BHP : Groundwater EIA Appendix A Jimblebar H3 report

Jimblebar

Hydrogeological

Assessment

7 December 2023

Contents

1	Introduction	3
2	Climate and rainfall	5
3	Hydrogeology	8
4	Existing Groundwater Users	22
5	Groundwater Investigations	25
6	Drilling	25
7	Test Pumping	27
8	Groundwater Chemistry	27
9	Groundwater Modelling	27
10	Assessment of Potential Impacts	87
11	Groundwater Monitoring	90
12	Management Approach	90
13	Conclusions	90
14	References	92
15	Appendix A: Conceptual model	93
16	Appendix B: Bore Logs	94
17	Appendix C: Groundwater Chemistry	95

Introduction

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1 Introduction

1.1 Overview

The Jimblebar mining operations is located in the Pilbara region, approximately 40km east of the town Newman. There are currently three approved proposals:

• Jimblebar Iron Ore Project (Revised Proposal) MS1126
• Orebody 31 Iron Ore Project MS1021
• Orebody 18 Iron Ore Mine MS439 (as amended by MS1012).

Under the approved Jimblebar Iron Ore Project (Revised Proposal), the mine features Wheelarra Hill, South Jimblebar and Hashimoto deposits. Jimblebar mine is situated on Mineral Licence M266SA and Miscellaneous Licences L52/108 and L52/109. Operations are situated in the East Pilbara sub-area of the Pilbara groundwater allocation plan (DoW, 2013) and underlain by fractured rock aquifers.

BHP refers to OB18 and OB31 mines collectively as the Shovelanna operations (Figure 1).

Key approved water activities are relating to Jimblebar (excluding Shovelanna) are:

• Mining above and below the water table
• Abstraction for groundwater for water supply and dewatering
• Surplus water management

1. Discharge of surplus water to Ophthalmia Dam from the Jimblebar and OB31 mines

1. Discharge of surplus water to Caramulla Managed Aquifer Recharge (MAR)

o Discharge of surplus water to Caramulla Creek and Jimblebar Creek.

Introduction

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Fig 1.1: Location of operations

Climate and rainfall

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1.2 Jimblebar 5C Licence

Jimblebar operations current 5C Licence to Take Water issued under the Rights in Water and Irrigation Act 1914 GWL158795(11) allows for an annual abstraction of 26,300,000 kL/a (26.3 GL/a) to align with the approved Jimblebar Optimisation Project. BHP WAIO will be referring the Jimblebar Hub Iron Ore Mining Operations Significant Amendment in late 2023 to the Environmental Protection Authority. The proposal will include the following key activities:

• Above and below water table mining at East Jimblebar
• Mine dewatering and surplus water at Jimblebar
• New overburden storage areas north of East Jimblebar
• New haul roads and creek crossings if required
• New beneficiation plant at Jimblebar and associated in-pit tailing storage facilities at OB18, OB31 and Jimblebar.

This H3 report (prepared in accordance with Operational policy no 5.12, (DoW, 2009) has been compiled to support the above project with BHP WAIO seeking a licence amendment of GWL158795(11) to an annual water entitlement of 51,100,000kL/a. The H3 level assessment supports the licence application assessing the drawdown, migration and magnitude from dewatering at a maximum rate of 140 ML/d via:

• Compilation and review of existing geological and hydrogeological data
• Update of the conceptual hydrogeological model of the Jimblebar area
• Update of the numerical groundwater model
• Calibration of the numerical model to available groundwater level data
• Predictive model runs to estimate the potential range in regional drawdown due to mine dewatering; and
• Review of potential impacts and management approach including update of a groundwater license operating strategy (GWOS), which will be submitted following this application.

2 Climate and rainfall

The nearest BoM weather station is located about 45 km southwest at Newman Airport. The Jimblebar mine site has a weather station installed at Wheelarra Hill, which has been in operation since 2000. Observed rainfall data (Figure 2.1) includes Wheelarra Hill and Newman Airport, gaps in the Newman Airport record have been infilled with data from the now closed Newman weather station.

The regional climate in the Jimblebar area is semi-arid. Rainfall is typically dominated by the influence of subtropical highs located to the south of the Pilbara. Rainfall throughout the year is variable, with distinct wet and dry seasons. The wettest months of the year are typically January to March, producing 60% of annual rainfall within the area (CSIRO, 2015). The larger summer rainfall events are generally associated with tropical lows, which develop from degrading tropical cyclones formed off the northwest coast of Western Australia (Charles et al, 2015). The mean annual distribution of rainfall across the Pilbara (during the period 1911-2012) is approximately 299 mm. There is a large year-to year variability with annual rainfall ranging from 48 mm in 1924 to 731 mm in 2000 (CSIRO, 2015).

The Pilbara is characterised by high evaporation rates and a generally low soil infiltration capacity. This results in recharge occurring exclusively during major rainfall events (15-25 mm/d). Within the Upper Fortescue region, this recharge is dominated by leakage from streambeds (Charles et al, 2015). The closest station which recorded evaporation was the Wittenoom BoM station 002056, located approximately 190 km northwest of Newman. Average

Climate and rainfall

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annual evaporation data from 1967 to August 2019 (station closure) for Wittenoom was 3,139 mm/yr, which exceeds annual rainfall by about 2,800 mm/yr.

Climate and rainfall

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Fig 2.1: Summary of Jimblebar and Newman Rainfall

Hydrogeology

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3 Hydrogeology

3.1 Introduction

An overview of the regional setting, conceptual model and key uncertainties is provided below. The evidence for all aspects of the conceptual model are provided in Appendix A.

3.2 Topography and Surface Water Drainage

The topography of the Jimblebar area is generally characterized by the prominent Wheelarra Hill in the north western part of the area and the lower lying hills of the Marra Mamba and Jeerinah Formations to the south (Figure 3.1). To the east the topography varies very little as far as the hills that rise just east of Thirteen Creek. The lowest topography is associated with the Tertiary filled valley between the Brockman orebodies in the north and the Marra Mamba orebodies in the south. In the valley area the topography is highest in the west. From just east of the Wheelarra Fault the ground surface falls from about 550 mRL to about 515 mRL by Capricorn / WHASH. From here to the east it falls very gently, reaching about 510 mRL roughly halfway between Caramulla Creek and Thirteen Creek. Towards Thirteen Creek it increases again slightly, reaching about 515 mRL by the creek.

Hydrogeology

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Figure 3.1: Jimblebar topography and surface water drainage

Hydrogeology

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The Wheelarra Hill consists of outcropping Brockman Iron Formation units with topographic highs in the order of ~700 mRL. Topographic highs in the lower lying Marra Mamba and Jeerinah Formation hills to the south are in the order of 560 mRL in the Mindoona area, with a gentle slope to the east. Ground elevation in the Tertiary filled valley is around 530 mRL.

The area is drained towards the north by the Jimblebar, Caramulla and Thirteen Creeks which have their headwaters along the southern margins of the project area. The main channel of the Jimblebar Creek passes adjacent to the eastern most South Jimblebar orebody. Copper Creek is the main tributary to the Jimblebar Creek in the area and it drains the broad valley between Wheelarra Hill and the South Jimblebar orebody. Figure 3.1 summarises the surface water drainage and topography.

The southern flank of the Wheelarra Hill and the broad area of Jimblebar ridge drain towards Copper Creek. The northern side of Wheelarra Hill is drained by numerous, northward flowing small channels and valleys, which then flow eastwards to join Jimblebar Creek. As with most of the rivers and creeks in the Pilbara, these channels are ephemeral and predominantly dry outside of seasonal rainfall events.

Innawally Pool is located where Jimblebar Creek passes through the WHASH/HASH deposits and forms a significant ephemeral wetland feature. The pool is fed by surface water from a localized, shallow, perched aquifer. The pool is hydraulically disconnected from the regional water table, which sits some 50 m below ground level.

3.3 Conceptual model

3.3.1 Introduction

The main conceptual model components are shown in Figure 3.2 and described below. The greatest detail is provided for the area encompassing Mindoona, Sylvania, Capricorn, WH123, WHASH and HASH deposits, as these are the areas with the most data.