Mine Water Releases Report
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APPENDIX 4 – MINE WATER RELEASES REPORT BYERWEN COAL PTY LTD – BYERWEN COAL PROJECT BYERWEN COAL PROJECT Mine Water Releases Prepared for: QCOAL PTY LTD 40 Creek Street BRISBANE QLD 4000 Prepared by: Kellogg Brown & Root Pty Ltd ABN 91 007 660 317 Level 11, 199 Grey Street, SOUTH BANK QLD 4101 Telephone (07) 3721 6555, Facsimile (07) 3721 6500 3 December 2013 BEW106-TD-WE-REP-0008 Rev. 0 CONTENTS Section Page 1 INTRODUCTION 2 RELEASE CRITERIA 2.1 Upper Suttor River Sub-Catchment 2-2 2.2 Rosella Creek Sub-Catchment 2-10 3 EFFECT OF RELEASES 3.1 Suttor River 3-1 3.2 Kangaroo Creek 3-5 4 CONCLUSIONS 5 REFERENCES BEW106-TD-WE-REP-0008 Rev. 0 iii 3 December 2013 1 Introduction The proposed mine water management strategy for the Byerwen Coal Project was described in Appendix 11 of EIS. This included details of the water management philosophy, expected water quality from the mine affected catchments, release strategy, proposed water infrastructure, water balance model and likely effects on hydrology, hydraulics and water quality. Since that report was prepared and based on discussions with the Department of Environment and Heritage Protection (EHP), the Department of Natural Resources and Mines (DNRM), and the Department of Science Information Technology, Innovation and the Arts (DISITIA), there have been some modifications to the proposed water quality objectives and release criteria which affect some of the water quality predictions associated with the Project. The purpose of this report is to explain the basis for the modified release criteria and to provide updated water quality predictions and impact assessment in the receiving environment upstream and downstream of the proposed mine. Water quality predictions are made using the water balance model detailed in the mine water management strategy (KBR 2013a). It is noted that the impact on water quality in the Suttor River associated with the mine water releases described herein, is based on revised water quality objectives for the Suttor River, updated as per discussions with EHP, DNRM and DISITIA, which is addressed in KBR (2013b), and on which this report relies. BEW106-TD-WE-REP-0008 Rev. 0 1-1 3 December 2013 2 Release criteria The proposed release criteria for the Project have been developed based on the Model Mining Conditions Guideline (EM944) – Version 4, 26 June 2013 (EHP, 2013) and have been developed with the objective of ensuring releases do not result in unacceptable water quality in the receiving environment. Several factors are considered when deriving release criteria in order to ensure this objective is met including: • receiving environment flow • receiving environment water quality • mine release rate • mine release water quality. Each of these aspects is described below to explain the basis for selection of the proposed criteria. 2.1 UPPER SUTTOR RIVER SUB-CATCHMENT 2.1.1 Derivation of release criteria Receiving environment flow Mine releases will only occur when flow conditions in the receiving environment are above a minimum level, and are derived from a runoff event. Runoff can be separated into two components: • surface runoff (storm flow), defined as the immediate runoff response of a catchment due to saturated soils or rainfall intensity becoming greater than soil infiltration rate • base flow, typically the delayed runoff response of a catchment and is caused by shallow infiltration that later feeds the surface water systems. An analysis of the hydrological regime of Suttor River was conducted in order to determine the flow threshold at which base flow dominates. The hydrological modelling approach was based on the Australian Water Balance Model (AWBM) and is detailed in Appendix 11 of the EIS. A comparison was made between observed data recorded at Eaglefield gauge on Suttor River and modelled runoff. The location of Eaglefield gauge is shown on Figure 2.2 and site details listed in Table 2.1. The comparison between observed and modelled duration curves are shown in Figure 2.2, suggesting that the hydrological model is suitable. BEW106-TD-WE-REP-0008 Rev. 0 2-2 3 December 2013 Table 2.1 Streamflow gauge details Station 120304A Station 120218A Name Suttor River at Eaglefield Kangaroo Creek at Byerwen Long/Lat 147.7143/-21.4504 147.9250/-21.1130 Catchment Area (km2) 1915 371 Data Period 17/08/1967 - Current 06/06/1979 - 01/10/1988 Data Completeness 84% 35% BEW106-TD-WE-REP-0008 Rev. 0 2-3 3 December 2013 Figure 2.1 GAUGING STATIONS USED FOR AWBM VERIFICATION BEW106-TD-WE-REP-0008 Rev. 0 2-4 3 December 2013 10000 1000 Observed runoff at Eaglefield Modelled runoff at Eaglefield 100 10 (m3/s) Flow 1 0.1 0.01 0.001 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Percentage of samples equalled or exceeded Figure 2.2 AWBM MODEL AT EAGLEFIELD (SUTTOR RIVER) The hydrograph was filtered using automated techniques described in Arnold et al (1995) to identify the baseflow component and the typical flow conditions at which baseflow prevails. Alternative methods were also used as a check, such as visual inspection of the hydrographs to identify the recession curve. The dominant flow regime is provided in Figure 2.3. This shows the component of runoff comprising “storm flow”. Approximately 15% of the time the flow in Suttor River is predominately “storm flow”. Storm flow Base flow 100% dominated dominated 90% 80% 70% "Stormflow" 60% comprising 50% 40% Runoff of 30% 20% Component 10% 0% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Percentage of samples equalled or exceeded Figure 2.1 FLOW REGIME EXCEEDENCE CURVE BEW106-TD-WE-REP-0008 Rev. 0 2-5 3 December 2013 Figure 2.4 shows in more detail the components of flow contributing to the hydrograph. The flow threshold at which storm flow and base flow components are equal is 0.75 m3/s. This value represents flow that is predominantly derived from a runoff event and therefore mine releases could occur. 10000 Storm flow component of Runoff 1000 Base flow component of Runoff Runoff 100 10 /s) 3 (m 1 "Base flow" dominant below 0.75 m3/s Flow 0.1 0.01 0.001 0.0001 0% 20% 40% 60% 80% 100% Probability of Samples Equalled or Exceeded Figure 2.2 BASE FLOW AND STORM FLOW COMPONENTS OF RUNOFF AT EAGLEFIELD (SUTTOR RIVER) Since there is no pre-existing gauge at the proposed flow gauging station for Byerwen, it is necessary to scale the hydrograph and proposed flow thresholds from the Eaglefield gauge to the proposed location. This is performed by scaling by catchment area, as presented in Table 2.2. Table 2.2 Derivation of low flow / recession flow trigger Suttor River @ Eaglefield gauge Suttor River @ (120304A) Byerwen Catchment area (km2) 1,915 825 Base flow / Storm flow 0.75 0.3 threshold (m3/s) (derived above) (scaled by catchment area) Adopted threshold (m3/s) 0.5 While the base flow / storm flow threshold is estimated to be 0.3 m3/s at the proposed gauging station at Byerwen, a conservative value of 0.5 m3/s (factor of safety of more than 1.5) has been adopted as the low/recession flow trigger. Triggers for medium, high, very high and flood flow regimes have been derived by analysis of the hydrograph. The frequency of exceedence for each flow regime is presented in Table 2.3. The very high and flood flow regimes are rarely met, and there is an even split between frequency of exceedance of the other flow regimes, suggesting that the proposed flow triggers are reasonable. BEW106-TD-WE-REP-0008 Rev. 0 2-6 3 December 2013 Table 2.3 Frequency of exceedance of nominated flow triggers Flow trigger Frequency of Flow regime (m3/s) exceedance (%) Low/Recession 0.5 13.5 Medium 1 10.9 High 5 5.2 Very High 15 2.2 Flood 50 0.7 Receiving environment water quality It is proposed to establish a water quality monitoring location downstream of the mine which can be used as a compliance point and referred to in an Environmental Authority (EA). Water quality between the release location(s) and the compliance point would not be influenced by third parties, such as discharges from Glencore’s Newlands Coal Project. The proposed compliance monitoring location is at the Byerwen lease boundary on the Suttor River, downstream of all potential mine releases. The proposed location is shown in Figure 2.5. In order to develop suitable water quality objectives at this location, a revised methodology and approach to deriving trigger values that will be representative of local site conditions is detailed in KBR (2013b). Releases from the mine would be structured such that they do not result in an increase in EC at the compliance location above the 75th percentile, which is 701 µS/cm, as per (KBR 2013b). Mine release rate The proposed release rates have been derived such that it is less than or equal to the natural flow in the receiving environment at the flow gauging station. The release rate has also been selected on the basis of dilution calculations in the receiving environment, using conservative end of pipe and receiving environment assumptions, incorporating a factor of safety. The proposed maximum combined release rate is shown in Table 2.4, together with the receiving flow trigger (derived earlier). Table 2.4 Comparison between flow trigger and maximum combined release rate Receiving environment Maximum combined Flow regime flow trigger (m3/s) release rate (m3/s) Low/Recession 0.5 0.5 Medium 1.0 0.5 High 5.0 2.0 Very High 15.0 4.0 Flood 50.0 10.0 BEW106-TD-WE-REP-0008 Rev.