APPENDIX 5 Updated Subsidence Assessment UMWELT (AUSTRALIA) PTY LTD Russell Vale Colliery: Subsidence Assessment for Proposed Workings in Wongawilli Seam at Russell Vale East UMW4609 REPORT TO David Holmes Principal Environmental Consultant Umwelt (Australia) Pty Ltd 75 York St TERALBA NSW 2284 TITLE Russell Vale Colliery: Subsidence Assessment for Proposed Workings in Wongawilli Seam at Russell Vale East REPORT NO UMW4609 PREPARED BY Stephen Wilson Ken Mills Date 3 October 2019 Stephen Wilson Mine Planner Report No Version Date UMW4609 Draft 16 June 2017 UMW4609 Final 10 July 2019 UMW4609 Version 2 3 October 2019 Ken Mills Principal Geotechnical Engineer RUSSELL VALE COLLIERY: SUBSIDENCE ASSESSMENT FOR PROPOSED WORKINGS IN WONGAWILLI SEAM AT RUSSELL VALE EAST SUMMARY Wollongong Coal Limited (WCL) is proposing to mine the Wongawilli Seam in the Russell Vale East area of Russell Vale Colliery located approximately 9km north-northwest of Wollongong. After consideration of the findings of two Planning Assessment Commission (PAC) reviews, WCL revised the proposed mining plan by removing secondary extraction by longwall method and to instead form first workings only with large width to height ratio pillars that are designed to be long-term stable. Umwelt Australia Pty Ltd (Umwelt), the lead consultant responsible for managing the Underground Expansion Project (UEP) approval process, commissioned SCT Operations Pty Ltd (SCT) to undertake a subsidence assessment for the revised mine plan layout. This report presents the results of our assessment. Our assessment indicates the proposed mining layout is likely to be long-term stable with low potential to cause significant surface subsidence, significant interaction with the overlying seams or significant interaction with existing groundwater systems. The proposed layout is not considered to have any potential to perceptibly impact natural surface features including upland swamps, cliffs including the Illawarra Escarpment, steep slopes, drainage lines, creeks, Cataract Creek and Cataract Reservoir. Assuming the overlying workings are not required to be drained for mining in the Wongawilli Seam, any impacts on groundwater are expected to be limited only to the immediate vicinity of the Wongawilli Seam and only in the area of the proposed mining. Some ongoing low-level ground movement, mainly horizontal movement associated with previous mining including the Wongawilli Seam longwalls, may not yet have ceased completely. This low-level movement has potential to continue to cause low-level impacts to Mount Ousley Road and valley closure across Cataract Creek that may be perceptible. This movement is a legacy of previous mining and is not expected to be influenced by the proposed mining. Movement may continue irrespective of any further mining in the Wongawilli Seam. Two power transmission lines, a 330kV line and a 132kV line both supported on steel truss pylons, traverse the surface to the east of Mount Ousley Road. The pylons are very sensitive to differential ground movements that may occur if any marginally stable Bulli Seam pillars are destabilised. Uncertainty remains as to the extent of marginally stable pillars in the vicinity of these pylons. An engineered solution is expected to be required by regulatory authorities to manage the very low-likelihood, very high consequence risk to the power transmission pylons within the Work Health and Safety (Mines and Petroleum Sites) Regulation 2014 given the uncertain nature of the Bulli Seam layout and the limited options to reduce this uncertainty. Existing management plans for management of subsidence impacts and the monitoring included in them are focussed on longwall mining. A review of these is recommended based on the significantly lower levels of surface subsidence anticipated for the proposed system of mining compared to longwall mining. There may be potential to modify the frequency and nature of monitoring to achieve more effective outcomes. SCT Operations Pty Ltd – UMW4609 – 3 October 2019 i RUSSELL VALE COLLIERY: SUBSIDENCE ASSESSMENT FOR PROPOSED WORKINGS IN WONGAWILLI SEAM AT RUSSELL VALE EAST TABLE OF CONTENTS PAGE NO SUMMARY ............................................................................................ I TABLE OF CONTENTS .............................................................................. II 1. INTRODUCTION ............................................................................... 1 2. CONCLUSIONS AND RECOMMENDATIONS .............................................. 1 3. OVERVIEW AND BACKGROUND ............................................................ 3 3.1 Site Overview ...................................................................... 3 3.1.1 Surface Features ....................................................... 5 3.1.2 Proposed Mining Geometry .......................................... 5 3.2 Project Background .............................................................. 6 3.3 Surface Ownership ............................................................... 7 3.4 Surface Infrastructure ......................................................... 9 3.5 Natural Features ............................................................... 10 3.6 Heritage Features ............................................................. 11 3.7 Geological Setting .............................................................. 11 3.7.1 Coal Seams .............................................................. 14 3.7.2 Geological Structures ............................................... 16 3.7.3 Overburden Depth .................................................... 18 3.8 Previous Mining.................................................................. 18 4. PILLAR STABILITY .......................................................................... 21 4.1 Deformation Characteristics of Pillars ................................. 21 4.2 Pillar Loading ..................................................................... 22 4.3 Pillar Stability Assessment ................................................. 23 4.4 Pillars in Flooded Overlying Workings .................................... 25 4.4.1 Overlying Pillar Stability ............................................. 25 5. FORECAST GROUND MOVEMENTS FOR THE PROPOSED WORKINGS ............. 28 6. IMPACT ASSESSMENT OF FORECAST GROUND MOVEMENTS ..................... 31 7. REFERENCES ............................................................................... 33 APPENDIX 1 ...................................................................................... 34 A1. Review of Previous Mining Activity and Associated Impacts.... 34 A1.1 Bulli Seam Workings and Associated Subsidence ......... 36 A1.2 Balgownie Seam Workings and Associated Subsidence 40 A1.2.1 Vertical Subsidence ................................... 41 A1.2.2 Horizontal Strains and Tilts ........................ 44 A1.2.3 Valley Closure and Upsidence...................... 46 A1.2.4 Total Cumulative Subsidence ...................... 47 A1.3 Wongawilli Seam Longwall Mining ............................... 47 A1.1.1 Vertical Subsidence ................................... 49 A1.1.2 Extent of Vertical Subsidence Outside the Panel .................................................. 58 A1.1.3 Far-Field Horizontal Movements ................. 60 A1.4 Historical Mining Impacts .......................................... 61 A1.4.1 Surface Cracks ......................................... 61 A1.4.2 Rock Falls ................................................. 63 A1.4.3 Iron Staining ............................................. 64 A1.4.4 Cataract Creek ......................................... 64 A1.4.5 Power Transmission Towers ....................... 65 A1.4.6 Mount Ousley Road ................................... 65 SCT Operations Pty Ltd – UMW4609 – 3 October 2019 ii RUSSELL VALE COLLIERY: SUBSIDENCE ASSESSMENT FOR PROPOSED WORKINGS IN WONGAWILLI SEAM AT RUSSELL VALE EAST 1. INTRODUCTION Wollongong Coal Limited (WCL) is proposing to mine the Wongawilli Seam in the Russell Vale East area of Russell Vale Colliery located approximately 9km north-northwest of Wollongong. After consideration of the findings of two Planning Assessment Commission (PAC) reviews, WCL revised the proposed mining plan by removing secondary extraction by the longwall method and to instead form first workings only with large width to height ratio pillars that are designed to be long-term stable. Umwelt Australia Pty Ltd (Umwelt), the lead consultant responsible for managing the Underground Expansion Project (UEP) approval process, commissioned SCT Operations Pty Ltd (SCT) to undertake a subsidence assessment for the revised mine plan layout. This report presents the results of our assessment. The report is structured to provide: • conclusions and recommendations • overview and background, including a description of the site and the proposed first workings mining geometry • a summary of the deformation characteristics of coal pillars and expectation of the stability of the proposed pillars under the range of loading conditions likely below extracted workings in the overlying seams • an assessment of the ground movements expected from the proposed first workings geometry with consideration of the potential for greater than expected ground movements including from seam interaction effects • an impact assessment for surface features and surface infrastructure based on the magnitude of ground movements expected. A review of previous mining activity in the