Evaluation of Void Water intercepted by Werris Creek Coal Mine Operations

Transcription

1 Evaluation of Void Water intercepted by Werris Creek Coal Mine Operations Prepared for: Werris Creek Coal Pty Ltd Prepared by: Australia Pty Ltd Date: 10 April 2014 Project Number:

2 10 April 2014 Prepared by: Authorised by: Name: Simon Gaskell Name: Fiona Robinson Title: Senior Hydrogeologist Title: Senior Manager Phone: Phone: Signature: Date: 10/4/14 Signature: Date: 10/4/14 This document is issued in confidence to Werris Creek Coal Pty Ltd for the purposes evaluating impacts to groundwater from the mining operations. It should not be used for any other purpose. The report must not be reproduced in whole or in part except with the prior consent of Australia Pty Ltd and subject to inclusion of an acknowledgement of the source. No information as to the contents or subject matter of this document or any part thereof may be communicated in any manner to any third party without the prior consent of Australia Pty Ltd. Whilst reasonable attempts have been made to ensure that the contents of this report are accurate and complete at the time of writing, Australia Pty Ltd disclaims any responsibility for loss or damage that may be occasioned directly or indirectly through the use of, or reliance on, the contents of this report. Australia Pty Ltd VERSION CONTROL RECORD Document File Name Date Issued Version Author Reviewer _338 Evaluation of groundwater inflows Werris Creek Coal Mine 2014_FINAL _338 Evaluation of groundwater inflows Werris Creek Coal Min 2014_FINAL 5 March 2014 Draft 1 S Gaskell/F Robinson F Robinson 10 April 2014 FINAL S Gaskell/F Robinson F Robinson

3 10 April 2014 Contents Page 1 Introduction Background Study Objective Scope of Work 1 2 Groundwater Level Observations 3 3 Water Balance 5 4 Conclusions and Recommendations 13 5 References 14 6 Limitations User Reliance 14 List of Figures Figure 1 Figure 2 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Monitoring Well Locations Flow Chart Pit Inflows Calibration of the bore field (observed versus predicted groundwater levels) Identified Runoff Areas Measured Results vs Initial WBM Results Groundwater Inflow Scenario 1 (13 ML per year) Measured Results vs Initial WBM Results (m3) Groundwater Inflow Scenario 2 (106 ML per year) Measured Results vs Initial WBM Results (m3) Groundwater Inflow Scenario 3 (300 ML per year) Measured Results vs Initial WBM Results (m3 List of Tables Table 1 Table 2 Table 3 Table 4 Groundwater Monitoring Data Measured Water Balance Volumes (ML) Measured Water Balance Volumes versus Initial WBM (ML) Predicted Groundwater Inflow, Apr 2012 Mar 2013 Monitoring Period

4 10 April 2014 Page 1 1 Introduction Werris Creek Coal Mine (WCCM) is situated in the North West Slopes and Plains of New South Wales and is located 4km south of Werris Creek. The mine operates under project approval PA 10_0059 MOD 1. During the 2012/2013 Annual Review, WCC identified that the volume of void water (water intercepted in pit) had increased beyond that could not be accounted for by the existing surface and groundwater site balance. In addition, the previous assumption that the former underground workings were to be dewatered had not occurred due to spontaneous combustion management resulting in changes required to the groundwater model. 1.1 Background In 2005, Werris Creek Coal Mine commenced mining of the Greta Coal Measures Werris Creek outlier, situated within the Werrie Basin. The coal measures overlie Werrie Basalt, which is directly beneath and surrounds the coal measures in all directions. The upper layers of the basalt have been shown to be highly weathered to form a clay aquitard providing confinement to semi-confinement between aquifers within the coal measures and underlying basalt hard rock. Underground mining of part of the coal seam was undertaken prior to the commencement of open cut mining in The open cut operations will mine through the former underground mine workings. Planning approval for the open cut mining operations was sought in two stages, representing the initial project and the Life of Mine Project (LOM). Each stage was subject to a groundwater impact assessment which involved three dimensional modelling of the aquifer systems to assess impacts from the proposed operations. Modelling was based on measured groundwater levels for the project site and known or assumed geological parameters. Modelling for the second project approval, the LOM project, also included calibration of the initial model to observed site conditions. 1.2 Study Objective The objective of this study is to validate the groundwater model and calibrate the model to site specific conditions. Where site specific conditions invalidate the previous model, to evaluate impacts to the aquifer system and assess the significance of these in relation to the project approval trigger conditions. 1.3 Scope of Work The following scope of works was proposed to meet the project objective. 1. Review site groundwater monitoring data to assess drawdown in the aquifer in response to mining; 2. Assess the water balance volumes between the period September 2012 and March 2013 to validate groundwater inflows against modelled predictions; 3. Compare the observed groundwater inflows against modelled groundwater inflows and if necessary,

5 10 April 2014 Page 2 - re-calibrate the groundwater model against observed data if necessary and evaluate impacts to the aquifer for forward mine plans; and - evaluate the groundwater table recovery and stabilised level following cessation of mining and land rehabilitation. 4. Document the study in a report.

6 10 April 2014 Page 3 2 Groundwater Level Observations A summary of this monitoring data is presented in Table 1 and graphically in the following figures. The ten monitoring well locations below are shown in Figure 1. Table 1 Groundwater Monitoring Data Monitoring Well # Depth in m Drawdown in m (difference between last and first reading) 1 P P MW MW MW MW4b NK 3.7 MW MW MW MW MW At February Destroyed, last monitoring in September Destroyed during rail construction September NK not known Monitoring wells P1, MW1, MW4b, MW6, MW9 and MW14 showed drawdown trends that represent a declining head at these locations. Monitoring wells MW2, MW3 and MW5 showed stable or increasing head. Of those wells showing declining heads, changes in head were less than 4.0m except at P1 where a decline of approximately 15m has been observed. P1 is located immediately adjacent to the open cut pit and therefore would be more affected by drawdown impacts given its proximity. Monitoring well MW8 is considered to represent background fluctuations in an area unaffected by mining. This monitoring well has shows a drawdown of 2.5m compared to the initial standing level. The results suggest that the regional groundwater table is depressed following a period of lower than average rainfall (Bureau of Meteorology website, for years 2012, 2013 and year to date 2014).

7 10 April 2014 Page 4 P1 Figure 1 - Monitoring Well Locations

8 10 April 2014 Page 5 3 Water Balance A water balance model (WBM) representing flow to the pit void is shown in Figure 2. Groundwater Sources Former underground mine workings (Volume not measured) Coal measures strata (non-mine) (Volume not measured) Basalt Aquifer (Volume not measured) PIT VOID WATER STORAGE Surface Water Sources Infiltration direct to pit footprint (surface water volume estimated from modelling by others) Overburden seepage (not measured) Pit out flow (Flow meter) + water curtain losses 5% (Flow meter, %loss estimated) Figure 2 - Flow Chart Pit Inflows Following from Figure 2, the groundwater inflows to the pit can be estimated by Equation 1. Groundwater inflows = Pit out flow + change in pit void water storage + water curtain losses - surface water inflows [1] In the above, groundwater inflows and overburden seepage are determined using the calibrated groundwater model. Surface water runoff is determined from rainfall rates, the catchment area and assumptions of infiltration. Overburden seepage is determined using the calibrated groundwater model, and is directly related to rainfall and infiltration assumptions. Pit void water storage has been surveyed by the site surveyor since August Pit outflows are measured through a flow meter that is routinely monitored.

9 10 April 2014 Page 6 Data measured at the site between September 2012 and March 2013 is presented in Table 2. This data set is the most comprehensive set measured to date. For other monthly data, the site either did not monitor pit void water storages or the discharged pit void measurements were difficult to interpret due to site water management requirements. At the beginning of September 2012, i.e. the beginning of pit outflow monitoring which is considered to be accurate, the volume of water contained within the void was calculated to be 410 ML. At the end of March 2013, the volume of water contained within the void was calculated to be 83 ML. The total change in storage was therefore calculated to be 327 ML. Water pumped out of pit and recirculated through the mine workings has not been included in the out of pit pumping total but has been included as a loss from the void. It has been assumed that 95% of this water returns to the void in-pit storage, and 5% is lost through the pumping and reticulation process. This approach is considered reasonable as the purpose of the curtain is to maintain saturation at the working face and therefore there is direct connectivity through the workings (post blast) to the pit void. To estimate the contribution from surface water runoff to the pit void, daily rainfall data was input to the WBM either directly to the void surface area or as a percentage of runoff from areas discharging into the void. The void surface area was calculated from the relationship between the geometry of the void space (using survey data between September 2012 and March 2013) and the volume of water in the void. This relationship is presented in Figure 3. Three areas were identified to provide runoff input to the void: the active open cut area [50% runoff] including Overburden Emplacement; bare/compacted soil area to the north of the active open cut area [60% runoff]; and undisturbed land to the north of the active open cut area ( old colliery hill) [20% runoff].

10 10 April 2014 Page 7 Figure 3 Identified runoff areas Runoff coefficients were taken from the GSSE surface water assessment 1. With the exception of the void surface itself, the effects of evaporation on surface water are incorporated in the runoff coefficients. Evaporative losses from the void surface are calculated on the basis of daily average evaporation (in mm derived from Bureau of Meteorology monthly averages at Quirindi Post Office) from the surface area of the void. The surface area of the void changes as a result of the geometry of the void area and the volume of water predicted to be within it. Initial model runs were carried out with no input from groundwater to examine the results in the context of modelled groundwater inflows. 1 GSSE, Surface Water Assessment, Life of Mine Project, December 2010

11 Evaluation of Impacts to Groundwater from the Werris Creek Coal Mine Operations 10 April 2014 Page 8 Table 2 Measured Water Balance Volumes (ML) Description Apr-12 May-12 Jun-12 Jul-12 Aug-12 Sep-12 Oct-12 Nov-12 Dec-12 Jan-13 Feb-13 Mar-13 Out of Pit Change in void storage NK NK NK NK NK water curtain losses average monthly rainfall Historical 90th percentile data (mm) Mean average rainfall for Werris Creek (mm) Measured site rainfall (mm) Rainfall compared to historical average average high average low average average low high high high average NK not known. 2 Bureau of Meteorology online historical data for Werris Creek Post Office. groundwater inflows Werris Creek Coal Mine 2014_FINAL.docx

12 10 April 2014 Page 9 Figure 4 presents the volume of water in the void calculated from the initial WBM run over 7 months between September 2012 and March 2013 against site measurements. Figure 4 - Measured Results vs Initial WBM Results The results presented in Figure 4 suggest that the WBM underestimates the volume of groundwater inflow to the void, and this is particularly evident in November and December The difference between monitored water volumes and modelled water volumes is presented in Table 3. Table 3 Measured Water Balance Volumes versus Initial WBM (ML) Description Sep-12 Oct-12 Nov-12 Dec-12 Jan-13 Feb-13 Mar-13 Void Water Volume (measured) Void Water Volume (WBM) Difference The data, presented for 7 months in Table 3, can be annualised for 12 months and equates to approximately 300 ML per year.

13 10 April 2014 Page 10 Previous modelling of groundwater inflow for the monitoring period April 2012 to March 2013 estimated inflow to be 106 ML (annual). This prediction was determined using the calibrated groundwater model developed for the assessment of impacts from the Life of Mine proposal (model groundwater 2010). The predicted groundwater inflow volumes were found to increase from the initial predictions (2010) due to the assumptions regarding dewatering of the mine workings that were made during the initial model development. In the 2010 groundwater model, it was assumed that the mine workings would be dewatered prior to mine encroachment, however mine workings have remained saturated for the purpose of managing spontaneous combustion risk and this is resulting in a higher than predicted contribution from groundwater to the void. The calculated groundwater flows from each groundwater component for the period are tabulated in Table 4. These predictions were made using the 2012 model which revised the boundary conditions for the mine void. Table 4 Predicted Groundwater Inflow, Apr 2012 Mar 2013 Monitoring Period Description Total groundwater inflow to void Contribution of seepage from basalt (i.e. outside of basin) Seepage from Coal Measures and workings Seepage to void from overburden Totals 106ML 10.6ML 93.0ML 2.1ML Water balance modelling was undertaken to test three groundwater inflow scenarios to determine the best fit against the WBM: 1. Groundwater inflow of 13 ML per year; 2. Groundwater inflow of 106 ML per year; and 3. Groundwater inflow of 300 ML per year. It has been acknowledged by the site that there may be error in measurements of the volume of water in the void each month and that these may be as large as ± 10 ML. Furthermore, the runoff coefficients assumed in the model are not based on any empirical data. A sensitivity test of a range of runoff coefficients, varied by ± 10% was also undertaken. Figures 5 to 7 present the results of these additional WBM runs.

14 10 April 2014 Page 11 Figure 5 - Groundwater Inflow Scenario 1 (13 ML per year) Measured Results vs Initial WBM Results (m 3 ) Figure 6 - Groundwater Inflow Scenario 2 (106 ML per year) Measured Results vs Initial WBM Results (m 3 )

15 10 April 2014 Page 12 Figure 7 - Groundwater Inflow Scenario 3 (300 ML per year) Measured Results vs Initial WBM Results (m 3 ) Of the three scenarios modelled, Scenario 3 appears to show the poorest fit. The closest fit appears to be achieved in Scenario 1, where 5 of the 8 measured volumes fall within the range of WBM water volumes at the end of the month. However, given the monitoring uncertainty and the fact that the beginning and end volumes appear to agree closest in Scenario 2, it may be that groundwater inflows are closer to 100 ML per year and is consistent with the 2012 groundwater model predictions. This also infers the additional water captured in the pit as void water was sourced from the high intensity rain events between November 2012 and February 2013 and not from an increase in groundwater flow from the basalt aquifer.

16 10 April 2014 Page 13 4 Conclusions and Recommendations In accordance with the Annual Review requirement of the Project Approval; have conducted an evaluation of inflow volumes to the mine void. This calculation has been undertaken by initially predicting the groundwater inflows using a calibrated model and then verifying the predictions by undertaking a water balance for the mine pit over a discrete period. The analysis found a good correlation between the water balance and the predicted groundwater inflows when considering the water management of the site. This process has further validated the groundwater model developed for the LOM project, which was refined in At the time of the LOM impact assessment, this model benefitted from real time calibration data recorded during the initial mining scenarios and was therefore considered to be a robust representation of the groundwater system. Minor modification of the boundary conditions adopted in the model was undertaken in 2012 following changes to the management of groundwater within the former mine workings. On this basis the predictions of impacts to the groundwater levels in the basalt aquifer are considered to remain valid. Groundwater levels in monitoring wells within the basalt aquifer have been observed to decrease in excess of that predicted to occur from mining operations. These effects are also observed at bores remote from the mining operations. On this basis it is considered that these effects are representative of a general decline in the groundwater level as a result of below average rainfall conditions. To further assess the variation in groundwater levels, it is recommended that the groundwater monitoring database be expanded to include a statistical analysis of groundwater level variations using a statistical trending analysis such as CUSUM. These tools allow for identification of trends that are independent of background variation. Through the above process of validation, the use of a discrete time interval WBM has proven to be a critical tool in validating the groundwater model predictions. This analysis has determined that groundwater inflows are closer to 100 ML per year as predicted in the 2012 groundwater model assessment. This also infers the additional water captured in the pit as void water was sourced from the high intensity rain events between November 2012 and February 2013 and not from an increase in groundwater flow from the basalt aquifer.

17 10 April 2014 Page 14 5 References RW Corkery & Co. Pty Ltd, Environmental Assessment for Werris Creek Coal Mine, Life of Mine Project, December Bureau of Meteorology ( Online historical data for Werris Creek Post Office 6 Limitations Australia prepared this report in accordance with the scope of work as outlined in our proposal to Werris Creek Coal Pty Ltd dated 19 th June 2013 and in accordance with our understanding and interpretation of current regulatory standards. Site conditions may change over time. This report is based on conditions encountered at the site at the time of the report and disclaims responsibility for any changes that may have occurred after this time. The conclusions presented in this report represent s professional judgment based on information made available during the course of this assignment and are true and correct to the best of s knowledge as at the date of the assessment. did not independently verify all of the written or oral information provided to during the course of this investigation. While has no reason to doubt the accuracy of the information provided to it, the report is complete and accurate only to the extent that the information provided to was itself complete and accurate. This report does not purport to give legal advice. This advice can only be given by qualified legal advisors. 6.1 User Reliance This report has been prepared exclusively for Werris Creek Coal Pty Ltd and may not be relied upon by any other person or entity without s express written permission.

18 By 21 st May 2014 Andrew Wright Environmental Officer Werris Creek Coal Whitehaven Coal Limited PO Box 125, Werris Creek NSW Re: CUSUM analysis tool for assessment groundwater impact Dear Andrew An assessment of groundwater bores was conducted where an analysis of variance in groundwater level data from each bore site was assessed to provide an early indicator of trends. The assessment analysis measured the variation of water levels against a background site and, where variations independent of the background site are observed, these may be indicative of mining, or other, independent interference. CUSUM Water level assessment tool The one-sided cumulative sum analysis (CUSUM) spreadsheet tool was developed to provide an early indication of a trend in the groundwater level. The initial twelve months of monitoring data was used as an establishment mean ground water level for each borehole. If groundwater levels for a particular bore are reducing beyond the established mean level by more than the water level variation observed in the background bore, then a positive value is produced by the CUSUM analysis and plotted on the graph. If the CUSUM statistical calculations show three values where the CUSUM value is greater than zero, this is deemed to be an indication of a trend occurring. Where the graph has data equal to zero there has not been a significant change from the establishment groundwater level. Where the CUSUM value exceeds the Action Level, the CUSUM spreadsheet flags the value in a red colour. The Action Level for each aquifer is calculated from the variance in the water level of the background borehole. For a CUSUM analysis to be conducted background bores were selected for a controlled comparison of sites. The purpose of the background sites is to provide information on the variation in groundwater level due to natural and seasonal fluctuation. Water level data for borehole MW8 was used as a background bore for the Werrie Basalt aquifer bores. Borehole MW28a was used as a background bore for Quipolly aquifer. Borehole MW8 was also used for the unknown bores as an initial background comparison; this can be updated as more information becomes available. Background sites were selected due to their location and availability of water level data. Bore Identification and trending comments. Tables 1 summarises findings of groundwater trends as indicated by the CUSUM tool. The CUSUM analysis is a trend identifying tool and is used as a preliminary screening evaluation to initiate further investigations at a trending well. It is through these further investigations that cause and need for mitigation are evaluated. Australia Pty Ltd, Level 2, Suite 19B, 50 Glebe Road, PO Box 435, The Junction, NSW 2291, Australia Tel: Fax: ACN ABN

19 Whitehaven Coal Pty Limited Statistical Trend Analysis of Groundwater Levels 21 May 2014 Page Action level met - Potentially affected by Mine activities (water level trending downwards) Groundwater bore sites listed below have shown a trend in the groundwater level as indicated by the CUSUM spreadsheet. All wells listed below are within the Werris Creek Coal Mine property boundary. Other wells do not show trends above the action criteria. However, increasing trends were observed for at least the last four monitoring events at wells MW8, MW9, MW14, MW21a and MW27. Table 1: Bores where CUSUM indicates a lowering of groundwater levels Groundwater bore identification MW1 MW6 P1 Aquifier Werrie Basalt Werrie Basalt Werrie Basalt Action level triggered Yes Comments where groundwater level is decreasing Slow downwards trend over three years ( ). Consistent downwards trend from Aug Yes Action level triggered in November First 12 months of water level data used as a basis for comparison is 2 m higher than current water levels. Yes Trend in decreasing groundwater levels commences April Action level attained March 2012 and continuing. Impact by mining activities? CUSUM suggests mine impacts. Well is immediately adjacent pit. Appendix A outlines the data gaps and the information sought from Werris Creek Coal Mine to assist with identification of the aquifers corresponding to the boreholes that were either not shown or a map or did not have aquifer details in the supplied database. Limitations Australia prepared this report in accordance with the scope of work as outlined in our proposal to Whitehaven Coal Pty Limited dated 19 th June 2013 and in accordance with our understanding and interpretation of current regulatory standards. A representative program of sampling and laboratory analyses was undertaken as part of this investigation, based on past and present known uses of the site. While every care has been taken, concentrations of contaminants measured may not be representative of conditions between the locations sampled and investigated. We cannot therefore preclude the presence of materials that may be hazardous. Site conditions may change over time. This report is based on conditions encountered at the site at the time of the report and disclaims responsibility for any changes that may have occurred after this time. The conclusions presented in this report represent s professional judgment based on information made available during the course of this assignment and are true and correct to the best of s knowledge as at the date of the assessment. did not independently verify all of the written or oral information provided to during the course of this investigation. While has no reason to doubt the accuracy of Project S:\Projects\Werris Creek Coal Mine\_338 Progressive groundwater impact assessment 2013\Reporting\ Letter_002.docx As130338

20 Whitehaven Coal Pty Limited Statistical Trend Analysis of Groundwater Levels 21 May 2014 Page the information provided to it, the report is complete and accurate only to the extent that the information provided to was itself complete and accurate. This report does not purport to give legal advice. This advice can only be given by qualified legal advisors. 1.1 User Reliance This report has been prepared exclusively for Whitehaven Coal Pty Limited and may not be relied upon by any other person or entity without s express written permission. Sincerely, Australia Pty Ltd Fiona Robinson Senior Environmental Engineer Project S:\Projects\Werris Creek Coal Mine\_338 Progressive groundwater impact assessment 2013\Reporting\ Letter_002.docx As130338

21 Whitehaven Coal Pty Limited Statistical Trend Analysis of Groundwater Levels 21 May 2014 Page Appendix A More information required: Data from the CUSUM analysis was classified according to aquifer; reference to background site information is included in each spreadsheet. The boreholes listed below are the data sets that did not include an identifier of either of the Werrie Basalt or Quipolly aquifers; confirmation of the aquifer associated with the borehole is required. Many of these sites had minimal to no data provided. Conclusions regarding any mining activity impacts of those boreholes with limited data may alter as more data becomes available. Bore site identification MW24a MW25a MW25b MW29 MW31 MW32 Comments Not shown on supplied map Not shown on supplied map Only two data points Not shown on supplied map. Only two data points Not shown on supplied map. Not shown on supplied map. Only five data points Information required from Werris Creek Coal Mine Aquifer identification and map showing location Aquifer Identification and map showing location Aquifer identification and map showing location Aquifer identification and map showing location Aquifer identification and map showing location Aquifer identification MW14b No shown on supplied Aquifer identification and map showing location map. MW5b Not shown on Aquifer identification and map showing location supplied map WCD No data Confirm Aquifer WCU No data Confirm Aquifer Project S:\Projects\Werris Creek Coal Mine\_338 Progressive groundwater impact assessment 2013\Reporting\ Letter_002.docx As130338

22 Determination of groundwater interception Werris Creek Coal Mine Prepared for: Whitehaven Coal Pty Limited Prepared by: Australia Pty Ltd Date: 27 May 2014 Project Number: AS130379

23 Whitehaven Coal Pty Limited 27 May 2014 Determination of Groundwater Interception Werris Creek Coal Mine Prepared by: Authorised by: Name: Fiona Robinson Name: Fiona Robinson Title: Senior Manager Title: Senior Manager Phone: Phone: Signature: Date: 27/5/14 Signature: Date: 27/5/14 This document is issued in confidence to Whitehaven Coal Pty Limited for the purposes determining the groundwater interception from the Werris Creek Coal operations for the period 2013 to It should not be used for any other purpose. The report must not be reproduced in whole or in part except with the prior consent of Australia Pty Ltd and subject to inclusion of an acknowledgement of the source. No information as to the contents or subject matter of this document or any part thereof may be communicated in any manner to any third party without the prior consent of Australia Pty Ltd. Whilst reasonable attempts have been made to ensure that the contents of this report are accurate and complete at the time of writing, Australia Pty Ltd disclaims any responsibility for loss or damage that may be occasioned directly or indirectly through the use of, or reliance on, the contents of this report. Australia Pty Ltd VERSION CONTROL RECORD Document File Name Date Issued Version Author Reviewer _379 Evaluation of groundwater inflows Werris Creek Coal Mine 2014_Draft_V2 27/5/14 Draft 1 F Robinson F Robinson AS S:\Projects\Werris Creek Coal Mine\_379 Groundwater Inflows 2014\Report\_379 Evaluation of groundwater inflows Werris Creek Coal Mine 2014_Draft_V2.docx

24 Whitehaven Coal Pty Limited 27 May 2014 Determination of Groundwater Interception Werris Creek Coal Mine Contents Page 1 Introduction Background Study Objective Scope of Work 2 2 Modelling 3 3 Conclusions 3 4 References 4 5 Limitations User Reliance 4 List of Tables Table 1 Predicted Groundwater Inflow, Apr 2013 Mar 2014 Monitoring Period AS S:\Projects\Werris Creek Coal Mine\_379 Groundwater Inflows 2014\Report\_379 Evaluation of groundwater inflows Werris Creek Coal Mine 2014_Draft_V2.docx

25 Whitehaven Coal Pty Limited Determination of Groundwater Interception Werris Creek Coal Mine 27 May 2014 Page 2 1 Introduction Werris Creek Coal Mine (WCCM) is situated in the north west slopes and plains of New South Wales and is located 4km south of Werris Creek. The mine operates under project approval PA 10_0059 MOD Background In 2005, Werris Creek Coal Mine commenced mining of the Greta Coal Measures Werris Creek outlier, situated within the Werrie Basin. The coal measures overlie Werrie Basalt, which is directly beneath and surrounds the coal measures in all directions. The upper layers of the basalt have been shown to be highly weathered to form a clay aquitard providing confinement to semi-confinement between aquifers within the coal measures and underlying basalt hard rock. Underground mining of part of the coal seam was undertaken prior to the commencement of open cut mining in The open cut operations will mine through the former underground mine workings. Planning approval for the open cut mining operations was sought in two stages, representing the initial project and the Life of Mine Project (LOM). Each stage was subject to a groundwater impact assessment which involved three dimensional modelling of the aquifer systems to assess impacts from the proposed operations. Modelling was based on measured groundwater levels for the project site and known or assumed geological parameters. Modelling for the second project approval, the LOM project, also included calibration of the initial model to observed site conditions. 1.2 Study Objective Mining operations occur within the Werrie basin. Whilst not mining the surrounding basalt aquifer, the removal of groundwater from the Werrie Basin can cause groundwater flow from the basalt aquifer to the Werrie basin to occur resulting in an incidental interception of groundwater within the basalt aquifer. The objective of this study is to determine the volume of groundwater intercepted from the basalt aquifer by the mining operations for the period April 2013 to March Scope of Work The following scope of works was proposed to meet the project objective. 1. Use the existing hydrogeological model (LOM model) to predict the volume of groundwater interception for the period; and 2. Document the study in a report. AS S:\Projects\Werris Creek Coal Mine\_379 Groundwater Inflows 2014\Report\_379 Evaluation of groundwater inflows Werris Creek Coal Mine 2014_Draft_V2.docx

26 Whitehaven Coal Pty Limited Determination of Groundwater Interception Werris Creek Coal Mine 27 May 2014 Page 3 2 Modelling Modelling of groundwater inflow for the monitoring period April 2013 to March 2014 estimated inflow to be 72 ML (annual). This prediction was determined using the calibrated groundwater model developed for the assessment of impacts from the Life of Mine proposal (model groundwater 2010). The calculated groundwater flows from each groundwater component for the period are tabulated in Table 1. Table 1 Predicted Groundwater Inflow, Apr 2013 Mar 2014 Monitoring Period Description Total groundwater inflow to void Contribution of seepage from basalt (i.e. outside of basin) Seepage from Coal Measures and workings Seepage to void from overburden Totals 72ML 32ML 55ML 4ML Mining operations are now reaching the greatest depth of extraction and therefore the impacts to the basalt aquifer are expected to increase. This is reflected by the increase in groundwater inflow from the basalt aquifer from 10ML for the modelled period to 35ML for the current period. Additionally, the contribution from the former mine workings has decreased, as extraction through the former workings progresses forward and the workings are increasingly depressurised. The model predicts that a change in storage occurred for the period, where water levels in the former workings were maintained by inflow (19ML) from the basalt aquifer. This volume is included in the total presented above as it was removed from the basalt aquifer, but has not been extracted from the pit. 3 Conclusions In accordance with the Annual Review requirement of the Project Approval; have conducted an evaluation of inflow volumes to the mine void. This calculation has been undertaken by predicting the groundwater inflows using a calibrated model. At the time of the LOM impact assessment, this model benefitted from real time calibration data recorded during the initial mining scenarios and was therefore considered to be a robust representation of the groundwater system. Minor modification of the boundary conditions adopted in the model was undertaken in 2012 following changes to the management of groundwater within the former mine workings. On this basis the predictions of impacts to the groundwater levels in the basalt aquifer are considered to remain valid. Groundwater levels in monitoring wells within the basalt aquifer have been observed to decrease in excess of that predicted to occur from mining operations. These effects are also observed at bores remote from the mining operations. On this basis it is considered that these effects are representative of a general decline in the groundwater level as a result of below average rainfall conditions. AS S:\Projects\Werris Creek Coal Mine\_379 Groundwater Inflows 2014\Report\_379 Evaluation of groundwater inflows Werris Creek Coal Mine 2014_Draft_V2.docx

27 Whitehaven Coal Pty Limited Determination of Groundwater Interception Werris Creek Coal Mine 27 May 2014 Page 4 4 References RW Corkery & Co. Pty Ltd, Environmental Assessment for Werris Creek Coal Mine, Life of Mine Project, December Limitations Australia prepared this report in accordance with the scope of work as outlined in our proposal to Werris Creek Coal Pty Ltd dated 11 th April 2014 and in accordance with our understanding and interpretation of current regulatory standards. Site conditions may change over time. This report is based on conditions encountered at the site at the time of the report and disclaims responsibility for any changes that may have occurred after this time. The conclusions presented in this report represent s professional judgment based on information made available during the course of this assignment and are true and correct to the best of s knowledge as at the date of the assessment. did not independently verify all of the written or oral information provided to during the course of this investigation. While has no reason to doubt the accuracy of the information provided to it, the report is complete and accurate only to the extent that the information provided to was itself complete and accurate. This report does not purport to give legal advice. This advice can only be given by qualified legal advisors. 5.1 User Reliance This report has been prepared exclusively for Werris Creek Coal Pty Ltd and may not be relied upon by any other person or entity without s express written permission. AS S:\Projects\Werris Creek Coal Mine\_379 Groundwater Inflows 2014\Report\_379 Evaluation of groundwater inflows Werris Creek Coal Mine 2014_Draft_V2.docx