review of water balance modelling · 2016. 12. 5. · daniel lambert signature draft 3 22 aug 2016...

This report takes into account the particular

instructions and requirements of our client.

It is not intended for and should not be relied

upon by any third party and no responsibility

is undertaken to any third party.

Job number 249312-00

Arup Pty Ltd

Level 10, 201 Kent Street

Sydney NSW 2000

AustraliaLeve

www.arup.com

NSW Department of Industry

Werris Creek Mine

Review of Water Balance Modelling

Rev C | 2� November 2016

http:www.arup.com

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Name Nathan Cheah Michael Chendorain Daniel Lambert

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NSW Department of Industry Werris Creek Mine


Contents

Page

1 Introduction 1

1.1 Basis of report 1 1.2 Report Limitations and Confidentiality 1 1.3 Scope of work 1 1.4 Documentation 2

2 Context for the Review 3

2.1 The site 3 2.2 Water management philosophy 4 2.3 Project conditions 4 2.4 Consultation 5

3 Approach 5

4 Site visit 5

5 Arup Comments on Water Balance Modelling 6

5.1 General 6 5.2 Modelling parameters 9 5.3 Verification water balance model 14 5.4 Predictive water balance model 16

6 Conclusions 17

7 Recommendations 19

Appendices

Appendix A

Letter of Engagement

Appendix B

Comments Register


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REVIEW REPORT_ISSUE_REVC.DOCX



1 Introduction

1.1 Basis of report

1. Arup Pty Ltd. (Arup) has prepared this report in response to the letter of engagement by the NSW Department of Primary Industries (DPI) dated 8 April

2016, and included as Appendix A to this report.

2. The Werris Creek Coal (WCC) mine uses water balance modelling for two purposes:

1. To estimate water management and use requirements for the operations as part of ongoing Environmental Assessment. For the purpose of this report,

this is known as the “predictive Water Balance Model” (predictive-WBM);

and

2. Relevant portions of the predictive-WBM is used as a tool for verifying groundwater model predictions. For the purpose of this report, this is

known as the “verification-WBM”.

Both the predictive- and verification-WBMs were reviewed in detail.

1.2 Report Limitations and Confidentiality

3. This report has been prepared for the New South Wales Department of Primary Industries (DPI) and takes into account the particular instructions and

requirements of DPI (as noted in section 1.3 below). It is not intended for and

should not be relied upon by any third party and no responsibility is undertaken to

any third party. The work documented in this report is a review of work

performed by others. As such, Arup has not performed its own independent site

water balance calculations.

1.3 Scope of work

4. The scope of work comprises a review of the water balance modelling performed for the Werris Creek Coal (WCC) Mine, in particular:

x A general review of the water balance; x Consideration of the validity of the assumptions used for the model, in

particular rainfall runoff assumptions; and

x Consideration of the validity of the conclusions of the model, in particular the conclusions with respect to the relative contribution of surface and

groundwater to the total pit volume.

5. Arup has not performed its own independent site water balance calculations as part of the review. A ‘start-from-scratch’ water balance modelling exercise was

outside of the above scope. Furthermore, detailed calculation checks have not

been undertaken with the reasonable assumption that Whitehaven and its

consultants work with an appropriate standard of care, including their own

calculation checks and review procedures.

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6. The information in the reports was used to produce a conceptual understanding of the mine site and void water management (i.e. where water was being moved to,

where water was directly measured, where estimates have been used, and the

certainty relating to selected parameters). Where available, the parameters and

assessment was evaluated using best practice guidance to ensure that numbers

used in the modelling were reasonable. Without access to the water balance

spreadsheets, and for reasons outlined in sections below (due to lack of clarity in

the written reports) no calculations were undertaken, except with the use of

numbers already produced by WCC (for instance in Table 4 below).

1.4 Documentation

7. The WCC mine water balance is referenced in a number of publicly available documents which are detailed below. It is clear however that there is no single

report which provides a detailed synopsis of the exact parameters and underlying

assumptions which have been used in the water balance. The primary documents

which have formed part of this review listed in Table 1.

Table 1. Primary documents used for review of water balance

Doc.

No

Reference

1 Environ Pty Ltd., (Environ) 2015a. Appendix 2 – Water Balance Assessment.

Appendix to Environmental Assessment Report for Werris Creek Coal Mine Life

of Mine Project Modification 2, Report No. 623/17. Dated 28 January.

2 Environ Pty Ltd. (Environ), 2015b. Determination of Groundwater Interception Werris

Creek Coal Mine, Appendix to Werris Creek Coal Mine Annual Environmental

Management Report. Dated June.

3 GSS Environmental (GSS), 2010. Surface Water Assessment for Werris Creek Coal

Mine Life of Mine Project, Specialist Consultant Studies Compendium, Volume 1,

Part 2. Dated December.

8. In addition, the documents listed in Table 2 have also been consulted to provide information on the water management at the site and water balance modelling.

Table 2: Secondary documents used for review of water balance

Doc.

No

Reference

4 Environ Pty Ltd., (Environ), 2014. Evaluation of Void Water Intercepted by Werris

Creek Coal Mine Operations. Dated 10 April.

5 Heritage Computing Pty Ltd. (Hydro Simulations), 2015. Peer Review of Memo

Titled “Groundwater Declines at Quipolly Creek – Overview”

6 Robert Carr & Associates Pty Ltd (RCA), 2010. Groundwater Impact Assessment for

Werris Creek Coal Mine Life of Mine Project, Specialist Consultant Studies

Compendium, Volume 1, Part 1. Dated December.

7 R.W. Corkery & Co. Pty. Limited (RWC), 2010, Environmental Assessment for

Werris Creek Coal Mine Life of Mine Project. Dated December.

8 R.W. Corkery & Co. Pty. Limited (RWC), 2015, Environmental Assessment for

Werris Creek Coal Mine Modification 2 (PA 10_0059). Dated April.





Doc.

No

Reference

9 Whitehaven Coal Pty Ltd. (Whitehaven), 2015. Werris Creek Coal Environmental

Management System, Site Water Management Plan. Dated 17 July.

10 Whitehaven Coal Pty Ltd. (Whitehaven), 2013. Werris Creek Coal Annual

Environmental Management Report, 2014 – 2015. Dated 31 March.

11 Whitehaven Coal Pty Ltd. (Whitehaven), 2014. Werris Creek Coal Annual Review

and Annual Environmental Management Report, 2014 – 2015. Dated 31 March.

12 Whitehaven Coal Pty Ltd. (Whitehaven), 2015. Werris Creek Coal Annual Review

and Annual Environmental Management Report, 2013 – 2014. Dated 31 March.

13 UNSW Australia, Water Research Laboratory (UNSW), 2015. Memorandum,

Groundwater Declines at Quipolly Creek – Overview. Dated 2 November.

9. A number of documents were read as part of the scope of works which did not form part of the formal review. For example, the numerical groundwater

modelling report which is described in detail in document 6 (Table 2) is used to

provide a key input into the water balance (groundwater inflows).

10. The numerical model has previously been assessed as part of the original environmental assessment. It has been accepted by the Department of Planning for

use as a tool for predicting the groundwater environment in the mining region.

This review does contains some comments relating to the numerical groundwater

modelling where it is deemed necessary as part of the review of the water balance

modelling. However, any comments on the groundwater model are made for the

purpose of reviewing water balance modelling, and not as a critical review of the

groundwater model.

11. No water balance model files have been made available as part of this review. The comments and discussion made in this report are based on publicly available

reports, a single round of consultation with WCC/Environ, and a site visit on 16

June 2016 (described below).

2 Context for the Review

12. The following sections provide a limited background for the Coal Mine project and is our understanding based on our review of documents provided in Table 1

and Table 2, our site visit, and responses to questions provided by WCC.

2.1 The site

13. The Werris Creek Coal Mine is located around 4km south of the town of Werris Creek in northern NSW. The mine is operated by Werris Creek Coal Pty Limited

(WCC), a wholly-owned subsidiary of Whitehaven Coal Limited, and currently

has project approval (PA 10_0059) for the complete recovery of coal contained

within the Werris Creek Coal Measures. WCC is licensed to extract or intercept

groundwater through two water access licences: WAL29506 (50Ml/a) and

WAL32224 (211Ml/a).





2.2 Water management philosophy

14. We understand that water management at the site is based on the separation and segregation of different streams of water. Based on the documents reviewed, the

streams of water at the site include categories (as defined by WCC)1:

1. ‘Void water’ – this includes surface run-off from the void (mine) catchment and groundwater seepage. Void water is pumped to the void water dams;

2. ‘Dirty water’ – surface water which is collected from ground previously disturbed by mining;

3. ‘Clean water’ – surface water which is collected from undisturbed areas; and

4. ‘Contaminated water’ – runoff from workshop and fuel farm areas.

15. Note that the distinction between ‘Dirty’ and ‘Contaminated’ water is apparently due to source of the water rather than a distinction of the quality of the water.

16. We understand that the various water streams described above are kept separated from one another on site. As part of existing consent agreements, clean water and

dirty water are allowed to be discharged off site. The void water stream is

currently managed under a zero discharge policy, however the 2015 LOM

assessment proposed using excess water for alternative beneficial agricultural uses

on land adjacent to the site (which would by definition be an off-site discharge of

the void water stream).

2.3 Project conditions

17. Conditions relating to the implementation of the WCC LOM Project were issued under the Project Approval 10_0059. Relevant to this review is Schedule 3,

Condition 23 outlines the requirements of the Water Management Plan. Condition

23(a) requires the inclusion of a site water balance that:

x Includes details of sources of water supply; x Includes details of water use on-site; x Includes details of water management on- site; x Includes details of reporting procedures, which provide for the update of the

site water balance in each annual review; and

x Describes what measures would be implemented to minimise potable water use on-site.

18. WCC have an approved Water Management Plan

1 Water which seeps through the overburden is partially collected in the void and some is diverted

as dirty water.





2.4 Consultation

19. A number of meetings were undertaken as part of the scope of works:

x A kick off teleconference meeting on 12th May 2016 attended by Arup, DPI, WCC and the Quipolly Water Action Group (QWAG); and

x A site visit to Werris Creek Coal Mine on June 16 2016 attended by Arup, DPI, WCC and Environ.

20. Arup is aware of ongoing groundwater disputes between the local community and Werris Creek Coal Mine. This report has been prepared to present the findings of

the review of information made available by WCC and DPI. Only publicly

available reports have been consulted (including the questions and responses

provided in Appendix B). The findings and recommendations of this review are

based on the information contained within the reports.

3 Approach

21. Documentation listed in Section 1 was consulted in order to familiarise the Arup review team with the approach to water management at the site. Reports which

related directly to the water balance were reviewed.

22. A comments and questions register was prepared and distributed to DPI. WCC provided responses to those comments and questions on 15 July 2016, which

Arup received on 18 July 2016. Appendix B provides the comments from Arup

and responses received from WCC.

23. Consultation (as described above) was performed to further discuss the water balance modelling.

24. This draft report was prepared based on the accumulation of information provided in the documents listed above, responses received from WCC, and the site visit on

16 June 2016.

4 Site visit

25. A site visit was undertaken on 16 June 2016 and was attended by representatives from WCC, Environ, Arup and DPI. The purpose of this site visit was to observe

the site conditions and discuss initial questions with mine representatives. The site

visit provided a useful context to provide a better understanding of the water

balance modelling performed by Whitehaven and its consultants. This site visit

allowed Arup to discuss the progress of our review and gain clarity on how site

conditions were being modelled. The outcomes of this visit were used to inform

this report.





5 Arup Comments on Water Balance

Modelling

5.1 General

26. As noted above, it is our understanding that WCC used two separate Water Balance Models (WBMs) for different purposes (summarised in Table 3). One

WBM is used as an apparent additional line of evidence to verify the

appropriateness of the numerical groundwater model to quantify groundwater

inflows; for the purpose of this review, this WBM is referred to as the

‘verification-WBM’. The second WBM is used to predict future water

management conditions based on changes to site conditions; and is referred to as

the ‘predictive-WBM’..

Table 3. Summary of Water Balance Models

Verification WBM Predictive WBM

Purpose/objective Used to validate the predicted

groundwater inflows into

mine void (as estimated by

the numerical groundwater

model).

Water balance modelling

results are intended to be used

as an additional partially

quantitative assessment of the

inflows to the mining void.

Used as a predictive water

management tool in order to

assess the likely site wide

balance of water under future

mining scenarios.

Water balance results used to

assess circumstances when

the mine void would contain

water, affecting the ability to

mine.

Scope Mining void only – inputs,

outputs and changes in

storage relate to the mine void

only

Site wide – includes inputs

and outputs from the mining

void and void water dams,

and consumptive water uses

Parameters x Groundwater inflows to void,

x Surface water run off to void,

x Direct rainfall, x Discharges to void (water

curtain, sprinklers),

x Evaporation, x Pumping from void, x Water curtain losses

x Groundwater inflows to void,

x Surface water runoff and direct rainfall,

x Evaporation (VWDs and mining void),

x Consumptive water use

27. WCC have indicated that the verification-WBM results “should be considered in relation to a partially qualitative, partially quantitative ‘magnitude of error’

assessment between the WBM and observations in the context of varied

groundwater inflows.”

28. WCC have indicated that “the predictive WBM is only intended to provide an additional quantitative basis for decision making”





29. The comments below are based solely on review of the principle reports and the answers from WCC to a comment register. As noted above, Arup were not

provided and therefore have not reviewed the water balance model spreadsheets

directly.

5.1.1 Documentation

30. The mine water balance modelling is described in various reports however there is no single report which fully describes the models. In our opinion, if such a

document were required, at a minimum, should include the following:

x Description of numerical modelling tools employed (software documentation and version) along with details on how the tools were used (data source, input

parameters, calibration method, boundary conditions, etc.);

x A full conceptual diagram showing the entire water balance (reports currently only show a conceptual model for the verification-WBM but not for the

predictive-WBM);

x Magnitude of selected input parameters and justification for their use. Where parameters are calculated (such as the runoff parameters), documentation of

the how the parameters were calculated and justification; and

x Model assumptions and evaluation of underlying uncertainty. 31. Consultation with WCC has indicated that all water balances are constructed in

MS Excel and use a daily-timestep input-output system.

32. The input parameters used for the verification-WBM are based on records from Bureau of Meteorology (BoM) and WCC (with some changes, which are outlined

in the relevant reports) and discussed below.

5.1.2 Conceptual water balance

33. The conceptual water balance used for the verification-WBM (as shown in Figure 1) refers solely to the water balance of the mine pit void.

34. As discussed in further detail below, it is Arup’s opinion that the conceptual model and water balance does not comprise all potential inflows into the pit, or at

the least, does not treat the inflows in a consistent way.

35. Specifically, we believe that the pre-strip sprinklers should be included as an input to the system, in the same way that the water curtain inputs are included. Similarly

the loss component for the pre-strip sprinklers should be included as a direct

output, just as the water curtain losses are. While we do not expect this change to

have an impact on the water balance estimates, we believe that treating the

parameters in a consistent manner will improve the clarity in the reporting.





Figure 1: Pit void conceptual water balance (Source: Environ, 2016).

36. The reports describe the void pit water balance as the site water balance, which leads to confusion as one would assume a site water balance to consider water

management across the entire mine site (i.e. to include other components such as

void water storage). Distinction between the verification-WBM (which we

understand is limited to the void pit) and prediction-WBM (which we understand

is site wide) in future reports is recommended.

37. In the Environ 2015b report (document 2, Table 1), Water Outputs from what we assume is the verification-WBM includes consumptive water use parameters.

In our opinion, the void water balance (i.e. the verification-WBM) does not

require consideration of consumptive water uses on site as a ‘Water Output’.

Water Output from the void is metered and can therefore be accurately relied

upon. Our understanding is that consumptive use water is not directly taken from

the void, but rather from the void water storage dams (VWDs), as illustrated in

Figure 2. As exceptions, we suggest that both the pre-strip sprinkler and water

curtain volume be included in the verification-WBM, but as inputs back to the

void (as noted above).

38. It is our understanding the predictive-WBM is a result of inclusion of all site wide consumptive water uses into the verification-WBM (such as the water balances

associated with the VWDs). As noted in the review documents, the use of the

predictive-WBM is to quantitatively evaluate potential impacts of any proposed

site wide water use changes. A graphical illustration of the components of the

predictive-WBM based on our understanding is provided in Figure 2.





Figure 2: Arup’s understanding of the Site wide conceptual water balance (i.e. the predictive-WBM).

5.2 Modelling parameters

39. Information relating to the input parameters has been collected from the primary documents under review. A summary of each of the key parameters along with

commentary is provided in the following sub-sections.

5.2.1 Rainfall and run-off

40. Rainfall data is available from three stations, one at the Quirindi Post Office (15km away from the mine), one at Werris Creek Post Office (4km from the mine

site, and one at the mine site. The modelling work undertaken uses the Werris

Creek Post Office data which has data dating back to 1908.

41. WCC indicated that the mine site rainfall data and that from Werris Creek Post Office (WCPO) have a good correlation (0.95) with site data collection which has

been collected over the past 10 years. This would indicate that rainfall measured

at the Werris Creek Post Office and used in the water balance modelling is

reasonably representative of site conditions. As a minor comment, the correlation

parameter used to quantify the agreement between WCPO rainfall data and site

rainfall data should be defined (i.e. r or r2).





42. The verification-WBM uses rainfall data from the Werris Creek Post Office for daily calculations. Since the modelling is used as a validation, the data used is

considered to be appropriate for purpose.

43. For the predictive-WBM, a statistical assessment of the long term rainfall records was undertaken by WCC to select the range of rainfall conditions used in the

modelling. The median, ‘dry’ case was taken as the 15th percentile of the data set

and the median ‘wet’ case was taken as the 90th percentile of the data set. The

use of the WCPO dataset provides long term data (dating back to 1908) which has

a strong correlation to site rainfall data (as noted above). In our opinion, use of

this dataset is sound for the purpose of predictive forecasting.

44. The predictive-WBM does not apparently include consideration of climate change impacts. In our opinion, given the relatively short future forecasting periods (of

no more than 10 years), climate change impacts will not have substantive impacts

on the model results. Should the period considered be required to be longer, then

climate change impacts may need to be considered, or at a minimum, justification

provided for why it has been excluded.

45. The verification-WBM incorporates a simplified runoff model incorporating a single surface store/base flow based on a modified version of Australian Water

Balance Model (AWBM). AWBM accounts for the antecedent moisture

conditions of the catchment in the determination of the runoff from the rainfall

data, hence provides a more robust and realistic estimation of runoff compared to

the approach using solely runoff coefficients, as was the case in the previous

surface runoff model developed (GSS, 2010). The use of AWBM is appropriate as

it should improve surface runoff estimation in WBM.

46. Based on our review, the magnitude of rainfall/runoff inputs used in both WBMs is reasonable for the geographical location and meteorological conditions of the

mine site. The spreadsheets used to estimate runoff were not provided and thus

not be reviewed.

5.2.2 Groundwater inflows

47. Groundwater inflows to the pit void (see the top-left box in Figure 1) are estimated using the calibrated numerical groundwater model. The setup,

calibration and results of the numerical model are described in RWC, 2010

(document 6 , Table 2). A technical review of the model was carried out in 2011

by Hydro Simulations (document 5, Table 2) and for the purposes of this review,

the model is assumed to be a reasonable working representation of the

hydrogeological system.

48. WCC have confirmed that the numerical groundwater model has the capacity to differentiate between inflows from the basalt, coal measures and overburden;

which is not explicitly stated in the reports reviewed (Table 1) Table 2).

49. Groundwater inflow into the void is not directly measured on site. The water balance indicates that groundwater contribution to void water inflow is

comparatively small in comparison to the other inflows (accounting for

approximately 5% of the total flow into the void). This result is as expected based

on the conceptual model which indicates that the on-site coal measures and the





weathered basalt clay are both of low permeability materials. However the

magnitude of losses associated with parameters such as the pre-strip sprinkler and

water curtain are of a similar order of magnitude as the groundwater contribution.

Given the apparent uncertainty in how these losses were estimated, there is some

corresponding uncertainty in how useful the verification-WBM is to verify the

numerical groundwater model.

50. WCC have commented (Appendix B) that “losses will occur however these cannot be measured accurately, therefore they are estimated based on

observations made onsite and the water balance reconciliation process”. Arup

agrees that directly measuring these parameters is not likely to be feasible and is

not considered to be common practice. However, as noted above, the scale of the

parameters is such that even a relatively small change in the estimated value can

be significant in comparison to the magnitude of groundwater inflow.

51. One methodology to assess this uncertainty associated with adjustment parameters would be to perform a sensitivity analysis on the parameters to evaluate how

much of an impact they have on the overall calibration.

52. The uncertainty associated with the loss parameters, which have been assumed (given their inability to be measured), impacts the robustness of conclusions

drawn from the verification-WBM. In light of this uncertainty and given that the

numerical groundwater model has already been peer-reviewed and accepted by

DPI, the use of the verification-WBM as an additional line of evidence in “a

partially qualitative, partially quantitative ‘magnitude of error’” manner is

reasonable.

5.2.3 Former mine working inflows

53. The WCC conceptual model contains groundwater inflow from: Former underground mine workings, Coal measures, and Basalt aquifer (Figure 1).

However Table 2, from Environ, 2015b, which quantifies the verification-WBM

results does not use the same terminology. Table 2, Environ 2015b indicates that

“Other Groundwater” is estimated using the groundwater numerical model. Arup

have also assumed, given the lack of clarity in the document, that “Recirculated

back to Pit/UG” refers to measurements at the pipeline which transfers water to

the water curtain.

54. Based on our review, it appears that the verification-WBM assumes that input to the water curtain results in a direct input to the void pit. In reality there is likely

to be a transient affect (i.e. a lag) between the water curtain input and impact on

water levels in the void pit. The uncertainty associated with this transient affect

should be appropriately addressed, particularly with respect to potential error in

the verification-WBM.

5.2.4 Evaporation

55. Evaporation rates are incorporated into both the verification- and predictive-VWDs. We understand that evaporation rates are estimated using monthly





measured surface water area from the various water surfaces2 and using Bureau of

Meteorology (BOM) estimated monthly averages from the Quirindi Post Office

(located around 13km from the site).

56. There are two sources of error in the evaporation estimates. The first being use of data from 13km from the site. The second being extrapolation of monthly average

rates to daily rates. Given the small contribution of evaporation to both WBMs, it

is unlikely that these sources of error contribute with any significance. The use of

BOM data to estimate evaporation rates is standard practice however both of these

errors could easily be removed through daily measurement of evaporation from an

on-site weather station.

5.2.5 Void pit discharge

57. Outflows from the pit void are monitored by a flow meter on the discharge pipeline. For the verification-WBM this provides an adequate record for the

largest output component from the void.

5.2.6 Parameter adjustments

58. Within the WBMs there are parameter adjustments to account for physical behaviours which are not being directly measured. The two relevant parameter

adjustments are associated with the water curtain and the Pre-strip sprinkler.

Water Curtain adjustment

59. For the water curtain, a loss is defined as: “losses which occur due to spontaneous combustion processes in the former coal workings” and “the pumping and

reticulation process” and has been estimated to be between 5 and 10% of the total

water curtain input to the void pit. We understand this to mean that as water is

applied to the water curtain system, 5 to 10% of the applied water volume is lost

and thus only 90 to 95% of the water curtain is counted as an inflow to the void

pit.

60. The cause of this loss has been explained to be as result of water turning to steam as it interacts with the former underground coal workings (Appendix B).

61. For 2014/2015, this loss factor is estimated to be 10%. In previous annual reports the loss factor was 5%. Environ/WCC have indicated that losses from the system

vary from year to year depending on a number of factors including the method of

reticulation and the distance from the working face of the mine.

62. Environ/WCC note that the losses cannot be measured accurately, therefore they are based on estimated observations made on site and the water balance

reconciliation process (Appendix B). However the details by which this factor is

quantitatively estimated or inferred have not been documented.

2 We understand that the verification-WBM estimates evaporation from the void pit; the

predictive-WBM estimates evaporation for the void pit and VWDs.





Pre-Strip Sprinkler adjustment

63. For the pre-strip sprinkler, Environ 2015b (document 2, Table 1) states that “approximately 25% of the surface sprinkler use is above (takes place over) the

workings and may find its way back into the void”. We understand this to mean

that 25% of volume of water used for the pre-strip sprinkler is counted as an

inflow to the void pit. While it is not explicitly stated what the fate of the other

75% is, we assume that it is not counted in the WBMs, being lost through

evaporation (the system being designed to maximise evaporation).

64. The pre-strip sprinkler has been developed to enhance evapotranspiration from the surface of the soon-to-be mined areas; which would explain why only 25% of the

sprinkler flow becomes an input to the void pit. However no details are provided

which indicate how this factor is quantitatively estimated or inferred.

Other adjustments and inconsistencies

65. The reporting of the verification-WBM discusses a further adjustment to the VWD evaporators by 8%. In a communication from WCC, this adjustment was

made based on the recommendation from the equipment supplier. However it is

unclear why this term is included in the verification-WBM description, as the

evaporators do not appear to input into, or output from, the void. We do note

however, that evaporators do impact water storage for the VWDs.

66. The water balance modelling appears to treat the water curtain and pre-strip sprinkler terms differently. The water balance treats the water curtain recirculation

as an input (100% of the measured value) and the loss (10%) as an output. In

contrast, the pre-strip sprinkler does not appear to be included as an input to the

water balance. Instead an adjustment to the consumptive use. It is our opinion

that the pre strip sprinkler term ought to be treated in the same manner as the

water curtain – as an input to the pit (i.e. as 25% of the measured value).

67. Comments provided in Appendix B describe the differences in loss terms as a result of being used for different purposes:

“The pre-strip sprinkler irrigated water onto the land surface to enhance

evapotranspiration of the water therefore it has a higher loss of 75%

(output) recognising that infiltration did occur on the land above the former

underground workings (25% input). However the water curtain had water

directly applied to, or the ground above, the former underground workings

to saturate and infiltrate (input 95%) recognising that a minor quantity of

water would be lost as steam (output 5%).”

68. While we recognise the difficulty in estimating the magnitude of the losses associated with the water curtain and pre-strip sprinklers, the uncertainty

associated with these terms impacts the robustness of the WBM as stand-alone

tool to quantitatively estimate groundwater impacts. However as an additional

line of evidence, the verification-WBM has been appropriately used.





5.2.7 Consumptive water use

69. As indicated in Table 2 of Environ 2015b, “consumptive water use” is expressed as an output from the site water balance. Consumptive water use comprises of the

following, some of which are measured and some of which are estimated:

x Dust suppression including haul roads (measured), crushing plant (estimated), train load out (estimated) and pre-strip sprinkler (measured);

x Workshop (measured); x Recirculated to water curtain (measured); and x Evaporators (measured).

70. We understand that, with the exception of the pre-strip sprinklers, the consumptive water use parameters are only relevant for the predictive-WBM and

are not relevant for the verification-WBM (which is only based on water balance

associated with the void pit). In other words, from a water balance perspective,

the consumptive use parameters comprise an output from the VWDs (in

combination with VWD evaporation) and are thus unrelated to output from the

void pit.

5.3 Verification water balance model

71. The verification-WBM was used to validate the results of the numerical groundwater model. The model evaluates the proportion of groundwater entering

the mine void using the parameters discussed above.

72. Environ 2015b details the use of the water balance to evaluate the contribution of groundwater inflow to the void between April 2014 and March 2015. As

described in the report, a sensitivity analysis was performed by varying the

groundwater inflow parameter to the verification-WBM to check (i.e. verify) the

predictions from the numerical groundwater flow model. The groundwater flow

input to the verification-WBM was varied by between 10% and 350% of the

groundwater flow as predicted by the numerical groundwater flow model; and the

impact on the verification-WBM calibration was evaluated. The calibration was

evaluated by comparing the calculated water volume to the actual volume of water

in the void (as estimated from monthly site surveys).

73. The verification-WBM incorporates a simplified runoff model incorporating a single surface store/base flow based on a modified version of Australian Water

Balance Model (AWBM). The modification of the runoff parameters appears to

have improved the data fit significantly, in comparison to the previous surface

runoff model (GSS, 2010).

74. The reports reviewed do not discuss the specific input parameters used in the revised surface water model, specifically those from the modified AWBM. These

parameters and assumptions should be explicitly detailed to provide confidence

that realistic values have been used.





75. Rainfall records used in the modelling have not been provided for this review as well as the WBM in MS Excel, thus the accuracy of the surface water inflows

cannot be ascertained.

76. As discussed above, it appears that the model does not necessarily take into account all inputs to the void pit in a consistent way. Specifically, the input from

pre-strip sprinklers is not accounted for in the same way as recirculation for

spontaneous combustion (i.e. water curtain).

77. The measured flow recirculated back to pit for spontaneous combustion (i.e. water curtain) is treated as an input to the water balance, whereas the input from the pre-

strip sprinkler is not. It is unclear from the available information reviewed why

this is the case, since both apparently discharge water into the void. This

inconsistency in how parameters are expressed is confusing and not adequately

explained within the reports. Confidence in the water balance models would be

gained by improving the clarity in the descriptions for the parameters used, as

well as ensuring that parameters are consistently used in the modelling.

78. The total water output for the 2014/2015 period (in Table 3 of Environ, 2015b) is 1045ML. This number matches the total measured discharge from the pit for the

same period (“pit dewatering” row in Table 1, Environ, 2015b). However the

“Water Outputs” value of 1045ML from Table 3 of Environ, 2015b appears to

include water curtain losses and pit evaporation. We would not expect either of

these terms to be part of the “Pit Dewatering” parameter listed in Table 1 of

Environ 2015b. Thus with the inclusion of water curtain losses and pit

evaporation, we would expect the actual output from the void pit to be 1115.2ML

(1045 ML + 34 ML + 36.2ML). Table 3 provides a summary of our interpretation

of the 2014/2015 verification-WBM for the void pit.

Table 4: Arup Interpretation of 2014/15 void pit water balance (i.e. the verification-

WBM).

Water Inputs (ML) Water Outputs (ML)

Rainfall Interception and runoff 672 Pit dewatering (2) 1045

Groundwater Intercepted 56 In pit evaporation 34

Other Groundwater 30 Recirculation losses

(Water Curtain)

36.2

Water recirculated back to pit

(Water Curtain)

358.9

Pre strip sprinkler discharge (1) 56.6

Total 1173.5ML Total -1115.2

NET WATER BALANCE +58.3 ML

Notes

All values taken from Environ, 2015b.

(1) The pre-strip sprinkler is treated as an input to the void water balance, as documented in

Environ 2015b, 25% of the measured flow (226.5ML) has been estimated to return to the void,

(2) Measured dewatering rate from outflow pipeline flow meter,





79. The difference between the net water reported in Environ, 2015b of +72ML and the interpreted value in Table 3 (of +58ML) is relatively small, however not

insignificant.

80. The method used to improve the verification-WBM calibration was based on changes to groundwater inflows where the best fits were for groundwater inflows

of 10ML and 86ML. We do note that while the calibration has improved there are

still periods with poor agreement to the calibrated model. For instance for the

month of October 2014, the water balance model under predicts the total volume

in void by 100ML; and for the month of January 2015 the model over predicts the

volume by around 80ML.

81. The comments document (Appendix B) states that “the difference in the model and actual pit water levels are due to runoff predictions used in the AWBM. The

AWBM requires soil to be saturated before runoff occurs and this results in a

runoff lag particularly in the dry months”. We agree that this type of lag will

impact the overall calibration. In addition transient affects associated with

movement of groundwater through the subsurface will also impact the overall

WBM calibration. However this affect is not discussed in the reports reviewed.

We also note that quantification and measurement of transient impacts are

difficult and complex.

5.4 Predictive water balance model

82. The predictive-WBM has been used to assess future water management scenarios on site. The key objective of this model was to "enable analysis of circumstances

under which open cut void would contain water, when pumping out from the void

to VWDs could not occur due to them being full" (Appendix B)

83. It is our understanding that the predictive-WBM has been developed by adjusting the verification-WBM to incorporate the following:

x Water balance parameters for the VWDs (including direct rainfall and evaporation),

x Consumptive water use, and x Future predicted groundwater inflows based on the numerical groundwater

model.

84. A schematic conceptual model of this system is not presented in the reports. Given the complexity of the system, a conceptual diagram showing the system

(such as for the in pit void) would be considered to be very useful. As part of our

review, we have a developed a conceptual water balance based on the information

provided (Figure 2).

85. A statistical assessment of rainfall/runoff was undertaken by Environ to assess surface water inflow under different scenarios (wet, median and dry years). The

calculations have not been reviewed as part of the report but the rationale behind

the assessment is considered to be reasonable (as discussed above).

86. As part of our review, we questioned whether under wet years, recharge to the aquifer would be higher and therefore groundwater inflow to the void might be





higher. As documented in Appendix B, Environ commented that “Adjusting for

low and high rainfall rates made little difference to the model inflow

predictions.”3 Arup have not verified this assertion, but presumably under a wet

scenario the amount of recharge to the groundwater system would increase, with a

corresponding increase in groundwater levels in the Werrie basalts outside of the

mine site. This would lead to increased head differentials across the clay layer and

presumably greater inflows into the void.

87. However given the relatively small contribution of groundwater predicted from the model, any changes under differing recharge scenarios would still likely be

small compared to the estimated surface water inflow component. In any case, it

would be useful to clarify the rationale for use of a single recharge scenario in

predictive modelling.

88. We also provided another question regarding the use of the same water use parameter regardless of differing rainfall scenarios. In addition, we note that the

water use parameter used in predictive modelling is significantly less than the

actual water use on-site (as documented in Environ, 2015b). As noted in

Appendix B, Environ responded that “it was not possible to identify, either from

monitoring data or from site observations, the extent to which water use may

change between dry and wet years. In the absence of any quantitative estimate of

the difference in water use between dry and wet years, it was considered better to

keep these parameters unchanged”, and “The assumptions used for predictive

scenarios did not foresee the significant reticulation of water for spontaneous

combustion. WCCM could not predict how much water would be utilised to

manage spontaneous combustion.”

89. By presenting only the base water use (i.e. dust suppression, workshop) and excluding water curtain use, the predictions are likely to represent a conservative

estimate of the likely water balance on site (i.e. an excess of water). In reality,

additional water use may be occurring on site during these periods through

evaporators and spontaneous combustion control. For water management planning

purposes it is considered reasonable to err on the conservative side as this allows

contingency to be built into future plans.

6 Conclusions

90. A review of the Environ/WCC water balance modelling reports has been undertaken by Arup. The scope of this review included the following:

x A general review of the water balance; x Consideration of the validity of the assumptions used for the model, in

particular rainfall runoff assumptions; and

x Consideration of the validity of the conclusions of the model, in particular the conclusions with respect to the relative contribution of surface and

groundwater to the total pit volume.

3 WCC have indicated in their review of an earlier draft of this report that rainfall impacts are

roughly 5% of the impacts of mining on groundwater levels across the clay layer.





91. The scope of works did not include a detailed review of the hydrogeological system or hydrogeological numerical modelling, and was restricted to published

documents outlined in Table 1 and 2 of this report.

General review of the water balance

92. It is our general opinion that Environ and WCC have a good understanding of the conceptual hydrogeology at the coal mine site however the water balance

modelling reports are generally poorly explained and at times difficult to

understand.

93. Water Balance Model spreadsheets were not directly reviewed. However, the methodologies described are appropriate and the results, based on the described

methodology and documented estimates, are reasonable.

94. The verification-WBM is used as a tool to substantiate the predicted groundwater inflows which have been estimated from the groundwater numerical flow model.

The use of the verification-WBM as “a partially qualitative, partially quantitative

‘magnitude of error’” estimate of groundwater inflow is reasonable. Given the

uncertainties noted in our review, we do not recommend relying solely on the

verification-WBM as a stand-alone tool to evaluate compliance of groundwater

take within the licensed entitlement or to assess groundwater impacts. However it

is useful as an additional line of evidence in addition to the primary compliance

tool (the numerical groundwater model).

95. The predictive-WBM is used to assess the likely future water demands on the mine site. Future water use has been underestimated as inputs to the predictive-

WBM which provides a conservative estimate of future water storage needs.

Thus the use of the predictive-WBM has been reasonably applied.

Validity of the assumptions used for the models

96. The treatment of inputs to the pit from water management on site (water curtain discharge and pre-strip sprinkler) should be treated in a consistent manner (i.e.

both as inputs to the water balance).

97. The inclusion of consumptive water uses in the reporting tables for the verification-WBM is confusing, particularly when they are not relevant to the

verification-WBM (as per the conceptual model, Figure 1).

98. The uncertainty associated with certain parameters is considered to be relatively large. In particular the estimated losses from the water curtain and the discharge to

the void from the pre-strip sprinkler. The inclusion of these parameters in the

water balance model appears to be valid and Arup is in agreement that they are

difficult parameters to accurately measure. However, the reporting and subsequent

commentary do not provide adequate justification for the chosen values.

99. In the absence of the rainfall records and WBM in MS Excel provided for this review, the suitability of the surface water parameters adopted in the modelling

cannot be ascertained which in-turn, could impact the accuracy of the estimation

of the surface water inflows. The use of the modified AWBM over the previously

overgeneralised runoff coefficients is deemed an appropriate approach





considering the improvement of the verification-WBM calibration as a result of

the change.

Validity of the conclusions of the models

100. The validation exercise indicated that the groundwater inflow component to the void is of a similar magnitude as predicted by the numerical groundwater model.

The results of the validation showed good a good calibration in some months but a

relatively poor calibration in other months. Environ commented that this is likely

to be as a result of lags in the surface water discharge predicted by the surface

water model used. The rationale for poor calibration months should be better

documented in future reports.

101. The inability to reliably estimate the “adjustment” parameters reduces the robustness of the verification-WBM. Given the scale of the adjusted parameters

compared to the total groundwater flow, even a relatively small change in the

estimated value for adjusted parameters can be significant in comparison to the

magnitude of groundwater inflow.

102. It is our opinion that the verification-WBM provides an additional line of evidence of the appropriateness of the numerical groundwater model to predict

groundwater inflows to the void. However, given the uncertainty in the

parameters described above, additional work could be undertaken to improve the

confidence in the water balance model output (see recommendations below).

103. Consistent with the approach undertaken for the verification-WBM, the modified AWBM has been adopted in the surface runoff estimation for the predictive-

WBM and this is deemed appropriate.

104. The presentation of surface water inflows during dry and wet years is reasonable. The data used for the statistical analysis is for an extensive period at a location

shown to have a good correlation with site data.

105. The predicted water use in future scenarios is based solely on dust suppression and miscellaneous uses. The omission of other uses such as evaporators and water

use for spontaneous combustion control is considered reasonable since it is

unclear whether they will be operational. This provides a conservative estimate

for the purposes of planning future water management requirements at the site.

7 Recommendations

106. The following provides a summary of recommendations noted above.

1. A single report should be generated to document the water balance model which, at a minimum, includes the following:

x Description of numerical modelling tools employed (software documentation and version) along with details on how the tools were

used (data source, input parameters, calibration method, boundary

conditions, etc.);





x A full conceptual diagram showing the entire water balance (reports currently only show a conceptual model for the verification-WBM but

not for the predictive-WBM);

x Magnitude of selected input parameters and justification for their use. Where parameters are calculated (such as runoff parameters),

documentation of the how the parameters were calculated and

justification; and

x Model assumptions and evaluation of underlying uncertainty. 2. In future reports, the rationale for poor calibration between the verification-

WBM and site data should be better documented.

3. All future reports should present all water balance components in a clear and consistent manner.

4. The correlation parameter used to quantify the agreement between WCPO rainfall data and site rainfall data (used in the predictive-WBM) should be

defined (i.e. r or r2).

5. The impacts of adjustment parameters on the verification-WBM calibration should be further evaluated by performing a thorough sensitivity analysis.

However, a multi-parameter sensitivity analysis can prove to be time

consuming, particularly as WCC have indicated that the verification-WBM

is used as a semi-quantitative tool. The availability of a fully calibrated and

peer-reviewed numerical groundwater model provides more confidence on

the accuracy of estimated groundwater flows than had the WBM been the

only tool available.

6. WCC should consider whether the inclusion of daily measurements of evaporation from an on-site location would reduce errors associated with

use of off-site monthly data.

7. Include a rationale for the use of a single recharge scenario in predictive modelling.



Appendix A

Letter of Engagement

Appendix B

Comments Register

NSW Department of Industry Werris Creek Mine Review of Water Balance Modelling

Contents

B1. Arup Memorandum dated 20 May 20016 titled “Werris Creek – Questions and Clarifications – Version 1”; which include responses from WCC.

Rev C | 25 November 2016 Page B1 \\GLOBAL.ARUP.COM\AUSTRALASIA\SYD\PROJECTS\249000\249312-00 WERRIS CREEK WATER\WORK\INTERNAL\FINAL REPORT\APPENDICES BACKUP\APP A COVER.DOCX

Memorandum

Q740335171010922diverg

To Alison Collaros Date of Review

20 May 2016

Copies Reference number

From Daniel Lambert

Nathan Cheah

Jon Leech

Michael Chendorain

File reference

Subject Werris Creek – Questions and Clarifications – Version 1

W:\ENVIRONMENTAL\2015-2016\7. GROUNDWATER\ARUP REVIEW OF GROUNDWATER BALANCE\WERRIS CREEK INITIAL QUESTIONS AND CLARIFICATIONS VERSION 1_RAMBOLL ENVIRON RESPONSES_FINAL.DOCX

Arup | F0.3 Page 1 of 10

ID Comment by Arup Response

Date

Response

Received

Request

Open/Closed

1. Comments relating to surface water modelling

1.1 The GSS 2010 study utilised the rainfall data from the Quirindi Post Office BOM

station (15km away from the Mine) and stated there is high correlation of this

rainfall dataset with the rainfall data from the rain gauge operated within the

Mine. The Environ 2015 study utilised the rainfall data from the Werris Ck Post

Office BOM station (4km away from the Mine).

1.1.1- Has there been a check conducted to compare the rainfall data from the

Werris Ck Post Office gauge with the Mine operated rain gauge?

1.1.2- Why are rainfall data from different gauges used in the different studies

and justification for using a particular gauge?

1.1.3- Why is the rainfall data directly from the site not used as the main source of

rainfall data?

1.1.4- Has any sensitivity analysis of rainfall been performed to calibrate the

model?

General - Comments have been received on two versions of WBMs that have

been used for two different purposes. The WBM used for verifying modelled

groundwater inflows (as described in the main body of report AS130433,

dated June 2015) is therefore referred to in our response below as the

‘groundwater-verification WBM’. There is also a version of the WBM which

was used for predictive modelling as reported in January 2015. This is

referred to below as the ‘predictive WBM’. The groundwater-verification

WBM incorporated some improvements on the predictive WBM and the

most recent version of the groundwater-verification WBM (for the 2015-

2016 reporting) is another step forward on that.

1.1.1 – Yes – a comparison on monthly rainfall rates between Werris Creek

Post office and the site rainfall data provides good correlation (0.95).

1.1.2 – not sure why GSS used Quirindi. Werris Creek is the closest site to the

mine and has been used in the more recent modelling.

1.1.3 - Both the groundwater-verification and predictive WBMs use a daily

time step based on real data (either from BoM or WCCM monitoring). Data

from the Werris Creek BOM station was utilised due to its historical data set

>100 years in comparison to 100 years to give us

an understanding of what would happen if similar rainfall conditions were to

occur over the next c.100 years. This was also not possible with site-derived

data.

1.1.4 – As mentioned above, sensitivity checking was undertaken by using as

complete a record of daily rainfall as possible over c.100 years. This enabled

us to derive likelihood statistics based on conditions representative of

median conditions, relatively ‘dry’ or relatively ‘wet’ years. It should be

borne in mind that the intention of the WBMs was (respectively) to provide

some quantitative verification of the groundwater model (the groundwater-

verification WBM) and to allow informed decisions to be made about future

water management on-site (both WBMs).

2. Comments relating to hydrogeological modelling

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Page 2 of 10

2.1 The water balance separates the groundwater inflow to the void into separate

inputs (i.e. from basalt, coal measures, underground workings).

- Are these explicitly determined by the numerical model?

2.1 - Yes, zones are included in the model to predict these explicitly.

2.2 The 2015 EA, Appendix 2 states that groundwater inflows and overburden

seepage are estimated using the groundwater model.

2.2.1- With reference to the overburden seepage, what are the infiltration

assumptions that the estimates are based on?

2.2.1 - A value of 0.5% of rainfall was adopted as recharge to aquifer from

rainfall in coal measures pre-mining. Following mining, a higher recharge

rate was adopted for the overburden area on the basis of the loose nature of

backfill, uneven ground surface and lower evapotranspiration due to low

vegetation. Infiltration to the aquifer for the overburden was increased to

10% of total rainfall.

2.3 The conceptual model indicates that the groundwater table is affected by

rainfall.

2.3.1- Why is it that the groundwater inflow remains the same for all scenarios

including the ‘dry’ and ‘wet’ scenarios?

2.3.2- Has the predicted inflow from groundwater been modelled under a single

recharge scenario?

2.3.1 - Recharge from infiltration is low, between 0.5% (coal measure

aquifer) and 2% (basalt aquifer) of rainfall. Adjusting for low and high rainfall

rates made little difference to the model inflow predictions.

2.3.2. - Yes, for the reasons stated above.

3. Comments relating to the Water balance



Page 3 of 10

3.1 3.3.1 What water balance modelling software is used? Can the software and

model files be provided?

What are the model parameter values adopted in the software which resulted in

better correlation between the modelled and the monitored results? More details

are required describing the parameter values used in the software.

3.1.1 - All WBMs were put together in MS Excel and are relatively simple

daily-timestep input-output models. The input parameters are all listed in

Figure 1 of the report (and the summary note for the predictive WBM) and

were included in MS Excel as a daily input or output (in m3). For the

groundwater-verification WBM, parameters such as rainfall, evaporation and

data for pumping out-of-pit etc. were input to the model based on records

from BoM and WCCM without any changes (other than corrections

described in the report AS130433, dated June 2015). Groundwater inflows

were then varied by substantial factors (10% - 350% of the groundwater

model results) to see which would provide the closest fit between

observations and WBM results. The groundwater-verification WBM results

should be considered (and are discussed in the report AS130433, dated June

2015) in relation to a partially qualitative, partially quantitative ‘magnitude

of error’ assessment between the WBM and observations in the context of

varied groundwater inflows. This is the only ‘calibration’ per se of the

groundwater-verification WBM.

For the predictive WBM, monitoring records (of the volume of water in the

void) were provided by WCCM between 2012 and 2014. Runoff calculations

were input to an initial version of the model from GSSE’s estimates of runoff

coefficients. All other input data were initially unchanged including an

estimate of groundwater inflows which were taken from Ramboll Environ’s

groundwater model. WCCM monitoring records were then compared with

the initial run of the predictive WBM results to review closeness-of-fit. It

was found that the model did not provide a very close fit between

observations and the initial predictive WBM results. The predictive WBM

was therefore changed to remove the simple runoff coefficients and replace

them with runoff rates based on the Australian Water Balance Model

(AWBM). This was the only parameter changed to get a closer fit between

observations and modelled results.



Page 4 of 10

3.2 The 2015 EA, Appendix 2 states that information on estimated water curtain

losses was provided to Environ by WCC. In the annual monitoring reports it

states that the water curtain losses are estimated by Environ.

- How is this term estimated and please clarify which party is estimating the loss?

3.2 - Water curtain losses were estimated by Environ based on an

understanding of geology and observations made on site. The purpose of the

water curtain is to manage spontaneous combustion through the saturation

of the former underground mine workings. Based on the geology, flow

through the former underground mine workings would drain to the void

which is not possible to measure and thus why the losses are estimated.

3.3 The 2015 EA, Appendix 2 report indicates that calibration of the water balance

model was undertaken using data from September 2012 and April 2014. The

text and calibration graphs appears to indicate only the void storage was

assessed to calibrate the model.

- Was the model not also calibrated to changes in VWD storage?

- Is the WBM described in the text not a site water balance?

- If so should all inputs, outputs and changes in storage (for the void water

system) not be included?

3.3 - The Void Water Dams (VWDs) are not subject to any runoff inflows as

they are mostly ‘turkey’s nest’-type isolated dams. As varying the runoff

coefficients was the only calibration undertaken for the predictive WBM, and

this does not apply to the VWDs, the VWDs were excluded from the

calibration. The WBMs were being used in the context of ‘magnitude of

error’ decision-making. it was not considered that further efforts at

calibration would be greatly beneficial.

3.4 2015 EA, Appendix 2 - Under predictive modelling (Future Scenarios) the text

indicates that additional parameters were required, for instance inputs and

outputs to the VWDs.

- It is unclear why a total site water balance was not undertaken for the

calibration phase - would this not have provided a better basis for future

predictions? Please comment

See comments above

3.5 2015 EA, Appendix 2 - Table 1 in future scenarios indicates that water use is

expected to be the same every year and in every weather scenario.

- Would activity such as dust suppression increase under drier climatic conditions?

3.5 - The predictive WBM is only intended to provide an additional

quantitative basis for decision making. It was not possible to identify, either

from monitoring data or from site observations/anecdotal evidence, the

extent to which water use may change between dry and wet years. In the

absence of any quantitative estimate of the difference in water use between

dry and wet years, it was considered better to keep these parameters

unchanged.



Page 5 of 10

3.6 2015 EA, Appendix 2 - The total water use in the predictive scenarios appears to

be significantly less than the actuals (as per the 2014/15 annual report). The

total use in table 2 in this report is 1,045ML which is significantly lower than the

365ML stated in the predictions.

How were these estimates of water use on site made?

3.6 - Based on information provided by WCCM, the assumptions used for the

predictive scenarios did not foresee the significant reticulation of water for

spontaneous combustion. The area and number of spontaneous combustion

areas that will be encountered was unknown within the former underground

workings and can only be determined at the time the underground workings

are encountered when mining. WCCM could not predict how much water

would be utilised to manage spontaneous combustion.

3.7 2015 EA, Appendix 2 - Does the future scenario predictions include inflow into

the pit from water curtain or is this included elsewhere? In the conceptual

model this is included as a groundwater component, however the groundwater

components in the table are small compared to the volume of water discharged

to the water curtain. Please comment

3.7 - The groundwater component does not include the amount of water

recirculated for spontaneous combustion at any time.

3.8 Annual monitoring report 2014/15 - The WB suggests that all of the pumped

water out (1045ML) is used for dust suppression and through other uses.

- Please clarify where the 358.9ML that was discharged for recirculation comes

and where this appears in the WB summary?

3.8 - The out-of-pit pipeline metered 1045ML pumped out of the open cut

pit for 2014/2015. Of which 358.9ML was metered or estimated to have

been used for spontaneous combustion management of the former

underground workings and hence returns back to the pit as described

previously and is an input in the water balance. The 10% loss during

spontaneous combustion is included as a loss.



Page 6 of 10

3.9 3.9.1 Annual monitoring report 2014/15 - The site conceptual water balance

does not include inflow from recirculation yet this is included in the actual water

balance as a term an input to the void (358.9ML). Please comment

3.9.2 In previous annual monitoring reports the recirculation back to pit term is

included in both input and outputs. In the 2014/15 report it is omitted from the

outputs - exclusion of this element from the output while including as an input

seems to underestimate the output side of the water balance.

Better justification for why this was done is necessary.

3.9.3 - Shouldn’t the recirculation input to void be 90% of 358.9 (using the 10%

loss figure given in the report)?

3.9.4 If the measured value of recirculation is 358.9ML prior to discharge then

the input to the void should presumably be 90% (322ML), given a 10% loss,

Please comment.

3.9.5 The report states “water pumped out of the open cut and recirculated

through the mine workings as a water curtain has not been included in the out of

pit pumping total but has been included as a simple loss from the void”. This is

poorly explained and clarification is required.

3.9.1 - The recirculation is included as an input ‘former underground mine

workings’ and a loss from the ‘water curtain’ in Figure 1.

3.9.2 - The change in the assessment of water being used for spontaneous

combustion management from an output to input was necessitated by the

removal (by mining) of “storage” that was previously available in the former

underground workings. The synclinal geology of WCCM meant that the

former underground workings acted like a basin that the majority of water

reticulated underground could be retained there (i.e. water output from the

WCCM void water system). However as the open cut mining advanced down

dip, the capacity of the former underground workings declined until a point

in time (2014) when mining removed the base of the syncline in the former

underground workings (equivalent to the E seam of the open cut) resulting

in no storage underground and the majority of water reticulated through the

former underground workings now able to freely drain back into the open

cut void (i.e. water input to the WCCM void water system).

3.9.3 - It is considered a more accurate to represent the term as 100%

volume input and 10% lost, as shown in Table 2 of the groundwater

verification report.

3.9.4 - As above.

3.9.5 - Please advise which document this quote has been referenced from

as could not be found in AEMR 2014/15 or Environ June 2015 reports?



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3.10 Annual report 2014/15 annual report. Paragraph 3, page 5

- What is the justification for the corrections to the metered data (i.e. 8% return

from the evaporator, 25% return from the pre strip sprinkler)

3.10 - The justification is from Environ June 2015 report “Initial calibration

suggested that the Evaporator/Sprinklers overestimated the volume of

water taken out of the VWDs. The eventual model used a figure which

reduced the figures for the Evaporator by approximately 8% which appears

to better correlate the modelled VWD volumes and those measured.

Likewise, approximately 25% of the surface sprinkler use is above the

workings and may find its way to the void. The total amounts for surface

sprinklers have therefore been adjusted and entered into the WBM.”

3.11 Annual report 2014/15 annual report. - Table 2 indicates that the recirculation

losses back to pit are 10%. The metered volume for recirculation is 358.9ML yet

the losses are 36.2ML (these numbers do not quite match) – please reconcile?

3.11 - It appears that the 10% has not been calculated accurately however,

the potential discrepancy is very minor (

3.14 Annual report 2014/15 annual report. Losses to curtain – in the 14/15 report

estimate of losses is stated to be 10%. In the 13/14 report, losses are stated to

be 5%. These are quite precise figures and their use in the calculation requires

justification.

-3.14.1 What is the basis of this estimate?

- 3.14.2 What is the mechanism for the losses to change year on year?

3.14.1 - Losses are an estimate and vary from year to year depending on a

number of factors including the method of recirculation of water and the

distance from the working face of the mine that water is recirculated from.

It is expected that losses will occur however these losses cannot be

measured accurately, therefore they are estimated based on observations

made onsite and the water balance reconciliation process.

3.14.2 As per above.

3.15 Annual report 2014/15 annual report - In Table 2 (annual report 2014/15, page

5) in-pit evaporation (34ML) is included in the total figure for water outputs

(1,045Ml.). This figure (1,045ML) matches the recorded outflow from the pit

dewatering flow meter, (obtained by adding the individual figures for pit

dewatering in table 1).

-3.15.1 However, should in-pit evaporation not be a separate term because this

will not be recorded by the flow meter, as it is lost to atmosphere, not by

pumping from the pit?

3.15.1 - Agreed, however this potential discrepancy is only minor (

3.18 Annual report 2014/15 annual report –Verification of the predicted

groundwater interception – it would be useful to review the values used for the

other inputs and outputs for this calibration assessment.

3.18 - Information on the calibration process for the groundwater model is

presented in the Werris Creek Coal Mine, Environmental Assessment

Modification 2, April 2015, Appendix 2.

3.19 Annual report 2014/15 annual report –Verification of the predicted

groundwater interception – The calibration appears to provide a reasonable

match to the VWD measurements but less so to the void pit water levels. In

some months the difference in predicted versus actual appears to be as much as

100ML

- Do you have an idea of what is causing the divergence in these months?

3.19 - The difference in the model and actual pit water levels are due to the

runoff predictions used in the AWBM. The AWBM requires soil to be

saturated before runoff occurs and this results in a runoff lag, particularly in

dry months.

Comments relating to on-site measurements

4.1 The 2014/15 annual report states “It has been estimated by WCCM that the

reporting error for measurements may be as high as +/-10Ml per month”.

- What is the basis for this estimate?

- What is the source of error – flow meter measurements, water storage

estimates in VWD and void?

4.1 - The specific reference to the +/-10ML per month is in relation to the

monthly survey of the in pit void water level and subsequent calculated

volume. The void surface underwater cannot be measured and is estimated

based on the post-mined surface from the previous year’s mining

operations. The source of error is due to changes that are likely to have

occurred to the underwater surface, estimates of void space in the dump

and differences in the calculation of the volume using different software

packages that have various algorithms to calculate surfaces/volumes of non-

uniform geometry.

4.2 The VWD storage volume is measured by survey (14/15 annual report)

– Is this the only way that the volume is measured?

- Are flow meters also used to measure flow in and out of the VWDs?

Comparing the water meters and survey estimates of storage could indicate any

error (or input from surface water, if this is not incorporated into the water

balance) – please comment.

4.2 - Survey of dam water levels is the most accurate method to calculate

void water dam storage. Given that the as constructed surface of each dam

is known, the volume can be confidently calculated. Water meters are not

considered as accurate as survey to calculate void water dam levels due to

day to day changes that occur in water management activities (pumping

directions, relocation of pipelines etc). For the purpose of verifying the

groundwater model (groundwater only acts as an inflow to the void and not

to the VWDs), the key element of the WBM is the rate and volume removed

from the pit and not necessarily how that water is disposed of at the VWDs.



Page 10 of 10

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