confidence in aquifer parameters and individual bore yields used for the model predictions RECHARGE To date the model predictions have assumed average long term rainfall recharge. No allowance has been made for extreme wet or dry rainfall conditions (significantly above or below the average conditions adopted) over the wet season months (i.e. January to March). As indicated by Scenario 8, the absence of recharge will adversely affect abstraction from the West Creek Borefield. Conversely, cyclonic recharge events have been known to recharge active borefields to above initial starting water level conditions AQUIFER CHARACTERISTICS AND CALIBRATION TO TRANSIENT DATA The sensitivity analysis suggests that the abstraction estimates presented in this report are particularly sensitive to the hydraulic conductivity and storage parameters of the calcrete. Currently there is little hydraulic testing data available for this unit. If however greater confidence could be placed in the West Creek Borefield data used to calibrate the model, the uncertainties associated with hydraulic conductivity and storage values would be reduced. As a result more confidence could be placed in the model predictions. However, if uncertainties with the pumping dataset cannot be resolved it is recommended that conceptual understanding and model setup is supplemented with targeted hydraulic testing for the calcrete aquifer. Our Reference 1134/C/104a Page 97

110 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING DISCUSSION 5 DISCUSSION 5.1 WATER SUPPLY OPTIONS Based on our current understanding of the West Creek hydrogeology, and the modelling reported above, we provide a discussion of our findings below: Palaeochannel aquifer- It is considered unlikely that a palaeochannel aquifer in the West Creek area will satisfy the water quality requirements of Wiluna Uranium Project. Additionally, based on the information currently available there is no certainty that such an aquifer exists in the area. Borehole logs for the area suggest that the sediments overlying bedrock are clayey to silty, with no significant coarse horizons. Maintenance of aquifer saturated thickness- The model results suggest that that a borefield installed in the calcrete where drawdown is limited to maintain 75% of the saturated thickness does not represent a plausible or practical solution to Toro s water requirement. We also consider that as a minimum, 60% of the initial saturated thickness should be maintained in the calcrete to facilitate efficient bore operation. Environmental factors (stygofauna habitat) may also place limits on the degree of dewatering permitted. Current West Creek Borefield- The model results suggest that the current West Creek Borefield (installed in the calcrete) comprising bores P18, P22, P61 and P62 will not satisfy the Toro s water demand of 0.70GL/year for the 10 year project life. These bores may be able to supply the required yield (1,920m 3 /day) for approximately twelve months (based on Scenario 2), however the modelling suggests that this borefield cannot sustain this yield over the longer term. We note that the borefield has in the past produced ~1,072m 3 /day for periods of approximately 2 years. However there is no record of sustained abstraction from this borefield to support the premise that an abstraction rate of 0.7GL/year for ten years is feasible. Based on the modelling undertaken for Scenario 2, the yield after 10 years is predicted to be ~790m 3 /day (0.288GL/year). Revised West Creek Borefield- The model results suggest that that a reconfiguration of the existing West Creek Borefield (comprising P18, P26, P62, P70 and P21) of could supply the 0.7GL/year water demand of the Wiluna Uranium Project. Based on the modelling undertaken for Scenario 4, the yield after 10 years is predicted to be 1,300m 3 /day (0.475GL/year). Expanded West Creek Borefield- The model results suggest that that an expanded West Creek Borefield (installed in the calcrete aquifer) is likely to supply more water than either the existing West Creek or a revised West Creek Borefield. Based on the modelling undertaken for Scenario 6, the yield after 10 years is predicted to be ~ 1,820m 3 /day (0.664GL/year). Supply is predicted to decline below 1920m 3 /day (0.70GL/year) after approximately 8 to 9 years of abstraction. The final water quality of the blend of an expanded West Creek Borefield will not be known until further hydrogeological data is collected. Expanded West Creek Borefield- bore locations- it should be noted that the new production bore locations used in Scenarios 6 to 12 are notional and have been located on the basis of the model geometry, which is in turn based on limited hydrogeological data. A key requirement of this borefield design would be to spread abstraction over as wide as area of the calcrete aquifer as possible, without moving too far south towards Lake Way where groundwater quality deteriorates. Any potential locations of new bores would need to be fully investigated with respect to both yields and quality before Toro committed to those locations. Well efficiency- Given the limited saturated thickness of the calcrete aquifer, bores installed in this unit will need to be constructed such they provide maximum efficiency (i.e. minimum drawdown per unit of yield). If low efficiency bores are installed the potential of the calcrete aquifer may not be realised. To provide high efficiency oversized large-diameter bores may be required. Page 98 Our Reference 1134/C/104a

111 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING DISCUSSION Apex Southern Borefield- Results from Scenario 9 indicate that if the Apex Southern Borefield (bores XP1 to XP5) is operated simultaneously with the Expanded West Creek Borefield, then yields from the latter will decrease to ~1,790m 3 /day (0.653GL/year) after 10 years of operation. It should be noted however that under this Scenario the Apex Southern Borefield is operated such that 60% saturation is maintained, and the yields of this borefield are predicted to decrease significantly over time. If an operator of the Apex Southern Borefield attempted to maintain abstraction rates by further lowering the watertable, we would expect to see yields from the Expanded West Creek Borefield decrease faster/further and possibly initiate flow reversal from Lake Way. Such a flow reversal would have serious deleterious effects on groundwater quality. Other areas for groundwater investigation- to date limited investigations have been undertaken in the north of the calcrete aquifer, or around the northern margins of the study area base of the Finlayson Ranges. It is possible that these areas could supply limited quantities of good quality groundwater due to their proximity to recharge zones associated with outcrops of fractured rock. Such a supply could assist Toro by providing good water for blending with that obtained from bores in more marginal areas. 5.2 PREDICTED DRAWDOWNS Predicted drawdowns for Scenarios 6, 8 and 9 are presented in Figures 4.17 to Table 5.1 shows a summary of model predictions for these Scenarios. Table 5.1: Areas of drawdown- Scenarios 6, 8 and 9 Scenario Scenario Description Drawdown Contour (m) Approximate Dimensions of Drawdown Area (km 2 Percentage Area of 6 Expanded borefield x 6 8 x x Expanded borefield (No recharge) 0.5^ x x x Expanded borefield with XP1 to XP5 operating x 6 8 x 4 3 x 2 Notes: *- Indicates saturation in cells containing simulation wells. ^ Indicates estimated drawdown due to abstraction only. Whole model area affected by nil recharge indicates dimensions are approximate only From Table 5.1 it can be seen that although a drawdown of 0.5m is predicted over a wide area of the calcrete aquifer, greater drawdowns are expected to impact significantly smaller areas. For Scenarios 6, 8 and 9 the modelling predicts that, even under conditions of no recharge, less than 10% of the calcrete aquifer will be impacted by waterlevel drawdowns of 4m or more. We consider that the relatively small zone of deeper drawdown predicted is due to the relatively low hydraulic conductivity of the calcrete aquifer. Our Reference 1134/C/104a Page 99

112 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING WEST CREEK BOREFIELD DEVELOPMENT COSTS 6 WEST CREEK BOREFIELD DEVELOPMENT COSTS 6.1 BORE CONSTRUCTION AND TESTING COSTS Development of the recommended borefield configuration (Scenario 6, Figure 1.3), consisting of 4 existing production bores (P18, P22, P62 and P70) and 6 notional production bores (N1, N2, N4, N5, as well as a standby production bore (SB1), has been costed assuming that: The existing production bores cannot be rehabilitated and that new production bores need to be constructed using a mud-rotary drilling rig. Initially, a 5 exploration hole will drilled at each of six proposed new production sites using an Aircore drilling rig. If the results suggest that suitable calcrete horizons are present, a 12 production bore will be constructed alongside the exploration hole using mud-rotary drilling. All boreholes will be drilled and constructed to a nominal depth of 35m. The 6 exploration holes will be equipped with 50mm Class 18 PVC casing for use as monitoring holes during the test-pumping, as well as for long-term groundwater level monitoring. The 10 production bores will be equipped with 200mm Class 12 PVC casing and gravel-packed screens. Each production bore will be test pumped to determine aquifer parameters and sustainable bore yields, by conducting a 6hr step-test followed a 48hr constant discharge test and 12hrs of recovery monitoring. The borefield development costs are estimated at approximately $1.3M (Table 6.1), which equates to an average cost per production bore of ~$123,400. Table 6.1: West Creek Borefield Development Costs Description Quantity Costs Exploration Bore Drilling and Construction* 16 $839,400 Test Pumping 10 $136,000 SUB-TOTAL $975,400 Contingency 10% $97,540 Hydrogeological EPCM 15% $160,941 TOTAL COST (Excl. GST) $1,233,881 Note: * - Includes 10 production bores and 6 monitoring holes. 6.2 PUMP, PIPELINE AND POWER SUPPLY CAPITAL COSTS A cost estimate has been made for piping water from the West Creek Borefield to the Centipede and Lake Way processing plants, as well as to the proposed mine village on the north-western edge of Lake Way. The conceptual design layout for the proposed water reticulation scheme is shown in Figure 1.3. The collector pipelines within the borefield were based on the use of PE PN6.3 pipework. It has been assumed that the bore pumps are set in the bore casing at a nominal 20m below ground. Bore pumps are selected to pump their design flow rate when the borefield is also producing its design flow rate (i.e. most of the bore pumps are operating simultaneously) of 1,918m 3 /day (~22L/s) and that the waterlevel remains with its design operating level. The proposed transfer pipelines were assumed to also be PE100 pipe PN6.3 (buried), with higher pressure rating pipe as required. Scour valves would be provided along the pipe lines at low points, enabling emptying of the pipe. Air valves would similarly be provided at pipe high points to remove accumulated air, and to allow air inflow for draining the pipeline. Depending on the longitudinal profile of the pipeline, section valving may be desirable to limit the time of scouring and refilling. The cost estimate includes new pipe construction to both the Centipede and Lake Way deposits. There may be some opportunity for cost savings by recovering the Page 100 Our Reference 1134/C/104a

113 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING WEST CREEK BOREFIELD DEVELOPMENT COSTS initial transfer pipe line to Centipede after cessation of mining operations, and relaying it to Lake Way, therefore avoiding the cost of purchasing new pipe. The overall water supply system would be controlled via an integrated radio-based telemetry control system requiring logic and interface at the individual control cubicles located at all pumps and tanks. Such a system would avoid excessive staffing costs for manual control at such remote sites. The operation of all bore pumps, transfer pumps and water levels in the tanks (if provided) under normal steady-state operation, would be controlled automatically by the system. Pumps, groundwater-levels and flow rates would be monitored from the telemetry base station at a control centre at the mine site. A transfer pump station (TPS) and collector tank has not been included within the cost estimates, as the concept system has low pumping heads and it has been assumed that the bores would pump directly to their demand centres (the mining camp, and Centipede or Lake Way Deposit). During design however a TPS may be required for operational control of borefield pumping, or it may be more economical to include a TPS and collector tank at the borefield for other reasons. Tanks are required for storage at the demand centres and have not been included in the costing provided. The tanks would be liner (reinforced PVC) tanks such as the Highline Water Advantage storage tanks and would include PE nozzles, galvanized steel external and 316 stainless steel internal ladders, and a cyclone rated dome-style roof. Each tank includes the construction of a concrete ring beam and bolting down of the tank walls. The capital costs for the water reticulation system to the Centipede processing plant and mine village are estimated as $7.8M, including the cost of power supply using individual gensets and contingency, contractor s preliminaries (including mob / demob) and an allowance for EPCM costs (Table 6.2). The comparative costs for constructing the scheme using a HV power system is $16.2M (Table 6.3). Overhead power line systems reduce the ongoing maintenance requirements compared to a genset power supply option. The overall operating cost for individual gensets would be much higher compared with power line installation, although the net present value of the two options may be similar. If the cheaper system using diesel gensets is initially adopted, then the option always remains of replacing diesel gensets with reticulated power. The capital costs for construction of a similar supply system to the Lake Way processing plant is estimated at $3.0M (Table 6.4) Table 6.2: Pumping, pipeline and genset power supply capital costs to Centipede Description Amount Bore Pumps, Headworks, Pipelines, genset Power Supply etc. $5,714,986 Contingency (10%) $571,499 Engineering Prelims (incl. Mob./Demob.) (15%) $857,248 EPCM (12%) $685,798 TOTAL COSTS (excl. GST) $7,829,531 Table 6.3: Pumping, pipeline and HV power supply capital costs to Centipede Description Amount Bore Pumps, Headworks, Pipelines, HV Power Supply etc. $11,814,946 Contingency (10%) $1,181,499 Engineering Prelims (incl. Mob./Demob.) (15%) $1,772,248 EPCM (12%) $1,417,798 TOTAL COSTS (excl. GST) $16,186,491 Our Reference 1134/C/104a Page 101

114 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING WEST CREEK BOREFIELD DEVELOPMENT COSTS Table 6.4: Pumping, pipeline and power supply capital costs to Lake Way Description Amount Bore Pumps, Headwork, Pipelines, genset Power Supply etc. $2,210,806 Contingency (10%) $221,081 Engineering Prelims (incl. Mob./Demob.) (15%) $331,621 EPCM (12%) $265,297 TOTAL COSTS (excl. GST) $3,028,804 The total capital costs for the genset powered, water supply scheme to the Centipede and Lake Way mines, as well as the mine village, is estimated as $12.1M (i.e. total costs from Tables 6.1, 6.2 and 6.4). Page 102 Our Reference 1134/C/104a

115 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING CONCLUSIONS 7 CONCLUSIONS Following the completion of this Study, the following conclusions are presented: Water quality within the calcrete aquifer in the study area is marginal at best with respect to the Wiluna Uranium Projects water quality constraints. Water quality within the deeper silty/clayey sediments underlying the calcrete aquifer is unlikely to meet Toro s water quality constraints. The model results indicate that borefield operating strategies limiting drawdowns to 25% of the saturated aquifer thickness will not satisfy Toro s water volume requirements for the Wiluna Uranium Project. The modelling indicates that the current West Creek Borefield (installed in the calcrete aquifer) comprising bores P18, P22, P61 and P62 is unlikely to satisfy Toro s water demand of 0.7GL/year for a project life of ten years. As indicated above, these bores may be able to supply the required yields (1,920m 3 /day) for approximately twelve months, however there is no data to suggest that they can sustain this yield over the longer term. The modelling indicates that a reconfiguration of the existing West Creek Borefield (comprising P18, P26, P62, P70 and P21) is unlikely supply the required 0.7GL/year for ten years. The modelling indicates that an expanded West Creek Borefield installed in the calcrete aquifer may meet the Projects water requirements (0.7GL/year) for 8 to 9 years, before declining to ~0.66GL in the tenth year. A key requirement of this borefield design would be to spread abstraction over as wide as area of the calcrete aquifer as possible, without moving too far south towards Lake Way where groundwater quality deteriorates. Following the cessation of pumping, predicted water levels suggest that the majority of groundwater recovery closer to 2.5 metres, is completed twenty years after water supply pumping ceases. A further 1.5 metres of recovery is predicted after a further forty years. The final water quality of the blend of an expanded West Creek Borefield will not be known until further hydrogeological data is collected. Operation of the Apex Southern Borefield at significant rates is likely to have a deleterious effect on the operation of the West Creek borefield. The capital costs of developing a 0.7GL/year capacity water supply scheme to pipe water from the West Creek Borefield to the Centipede and Lake Way mines, as well the mine village, is estimated at $12.1M. It should be noted that the modelling results presented in this report are based on the current model geometry, which has in turn been developed from the current limited dataset, and it assumes average rainfall conditions. We currently consider that there is insufficient data to develop such a borefield and further hydrogeological investigations are required. The limitations of the modelling work undertaken is presented in Section 4.8. Our Reference 1134/C/104a Page 103

116 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING RECOMMENDATIONS 8 RECOMMENDATIONS A number of data gaps were identified during this investigation and the following study recommendations are listed to allow final development of a borefield in the West Creek area; Further hydrogeological investigation of the study area should be undertaken. This should focus in areas of the calcrete that could potentially host an Expanded West Creek Borefield, and areas that could potentially contribute high quality groundwater. The investigation should include: Refurbishment/rehabilitation of damaged bores of interest in the study area. We understand that a number of bores have been vandalised. Installation of a number of monitoring bores so that groundwater samples can be collected for subsequent analysis, water levels gauged and slug permeability testing undertaken. All existing bores in the study area be sampled where practicable. Assuming the above investigation provides favourable results, we recommend the following further actions: New test production bores should be installed and test pumped to provide greater information with respect to the hydraulic parameters of the calcrete aquifer. Toro should consider the business case for installing these bores as full production specification items to potentially save costs/time in developing the borefield. Test pumping of rehabilitated production bores. Monitoring bores will be required to be installed in the vicinity of the pumping bores. Monitoring bores should also be installed in the silt/clay underlying the calcrete to monitor for potential upconing effects. All existing bores in the study area be re-sampled where practicable. Update the groundwater model for the Study area to include data generated during the above investigations. Water supply predictions should be rerun using the updated model to confirm the current understanding of the West Creek hydrogeology. If Toro consider that an Expanded West Creek Borefield represents a key component of the Wiluna Uranium Project s water supply, we recommend that a permanent monitoring network is installed, as soon as possible, with background data collected well in advance of the commissioning of any borefield. Reassessment of the borefield infrastructure development costs. Page 104 Our Reference 1134/C/104a

117 WEST CREEK WATER SUPPLY GROUNDWATER MODELLING REFERENCES 9 REFERENCES Aquaterra, (2007a): Lake Way / Centipede Deposit Stage 1: Data Review and Scope of Work, report for Nova Energy Limited, August 2007, Report Number 793/B1/018c, Perth, WA, 24p. Aquaterra (2007b): Costean Programme Dewatering Assessment Centipede Deposit, report to Nova Energy Ltd, October 2007, Report No. 793/B2/045a, Perth, WA. Aquaterra (2010): Wiluna Uranium Project Groundwater and Surface Hydrology Studies: Proposal, Document No. 1134B/CA/005b, project proposal submitted to Toro Energy on 6 th December Australian Groundwater Consulting (1985): Wiluna Gold Project Water Supply Appraisal (Stage 2), Technical Report 1254 dated November 1985 for Chevron Exploration Corporation, 12p. Australian Groundwater Consulting (1986): Mt Wilkinson Gold Project Water Supply Appraisal Stage 3, Draft report prepared for the Chevron Exploration Corporation, May 1986, AGT Report Number 1254, 55p. Argent Exploration Services, (1987): Report on Hydraulic Test Data Analysis Mt. Wilkinson Gold Project, for Chevron Exploration Corporation, 15 th January Bureau of Meteorology, Actual Areal Evapotranspiration Map. Department of Water, Electronic data supplied on 9 th March Geoscience Australia, :250,000 Sheet SG51-09, Wiluna (2 nd Edition). Geological Survey of Western Australia, Groundwater Regimes and Their Exploration for mining development in the Eastern Goldfields of Western Australia. Record 1992/3. Geological Survey of Western Australia, Geological sheet SG51-09, Wiluna (2 nd Edition).. Geological Survey of Western Australia, Explanatory notes. Geological sheet SG51-09, Wiluna (2 nd Edition). KH Morgan and Associates (1997): Annual Groundwater Monitoring Report: April 1996 to March 1997 Groundwater Licence 32082, Wiluna South Borefield, Project 748, 26 th October 1997, report for Wiluna Gold Pty Ltd. KH Morgan and Associates (2006a): Groundwater development planning for mining Centipede and Lake Way uranium deposits for Nova Energy, 4 th April KH Morgan and Associates (2006b): Annual groundwater monitoring to March 2006, GWL 57622(3), Eastern Borefield for Agincourt Resources Ltd, 15 August Murray Darling Basin Commission (2001), Groundwater flow modelling guideline. National Health and Medical Research Council (NHMRC) and Natural Resource Management Ministerial Council (NRMMC), Australian Drinking Water Guidelines. Resource Investigations, (1989): Review of groundwater production Mt Wilkinson Gold Project, 19 th April 1987 to 30 th April 1989 for Chevron Exploration Corporation, 1 st June Resource Investigations, (1991): Report on groundwater Production and Water Level Monitoring 30/4/89 to 16/1/19, Matilda Gold Project, Wiluna, WA Groundwater Well Licence Numbers 32065, 32069, and , for Eon Metal NL, Project No , 23 rd May Rockwater, 1978: Lake Way Uranium Project - Preliminary Groundwater Investigation, October 1978, commissioned by Public Works Department of W.A., on behalf of Wyoming-Delhi-Vam Joint Venture, 34p. Toro Energy (2010): Wiluna Uranium Project Environmental Scoping Document, Report No PM-WIL-ENV-LC, Toro Energy Ltd, 14 May Water and Rivers Commission, (1999): Groundwater Resources of the Northern Goldfields, Western Australia. Report HG2. Our Reference 1134/C/104a Page 105

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119 APPENDIX A ACTUAL AREAL EVAPOTRANSPIRATION MAP

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121 From