12 Groundwater 12

Groundwater 12

12.1 Introduction and the potential impact on users of the groundwater resources 12 and other sensitive receptors. Olympic Dam is located in an area of low rainfall, low rates of groundwater flow and recharge, and low topographic relief. No groundwater affecting activities would occur as a result of As a consequence, most groundwater within 50 km or more of construction or operation of the proposed concentrate handling the current operation is saline (i.e. salty) and little-used. facilities at the Port of Darwin. These facilities would be Olympic Dam currently uses less than 1 ML/d of local constructed within the reclaimed area of the East Arm where groundwater for dust suppression, and there are three known groundwater is not naturally occurring. Consequently, the local shallow groundwater wells within 50 km that use saline and regional groundwater systems of the Darwin area are not groundwater for stock (all three are within pastoral leases held discussed here. Information relating to the risk to groundwater by BHP Billiton). from accidental spills or leaks is discussed in Appendix E4.

The primary water supply for the existing Olympic Dam Groundwater in the vicinity of the desalination plant would not operation is groundwater extracted from Wellfields A and B be used and the proposed expansion would not affect the located in the Great Artesian Basin (GAB), about 120 and natural interactions between groundwater and seawater. 200 km north of Olympic Dam, respectively. These wellfields supply an average of 37 ML/d to the existing operation. The The potential for, and implications of, water accumulating in extraction of groundwater is monitored extensively to the bottom of the open pit after mine closure are discussed demonstrate compliance with licence conditions and to prevent in Chapter 11, Surface Water. The rehabilitation and impact to the GAB springs. decommissioning of the wellfields after the mine has closed are discussed in Chapter 23, Rehabilitation and Closure. The proposed Olympic Dam expansion would require an The existing management and monitoring programs, and the additional 183 ML/d (peak requirement). The primary water requirements for the proposed expansion are discussed in supply for the proposed expansion is a desalination plant Chapter 24, Environmental Management Framework. located at Point Lowly, not groundwater from the GAB. No new water would be obtained from the GAB beyond that which is available under approvals from the South Australian Government. 12.2 assessment methods 12.2.1 Geological setting A supplementary, low-quality water supply, primarily for dust Groundwater systems and the associated water resources are suppression, would be sourced from saline aquifers close to the closely linked to geology and rock properties. A summary of the current operation. geology and geochemical properties of subsurface materials is presented in this chapter and further detail is provided in This chapter describes the local and regional groundwater Appendix K1. systems of the wider Olympic Dam region and identifies activities to be undertaken as part of the Olympic Dam Geological maps and soil descriptions were sourced from expansion that may have the potential to affect groundwater various publications, including the Geological Survey of South during operations and post closure. The assessment identifies Australia map sheets (Geological Survey of South Australia the extent of the area likely to be affected by these activities 1981, 1982 and 1992), Atlas of Australian Soils map sheets and explanatory data (CSIRO 1960 and 1968), and assessments

Olympic Dam Expansion Draft Environmental Impact Statement 2009 337 undertaken as part of the 1982 and 1997 Olympic Dam EIS It was apparent that there were no drill holes (and therefore no (Kinhill-Stearns Roger 1982; Kinhill 1997). groundwater data) in the north-east region of the project area, between the SML and Lake Torrens, and further beyond to the In addition, a sampling and analytical program has been GAB. To fill this gap, nine additional, multi-nested groundwater established since mining began at Olympic Dam and data have monitoring wells, ranging from around 70 m to more than been compiled into an extensive geology, hydrogeology and 600 m deep, were drilled to assess the horizontal and vertical geochemistry database. Figure 12.1 provides an indication of hydraulic gradients, aquifer parameters, the potential for inter- the resource drilling that has been undertaken in order to aquifer connection and regional groundwater discharge identify the extent of the Olympic Dam ore body and its processes (see Figure 12.2 for location of groundwater properties. The database of borehole logs and the analytical monitoring wells). results from around 2.5 million samples provided an important resource for understanding the geology of the mine site and A desktop review of baseline groundwater conditions wider region. associated with both the gas pipeline corridor options and the southern infrastructure corridor was also undertaken (see 12.2.2 regional groundwater data collection Appendices K1 and K3 for details). In addition to the desktop Numerous regional groundwater studies have been undertaken assessment, a field investigation was undertaken along the in the EIS Study Area, including assessments presented in the southern infrastructure corridor. Groundwater samples could two previous Olympic Dam EIS (Kinhill-Stearns Roger 1982; not be collected from the gas pipeline corridor options because Kinhill 1997). Groundwater data used in these assessments most of these areas are accessible only by helicopter. The were largely obtained from borehole drilling records kept by the baseline groundwater parameters for wells located along the Department of Water, Land and Biodiversity Conservation corridors have been summarised from drilling records. (DWLBC) and WMC Limited drilling programs that focused on the GAB. While this database represents an important resource, As part of the field investigation, drilling records from the particularly in the area of the GAB, data have been collected DWLBC were reviewed and 46 sites were chosen for field over more than 100 years and the completeness, consistency inspection, and groundwater samples were obtained from 21 of and integrity of historic records varies. these wells (see Figure 12.2, Plate 12.2). The groundwater sampling and water quality results are presented in For the current assessment, the existing data were Appendix K3. supplemented by an extensive hydrogeological drilling and testing program over a broader area, as outlined below and detailed in Appendices K1 and K2. The area studied for the regional groundwater assessment is shown in Figure 12.2 (to avoid confusion with the EIS Study Area, this broader area is termed ‘project area’ hereafter).

Groundwater levels and water quality Groundwater levels, flow and quality on and around the existing SML are well understood through a groundwater monitoring program that has been operating for 25 years and is documented in the annual Environmental Management and

Monitoring Report (see BHP Billiton 2007 for latest). However, Plate 12.1 Differential GPS equipment limited data were available for the wider region around Olympic Dam and the proposed infrastructure corridors.

Desktop and field investigations were undertaken to collect regional groundwater level data. Groundwater well locations were obtained by searching the DWLBC database and consulting with landholders. Seventy-four wells (including mechanically drilled ‘bores’ and hand-dug ‘wells’) were located, inspected and surveyed with a differential GPS (see Plate 12.1). Where possible, a water sample was collected and analysed in the field for temperature, electrical conductivity, pH, dissolved oxygen and reduction/oxidation (redox) potential (see Appendix K2 for details).

Plate 12.2 Groundwater wells being sampled

338 Olympic Dam Expansion Draft Environmental Impact Statement 2009 Ore body 12 1975 to March 2007) (8,417 holes drilled from Resource drill hole locations Conceptual open pit (pit benches not shown) Existing metallurgical plant Note: darker areas of the drill holes denote sections where samples were undertaken to determine mineralisation Figure Resource 12.1 drilling of the proposed open pit

Olympic Dam Expansion Draft Environmental Impact Statement 2009 339 Moomba

Lake Eyre North

William Creek Roxby Downs

Port Augusta

Whyalla Lake Eyre Port Pirie South

Adelaide

Marree

OLYMPIC DAM Andamooka Roxby Downs

Woomera Lake Lake Windabout Torrens Pimba

Island Pernatty Lagoon Lake Lagoon Gairdner

Port New groundwater monitoring wells Augusta Regional groundwater elevation and users survey Baseline groundwater quality survey Existing rail line Gas pipeline alignment options Water pipeline alignment Rail alignment Transmission line alignments Whyalla Point Lowly Port Access corridor Pirie Existing Olympic Dam Special Mining Lease Existing Roxby Downs Municipality 01020304050 EIS Study Area km

Figure 12.2 Regional groundwater study area and groundwater sampling locations

340 Olympic Dam Expansion Draft Environmental Impact Statement 2009 Groundwater users survey • Geotechnical drill logs were reviewed to understand the During the regional groundwater assessment, pastoralists in the near-surface geological conditions below the existing and project area were consulted to establish current groundwater future footprint of the TSF. Simplified but conservative use. Of the 16 pastoral stations consulted, eight were able to overall acid-neutralisation calculations were also completed provide details on the following information relating to for the subsoils, and estimates were made of the potential groundwater use (see Appendix K2): for limestone dissolution within the Andamooka Limestone Formation. • purpose (e.g. stock or domestic use) • Seepage rates were used to establish the potential short- • number of stock supported and medium-term effects for these calculations. • number of days used per year Geochemical speciation modelling (i.e. MINTEQ and • depth to groundwater PHREEQC) was undertaken to understand the interaction • well depth between the subsoils and the seepage from the tailings. • pumping equipment • The groundwater quality monitoring results were reviewed to understand the potential interaction with the basement • pump depth and typical pump rate rock, particularly for evidence of changes in concentrations • geological and drillers logs, where available. over time and to determine current effects.

12.2.3 Geochemistry assessment More recently, holes were drilled in the existing TSF to obtain Tailings storage facility tailings samples for geochemical characterisation, and pore A conceptual geochemical model was developed to assess the water was collected to determine water quality within the 12 potential for solutes to be released from the TSF into the tailings. Soil and sediment samples were also obtained from underlying groundwater systems. As the processing methods beneath the TSF base to determine interaction with seepage and the geochemical properties of the ore are not expected to from the tailings. be significantly different between the expanded and existing operations, the model was based on the observed conditions Rock storage facility within and below the existing TSF. Results from supplemental The geology and geochemistry database was evaluated as part geochemical laboratory testing were also considered. of the Draft EIS assessments, and supplementary sampling and analytical test work was undertaken to characterise the mine The overall objective of the TSF geochemistry assessment was rock that would be generated during the proposed expansion. to develop estimates of solute concentrations in the seepage The review and analytical test work targeted the sedimentary from the tailings into the underlying sediments and aquifers. layers above the ore body (overburden) and the basement rocks The conceptual model addressed the release and mobility of that contain the ore body. The detailed methodology is acidity, heavy metal contaminants and radionuclides to the presented in Appendix K5, and comprised geochemical testing extent that the data allowed. and modelling to predict potential solute concentrations in the seepage from the RSF. The analytical geochemical testing It is noted, that in this chapter, the term ‘seepage’ refers to included: liquid percolating from the base of the facility into the • geochemical assays – to determine the elemental underlying sediments and does not refer to expression of liquid composition, particularly the metals content, of each of the at the ground’s surface. rock types present at Olympic Dam • acid-base accounting – to evaluate the balance between The general approach adopted to develop the conceptual acid generation processes and acid neutralising processes geochemical model was as follows (see Appendix K4 for details): • kinetic testing – time-based laboratory testing of the rock types to assess sulphide reactivity, weathering rates, metal • Available geochemical information from the tailings and solubility, metal loads and potential leachate composition underlying soils and substrates was reviewed and summarised. • contact tests – to assess solute attenuation reactions that may occur within the soils underlying the RSF. • Geochemical speciation modelling (i.e. MINTEQ and PHREEQC) and supplementary calculations were undertaken to support the conclusions from the initial review of the Solute release modelling was also completed. The modelling tailings geochemistry. The calculations included preliminary included conversion of solute release rates from the laboratory estimates of the potential overall acidity that may be tests to field conditions expected in the RSF and geochemical released from the tailings. speciation modelling (i.e. PHREEQC) to understand the controls within the RSF on solute release to seepage from the base of the RSF. Assessment of the interaction between the subsoils and the percolate from the RSF was based on the contact test results as well as using the TSF as an analogue (i.e. a working example) for seepage and subsoil interaction.

Olympic Dam Expansion Draft Environmental Impact Statement 2009 341 12.2.4 regional groundwater model 12.3.1 regional geological setting Numerical groundwater flow model Australia is divided into a number of geological provinces that A regional numerical groundwater flow model has been describe the significant stages of geological formation from a developed to simulate historical groundwater behaviour at spatial and temporal perspective. The geological provinces of Olympic Dam and as a tool to aid in the prediction of a southern South Australia and the corresponding surface groundwater response from groundwater-affecting activities geology are presented in Figures 12.3 to 12.5. Although the during operations and post closure. groundwater systems most likely to be affected by operations at Olympic Dam occur within the rocks of the Stuart Shelf, other The regional numerical model was constructed using a finite geological provinces are relevant to Olympic Dam in the context element groundwater model (FEFLOW) and consists of three of regional groundwater interactions and potential main simulations. A steady state model was developed to environmental issues. These are summarised below and detailed represent groundwater conditions prior to mine development at in Appendix K1. Olympic Dam; transient calibrations were used to simulate the historical groundwater response from 1993 through to 2007; Stuart Shelf and a predictive model was used to simulate (predict) future The Olympic Dam mine and the southern infrastructure groundwater behaviour in relation to the groundwater-affecting corridors are located within the Stuart Shelf geological activities of the proposed expansion. These latter activities province, a relatively thin sequence of sedimentary rocks that include: lies above the Gawler Craton. The basement rocks of the • open pit mining Gawler Craton contain the Olympic Dam ore body (see Chapter 2, Existing Operation, for a geological description of • groundwater extraction from depressurisation of the open the ore reserve). pit

• seepage from the TSF and RSF The most significant sedimentary rocks of the Stuart Shelf • extraction of groundwater from primary and satellite saline include the Andamooka Limestone and the Tent Hill Formation, wellfields which comprises the Arcoona Quartzite, Corraberra Sandstone • underground mining and operation of the raise bores. and Tregolana Shale. Beneath the Special Mining Lease (SML) these layers are relatively shallow and thin, but further away from Olympic Dam they become deeper and thicker (see The groundwater modelling needed to cover a large temporal Figure 12.6). and spatial range. Given the inherent uncertainties with modelling of this scale and complexity, sensitivity analysis was Adelaide Geosyncline undertaken to define limits of prediction (i.e. data may only be suitable for predicting outcomes over a 500-year period) and to East of the Stuart Shelf are the highly folded sedimentary rocks provide a conservative approach to predicting and managing of the Adelaide Geosyncline. These units are geologically impacts. The results of the groundwater modelling are equivalent to the rocks of the Stuart Shelf but have been presented in this chapter and detailed modelling methods and separated by a zone of extensive faulting and deformation results of the sensitivity analysis are provided in Appendix K6. known as the Torrens Hinge Zone, which is bounded by the Torrens and Norwest faults (see Figure 12.3). Figure 12.7 shows 12.2.5 Impact and risk assessment a schematic geological cross-section of the Stuart Shelf and the westerly extent of the Adelaide Geosyncline. The assessment of impacts and risks for the proposed expansion has been undertaken as two separate, but related, Eromanga Basin processes (see Section 1.6.2 of Chapter 1, Introduction, and Figure 1.11). Eromanga Basin is the largest of three sedimentary basins that together form the Great Artesian Basin (GAB, see Section Impacts and benefits are the consequence of a known event. 12.3.2). The important units of the Eromanga Basin in South They are described in this chapter and categorised as high, Australia in relation to groundwater are the Cadna-owie moderate, low or negligible in accordance with the criteria Formation, Algebuckina Sandstone and Bulldog Shale. Of these, presented in Table 1.3 (Chapter 1, Introduction). A risk only remnants of Bulldog Shale are present around Olympic assessment describes and categorises the likelihood and Dam. Figure 12.6 presents a conceptual cross-section of the consequence of an unplanned event. These are presented in Stuart Shelf and the south-westerly extent of the Eromanga Basin. Chapter 26, Hazard and Risk. Arckaringa Basin 12.3 existing environment West of Olympic Dam, the rocks of the Stuart Shelf are overlain by the younger sediments of the Arckaringa Basin, which This section summarises the geology and hydrogeology of the covers an area of around 80,000 km2. The formations of the Olympic Dam region and the wider project area (including the Arckaringa Basin are largely restricted to the subsurface, due to proposed infrastructure corridors; see Figure 12.2). It also the presence of even younger sediments above, such as the describes possible interactions with, and the influence of, Eromanga Basin (see Figure 12.3). neighbouring groundwater flow systems (see also Appendix K1).

342 Olympic Dam Expansion Draft Environmental Impact Statement 2009 Moomba

Lake Eyre Eromanga North Basin

Lake Eyre na Basin than oor B t Faul

No rw es Arckaringa Basin t To underlying the rr en Marree Eromanga Basin s Fa ul To t rre Fa ns ul Hi t ng e Zo OLYMPIC DAM ne Lyndhurst

Andamooka Roxby Downs Lake 12 Frome Stuart Shelf Arrowie Lake Woomera Lake Windabout Basin Torrens Pimba Pernatty To rrens Lagoon Basin Broken Hill To Region

rrens

Lake

MacFarlane Fa

ul

t

Adelaide Port Augusta Geosyncline Gawler Craton

Whyalla Port Pirie

Polda Region

Spencer Stansbury Gulf Basin

River Murray St Vincent Region Kanmantoo Port Lincoln Region Gulf St Vincent ADELAIDE

Existing Olympic Dam Special Mining Lease Existing Roxby Downs Municipality 020406080100 EIS Study Area km

Figure 12.3 Geological provinces and basins of South Australia

Olympic Dam Expansion Draft Environmental Impact Statement 2009 343 p p p p p p p Tm Tm Tm Tm Tm ba p Tm p p Tm p p Tm oom Tm Tm M Tm Tm p km de p 0 ai Tm ta el e Tm p ri Ad gus p Q Pi s Au rt Tm 05 Tm wn rt Po Po Do p p

by Tm Tm 04 Rox p p p Whyalla Tm Tm 03 Tm p Tm 02 p Moomba Tm p 01 Tm 1 p p Qr Tm Te Tm b Q e n Km M- Mm ch ke p Q e1 an La Tm Q Ta Bl w Mm Qa w Ny e1 Tp 2 b Ta Qa Kn Tp Km Q w e1 Ny o Mm Lr Nw p Qa Ta o Km Tp Tm Km 0 Nb Mm M3 p Np e1 owie Nb Nu p 2 Tm Ta pe Tm Kn b 4 Ne rn Km 2 Kn Np p Kn Ny Mu 3 Np Tm e1 e1 Eo e1 Ta Ta e1 e1 Ta 2 Ta Ta Nw 2 o Kn Ne 2 Nw Kn Nb Km 2 Kn Kn o 3 e1 Nu e1 Np p Km Ta Ta Eo e1 6 e1 e1 Ta Tm Nu e1 Nc Ta Ta Ta 2 Nw o e1 e1 Nw Ne Kn Ta Ta Km Nu e1 Ta e1 6 o Q e1 Ta Nu Nc Km c Nw Ta Np e1 b 2 Km Ta b Kn Km Ny e1 7 Km e1 Ta Nu b Qa Ta e1 Tp Km p Nb Ta 1 e1 b 1 Tm p Ta Qr e1 p c Ne Km Qr Q Te Ta Tm Tm Te Nb e1 7 Q Km Nb 7 ee Ta Qa Qa p e1 7 rr Nb Tp Nw Tp Ta b 7 Tm Qa Nb Nb b Q Ma Tp Km Qa Km Tp o Nu Ny p 7 7 Km Nc 2 Tm p Qa Qa b 7 2 Kn Nc 1 Tp Tm Tp Qa Nc Km Kn Qr 7 e1 Tp Te Nb Ta o p Qa Nb Tp 2 Km Tm Q Nb Q b Kn Nc Q 7 Km Nb Qa Ny Nu

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pi o ti ti St dunna Km 20 ge ar da C s ll dog rr Km dn lla coon is is re nt to b Km S o o odna o Km y oor r 3 b p Ga Ex Ex EI Qu Willawo Eta Ey Winton O C Bu Ca Algebu An AB Ar Te Bu Ca Km b le Km Km Km Eo fe icial Tm Km w c p Km 2 o b 4 a 3 -a rf sts Q 3 4 Q Re Qa ae1 Nc b b Nb Nw Ns Kn Kn Eo N JK Tm T Km p Km Km Figure Surficial 12.4 geology of the gas pipeline corridor options Cow c b c b Tp b b Eo * ( Su Kn b Km Km Tm Km Km Km mp Km Km Km Km T

344 Olympic Dam Expansion Draft Environmental Impact Statement 2009 Kmb Nu Nb Nc Ne CP1 TeQr1 Nb TeQr1 Kmb Tmp2 Nu Nsa Nb Moomba Ny Nb TeQr1 CP1 Kmb Tmp2 Nw Nb Tae1 Tmp2 Eo4 Eo3 Kmb TeQr1 Tmp2 Q Kmb TeQr1 Eo3 Nb Nu Nu Ny Eo3 No Kmb Roxby Downs TeQr1 Q Nb CP1 Kmb Kmb Nb Kmb Eo3 Eo3 OLYMPIC DAM Eo3 Eo3 Nb Nb Eo3 Np Kmb Nw Port Augusta Eo3 Kmb JK-a Kmb Ny Eo3 Whyalla AndamookaNsts Eo3 Tmp3 Nsts Nsts Port Pirie Nb Kmb No Nu Kmb TeQr1 Kmb Eo3 Eo3 Roxby Downs Kmb Adelaide Nsts Kmb Eo3 Nw Np Eo3 Nsts Nw Eo3 Q Tmp2 Eo3 Eo3 Q Nw Nw Nw Nsts Np Eo3 Nsa Nsts Kmb Eo3 Kmb Nsts Np Nc6

Tmp2 Kmb Kmb Eo3 Tmp2 Eo3 Eo3 Nw Tae1 Nsts Np Nw Tae1 Kmb Nsts Nw Nw

Nsts Lake Nw Np Torrens Eo3 Nsts Nw

Nw Nw TeQr1 Nsts Nw M-p WoomeraKmb Nw Nw Nsts Nsts TeQr1 12 M-p Kmb Nsts Pimba Nsts Nsts Nw Lake Nsts Kmb Windabout Nw Nw Nsts Q Q Nsts Nw Nsts Nw Nsts M-p Nw Nw Pernatty Island Nw Nw Lagoon Nu Lagoon Nsa M-p Q Nsts M-p Ne Q TeQr1 Nw Nw Nu Nw Eo4 Ne Nw Ne Ne M-p Ne Nsa M-p Ne Eo3 Ne Np Nu Nsts Ne Ne Nw Eo3 M-p Ne Ne TeQr1 Ne Nw Nw Lake Nw M-p M-p TeQr1 Dutton Nsts Np Np Ne Np Landing facility Ne Nsts Ne Nu M-p Ne Nw Desalination plant Nsts Eo3 Lake Ne Nw Ne Np Gas pipeline alignment options Ne Nw Nw Nsa MacFarlane M-p Ne Nsts Eo3 Nw Water pipeline alignment Ny Ma10 Eo3 TeQr1 TeQr1 TeQr1 Np Np Rail alignment Ny Nu Ma10 Nw TeQr1 Nw Nw TranTesmQr1 ission line alignments TeQr1 Q Ny TeQr1 No Nsa Access corridor Ma10 M-p Np Nw Nsts TeQr1 M-p Nu Existing Olympic Dam Special Mining Lease Nu Nb Nsa Nsts Ny Existing Roxby Downs Municipality Nu Nw Ma10 Nc6 TeQr1 EIS Study Area Ma10 Nw Nsa TeQr1 Nw Ma10 Nw Nw Ne Surficial geology (EIS Study Area) Ne Nw Nw Ny Nsa Ny Q Quarternary sediments M-p TeQr1 Nw Port Augusta Nsa Undifferentiated Tertiary sands Ny Ma10 Ly TeQr1 TeQr1 TeQr1 Ne Nsts Ne (DoonbuMarra10 Formation) Ly Q Nu Ny Nb Ll Ma10 Ma10 Lo Ly Nw Tae1 Lhw Ll Ll Eyre Formation Ll TeQr1 Nc Nsts Q Nu Mcc Ly Ll Kmb Nb Ma10Bulldog ShaleTQr1 Mcc TeQr1 Lo Ll TeQr1 Ma10 Nw Nw Nw Lhw TeQr1 Ly Eo4 Nc Nsts Nsa Yarra Wurta ShaleLl Ll Ll Ly Ll Ll Lm Nsa Nsa Nb Ny Eo3 AndaLlmooka Limestone (Hawker Group) Ll Mh No Ll Nb Lhw Li1 M-p Nw Nsa Nsa Lhw TQr1 Li1 Ly ABC Range Quartzite Member Ll Ly Ly Ma10 Nw Lhw Nsts Ll Ll Mh Mh Arcoona Quartzite Member Ll Lm Nu TQr1 Ll Ll Nc9 Ll Li1 Ny Nw Tent Hill Formation/ WilpenaTQr1 Group Li1 Point Nb Ll Ly Ll TeQr1 Lm TQr1 Li1 Lowly Ny Li1Yerelina Subgroup Ld Lm Lo Li1 Lh Ne No Ny (includes Whyalla SaLondstone) Lo Whyalla Lh Lhw Ld Ld Ly Ll Nu Umberatana Group Lm Nsa TeQr1 Ny Lo Ld Li1 Llw Nb Ll Ly Lo M-p PundurLhw ra Formation Upper TeQr1 Lli Ld Spencer Gulf Ma GawlerLl Range volcanics Ld Lhw Li1 No TeQr1 Lo Lm Lhw Port Pirie Lhw * LlRei fer to Geological Map South Australia Lo Ld 010203Nsa 04Nb 050 (Cowley 20Lh01) for further detail Mh Lo Lhw L-m km Li1 Lli Mcc TeQr1 TeQr1 Figure 12.5 Surficial geology of the Special Mining Lease and southern infrastructure corridor

Olympic Dam Expansion Draft Environmental Impact Statement 2009 345 I A HH 2 e

on Lake Z Torrens e I g n A i H s n e Lake Eyre South HH2 r r Lake o

GAB1 T GAB 1 Eyre South 6338-28 Andamooka RD16 Roxby Downs Saddle Hill A km ACD1 40 Olympic Dam 6338-28 Basin extent Great Artesian 20 0 Torrens Hinge Zone Torrens Fault km 20 Hill 10 Olympic Dam Breccia Complex Roxby Downs Granite Approximate groundwater level Saddle Horizontal P P 0 Early – Mid Proterozoic RD 16 Sand Plains Bulldog Shale Cadna-owie Formation Algebuckina Sandstone Shale Yarrawurta Andamooka Limestone Yarloo Shale Yarloo Hill Formation: Tent Arcoona Quartzite Corraberra Sandstone Shale Tregolana Nuccaleena Formation Brachina Formation Burra Group Pandurra Formation Dam Olympic Ja y Kc a Pb P-p Pwr Pwx Qhs Pws Pwc Pwn Kmb Pwm Late Mesozoic Palaeozoic Quaternary Proterozoic ACD 1 A

-300

-400 -500 -600 -100 -200 +100 Depth (m AHD) (m Depth Sea level 0 m AHD Source: Adapted from Geological Survey of South Australia, Andamooka Map Sheet SH53-12 Figure Schematic 12.6 geological cross-section of northern Stuart Shelf and southern Great Artesian Basin

346 Olympic Dam Expansion Draft Environmental Impact Statement 2009 I B I B e

on Lake Z Torrens e g n

Basin extent i Hill Great Artesian

South H s n re r o T Andamooka Stony Range km 0 Saddle Hill 4 Roxby Downs 0 2 Olympic Dam B 0 km 20 Torrens Hinge Zone

10 12 Horizontal 0 Roxby Downs Granite Skillogalee Dolomite Equivalent Sandstone Sequence with dolomite siltstone interbeds Witchelina Quartzite Callanna Beds Quartzite of South Hill and dolomite with stromatolites overlying buff Dolerite Plugs Pandurra Formation 2 1 Hill P Arthur

Pc

Pc Pc P-p Pbk Pbw Late Proterozoic Late Lake Torrens Early – Mid Proterozoic Hill Saddle Pound Quartzite Formation Wonoka Bunyeroo Formation ABC Range Quartzite Brachina Formation Nuccaleena Formation Elatina Formation Amberoon Formation Hill Formation Tapley Shale Tindelpina Sturtian Glacial Unit siltstones, flaggy sandstones Undifferentiated Myrtle Springs Formation Pft Pu Pb Phl Pfa Pfd Pwr Pwp Pwb Pwa Pwn Pbm Pww

Adelaide Geosyncline Late Proterozoic Late Alluvium Sand Plains Bulldog Shale Yarrawurta Shale Yarrawurta Andamooka Limestone Shale Yarloo Hill Formation: Tent Arcoona Quartzite Corraberra Sandstone Shale Tregolana Nuccaleena Formation y a Qhs Pwx Pws Pwc Qha Pwn Kmb Pwm B Shelf Facies

-400 -500 -600 -700 -100 -200 -300 +100 Proterozoic Late Depth (m AHD) (m Depth Sea level 0 m AHD Mesozoic Palaeozoic Quaternary Figure Schematic 12.7 geological cross-section of northern Stuart Shelf and westerly extent of the Adelaide Geosyncline Source: Adapted from Geological Survey of South Australia, Andamooka Map Sheet SH53-12

Olympic Dam Expansion Draft Environmental Impact Statement 2009 347 Torrens Basin Towards the southern limits of the Andamooka Limestone, the 2 The Torrens Basin is an elongated structural depression that is transmissivity decreases considerably (i.e. 4 to 120 m /d), coincident with the Torrens Hinge Zone and bordered on the suggesting that dissolution features, which have been observed west by the Torrens Fault. The basin has been in-filled with in drill samples in the unsaturated portion of the limestone unit, Tertiary-aged sediment to depths of up to 300 m. are absent or rare beneath the natural water table level.

12.3.2 Groundwater flow systems Groundwater salinity typically ranges between 20,000 mg/L and 60,000 mg/L (Golder Associates 1995; Kellett et al. 1999; REM Groundwater in the Olympic Dam region generally occurs in 2007), but the groundwater salinity increases to as much as fractured rocks tens of metres below the surface. It moves very 200,000 mg/L closer to Lake Torrens. This compares with the slowly (<1 m per year) from a west to east direction and salinity of seawater, for example, which is about 36,000 mg/L. ultimately discharges to Lake Torrens, an evaporative sink (Golder Associates 1995; REM 2007). It is estimated that it Tent Hill aquifer would take thousands of years for groundwater at Olympic Dam The Tent Hill aquifer is extensive and forms the most important to reach Lake Torrens. Other groundwater flow systems in the aquifer over the southern portion of the Stuart Shelf, where the region are also present in the rocks of the Eromanga and Andamooka Limestone aquifer is either very thin or absent. Arckaringa basins. It includes the lower parts of the Arcoona Quartzite and the Corraberra Sandstone units of the Tent Hill Formation and is Stuart Shelf therefore sometimes referred to as the Arcoona Quartzite Although the Olympic Dam ore body is located within rocks of aquifer or the Corraberra Sandstone aquifer. The aquifer the Gawler Craton, it is the Stuart Shelf that is important occurrences reduces to the north of the SML due to a deepening hydrogeologically and in relation to activities to be undertaken of the unit and reduction in permeability. as part of the proposed expansion that would affect groundwater. At Olympic Dam, this aquifer typically occurs 160–200 m below There are two important groundwater systems in the Stuart ground level (about –60 m AHD to –100 m AHD). The depth Shelf: the Andamooka Limestone aquifer and the Tent Hill increases moderately to the north, west and south, with the aquifer. The general characteristics of these aquifers and the base of the unit occurring at around 225 m below ground level units that separate them are summarised below (see also (–125 m AHD) near the existing underground mine (see Appendix K1). Figure 12.8 shows a conceptual cross-section of Figure 12.6) and more than 400 m below ground to the north these units as they occur beneath the current operation. of Olympic Dam.

Andamooka Limestone aquifer A high degree of variability is reported for the Tent Hill aquifer Where it is saturated, the Andamooka Limestone is the parameters across the Stuart Shelf. Reported groundwater shallowest of the aquifers in the Stuart Shelf, and forms the yields are highest in the vicinity of the SML and consistent with regional ‘water table’ aquifer to the north of Olympic Dam. the inferred alignment of a major structural zone referred to as It covers an area of approximately 14,500 km2, extending from Mashers Fault (see Figure 12.9). around 50 km south and 80 km north-west of Olympic Dam, to around 35 km north of the top of Lake Torrens. South of Groundwater salinity in the Tent Hill aquifer is generally higher Olympic Dam the base of the Andamooka Limestone becomes than the Andamooka Limestone, with reported concentrations shallower and the aquifer becomes unsaturated (i.e. it does not ranging from about 35,000 mg/L to more than 100,000 mg/L in contain water). the vicinity of Olympic Dam, and ranging to around 200,000 mg/L closer to Lake Torrens. The water table typically occurs about 50 m below ground in the area of the mine (i.e. 50 m Australian Height Datum (AHD) The upper section of the Arcoona Quartzite unit forms an as Olympic Dam is at 100 m AHD). Groundwater in the aquifer aquitard. This is a low permeability layer that acts to restrict moves from the west of the Stuart Shelf to the northern end of the movement of groundwater between the Andamooka Lake Torrens, where the water table typically occurs less than Limestone aquifer and the Tent Hill aquifer. 10 m below ground. Eromanga Basin To the north of Olympic Dam the Andamooka Limestone aquifer The Eromanga Basin, together with the Surat Basin and the has a high secondary porosity and permeability that is Carpentaria Basin, form the Great Artesian Basin (GAB) (see associated with dissolution features. Recent investigations Figure 12.10), which contains one of the largest groundwater undertaken by BHP Billiton during water supply studies show systems in the world. The GAB underlies almost 1.7 million km2 high transmissivity (i.e. 100 to 4,000 m2/d) and groundwater of central and north-eastern Australia. yields from wells drilled in this area (see Appendix K1 for details).

348 Olympic Dam Expansion Draft Environmental Impact Statement 2009 km 2 1 Horizontal 0 wellfield Saltwater Shaft Whenan 12 Indicative mine decline Pre-development groundwater level (1982) Andamooka Limestone groundwater level (late 2005 / early 2006) Potentiometric surface within the Corraberra Sandstone and Arcoona Quartzite (late 2005 / early 2006) Basal Conglomerate aquifer Olympic Dam Breccia Complex (mineralised ore) Roxby Downs Granite basement P P P Metallurgical plant Early – Mid Proterozoic Production bore LP02 Surficial Deposits Andamooka Limestone aquifer Hill Formation: Tent Arcoona Quartzite aquitard Corraberra Sandstone aquifer Shale aquitard Tregolana facility Tailings storage a Qhs Pws Pwc Pwm 50 -50

Sea 100

-100 -150 -200 -250 -300 -350 level Depth (m AHD) (m Depth Palaeozoic Late Proterozoic .8 Schematic hydrostratigraphic cross-section of the Olympic Dam mine site Cainozoic and Mesozoic 2 1 Figure

Olympic Dam Expansion Draft Environmental Impact Statement 2009 349 5 km .2 11 75 0. .5 50 .2 00 t af Sh

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350 Olympic Dam Expansion Draft Environmental Impact Statement 2009 Carpentaria Basin Northern Queensland Territory Eromanga Basin

Surat Basin Artesian extent of the Great Artesian Basin

Moomba Wellfield Wellfield A B Extent of the Great Artesian Basin Coober Pedy lia tra s

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Generalised cross-section of the Great Artesian Basin

Source: Adapted from Natural Resources and Water 2006

050100 150200 250 Source: Geoscience Australia 2006; Habermehl and Lau 1997 km

Figure 12.10 Locality plan of the Great Artesian Basin

Olympic Dam Expansion Draft Environmental Impact Statement 2009 351 In South Australia, there are two types of aquifers associated the artesian GAB aquifers, where they are close to the surface, with the Eromanga Basin – artesian GAB aquifers and non- natural geological structures such as faults provide a path for artesian aquifers – and there is very little, if any, hydraulic groundwater to express at the surface and form GAB springs connection between the two (Kellett et al. 1999), or between (see Chapter 15, Terrestrial Ecology, for further detail of GAB the artesian GAB aquifers and the Stuart Shelf. springs). The nearest GAB spring is around 95 km north of Olympic Dam and is not in hydraulic connection with the Artesian GAB aquifers primary Stuart Shelf groundwater flow aquifers. Artesian aquifers have a ‘potentiometric surface’ that is above ground level. This means the pressure within the aquifer would The salinity of groundwater in the artesian GAB aquifers is low, cause the water to rise above the ground surface if a hole was generally ranging from less than 1,000 mg/L to around drilled into the aquifer (see Plate 12.3). The artesian GAB 2,500 mg/L, providing an important resource for communities aquifers extend from Queensland through northern New South in the Far North of South Australia, as well as for the mining, Wales to the north-eastern section of South Australia (see and oil and gas industries. Olympic Dam currently sources most Figure 12.10). No artesian GAB aquifers occur within 95 km of of its mine and process water from the groundwater resource of Olympic Dam. the artesian GAB aquifers (see Plate 12.4).

The artesian pressures observed in the GAB aquifers are derived Non-artesian Eromanga aquifers primarily from rainfall recharge along the Queensland portion Non-artesian aquifers in the Eromanga Basin do not have of the Great Dividing Range (Habermehl 1980). Near the edge of potentiometric surfaces above ground level and, consequently, do not produce free-flowing wells or natural springs. These are present in a relatively small area to the south and south-west of the artesian GAB aquifers, and typically form shallow water table aquifers that do not support GAB springs. These aquifers are isolated in their extent, are recharged from local rainfall and are not in connection with the primary GAB aquifers.

Arckaringa Basin The Arckaringa Basin occurs around 100 km to the north-west of Olympic Dam (see Figure 12.3). Historically, its groundwater system has not been investigated in detail, probably as a result of the ability to more easily develop groundwater supplies from the shallower non-artesian Eromanga Basin aquifers and the previous absence of mining operations in the area west of Olympic Dam. The Prominent Hill mine is now in this area and sources water from the Arckaringa Basin.

Two main groundwater systems have been identified in Plate 12.3 GAB groundwater pressure the Arckaringa Basin: the Mount Toondina aquifer and the Boorthanna aquifer. The Mount Toondina aquifer is a sub- artesian aquifer that occurs primarily north of the Boorthanna Fault (see Figure 12.3), at relatively shallow depths. Its salinity is variable (but mostly above 5,000 mg/L) and it may have an hydraulic connection to the overlying artesian GAB aquifers. South of the Boorthanna Fault, the Boorthanna Formation is known to form an extensive confined aquifer, with varying salinity (<10,000 mg/L to >30,000 mg/L) and moderate transmissivity.

Infrastructure corridor groundwater systems Gas pipeline corridor options Between Olympic Dam and Lake Torrens, the gas pipeline corridor options traverse the Stuart Shelf geological province (although Eromanga Basin sediments overly the Stuart Shelf in this area), and the groundwater systems are as described above.

Plate 12.4 GAB production bore in Wellfield A

352 Olympic Dam Expansion Draft Environmental Impact Statement 2009 To the north of Lake Torrens, where the Stuart Shelf is not • Recharge occurs to the south from the Arcoona Plateau and present, the occurrence of shallow groundwater is dominated west via through-flow from the Arckaringa Basin. Recharge by the typically artesian GAB aquifers of the Eromanga Basin. also occurs from rainfall over the entire Stuart Shelf, which Some discrete aquifers are also common within the overlying is estimated at 0.1 to 0.2 mm/y (see Appendix K1; Golder Bulldog Shale. Associates 1995; Kellett et al. 1999). • Low hydraulic gradients (which affect how fast and in what In the far north-east section of the gas pipeline corridor direction groundwater moves) occur north of Olympic Dam, options, the Eromanga Basin is overlain by the Lake Eyre Basin. where the regional system is dominated by the Andamooka Shallow groundwater occurs in the Eyre and Namba Formations Limestone aquifer. This is a result of higher aquifer of the Lake Eyre Basin (see Figure 12.4) which ranges from fresh transmissivity. to saline across the project area – typically from around • Lake Torrens has generated high density brines that have 1,000 mg/L to up to 34,000 mg/L. migrated west from the lake to form a high salinity groundwater zone in the base of the Andamooka Limestone The main groundwater discharge zones along the gas pipeline aquifer. corridor options are GAB springs, saline lake systems, such as Lake Eyre and the larger ephemeral watercourses such as • Steep hydraulic gradients occur to the south and west of Cooper Creek. Olympic Dam, suggesting that low permeability, due to a reduction in the Andamooka Limestone aquifer thickness Southern infrastructure corridor and dominance of the Tent Hill aquifer, occurs in these Groundwater occurrence along the infrastructure corridor is areas. mainly characterised by fractured rock aquifer systems similar • Groundwater moves towards the northern end of Lake 12 to those occurring in the Olympic Dam area. Torrens where it discharges via evaporative processes. Some groundwater flow and evaporative discharge also occurs Apart from a small number of water supply development studies along the northern boundary of the Stuart Shelf. for road and rail construction works, there is little information available relating to the groundwater resources along the Great Artesian Basin proposed infrastructure corridors. Some extraction wells have Figure 12.12 presents a conceptual model of the interaction been developed in these areas to supply water for livestock, but between the Stuart Shelf and GAB groundwater systems (also these are small and undocumented. see Appendix K1). Most importantly, Figure 12.12 shows that:

Groundwater can be expected to be of poor quality, being • the artesian GAB aquifers are separated by geological and saline (more than 10,000 mg/L), to hypersaline (more than structural controls associated with the low permeability 100,000 mg/L), especially in the deeper fractured rock aquifers. rocks of the Adelaide Geosyncline and Torrens Hinge Zone However, fresh to brackish groundwater has been recorded • groundwater discharges at the edge of each groundwater where localised recharge takes place, for example along system, via evaporation, and does not flow laterally creek lines. between systems • GAB springs are supported by groundwater flow from the 12.3.3 regional groundwater interactions artesian GAB aquifers to the north-east and are not Stuart Shelf supported by groundwater flow from the Stuart Shelf. Groundwater level data from recent surveys and drilling investigations (see Figure 12.11) have been used to interpret The conceptual model is also supported by hydrogeochemical groundwater flow paths across the Stuart Shelf. The data and isotope data, which show that the composition of suggest that there is no interaction between the artesian GAB groundwater sampled from the GAB aquifers is significantly aquifers and the primary Stuart Shelf groundwater flow systems different to groundwater from the Stuart Shelf (see Appendix (Andamooka Limestone and Tent Hill aquifers). The data also K1 for details), and the outputs of the numerical groundwater suggest that interactions occur between the Stuart Shelf flow model (see Appendix K6). groundwater systems and those of the Arckaringa Basin and Adelaide Geosyncline. These interactions form a regional 12.3.4 Groundwater quality and beneficial use groundwater system. Groundwater was sampled from wells across the Stuart Shelf and the southern infrastructure corridor to determine baseline The main characteristics of the regional groundwater flow groundwater quality and whether it may have a beneficial use. systems are as follows: A summary of results and sampling locations is shown in • Olympic Dam lies at the southern edge of the regional Figure 12.13, with further details provided in Appendix K3. groundwater system. • The groundwater catchment extends south of Woomera and west into the Arckaringa Basin. It is bounded to the north by the Adelaide Geosyncline rocks and to the east by Lake Torrens.

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354 Olympic Dam Expansion Draft Environmental Impact Statement 2009 I

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Lake Eyre South n re r Lake I o T A Eyre South Andamooka A Roxby Downs Great Artesian Basin km Olympic Dam 40 20 0 GAB Spring 12 Adelaide Geosyncline Torrens Hinge Zone Torrens Bulldog Shale Cadna-owie Formation / Algebuckina Sandstone Shale Yarrawurta Andamooka Limestone Yarloo Shale Yarloo Arcoona Quartzite Corraberra Sandstone Brachina Formation Burra Group y a Pb Pwr Pwx Pws Pwc Kmb Klc/Ja Late Mesozoic Palaeozoic Proterozoic Torrens Fault Torrens Lake Torrens Stuart Shelf Seepage and evaporation losses Groundwater flow direction Groundwater level (water table) Confined pressure head Brine A Figure 12.12 ConceptualFigure 12.12 model illustrating the separation between the Stuart Shelf and Great Artesian Basin Source: Adapted from Geological Survey of South Australia, Andamooka Map Sheet SH53-12 and Curdimurka SH53-8

Olympic Dam Expansion Draft Environmental Impact Statement 2009 355 Moomba See inset

OLYMPIC DAM

Roxby Downs

Andamooka Port Augusta Whyalla Roxby Downs Port Pirie Lake Torrens

Adelaide WB4 LR11 Purple Downs LR10

QR01 LR08 WB7 LR02

Paradise Well LR01 QR02

LR04 QT02 Woomera MW4 Lake Windabout GW104 Pimba QT04

QR3 Wirrapa Dam Well Island Pernatty LR3 Lagoon Lagoon

Bellamy Well LR6

WB4 Dog Hollow Well Inset Purple Downs

Warkanna Well

Uro’s Bluff Bore

643300050

John Wayne Port 643300509 Augusta Weg Rock MB15

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Baseline groundwater quality survey Comet Bore Existing Olympic Dam Special Mining Lease Existing Roxby Downs Municipality EIS Study Area Sampled heavy metal concentrations in Point excess of the following SA EPA EPP Whyalla Lowly (Water Quality) 2003 guideline and NHMRC drinking water guidelines 2004: Potable use Port Irrigation Pirie Livestock Drinking water (health) 01020304050 km

Figure 12.13 Water quality survey showing groundwater guideline exceedances

356 Olympic Dam Expansion Draft Environmental Impact Statement 2009 As mentioned above, most of the groundwater across the Stuart Shelf ranges from saline to hypersaline (greater than 10,000 mg/L and 100,000 mg/L, respectively). Based on guidelines of the Australian and New Zealand Environment and Conservation Council (ANZECC/ARMCANZ 2000), and the South Australian Environment Protection (Water Quality) Policy 2003 (SA EPA 2003), most groundwater does not meet the criteria for freshwater aquatic ecosystems, drinking water, stock water or recreational use. Some groundwater suitable for stock use (less than 5,000 mg/L) was identified along the southern infrastructure corridor and is likely to be associated with localised recharge and limited in extent.

Background metal concentrations in both the Andamooka Limestone and Corraberra Sandstone are relatively low, although concentrations can exceed one or more water quality criteria. Specifically, in terms of uranium, groundwater concentrations are typically between 0.01 and 0.03 mg/L. The South Australian potable water quality criterion for uranium is 0.02 mg/L (SA EPA 2003). 12 12.3.5 Groundwater users Stuart Shelf Even though the salinity of groundwater in the project area is generally high, the absence of permanent surface water and the sporadic nature of rainfall means that, although limited, most pastoral stations use groundwater to some degree.

A survey undertaken for the Draft EIS identified 14 groundwater wells that are currently in use within a 60 km radius of the existing Olympic Dam (see Figure 12.11 and Plates 12.5 and 12.6). Of these, seven are located on pastoral leases held by BHP Billiton (Andamooka, Purple Downs and Roxby Downs), Plate 12.5 Southern Cross Well at Parakylia Station four are located on Parakylia Station and three are located on Parakylia South Station.

Local groundwater is not currently used in Andamooka Township (G Murray, President Andamooka Progress and Opal Miners Association, pers. comm., 2006). Water is now piped to Andamooka from the desalination plant at Olympic Dam, which is supplied by water from the GAB.

Gas pipeline corridor options Several pastoral stations along the gas pipeline corridor options rely on groundwater from the artesian GAB or Lake Eyre aquifers to meet some or all of their stock and domestic water needs. Although the active use of groundwater wells could not be confirmed, government database records indicate that more than 100 potentially operational wells are located in the vicinity of the corridors. The majority of these wells are constructed to abstract water from depths greater than 20 m, with salinities likely to be less than 10,000 mg/L (see Appendix K1 for details).

Plate 12.6 Groundwater well with pump on Arcoona Station

Olympic Dam Expansion Draft Environmental Impact Statement 2009 357 Southern infrastructure corridor 12.4.1 existing operation About 80 wells or water points are located on pastoral stations Dewatering along the southern infrastructure corridor. Some of these wells Groundwater from the underground workings drains into, and is are used for stock water. It is not known whether the wells are collected from, 28 raise bores (ventilation shafts) that have used for domestic supply, although the groundwater quality been developed from the surface to the ore body, and penetrate would suggest that if this does occur, pre-treatment would be both the Andamooka Limestone aquifer and the Tent Hill required. Groundwater salinities from these wells range from aquifer. Water collected from the raise bores is pumped to the less than 5,000 mg/L to more than 50,000 mg/L, and the depths surface and used in the mine process. Historically, groundwater to groundwater in sampled wells range from 0.5 m below has been extracted from the raise bores (referred to as ‘mine ground level, near Port Augusta, to about 50 m below ground dewatering’) at rates between 1.3–2.1 ML/d. level near Roxby Downs (see Appendices K2 and K3 for details). Drawdown of groundwater (i.e. a ‘cone of depression’) has 12.3.6 Groundwater dependent ecosystems occurred in the Tent Hill aquifer as a consequence of the mine A number of hypersaline springs and seeps are located around dewatering (see Figure 12.8), and extends up to 10 km to the Lake Torrens. Only one of these, the Yarra Wurta spring group, north and east of the mine and around 5 km to the south-west. is known to have an ecosystem with an obligate dependence on The decline in groundwater levels has been variable (up to groundwater. Yarra Wurta spring is located on the northern 100 m), depending on proximity to the underground mine limit of the Torrens Hinge Zone and is underlaid by the Adelaide decline, ventilation shafts and raise bores, but has approached Geosyncline rocks and the Andamooka Limestone. The a steady state condition. ecological significance of Yarra Wurta spring has been assessed and findings are presented in Chapter 15, Terrestrial Ecology. Water supply A saline wellfield comprising four production wells established A number of freshwater swamps and terminal drainage features in the Tent Hill aquifer in the late 1990s (see Figure 12.9) to occur on the Stuart Shelf. The closest, Coorlay Lagoon, located provide the existing operation with water for dust suppression approximately 25 km south of Olympic Dam, is a final drainage and other low-end uses. Extraction of groundwater has point for a number of watercourses that drain the Arcoona historically ranged from almost zero to 1.1 ML/d with an Plateau. The water table at this location occurs within the average of around 0.2 ML/d. Drawdown of up to 40 m has been Arcoona aquitard and is very close to the surface. Given that observed in the Tent Hill aquifer in the vicinity of the wellfield. the salinity of groundwater in this area is typically greater than 50,000 mg/L, it is unlikely that any vegetation is reliant Tailings and water storages upon groundwater. Seepage from the TSF and mine water evaporation ponds (MWEP) have formed a mound within the Andamooka Limestone A stygofauna assessment was carried out for the Draft EIS and aquifer. The mound had risen about 20 m above the historic results are presented in Chapter 15, Terrestrial Ecology. water table to approximately 30 m beneath the ground surface (about 70 m AHD) by 1998 and is mostly attributed to early 12.4 Groundwater-affecting activities tailings deposition and leakage from the old MWEP. Groundwater-affecting activities are those components of the Subsequently, a dedicated production well (LP02) was installed mining and processing operation that have the potential to alter to recover water from the mound beneath the TSF for reuse groundwater systems on a local or regional scale. These usually within the metallurgical plant. The MWEP was decommissioned include extracting groundwater for mine dewatering or water in 2001 and a new MWEP was established to the north-east of supply, and seepage from above-ground sources such as the mine. The seepage rate from the TSF is currently estimated tailings and water storages. at between 0.5 and 1.5 ML/y and the mound is currently around 35 m beneath the ground surface. This section describes the groundwater-affecting activities of the existing operation and the proposed expansion. It also Seepage from the base of the TSF moves downward through the summarises the current response to groundwater beneath the underlying sediments and the unsaturated zone of the SML from the existing operation, which is monitored by a Andamooka Limestone, where it undergoes a natural process of dedicated network of more than 80 wells and reported annually in situ neutralisation during which the pH increases to near to DWLBC, Environment Protection Authority (SA EPA), and the neutral values. As a result of the reactions that occur, the Department of Primary Industries and Resources (PIRSA). The concentration of heavy metals in the TSF liquor is greatly predicted response to groundwater from the proposed reduced by the time it reaches the groundwater. For example, expansion is presented in Section 12.6. the concentration of uranium in tailings water is up to 180 mg/L, but groundwater monitoring shows that the concentration of uranium in seepage reaching the groundwater is less than 1 mg/L.

358 Olympic Dam Expansion Draft Environmental Impact Statement 2009 Groundwater monitoring data show that local groundwater The Andamooka Limestone aquifer is mainly dewatered in the chemistry in the Andamooka Limestone aquifer around the vicinity of the open pit due to current operation. The Tent Hill TSF is similar to the regional groundwater chemistry, with the production wells would also be screened across this aquifer and exception of slightly elevated uranium concentrations and capture residual groundwater. The low permeability rocks slightly decreased pH. The average concentration of uranium underlying the Tent Hill aquifer would be depressurised through in the groundwater beneath the TSF is around 0.09 mg/L, the use of sumps in the base of the pit and horizontal drain compared to an average background concentration of holes in the pit walls. around 0.03 mg/L. Water supply The downward movement of water from the Andamooka The proposed coastal desalination plant would supply primary Limestone aquifer to the deeper Tent Hill aquifer is restricted potable and process water. Additional sources of water would by the Arcoona aquitard. However, water level monitoring be needed during the construction phase for activities such as results across the SML indicate that some ‘leakage’ through dust suppression. This demand would be met by using the the overlying aquitard occurs in areas of increased drawdown groundwater from the depressurisation activities and extracting and mounding. groundwater from local saline aquifers.

12.4.2 proposed expansion The primary supply of saline water would be sourced from the Changes associated with the proposed expansion, particularly ‘Motherwell’ saline wellfield in the Andamooka Limestone those relating to the mining method and scale, would alter the aquifer, approximately 30 km north of Olympic Dam (see groundwater-affecting activities in the following ways: Chapter 5, Description of the Proposed Expansion, Figure 5.25). 12 • A new open pit would operate and would require dewatering Extraction rates are estimated to range between 15 and 28 ML/d. and depressurisation to control potential inflows of groundwater to the pit and to reduce residual pore pressures Smaller ‘satellite’ wellfields would be located in the vicinity of behind the pit walls. Dewatering and depressurisation of the the TSF, mine maintenance industrial area, Roxby Downs and open pit would result in more groundwater being removed the proposed airport, and would extract water from the Tent from the local aquifers than currently occurs from Hill aquifer (see Chapter 5, Figure 5.26). It is expected that groundwater discharge into the underground workings. these wellfields would provide a total of around 7–10 ML/d of saline water. • New saline water supply wellfields would be constructed to extract water from the local saline aquifers. Open pit • Unlike the underground mine post closure, the completed After mining finished and dewatering operations stopped, open pit would become a long-term, regional groundwater groundwater would begin to seep into the pit. Due to the high sink affecting the direction of groundwater flow and evaporation rates, much of the groundwater would evaporate regional groundwater levels. from the pit walls. However, some may reach and accumulate at • The design, construction and size of the tailings storage the base (see Chapter 11, Surface Water, for detail of pit lake facility would be different from the existing TSF and would formation). Given the relatively low groundwater inflow rates result in a change in the rate and area of seepage. (around 3.5 ML/d) compared to the evaporation, the height of • A rock storage facility (RSF) would be constructed. This the pit lake would not reach the level of the Tent Hill or could facilitate higher local recharge beneath the RSF by Andamooka Limestone aquifers and water would continue to increasing the amount of rainfall that reaches the underlying flow into the pit. As a result, the pit would become a aquifers. permanent groundwater sink.

To provide context and describe their relevance to the impact Tailings storage facility assessment, the groundwater-affecting activities are described Process tailings from the existing and expanded metallurgical in more detail below. plants would be disposed of in a new tailings storage facility (TSF). Although improvements to the design and construction Dewatering and depressurisation of the TSF would reduce the rate of seepage per unit area, Prior to commencing mining it would be necessary to remove seepage would occur over a greater area due to the increased groundwater from the overburden (including the Andamooka scale of the facility, and the total seepage rate will be higher Limestone and Tent Hill aquifers) and the ore body to ensure dry than for the existing TSF. Seepage from the new TSF would and safe mining conditions. Removal of water from the rock probably contribute to the lateral and vertical extent of the material surrounding the pit increases pit slope stability and is existing groundwater mound and would affect the local referred to as depressurisation. Up to 30 production wells groundwater chemistry. would be installed into the Tent Hill aquifer (see Chapter 5, Description of the Proposed Expansion, Figure 5.12 for the proposed layout). Initially, groundwater extraction is expected to be around 15 ML/d but would reduce rapidly to around 8 ML/d within one year, and 5 ML/d within five years.

Olympic Dam Expansion Draft Environmental Impact Statement 2009 359 Rock storage facility • Constructing internal curtain drains and toe drains around For the natural undisturbed regional area it is estimated that the perimeter of the TSF to prevent lateral escape of less than 0.2% of the average annual rainfall, or around 0.1 to seepage and surface expression. 0.2 mm/y, actually travels down through the soil profile and • Capping the TSF at closure to reduce the infiltration of enters the groundwater. This is due to surface ponding and surface water. Eventually the TSF would drain completely evaporation, and storage in the few metres of the soil profile, and seepage would decrease to very low levels controlled where it is available for plant uptake and evaporation before it by natural infiltration of rainwater through the TSF capping moves downward. material.

Mine rock stored in the RSF is essentially dry and therefore has The greatest effect of the RSF on groundwater is the infiltration no inherent ability to release water. However, due to blasting of incident rainfall through the RSF to the base of the facility, and fracturing of the mine rock, its porosity and permeability resulting in a localised increase in groundwater recharge. Water increase and water may flow more rapidly through it than stored or moving through the RSF would contact mine rock and through the natural soils. As a result it is possible that more its metals concentrations would increase. The main design rainfall may reach the base of the RSF. When the water is in the controls in place to address this are: soil profile beneath the RSF it would not evaporate, but instead • minimise rainfall infiltration by traffic compaction on all would continue to move down the profile, eventually reaching surfaces except the ultimate inner and outer RSF slopes the groundwater and increasing the natural recharge. Water leaving the base of the RSF could also affect local groundwater • surround all reactive rock in the RSF with benign and/or chemistry through contact with mine rock. neutralising material • place a layer of benign and/or neutralising materials (overburden) at the base of the RSF to increase the potential 12.5 design modifications to protect for neutralisation and natural attenuation of seepage fluid. environmental values 12.5.1 environmental values Additional mitigation measures and standard controls to avoid The main environmental values of the project area in relation or reduce impacts on groundwater are presented in to groundwater are (see Section 12.3): Section 12.6. • groundwater systems of the Stuart Shelf • neighbouring groundwater systems of the GAB and 12.6 Impact assessment and management Arckaringa Basin 12.6.1 changes to groundwater levels • users of the identified groundwater resources A regional numerical groundwater model was constructed to • ecosystems in the Stuart Shelf that are dependent on predict the changes in groundwater levels across the Stuart groundwater for their survival. Shelf during construction, operation and post closure. The model predicts the area over which groundwater levels are 12.5.2 major elements of the project design changed from their natural state. This is referred to as the extent of groundwater drawdown or the zone of influence. The main components of the project design that influence the For the purpose of this assessment, the extent of groundwater assessment and management of groundwater resources (see drawdown is defined by the 1 m vertical drawdown contour, Chapter 5, Description of the Proposed Expansion, for the full which is considered the limit of accuracy given the regional description of the project components) are discussed below. scale of the model and the timeframe of model predictions.

The risk-based design of the TSF considers a range of issues, The groundwater model shows that dewatering and including safety, effective use of mine rock, effective depressurisation of the open pit and extraction of groundwater containment and stability of tailings, and control and for construction water supply would result in an overall loss of minimisation of seepage. The main controls that have been groundwater from the system and drawdown in the Andamooka incorporated into the design of the TSF to address seepage are Limestone and Tent Hill aquifers. Changes to groundwater levels (see also Chapter 5, Section 5.5.6): on a regional basis would mostly occur post closure due to flow • Thickening the tailings from their current solids of groundwater into the pit and subsequent evaporative losses. concentration of about 47% to 52–55%. This would reduce Results of the groundwater modelling are summarised below the amount of free liquor and the driving head to downward and further detailed in Appendix K6. movement of liquor. Thickened tailings also increase the consolidation of tailings and make them less permeable. • Constructing a liner (1.5 mm high density polyethylene (HDPE)) and underdrainage beneath and around the central decant pond area to collect seepage that can then be reused and recycled.

360 Olympic Dam Expansion Draft Environmental Impact Statement 2009 Tent Hill aquifer start to dominate and the mound under the TSF would be The average extraction of groundwater from the Tent Hill underdrawn and disappear. aquifer is expected to range from around 12 ML/d, including depressurisation and water supply, during early mining to It is important to note that although formation of a around 3.5 ML/d post closure. At the end of the construction groundwater mound beneath the TSF would affect groundwater period (scheduled for 2017), localised vertical drawdown is levels for up to 6 km, transport of solutes in the seepage from expected around the satellite wellfields and the open pit the TSF would not extend that far. It is unlikely that solutes (see Figure 12.14). would travel more than a few hundred metres from the edge of the TSF due to the very low rates of groundwater flow. No Groundwater drawdown is initially driven from the dewatering groundwater mound is expected to form beneath the RSF due to and satellite wellfields during the construction phase but is the very low rates of seepage (see Section 12.6.2 for further gradually overridden by the effects of groundwater flow to the discussion about seepage from the TSF and RSF). open pit. At the modelled 40-year mine life, the zone of influence is expected to have stabilised north of Olympic Dam Although the groundwater mound would recede and then but would continue to develop to the south over the very long disappear post closure, the residual impact is categorised as term. The final zone of influence (500 years post closure) is moderate as it represents a long-term impact to a common expected to be around 20 km north and up to 45 km south of receiver. Olympic Dam (see Figure 12.14). The residual impact is categorised as moderate as it represents a long-term impact to Groundwater flow to the open pit a common receiver. As mentioned above, groundwater flow into the open pit would be very low during mine operations because of the effects of 12 Andamooka Limestone aquifer mine dewatering and depressurisation. Inflow into the pit is expected to reach a maximum of 1 ML/d after around 15 years The groundwater levels in the Andamooka Limestone aquifer of mining due to the influence of the groundwater mound that would change because of removal of groundwater from the would have formed beneath the TSF. Motherwell wellfield, addition of seepage from above ground sources and groundwater flow towards the pit. Post closure, groundwater from the Andamooka Limestone aquifer would not flow directly to the pit; instead, it would Saline water supply preferentially flow downwards through the Arcoona aquitard to Groundwater extraction from the Motherwell saline wellfield the Tent Hill aquifer, from where it would then flow to the pit. during the construction period is expected to peak at around 28 ML/d and would result in groundwater drawdown. The Groundwater drawdown of up to 10 m below pre-mining levels predicted zone of influence (as defined by the 1 m drawdown is expected in the Andamooka Limestone beneath the SML, post contour) is shown on Figure 12.15. By the end of the assessed closure. The zone of influence in this aquifer is expected to mining operation (i.e. Year 40), groundwater levels in this area extend up to 5 km north of the expanded SML and up to 20 km would have recovered to pre-mine conditions (see Figure 12.15). to the south-west (see Figure 12.15 and Table 12.1). The residual impact of operating the saline wellfields is categorised as low as it represents a short-term impact to a Regional groundwater interactions common receiver. Changes in groundwater levels across the regional groundwater Seepage flow system are most obvious south of Olympic Dam. This is Seepage from the TSF would cause a groundwater mound to because groundwater flowing from the Arckaringa Basin to the form beneath the facility. The mound is expected to rise to a Andamooka Limestone aquifer (across the northern part of maximum of 14 m above existing water levels (around 35 m the Stuart Shelf) dominates the Stuart Shelf groundwater below ground) during the first 10 years of mining and then system and limits the impacts between Olympic Dam and gradually subside as seepage rates decrease. Post closure, the groundwater systems to the north. The residual impact as a influence of the open pit as a regional drawdown sink would result of regional groundwater drawdown is categorised as moderate as it represents a long-term impact on a common receiver and not a direct impact to a receptor.

Table 12.1 Predicted effects in the Andamooka Limestone aquifer

Groundwater-affecting Groundwater extraction Zone of influence Comment activity (or addition1) Saline water supply Up to 28 ML/d <2 km from wellfield Wellfield operational during construction period only Seepage from TSF 3.2 ML/d (see Section 12.6.2) Up to 6 km from TSF Height of mound continues to decrease after 2020 Flow toward pit Up to 1 ML/d 5 km north Post closure effect overprints (dominates) all 20 km south-west influence from the TSF and wellfield

1 Seepage from the TSF results in addition of water to the system.

Olympic Dam Expansion Draft Environmental Impact Statement 2009 361 Yarra Wurta spring

Old Homestead Well North Dam Bore Southern Cross Well Comet Well New Parakylia Bore Andamooka

20 10 10 1 20 Roxby Downs

Sister Well 2

Alex’s Bore 2 Bambridge Well Coorlay Lagoon Knoll Well 2 Purple Swamp 1 0510 15 20 25 No. 1 Well km

Year 2017

30

10 20

1

Year 2050

Wells in use within 60 km radius of Olympic Dam BHP Billiton well Third party well Drawdown (m) 1 20 40 30 50 30 60 80 20 90 110 10 120 140 Expanded Special Mining Lease 1 Existing Olympic Dam Special Mining Lease EIS Study Area

Year 2550

Figure 12.14 Predicted drawdown in the Tent Hill aquifer

362 Olympic Dam Expansion Draft Environmental Impact Statement 2009 Yarra Wurta spring

1

Old Homestead Well Southern Cross Well North Dam Bore Comet Well 3 New Parakylia Bore

1 2 Andamooka

Roxby Downs

Sister Well 2 Alex’s Bore 2 Bambridge Well Coorlay Lagoon Knoll Well 2 Purple Swamp 1 0510 15 20 25 No. 1 Well km Year 2017 12

2 3 1

Year 2050

Wells in use within 60 km radius of Olympic Dam BHP Billiton well Third party well Mounding (m) 14 0 Drawdown (m) 0 10 10 20 4 5 6 7 2 3 Saturated extent of the 1 Andamooka Limestone aquifer Motherwell Wellfield Expanded Special Mining Lease Existing Olympic Dam Special Mining Lease EIS Study Area

Year 2550

Figure 12.15 Predicted drawdown and mounding in the Andamooka Limestone aquifer

Olympic Dam Expansion Draft Environmental Impact Statement 2009 363 The groundwater model predicts no change in flow (and no groundwater flow, the location of potential receptors in relation residual impact) to the northern boundary between the Stuart to groundwater movement, and the sensitivity of receptors to Shelf and the GAB, even under the upper limits of sensitivity changes in water quality. analysis (see Appendix K6 for sensitivity analysis). The detailed design of the RSF and TSF, including the methods The model also shows that groundwater response to activities at proposed to minimise seepage and the characterisation of mine Olympic Dam is due to removing groundwater already stored rock and tailings (i.e. operational inputs), are provided in within the aquifers of the Stuart Shelf rather than drawing more Chapter 5, Description of the Proposed Expansion, Sections 5.4.6 water from other groundwater systems (i.e. Arckaringa Basin). and 5.5.6, and are detailed in Appendices F1 and K5. This results in very little effect (<2%) on the amount of water flowing into the Stuart Shelf from the Arckaringa Basin. Table 12.2 Seepage rates summarises the predicted changes in inflow and outflow Tailings storage facility at the boundaries of the Stuart Shelf groundwater system. Flow modelling was carried out to predict seepage rates from the proposed TSF (see Table 12.3). The assumptions for the 12.6.2 Groundwater quality model were based on measured and interpreted rates from As well as changing groundwater levels (as discussed in Section the current facility and a comparison of the surface water 12.6.1), seepage from above ground sources such as the TSF balance for the existing and new facilities. The modelling and RSF may contain elevated concentrations of metals and indicated that (see Appendix F1 for detail): increased acidity and therefore could change the chemical • The water balance for the new cells is similar to that of the properties (or water quality) of the groundwater beneath them. existing TSF Cell 4. Because of the higher solids content (thickening) of the future tailings, less free liquor would The rate of seepage, extent of change and the final occur on the surface of the tailings, resulting in less seepage groundwater quality would depend on the design and operation per unit area. of the facility, the properties of the tailings and mine rock, the • Initially, the seepage rate from each cell would be around interaction of seepage with the sediments beneath the 4 m3/ha/d. This would decrease over the first two years as respective facilities, and closure management. the tailings consolidated and formed a layer with very low permeability. Steady state seepage from each cell during When seepage has reached the groundwater table, the operations would be around 0.88 m3/ha/d. potential for environmental impact would depend on continued chemical reactions within the aquifer, the direction of

Table 12.2 Maximum predicted change in groundwater inflow and outflow across the Stuart Shelf

Pre-mining (kL/d) Post closure (kL/d) Change (kL/d) Inflow to the Stuart Shelf from the Arckaringa Basin 3,060 3,000 601 Outflow from the northern boundary of the Stuart Shelf (adjacent 43 43 0 GAB) due to evaporative loss Outflow from the Stuart Shelf to the northern end of Lake Torrens 5,250 5,050 2002 due to evaporative loss

1 Predicted at 500 years post closure. 2 Predicted at mine closure and 100 years post closure.

Table 12.3 Predicted rates of seepage from the TSF

Indicative time frame Activity Total seepage area Seepage per hectare Total seepage (ha) (m3/ha/d) (ML/d) Years 1–5 Commissioning and operation of cell 1 400 4.0 1.6 Years 5–10 Seepage rate increases as more cells are 1,200–3,200 1.9–3.2 3.6–7.8 commissioned Maximum seepage rate reached as last cell is 3,600 2.3 8.2 commissioned Years 12–40 Seepage reaches operational steady state 3,600 0.88 3.2 Year 40 (closure) TSF is decommissioned and capped 3,600 <0.88 <3.2 Seepage begins to decrease as no more tailings are added to the facility Post closure Tailings drain down over time and eventually 3,600 Trending to Trending to reach steady state background background

364 Olympic Dam Expansion Draft Environmental Impact Statement 2009 • Post closure, seepage from the TSF would be significantly • Results from geotechnical testing within the footprint of the reduced as the tailings pond was removed, the facility proposed TSF indicate that layers of sands, clays and covered, and the tailings drained. In the long term, recharge calcareous soils of varying thickness would underlie the rates would approach the natural regional rate that occurs proposed TSF. Geochemical testing indicated that of these, due to rainfall infiltration. the calcareous clays would have the highest acid neutralising capacity (ANC) and would neutralise acidic Rock storage facility seepage from the tailings most effectively. Blasting would cause the porosity and permeability of the mine • Geochemical testing showed that the Andamooka Limestone rock placed in the RSF to be greater than that of the natural Formation is dolomitic in this location and has a high ANC. undisturbed terrain. Because of this, the rainfall recharge Within the unsaturated zone it may be possible that secondary across the RSF footprint would increase due to preferential flow minerals could form that may ‘blind’ the rock, making it paths in the rock. Seepage from the RSF would be expected unavailable for further reaction with the seepage fluid. to be around 1% of annual rainfall, or around 0.3 ML/d • The seepage beneath the TSF is being naturally ‘treated’ 3 (<0.05 m /ha/d). through neutralisation by the carbonate materials as well as sorption and precipitation of secondary minerals. This leads The proposed construction of the RSF would result in the to improved water quality through natural attenuation of surface of each bench being continually compacted by the earth contaminants before they reach the groundwater system. moving equipment. This would help to minimise rainfall Although most contaminants are removed by these infiltration and promote surface water run-off, ponding and processes, selenium and uranium (albeit much reduced from evaporation (see Chapter 5, Description of the Proposed the concentrations in the tailings percolate) remain elevated 12 Expansion, Figure 5.16). above background levels. In situ reactions of the seepage with the carbonate minerals in the soils, clays and the Seepage quality Andamooka Limestone also lead to bicarbonate Materials such as mine rock and tailings have unique concentrations exceeding background levels. geochemical properties that affect their behaviour when they • There is a possibility that the clays could become less are exposed to the atmosphere and are subjected to permeable over time due to the accumulation of secondary weathering. As a result, these materials could release metals, minerals, decreasing the overall ability of the calcareous acid, soluble salts or radioactive compounds to water that clays to neutralise the acidity immediately below the TSF. percolates through them. However, the characteristics of The reduced permeability could also lead to changes in flow seepage that reaches the groundwater are not necessarily the path directions. However, changes to flow direction would same as that which leaves the base of the storage facility. bring the percolate into contact with ‘fresh’ clays and The seepage travels through various sediments and rock layers, would promote further neutralisation. which may be acid neutralising, cause metals to precipitate as • In the longer term, existing dissolution features in the secondary minerals, or to sorb to reactive surfaces. These Andamooka Limestone are likely to be locally enhanced by processes are referred to as natural attenuation. The the neutralising reactions and may lead to marginal increases geochemical properties of the soil and rock materials will in horizontal and vertical permeability. Like the calcareous determine how they react with the seepage, and ultimately the clays, these effects would expose fresh reaction surfaces quality of flows entering the groundwater. within the limestone and neutralisation would continue. • The water quality monitoring results for the existing Geochemical investigations were undertaken for the materials groundwater mound have been used to infer the water to be placed in the TSF and the RSF. Details are presented in quality of seepage reaching the groundwater beneath the Appendix K4 and K5 and are summarised below. existing TSF (see Table 12.4). Tailings storage facility As the geochemical properties of the future tailings are not Rock storage facility expected to differ significantly from those of the current Geochemical test work was undertaken on various Olympic Dam tailings, geochemical processes within and beneath the rock types to characterise them into classes based on their proposed TSF are expected to be similar to those within and potential for acid and/or metal generation. This was used in the beneath the existing facility (as established through data from design of the RSF, particularly the selective placement of geological logs). As such, the geochemical observations for the different rock types within the facility (see Chapter 5, existing TSF have been used to predict future conditions. Description of the Proposed Expansion, Table 5.12). The Results of the geochemical assessment are summarised below description of mine rock types and volumes generated over time and detailed in Appendix K4: are shown in Table 12.5 and Figure 12.16. • Some secondary minerals may form within the tailings and may keep some of the acidity within the tailings. However, seepage from the base of the TSF would remain acidic and be characterised by elevated solute concentrations similar to that of the decant liquor.

Olympic Dam Expansion Draft Environmental Impact Statement 2009 365 Table 12.4 Inferred changes to water quality parameters in the seepage mound based on comparison of current groundwater monitoring results with background concentrations

Parameter Background concentration (mg/L) TSF mound concentration (mg/L) pH (no units) 7.1 6.8

HCO3 188 553 Total dissolved solids 22,000 27,950 Calcium 893 954 Chloride 11,202 12,155 Potassium 44 55 Magnesium 614 1,010 Sodium 5,790 7,660 Sulphate 3,575 5,100 Uranium 0.027 0.088 Silver 0.0008 0.0008 Aluminium 0.05 0.03 Arsenic 0.003 0.005 Boron 3.8 6.8 Barium 0.029 0.013 Cadmium 1 1 Cobalt 0.004 0.007 Chromium 0.003 0.003 Copper 0.019 0.034 Iron 0.43 0.19 Mercury 0.2 0.1 Manganese 0.74 0.52 Nickel 0.015 0.014 Lead 0.003 0.004 Selenium 0.01 0.05 Zinc 0.033 0.042

Table 12.5 Geochemical classifications of Olympic Dam mine rock types

Class Geological unit Geochemistry A Low-grade ore (ODBC) Material with moderate metals mobilisation potential and negligible acid neutralising capacity B Basement (ODBC) Material with low to moderate metals mobilisation potential and negligible acid neutralising capacity C Overburden (Tregolana Shale, Arcoona Quartzite Red, Material with low metals mobilisation potential Arcoona Quartzite White, Arcoona Quartzite Transition, Corraberra Sandstone) D Overburden (Andamooka limestones, dolomite, Material for which the neutralising potential greatly calcareous clays) exceeds metals mobilisation potential

Geochemical test work was undertaken to characterise Overall, the mine rock in the RSF would be net acid consuming; potential seepage quality from the RSF (see Appendix K5 for therefore seepage is expected to be neutral, not acidic. Zones further detail). The assessment of seepage quality considers the of acidity could form, however, particularly when water geochemical processes within the RSF and the interactions with infiltrating the RSF comes into contact with reactive rock the underlying soils. (i.e. class A and B). To address this, mine rock would be placed selectively (i.e. in particular locations) within the RSF so that it Almost all of the overburden material was found to be non- was completely surrounded by overburden material. In addition, reactive, net acid consuming and is considered to have a low a layer of benign material would be placed at the base of the potential for solute release. However, the basement rocks contain RSF, so that water coming into contact with reactive rock would elevated concentrations of a range of metals which have the have to travel through overburden material, which has a high potential to be released into water that infiltrates the RSF. acid neutralising capacity and an ability to attenuate the

366 Olympic Dam Expansion Draft Environmental Impact Statement 2009 400

350

300

250

million tonnes) 200 (

k c r o

e 150 n M i

100 50 12 - 1 5 10 15 20 25 30 35 40 Production year

Class A: low grade ore Class C: overburden (shales, quartzites and sandstones)

Class B: basement material Class D: overburden (limestone, dolomite and clays)

7,000

6,000

5,000 million tonnes)

( 4,000

k c r o

e

n 3,000 M i

2,000

1,000

- 1 5 10 15 20 25 30 35 40 Production year

Class A: low grade ore Class C: overburden (shales, quartzites and sandstones)

Class B: basement material Class D: overburden (limestone, dolomite and clays)

Figure 12.16 Mine rock extraction by type over time

Olympic Dam Expansion Draft Environmental Impact Statement 2009 367 dissolved metals naturally, before it leaves through the base of In particular, if an exemption were sought and BHP Billiton the facility. Therefore, interaction with the overburden established an attenuation zone, it is anticipated that the materials would ensure that the percolate from the base would boundary of the zone would coincide with the expanded SML be neutral in pH and would cause the removal of dissolved boundary in most areas. The exception is the area immediately metals before it exits the facility. south and west of Arid Recovery, where there is less than a 1 km buffer between the TSF and the edge of the SML. If an Sediments beneath the RSF are similar to those beneath the TSF. attenuation zone extended further than this boundary it would Similarly, the calcareous clays have a high capacity to attenuate not affect any third party users. Elevated concentrations of metals that may remain in the seepage even after it has passed metals in groundwater would not adversely affect native flora through the overburden materials. The rate of seepage from the and fauna because the groundwater would be well below the RSF would be much less than that of the TSF, is likely to be non- ground surface and well below the depths of tree roots (Jackson acidic and is likely to have lower concentrations of metals. et al. 1999). Consequently, the affects on groundwater would be considerably less than observed for the TSF. Summary of seepage to the groundwater Table 12.6 presents a summary of factors that influence Fate of contaminants seepage from the TSF and RSF. Particle tracking of solutes has been carried out as part of the numerical groundwater modelling to predict the movement of Based on current modelling, seepage from on-site facilities such seepage from the TSF and the RSF when it reaches the as the TSF and RSF is not expected to pose an environmental groundwater. The model predicts that flows entering the risk. Nevertheless, BHP Billiton Group standards require that Andamooka Limestone beneath the TSF or RSF would first the designs of water containment and tailings storage facilities mound and then move away laterally from these facilities. aim to minimise seepage. Control measures have been considered in the design of the TSF. The RSF would be operated Movement through the aquifer is likely to be very low due to and closed to minimise infiltration of rainwater into zones the low hydraulic gradient and is expected to be much less than containing potentially reactive material, minimising seepage 1 m/y. By the end of mining, seepage would not be likely to from these areas. have travelled more than 100 m from the TSF or the RSF. The existing groundwater monitoring program would be The maximum distance that solutes could move away from the extended to monitor effects on groundwater quality from facilities would occur between 100 and 500 years post closure, seepage and would be compared against predicted solute before the effect of the drawdown from the open pit dominated movement. The data would be assessed regularly and and regional groundwater flowed towards the pit. Simulation of incorporated into the BHP Billiton Environmental Management seepage movement in groundwater shows that, in the longer Program (EM Program). If rates of seepage transport away from term, drawdown caused by the open pit would effectively the TSF or RSF were higher than predicted, risks would be capture contaminants that entered the groundwater system reviewed and remedial actions would be investigated. from the TSF and RSF. The current licence to operate at Olympic Dam requires Attenuation zone and water quality criteria groundwater levels to not rise above 80 m AHD (approximately As discussed earlier, the groundwater beneath Olympic Dam is 20 m below ground level). Modelling predicts that the maximum highly saline and has naturally high concentrations of metals, height of the mound would be around 65 m AHD (35 m below which make it unsuitable for domestic or stock use. The South ground level) and would therefore comply with current Australian Environment Protection (Water Quality) Policy 2003, requirements. The current program of harvesting and recycling however, specifies that groundwater-affecting activities should of water from the mound beneath the TSF would continue and not alter groundwater chemistry even when natural would further limit the height of the mound. groundwater quality exceeds criteria prescribed by the policy. Furthermore, if changes to groundwater chemistry are likely, The residual impact from seepage to the groundwater is the person undertaking those activities is to either obtain an categorised as moderate as it represents a long-term impact to exemption from the obligation to comply with the water quality a common (local) receiver. However, if the application for an criteria (which also requires the establishment of an attenuation attenuation zone is approved, or if the groundwater quality zone), or seek to have the water quality criteria amended to criteria are amended, the residual impact from seepage to reflect the naturally occurring groundwater quality. groundwater would be categorised as low as concentrations would be within legislated compliance limits (see Chapter 1, As seepage from the TSF and RSF would change the Introduction, Section 1.6.2, for details of management concentrations of most elements in the vicinity of these categories). facilities, BHP Billiton proposes to either apply for an exemption or seek a variation to the groundwater quality criteria of the local groundwater system. BHP Billiton could readily comply with the requirements of the EPP under each scenario.

368 Olympic Dam Expansion Draft Environmental Impact Statement 2009 Table 12.6 Factors that influence seepage from the TSF and RSF

TSF RSF Facility design Central rock lined decant pond and liquor Classification of mine rock based on potential recycling would significantly reduce the amount reactivity would facilitate appropriate of free water available to infiltrate into the placement of potentially reactive rock within tailings the facility Amount and characteristics of facility inputs, Thickening the tailings to around 52–55% solids Appropriate placement of mine rock would including the influence of rainfall and would reduce free water and subsequently minimise exposure to weathering and reduce evaporation reduce infiltration and seepage leaching of metals and acidity Quantity of seepage from the base of Expected to be higher in the first two years Seepage from the base is expected to be the facility following cell commissioning, after which around 1% of rainfall (5–10 times greater than tailings would consolidate and form a low the natural recharge rate) due to preferential permeability base flow paths Post closure, TSF would be covered, infiltration would decrease and the TSF would gradually drain, reaching steady-state, low-flow conditions Geochemical processes in soil and Calcareous clays and Andamooka Limestone Calcareous clays and Andamooka Limestone groundwater beneath the facility beneath the TSF have been demonstrated to, beneath the RSF are expected to attenuate and are expected to continue to, attenuate most metals most metals Groundwater chemistry under the existing TSF 12 is stable and is characterised by a slight local increase in uranium and salinity Transport of seepage water within Seepage movement would be very low The expectation is that no groundwater groundwater A groundwater mound would form beneath the mound would form beneath the RSF due to the TSF and would influence groundwater levels for very low infiltration rates and the unsaturated up to 6 km extent of the Andamooka Limestone Groundwater modelling shows that solute Groundwater modelling demonstrates that transport would be constrained to within a few seepage would travel no more than a few hundred metres of the TSF hundred metres from the RSF and would ultimately be captured by drawdown from the All seepage would be captured by drawdown open pit from the open pit Receptors Nearest sensitive receptor (pastoral well) is Nearest sensitive receptor is Lake Torrens, around 55 km up hydraulic gradient and would around 40 km east of the RSF, and would not not be adversely affected by either the be adversely affected by seepage from the RSF groundwater mound or seepage from the TSF

Other potential contaminant sources hydrocarbons. In addition, construction works would comply During construction, operation and maintenance of other with environmental management specifications designed to proposed expansion infrastructure, other potential contaminant address contamination risks associated with the activities sources could be: (see Chapter 24, Environmental Management Framework). For further detail about the storage of potentially hazardous • the expansion of the metallurgical plant or contaminating sources see Chapter 5, Description of the • worksite compounds used as a base for vehicles and other Proposed Expansion, Section 5.5.5 and Chapter 22, Hazard equipment and Risk, Section 22.6.8. • fuel stores, including tank farms and mobile tankers • hazardous goods compounds, including chemicals and 12.6.3 third-party groundwater users explosives Stuart Shelf • machinery and equipment workshops (e.g. for the There are four pastoralist stockwater supply wells located in, manufacture and maintenance of machinery). or close to, the predicted zone of drawdown from the open pit (see Figures 12.14 and 12.15). These wells are located on The chemical and hazardous goods storages and fuel storage pastoral leases held by BHP Billiton. would be bunded in accordance with the South Australian EPA requirements of bund sizes and volumes to be 120% of the net The closest third-party supply wells are located more than capacity of the largest tank and 133% for flammable material, 15 km outside the 1 m drawdown contour predicted by the resulting in a low potential for groundwater contamination. model (see Figure 12.14). Any change to the water levels in Workshops and vehicle compounds would be equipped with third-party wells, should it occur, would be in the range of hydrocarbon and chemical interception facilities to minimise centimetres rather than metres. This is considered insignificant the discharge to groundwater of hazardous materials including

Olympic Dam Expansion Draft Environmental Impact Statement 2009 369 in terms of the total water column usually intersected by Although it is unlikely that the ecological values of Yarra Wurta pastoral wells (5–10 m; see Appendix K2 for detail). It is would be negatively affected, surveys were undertaken as part therefore concluded that groundwater drawdown would not of the Draft EIS to determine their ecological significance (see have an adverse impact on the pumping capacities of these Chapter 15, Terrestrial Ecology). stockwater wells and there would be no residual impact. 12.7 fIndings and conclusions The groundwater levels in wells in the Olympic Dam region would be monitored throughout the operation phase. Groundwater drawdown Information would be incorporated into the groundwater model Drawdown of up to 10 m below pre-mining levels is expected in to confirm its accuracy and the model would be refined if the Andamooka Limestone beneath the SML. The zone of required. If monitoring showed that drawdown was affecting influence in this upper aquifer is expected to extend up to 5 km current third-party users, alternative water supply options north of the SML and up to 20 km to the south-west. would be investigated. These may include relocating or deepening existing groundwater wells, or providing an Groundwater drawdown in the lower Tent Hill aquifer would be alternative water supply. Options would be considered in driven at first by the satellite water supply wellfields and would consultation with the third-party user. be gradually overridden by the effects of groundwater flow to the open pit. The final zone of influence (500 years post Infrastructure corridors closure) is expected to be around 20 km north and up to 45 km In addition to near-mine water supplies, it would be necessary south of Olympic Dam. Regional groundwater drawdown would to develop groundwater supplies along the infrastructure not affect flora and fauna, however, as it represents a long- corridors to provide the volumes of water required during term impact to a common receiver, the residual impact is construction. Although the exact location of groundwater supply categorised as moderate. wells is not known, it is anticipated that supply centres would be 10–20 km apart along the linear infrastructure corridors. The effects of changes in groundwater levels are most prominent south of Olympic Dam because groundwater flowing The residual impact of construction water supply wellfields on from the Arckaringa Basin (across the northern part of the third-party water users is categorised as low as it would be Stuart Shelf) acts as a buffer between Olympic Dam and short-term and would be managed by targeting deeper saline groundwater systems to the north. Groundwater drawdown, aquifers, and ensuring wells are located to minimise potential due to the open pit and saline water supply, would not affect interference between those used for construction and those for the northern boundary of Stuart Shelf and there would be no pastoral uses. impact on the artesian aquifers of the GAB and the corresponding springs.

12.6.4 Groundwater-dependent ecosystems Three BHP Billiton-owned groundwater wells occur within the The closest known obligate groundwater-dependent ecosystem predicted zone of groundwater drawdown. No third-party is the Yarra Wurta spring group located at the northern end of groundwater wells occur within this zone; the nearest is around Lake Torrens, around 45 km from Olympic Dam (see 55 km from the mine site. No residual impact to third-party Figures 12.14 and 12.15). groundwater users is expected.

Although there is some evidence that groundwater feeding the Water supply development Yarra Wurta springs may originate from the Adelaide Geosyncline rocks east of Lake Torrens rather than from the Saline water for dust suppression and other low-quality uses aquifers of the Stuart Shelf, this is not definite (see Appendix K1). would be sourced from a primary saline wellfield (Motherwell) It is possible that groundwater from the Andamooka Limestone in the Andamooka Limestone around 30 km north of Olympic aquifer may also contribute to spring flows. Dam, and from various satellite wellfields within and close to the SML. Water recovered from depressurisation activities For the purpose of the groundwater model, and to be would also be recycled and reused. Total groundwater conservative, it was assumed that Yarra Wurta springs depend extraction would be around 12 ML/d from the Tent Hill aquifer entirely on groundwater flow from the Stuart Shelf. Modelling and around 28 ML/d from the Andamooka Limestone aquifer. predicts that the post closure 1 m drawdown contour is more Groundwater drawdown is initially driven from the dewatering than 15 km from the springs. Any drawdown at Yarra Wurta is and satellite wellfields during the construction phase but is likely to take more than 100 years to develop and be in the gradually overridden by the effects of groundwater flow to the order of centimetres rather than metres. Ongoing monitoring open pit. of groundwater levels and spring flow at Yarra Wurta springs would occur and would be used to validate and update the Temporary water supply wells may be required about every groundwater model as required. 10–20 km along the linear infrastructure corridors, but these would only be required for a short term and would be located so that they have minimal impact on third-party users. Consequently, the residual impact is categorised as low.

370 Olympic Dam Expansion Draft Environmental Impact Statement 2009 No groundwater would be extracted from the GAB outside of approval from the South Australian Government, resulting in no residual impact.

Seepage and water quality Seepage from the TSF during the first 10 years of the expanded operation at Olympic Dam would range up to a maximum of 8.2 ML/d. This would then decrease to an operational steady state of around 3.2 ML/d. Post closure, seepage would decrease to very low levels after the facility drains down. The time to steady state conditions would be accelerated by the installation of a cap over the tailings to reduce rainfall infiltration.

The RSF would be a source of enhanced local rainfall recharge due to infiltration of water into the facility and movement through preferential flow paths. Seepage from the RSF would be expected to be around 1% of the rainfall recharge (5–10 times greater than natural recharge), or around 0.3 ML/d. A groundwater mound to around 35 m below the surface would 12 form beneath the tailings and would affect water levels for up to 6 km. Due to the very low permeability of the Andamooka Limestone, however, lateral movement of potential contaminants would be constrained to within a few hundred metres of the TSF. No groundwater mound is expected to form beneath the RSF.

The potential for acid generation from the RSF is low. The neutralising base layer of the RSF and the naturally occurring calcareous clays and Andamooka Limestone beneath the TSF and RSF are expected to attenuate most metals.

Eventually, the open pit would act as a regional groundwater sink, capturing all seepage from the TSF and RSF. The residual impact on the groundwater is considered moderate as it represents a long-term impact to a common receiver.

Olympic Dam Expansion Draft Environmental Impact Statement 2009 371 372 Olympic Dam Expansion Draft Environmental Impact Statement 2009