Application for Subsidence Management Approval. Subsidence Management Plan ANNEX D. Bettys Creek Subsidence Management Plan

Transcription

1 Application for Subsidence Management Approval Subsidence Management Plan ANNEX D Bettys Creek Subsidence Management Plan

2 Subsidence Management Plan Bettys Creek Glennies Creek Longwall Panels 10 to 17 Application for Subsidence Management Approval Bettys Creek Subsidence Management Plan for Glennies Creek Coal Management Pty Ltd January Delivering sustainable solutions in a more competitive world

3 Project Manager: Signed: Date: Partner: Joanne Woodhouse January 2007 Mike Shelly Glennies Creek Longwall Panels 10 to 17 Application for Subsidence Management Approval Bettys Creek Subsidence Management Plan Date: January 2007 Environmental Resources Management Australia Pty Ltd Quality System for the Glennies Creek Coal Management Pty Ltd January 2007 Project No This report has been prepared in accordance with the scope of services described in the contract or agreement between Environmental Resources Management Australia Pty Ltd ABN (ERM) and the Client. The report relies upon data, surveys, measurements and results taken at or under the particular times and conditions specified herein. Any findings, conclusions or recommendations only apply to the aforementioned circumstances and no greater reliance should be assumed or drawn by the Client. Furthermore, the report has been prepared solely for use by the Client and ERM accepts no responsibility for its use by other parties.

4 CONTENTS 1 INTRODUCTION 1.1 DESCRIPTION OF BETTYS CREEK MT OWEN MINE - BETTYS CREEK DIVERSION 2 2 SUBSIDENCE ASSESSMENT 2.1 SUBSIDENCE PREDICTIONS SUMMARY OF IMPACTS ON BETTYS CREEK 4 3 MANAGEMENT 3.1 NOTIFICATION REMEDIATION AND RESTORATION 5 4 MONITORING 5 AUDIT AND REVIEW REFERENCES ANNEXURES ANNEX A SUBSIDENCE INSPECTION FORM BETTYS CREEK LIST OF FIGURES FIGURE 1 LOCATION OF BETTYS CREEK 1 FIGURE 2 PROPOSED BETTYS CREEK DIVERSION 3 FIGURE 3 ARCHAEOLOGICAL SITES IDENTIFIED ALONG BETTYS CREEK 6

5 1 INTRODUCTION Environmental Resources Management Australia Pty Ltd (ERM) has been engaged by Glennies Creek Coal Management (GCCM) to prepare a subsidence management plan for Bettys Creek within the context of an overall Subsidence Management Plan (SMP) for mining Longwalls 10 to 17 in the Middle Liddell seam. The SMP is based on a risk assessment, and addresses potential subsidence impacts as a result of extracting these longwall panels. Longwall Panels 1 to 6 in the Middle Liddell seam were the subject of s138 approvals under the Coal Mine Regulations Act 1982 and extraction of those panels is complete. GCCM obtained SMP and s138 approval for Longwalls 7 to 9 in March and April 2006 respectively. The Mt Owen Mine, currently owned by Xstrata Mt Owen (XMO), has approval for open cut mining across approximately 200 hectares of the surface area covered by this SMP. It is anticipated that this open cut mine (known as the Eastern Rail Pit) will significantly change aspects of the existing local environment including changes which occur as a consequence of the realignment of Bettys Creek, which XMO have advised is expected to be complete by the end of DESCRIPTION OF BETTYS CREEK Bettys Creek is an ephemeral fourth order, Schedule 1 or 2 stream (DIPNR, 2005) that extends from Ravensworth State Forest southwards to the confluence of Bowmans Creek and Swamp Creek. In its current state, Bettys Creek has prolonged periods without flow with small permanent and semipermanent waterholes typically of moderate to high salinity. The Bettys Creek catchment has been extensively modified through logging, and clearing for mining and grazing. Relatively continuous riparian vegetation exists along the creek and is dominated by Casuarinas on the banks, along with sedges, rushes and grasses in the channel. In the upper sections of Bettys Creek, along Longwall 15 (refer to Figure 1), the creek is typically a Schedule 1 stream (DIPNR, 2005) characterised by a V shaped channel some 50m wide with little to no floodplain and bed slopes of the order of 0.6% to 1%. As the creek traverses Longwalls 10 to 14, it becomes a Schedule 2 stream (DIPNR, 2005) with bed slope decreasing to about 0.3% to 0.6%. Within this area the main channel becomes more sinuous and floodplain width increases (GeoTerra, 2006). Stream flow in Bettys Creek and its tributaries has been essentially absent due to the drought which persisted throughout the study period. Isolated storm events have generated short-term ponding, albeit with no stream flow. ENVIRONMENTAL RESOURCES MANAGEMENT AUSTRALIA _BETTYS CREEK/FINAL/3 JANUARY

6 Jobs/2005/ Bettys CreekMP-Fg1 Location.cdr SP Environmental Resources Management Australia Pty Ltd tion Area LW SMP Applica Source: Glennies Creek Coal Management Figure 1 Legend Location of Bettys Creek SMP Application Area 0 200m Mine Workings Proposed Mine Workings Glennies Creek Coal Management Pty Ltd Bettys Creek Management Plan

7 1.2 MT OWEN MINE - BETTYS CREEK DIVERSION XMO propose to divert Bettys Creek to the east around the Eastern Rail Pit, rejoining the natural creek downstream and south of the Pit. The diversion is to be undertaken as a three stage process (refer to Figure 2). Based on advice from XMO, the diversion is assumed to be complete prior to undermining in 2010 As indicated by GeoTerra (2006), the diversion may have the following effects on the natural channel of Bettys Creek within the Application Area. significant reduction in creek flow downstream of Mt Owen Mine workings due to runoff interception by the Eastern Rail Pit; reduced flooding and ponding, along with retention of flow in the diversion channel; reduced flood height and lateral extent of the 100 year ARI flood; lower alluvial groundwater levels; increased sediment discharge and accumulation in Bettys Creek downstream of the Stage 2 re-entry point (ie downstream of Longwall 14, refer to Figure 2); potential scouring of the natural bed and banks at the re-entry point of the Stage 2 diversion; potential loss of flow from the Stage 2 diversion into the Eastern Rail Pit if settlement and cracking of backfill and the compacted clay lined channel occurs; increased salinity in the creek waters if any overflow from the waste rock filled pit occurs; and increased siltation if new channels are not sufficiently stable. The creek bed over Longwalls 10 to 13 will not be directly mined by XMO, but may be affected by downstream changes in creek flow, sediment transport and stream water quality as a direct or indirect consequence of the Eastern Rail Pit operations. Reduced flows associated with Stage 3 of the diversion will significantly reduce the flow velocity, shear stress and stream power in Bettys Creek during flood events, which will reduce the potential for erosion. Bettys Creek may silt up over Longwall Panels 10 to 14 if there is insufficient flow to flush out the increased sediment loads. ENVIRONMENTAL RESOURCES MANAGEMENT AUSTRALIA _BETTYS CREEK/FINAL/3 JANUARY

8 2 SUBSIDENCE ASSESSMENT A subsidence assessment was carried out for Longwalls 10 to 17 in the Middle Liddell seam by Strata Control Technology (SCT) Pty Ltd (2006). This report is included as Annex F of the SMP Application Written Report. A surface and groundwater assessment was carried out by GeoTerra Pty Ltd (2006) with specific reference to subsidence impacts on surface drainage within the Longwall 10 to 17 Application Area. This report is included as Annex D of the SMP Application Written Report. 2.1 SUBSIDENCE PREDICTIONS Subsidence monitoring results from Longwalls 1 to 6 have provided a basis for SCT to estimate subsidence over future Middle Liddell seam longwall panels. As additional monitoring results become available, it will be possible to provide an increasingly greater level of confidence in these predictions. Table 2.1 summarises the maximum, ie. worst case subsidence predictions for Longwalls 10 to 17. Maximum subsidence of 1.6 metres is predicted over the longwall panels based largely on the expectation that estimated maximum subsidence will not exceed 65% of seam thickness mined. Table 2.1 Estimated Maximum Subsidence in Longwall Panels 10 to 17 Longwall Panel Maximum Predicted Subsidence (mm) Maximum Predicted Strain in Tension (mm/m) Maximum Predicted Strain in Compression (mm/m) Maximum Predicted Tilt (mm/m) Source: SCT (2006) Maximum subsidence is expected to develop following extraction from two or more subsequent longwall panels, so any point on the surface is likely to experience up to three separate phases of subsidence as subsequent adjacent panels are mined. Hence, at the completion of Longwall 10, the subsidence of a point on the surface above Longwall 10 will not yet have experienced maximum subsidence. Maximum subsidence above Longwall 10 will only occur after Longwalls 11 and 12 are mined. However, maximum tilts and strains are likely to develop over each individual longwall as they are mined. ENVIRONMENTAL RESOURCES MANAGEMENT AUSTRALIA _BETTYS CREEK/FINAL/3 JANUARY

9 D17/1 Bettys Creek Diversion - Stage 1C D15/1 D15/2 TRIBUTARY 1 Bettys Creek Diversion - Stage 1A Jobs/200 5 / BCMP -F g2proposed Creek Diversion.cdr SP Environmental Resources Management Australia Pty Ltd Source: Glennies Creek Coal Management D10/9 D11/1 D10/8 TRIBUTARY 4 D9/1 D12/1 D12/2 D11/2 D14/1 D13/1 D13/2 MT OWN RAIL SPUR FOREST ROAD BETTYS CREEK Bettys Creek Diversion - Stage 2 D9/3a D9/3 TRIBUTARY 3 D10/5 D10/6 D10/4 D9/4 D9/5 D9/6 TRIBUTARY 2 D13/3 Bettys Creek Diversion - Stage 1D D13/4 D10/7 Bettys Creek Diversion - Stage 1B LW SMP Application Area 0 200m Legend Mine Workings Waterway Surveyed Dam Figure 2 Proposed Bettys Creek Diversion Glennies Creek Coal Management Pty Ltd - Bettys Creek Management Plan Proposed Mine Workings

10 Subsidence troughs of up to 1.6 m deep are predicted to develop over Longwalls 10 to 17, with the greatest subsidence occurring over the longwall centres. Remnant highs will remain over the chain pillars within the overall subsidence trough, with around 0.4m subsidence developing over the chain pillars between Longwalls 10 and 11. The magnitude of subsidence over the chain pillars will reduce to around 0.1m between Longwalls 16 and 17 due to the increased depth of cover (GeoTerra, 2006). 2.2 SUMMARY OF IMPACTS ON BETTYS CREEK As indicated by GeoTerra (2006), the following subsidence impacts are likely to occur within Bettys Creek itself, particularly to the south of the proposed diversion. stream water quality, flow volumes and creek stability is not anticipated to be adversely affected due to extraction of Longwalls 10 to 17. However, some additional ponding may occur in subsidence troughs within the creek; no significant erosion or bedload sediment transport has been observed to date in Bettys Creek over Longwalls 10 to 17 due to the stabilising effect of the riparian vegetation. Similarly post subsidence erosion and deposition rates are not expected to significantly increase; and subsidence will increase the left and decrease the right over bank flows downstream of the Mt Owen Rail Spur for the 100 Year ARI design flood. However, the change is unlikely to cause major channel erosion in either the short or long term. Within the area of the proposed Bettys Creek diversion, GeoTerra (2006) predicts the following subsidence impacts are likely to occur. the XMO developments in Bettys Creek will overwhelm any adverse changes that may occur from subsidence over Longwalls 14 to 16; the Stage 1 and upstream (out of pit) Stage 2 diversions may be adversely affected by subsidence in terms of channel stability and erosion; and the Stage 2 diversion in the backfilled Eastern Rail Pit may be adversly affected in terms of channel stability and integrity. However, the channel is anticipated to be in operation for approximately 3.5 years before it is undermined by Longwall 13, thereby enabling an assessment of its inherent stability. ENVIRONMENTAL RESOURCES MANAGEMENT AUSTRALIA _BETTYS CREEK/FINAL/3 JANUARY

11 3 MANAGEMENT GCCM will be responsible for all costs involved with the monitoring and subsequent remediation and repair works associated with subsidence related impacts on the natural channel of Bettys Creek and, in conjunction with the Mine Subsidence Board (MSB), will be responsible for all costs involved with the monitoring and subsequent remediation and repair works associated with subsidence related impacts on the Bettys Creek diversion. It is important to note that the diversion has not yet been approved by the MSB as plans have not been submitted by XMO. GCCM, in consultation with DNR and the landowner, will manage any subsidence related impacts on the creek, with the management processes implemented dependent on the level of impact and the actual and potential consequences. 3.1 NOTIFICATION GCCM will provide all affected landowners with a monthly update of the current location of the longwall face and the estimated progress of the longwall during the following month. This will ensure that landowners are aware of impending potential subsidence impacts on Bettys Creek and the diversion. 3.2 REMEDIATION AND RESTORATION If adverse effects on Bettys Creek due to subsidence are observed, the creek and/or diversion will be rehabilitated to an appropriate standard. No specific mitigation measures are proposed for either the Bettys Creek main channel or floodplain. However, a monitoring program will be developed to determine if rapid changes in channel or floodplain form occurs and implement remediation measures (refer to Section 4.0). GCCM, in consultation with the landowner, will carry out any works that are required to return the creek, diversion channel and floodplain to a similar state as existed prior to subsidence. This may include, but is not limited to, draining ponded areas, re-establishing drainage paths or diverting surface water flows from areas of potential ponding. If remediation earthworks are required within an area of a recorded archaeological site, no disturbance will commence prior to the issuing of a Section 90 Permit by the Department of Environment and Conservation (DEC). Figure 3 shows the location of sites recorded within the Longwall 10 to 17 Application Area. ENVIRONMENTAL RESOURCES MANAGEMENT AUSTRALIA _BETTYS CREEK/FINAL/3 JANUARY

12 If remediation earthworks are required on protected land, as defined under the Rivers and Foreshores Improvement Act 1948, a Section 3A permit will be obtained prior to commencing disturbance. ENVIRONMENTAL RESOURCES MANAGEMENT AUSTRALIA _BETTYS CREEK/FINAL/3 JANUARY

13 Jobs/200 5 / BCMP -F g 3 Arch Sites Identified.cdr SP Environmental Resources Management Australia Pty Ltd Source: Glennies Creek Coal Management LW SMP Application Area 0 200m Legend SMP Application Area Mine Workings Waterway Surveyed Dam Existing Contour Figure 3 Archaeological Sites Identified along Bettys Creek Glennies Creek Coal Management Pty Ltd - Bettys Creek Management Plan Proposed Mine Workings Archaeological Site

14 4 MONITORING The monitoring of subsidence impacts will comprise three phases and will be based on the landowner providing access: Pre-mining monitoring to establish a baseline for subsequent monitoring and impact assessment. Monitoring within the predicted subsidence impact zone during mining to allow the implementation of subsidence impact management processes as required. Post-mining monitoring to establish that no further subsidence impacts are likely and to allow the completion of subsidence impact management processes. Cross-sections across Bettys Creek will be established approximately 100m apart prior to mining Longwall 10 to allow the measurement of any valley closure. Each cross-section will have survey monuments placed approximately 10m apart and will extend a minimum of 20m beyond the defined edge of the creek channel. A detailed monitoring program will assess whether rapid changes in channel or floodplain form occur following storm events which may require remediation if adverse effects occur due to subsidence. Water level loggers along with flow gauging and sediment deposition monitors will be installed in the creek at the Mt Owen Rail Spur bridge and downstream of Longwall Panel 10, outside the 20mm subsidence area, to monitor changes in the creek due to weather variations, XMO operations and subsidence activity. Visual inspections of Bettys Creek through the various stages of diversion and undermining will be recorded on a Subsidence Inspection Form Bettys Creek, included as Annex A to this document. The pre-mining monitoring will comprise: an initial study and assessment of the surface water systems; an initial survey of Bettys Creek cross-sections to determine a baseline for valley closure; documented visual inspections of any ponded areas during and after rain events; photographic records of any observed changes; recording daily rainfall at the mine site; and ENVIRONMENTAL RESOURCES MANAGEMENT AUSTRALIA _BETTYS CREEK/FINAL/3 JANUARY

15 opportunistic inspections by the landowner. main channel flow; bed and bank stability; erosion and sedimentation; riparian vegetation, and; flooding. The monitoring during mining will comprise: documented visual inspections of the main channel and floodplain during and after rain events; photographic records of any observed changes; recording daily rainfall at the mine site; and opportunistic inspections by the landowner. The post-mining monitoring will comprise: a survey of Bettys Creek cross-sections at the completion of each longwall panel to determine the extent (if any) of valley closure; documented visual inspections of subsidence impacted areas during and after the first two significant rain events, after the second subsequent longwall panel is complete; and photographic records of any detected changes. ENVIRONMENTAL RESOURCES MANAGEMENT AUSTRALIA _BETTYS CREEK/FINAL/3 JANUARY

16 5 AUDIT AND REVIEW An audit of this management plan will be carried out at the completion of each longwall panel as per Section 11 of the SMP Application Subsidence Management Plan. A review of this management plan in terms of monitoring intensity/frequency, management responses and overall practicality will be carried out at the completion of each longwall panel and refinements introduced as appropriate. Of particular note during the review process will be the status of the Bettys Creek diversion and the results of the GCCM and XMO monitoring programs. This information will be used to refine the management and monitoring processes proposed prior to undermining the diversion. ENVIRONMENTAL RESOURCES MANAGEMENT AUSTRALIA _BETTYS CREEK/FINAL/3 JANUARY

17 REFERENCES DLWC (2000) Draft Guidelines for Management of Streams in Coal Mining Hunter Valley. Department of Land and Water Conservation. GeoTerra (2006) Longwall Panels 10 to 17 Surface Water and Ground Water Assessment, Glennies Creek Colliery NSW. Prepared for Integra Coal Pty Ltd, July SCT Pty Ltd (2006) Subsidence Assessment for Longwalls 10 to 17 at Glennies Creek Colliery. Prepared for Glennies Creek Coal Management Pty Ltd, July ENVIRONMENTAL RESOURCES MANAGEMENT AUSTRALIA _BETTYS CREEK/FINAL/3 JANUARY

18 Annex A Subsidence Inspection Form Bettys Creek

19 Glennies Creek Colliery Subsidence Management Plan Bettys Creek Subsidence Inspection Form Bettys Creek Date of Inspection: Longwall being Mined: Time of Inspection: Longwall Face Chainage: Landowner: Rainfall in Last 7 Days (mm): OBSERVATION YES NO COMMENTS/ACTIONS Bettys Creek Floodplain Evidence of subsidence induced cracking? Evidence of subsidence induced erosion? Evidence of any ponding? Bettys Creek Channel Have water level loggers, flow gauging and sediment deposition monitors been downloaded? Evidence of channel erosion? Evidence of any ponding? Disturbance to riparian vegetation? Bettys Creek Diversion Evidence of channel erosion? Evidence of any ponding? Disturbance to riparian vegetation? Attach results from the water level loggers, flow gauging and sediment deposition monitors

20 Glennies Creek Colliery Subsidence Management Plan Bettys Creek Summary of Water Monitoring Results: Other Observations/Comments: Name: Signature:

21 ERM consulting services worldwide Environmental Resources Management Australia 53 Bonville Ave Telephone (02) Thornton NSW 2322 Facsimile (02)