Latrobe Valley Regional REHABILITATION STRATEGY

Regional Water Study Synopsis Report Published by the Department of Jobs, Precincts and Regions 1 Spring Street , 3000 Telephone (03) 9208 3799 Prepared by the Department of Environment, Land, Water and Planning 8 Nicholson Street East Melbourne, Victoria 3002 Telephone 13 61 86 October 2019 © Copyright State Government of Victoria 2019 This publication is copyright. No part may be reproduced by any process except in accordance with provisions of the Copyright Act 1968. Authorised by the Victorian Government, Melbourne. Designed by DJPR Design Studio ISBN 978-1-76090-203-2 (Print) ISBN 978-1-76090-204-9 (Online) Disclaimer This publication may be of assistance to you but the State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication. Accessibility This publication is published in PDF and Word formats on djpr.vic.gov.au

Contents

Context and scope 2

Key findings 3

1. Water availability 3

2. Alternative water sources 4

3. Water quality 4

4. Ecological implications 5

5. Groundwater Monitoring 5

Technical summary 6

1. Environmental effects scoping study 6

2. Climate change projections 6

3. Water supply options feasibility assessment 7

4. Integrated water resource modelling scoping study 8

5. Pit water quality modelling scoping study 8

6. Environmental flow recommendations 9

7. Water availability 11

8. Water use scenarios 12

9. Groundwater flux modelling 12

10. Regional groundwater projections 13

11. Water-related effects 13

12. Pit lake modelling 14

13. Water availability for mine rehabilitation 14

LATROBE VALLEY REGIONAL REHABILITATION STRATEGY 1 REGIONAL WATER STUDY SYNOPSIS REPORT CONTEXT AND SCOPE The Latrobe Valley Regional Rehabilitation Strategy (LVRRS) is part of the Victorian Government’s response to the findings of the Hazelwood Mine Fire Inquiry (HMFI), which found significant uncertainties and knowledge gaps surrounding the rehabilitation and closure of the Latrobe Valley’s three brown coal mines. The HMFI’s Board of Inquiry found that, with the current knowledge available, some form of water body was the most viable rehabilitation option for the coal mine voids, but that many unanswered questions remain concerning the feasibility of the potential mine pit lakes1. The Strategy will address some of these knowledge gaps through technical studies undertaken as part of the Latrobe Valley Regional Rehabilitation Strategy. The Strategy considers the mines individually and collectively in the context of potential impacts (positive and negative) on the environment, Aboriginal and non-Aboriginal cultural heritage values, infrastructure and land uses in the Latrobe Valley, with a particular focus on water and land stability. The primary objective of rehabilitation is to achieve a safe, stable and sustainable landform for the closed mines.

The Regional Water Study assessed: This synopsis summarises the key 1. Potential water availability and findings of the Regional Water use of regional water resources Study, covering the following areas: for mine rehabilitation 1. Environmental effects 2. Potential alternative water 2. Climate change projections sources to those currently 3. Water supply options available to the three mines 4. Integrated water resource 3. Potential water quality impacts modelling in water bodies, groundwater and off-site surface waters 5. Pit lake water quality modelling 4. Potential impacts on aquatic 6. Environmental flow ecosystems and downstream recommendations users 7. Water availability 5. Scope of likely requirements for 8. Water use scenarios long-term regional groundwater monitoring. 9. Groundwater flux modelling 10. Regional groundwater projections 11. Water-related effects 12. Pit lake modelling 13. Water availability for mine rehabilitation

1 http://hazelwoodinquiry.vic.gov.au/201516-report/volume-iv-mine-rehabilitation/index.html

2 LATROBE VALLEY REGIONAL REHABILITATION STRATEGY REGIONAL WATER STUDY SYNOPSIS REPORT KEY FINDINGS

1. WATER AVAILABILITY • In three consecutive years It would take 15 to 30 years to fill (2011–2013) since 1997, inflows each mine pit with water using The Latrobe Valley has experienced significantly exceeded existing water sources dry conditions since 1997, and minimum flow needs and • Hazelwood has a void volume the LVRRS will need to be able consumptive use, indicating of 640 GL, and using a to account for uncertainty that climate and streamflow combination of groundwater around future climate and water still has the capacity to deliver (pumped for stability) and availability by planning for a good water years, although surface water, would take continuation of this drying trend potentially at a reduced 15 to 20 years to fill without and a drier future. frequency compared to interruption. If the dry conditions currently being pre-1997 conditions. • Yallourn has a predicted experienced in continue • Under long-term average final void volume of 725 GL into the future, there is a risk of conditions with a median climate at closure (2032), and using impacts if surface water is supplied change projection, average the same amount of surface for mine rehabilitation without water availability is likely to be water currently used for power conditions that protect other water sufficient to allow the mines to fill generation plus a supply of users and the environment. at a rate limited to current levels surface water equivalent to that of consumptive use for power • Average inflows since 1997 supplied to Hazelwood after generation without significantly into the system supply to Hazelwood ceases, impacting river function or water have declined sharply from would take 20 to 25 years to fill security until about 2035, after pre-1997 levels – from 800 GL/y without interruption. to 600 GL/y. which water availability may become more limited. • Loy Yang has a predicted final • Climate change projections for void volume of 1,420 GL at closure • Under current conditions or the region indicate a wide range (2048), and at current levels of a dry climate, average water of possible futures, from very groundwater and surface water availability is significantly lower, dry (500 GL/y average at 2040) usage would take 25 to 30 years with a relatively large proportion to wet (1,000 GL/y at 2040). The to fill without interruption. median prediction is a marginal of years in which surface water decline to 700 GL/y average supply for mine rehabilitation • These timeframes could be by 2040, and 650 GL/y by 2065. could not be sustained, although extended significantly if filling there could also be years of from surface water sources is • Water resource modelling relatively high water availability delayed due to dry conditions, or indicates that the recent dry in which water for rehabilitation shortened if smaller fill volumes period since 1997 could imply could be accommodated. are needed or additional water different trajectories for sources come available for use. future climate: • Although filling the mine voids with water would pose – The decline could be ‘on- a significant demand on the trend’, following a drying Latrobe system, supply of climate projection water for this purpose could (i.e. not a drought but be feasible if it is accepted the ‘new normal’) that the filling rate is limited – The decline could be a to the power stations’ current drought (temporary), with the annual net usage and that possibility of reversion to the filling is restricted or halted long-term average (closer to under dry conditions to prevent 800 GL/y) subject to a future unacceptable impacts on water possible decline associated security, other water users and with climate change. values including river function and the Lower Latrobe wetlands • Since 1997, there have been and Gippsland . shortfalls in river flows in 15 of 21 years, by up to 67% compared to • New water demands or future an average year, after extraction growth in the Latrobe Valley for consumptive uses. could reduce the amount of water available for mine rehabilitation if water availability is limited in the future and new sources of water are not found.

LATROBE VALLEY REGIONAL REHABILITATION STRATEGY 3 REGIONAL WATER STUDY SYNOPSIS REPORT Top-up for evaporative losses would 2. ALTERNATIVE WATER 3. WATER QUALITY be needed to maintain pit lakes SOURCES Water quality risks are not • An external supply of water Currently there are no alternative significant and are manageable would be needed to make up for water sources that are considered evaporative loss from potential • No significant sources of more feasible than existing water potential pollutants were pit lakes in order to maintain sources for mine rehabilitation, the required lake level. identified in the Hazelwood and although this may change in Loy Yang mine voids, and no • Under current climate conditions, the future significant water quality risks about 4–6 GL per year per • No alternative water sources were identified based on known mine void would be needed to of suitable quality, volume or mine materials at these sites. maintain water levels, totalling comparative cost are currently about 15 GL/y for all three mines. • Yallourn has a significant considered feasible at the quantity of stockpiled acid This is likely to increase under present time to assist in mine a drying climate. sulphate soils in the western rehabilitation compared to mine void, which will act as • For comparison, over 2017/18, existing water sources, although an ongoing source of acidity Gippsland Water supplied about this may change in the future. unless covered or inundated. 13 GL of water to its residential • Large volumes of water, of The impact of these materials and non-residential customers more than 5–10 GL/y, would be on water quality during filling is 2 (excluding major industry) . needed to materially hasten the expected to be manageable, and Keeping Hazelwood and Loy filling process, although smaller once treated, are not expected Yang dry would require ongoing volumes may become more to have any long-term impact. groundwater pumping important if mine void filling • Although no significant water occurs slowly. • Keeping these two mine voids quality risks were identified at a empty would require significant • Source water would need to be high level, the potential for water ongoing groundwater pumping of acceptable quality, including quality risks needs to be studied to maintain the safety and low nutrients and dissolved in detail at the end of mining stability of the mine voids. This contaminants. operations based on reliable and representative data. would likely result in ongoing • Treated recycled water from regional and local ground the , • Mine water bodies that are not subsidence. for example, while potentially regularly flushed may experience • Ongoing groundwater pumping offering high volumes (100 GL/y), a gradual decline in water quality is unlikely to be needed at the was found to have unacceptably over time (many decades) due Yallourn mine, even if it were high nutrient levels, which would to evaporative concentration of not to be filled with water, but result in high treatment costs salinity and other accumulated this could change depending in addition to the capital and contaminants, but the impact on the final mine void and the operating costs of a pipeline on water quality is not expected rehabilitation approach adopted to the Latrobe Valley. to be significant. at the other mines (which could • Some alternative water sources, • The main factor influencing increase groundwater levels in such as recycled treated water quality in the mine voids the area of the Yallourn mine). wastewater, may become more is the quality of the water used feasible or attractive if low to fill the voids. water availability in the Latrobe • Acceptable water quality system limits rehabilitation objectives are considered to progress significantly. be achievable without ongoing in-pit treatment if the water used to fill the mine voids is of suitable quality. • Any releases from the pit lakes would need to meet applicable water quality standards, and the final landforms should be configured to allow releases to be ceased or controlled. • Due to the very low rates of groundwater interaction with the pit lakes and the broadly benign water quality, no significant risk of groundwater quality impacts was identified.

2 https://www.gippswater.com.au/residential/about-us/governance/corporate-documents/annual-reports

4 LATROBE VALLEY REGIONAL REHABILITATION STRATEGY REGIONAL WATER STUDY SYNOPSIS REPORT 4. ECOLOGICAL 5. GROUNDWATER IMPLICATIONS MONITORING Failure to deliver minimum flow Existing groundwater monitoring requirements in the Latrobe River activities appear to be adequate would likely result in unacceptable considering the known risks impacts • Additional groundwater quality • Some Ramsar wetlands at monitoring near the mine pits the lower end of the Latrobe is expected to be required only River system have undergone if a water quality issue in a pit significant salinisation in lake is identified. No such issues recent years due to insufficient are predicted. freshwater flushing, caused • Groundwater drawdown and by a combination of dry recovery rates can be adequately conditions, lack of freshwater monitored using the existing flows, rising sea level and saline monitoring network if the inundation events. monitoring bores are maintained • Updated flow recommendations in adequate condition and data for the Latrobe River and lower is made available. estuary and wetlands quantify • Potential impacts on other the minimum flows needed consumptive users of to maintain sufficiently fresh groundwater would need to conditions in the lower reaches be assessed if any increase of the river, to counter salinisation in groundwater pumping of the highly valued Ramsar rates beyond those required wetlands and other fringing for maintaining stability or environments of the lower Latrobe extension of pumping duration River and Lake Wellington. is proposed. • Under a drying climate, the physical and ecological function of the river will inevitably change due to a natural decline in inflows, even before any consumptive use. • The impact of consumptive use, including for rehabilitation, is therefore expected to increase over time under a drying climate. • Sustained shortfalls in minimum flow requirements are likely to result in ongoing salinisation of previously freshwater wetlands and ecological areas, noting that shortfalls in flows from the Thomson and Macalister rivers also contribute to such impacts in the lower Latrobe estuary and Lake Wellington.

LATROBE VALLEY REGIONAL REHABILITATION STRATEGY 5 REGIONAL WATER STUDY SYNOPSIS REPORT TECHNICAL SUMMARY

1. ENVIRONMENTAL • It is important to investigate the • Rainfall, streamflow, evaporation EFFECTS water quality implications of and temperature factors were potential cumulative deposition provided for the 10% (dry), SCOPING STUDY issues arising from toxicants median and 90% (wet) The purpose of this aspect of the that may be introduced into the projections from the set of 42 study was to: mine void. global climate models considered in the Victorian Climate Initiative • It is necessary to further • understand whether sufficient in order to inform the range understand the geomorphic information is available to of possible futures. assess the potential effects processes in the area, of mine rehabilitation on specifically changes to erosion • Gridded scaling factors were water- dependent processes, sediment supply recommended for rainfall, environmental values. and geomorphic characteristics temperature and evaporation of the system. while catchment-aggregated • identify key information gaps change factors were that could be realistically filled 2. CLIMATE CHANGE recommended for streamflow. through the Strategy. Annual scaling was considered • provide the information needed PROJECTIONS to introduce less uncertainty to plan the remainder of the The purpose of this aspect of the than seasonal scaling factors, technical studies. study was to: subject to sensitivity analyses. The potential physical, hydrologic • understand potential changes • It was recommended that the and water quality changes that to water availability as a result full available climate dataset may occur as a result of mine of climate change and long-term from 1957 be used to model rehabilitation were assessed, climate variability using future scenarios (with climate and the processes that may the framework and guidelines scaling factors applied), with be influenced by these changes of the Victorian Climate Initiative. pre-1975 data scaled to post- (in Gippsland waterways) and 1975 conditions to correct for water-related ecological assets Any assessment of the viability the 1975 step change. of water bodies (pit lakes) over that are vulnerable to these • It was concluded that modelling changes were identified. the medium to long term, during the rehabilitation (filling) period beyond 2090 is highly uncertain Key outcomes and into the future, needs to take and could be considered only account of potential changes to in a very qualitative sense. • The lower Latrobe estuary and water availability as a result of wetlands have experienced • The uncertainty associated climate change and long-term significant salinisation impacts with climate change is one climate variability (such as periods in recent years. Understanding of many that impact the of prolonged drought). Climate the drivers of this process Strategy, including changes projections were derived for use in is essential to assess the in consumptive water demand, modelling rehabilitation scenarios, potential for these impacts bushfire risk, and land use- water sources and fill rates. to be exacerbated by mine driven changes to streamflow. rehabilitation. Key outcomes • Up-to-date knowledge of • The climate factors environmental flow requirements recommended by the Victorian for the length of the Latrobe Climate Initiative Guidelines3 River from Lake Narracan to (using the empirical downscaling Lake Wellington is essential to method) at 2040 and 2065 for assess potential flow-related the climate scenario accepted impacts of mine rehabilitation. as being representative of current trends were found to be adequate for projections up to about 2090.

3 DELWP, 2016. Guidelines for assessing the impact of climate change on water supplies in Victoria. Department of Environment, Land, Water and Planning. December 2016. https://www.water.vic.gov.au/climate-change

6 LATROBE VALLEY REGIONAL REHABILITATION STRATEGY REGIONAL WATER STUDY SYNOPSIS REPORT 3. WATER SUPPLY • New or alternative water sources – Other local recycled water OPTIONS FEASIBILITY were found to be comparatively and stormwater streams are more expensive, too difficult considered to be of too small ASSESSMENT to access, and/or of too small a volume to meaningfully The purpose of this aspect of the a volume to materially contribute impact regional rehabilitation study was to: to rehabilitation at this point decisions at the present in time, although this may time, but may become more • investigate potential water change in the future with attractive if water availability sources, in addition to existing changes in water availability becomes more constrained water sources that are being and/or investment in alternative in future. used for power generation, that water sources. could be considered for use in – Although the rapid mine rehabilitation. • Specific water sources assessment did not reveal of note include: any feasible alternative A comprehensive list of ideas water supply options, a – Recycled water from the for possible alternative water more thorough assessment Eastern Treatment Plant sources was developed through of specific options could be could potentially provide a stakeholder workshop. warranted in future. Such an large volumes (100 GL/y) of These ideas were then subjected investigation could include reliable flow and is broadly of to a rapid desktop assessment environmental, economic acceptable quality, but would based on potential water volumes, and broader social impacts. costs, water quality, logistics, require significant investment infrastructure requirements, timing, in a pipeline. However, the availability, regulatory and licensing water’s elevated nutrient levels requirements, and stakeholder could potentially present an planning and integration aspects. unacceptable risk for a pit Ideas with potential feasibility lake. Investment into treatment for mine rehabilitation would then was considered to be required be assessed in more detail to reduce this water quality in follow-up studies. risk to acceptable levels. The potential sources of water – Water sourced via a included various sources in connection to the Victorian the Latrobe system, stormwater, water grid would compete recycled water, wastewater, with urban uses, which are desalinated water and water already under significant from the Victorian water grid. pressure, and expected to be much more costly than local Key outcomes water sources. • No new or alternative water – Desalinised seawater was sources were found to be considered to be prohibitively feasible for mine rehabilitation expensive, and raw seawater at this point in time. to present significant risks • Existing groundwater extraction to freshwater groundwater and supply from the Latrobe systems and water-dependent River, its tributaries and storages ecosystems. are therefore considered the most feasible source of water, subject to appropriate access arrangements, infrastructure and management constraints.

LATROBE VALLEY REGIONAL REHABILITATION STRATEGY 7 REGIONAL WATER STUDY SYNOPSIS REPORT 4. INTEGRATED WATER • The impact on streamflow from 5. PIT LAKE WATER RESOURCE MODELLING groundwater dewatering of QUALITY MODELLING deep regional aquifers can be SCOPING STUDY considered by a surface water SCOPING STUDY The purpose of this aspect of the model. It is expected that losses The purpose of this aspect of the study was to: from streams to groundwater study was to: will not change significantly • understand the requirements and may not occur for decades • assess geochemical and and technical constraints or indeed centuries. water-related risks associated for modelling the pit lakes’ with rehabilitation of the three interaction with surface water • A pit lake model is needed to Latrobe Valley mines. and groundwater. integrate water from surface water, evaporation and • develop an approach to • develop a framework and groundwater. The pit lake and modelling the three systems approach for completing the surface water models need to based on risk prioritisation. modelling studies. synchronise volume and rate As part of the study, a technical Workshops were held to deliberate data from surface water sources panel of geochemists toured on possible approaches and to the pit lakes, and the pit lake each of the mines to identify mine available knowledge. The results of model and groundwater model domains (e.g. overburden dumps, the study were used to develop an fluxes will need to be reconciled. drains, ash dumps), materials of implementation or project execution • The GoldSim software package interest and potential water quality plan as an extension of this task. should be used to model pit lake risks based on observation and available knowledge. Key outcomes filling and water quality evolution. Key outcomes • A proprietary groundwater • The filling of pit lakes should model maintained by GHD consider solute transport, and the • No significant or unmanageable should be used to model pit lake model can then examine risks were identified based on groundwater behaviour near changes in concentration over an order of magnitude and in the pit lakes. time. The movement of chemicals assessment, although each site in groundwater can be assessed has specific risks that should be • A regional groundwater model using particle tracking. accounted for: maintained by the Geological Survey of Victoria should be used – Hazelwood is considered to to model groundwater behaviour have no significant identified on a regional basis. potential for pollution or water quality impacts related to the • The REALM (REsource ALlocation mineralogy and materials Model) modelling tool should in the mine pit. be used to model surface water in the Latrobe River system. – Yallourn is considered to have no significant contemporary • The near-pit surface and potential for pollution or water groundwater models can quality impacts in the Maryvale be run separately because and East Fields. However, surface water extraction is not the site is known to have a considered to have a material stockpile of acid-forming impact on groundwater, based materials (acid sulphate soils) on a lack of strong interaction in the legacy Township field between the shallow aquifer pit. These materials will release system and the deeper acidity, which will need to be regional aquifers. treated while the void is dry and during any filling process. There are predicted to be no ongoing acid inputs if inundated.

8 LATROBE VALLEY REGIONAL REHABILITATION STRATEGY REGIONAL WATER STUDY SYNOPSIS REPORT – Loy Yang has notable horizons 6. ENVIRONMENTAL FLOW The Latrobe system was of marcasite – a potentially RECOMMENDATIONS dividedinto 11 reaches, with acid-forming sulphide mineral. flow recommendations derived However, these horizons are The purpose of this aspect of the foreight using the latest methods only up to 15 cm thick and study was to: and an expert process to meet objectives set in reference are exposed very rarely in • understand the minimum flow to the present geomorphology the mine pit batters. They requirements for the Latrobe and values of the Latrobe are therefore predicted to system as a key input to the system(which reflect the have no discernible impact assessment of water availability current flow regime after on the water quality of a pit for mine rehabilitation. lake. Under a partial pit lake consumptive extraction). scenario, slow release of acid The Latrobe River, its tributaries, The flow recommendations were is possible (due to exposure estuary and wetlands are subject set according to the seasonal of acid-forming materials to a highly regulated flow regime timing and minimum duration, to air) but expected to be as a result of water resource magnitude (daily flow volume) and of minor significance, and development and water use in frequency of flow events needed could be minimised through the catchment. The study was to meet the established objectives. appropriate cover design. conducted for the system from The flow events represent different Lake Narracan to Lake Wellington, elements of a natural flow regime, • All three mines have external including the main tributaries as depicted in Figure 1. overburden and ash dumps that (Morwell River, Traralgon Creek, have the potential to release Tyers River and ), the Key outcomes acid and other pollutants, and Lower Latrobe Wetlands, the these are currently, and should Latrobe Estuary and the • Flow recommendations continue to be in the future, Thomson Estuary. are largely consistent with managed separately from the previous studies, and the new mine pits. The Hazelwood mine The study was conducted using recommendations for additional void also contains an internal a standard FLOWS method4 in reaches are consistent with ash dump that will be required combination with the Estuary upstream flows. to be encapsulated in a way that Flows Method (EFAM)5, which are • The target reach for achieving prevents or minimises potential appropriate for estuarine and minimum flows (based on contribution of pollutants wetland areas. The assessment highest water demand) is the to a waterbody. sought to understand the minimum functional flow requirements in reach of river upstream of • The water quality of any reference to water-dependent Rosedale. The total amount of waterbody at all three mines ecological values using the best water required to deliver all the will be mainly influenced by available ecologic, hydrologic, flow recommendations for this the chemistry of the water hydraulic and geomorphic reach under an average climate used to fill the mine voids. information. scenario is about 560 GL/y. • Water body hydrodynamics It built on the previous Latrobe • If flow recommendations are met (limnology) in the mine pit would River environmental flow for the Latrobe and Thomson be difficult to predict due to the recommendations study completed rivers, this flow target is expected unusual thermal profile of the in 20076 and 20137, which was to achieve sufficiently regular voids (warm at base) and the yet- limited to the freshwater sections freshwater flushing of the lower to-be-determined quality of the Latrobe system upstream Latrobe estuary. Freshwater of water used to fill the void. of the Thomson River confluence. flushing has been deficient A risk management approach in recent years, resulting in (minimising nutrient and salinity significant salinisation impacts inputs) is considered appropriate in the estuary and dependent to meet water quality objectives wetlands. Opportunities to that would potentially support improve environmental flow beneficial use or discharge to regimes will be explored further receiving waters. through the LVRRS.

4 Department of Environment and Primary Industries. 2013. FLOWS – a method for determining environmental water requirements in Victoria. Victorian Government. Melbourne, Australia. (online) URL: https://rbms.com.au/wp-content/uploads/2014/06/DEPI-FLOWSmethodEdition2_WEB.pdf

5 Department of Sustainability and Environment. 2012. EFAM – Estuary environmental flows assessment methodology for Victoria. Victorian Government. Melbourne, Australia. (online) URL: http://hdl.handle.net/10536/DRO/DU:30056781

6 Earth Tech. 2007. Assessment of Environmental Flow Requirements for the Latrobe River – amended final recommendations report. Melbourne, Australia. (online) URL: http://www.vewh.vic.gov.au/__data/assets/pdf_file/0003/371883/Latrobe-River-Environmental-Flow-Assessment-Final- Recommendations-FINAL-compressed.pdf

7 Water Tech (2013). Latrobe River Estuary Environmental Flows Investigation. Melbourne, Australia.

LATROBE VALLEY REGIONAL REHABILITATION STRATEGY 9 REGIONAL WATER STUDY SYNOPSIS REPORT Overbank

Bankfull Wet Season Fresh

Dry Season

Flow volume Flow Fresh

Dry Season Wet Season Baseflow Baseflow

Example of a river Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec cross section

Figure 1: Notional hydrograph of the terms used to describe the flow regime, and thus flow recommendations, for the environmental flow recommendations study for the Latrobe River, estuary and Lower Latrobe Wetlands.

7. WATER AVAILABILITY Key outcomes • The results therefore indicate that the possibility of a dry • The historic water availability The purpose of this aspect of the climate needs to be planned in the Latrobe system appears study was to: for while remaining flexible to to have undergone a step the relative opportunities of • quantify historical water change since 1997 corresponding a possible return to long-term availability in the Latrobe to a reduction in long-term average or wet conditions. River system. average flow of about 800 GL/y • model water availability over the to an average of about 600 • Under a dry climate, flows timeframe of mine rehabilitation GL/y over the past 20 years in the Latrobe system could considering possible climate (illustrated by the dashed green decline significantly by 2060 change futures and long-term line in Figure 2). to about 400 GL/y on average. Such a decline would drive an climate variability. • The ‘dry climate’ projection incremental change in character based on the post-1997 period, This study used the reconstructed for the Latrobe River system, and which includes the Millennium unimpacted historic inflows into would require re-assessment of Drought, is possibly consistent the Latrobe River (upstream the minimum environmental flow with the observed step change of Rosedale) derived using the requirements for the system. Latrobe REsource ALlocation Model in the Latrobe system since 1997 (REALM)8 for 1957 to 2017, with pre- (average 600 GL/y). 1975 streamflow data scaled to • This step change (post-1997) match post-1975 climate conditions. and ‘dry climate’ projection could This dataset represents streamflow have two possible interpretations in the absence of all consumptive – continued drought period and/ water use and farm dams. or drying trend, which makes To model the potential change modelling future scenarios in water availability into the future, difficult and uncertain. By using climate change factors were a long-term dataset, the drought applied to the long-term inflow represents an anomaly and thus average under the wet, median modelling intrinsically shows and dry climate scenarios, a return to long-term average interpolating the factors between conditions. 1995 and 2040, and between 2040 • To overcome this, an analytical and 2065, and extrapolating the approach based on climate 2040–2065 trend beyond 2065. statistics was adopted, and the The sensitivity of the results on two interpretations considered the 1995 start date (mid-point of separately as equally possible the 1975–2014 Victorian Climate climate pathways. Change Initiative analytical period) for applying incremental climate change (and plausible alternatives) is considered in the findings9.

8 GHD. 2018. Latrobe Water Resource Model Daily Input – Stage 2 Input Derivation and Validation. A report written for the Department of Environment, Land, Water and Planning. Melbourne, Australia. 9 DELWP, 2016. Guidelines for assessing the impact of climate change on water supplies in Victoria. Department of Environment, Land, Water and Planning. December 2016. https://www.water.vic.gov.au/climate-change.

10 LATROBE VALLEY REGIONAL REHABILITATION STRATEGY REGIONAL WATER STUDY SYNOPSIS REPORT 1600 Future projections

1500 Actual 1400 inflows

1300 1-IN-20 WET (LONG TERM)

1200

1100

1000 Wet climate projection

900 Long-term average 800

700

600 Median climate projection Average since 1997 500

400 1-IN-20 DRY (LONG TERM)

300 Dry climate projection

200

100

0

1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030 2035 2040 2045 2050 2055 2060 2065 2070 2075 2080 2085 2090

Figure 2: Total water availability in the Latrobe system (upstream of the Latrobe-Thomson confluence) using historical inflows and climate projections.

LATROBE VALLEY REGIONAL REHABILITATION STRATEGY 11 REGIONAL WATER STUDY SYNOPSIS REPORT 8. WATER USE SCENARIOS • Under a full pit lake scenario, Key outcomes top-up to account for • Due to the need to maintain The purpose of this aspect of the evaporative losses would in low aquifer pressures (by study was to: the first instance be sourced groundwater pumping) during via existing pipelines from the • model filling of the mine voids filling the mine void with water, Latrobe River and not local with water to full and partial levels groundwater seepage is not catchments. and fill rates using potentially a material contributor to the locally available water sources Key outcomes filling volume (although pumped in order to determine filling groundwater is assumed to be • Water use scenario modelling timeframes and interactions transferred to the mine void shows that under the above among the three filling pits and during pit filling as a significant assumptions, there is no operating power stations. proportion of the final lake material change to current volume). The key assumptions adopted patterns of water use over the for the modelling analysis, which course of rehabilitation, and no • Groundwater fluxes (inward would be revisited as part of the undesirable effects due to early and outward) under a full pit analysis supporting any future closure (i.e. stacking of impacts). lake scenario are considered mine rehabilitation planning, to be very small (<0.5 ML/d), in • Evaporation from the pit lakes are as follows: comparison to pit lake volume, should be estimated in the and change in direction over • In order to prevent instability, first instance using Morton’s time and location in the mine groundwater pumping continues shallow lake evaporation, which void (both in terms of elevation until stability is achieved and is available as gridded data in and pit perimeter) in response then is slowly ramped down the Latrobe Valley. Evaporation to recovery of groundwater based on mine configuration under current conditions is pressures. and known risks. This effectively predicted to be of the order decouples this analysis of of 4–6 GL/y per water body. • The contribution of groundwater pit filling from groundwater seepage to pit lake filling, either • The timeframe for filling behaviour in the confined losing or gaining, is less than of the mine pits under these aquifers (underlying Hazelwood 0.5% of annual fill rates. and Loy Yang) and allows assumptions is in the range groundwater modelling to be of 15–20, 20–25 and 25–30 years • At Hazelwood, due to the low flux conducted using a simplified for the Hazelwood, Yallourn and rates, it is considered there will groundwater pumping scenario. Loy Yang mines, assuming that be little interaction between the all mines continue operating to pit lake and groundwater. • Only existing physical water planned closure and there is no • At Hazelwood, net groundwater access arrangements for the interruption of surface water fluxes into the pit, after recovery three mines and power stations supply (noting that interruption of groundwater pressures do are considered as potential local of water supply over these time not appear sufficient to support water sources. frames is likely and would result a stable pit lake level, meaning in extension of these timeframes • A supply of surface water, such that additional water would be for filling). as that supplied in the past required to maintain a stable by Gippsland Water for power partial pit lake level (~1 ML/d of generation, could be made 9 GROUNDWATER FLUX inflows versus net evaporative available to all mine operators MODELLING loss of ~11 ML/d). in a sequential manner over time. The purpose of this aspect of the • The accuracy of modelling • Water extraction from study was to: is subject to ongoing review; the Latrobe River under however, given the very small arrangements similar to the • predict the likely movement of interaction with groundwater, existing arrangements for power groundwater into and out of the significant error in flux generation would be limited to mine voids and possible pit lakes predictions does not materially the current level of consumption in the context of rehabilitation, in change the outcomes. (i.e. not the full nominal volume order to understand the potential of the entitlement or licence). contribution of groundwater to • Similar findings hold for the This acknowledges that the the water balance during and Yallourn and Loy Yang mines, effects of current usage are well post filling, and the potential for but would need to be re- understood and serves as a local groundwater contamination evaluated once mining ceases. benchmark for potential future or other groundwater impacts. provision of water for mine rehabilitation.

12 LATROBE VALLEY REGIONAL REHABILITATION STRATEGY REGIONAL WATER STUDY SYNOPSIS REPORT 10. REGIONAL 11. WATER-RELATED • Water use for mine rehabilitation, GROUNDWATER EFFECTS if limited to the current volumes of water use associated with PROJECTIONS The purpose of this aspect of the power generation, is considered The purpose of this aspect of the study was to: to have no additional significant study was to: • identify the aquatic ecosystem effect on the seasonal or total values that could potentially be annual flow in the Latrobe • predict the recovery and future system. trajectory of groundwater levels impacted by mine rehabilitation. and pressures in the context • describe the current condition • However, under an increasingly of mine rehabilitation, climate and existing trajectories of drying climate (as indicated by change and other factors such these values. modelling), the total footprint of as offshore oil and gas extraction water take for mine rehabilitation (which uses significant volumes • determine the potential effects would increase. of groundwater from regional of mine rehabilitation on these • While there is insufficient aquifers). ecosystems. evidence to draw definite The study provides an • recommend ways to improve the conclusions, the study understanding of whether regional condition of these ecosystems. proposed that continued extraction of water at current aquifers are likely to eventually The study considered the system levels (without conditions) under recover to pre-mining levels and as five mega-habitats, including a drying climate scenario would identify the need for, and location shallow lakes (Lake Wellington), likely exacerbate the existing of, groundwater monitoring. freshwater wetlands (Sale negative impacts on the high Common), variably saline wetlands Key outcomes value aquatic ecosystems (Heart and Dowd Morasses), of the Latrobe. • Groundwater pressures in the Latrobe estuary, Latrobe River and deep confined aquifers currently the tributaries. Rehabilitation water pumped by the mines to maintain use scenarios were used to assess stability are considered unlikely the impacts on the flow regime to fully recover to pre-mining and thus the potential effects levels on a regional basis due to on aquatic ecosystems. insufficient recharge under most future climate scenarios. Key outcomes • The predicted degree of • The condition of many aquatic permanent decline depends ecosystems in the Latrobe system on the climate scenario used. are considered to be in decline. This is especially significant for • These results potentially the end-of-system Ramsar sites, have implications for future recognised as wetlands groundwater management and of international significance. sustainable yields in the region. • Power generators discharge • Whether rehabilitation results slightly turbid and saline waters in a partial or full pit lake is into Morwell River and Traralgon considered to have no material Creek as a result of their effect on the recovery of deep operations. The cessation of groundwater pressures, other coal-fired power generation will than potentially delaying mean that these tributaries may recovery if groundwater pumping experience better water quality continues for an extended period. but a higher frequency of cease- • No need for additional to-flow periods. groundwater monitoring beyond • Further reduced freshwater the existing monitoring network inflows and rising sea levels was identified. could increase salinity in Lake Wellington, the Latrobe estuary and fringing wetlands, reducing freshwater habitat.

LATROBE VALLEY REGIONAL REHABILITATION STRATEGY 13 REGIONAL WATER STUDY SYNOPSIS REPORT 1600 Back-casting of 2015 allocations Future projections Latrobe River System Inflows and Use Power Generation 1500 Actual Other existing water users Minimum Environmental Water Requirements 1400 inflows

1300

1200

1100

1000 Wet climate projection

900 Long-term average 800

700

Average 600 since 1997 Median climate projection

500

400

300 Dry climate projection

200

100 Estimated average minimum flow requirements

0

1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030 2035 2040 2045 2050 2055 2060 2065 2070 2075 2080 2085 2090 Figure 3: Water availability in the Latrobe River system – Latrobe River inflows compared with minimum river flow recommendations and consumptive uses, including power generation and possible future pit lake filling. This assumes no change in future demand for non-mining consumptive use.

12. PIT LAKE MODELLING Key outcomes 13. WATER AVAILABILITY The purpose of this aspect of the • The modelling shows that the FOR MINE study was to: water quality of the pit lakes REHABILITATION is dominated by the quality of This aspect of the study integrated • develop a fit-for-purpose model water sources used to fill the the technical studies to: that could be used to simulate mine void, and not potential filling of the mine voids, including local pollution sources. • understand the implications for water balance and water quality mine rehabilitation and the types • The scenario of a pit lake with evolution, using the information, of decisions that would need to ongoing external water input parameters and assumptions be made to develop the Strategy. captured and derived during the (of suitable quality) and outflow Regional Water Study that can is more likely to achieve and Key outcomes maintain higher water quality. be updated in the future. • Water availability in the Latrobe The model was implemented in • Mine water bodies that are River system is uncertain given GoldSim using a daily timestep, with not regularly flushed are likely the wide range of possible many options for configuration and to undergo gradual decline in climate projections, as depicted testing of rehabilitation parameters water quality over time (e.g. 100 above in Figure 3. such as water sources and fill rates, years) due to accumulation and evaporative concentration of • In dry periods, water availability catchment interception, climate can fall significantly short of projections and input water salinity and potentially other contaminants in supplied water. minimum environmental flow quality parameters. requirements and consumptive • No significant water quality risks usage. were identified at this stage, although this would need to be • In wet periods, there are reassessed at the end of mining sufficient local water resources operations and consider also to meet all demands including the water quality of the proposed potentially mine rehabilitation. water supply. • The frequency of dry and wet periods is uncertain, and more frequent dry periods could result in limitation to water availability and delays to mine rehabilitation if based on a partial or full pit lake.

14 LATROBE VALLEY REGIONAL REHABILITATION STRATEGY REGIONAL WATER STUDY SYNOPSIS REPORT Contact us This report is available at www.water.vic.gov.au/ waterways-and-catchments/our-catchments/RWS/ Please visit earthresources.vic.gov.au/projects/lvrrs to learn more about the Latrobe Valley Regional Rehabilitation Strategy or you can contact the project team at [email protected]