Groundwater Aquifer Connectivity in Queensland, Australia

Technical Communication 1 November 2014 About GasFields Commission Queensland The GasFields Commission is the independent statutory body formed to manage and improve sustainable coexistence between rural landholders, regional communities and the onshore gas industry in Queensland, Australia. The Commission’s formal powers and functions are enshrined in the Gasfields Commission Act 2013 which took effect from 1 July 2013. These include: review and provide advice on the effectiveness of legislative frameworks for the onshore gas industry; encourage factual information and scientific research to help address concerns about the potential impacts of the onshore gas industry on water and other resources; and level the playing field in land access and compensation negotiations between landholders and gas companies through more and better information. For more information visit the GasFields Commission website at www.gasfieldscommissionqld.org.au

About this Technical Communication One of the Commission’s key functions is to obtain and publish information that can assist in improving knowledge and understanding about the onshore gas industry including its interactions with and impacts on rural landholders and regional communities. The Commission’s technical communications aim to fill a gap in information between the simple fact sheet and the full technical reports or scientific papers. They provide an easy to read collation of the science and draw on technical material from a range of sources including CSIRO, universities, Australian and Queensland Government departments, independent technical specialists and scientific experts, and Queensland’s onshore gas industry.

Disclaimer This technical communication is distributed by the GasFields Commission Queensland as an information source only. It provides general information which, to the best of our knowledge, is correct as at the time of publishing. Any references to legislation are not an interpretation of the law. They are to be used as a guide only. The information contained in this technical communication does not constitute advice and should not be relied on as such. While every care has been taken in preparing this technical communication, the GasFields Commission Queensland accepts no responsibility for decisions or actions taken as a result of any data, information, statement or advice, expressed or implied, contained within. Where appropriate, independent legal advice should be sought.

© 2014 GasFields Commission Queensland.

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Contents

Introduction 4 Confined and Unconfined Aquifers 4 What is Aquifer Connectivity? 5 What determines the degree of connectivity between geological formations? 7 How has aquifer connectivity been measured and monitored? 11 What are the expected impacts of induced aquifer leakage? 14 Conclusion 18 Glossary 19 References 20

Tables

Table 1: Hydraulic features of geological formations in the Surat and southern Bowen Basins. 8 Table 2: Typical vertical separation distances between the shallowest coal measures and closest overlying aquifer for the Surat, Bowen and Galilee Basins. 9 Table 3: Number of bores within LAAs impacted by induced aquifer leakage associated with CSG production within the Surat CMA. 16

Figures

Figure 1: Location of Surat, Bowen and Galilee Basins in relation to the Great Artesian Basin. 4 Figure 2: A conceptual groundwater system. 4 Figure 3: Schematic representation of groundwater water pressure and vertical flow direction. 5 Figure 4: Conceptual equation for cross formation water flow. 6 Figure 5: Close up photograph of a section of a rock core sample from the Moolayember Formation (a low permeability aquitard) in the Galilee Basin. 7 Figure 6: Direct contact zone between Bandanna Formation and Precipice Sandstone aquifer. 9 Figure 7: A knowledge improvement cycle for preparing and implementing an Underground Water Impact Report (UWIR) for a CSG project. 11 Figure 8: Comparison of estimated annual groundwater extraction and induced flow rates in the Surat CMA. 14 Figure 9: Extent of the Long-term Affected Areas in the Surat CMA 15 Figure 10: Make good obligations. 17

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Introduction The management of groundwater aquifers is critical to ensuring coexistence of rural landholders, regional communities and the onshore gas industry. Aquifer connectivity is important as it underpins our understanding of the groundwater impacts from CSG development. This paper explores the concept of aquifer connectivity and the key factors that regulate it. Importantly, discussion is also provided on how connectivity in relation to CSG production has been measured and monitored in Queensland.

Confined and Unconfined Aquifers Figure 1 provides an overview of the principal CSG geological basins in relation to the Great

Artesian Basin (GAB), one of the world’s largest groundwater systems. The GAB includes the Figure 1: Location of Surat, Bowen and Galilee geological formations of the Surat Basin and the Basins in relation to the Great Artesian Basin. Source: DoE, 2014 upper Triassic formations of the Bowen and Galilee Basins. The deeper, older formations of the Bowen and Galilee Basins are not within the GAB.

Figure 2: A conceptual groundwater system showing a confined aquifer, unconfined aquifer and aquitard layers. Source: QWC (2012)

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The GAB is a groundwater basin made of rock Water flows from areas of higher water level or layers (called formations) that form aquifers water pressure to areas of lower water level or (permeable layers that readily transmit water) water pressure. In aquifers, most flow is and aquitards (the confining layers that restrict horizontal (DoE, 2014). In aquitards, most flow is groundwater flow) (Figure 2). The aquifers of the vertical (DoE, 2014) due to the upwards or GAB are confined as they are overlain by downwards leakage of water from aquifers. aquitards which restrict the vertical movement of In the undisturbed groundwater systems of the water and enable water pressure to develop in Surat, Bowen and Galilee Basins, natural aquifer the aquifer. On top of the GAB lie more recently leakage is usually upwards from deep formations deposited rock layers. Near the surface some of under higher pressure to overlying formations these materials, such as river gravels and sands under lower pressure (CSIRO 2012b and DoE, or basaltic rock from ancient volcanic activity, 2014) (Figure 3a), although this trend is not form shallow, unconfined aquifers (permeable consistent within the Surat Basin. layers that readily transmit water but are not covered by an aquitard). When the hydrological system is disturbed by activities such as groundwater extraction, the What is Aquifer Connectivity? direction of natural vertical aquifer leakage can be reversed if the water pressure in the deeper Connectivity describes the ease with which formations is reduced (CSIRO 2012b and DoE, groundwater can flow within or between 2014) (Figure 3b). Aquifer leakage that occurs in geological formations (QWC, 2012). It is response to a disturbance to the groundwater controlled by the resistance to flow between system is called induced aquifer leakage. geological formations, which is determined by the When considering vertical water leakage rock type, its porosity and how well pores are between geological formations under natural and connected. Also, discontinuities such as disturbed conditions, the water pressure geological fractures (e.g. natural vertical cracks difference (called the hydraulic gradient) is in formations) or poorly constructed bores or important but is only part of the equation. A wells (e.g. bore or well casings that are not sufficient degree of connectivity is also required properly sealed between formations) can between the formations for water to flow (CSIRO increase connectivity. 2012b) (Figure 4).

b) a) Undisturbed groundwater system Disturbed groundwater system Figure 3: Schematic representation of groundwater water pressure and vertical flow direction in a hypothetical groundwater system under both a) undisturbed and b) disturbed conditions. Water pressure in the confined aquifer is indicated by the potentiometric surface and by the water table level for the unconfined aquifer. Source: National Groundwater Association (NGWA) cited in DoE (2014). Note: 3a shows natural upwards vertical leakage from the higher pressured confined aquifer to the lower pressured unconfined aquifer and 3bshows a decline in the water pressure level of the confined aquifer near the well due to groundwater pumping and a reversal in vertical leakage. Induced aquifer leakage occurs near the well as water pressure is higher in the unconfined aquifer.

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Sufficient Adequate Cross degree of hydaulic formation connectivity gradient water flow

Figure 4: Conceptual equation for cross formation water flow. Source: CSIRO, 2012b

Connectivity is commonly expressed in simple and b; Marsh et al., 2008; RPS, 2012 and QWC, terms as low, medium or high. It can be different 2012) due to: depending on the direction of water flow. Since . The low vertical permeability of the coal geological formations are typically layered measures consisting of primarily mudstone, reflecting geological history, the resistance to siltstone and intervening discontinuous coal flow will vary depending on whether flow is layers and separating aquitard layers; and vertical or horizontal. . The vertical separation of varying degree While there will be no flow between formations between coal measures and aquifers. with high connectivity if there is no hydraulic gradient between them, there will be flow The low degree of connectivity between coal between formations with low connectivity if a measures and aquifers plays an important role in sufficiently large hydraulic gradient exists (QWC, minimising the impacts of CSG development on 2012). However, the rate of flow is likely to be groundwater resources by limiting induced extremely slow and cause a significant delay aquifer leakage. Further discussion is provided between the time of creation of the hydraulic in the following sections on the key factors that gradient and the time when the flow between the determine connectivity (vertical permeability and formations peak (CSIRO 2012b and QWC 2012). separation), the ways that connectivity has been measured and how it is predicted to limit the Current studies have found that low connectivity impacts to groundwater resources. is a dominant geological characteristic of aquifers across the Surat, Bowen and Galilee Basins (Australian Government, 2014; CSIRO, 2012a

Summary: What is aquifer connectivity? 1. Connectivity describes the ease with which water can move between geological formations. 2. Low connectivity is a dominant feature of the Surat, Bowen and Galilee Basins and means that water flow between formations will be extremely slow. 3. Low connectivity minimises the groundwater impacts of CSG development by restricting induced aquifer leakage.

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What determines the degree of Regional scale permeability data for selected connectivity between geological geological formations found in the Surat and southern Bowen Basins are provided in Table 1. formations? Permeability varies greatly between the different Low vertical permeability and generally large formation types and basins as well as between vertical separation distances act together to limit the horizontal and vertical directions. aquifer connectivity between coal measures and Vertical permeability influences connectivity aquifers across most parts of the Surat, Bowen between formations due to the effect it has on and Galilee Basins. the rate of vertical water movement. Typically, Groundwater does not flow in ‘underground the rate ranges from millimetres per year in rivers’; instead it flows slowly between the aquitards and coal measures to kilometres per connected pores and fractures or fault lines in year in aquifers. The time required for water to geological formations. The term “permeability” is travel 100 metres vertically in geological used to describe the ease with which water can formations ranges from days and decades in flow horizontally and vertically though a aquifers to millennia in aquitards and coal geological formation. measures. The limiting effect of these extremely slow speeds of vertical water movement in In sedimentary materials, such as those found in aquitards and coal measures on connectivity is the Surat, Bowen and Galilee Basins, vertical further compounded by vertical separation permeability is typically at least 100 to 1,000 between aquifers and coal measures. times less than horizontal permeability (QWC, 2012). This is due to the layered structure of The target coal measures are usually located at sedimentary formations (Figure 5), which means considerable depths from the surface and the that it is easier for water to move horizontally thin coal seams are physically separated from along the sedimentary layers than vertically overlying or underlying aquifers by low across them (QWC, 2012). Figure 5 shows very permeability interburden materials and normally fine grained sandstone (light brown) and at least one or more low permeability, thick mudstone (dark grey) layers in a low permeability aquitard layers (Australian Government, 2014; aquitard in the Galilee Basin. CSIRO, 2012a and b; Marsh et al., 2008; RPS, 2012 and QWC, 2012). As vertical separation between formations increases, the connectivity decreases (QWC, 2012). Therefore, the total depth of the target coal seam and the thickness of low permeability geological formations separating the coal seam from an aquifer are important factors in restricting connectivity between coal seams and aquifers. Examples of typical vertical separation distances for the shallowest target coal measures and their Figure 5: Close up photo of a rock core sample closest overlying aquifer for the Surat, Bowen from the Moolayember Formation in and Galilee Basins are provided below (Table 2). the Galilee Basin. Source: adapted from Rawsthorn et al. (2009).

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Table 1: Typical hydraulic features of geological formations in the Surat and southern Bowen Basins.

Aquifer Aquifer: Formations with a high permeability, such as sands, porous sandstones or basalt, are called aquifers. The high permeability of aquifers is attributed to the connected spaces or pores between sand grains or fractures and cracks in rock that allow water to flow with little resistance. Aquifers are important sources of water in many rural areas and are accessed by bores. Permeability1: tens of metres per year to several thousand metres per year, similar in both vertical and horizontal directions. Examples include: Condamine Alluvium in Surat Basin and Clematis Adapted from Co2crc (2014) Sandstone in Bowen Basin. Aquitard Aquitards: Formations with a low permeability, such as siltstone or mudstone, are called aquitards. The low permeability of aquitards reflects the poor connection between the microscopic pores of fine grained and compacted geological materials, with resultant high resistance to water flow. Aquitards are common and play a role in maintaining groundwater pressure in aquifers by restricting aquifer leakage. Permeability1: 0.5 meters per year in horizontal direction 0.002 meters per year in vertical direction Adapted from Co2crc (2014) Examples include: Westbourne Formation in Surat Basin. Coal Measure Coal measures: Formations that contain many thin coal seams separated by low permeability rock (interburden) are called coal measures. They are often considered to be aquitards because of their low vertical permeability. Permeability1: 10 meters per year in horizontal direction 0.002 meters per year in vertical direction Examples include: Walloon Coal Measures in Surat Basin and Bandanna Formation in Bowen Basin. Adapted from APLNG (2011)

Note 1: Permeability is a measure of how freely water can flow through a rock stratum and can vary depending on flow direction. This value indicates how far water would move in a year under a unit pressure gradient. Values range from millimetres to kilometres/year. Source: permeability values from GHD (2012).

The vertical separation data provided in Table 2 Despite these unique characteristics of the Surat highlight some important differences between the Basin, a low degree of connectivity exists basins: between aquifers adjacent to the Walloon Coal Measures (QWC, 2012). Vertical separation of 1. Coal measures targeted for CSG aquifers and coal measures by one or more low development outside the Central permeability aquitards occurs across most parts Condamine Area of the Surat Basin are of the basins, but there are locations within each very deep; and basin where the aquitard is absent and direct 2. Relatively thin aquitards immediately contact between coal seams and aquifers occurs overlie the Walloon Coal Measures in the (i.e. no vertical separation exists) (RPS, 2012 Surat Basin compared to the much thicker and QWC, 2012). An example from the Bowen aquitards in the Bowen and Galilee Basins. Basin adjacent to the Spring Gully and Fairview CSG fields is provided in Figure 6.

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Table 2: Typical vertical separation distances between the shallowest coal measures and closest overlying aquifer for the Surat, Bowen and Galilee Basins.

Basin Name Coal Measure – depth to Overlying Aquitard – average Closest Overlying formation (m) thickness / vertical separation Aquifer (m)

Surat (Central Walloon Coal 30-130 Transition zone between 30 Condamine Alluvium Condamine Measures (WCM) Condamine Alluvium Area) (CA) and WCM

Surat Walloon Coal 700 Upper aquitard of WCM 15 Springbok Measures Sandstone

Bowen Bandanna 300-800 Rewan 300 Clematis Sandstone Formation

Galilee Betts Creek Beds 700 + Rewan 3001 Clematis Sandstone/Dunda Beds

Note 1: Assumed same as Bowen Basin. Geoscience Australia (2014) note a maximum thickness of 840 metres for this formation in the Galilee Basin.

Sources: AGL, 2013; Arrow Energy, 2012a; Comet Ridge, 2014; DNRM, 2014; RPS, 2012 and QWC, 2012

Figure 6: Direct contact zone between Bandanna Formation and Precipice Sandstone aquifer in the Fairview and Spring Gully CSG production area in the Bowen Basin near Roma. Direct contact occurs between the formations due to erosion of the Rewan Formation (aquitard) and Clematis Sandstone aquifer prior to deposition of the Precipice Sandstone sediments. Source: QWC, 2012

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In this specific location a higher degree of However, groundwater impact assessments of connectivity and leakage from the aquifer CSG production in areas with direct contact induced by CSG development was expected due zones conducted by the Queensland Water to the absence of the Rewan Formation aquitard. Commission, now the Office of Groundwater However, CSG production commenced in this Impact Assessment (OGIA), in the Surat Basin area in 1996 and water pressure monitoring over (2012) and AGL in the Galilee Basin (2013) do this time has not shown a discernible effect on not predict significant levels of induced aquifer water pressures in the Precipice Sandstone leakage. The lack of measured and predicted aquifer due to depressurisation of the Bandanna impacts on aquifers in these circumstances may Formation coal seam from CSG activity. This reflect a low level of aquifer connectivity, or means that this aquifer has not been adversely suggest that CSG production in these areas will impacted by CSG production (QWC, 2012). not produce a sufficient hydraulic gradient (pressure difference between geological Direct contact zones also occur between the formations) to induce groundwater to flow from Condamine Alluvium (CA) and the Walloon Coal aquifers, known as induced aquifer leakage. Measures (WCM) in the Surat Basin and the Hutton Sandstone and the Betts Creek Beds in the Galilee Basin (RPS, 2012 and QWC, 2012).

Summary: What determines the degree of connectivity between geological formations? 1. Connectivity between geological formations is dependent upon their vertical permeabilities and vertical separation. 2. Vertical permeabilities of aquitards and coal measures are very low due to their layered sedimentary structure. 3. Coal measures are usually located at great depths and separated from aquifers by low permeability interburden materials and some aquitard. 4. Low vertical permeabilities and separation distances between geological formations create a high resistance to flow and a low degree of aquifer connectivity in the Surat, Bowen and Galilee Basins.

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How has aquifer connectivity prepared by the former QWC in 2012 and is now been measured and monitored? administered by the OGIA. The Surat CMA groundwater model is widely Aquifer connectivity is determined by a process accepted as the most appropriate tool for of measurement and modelling (DoE, 2014). assessing the regional groundwater impacts of There are numerous methods of measurement CSG development (OGIA, 2013) and was used available: hydraulic assessment (pump tests and by the Commonwealth Scientific and Industrial application of groundwater responses); Research Organisation (CSIRO, 2012b) in the laboratory tests (permeability analysis of rock Water Resource Assessment for the Surat cores); geophysical assessment of stratum; and Region. The reliability of any model however geochemical analyses (water chemistry depends on the accuracy of values, such as analysis). Data obtained are used to develop a vertical permeability, used to build the model. conceptual model of the system which is then The measured vertical permeabilities used to built into a computer-based mathematical develop the Surat CMA model are considered to representation of the groundwater system. The be sufficient for general characterisation of the mathematical model is tuned to all available geological formations (DoE, 2014). Ongoing measured groundwater responses and then monitoring is being undertaken to gather applied to explore changes imposed by water additional data to improve confidence in the extraction and management activities. While the conceptual and computer model of the mathematical model is only a partial description groundwater system (Figure 7). of the groundwater systems, confidence in these models improves as new data become available from the monitoring program. The Australian Government Department of Measure Environment commissioned a background review (DoE, 2014) to describe the methods used to measure and model connectivity in any Review Model groundwater system, and the understanding of aquifer connectivity within the Surat, Bowen and Galilee Basins. This review was conducted on the advice of the Independent Expert Scientific Committee on Coal Seam Gas and Large Coal Mining Development (IESC). The review Report Monitor highlights a continuing need for additional measurements and analysis to improve conceptual understanding of connectivity and Figure 7: A knowledge improvement cycle for thus improve the prediction of impacts through preparing and implementing an modelling. Underground Water Impact Report (UWIR) for a CSG project. In Queensland, regional scale assessment of connectivity and aquifer leakage from CSG Project based research monitoring is being development has been conducted in the Surat conducted by the OGIA for the Surat CMA. One Cumulative Management Area (Surat CMA). The example is the Condamine Interconnectivity most comprehensive study regarding the Research Project (CIRP) which employs several measurement of aquifer connectivity in CSG techniques to obtain locally measured values of development areas is the Underground Water connectivity to confirm the accuracy of values Impact Report (UWIR) for the Surat Cumulative used in the Surat CMA model for the Condamine Management Area. The Surat CMA UWIR was Alluvia (CA) and the underlying Walloon Coal Measures (WCM).

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The CIRP is being conducted by the OGIA with production or testing activities in the northern support from Arrow Energy, research Bowen or Galilee Basins. organisations and the Department of Natural However, based on the DoE’s (2014) findings, it Resources and Mines (DNRM). The purpose of is possible that impacts may be under-predicted this research is to characterise the relationship where connectivity has been measured over between the groundwater systems of the CA and small areas. To address this potential issue, WCM by compiling multiple lines of evidence CSG activities under an UWIR are subject to from analysis of existing water quality data sets, ongoing monitoring, annual reviews and regular field studies such as water level mapping and revision to give confidence in the reliability of pump testing and computer modelling of conceptual and computer models. geological conditions. Preliminary results from the CIRP show that the upper WCM and To build on the current knowledge and transition layer have low vertical permeabilities understanding of aquifer connectivity in the (OGIA, 2014). While a hydraulic gradient exists Surat, Bowen and Galilee Basins, regional scale between the WCM and the CA, there are measurement, monitoring and research significant differences in formation water programs are underway and include: chemistry, which indicates no significant cross . Ongoing regional scale water pressure formation flow. This means that there is low monitoring and expansion of the monitoring connectivity between the CA and WCM (OGIA, network as required under the Surat CMA 2014). UWIR; . Six separate research projects by the OGIA “We prepared the Surat Underground investigating connectivity, geological Water Impact Report in 2012 using structures and modelling, groundwater available knowledge. We are currently modelling techniques and springs in the Surat carrying out research projects to CMA. The new knowledge gained from these improve knowledge of the groundwater studies will be used to build a new regional flow system, which includes the groundwater flow model and update the Surat connectivity between formations. The CMA UWIR in December 2015; and new knowledge will be incorporated . A program of scientific bioregional into the construction of a new regional assessments to better understand the groundwater flow model which will be potential water impacts of coal seam gas and used to update the Surat Underground large coal mining developments being Water impact Report in December undertaken by a collaboration of Australian 2015.” Government organisations (Department of the – Randall Cox, General Manager, Environment, Bureau of Meteorology, CSIRO Office of Groundwater Impact and Geoscience Australia). These Assessment assessments include measurement and modelling of aquifer connectivity and are scheduled for completion in 2016. No adverse aquifer impacts are predicted in the UWIRs prepared by CSG operators for

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Summary: How has aquifer connectivity been measured and monitored? 1. Connectivity is determined by direct measurement and computer modelling. 2. Field and laboratory data are used to develop a conceptual model and then to build a computer-based mathematical representation of the groundwater system. 3. Regional scale estimations of aquifer connectivity are being improved through various studies by OGIA and other agencies. 4. Regulatory controls exist to assess the accuracy of aquifer connectivity predictions. 5. Data from ongoing monitoring and measurement will build confidence in the conceptual and computer models used to predict groundwater impacts from CSG development.

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What are the expected impacts of good agreement with the landholder so the induced aquifer leakage? landholder is not disadvantaged by their activities. CSG extraction in the Surat, Bowen and Galilee Between now and 2050 it is estimated that CSG Basins is expected to induce groundwater production in the Surat CMA will extract on leakage from some aquifers due to average approximately 95,000 ML of depressurisation of the target coal measures. groundwater per year (QWC, 2012). The total This section discusses the expected impacts of amount of induced leakage from all formations induced aquifer leakage from CSG production that overlie or underlie the WCM will be and the management measures available to approximately 50% of the total amount of water ameliorate their predicted extent and magnitude. extracted for CSG production (Figure 8). At the The Water Act 2000 defines two measures of regional scale, the predicted annual volume of future groundwater level impact on an aquifer: induced leakage is approximately 20% of total the Immediately Affected Area (IAA) and Long groundwater extraction in the Surat CMA for non- Term Affected Area (LAA). An IAA for an aquifer petroleum and gas purposes (e.g. agriculture, is the area within which water level (or pressure) stock and town water supply). Understanding reductions are predicted to exceed a trigger the expected extent of induced aquifer leakage in threshold within three years. A LAA for an terms of geographic area and water pressure aquifer is the area within which water pressure reduction is important for estimating impacts to reductions are predicted to exceed a threshold at water supply bores and springs. any time in the future. Threshold values have been set at 5 metres for consolidated aquifers 250000 (such as sandstones) and 2 metres for Groundwater extraction for CSG unconsolidated aquifers (such as sand aquifers). production 200000 UWIRs prepared by CSG operators for projects Induced aquifer leakage to the WCM in the northern Bowen and Galilee Basins (AGL, 150000 2013, Arrow Energy 2012a,b,c, 2014b, Blue Non-CSG groundwater extraction

Energy, 2012, CDM Smith, 2013a, b, c, d and perMLyear 100000 from formations adjacent to the Comet Ridge, 2014) do not predict induced WCM (see note) aquifer leakage to cause a decline in water 50000 Non-CSG groundwater extraction pressures for aquifers or springs that exceed from the Surat CMA trigger thresholds during CSG production. That 0 is, existing and currently proposed CSG development in these basins is not expected to Figure 8: Comparison of estimated annual cause enough leakage to create IAA or LAAs in groundwater extraction and induced aquifers. flow rates in the Surat CMA. In the Surat CMA, induced aquifer leakage is Source: original data sourced from predicted to impact some aquifers. A reduction QWC (2012). Note: Based on extraction rates for formations adjacent to in source aquifer water pressure of more than 5 the WCM including the Condamine metres may affect up to 1% of water supply Alluvium, Springbok Sandstone, Marburg bores in the Surat CMA, and a reduction of water Sandstone, Hutton Sandstone and pressure of up to 1.5 metres in the spring source Eurombah Formation. aquifer could occur at the location of 5 spring No IAAs or LAAs are predicted for the complexes (QWC, 2012). If a bore in an IAA is Condamine Alluvium. Induced leakage from the assessed as experiencing or likely to experience CA to the WCM is estimated at 1,100 ML per impaired function due to CSG activities, the CSG year over the next 100 years (QWC, 2012). This operator is legally obliged to enter into a make volume of water is equivalent to a layer of water

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0.2 millimetres deep per year across the IAAs are not large, and there are no water supply Condamine Plain which has an area of 7,000 km2 bores that access these aquifers within the IAAs (Dafney and Silburn, 2013). Induced leakage (QWC, 2012). The LAAs for these two aquifers from the CA is predicted to result in an overall are more extensive, and springs and water decline in water levels over the next 100 years by supply bores in these LAAs are expected to be approximately 0.5 metres on average across the impacted by reductions in water levels (or area which is less than the major reduction that pressure) (QWC, 2012) (Figure 9). Small LAAs has already occurred from extraction for irrigation from CSG production are also predicted for the and town water supply (QWC, 2012). Gubberamunda Sandstone and Precipice Sandstone and Clematis Sandstone. LAAs for Induced leakage will primarily affect the the Precipice Sandstone and Clematis Springbok Sandstone and Hutton Sandstone Sandstone west of Moonie are related to aquifers which overlie and underlie the WCM conventional oil and gas production, not CSG respectively. Small areas of IAAs are identified production (QWC, 2012). by the QWC (2012) for the Springbok Sandstone at locations south and west of Chinchilla. These

Figure 9: Extent of the Long-term Affected Areas in the Surat CMA Source: QWC (2012)

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Table 3: Number of bores within LAAs impacted by induced aquifer leakage associated with CSG production within the Surat CMA.

Aquifer Total No. of bores in No. of impacted bores Percentage of impacted formation in LAA bores in formation

Springbok Sandstone 223 104 47%

Hutton Sandstone 2,828 23 <1%

Precipice Sandstone 292 0 0%

Gubberamunda 908 1 <1% Sandstone

Total 4,251 128 3%

Source: original data sourced from QWC (2012)

There are 71 spring complexes (a complex is a of the total number of all private bores (21,192) in group of springs) and 43 watercourse springs in the Surat CMA. the Surat CMA. A total of five spring complexes Water levels in bores tapping the Springbok associated with the LAAs of the Precipice, Hutton Sandstone will be most heavily affected, mainly and Gubberamunda Sandstones are predicted to between 2060 and 2075. Lowering of water experience water pressure declines above the levels beyond the trigger thresholds places the trigger threshold. The estimated declines in impacted bores at a greater risk of a reduced water pressures are not expected to occur earlier water supply; however, controls exist under than 2017 and may affect the ecological and Chapter 3 of the Water Act 2000 to prevent bore cultural heritage values of the five potentially owners being disadvantaged by CSG production, impacted spring complexes. The OGIA are such as ‘make good obligations’. currently conducting the Spring Knowledge Project to improve the scientific understanding of If a bore in an IAA is assessed as experiencing springs to determine the most appropriate or likely to experience impaired function due to mitigation measures for the five potentially CSG activities, the CSG operator is legally impacted spring complexes. obliged to enter into a make good agreement with the landholder. The make good agreement Water bores in the Surat CMA provide water for outlines the make good measures to be agriculture, industry, urban, stock and domestic implemented by the CSG operator so the uses. There are a total of 4251 bores extracting landholder is not disadvantaged by their groundwater from CSG affected aquifers within the activities. The make good obligations of CSG Surat CMA area. However, only 128 are predicted operators outlined in the Queensland to experience a reduction in water pressures from Department of Environment and Heritage aquifer leakage due to CSG production (Table 3). Protection’s (2013) guideline to make good At a regional scale, the number of bores predicted obligations are shown in Figure 10. to be impacted by induced leakage is less than 1%

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Figure 10: Make good obligations. Source: DEHP (2013)

Significant CSG development in the Surat CMA Arrow Energy, 2013; QGC, 2013 and Santos, is expected to cease by 2050, but the effects of 2013). groundwater extraction and induced aquifer The QWC (2012) model also does not account leakage will be experienced after development is for the expected benefits to be delivered by the finished. Natural recovery timeframes for Great Artesian Basin Sustainability Initiative affected geological formations have been (GABSI) (i.e. a water bore efficiency estimated at 50% recovery by 30 to 80 years improvement program) to the Surat Basin after peak CSG development has occurred groundwater systems. The CSIRO (2012b) (QWC, 2012). However, the application of estimate that groundwater pressure decrease mitigation measures, including aquifer reinjection from CSG development is less than the potential and groundwater use efficiency improvements, is groundwater pressure increase assuming the expected to significantly reduce this period. GABSI is run to completion. For the Reinjection of treated CSG water to depleted Gubberamunda Sandstone for example, the formations may play an important role in QWC (2012) model predicts that by 2070 water mitigating the effects of CSG production on pressures over most of the aquifer reduce by less groundwater systems by increasing groundwater than 0.2 metres. However, over this same pressures in the injected formation and reducing period, the CSIRO (2012b) expect that water the hydraulic gradient with adjacent formations. pressures in the Gubberamunda Sandstone will Feasibility studies have shown that this increase by between 5 and 25 metres if the full technique can work under the right hydraulic and benefits of the GABSI are achieved. The CSIRO geochemical conditions (Klohn Crippen Berger, (2012b) conclude that the estimated decrease in 2011 and Santos, 2013), and trials are underway groundwater pressures from CSG development to determine the potential for broader application in the Surat Basin is relatively small, especially if of this impact mitigation strategy (APLNG, 2014; the GABSI is fully implemented.

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Summary: What are the expected impacts of induced aquifer leakage? 1. Induced aquifer leakage is predicted to impact a small number of spring complexes and water bores. Widespread, negative groundwater impacts are not expected due to low connectivity. 2. Water level reductions increase the risk of either bore impairment or harm to the ecological or cultural heritage values of springs. 3. Measures, such as Make Good Agreements, are in place to make sure bore owners are not disadvantaged and to determine the most appropriate impact mitigation techniques for springs. 4. Predicted groundwater impacts for the Surat CMA are expected to be reduced by aquifer reinjection and groundwater use efficiency improvements (i.e. the GABSI). 5. Ongoing groundwater monitoring and updating of regional groundwater models are continuing to improve the scientific understanding of groundwater impacts from CSG development.

Conclusion CSG development is expected to induce aquifer leakage, but the low degree of aquifer Aquifer connectivity describes the ease with connectivity means that widespread, negative which water can flow between geological impacts are not predicted. Current forecasts of formations. Water will only move between groundwater impacts from CSG production are formations if there is a large enough hydraulic limited to some aquifers in the Surat and gradient to overcome the resistance to flow that southern Bowen Basins. Predicted groundwater is provided by their vertical permeabilities and impacts could potentially be reduced by vertical separation. The results of field and reinjecting treated CSG water into aquifers and laboratory measurements and computer improving groundwater use efficiency. Also, modelling show that low aquifer connectivity is a where the function of bores in the Immediately dominant geological characteristic of aquifers Affected Area is impaired by CSG activities, CSG across the Surat, Bowen and Galilee Basins. operators are legally obliged to make good the The low degree of connectivity reflects a high bores so that landholders are not disadvantaged resistance to cross formation flow due to the low by their activities. Data from ongoing monitoring vertical permeabilities of coal measures and and research projects will provide new aquitards and the often considerable vertical knowledge of aquifer connectivity and continue to separation distances between aquifers and coal build confidence in the predicted effects of CSG measures. development on groundwater resources.

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Glossary

Term Definition

Aquifer A saturated underground geological formation or group of formations, that can store water and yield it to a bore or spring. A saturated formation that will not yield water in usable quantities is not considered an aquifer. Aquitard A geological formation that prevents significant flow of water, e.g., clay layers or tight deposits of shale; geological material of a lower permeability. Basin (Geological) An area in which the rock layers dip from the margins towards a common centre; the site of accumulation of a large thickness of sediments. Confined Aquifer A saturated aquifer bounded between low permeability materials like clay or dense rock. Fault A crack in a geological formation caused by up shifting, or tectonic movement and uplift, of the earth’s crust, in which adjacent features of the formation are displaced relative to one another and parallel to the plane of fracture. Formation A sediment or rock, or group of sediment or rocks. Geologists often group rocks of similar types and ages into named formations. GABSI Great Artesian Basin Sustainability Initiative Geological See Formation Formation Groundwater (or underground water) Water found in the cracks, voids or pore spaces or other spaces between particles of clay, silt, sand, gravel or rock within the saturated zone of a geological formation. Hydraulic Gradient The difference in water pressure or water level across one or more formations over a unit distance. The hydraulic gradient indicates which direction groundwater will flow and how rapidly. Induced Aquifer Aquifer leakage that occurs in response to a disturbance to the groundwater system. Leakage Connectivity The ease with which groundwater can flow within or between geological formations. Immediately The area within which water level (or pressure) reductions are predicted to exceed a Affected Area (IAA) trigger threshold within three years. Threshold values have been set at 5 metres for consolidated aquifers (such as sandstones) and 2 metres for unconsolidated aquifers (such as sand aquifers). Long Term Affected The area within which water level (or pressure) reductions are predicted to exceed a Area (LAA) threshold at any time in the future. Threshold values have been set at 5 metres for consolidated aquifers (such as sandstones) and 2 metres for unconsolidated aquifers (such as sand aquifers). Measures A series of coal bearing rocks. Make Good See Water Act 2000 Agreement Permeable Capable of transmitting water through porous rock, sediment or soil. Permeability The property of a soil, sediment or rock indicating how easily water will be transmitted through it under a gradient. Sedimentary basin A geological basin containing a sequence of dominantly sedimentary rocks. Unconfined Aquifer An aquifer with no overlying low permeability layers that restrict water movement into the aquifer. The water level in an unconfined aquifer is known as the water table. Vertical The property of a formation indicating how easily or rapidly water will be transmitted Permeability vertically.

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