end of panel report longwall 15 -...

APP79579

End of Panel Report

Longwall 15

Mandalong Mine

July 2014

Mandalong Mine LW15 End of Panel Report – July 2014

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Table of Contents

1 INTRODUCTION ....................................................................................................................................... 1

2 SUBSIDENCE RESULTS ............................................................................................................................. 1

2.1 BACKGROUND ............................................................................................................................................... 1 2.2 DESCRIPTION OF IMPACT ................................................................................................................................. 1 2.3 MONITORING RESULTS ................................................................................................................................... 2

2.3.1 Monitoring Data .............................................................................................................................. 2 2.4 PERFORMANCE AGAINST PREDICTION ................................................................................................................ 3

2.4.1 Longwall Summary ........................................................................................................................ 10

3 SUBSIDENCE MANAGEMENT ................................................................................................................. 10

3.1 NOTIFICATIONS ........................................................................................................................................... 10 3.2 SUBSIDENCE MANAGEMENT PLAN TRIGGERS .................................................................................................... 10 3.3 REMEDIAL ACTIONS...................................................................................................................................... 11 3.4 SUBSIDENCE MANAGEMENT STATUS REPORTS .................................................................................................. 11

4 ENVIRONMENTAL CONSIDERATIONS .................................................................................................... 11

4.1 GROUNDWATER .......................................................................................................................................... 11 4.2 SURFACE HYDROLOGY .................................................................................................................................. 14

4.2.1 Stream Channel and Floodpaths ................................................................................................... 14 4.2.2 Wetland Monitoring ...................................................................................................................... 15 4.2.3 Surface Water Monitoring Mandalong ......................................................................................... 17

5 COMMUNITY CONSULTATION ............................................................................................................... 19

5.1 COMPLAINTS .............................................................................................................................................. 19 5.2 INQUIRES ................................................................................................................................................... 19 5.3 MANDALONG MINE COMMUNITY CONSULTATIVE COMMITTEE ............................................................................ 19

6 BIBLIOGRAPHY ...................................................................................................................................... 20

List of Figures

FIGURE 1 - TOPOGRAPHY AND SUBSIDENCE LINES MEASURED FOR LW15 .............................................................................. 2 FIGURE 2 - DEPTH OF COVER OVER LW1 TO LW15 ........................................................................................................... 3 FIGURE 3 - PREDICTED SUBSIDENCE LW1-15 .................................................................................................................... 4 FIGURE 4 - VISUALISATION OF MEASURED SUBSIDENCE LW1-15 .......................................................................................... 4 FIGURE 5 - DIFFERENCE BETWEEN PREDICTED AND ACTUAL SUBSIDENCE ................................................................................ 5 FIGURE 6 - COMPARISON OF PREDICTED VISUALISATION AND MEASUREMENTS ALONG CROSSLINES 2 AND 8 .................................. 5 FIGURE 7 - LW15 TILT HISTOGRAM ................................................................................................................................ 6 FIGURE 8 - LW15 COMPRESSIVE STRAIN HISTOGRAM ........................................................................................................ 7 FIGURE 9 - LW15 TENSILE STRAIN HISTOGRAM ................................................................................................................. 7 FIGURE 10 - RELATIVE AND CUMULATIVE FREQUENCY GRAPH OF MEASURED AND PREDICTED VERTICAL MOVEMENTS ................... 9 FIGURE 11 - RELATIVE AND CUMULATIVE FREQUENCY GRAPH OF MEASURED AND PREDICTED TILTS ............................................ 9 FIGURE 12 - NESTED MONITORING - HYDROGRAPH OF BORES BH25A, 25B, 25C ................................................................ 12 FIGURE 13 - GROUNDWATER MONITORING BORES AND MINE PLAN ................................................................................... 13 FIGURE 14 - WETLAND MONITORING LOCATIONS AND UNDERGROUND WORKINGS ............................................................... 16

List of Tables

TABLE 1 - LONGWALL 15 MINING PARAMETERS ................................................................................................................ 1 TABLE 2 - FREQUENCY HISTOGRAM SUMMARY LONGWALLS 6 TO 15 ..................................................................................... 8 TABLE 3 - SUMMARY OF MONITORING LOCATIONS WITH RESPECT TO POSITION WITHIN THE CATCHMENTS ................................... 17 TABLE 4 - AVERAGE SURFACE WATER QUALITY FOR THE MANDALONG VALLEY FOR THE 12 MONTH PERIOD FROM JANUARY 2013 TO

DECEMBER 2013 AND THE LONG-TERM AVERAGE ................................................................................................... 18


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Document Control Details DOCUMENT DETAILS

Name: Longwall 15 End of Panel Report

Author: Phil Enright

Reference: LW15 End of Panel Report.docx

Revision No.: 1

Document Status Final

APPROVAL DETAILS

Revision No.

Date Sent Details of Approval Approved By Approval Date

0 14/07/14 Draft for comment J Dunwoodie 18/07/14

1 25/07/14 Approved for Submission

C Macdonald 25/07/14

Director of Environmental Sustainability

NSW Department of Trade and Investment, Regional Infrastructure and Services

1

Principal Subsidence Engineer

NSW Department of Trade and Investment, Regional Infrastructure and Services - Resources & Energy

1

Director General Department of Planning & Environment

1

Regional Hydrologist NSW Office of Water 1

Manager, Mining & Extractive Industries

Environment Protection Authority

1

Chairman Mandalong Community Consultative Committee

1

Chairman Mine Subsidence Board 1

Technical Services Superintendent

Mandalong Mine Technical Services

1


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1 Introduction The Subsidence Management Plan Approval for Longwalls 15 to 17, condition 18, requires an end of panel report to be submitted to the Director, Environmental Sustainability of NSW Trade and Investment, Regional Infrastructure & Services – Division of Resources & Energy (DRE) within four months of the extraction being completed of each longwall panel. This report aims to fulfil this condition and encompasses all environmental and subsidence monitoring, including a comparison of actual subsidence impacts with predicted subsidence impacts, subsidence trends and management actions. Development Consent condition 18 also requires an end of panel report to be provided within 4 months of panel completion to the Director General of the Department of Planning & Environment (DP&E) and submitted to the Mandalong Community Consultative Committee (CCC), DRE, Environment Protection Authority (EPA), NSW Office of Water (NOW) and any other relevant agency.

2 Subsidence Results

2.1 Background

The extraction of Longwall 15 occurred over a period of seven months, commencing on 24 September 2013 and finishing on 22 April 2014. Longwall 15 had an extraction width of 160m, with Maingate 15 chain pillars 46m wide and the three heading tailgate pillars 39m and 52m wide. The depth of cover ranged from 230m to 260m over the panel, with a summary of the mining parameters provided in Table 1.

Table 1 - Longwall 15 Mining Parameters

Longwall 15 Parameters

Length 2934m Face Width 150m Void 160m Extraction Height 3.4m to 4.8m Chain Pillar Width Maingate 46m, Tailgate 39m and 52m Cover Range 230m to 260m Commenced 24 September 2013 Completed 22 April 2014 Coal Extracted 3.0 million tonnes

A variation to the SMP was sought and approved by the Director-General (DRE) on 16 August 2013 to reduce the approved length of the longwall block by a total 99m. The variation was due to the presence of a hard silica rich dyke and reduced seam thickness at the commencement end of the longwall block as well as a roof collapse at the installation roadway. The new installation roadway was driven 29m outbye the original roadway and located within the stress relief zone.

2.2 Description of Impact

The area affected by Longwall 15 covered properties both above and within the Mandalong floodplain. This area includes a total of 12 properties and three dwellings. Surface features include Stockton Creek, Mandalong Rd, Browns Rd, Telstra communications network and the Ausgrid network. The Subsidence Management Plan predicted low impact across the area influenced by the extraction of Longwall 15.


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Following the completion of the longwall panel, there have been no reports of subsidence damage to any of the 12 properties or three private dwellings impacted by subsidence. There have been no observed or reports of damage to infrastructure during the extraction of Longwall 15 other than a minor compression hump (10mm) that developed into small potholes on the Mandalong Rd pavement. The potholes have been repaired by LMCC.

2.3 Monitoring Results

2.3.1 Monitoring Data

Subsidence monitoring was completed in accordance with the approved subsidence monitoring programme. Following the completion of Longwall 15, Seedsman Geotechnics (2014b) reviewed the data and provided a report on the measured subsidence and subsidence performance. Subsidence surveys were completed on all or part of seven subsidence lines and a number of dwellings. Figure 1 shows the topography and subsidence lines occupied during Longwall 15 extraction. The largest vertical subsidence recorded during the retreat of Longwall 15 was 0.47m measured on Crossline 2. Maximum subsidence over the majority of the panel was typically 0.3m.

Source: (Seedsman Geotechnics, 2014b)

Figure 1 - Topography and Subsidence Lines Measured for LW15


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2.4 Performance against Prediction

The depth of cover ranged between 230m and 260m over the panel. The variation in depth of cover is primarily driven by the surface topography over Longwall 15. Figure 1 above and Figure 2 below illustrate the topography and depth of cover.


Figure 2 - Depth of Cover over LW1 to LW15 To compare performance against predictions, Figure 3shows the predicted subsidence visualisation over LW1-15, while Figure 4 presents a visualisation of the vertical subsidence over the whole area based on interpolation of the measured survey data.


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Figure 3 - Predicted Subsidence LW1-15


Figure 4 - Visualisation of Measured Subsidence LW1-15


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Figure 5 below, illustrates the difference between actual and predicted subsidence, where green shading is where actual subsidence is less than predicted and red shading is where actual subsidence greater than predicted. As indicated in the figure, two areas measured subsidence slightly above the predicted maximums, while the remainder of the panel was within the predicted range.


Figure 5 - Difference between Predicted and Actual Subsidence Figure 6 compares a visualisation of predicted subsidence along Crossline 2 and Crossline 8 (Mandalong Rd) to measured subsidence. The graph shows the reduction of subsidence over the three heading Maingate 15 between LW14 and LW15.


Figure 6 - Comparison of predicted visualisation and measurements along Crosslines 2 and 8


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To assess the range of tilt and strain measurements across Longwall 15, frequency histograms for tilt, tensile strain and compressive strain have been produced. The histograms are based on the results of the three subsidence monitoring lines located over Longwall 15 (Crosslines 2, 3EX and 8). The histograms compare the subsidence results against the Safe Serviceable and Repairable (SSR) criteria for dwellings, being less than 5mm/m for tensile and compressive strains and less than 7mm/m of tilt. Figure 7 indicates that almost 97% all of measured tilts over Longwall 15 were below SSR criteria of 7mm/m for dwellings. All compressive strain and tensile strain measurements recorded were below SSR criteria of 5mm/m for dwellings as shown in Figure 8 and Figure 9. A summary table of the histogram results for Longwalls 6 to 15 confirms the high level of confidence in the mine design achieving low levels of subsidence. Table 2 summarises these results compared to SSR criteria for dwellings.

Figure 7 - LW15 Tilt Histogram


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Figure 8 - LW15 Compressive Strain Histogram

Figure 9 - LW15 Tensile Strain Histogram


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Frequency Histogram Summary for Longwalls 6 to 15 Compared Against SSR Criteria for Dwellings

Longwall Panel Tilt

Less that 7mm/m Tensile Strain

Less than 5mm/m Compressive Strain Less than 5mm/m

LW6 97.7% 99.8% 97.4%

LW7 97.6% 100% 97.8%

LW8 100% 100% 99.4%

LW9 100% 100% 100%

LW10 98.8% 100% 98.5%

LW11 96.5% 100% 100%

LW12 96.4% 100% 93.3%

LW13 95.6% 100% 95.6%

LW14 100% 100% 100%

LW15 96.9% 100% 100%

Average 98.0% 99.9% 98.2%

Table 2 - Frequency Histogram Summary Longwalls 6 to 15 Part of the SMP risk assessment process looks at the likelihood of maximum predicted subsidence being exceeded by a factor of one and a half times (1.5x) and two times (2x) the maximum predicted subsidence. To review the performance of subsidence against these sensitivities, Seedsman Geotechnics (2014a) produced frequency graphs comparing the ratio of the predicted contour data against measured contour data, similar to that shown in Figure 3 and Figure 4. The plots were based a 10m grid and consisted over 83,000 data points. From Figure 10, it can be seen the majority of the actual subsidence measurements are below prediction, while 15% of the database measurements were greater than predicted. Only 2% of measurements have exceeded the prediction by 1.5 times (150%) and 0.6% of measurements exceeded the predictions by two times (200%). These high percentage exceedances occur at low levels of vertical movement.


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Source: (Seedsman Geotechnics, 2014a)

Figure 10 - Relative and Cumulative Frequency Graph of Measured and Predicted Vertical Movements

The predicted vertical subsidence grids have also been generated to produce grids of the associated tilts and frequency graphs produced. Because the first derivative of the vertical subsidence is being examined, the comparison of tilts is not as good. The measured tilt is less than or equal to the prediction about 70 % of the time. The measured tilt is 1.5 times higher (150%) than the prediction about 20 % of the time and the measured tilt is twice as high about 10 % of the time. These exceedences typically develop at tilts less than the SSR value of 7 mm/m the vast majority of the time (98%) as detailed in Table 2.

Source: (Seedsman Geotechnics, 2014a)

Figure 11 - Relative and Cumulative Frequency Graph of Measured and Predicted Tilts

15% 2% 0.6%

Prediction 1.5x 2x

30%

20% 10%


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2.4.1 Longwall Summary

Longwalls 1 to 12 Subsidence monitoring over the major crosslines including annual surveys has shown that subsidence has remained stable. Longwall 13 Only minor settlement has been recorded over Longwall 13 following the extraction of Longwall 15, with less than 20mm recorded on Crosslines 2, 3Ex and 9. Longwall 15 pre-mining surveys on Crosslines 8 and 17 also indicated movements of less than 20mm. Longwall 14 Settlement of Longwall 14 has occurred following the extraction of Longwall 15, with maximum vertical subsidence increasing by around 50mm. As anticipated, the settlement of the chain pillars between Longwall 14 and Longwall 15 has been reduced due to the additional pillar in Maingate 14. Monitoring on Crossline 2 and Crossline 3Ex has measured subsidence between 0.1m to 0.15m over the chain pillars. Longwall 15 Maximum subsidence recorded on Crosslines 2, 3Ex and 8 was 0.47m, 0.31m and 0.27m respectively. Monitoring along Morans Creek recorded maximum subsidence of 0.41m.

Three private dwellings were impacted directly by subsidence from Longwall 15. All properties were predicted to and remained Safe Service Repairable and there have been no reports of damage to date. Subsidence monitoring was undertaken on one of the dwellings located approximately 20m off the centre of the panel. The maximum subsidence recorded on the dwelling was 0.23m, with tilts up to 1.7mm/m and strains measuring between 1.5mm/m and -1.5mm/m. It is expected the two dwellings, where monitoring was declined, have been exposed to similar levels of subsidence, with the nearby Crossline 8 monitoring line recording 0.27m of vertical subsidence, compressive strains of -2mm/m and tilts less than 1.5mm/m.

3 Subsidence Management

3.1 Notifications

All one month mining notifications were issued to landowners, tenants and infrastructure owners affected by Longwalls 15.

3.2 Subsidence Management Plan Triggers

Subsidence damage to a private farm dam and access road was observed in late 2013 over a previously mined area. The dam is located over the centre of Longwall 7 and appears that minor cracking to the dam wall most likely occurred at the time of mining. The cracks have subsequently opened up during dry periods of weather. Subsidence monitoring indicated that the area is stable, with tensile strains remaining low (<2mm/m). The dam was repaired in December 2013 and covered by the Mine Subsidence Board (MSB).

Cracking to a section of sealed access road pavement on the same property that is located over the edge of Longwall 8 was also observed in late 2013. Subsidence monitoring indicates vertical movements of less than 20mm in the area over the past two years. The MSB arranged repairs during December 2013.


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3.3 Remedial Actions

A minor compression hump (10mm) developed on a section of Mandalong Rd pavement located over the centre of Longwall 15. The compression hump developed into two small potholes that were repaired by LMCC during routine road maintenance. Subsidence monitoring for Mandalong Rd (Crossline 8) measured maximum vertical subsidence of 0.27m and maximum compressive strain of -2.2mm/m in the location of the pavement damage.

3.4 Subsidence Management Status Reports

Fortnightly Subsidence Management Status reports were prepared in accordance with SMP LW15-17 approval. Thirteen reports were prepared during the extraction of Longwall 15. There were two Subsidence Management Status Reports (four monthly) produced during the extraction of Longwall 15. Subsidence Management Status Report #30 for 1 September 2013 to 31 December 2013 and # 31 was for the period 1 January 2014 to 30 April 2014. The reports were provided to all relevant agencies and stakeholders and made available on the Centennial Coal website.

4 Environmental Considerations

4.1 Groundwater

An extensive groundwater monitoring network has been established and a monitoring program implemented at Mandalong Mine, commencing in August 1997 and approximately eight years prior to the commencement of longwall mining. This program has been established to provide timely warnings of deviations from natural or background levels, so that if necessary, remedial measures and/or management strategies can be put in place. The current monitoring network consists of 45 bores; 20 alluvial monitoring bores, 23 overburden monitoring bores and 2 coal seam monitoring bores. The bores consist of 12 nests of 2 or 3 bores monitoring strata at increasing depth at the same site and 13 single bore sites (refer Figure 13 for location of bores). The bores are monitored every month with the water level, EC and pH being measured. At Mandalong, the alluvium forms an unconfined shallow aquifer with a water table typically ranging in depth from less than 1m and up to about 3m below ground level and aquifer thickness less than 20m. Monitoring within the alluvium has indicated that there is regular seasonal fluctuation in water level around 0.5m in the lower catchment and fluctuations between 1.5m to 2.0m in the middle to upper catchment areas. The alluvial groundwater is moderately acidic to slightly alkaline, brackish to saline, extremely hard and of sodium chloride type. Reported groundwater electrical conductivity (EC) throughout the Mandalong Mine approval area exceeds 10,000 μS/cm at some locations. Due to the relatively high silt and clay content of the alluvium, the groundwater yields are relatively low (typically less than 1 L/s). As a result of the low yield and relatively poor water quality, there are very few registered private alluvial groundwater bores. The environmental value of the alluvial groundwater is considered to be ‘primary industry’ (specifically stock watering), with the saline groundwater only suitable for stock watering. The most recent review of the monitoring network was undertaken in January 2014 by AGE (2014) in preparation of the Annual Environmental Management Report (AEMR) for 2013. As part of the review, groundwater hydrographs were plotted for each of the alluvium bores and compared to the CRD (Cumulative Rainfall Departure) curve for the rainfall dataset to establish the relationship between groundwater levels and rainfall and to identify whether other natural or anthropocentric factors have been influencing these groundwater levels.


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The most recent bore site to be undermined was BH25 located near the end of Longwall 14. Figure 12 shows the hydrograph of the nested bores, monitoring groundwater to depths 2.5m to 9m (BH25A), 20m to 30m (BH25B) and 51.5m to 58m (BH25C). According to AGE (2014), the groundwater level in the alluvium, monitored in BH25A, trends closely with the CRD. The alluvial hydrograph is relatively stable with little fluctuation between RL12.5 m and RL14 m and appears not to be impacted by mining. Water levels in the intermediate and deeper strata, BH25B and BH25C, are relatively stable at around RL11 m and RL8 m respectively until September 2012. After passing of Longwall 13 in November 2012, water levels declined slightly below their long-term levels. After Longwall 14 passed, water levels inclined by 1.7m (BH25B) and declined by 5 m (BH25C). While BH25B stabilises at about RL10 m just 1 m below its long-term water level, the levels in BH25C appear to stabilise at about RL5 m, which is about 3 m below its previous long-term water level. These effects are likely responses due to compression and subsequent dilation during approaching and passing of the longwalls. During 2013 and for the deeper strata it appears, that water went into storage in the dilated rock mass causing a temporary decline in water level, followed by some recovery (AGE, 2014). The AGE (2014) report concluded that the data has confirmed the Kendorski model and previous assessments of the potential impact of goafing associated with longwall mining. The most recent monitoring has shown water levels in the alluvium and shallow overburden are not impacted by mining, the exception being a temporary decline of 1.8m at site BH22, located over Longwall 9 followed by a period of fluctuating water levels. The data indicates that a hydraulic connection has not been established from the alluvium at BH22A to the workings and that the decline and temporary declines occur as a result of short-term depressurisation of the dilated zone. Water bearing overburden strata to depths in excess of 50m are impacted by compression and dilation of the strata due to the passage of mining along the longwall panel, resulting in an increase or decrease in water level, but without hydraulic connection to the mine. Water levels are expected to recover within this zone over time.

Source: (AGE, 2014)

Figure 12 - Nested Monitoring - Hydrograph of Bores BH25A, 25B, 25C


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Source: (AGE, 2014)

Figure 13 - Groundwater Monitoring Bores and Mine Plan


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4.2 Surface Hydrology

4.2.1 Stream Channel and Floodpaths

The Mine’s development consent requires the condition of major floodpaths be inspected every six months or following a flood event in an area subject to a Subsidence Management Plan (SMP) application. The Floodpath Condition Report for 2013 has been developed to compile survey and photographic records of subsidence induced changes to Stockton Creek as per assessment methodology in Section 1.2 of the report. The full report is contained within the Annual Environmental Management Report 2013 (AEMR) (Centennial Mandalong, 2014). The Floodpath Condition Report assesses the changes to the condition of floodpaths along stream reaches mined beneath by Longwalls 14 and 15 extracted in 2013 and previously subsided Longwalls 1 to 13, identifying the effects of subsidence on the floodpaths. The pre-mining condition of the floodpaths above Longwall 14 and 15 is also documented in this report. On the basis of the information obtained from field surveys the pre mining characteristics of Stockton Creek and the associated tributary in the mining area are described as having a deep bed broad stream section with some pre mining erosion on bank areas above Longwalls 4 and 5. Pre-mining stream condition above Longwalls 7 to 10 has stream widths broadening to some 7 to 20 m wide and low bank heights of 0.5m to 2 m. Surveys in June and December 2013 and June 2014 recorded some further minor erosion of stream banks along these stream sections likely to be caused by a combination of stock access exposing soils and concentrated flows scouring the banks. Areas of subsidence induced remnant ponding were also identified. The subsidence levels above Longwalls 3 to 6 remained unchanged in 2013. The stream condition in 2013 above Longwall 1 to 3 and 6, where stock have been excluded, were in a similar condition to that recorded pre mining. No change to the well-established riparian vegetation was found on stream banks and with no further bank erosion. The bank widening and erosion process above Longwalls 4 and 5 in Stockton Creek has been occurring prior to mining and for a considerable length of time prior to mining given the large difference in stream widths compared to other stream sections. This erosion process is unlikely to have been caused by subsidence as the areas of erosion identified prior to mining were observed in June 2008 to be a result of the concentrated flows on the opposing bank causing further erosion. In addition to areas identified in previous reports, remnant ponding was evident on a Centennial property above Longwall 11 in 2012 and 2013. The ponding is located on an area of Redgum Rough-bark Apple Forest and pasture. To date only minor dieback of the vegetation community has occurred and an ecologist is monitoring the area to assess the effects of ponding on this vegetation community. At present due to limited impact, remediation works are being assessed and may be considered if recommended by the external ecologist. The maximum subsidence levels recorded in 2013 on Longwall panels 11 to 14 are within the predicted range, with the changes in stream grade above these panels similar to pre-existing grades occurring on Stockton creek. All subsidence and stream grade changes are below the anomalous results triggers in the UMEMP therefore, further stream impact assessment or remedial works are not required. Given the unchanged stream condition recorded following mining and the low subsidence levels on Stockton Creek, it is likely that recent subsidence above Longwalls 13 and 14 has had minimal adverse impacts to the stream flow conveyance.


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The pre-mining condition of the Morans Creek floodpath above Longwall 15 and 16 was surveyed in March 2014. A further survey in June 2014 identified no visible changes to the stream condition following the mining of Longwall 15.

4.2.2 Wetland Monitoring

Condition 74 of Development Consent for the Mine requires monitoring and management of wetlands in the mining area. The wetlands management and monitoring plan (WMP) approved by LMCC was prepared by Hunter Eco (Centennial Mandalong, 2009), identifying eight (8) wetlands for monitoring as shown in Figure 14. Wetlands 1, 2, and 3 are located outside of the subsidence zone and are control sites while the remaining five wetlands are within the proposed mining area. In April 2009 a baseline report was prepared (Hunter Eco, 2009) which described the status of the wetlands prior to any subsidence having occurred. In 2013 Hunter Eco conducted two monitoring rounds in April (Hunter Eco, 2013a) and November (Hunter Eco, 2013b). The following is a summary monitoring results from the reports. The purpose of this monitoring program, as prescribed in the Conditions of Consent, is to determine what, if any, changes in the monitored wetlands in the Mandalong floodplain can be attributed to subsidence. Monitoring of eight wetlands commenced in April 2009 so as at November 2013 the total monitoring period has been over four years, ten monitoring occasions. All wetlands started out with water then began to dry until May 2010 when only Wetlands 1 and 3 had water. There has been an increasing rainfall trend up to May 2012 falling to November 2012 after which it has risen to the highest level since the start of monitoring. Clearly these wetlands are dynamic ecosystems with species composition and diversity varying with the amount of available water and seasons. Variable land-use activities also have an influence on the state of the wetlands. Water analysis results continue to be highly variable, showing no trends over time or within or among wetlands. Wetland 6 is located over a pillar between Longwalls 11 and 12, both panels having been subsided. The most noticeable change at this wetland is the change from dry to margin habitat at the beginning of the transect. This change appears to now be a feature of this transect. Wetland 8 has been subject to subsidence for over three years and there is no change in the wetland vegetation and water levels that can clearly be assigned to being an impact of subsidence. Around the middle of 2012, Longwall 13 was subsided beside Wetland 7 which is located over a pillar between Longwalls 13 and 14. There is no subsidence monitoring through this wetland and it is too soon to detect any impact on the structure of this wetland.


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Source: (Hunter Eco, 2013b)

Figure 14 - Wetland Monitoring Locations and Underground Workings


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4.2.3 Surface Water Monitoring Mandalong

There is an established surface water quality monitoring program for the Mandalong catchment conducted by the Mine. Periodic sampling commenced in 1996, with the program established on a regular monthly frequency since August 1999. Three surface water monitoring points (SW13-15) above the Licenced Discharge Points LDP001 & LDP002 and two monitoring points (SW16-17) in the receiving waters below the LDP’s were added in late 2011 at the Cooranbong Services Site, remote from the current mining area. The monitoring locations are summarised below in Table 3.

Table 3 - Summary of monitoring locations with respect to position within the catchments

Location Reference Creek Sub-catchment Position along Creek Sub-catchment

SW008 Stockton Creek Upper

SW004 Stockton Creek Mid

SW012 Stockton Creek Lower

SW011 Moran’s Creek Upper

SW003 Moran’s Creek Mid

SW006 Moran’s Creek Lower

SW002 Stockton and Moran’s At Confluence

SW001 Stockton Creek Downstream Confluence

SW009 Pourmalong Creek South

SW010 Pourmalong Creek North

SW13 Muddy Lake (Unnamed tributary upstream LDP001).

Upper


Upper


Upper

SW16 Muddy Lake (Unnamed water body 1km downstream Simpson Rd Causeway Crossing)

Mid

SW17 Muddy Lake (North Dora Creek Village) Lower

Surface water quality is monitored at 15 locations on a monthly or quarterly basis. These locations encompass four different catchment areas. The water is tested for pH, Total Suspended Solids (TSS) and Specific Conductance/Electrical Conductivity (EC). The annual and long-term average (LTA) results are summarised in Table 4.


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Table 4 - Average surface water quality for the Mandalong Valley for the 12 month period from January 2013 to December 2013 and the long-term average

Site Location Catchment

pH TSS Specific Conductance

uS/cm

Average LTA Average LTA Average LTA

SW008 Stockton 7.0 6.0 4.6 32.0 905.3 863.5

SW004 6.9 6.7 23.7 18.9 605.2 634.4

SW012 6.5 6.1 13.0 29.7 1280.4 1133.6

SW018 7.1 7.2 49.4 30.0 606.0 538.2

SW011 Moran’s 6.8 6.6 16.2 53.2 547.1 561.9

SW006 6.5 6.6 34.9 18.8 384.9 537.0

SW003 6.4 6.4 9.1 15.0 383.1 486.9

SW002

Stockton and Moran’s Creek (Confluence) 6.9 7.0 10.9 15.2 8019.4 14862.5

SW001 6.9 7.1 7.8 12.3 18488.1 30336.8

SW009 Pourmalong 6.7 6.6 14.5 18.8 403.5 295.5

SW010 5.8 6.1 11.8 18.3 945.0 432.2

SW013 5.2 6.2 7.0 20.9 3224.6 1599.8

SW014 6.9 7.1 7.8 20.1 380.4 463.0

SW015 Muddy Lake 5.7 5.9 80.6 81.3 80.2 98.1

SW016 8.3 8.2 12.6 16.7 2663.3 2249.8

SW017 8.1 8.1 849.5 943.9 2898.2 3040.0

Source: (Centennial Mandalong, 2014)

The results presented in Table 4 are characteristic of the natural conditions of the area, particularly Stockton and Moran’s Creek. Both Stockton and Moran’s creek are the main drainage systems for the Mandalong area. Stockton Creek is located within the longwall mining area, while Moran’s Creek has been situated outside the longwall mining area (LW1-14) until being undermined by Longwall 15. SW013 to SW017 are located in the Muddy Lake catchment, near the Cooranbong Services Site.

Surface waters are tested for pH, Total Suspended Solids (TSS) and Specific Conductance/Electrical Conductivity (EC) and the annual and long-term average (LTA) results are summarised in the AEMR 2013 and contain graphs of EC, pH and TSS for each of the surface water monitoring points sampled in 2013.


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The EC (salt content) for the 2013 period shows a relatively consistent level compared to the long-term average. The average EC recorded for sites SW01, SW03, SW06, SW014, SW015 and SW017 this period is lower than the long-term average. The average total suspended solids (TSS) for 2013 are relatively low and are characteristic of natural surface water conditions in creeks. SW017 (Muddy Lake) recorded the highest annual average TSS of 849.5 mg/L in 2013. At sites SW01, SW02, SW03, SW08, SW09, SW010, SW011, SW012, SW013, SW014, SW015, SW016 and SW017, the 2013 average was lower than the LTA. At the majority of monitoring points, the results showed an annual average pH similar to the long-term average. SW013 had the lowest pH average of 5.6. SW013 and SW015 had the lowest pH average of 5.2 and 5.7 respectively. The highest pH average recorded during 2013 was 8.3 recorded at SW016 which is located outside the mining area.

5 Community Consultation

5.1 Complaints

There was one community complaint received in February 2014 that related to subsidence management. The complainant stated that Mandalong Mine had not replied to their emails within a reasonable time frame. The mine has met and provided additional information to the landowner regarding the proposed mining and subsidence.

5.2 Inquires

During the extraction of Longwall 15, a number of inquiries were made by the public regarding potential purchase of properties or rental of Centennial owned properties located over the Mandalong mining area.

5.3 Mandalong Mine Community Consultative Committee

During the extraction of Longwall 15, one meeting of the Mandalong Mine Community Consultative Committee (MMCCC) was held on the 18 February 2014 at Mandalong Mine. A subsequent site inspection by CCC members of the Cooranbong Service Site and water management facilities was undertaken on 1 April 2014. A copy of the meeting minutes and presentation material is available on the Centennial Coal website.


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6 Bibliography

AGE. (2014). Mandalong Longwall Coal Mine, Groundwater Monitoring Review for AEMR 2013, Project No. G144/J.

Centennial Mandalong. (2009). Weltand Management Plan.

Centennial Mandalong. (2014). Annual Environmental Management Report 2013.

Hunter Eco. (2009). Centennial Coal Mandalong Underground Coalmine Wetlands Monitoring Baseline Report April 2009.

Hunter Eco. (2013a). Monitoring the Impact of Subsidence on Wetlands of the Mandalong Floodplain - Wetland Monitoring Report April 2013.

Hunter Eco. (2013b). Mandalong Underground Coalmine Wetlands Monitoring Report November 2013.

Seedsman Geotechnics. (2014a). Likelihood of 1.5 times and 2 Times Maximum Subsidence Base on Previous Longwalls - MAND14-01.

Seedsman Geotechnics. (2014b). Review of Subsidence LW15 - MAND14-02.

Centennial Coal Company Limited P O Box 1000 Toronto NSW 2283 www.centennialcoal.com.au

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