BHP : Jimblebar Hub Groundwater EIA

Jimblebar Hub: Groundwater Impact Assessment

December 2023

Version 1.0

Authorisation

Version	Description of Version	Position	Date
0	Initial version for Traditional Owner	Superintendent, Water	29	October 2023
	information	Stewardship & Approvals (Water
		Planning)
1.0	Final as part of Jimblebar Hub	Superintendent, Jimblebar	06	December 2023
	Significant Amendment referral to	Hydrogeology
	EPA

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BHP	Jimblebar Hub: Groundwater impact assessment

Contents

1	Purpose	1
2	Scope		1
3	Existing environment and environmental values	1
4	Hydrogeology	4
4.1	Jimblebar mine area conceptualisation	4
4.2	Shovelanna mine area conceptualisation	4
4.3	Regional conceptualisation from Jimblebar Hub to Ethel Gorge area	4
5	Historical and current groundwater levels	7
5.1	Jimblebar mine area groundwater levels	7
5.2	Shovelanna mine area groundwater levels	7
5.3	Ethel Gorge area groundwater levels	7
6	2023 Jimblebar mine groundwater modelling	10
6.1	Sensitivity analysis and predictive confidence	10
6.2	Predicted groundwater abstraction rates and drawdown	10
6.3	Post-mining groundwater level recovery	15
7	Groundwater abstraction and drawdown assessment	16
7.1	Change in Jimblebar mine groundwater abstraction and drawdown	16
	7.1.1	Assessed abstraction and drawdown for the Jimblebar Approved Proposal	16
	7.1.2	Predicted 2023 Jimblebar groundwater abstraction and drawdown	18
	7.1.3	Change in Jimblebar groundwater abstraction and drawdown predictions	18
7.2	Combined Jimblebar Hub groundwater abstraction and drawdown	20
	7.2.1	Assessed abstraction and drawdown for the Jimblebar Hub Approved Proposals	20
	7.2.2	Combined abstraction and drawdown for the Jimblebar Hub	20
8	Post-mining groundwater level change assessment	23
8.1	Jimblebar mine post-mining groundwater level recovery	23
	8.1.1	Assessed post-mining groundwater recovery for the Jimblebar Approved Proposal ....	23
	8.1.2	Predicted 2023 Jimblebar post-mining groundwater level recovery	23
	8.1.3	Change in Jimblebar post-mining groundwater level recovery predictions	23
8.2	Combined Jimblebar Hub post-mining groundwater level changes	23
9	References	25
Appendices	26
Appendix A Jimblebar Hydrogeological Assessment	26

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BHP	Jimblebar Hub: Groundwater impact assessment

Figures
Figure 1: Regional context	3
Figure 2: Conceptual groundwater system - operations	6
Figure 3: Pre-development groundwater levels	8
Figure 4: Observed groundwater levels in the Jimblebar and Shovelanna areas	9
Figure 5: Observed groundwater levels in the Ethel Gorge area	9
Figure 6: Target Jimblebar mine pit groundwater levels	11
Figure 7: Predicted Jimblebar mine dewatering rates	12
Figure 8: Predicted Jimblebar mine drawdown at 2052	14
Figure 9: Conceptual pit lake diagram - sink	15
Figure 10: Comparison of assessed drawdown for the Jimblebar mine Approved Proposal	17
Figure 11: Comparison of assessed and 2023 predicted Jimblebar mine drawdown	19
Figure 12: Jimblebar Hub combined groundwater drawdown extent	22

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BHP	Jimblebar Hub: Groundwater impact assessment

1 Purpose

The purpose of this document is to provide an assessment of the impacts on groundwater water resources from the proposed increased groundwater abstraction for mine dewatering from the Jimblebar mine to support the Jimblebar Hub Iron Ore Mining Operations Significant Amendment (Jimblebar Hub Proposal) (BHP 2023a).

The Jimblebar Hub: Ophthalmia Dam surplus water impact assessment update (BHP 2023b) documents the assessment of the impacts of discharge of surplus mine dewater from BHP's Eastern Pilbara mines to Ophthalmia Dam (including the contribution from the Jimblebar Hub).

2 Scope

The Jimblebar Hub Proposal includes a new mine area (East Jimblebar deposit) and increased abstraction (for dewatering) of approved deposits at the existing Jimblebar mine and dewatering of the East Jimblebar deposit. No changes are proposed to the approved groundwater abstraction (including dewatering) rates for the other existing mines in the Jimblebar Hub (Orebody 31 and Orebody 18). BHP has undertaken the Jimblebar Hydrogeological Assessment (140 ML/d) (Appendix A; BHP 2023c) to assess the potential impacts from the current (2023) long-term mine (and dewatering) plan at the Jimblebar mine, to support Rights in Water and Irrigation 1914 (RiWI) 5C licence and Environmental Protection Act 1986 (EP Act) Part IV approval processes.

However, as the Jimblebar Hub Proposal is a significant amendment (BHP 2023a) to Approved Proposals under Part IV of the EP Act in the Jimblebar Hub (the existing Jimblebar, Orebody 31 and Orebody 18 mines), BHP has provided information in this document on the previous assessments of groundwater abstraction for the existing mines and the combined effects that the Approved Proposals and the Jimblebar Hub Proposal might have on the environment.

The key previous assessments for the Approved Proposals are:

• Hydrogeological Assessment for Jimblebar Iron Ore Project (Aquaterra 2009); Appendix G to Jimblebar Iron Ore Project Environmental Protection Statement (BHP Billiton 2010)
• Jimblebar Detailed Hydrogeological Assessment (BHP Billiton 2017)
• Jimblebar Detailed Hydrogeological Assessment - 72ML/d (BHP 2021)
• Orebody 31 Hydrogeological Impact Assessment: Summary Document (BHP Billiton 2015a); Appendix I to Orebody 31 Iron Ore Mine Project Environmental Referral Document (BHP Billiton 2015b).

3 Existing environment and environmental values

BHP's Jimblebar Hub comprises existing mining operations at the Jimblebar, Orebody 31 and Orebody 18 mines, and is located approximately 40 km east of the town of Newman (Figure 1). Mining operations commenced at the Jimblebar Hub over thirty years ago. There are three current Approved Proposals (existing projects) for the Jimblebar Hub operations:

• Jimblebar Iron Ore Project (Revised Proposal): Ministerial Statement (MS)1126
• Orebody 31 Iron Ore Project: MS1021
• Orebody 18 Iron Ore Mine: MS439 (as amended by MS1012).

The approved Orebody 18 mine comprises the Orebody 17 and Orebody 18 deposits. When referring to the approval title under Part IV, BHP refers to Orebody 18. When discussing the mine and/or deposits, BHP refers to Orebody 17/18 (OB17/18). BHP also refers to the Orebody 18 and Orebody 31 mines collectively as the Shovelanna area.

The groundwater regime has been altered by groundwater abstraction for water supply and for dewatering orebodies to access below water table ore. Groundwater abstraction for water supply commenced at Jimblebar in 1994. Groundwater abstraction for mine dewatering activities commenced at Jimblebar in 2011 and Shovelanna (OB17/18

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BHP	Jimblebar Hub: Groundwater impact assessment

and OB31) in 2015. Mining and dewatering is active at the Jimblebar and Orebody 31 mines. Dewatering at OB17/18 has ceased. BHP also injects surplus groundwater in the Orebody 18 (Ninga) managed aquifer recharge (MAR) and Caramulla MAR scheme areas.

The Ophthalmia Dam system, located approximately 20 km from the Jimblebar Hub, partially overlies the Ethel Gorge aquifer which supports the Ethel Gorge aquifer stygobiont community Threatened Ecological Community (Ethel Gorge TEC). Ophthalmia Dam was commissioned in 1981 as a MAR scheme, to maintain groundwater levels within the Ethel Gorge aquifer and to support the Ophthalmia Borefield, which BHP has operated since the 1970s. The Ophthalmia Dam system continues to maintain groundwater levels within the Ethel Gorge aquifer to protect the Ethel Gorge TEC habitat and also provides a discharge location for surplus water from BHP mines in the Eastern Pilbara area (currently Eastern Ridge, Orebody 29/30/35, Jimblebar and Orebody 31) (BHP 2023b).

The main water-related environmental values that potentially may be impacted by groundwater abstraction from the Jimblebar Hub are (Figure 1):

• local groundwater resource in the Jimblebar Hub area
• Ethel Gorge aquifer (and TEC).

The hydrogeological assessment for the current (2023) Jimblebar long-term mine plan (BHP 2023c) identifies other groundwater users. Most of the nearby users are other BHP operations. Other third party users have been identified but are unlikely to be impacted by abstraction from the Jimblebar mine. BHP will provide a monitoring strategy as part of the Rights in Water and Irrigation Act 1914 (RiWI Act) s5C Licence to Take Water Groundwater Operating Strategy if any third party groundwater users may negatively impacted (BHP 2023c).

The Fortescue Marsh is located approximately 120 km north (downstream) of Ophthalmia Dam along the Fortescue River at the terminus of the Upper Fortescue River. The aquifer system underlying Fortescue Marsh is not connected to the Jimblebar Hub orebody aquifers and will not be impacted by groundwater abstraction (including for dewatering) at the Jimblebar Hub.

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GROUNDWATER

ENVIRONMENTAL IMPACT ASSESSMENT

Regional context

0

10

PLANNING & STANDARDS - IRON ORE

KILOMETRES

SCALE @ A4:

1:300,000

PREPARED: SPATIAL DATA

FIGURE:

1021/131A

GDA 1994 MGA ZONE 51

DATE:

4/12/2023

REQUESTOR: ENV. APPROVALS

NO:

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BHP	Jimblebar Hub: Groundwater impact assessment

4 Hydrogeology

Regional aquifers are located through the central valleys of the Jimblebar Hub area (vicinity of the proposed Development Envelope shown in Figure 2) and are made up of:

• weathered Paraburdoo (and Bee Gorge) Members of the Wittenoom Formation; the Paraburdoo dolomite in particular can be karstic and highly permeable
• sand and gravel occurrences in the Tertiary Detritals; the detritals are very thick in places, ranging from 200 to 360 m thick.

At the local scale, orebody aquifers in the Jimblebar Hub are made up of mineralised and submineralised material:

• The Marra Mamba Formation forms an almost continuous east/west striking aquifer in the south, with some orebodies reaching depths of approximately 110 m below water table (BWT). The Marra Mamba Formation hosts the South Jimblebar deposits at the Jimblebar mine.
• The Brockman Iron Formation, which also forms almost continuous east/west striking aquifers in the north; whilst these aquifers are discontinuous, they can be very large, reaching depths of approximately 110 m to 140 m BWT. The Brockman Iron Formation hosts the OB17/18 and OB31 in the Shovelanna mine area, and the Wheelarra Hill, Hashimoto and East Jimblebar deposits at the Jimblebar mine (BHP 2023c).

Figure 2 shows the hydrogeological conceptualisation in the Jimblebar Hub area during operations (i.e. with groundwater abstraction and injection activities). There is no hydraulic connection between the Jimblebar mine area and the Shovelanna mine area (OB31 and OB17/18) due to the presence of the Wheelarra Fault.

4.1 Jimblebar mine area conceptualisation

Regional and local geological structures act as groundwater flow barriers. There is little or no groundwater flow across the Wheelarra Fault in the west and the northeast-southwest trending structures (including the Khyber Fault) in the east (Figure 2). Locally there are several structures that, as shown by the propagation of drawdown, provide either partial or complete barriers to groundwater flow. These include the Central, Comedy and Monster faults (Figure 2). Groundwater flow is inferred to be generally from the south to the north. To the west of the Central Fault, dewatering activities (especially dewatering at the South Jimblebar deposits) result in groundwater flow towards the South Jimblebar deposit, and a southerly flow component across much of western part of the Jimblebar operations.

4.2 Shovelanna mine area conceptualisation

Current groundwater flow is generally from the west to east in the regional aquifer and then north into OB31, with localised radial flow towards OB18 and OB31, where dewatering activities occur (Figure 2). There is a hydraulic barrier (likely a dyke) through the weathered Wittenoom regional aquifer (and probably orebody aquifers) between OB18 and OB17. OB17 and OB31 are hydraulically connected, likely through the Brockman orebody. Since the Orebody 18 mine was approved under Part IV of the EP Act, BHP now refers to the portion of the OB18 mine originally referred to as the OB18 North pit as the OB17 Swan pit. This is consistent with the hydrogeological conceptualisation that OB18 is not hydraulically connected to OB17.

4.3 Regional conceptualisation from Jimblebar Hub to Ethel Gorge area

The regional aquifer (made up of weathered Wittenoom Formation and Tertiary Detritals) is continuous from the east (OB31) to the west (Ethel Gorge). However, there are at least two partial groundwater flow barriers (probably dykes) along this flow path (Figure 2). These form three distinct aquifer compartments between OB31 and the Ethel Gorge aquifer. The OB17 and OB31 deposits are within the orebody aquifer compartment furthest from the Ethel Gorge aquifer, a compartment defined by flow barriers on all sides. Pre-development, it was likely that there was only low

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BHP	Jimblebar Hub: Groundwater impact assessment

groundwater flow from the OB17 and OB31 orebody aquifer compartment from east to west across the dyke towards the Ethel Gorge aquifer (20 km to the west of the Jimblebar Hub). With dewatering of OB31 and operation of the Orebody 18 (Ninga) MAR, the flow direction has reversed (ie is from west to east) up to roughly the area of the Orebody 18 (Ninga) MAR.

There is no hydraulic connection from the Jimblebar orebody aquifers to the Ethel Gorge aquifer, due to the presence of the Wheelarra Fault.

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Proposed Development Envelope Flow barrier

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Existing pits

Proposed pits

Groundwater flow

							GROUNDWATER		PUBLIC
	±5
			ENVIRONMENTAL IMPACT ASSESSMENT
				Conceptual groundwater system
0	10		PLANNING & STANDARDS - IRON ORE
	KILOMETRES			SCALE @ A4:	1:300,000	PREPARED: SPATIAL DATA	FIGURE:	2
	GDA 1994 MGA ZONE 51			DATE:	14/12/2023	REQUESTOR: ENV. APPROVALS	NO:	1021/132B

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