Appendix 13 Groundwater Modelling - Bickham Coal 2_Appendices1_16/App… · Appendix 13 –...

Bickham Coal WRA & Draft WMP

Appendix 13 – Groundwater Modelling

March 2009

Appendix 13 Groundwater

Modelling



March 2009

Table of Contents

Page No.

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

1.1 Objectives ............................................................................................ 1

1.2 Methodology ......................................................................................... 2

1.3 Modelling Software ................................................................................ 3

2. CONCEPTUAL MODEL.....................................................................................4

2.1 Hydrology, Geology and Hydrogeology...................................................... 4

2.1.1 Surface Hydrology ................................................................................. 4

2.1.2 Hydrogeological Units ............................................................................ 6

2.2 Groundwater Recharge........................................................................... 8

2.3 Groundwater Discharge .......................................................................... 9

2.3.1 Evapotranspiration ................................................................................ 9

2.3.2 Baseflow ............................................................................................ 10

2.3.3 Dewatering ........................................................................................ 10

2.3.4 Groundwater-Surface Water Interaction.................................................. 10

2.4 Bickham Model Extent, Grid, Layers and Boundary Conditions .................... 11

2.4.1 Model Extent and Grid.......................................................................... 11

2.4.2 Model Boundary Conditions................................................................... 11

2.4.3 Model Layers ...................................................................................... 11

3. MODEL CALIBRATION .................................................................................14

3.1 Steady State Calibration ....................................................................... 14

3.1.1 Discussion of Steady State Calibration Results ......................................... 14

3.1.2 Steady State Baseflow ......................................................................... 17

3.1.3 Comparison with Baseflow Estimated from Blandford Gauge Flow Data ....... 20

3.2 Transient Model Calibration ................................................................... 22

3.2.1 Discussion of Transient Calibration Results.............................................. 24

3.2.2 Scaled Root Mean Square (SRMS) Performance Indicator .......................... 24

3.2.3 Transient Calibration Water Budget........................................................ 25

3.2.4 Model Predicted Baseflows During Bulk Sample Dewatering ....................... 25

3.3 Sensitivity Analysis .............................................................................. 29

3.3.1 Hydraulic Conductivity ......................................................................... 30

3.3.2 Recharge ........................................................................................... 31



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3.3.3 River Bed Conductance ........................................................................ 31

3.3.4 Storage Parameters............................................................................. 33

4. PREDICTIVE MODELLING ............................................................................35

4.1 Simulation of Mining and In-pit Overburden Disposal ................................ 35

4.2 Model Parameter Changes with Time ...................................................... 35

4.3 Simulation of Mine Dewatering .............................................................. 38

4.3.1 Dewatering Approach........................................................................... 38

4.3.2 Predicted Dewatering Rates .................................................................. 38

4.4 Predicted Baseflow Impacts................................................................... 41

4.4.1 Pages River ........................................................................................ 41

4.4.2 Kingdon Ponds.................................................................................... 42

4.5 Predicted Water Level Impacts .............................................................. 45

4.5.1 Mining Period...................................................................................... 45

4.5.2 Post Mining Water Levels...................................................................... 45

4.5.3 Post Mining Pit Void Water Level............................................................ 46

4.6 Water Quality Impacts.......................................................................... 46

4.6.1 Pit Inflow Salinity During Mining Period................................................... 46

4.6.2 Post-Mining In-Pit Salinity .................................................................... 48

4.6.2 Pit Void Salinity................................................................................... 49

4.6.3 Post-Mining Migration of Groundwater from Pit ........................................ 50

4.6.4 Salinity of Drainage From Out-of-Pit Overburden Dump ............................ 51

4.7 Bickham Model Mass Balance Evaluation ................................................. 51

4.9 Uncertainty Analysis ............................................................................ 61

4.10 Impact of Old Mine Workings................................................................. 64

4.11 High Conductivity Zone between Mine and Long Pool on Pages River ........... 68

5. MODEL LIMITATIONS..................................................................................70

6. INDEPENDENT REVIEW...............................................................................72

7. REFERENCES ...............................................................................................73

List of Tables

Table 2-1 Long-term Average Monthly Rainfall at Murrulla (BoM Station No. 061079) .......... 8

Table 2-2 Mean Monthly Evaporation Data at Scone (BoM Station No. 61089)..................... 9

Table 2-3 Summary of Model Layers and Geometry ...................................................... 12



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Table 3-1 Steady State Calibration Performance ........................................................... 15

Table 3-2 Steady State Calibration Data ...................................................................... 15

Table 3-3 Groundwater Budget for Bickham Model Steady State Calibration ..................... 16

Table 3-4 Pages River Baseflow - Steady State Calibration ............................................. 17

Table 3-5 Kingdon Ponds Baseflow - Steady State Calibration......................................... 17

Table 3-6 Calibrated Bickham Model Aquifer Parameters................................................ 23

Table 3-7 Transient Calibration Performance ................................................................ 24

Table 3-8 Bickham Model Global Water Budget at the End of the Transient Calibration Period

............................................................................................................................. 25

Table 3-9 Parameters, Zones and the Multipliers Tested in the Sensitivity Analysis Process. 30

Table 3-10 Sensitivity Analysis of Horizontal and Vertical Hydraulic Conductivity Values in the

Bickham Model ........................................................................................................ 32

Table 3-11 Sensitivity Analysis of Recharge, River Bed Conductance, Storage Coefficient and

Specific Yield Values in the Bickham Model .................................................................. 33

Table 3-12 Sensitivity Analysis of River Bed Conductance on Pages River and Kingdon Ponds

Baseflows in the Bickham Model................................................................................. 34

Table 4-1 Base Case Predictive Model Run Predicted Annual Dewatering Rates by Model Layer

............................................................................................................................. 40

Table 4-2 Average Salinity Based on Annual Groundwater Storage Changes for Each Model

Layer (kL/d)............................................................................................................ 47

Table 4-3 Average Salinity Based on Weighted Average Annual Pit Inflows from Each Model

Layer (kL/d) 48

Table 4-4 Bickham Model Range of Uncertainty Predictions in Terms of Predicted Inflow Rates

............................................................................................................................. 62

Table 4-5 River Baseflow Reduction - Potential Impact of the Old Mine Workings............... 67

List of Figures

Figure 2.1 Extent of Model .......................................................................................... 5

Figure 2.2 Conceptual Model – Key Features and Processes.............................................. 5

Figure 2.3 Groundwater Investigations – Piezometers/Exploration Bores and Test Bore

Locations ................................................................................................ 7

Figure 2.4 East-West Model Cross-Section ................................................................... 13

Figure 2.5 North-South Model Cross-section................................................................. 13



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Figure 3.1 Scatter Plot for Bickham Steady State Calibration .......................................... 18

Figure 3.2 Reach Location Map for the Pages River ....................................................... 19

Figure 3.3 Reach Location Map for Kingdon Ponds......................................................... 19

Figure 3.4 Measured and Model-Predicted River Baseflow at Blandford............................. 21

Figure 3.5 Model-Predicted River Baseflow Upstream and Downstream of Blandford........... 21

Figure 3.6 Scatter Plot for Bickham Transient Calibration (Bulk Sample Dewatering) .......... 26

Figure 3.7 Pages River Baseflow Hydrographs During Transient Calibration Modelling......... 28

Figure 3.8 Model Predicted River Baseflow Change Due to Pumping from DW1 and DW2 .... 28

Figure 3.9 Kingdon Ponds Baseflow Hydrographs During Transient Calibration .................. 29

Figure 4.1Mine Plan and Dewatering Bore Locations ...................................................... 37

Figure 4.2 Base Case Predictive Model Run – Predicted Bickham Mine Dewatering Rates..... 37

Figure 4.3 Pages River – Predicted Baseflow and Baseflow Reduction............................... 43

Figure 4.4 Kingdon Ponds - Predicted Baseflow and Baseflow Reduction ........................... 44

Figure 4.5 Predicted Water Level Drawdowns – Model Layer 1 (End of Year 25)................. 52



Figure 4.8 Predicted Water Level Drawdowns – Model Layer 1 (End of Year 125)............... 55

Figure 4.9 Predicted Water Level Drawdowns – Model Layer 2 (End of Year 125)............... 56

Figure 4.10 Predicted Water Level Drawdowns – Model Layer 6 (End of Year 125) ............. 57

Figure 4.11 Predicted Pit Void Water Level During Recovery Simulation............................ 58

Figure 4.12 Predicted In-Pit Salinity............................................................................ 58

Figure 4.13 Particle Tracking Plot for the Western Side of the Pit..................................... 59

Figure 4.14 Particle Tracking Plot for the Eastern Side of the Pit...................................... 59

Figure 4.15 Particle Tracking Plot for the Out-of-Pit Overburden Dump ............................ 60

Figure 4.16 Cumulative Mass Balance Discrepancy Plot.................................................. 60

Figure 4.17 Predicted Pages River Baseflow and Mine Dewatering Rates (Uncertainty Analysis)

........................................................................................................... 63

Figure 4.18 Assumed Extents of Old Mine Workings for Uncertainty Analysis..................... 65

Figure 4.19 Pages River Predicted Baseflow and Pit Inflow – Impact of Old Mine Working

(Uncertainty Analysis) ............................................................................ 66

Figure 4.20 Assumed High Hydraulic Conductivity Zone for G Seam ................................ 69



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Figure 4.21 Predicted Baseflow Reduction During High Hydraulic Conductivity Scenario

(comparison to Base Case)...................................................................... 69

List of AnnexuresAnnexure A Bickham Model Boundary Conditions, Layer Elevations and Residual Head Map

Annexure B Bickham Model Steady State Calibration

Annexure C Bickham Model Calibrated Parameters

Annexure D Bickham Model Transient Calibration

Annexure E Bickham Model Recovery Run Results

Annexure F Bickham Out-of-Pit Overburden Dump Drainage Modelling

Annexure G Independent Expert Review Report



Page 1 March 2009

1. INTRODUCTION

The Bickham Coal Mine Project is a proposed open cut mining operation located between

Blandford and Wingen in the upper Hunter Valley of NSW. The Bickham Coal Company

engaged Aquaterra to undertake hydrogeological investigations to support the preparation of

a Water Resource Assessment and draft life-of-mine Water Management Plan, including water

management relating to mine closure and post-mining. As part of these investigations,

Aquaterra has developed a numerical groundwater flow model of the area.

This report details the development and calibration of the Bickham Coal groundwater model

(Bickham Model) and the subsequent predictive modelling of mine dewatering operations and

post-mining recovery.

Hydrogeological investigations were undertaken to consider potential groundwater-related

impacts on the hard rock aquifers around the proposed mine, potential impacts on upstream

and downstream alluvial aquifers, interactions with the Pages River and Kingdon Ponds

systems, and potential impacts downstream or down-gradient from the study area, that may

arise due to the mining and closure operations, associated water supply, dewatering and

other water management activities.

The hydrogeological investigations (including modelling) have been undertaken with

reference to the ‘Guidelines for Management of Stream/Aquifer Systems in Coal Mining

Developments – Hunter Region’ (DIPNR, April 2005), and the groundwater modelling has

been carried out in accordance with the best practice guidelines on groundwater flow

modelling (MDBC, 2001). The Department of Planning’s report Coal Mining Potential in the

Upper Hunter Valley - Strategic Assessment (DOP, 2005) has also influenced the

methodologies applied to these investigations.

The Bickham Model has been subject to independent expert review at all stages, from initial

conceptual design through to post-mining prediction modelling, by Dr Noel Merrick.

1.1 Objectives

The broad objectives of the modelling carried out with the Bickham groundwater flow model

(referred to as the “Bickham Model”) were:

To assist in the overall hydrogeological assessment, and the design of the dewatering

and water supply systems to support the proposed coal mining operation;

To examine connectivity between the hard rock Permian coal measures aquifer

system and the Pages River and its associated alluvium in the vicinity of the proposed

mine; and,

To predict potential impacts of the proposed mining operation on the groundwater and

surface water resources.

Specific outcomes from the modelling were:

Determination of mine dewatering rates required for the mining operation;

Assessment of groundwater responses to dewatering / water supply abstractions;



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Quantification of the degree of connectivity between the Permian coal measures

aquifer system and the Pages River and its associated alluvium, and its role in

contributing to streamflow to downstream areas;

Determination that the mining operation would not result in any water from either

Pages River or any protected alluvial aquifer flowing into the mine;

Provision of water balance information for others to examine ways of minimising the

generation of surplus mine wastewater through limiting dewatering flows and

maximising use or re-use of mine water, and to assess options for the mine to

achieve a “nil discharge” status;

Demonstration that mitigation measures and contingency plans are capable of

adequately addressing any risks to flow or water quality in Pages River (and Kingdon

Ponds) as a result of mining; and

Assessment of post-mining recovery for up to 100 years including evaluation of the

potential final void configuration and its impact on the rate of groundwater recovery,

assessment of post-mining management and mitigation options for any residual water

resources impacts.

1.2 Methodology

The groundwater modelling guideline (MDBC, 2001) specifies a staged approach, beginning

with a review of the available data to devise a conceptual hydrogeological model, which is

then used as the basis to design a numerical groundwater flow model. In accordance with

the MDBC guidelines, the Bickham Model development methodology involved the following

tasks and outcomes:

The hydrogeological conceptualisation of the aquifer system and surface-groundwater

interaction processes (natural and developed) was defined and implemented in a

numerical groundwater flow model. A model design report (Aquaterra, 2006) was

prepared, and was independently reviewed by Dr Noel Merrick.

The model was calibrated to ensure that it reproduced measured aquifer water levels

at a range of monitoring locations, and over time under a range of climatic conditions

and pumping stress. Initial model calibration was undertaken in steady state (“long

term average”) mode, to establish a match to interpreted average groundwater

conditions. The steady state calibration formed the initial conditions for a subsequent

transient model calibration (“history match”) run covering a five year period that

included a period of 6 month bulk sample dewatering and a range of climatic

conditions. The calibration involved spatial and temporal water level calibration, as

well as calibration against Pages River baseflow.

Calibration/validation performance criteria were addressed in terms of quantitative

(statistical) and qualitative (pattern-matching) measures. The model design report

(Aquaterra, 2006) proposed a scaled RMS (SRMS) criterion of 5% to 10%, which is

consistent with the MDBC guidelines for a first generation version of a model suitable

for impact assessment.

Scenario modelling was undertaken using the calibrated model to predict the

behaviour of the aquifer system in response to the proposed mining operation, and to

help assess and optimise water management and planning strategies, both during

mining and post-mining.



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The model was used to guide decision-making by demonstrating and quantifying

uncertainties through sensitivity analysis.

The model was used to identify if there are any data deficiencies that might critically

constrain the use of the model as a management tool, and to make recommendations

on how any such deficiencies can be addressed.

The following sections of this report provide details on the:

Key features of the conceptual hydrogeological model, and design of the numerical

model consistent with the conceptual model, including details on the model extent,

grid, layers and boundary conditions.

Model calibration, including calibration data, calibration approach, model performance

and sensitivity analysis.

Prediction scenarios, including post-mining recovery, and uncertainty model runs.

Limitations of the modelling.

Independent expert review.

1.3 Modelling Software

A 3-Dimensional finite difference model has been used, based on the MODLFOW code

(McDonald and Harbaugh, 1988) in conjunction with the MODFLOW-SURFACT (Version 3)

code to allow for both saturated and unsaturated flow conditions. The modelling has been

undertaken using the Groundwater Vistas (Version 5.16) software package (ESI, 2006).



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2. CONCEPTUAL MODEL

The conceptual model is a simplified representation of the real system, incorporating the

most important geological units and hydrogeological processes, while acknowledging that the

real system may be hydrologically and geologically much more complex. The conceptual

model forms the basis for the computational groundwater flow model.

The extent of the model in relation to the proposed mining operation is shown in Figure 2.1.

The key features and hydrological processes of the conceptual model are graphically

illustrated on Figure 2.2 and are described further below.

2.1 Hydrology, Geology and Hydrogeology

The hydrology, geology and hydrogeology of the Bickham Project area has been described in

detail in Sections B4.1, B4.2 and B4.3 of the Water Resource Assessment report respectively.

Background geological and hydrogeological information can also be found in a number of

reports by Peter Dundon and Associates (2003, 2005a, b and c), which were used to design

the conceptual hydrogeological model for the area.

2.1.1 Surface Hydrology

Surface drainage in the Bickham Project area drains mainly to the east and south via the

Pages River, with a smaller portion draining west and south to a small headwater sub-

catchment of the upper part of Kingdon Ponds.

The Bickham Model incorporates less than 50% of the total Pages River catchment above the

Department of Water and Energy’s Blandford gauge, which is located upstream from

Bickham. The main catchment areas not included in the Bickham Model are the upper Pages

River above Blandford, and Warlands Creek which joins the Pages River just above Blandford

township. The upper reaches of Scotts Creek and Splitters/Sandy Creek are also not

included, but these streams join the Pages River from the east just downstream from the

Blandford gauge.

Extensive alluvial/floodplain deposits are associated with the upper Pages River, extending

from approximately Murrurundi to downstream of the confluence with Splitters Creek, ending

about 2 km upstream from the Bickham Project. Thereafter, and including the immediate

Bickham Project area, the Pages River flows within a gorge setting incised into the Permian

rocks, with only minor isolated and disconnected alluvium occurrences, until the downstream

end of Camerons Gorge about 15 km downstream of the Bickham Project. There are no

significant tributary inflows between Splitters Creek (3 km upstream of Bickham) and Box

Tree Creek (6 km downstream from Bickham).

The Pages River flows southwards from Camerons Gorge for approximately 10km before

being joined by the Isis River above Gundy, and then 15 km further south joining the Hunter

River near Aberdeen. Substantial alluvial deposits occur within the lower Pages River valley.

The Pages and Isis Rivers are major tributaries of the Hunter River.

The Kingdon Ponds is a minor headwaters tributary with an intermittent flow regime, flowing

southwards from the west side of the Bickham Project area to join Dart Brook, itself a

significant tributary of the Hunter River.

CONCEPTUAL MODEL-KEY FEATURES AND PROCESSES FIGURE 2.2

BICKHAM COAL MINE LOCATION AND MODEL EXTENT FIGURE 2.1



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2.1.2 Hydrogeological Units

For the purposes of modelling, the Permian (hard rock) formations have been sub-divided

into a number of separate hydrogeological units on the basis of their hydraulic properties,

stratigraphic relationship to the proposed mining operation, and regional context.

The adopted hard rock hydrogeological units are:

Permian Murrulla Beds (Upper Coal Measures) and Bickham Formation (marine

sequence).

E Seam overburden (sediments from the top of the Koogah Formation down to the top

of the E Seam). This unit contains the thin A, B, C and D coal seams, which are

relatively minor in thickness and hydraulic importance in this study.

E Seam of Koogah Formation.

E to G Seam interburden (sediments of the Koogah Formation between the two main

coal seams). This unit includes the thin F seam.

G Seam of Koogah Formation.

Basal Koogah Formation (sediments between the base of the G Seam and the base of

the Koogah Formation). Also known as the G Bottoms.

Werrie Basalt.

The role of the surficial unconsolidated units, comprising the regolith, or weathered near-

surface overburden material and alluvium where present, as the primary medium for rainfall

recharge to the underlying less weathered hard rocks, has also been recognised. The surficial

material has been divided into two distinct hydrogeologic units, viz:

Alluvium present as a minor feature in some drainages, and on the floodplain flanking

Pages River upstream from Bickham.

Regolith (incorporating weathered material overlying unweathered hard rock, local

stream-bank alluvium proximal to Pages River (where present), and colluvium).

Minor local occurrences of igneous intrusives have not been recognised as separate

hydrogeological units in the model, but instead have been incorporated within the unit into

which they have intruded. Although the intrusives can be quite permeable, their limited

lateral extent means that they will not be regionally important in relation to potential mine

impacts.

Aquifer hydraulic properties have been derived from the results of hydraulic testing combined

with model calibration. Initial values were determined from the results of hydraulic testing,

and were adjusted through the calibration process. The calibrated hydraulic properties have

subsequently been applied for predictive scenario modelling of the effects of dewatering, for

the proposed mine plan. The locations of all groundwater monitoring bores installed for

monitoring and hydraulic testing are shown in Figure 2.3.

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Page 8 March 2009

2.2 Groundwater Recharge

Rainfall infiltration is the primary groundwater recharge process and is a function of rainfall

intensity, evaporation, vegetation coverage and density, topography and soil properties of

the land surface. The coal seams are recharged primarily through downward percolation of

rainfall through the overlying regolith layer in areas of coal seam subcrop, with groundwater

then flowing along the bedding within the more permeable coal seams. After reaching the

water table, flow is predominantly down-gradient along the more permeable horizons, while

only a very small component of downward flow occurs across the bedding through

interburden strata to deeper coal seam aquifers.

The hydrogeological investigations, monitoring and analysis (described in Part B of the WRA)

have shown that groundwater levels respond to significant local rainfall events when

precipitation is high enough to cause infiltrating rainfall to reach the water table. Stream

levels also rise when runoff is sufficient to increase flows in the streams, usually in a more

immediate response than groundwater responds to rainfall. The data also shows that stream

flow can respond to rainfall anywhere in the upstream catchment (ie anywhere upstream of

Bickham), whereas groundwater levels under the Bickham Project area can only respond to

rainfall in the Bickham area, which may be either localised or part of a regional-scale event.

Localised rainfall in other parts of the catchment will have no recharge effect at Bickham, but

may cause river levels to rise. Further, rainfall in the Bickham area may be sufficient to show

a water table response, but not necessarily a stream flow response, if there has been only

limited rain in the upstream parts of the catchment.

The hydrogeological response to specific recharge events and climate seasonality are

sufficiently attenuated that it is not deemed necessary to incorporate seasonality and episodic

recharge events in the Bickham Model when used for long term predictions. The model

assumes rainfall recharge at a constant average rate. This simplifying assumption is

consistent with the groundwater flow modelling guideline (MDBC 2001), and with approaches

typically applied to coal mine projects in the Hunter Valley.

The nearest Bureau of Meteorology (BoM) station to the Bickham project area is Murrulla

(Station No. 061079). Rainfall has been recorded at Murrulla since 1877, providing a

continuous record of almost 130 years of daily rainfall data. The maximum recorded annual

rainfall was 1,295 mm in 1950, and the minimum was 313 mm in 1888. Long-term average

monthly rainfall totals are shown in Table 2.1.

Table 2-1 Long-term Average Monthly Rainfall at Murrulla (BoM Station No.

061079)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year

AverageMonthly

Rainfall (mm)83 77 63 48 46 53 50 48 50 61 65 76 724

The percentage of rainfall that recharges to the water table varies depending on the nature of

surficial outcrop and topography, as well as the intensity of rainfall occurrence. For the

steady-state Bickham Model, recharge rate has been modelled by applying spatially-variable

percentages of average rainfall as recharge rates to specified zones, ie a constant rate in

each zone.



Page 9 March 2009

The Bickham Model has been divided into 5 zones, with recharge rates generally ranging from

1.33% to 3%, but with one small zone of 7% recharge atop the catchment boundary between

Pages River and Kingdon Ponds and including part of the mine area, in an region bounded

between two mapped (low permeability) faults. Recharge was applied to the highest active

layer in the Bickham Model.

These recharge percentages were carried forward to the transient calibration model, but were

applied in each zone to the actual daily rainfalls recorded at the Murrulla gauge during the 5-

year calibration period (2001 to 2006). For the forward predictions of mine dewatering,

constant recharge rates have again been used in each zone, by applying the same zone

percentages to the average rainfall rate.

The recharge zones for the calibrated model are presented in Annexure C.

2.3 Groundwater Discharge

Natural groundwater discharge occurs through evapotranspiration, seepage and spring flow

where the water table intersects the land surface, and through baseflow contributions to

creeks and rivers, including discharge to the alluvium where it occurs in areas upstream from

Bickham. Dewatering abstractions for the proposed Bickham mining operation will comprise

a new temporary discharge process.

2.3.1 Evapotranspiration

The nearest Bureau of Meteorology (BoM) station to the Bickham project area for which

evaporation data are available is Scone (BoM Station No. 61089). Average Class A pan

evaporation data for the site are available since 1965. Comparison of mean monthly rainfall

and evaporation data (Table 2.1 and Table 2.2) shows that on average, evaporation

exceeds rainfall throughout the year, except for June and July, when rainfall and evaporation

averages are virtually equal.

Table 2-2 Mean Monthly Evaporation Data at Scone (BoM Station No. 61089)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year

MeanMonthly

Evaporation(mm)

214 174 154 107 72 50 59 86 116 159 180 219 1,591

An evapotranspiration (“ET”) feature is applied in the model across the entire model area, but

this process operates in the model only in areas where the water table is shallow, through

use of the extinction depth in the ET feature, but was also used during recovery period

modelling to represent evaporation from water filled pit voids. The evaporation feature acts

as a surrogate for spring and/or baseflow discharge, where shallow water tables occur and is,

therefore, typically active in low-lying areas along creeks and stream alignments.

The ET parameter values adopted in the Bickham Model assume an average rate of

650 mm/yr (about 1.8 mm/day) and an extinction depth of 3 metres below the specified

topographical surface. The value of 650 mm/yr was selected from maps of the average

annual “areal actual” evapotranspiration (i.e. the evapotranspiration that takes place from a

large area where the available water is not unlimited) in the Climatic Atlas of Australia



Page 10 March 2009

(Bureau of Meteorology, 2001). The average annual “areal actual” evapotranspiration value

from the Climatic Atlas is about 41% of the mean pan evaporation for the area.

2.3.2 Baseflow

Baseflow contribution to river and stream features represents one of the primary natural

groundwater discharge processes, the other main discharge process applicable to this area

being evapotranspiration. The creeks in the area are considered to be generally “gaining”, i.e.

they generally receive baseflow discharges from the groundwater system. Ephemeral creek

characteristics are apparent where the baseflow is insufficient to maintain permanent creek

flow.

In areas where the groundwater levels may be lower than the creek system (not around the

Bickham Project area, but in some areas well upstream and well downstream), the creeks

may be “losing” streams, i.e. they may lose water by seepage to adjacent or underlying

aquifers. It is possible for larger river/creek systems to provide some recharge to the aquifer

system at least periodically, when river and creek levels may be temporarily higher than

groundwater levels following heavy rainfall events.

The Bickham Model is designed to allow both processes (i.e. baseflow discharge and

groundwater recharge) to occur.

2.3.3 Dewatering

Dewatering has been represented as a drainage feature in the Bickham Model, using the

MODFLOW Drain package.

Mining has been simulated as a progressive advancement of active open cut areas, and

subsequent progressive backfilling of mined-out areas with overburden. The mining

simulation has been divided into a series of sequential transient model runs or “time-slices”,

each time slice representing one year of the 25 year mine life. The active open cut has been

represented in the Bickham Model using drain cells within the mined coal seams (Layers 1 to

6) and assuming a relatively high conductance value. The modelled drain elevations were set

to 1m below the base of Layers 1 to 5, and 0.5m above the base of the G Seam layer

(Layer 6) to ensure model numerical stability. These drain cells have been assigned

progressively to active mining areas in accordance with the proposed mine plan.

The drain cells were progressively de-activated from mined out cells as waste rock was

placed into the pit, in accordance with the proposed waste backfilling plan.

2.3.4 Groundwater-Surface Water Interaction

As dewatering may result in a lowering of groundwater levels near the streams, the Bickham

Model was set up with stream-aquifer interaction features to represent existing surface and

groundwater interactions, and to predict the amount of any reduced baseflow to streams

and/or induced leakage from the Pages River, Kingdon Ponds and their tributary streams.

Monitoring during higher rainfall events (for example, early June 2007 and mid-August 2007)

has shown that groundwater levels remain above stream levels even in times of moderately

high river flow. It should be noted that the minor streams in the study area are mainly

ephemeral because baseflow support is relatively short, and extensive periods of no flow

occur naturally. For example, Kingdon Ponds does not support visible surface flow

permanently in the headwaters area near Bickham. However, Pages River flows virtually



Page 11 March 2009

permanently, supported mainly by flow from the upstream catchment, including upstream

groundwater baseflow.

2.4 Bickham Model Extent, Grid, Layers and Boundary Conditions

2.4.1 Model Extent and Grid

The Bickham Model covers an area of approximately 18 km x 15 km as shown in Figure 2.1.

The Bickham Model was designed using Groundwater Vistas and MODFLOW-SURFACT

software, with a variable grid size ranging from 20 m x 20 m in the central area around the

proposed mine and increasing gradually up to 200 m x 200 m near the regional boundaries.

This gave a grid mesh of 383 rows and 360 columns, i.e. 137,880 cells per layer, or a total of

1,103,040 cells for the full 8-layer model. The fine grid (20m x 20m) was selected for the

mine area to permit accurate modelling of stream-aquifer interaction processes, and also to

allow better resolution of the dipping layer geometry and the areas of potentially steep

curvature in the water table around the proposed mine dewatering operations.

2.4.2 Model Boundary Conditions

Model boundaries are mostly set at least 3km from the proposed mine site, generally

coinciding with topographic divides, which have been assumed to be no flow boundaries. The

north-westerly dipping Bickham Formation and Koogah Formation coal measures pinch out at

outcrop along the axis of the proposed mine, and areas east and south-east of the mine are

occupied by the low permeability basal aquitard Werrie Basalt. Given the very low

permeability conditions in this southeastern area, it was considered appropriate to set the

southern model boundary at about 2 km from Bickham in that region. It was expected that

any predicted drawdown in this area would be minor.

The outflow areas of the Pages River and Kingdon Ponds at the southern model boundary and

the inflow of the Pages River at the northern model boundary have been defined as general

head (head-dependent flow) boundaries. The Pages River and the Kingdon Ponds tributaries

are represented using the River package of MODFLOW, with river stage elevations set equal

to topography, and river bed level set to 0.2m below the stage in the main rivers and at the

same level as the stage in the tributary streams. With this arrangement, the minor tributary

streams, which are ephemeral, act only as baseflow-fed groundwater discharge features in

the model, not potential recharge features; whereas the main rivers can act as either

groundwater discharge or recharge features, depending upon whether the simulated

groundwater level is above or below the specified stage level. The riverbed conductance

parameter ranged between 0.1 m2/day and 50 m2/day; sensitivity runs were undertaken on

this parameter.

2.4.3 Model Layers

The conceptual hydrogeological model has been represented numerically by 8 layers in the

Bickham Model, with the main coal seams and interburden represented separately. The top

elevation of Layer 1 was set equal to the surface topographic elevations derived from the

surface topography DEM. The coal seam top and base elevations in the immediate Bickham

Project area were derived from the Bickham geological model (MEGS, 2006) and extended

regionally using information from published geological maps (Beckett, 1988).

The layer thicknesses in the Bickham model vary from 15m in Layer 1 up to 400 m in the

Bickham Formation (Layer 2). The E Seam (Layer 4) and G Seam (Layer 6) have thicknesses



Page 12 March 2009

of 10 m and 12 m respectively. The thicknesses of the interburden layers (Layers 3 and 5)

are about 45 m and 35 m respectively. The basal Layer 8 (Werrie Basalt) has been assigned

a uniform 100 m thickness. Bickham model layering and typical layer thickness are

summarised in Table 2.3. Figures 2.4 and 2.5 are cross-sections from the Bickham Model

through the proposed mine area, showing the above layering methodology.

Layers 1 to 7 were defined in the Bickham Model as semi-confined aquifers with variable

transmissivity (Type 3), and Layer 8 as confined (Type 0). The Bickham Model has been

simulated by implementing variably-saturated flow with the pseudo soil function in the

MODFLOW-SURFACT BCF4 package.

Layer Elevation maps, showing adopted boundary conditions are presented in Annexure A.

Table 2-3 Summary of Model Layers and Geometry

Layer Description ExtentTypical thickness

(m)

1Weathered regolith and alluvialdeposits.

Typical thickness 15 m, belowsurface topography from DEM.

2Bickham Formation (plus higherunits – Upper Coal Measures,Narrabeen Group, etc).

Pinches out at Bickham; up to400 m thick down-dip.

3

E Seam overburden (coalmeasures above top of E Seam,including minor A to D coalseams).

Around 45 m.

4 E Seam. Around 10 m.

5Interburden from bottom of ESeam to top of G Seam (includesminor F seam).

Around 35 m.

6G Seam (considered the mostproductive “aquifer” in Bickhamarea).

Layers 1 to 6 are active only in thenorth and west. The regolith isdraped over the underlying units,and so, as these deeper unitsprogress towards outcrop in thesouth and west (ie. up-dip), theshallow layers are gradually de-activated, and the regolithtransitions through layers 2 to 7,along with the alluvium where itoccurs.

Around 12 m.

Basal Koogah Formation.Koogah Formation below the GSeam in the north and west (alsoknown as “G Bottoms”).

Basal Koogah is around 35 mthick.

7

Weathered regolith in areaswhere coal measures absent.

Weathered regolith occurs abovethe Werrie Basalt in the south andeast, where the coal measureshave been eroded away.

Regolith is assumed 10 m thickin south and east.

8 Werrie Basalt.Extends across entire model as thebasal layer, and is represented withuniform transmissivity.

Assumed constant 100 mthickness.

EAST-WEST MODEL

NORTH-SOUT

FIGURE 2.5

W

N

fault

CROSS-SECTION IN THE VICINITY OF THE BICKHAM MINE AREA FIGURE 2.4

H MODEL CROSS-SECTION IN THE VICINITY OF THE BICKHAM MINE AREA

Bickham Mine area PagesRiver

fault

E

SBickham Minearea

Regolith

Alluvium

Bickham Formation + Muralla Beds

E overburden

E and G Coal Seams

E to G seam Interburden

Basal Koogah Formation

Werrie Basalt

Regolith

Alluvium

Bickham Formation + Muralla Beds

E overburden

E and G Coal Seams

E to G seam Interburden

Basal Koogah Formation

Werrie Basalt



Page 14 March 2009

3. MODEL CALIBRATION

Calibration is the process by which the independent variables (parameters and boundary

conditions) of a model are adjusted, within realistic limits, to produce the best match

between simulated and measured data. The Bickham Model has been calibrated through

both steady state and transient calibration simulations.

Maps of model parameters derived from the calibration are presented in Annexure C.

3.1 Steady State Calibration

The Bickham Model was set up and initially run in steady state mode, to represent long term

average aquifer conditions. The objective was to derive a comprehensive simulation of pre-

mining steady-state conditions, and to derive a set of aquifer heads from the model that

equate to the interpreted long-term average groundwater levels, based on hydrographs of

water levels, which have been monitored approximately monthly in a network of bores in the

Bickham Project area, from mid 2002 up to the present time. The monitoring network

includes bores completed to various depths in all of the main hydrogeological units.

The steady state calibration was achieved with sequential model runs by manually adjusting

the horizontal and vertical hydraulic conductivity and recharge values until the best fit

between the simulated water levels and interpreted long-term average water levels was

obtained.

3.1.1 Discussion of Steady State Calibration Results

A very good steady state model calibration was obtained, demonstrated in quantitative and

qualitative terms by the following measures:

Scatter plots of modelled versus measured heads show a good agreement between

the observed and computed heads across all model layers, with a scaled root mean

square (SRMS) error of 6.2% (within the target range of 5-10%), and coefficient of

determination of 1.3 (Table 3.1 and Figure 3.1). A comparison between observed

and modelled heads at each of the 43 target bores is presented in Table 3.2. Bores

screened across more than one aquifer are listed separately for each model layer in

the table.

A very small water balance residual of 0.018% was obtained (Table 3.3).

Contour plans of modelled heads for each layer (Annexure B) are consistent with the

observed contour pattern shown in Figure B4.8 and Figure B4.9 (in Part B of the

WRA).

The scaled RMS (SRMS) value (Table 3.1) is the RMS value divided by the range of heads

across the site, and forms the main quantitative performance indicator. This approach is

consistent with the groundwater modelling guideline (MDBC, 2001).



Page 15 March 2009

Table 3-1 Steady State Calibration Performance

Calibration Parameters Value

Count n 49

Sum of Residuals R 69 m

Sum of Absolute Residuals SR 211 m

Scaled Mean Sum of Residuals SMSR 1.49 %

Root Mean Square RMS 5.86 m

Scaled RMS SRMS 6.23 %

Root Mean Fraction Square RMFS 1.39 %

Scaled RMFS SRMFS 6.00 %

Coefficient of Determination CD 1.28

Table 3-2 Steady State Calibration Data

Bore Easting NorthingObserved Head

(mAHD)

Simulated Head

(mAHD)

Head Difference

(m)Layer

DW1 305841.42 6475797.74 376.30 380.94 -4.64 5

DW1 305841.42 6475797.74 376.30 379.79 -3.49 6

DW2 305707.59 6475752.73 387.60 385.20 2.40 5

DW2 305707.59 6475752.73 387.60 384.71 2.89 6

OH38 304298.19 6474489.54 448.10 444.42 3.68 6

OH56B 304880.97 6474790.18 437.90 434.19 3.71 5

OH57 305689.44 6475741.95 387.50 385.65 1.85 5

OH65 305856.44 6475787.31 376.60 380.07 -3.47 6

OH69A 306012.47 6476090.85 375.20 376.17 -0.97 5

OH69A 306012.47 6476090.85 375.20 376.83 -1.63 6

OH69B 306013.57 6476091.95 375.20 376.14 -0.94 5

OH70A 305450.77 6476215.61 383.10 384.84 -1.74 6

OH70B 305452.88 6476211.28 383.70 384.72 -1.02 4

OH70C 305455.18 6476207.07 381.40 379.08 2.32 2

OH71A 305013.29 6475254.3 430.70 425.77 4.93 6

OH71B 305014.74 6475258.85 446.00 429.41 16.59 3

OH71C 305016.54 6475264.28 433.30 426.94 6.36 4

OH75A 306002.67 6475861.7 372.80 373.97 -1.17 6

OH75B 306000.28 6475860.4 372.30 375.37 -3.07 7

OH77 303035.22 6474542.98 448.60 434.43 14.17 3

OH78 306038.99 6475964.46 372.70 374.26 -1.56 6

OH79 306070.62 6476043.31 374.30 375.34 -1.04 6

DDH85B 305758.07 6475751.71 387.60 384.28 3.32 5

DDH85B 305758.07 6475751.71 387.60 384.00 3.60 6

OH87 304993.46 6475146.7 445.00 434.80 10.20 2

OH87 304993.46 6475146.7 445.00 431.98 13.02 3

OH88 304954.83 6475166.79 438.00 435.99 2.01 2

OH88 304954.83 6475166.79 438.00 432.55 5.45 3

OH90 305003.96 6475361.21 437.40 429.32 8.08 2

OH91 304939.46 6475161.8 439.20 436.28 2.92 2

OH92 305789.91 6476119.11 377.10 379.36 -2.26 6

OH93 305789.02 6476114.91 377.40 381.02 -3.62 3

OH94 304553.96 6476624.68 387.60 397.03 -9.43 2

OH95 306037.31 6475756.85 372.90 376.43 -3.53 7

OH97 303966.17 6475206.46 435.50 437.51 -2.01 2



Page 16 March 2009

Bore Easting NorthingObserved Head

(mAHD)

Simulated Head

(mAHD)

Head Difference

(m)Layer

DDH99 304285.28 6475361.2 435.50 431.11 4.39 3

OH100 303190.78 6474631.2 448.50 448.45 0.05 2

OH102 303629.72 6474708.33 451.70 452.01 -0.31 2

OH105 302511.64 6474381.69 426.30 425.01 1.29 2

OH106 302719.91 6474218.03 427.00 428.06 -1.06 6

OH108 302757.3 6474110.73 427.20 430.04 -2.84 3

OH110 303065.7 6474436.29 448.30 435.30 13.00 3

OH111A 305998.7 6475305.12 374.20 375.03 -0.83 8

OH111B 305995.89 6475298.09 372.00 375.19 -3.19 8

OH112 302586.57 6474238.55 427.80 426.76 1.04 2

OH113A 300039.52 6474507.26 357.66 369.90 -12.24 2

OH113B 300039.52 6474507.26 365.07 369.90 -4.83 2

OH114 300760.54 6476807.61 441.82 431.46 10.36 2

OH115 302322.7 6475934.7 429.43 427.37 2.06 2

Average 406.19 404.78 1.40 -

Minimum 357.66 369.90 -12.24 -

Maximum 451.70 452.01 16.59 -

Range 94.04 82.11 - -

The overall steady state water balance across the entire Bickham Model is summarised in

Table 3.3. The total inflow to the aquifer system is 7.49 ML/d, comprising rainfall recharge

(91.4%), leakage from the river into the aquifer (3.9%) and model boundary inflow (4.7%).

The total groundwater outflow across the Bickham Model (7.49 ML/d) comprises

evapotranspiration (54.5%), Pages River baseflow (35.2%), Kingdon Ponds baseflow (2.4%),

and model boundary outflow (7.9%). The discrepancy between total inflow and total outflow

for the steady state simulation period was 0.018%.

Table 3-3 Groundwater Budget for Bickham Model Steady State Calibration

ComponentGroundwater Inflow

(ML/d)Groundwater Outflow

(ML/d)

Recharge 6.85 0.00

ET 0.00 4.08

Pages River 0.29 2.64

Kingdon Ponds 0.00 0.18

GHB 0.35 0.59

Well 0.00 0.00

TOTAL 7.49 7.49

Discrepancy (%) 0.018

From Table 3.3, it can be seen that over the total model area, the steady state calibration

indicates a net discharge of groundwater to the Pages River (or baseflow contribution) of

2.64 ML/d. This is consistent with a range in baseflow of 1 to 4 ML/d at Blandford gauging

station, derived by application of a baseflow filtering technique to measured flows, as detailed

in Section 3.1.3. The Pages River is a gaining stream over most of the model area (i.e.

groundwater discharges to the river), but the steady state modelling indicated that it loses

water to the groundwater system over a small part of the model area, notably in the first

10km downstream from the northern model boundary, well upstream from Bickham. This is

discussed further below.



Page 17 March 2009

3.1.2 Steady State Baseflow

Pages River in the Bickham Project area is a gaining stream, i.e. the groundwater discharges

to the river in this area. Thirteen reaches have been defined for Pages River in the Bickham

Model as shown on Figure 3.2.

Kingdon Ponds is an ephemeral stream in the upper catchment area nearest to the Bickham

Project. Eight reaches have been defined for the main tributaries of Kingdon Ponds, as

shown in Figure 3.3.

Model-calculated baseflow contributions to river/stream flow were evaluated separately for

each reach within both the Pages River and Kingdon Ponds catchments. Table 3.4 and

Table 3.5 summarise the computed baseflow values for each reach in Pages River and

Kingdon Ponds respectively, derived from the steady state calibration.

Table 3-4 Pages River Baseflow - Steady State Calibration

Reach No. Layer Baseflow (m3/d)

101 1 132

102 2 50

103 2 34

104 3 8

105 5 6

106 6 3

107 7 4

108 8 357

109 7 3

110 6 58

111 7 7

112 8 28

113 8 138

Table 3-5 Kingdon Ponds Baseflow - Steady State Calibration

Reach No. Layer Baseflow (m3/d)

153 1 10

154 1 6

155 1 13

156 1 8

157 1 4

158 1 2

159 1 0*

160 1 0*

Note: * Layer 1 is unsaturated in this region

SCATTER PLOT FOR BICKHAM STEADY STATE CALIBRATION FIGURE 3.1

SCATTERGRAM

350

370

390

410

430

450

470

350 370 390 410 430 450 470

Measured Head (m AHD)

Mo

del

led

Hea

d (

m A

HD

)

REACH LOCATION MAP IN THE PAGES RIVER CATCHMENT FIGURE 3.2

REACH LOCATION MAP IN THE KINGDON PONDS CATCHMENT FIGURE 3.3



Page 20 March 2009

3.1.3 Comparison with Baseflow Estimated from Blandford Gauge Flow Data

Using measured streamflow at Blandford Gauging Station (Station No. 210061) on the Pages

River during 2002 and 2003, an analysis was undertaken to determine the possible baseflow

component of total flow at the gauge site. Using an automatic filtering technique described

by Nathan and McMahon (1990), baseflows in the range 1 to 4 ML/d were estimated

(Figure 3.4).

For comparison, Figure 3.5 shows the baseflow for the catchment area above the Blandford

site predicted by the Bickham Model. Baseflow is fairly steady at around 0.6 to 0.7 ML/d and

lies within the range determined by the filtering analysis, albeit at the lower end of the range.

The comparison shows that in respect of baseflows, the Bickham Model is consistent with the

actual streamflow measurements, although it does not show the same temporal variations as

the measured flows, presumably because approximately half of the catchment above

Blandford is not represented in the Bickham Model.

The baseflow computed by the Bickham Model for the catchment upstream of Blandford is

slightly less than that for the catchment downstream of Blandford. It also shows that the

baseflow computed for the thirteen Pages River reaches in the Bickham Project area, i.e.

downstream of the Blandford gauge, sums to about 0.75 to 0.85 ML/d, which is very

consistent with the results of the low flow gauging undertaken as part of the Bickham studies,

which indicated baseflow contributions is in the range 0.65 ML/d to 0.86 ML/d – refer to Part

B of the WRA, Section B4.10.

MEASURED AND MODEL PREDICTED RIVER BASEFLOW AT BLANDFORD FIGURE 3.4

MODEL PREDICTED RIVER BASEFLOW UPSTREAM AND DOWNSTREAM OF

BLANDFORD FIGURE 3.5



Page 22 March 2009

3.2 Transient Model Calibration

A transient calibration of the Bickham Model was carried out by matching model predictions

with the observed groundwater levels during the 5 year period January 2001 to February

2006. This period included the effects of Bickham’s bulk sample dewatering, as well as

varying recharge conditions in response to rainfall.

A bulk sample of coal was recovered from a small bulk sample pit near the north-eastern end

of the proposed mine. Two dewatering bores DW1 and DW2 located either side of the pit

were used to dewater the pit, pumping mainly from the G Seam. Pumping continued from

July to December 2004.

Water levels have been monitored in the Bickham monitoring bores approximately monthly

between mid 2002 and the present time, but monitoring frequency was increased

significantly during the bulk sample program. The recorded bore water levels and the

recorded pumping rates from bores DW1 and DW2 over the 6 months bulk sample

dewatering, were used in the calibration process.

The transient simulation period (January 2001 to February 2006) was divided into a number

of stress periods to allow progressive changes to the assumed hydrogeological stresses to be

made. A stress period is a timeframe in the model when all hydrological stresses (eg

recharge, mine dewatering) remain constant.

The first stress period was 365 days in length, to allow equilibrium conditions to develop in

the model, prior to the commencement of the transient calibration. Subsequent stress

periods were generally monthly, but during the bulk sample dewatering period shorter stress

periods of 4 days to 15 days were used.

For the transient calibration run, actual rainfalls and actual dewatering pumping rates were

specified to represent the varying recharge conditions and varying pumping stresses. Actual

daily rainfalls recorded at the Murrulla Rainfall Station were accumulated to determine an

average rainfall rate for each stress period, which were applied at the specified percentage

rates to the five rainfall recharge zones (see Annexure C). Actual dewatering rates from

DW1 and DW2 were averaged for each stress period. River stages were not varied in the

model during the transient calibration modelling.

The initial conditions in the transient calibration model were based on the heads previously

generated by the steady state model. The transient calibration was run, and the key aquifer

parameter values (hydraulic conductivity, unconfined specific yield and confined storage

coefficient), were further adjusted manually until reasonable matches were obtained between

the observed and simulated water level hydrographs.

The calibrated aquifer hydraulic parameters resulting from the steady and transient

calibration modelling are summarised in Table 3.6. Detailed maps for the hydraulic

parameter zones for each layer are presented in Annexure C. The ratio of Kh to Kv was

generally assumed to be 10:1, except for fault zones, where Kv was assumed to be higher

than Kh, to allow for possible flow along the fault structures.



Page 23 March 2009

Table 3-6 Calibrated Bickham Model Aquifer Parameters

Main

LayerAquifer/Aquitard

T

(m2/d)

Kh

(m/d)

Kv

(m/d)

Unconfined

Sy (-)

Confined

S (-)

1 Weathered regolith andalluvial deposits

- 0.1 – 1.0 0.01 - 0.10 0.05 - 0.15 n/a

Bickham Formation +Upper Coal Measures

- 0.004 - 0.01 0.002 - 0.01 0.02 2e-042

Faults (mapped) - 0.001- 0.005 0.005 - 0.01

E Seam overburden - 0.001 - 0.01 0.001 0.01 1e-043

Faults (mapped) - 0.001 - 0.005 0.005 - 0.01

E Seam - 0.02 - 0.05 0.01 0.03 3e-044

Faults (mapped) - 0.001 - 0.005 0.005 - 0.01

E Seam to G Seaminterburden

- 0.003 – 0.01 0.001 - 0.003 0.01 1e-045

Faults (mapped) - 0.001 - 0.005 0.005 - 0.01

G Seam - 0.01 - 30 0.001 - 0.05 0.05 5e-046

Faults (mapped) - 0.001 - 0.005 0.005 - 0.01

Basal Koogah Formationand weathered regolith

- 0.005 - 0.010.0001 –

0.0010.01 1e-04

7

Faults (mapped) - 0.001 - 0.005 0.005 - 0.01

Werrie Basalt 0.5 - 15 - 0.0005 - 3e-048

Faults (mapped) 0.1 - 0.5 - - -

The simulated versus observed hydrographs are plotted for all 29 bores used during

calibration in Annexure D. The hydrographs in most cases illustrate a good replication of

actual water level responses to the seasonal recharge pattern, and drawdown responses due

to the pumping from DW1 and DW2.

The simulated hydrographs for bores close to the bulk sample pit, OH70A, OH69A, OH69B,

OH65, OH57, DW1, DW2 and DDH85 (see Figure 2.3 for locations), showed a very good

correlation to the actual observed drawdown response to pumping from the bulk sample

dewatering bores DW1 and DW2. The transient calibration model run also predicted small

drawdown responses in a number of other nearby bores, ie OH75A, OH75B, OH78, OH79,

OH71A, OH71B and OH71C, even though none showed any actual response to the pumping.

In this respect, the calibrated model is considered to be conservative, and would tend to

over-estimate drawdown impacts.

The simulated hydrographs for OH70B and OH70C showed no drawdown influence due to the

bulk sample dewatering, although significant responses were observed in both bores. The

measured drawdown response at bores OH70B and OH70C is believed to be due to a failure

of the bentonite seal above the screen in OH70A, allowing all three bores to become

hydraulically connected.

Apart from these two bores, the overall simulated hydrographs coincide very well with the

actual hydrographs, confirming the model as a good predictive tool to simulate the complex

multi-layered Bickham aquifer system.



Page 24 March 2009

3.2.1 Discussion of Transient Calibration Results

The good calibration performance of the Bickham model for the transient calibration period to

February 2006 has been demonstrated in quantitative terms by potentiometric head matches

and statistical measures, and in qualitative terms by pattern-matching, as follows:

The scatter plot of modelled versus measured potentiometric head (Figure 3.6)

shows good agreement, and the associated statistical measure of the scaled root

mean square (SRMS) value was 6.4%, below the target upper limit value of 10%

(Table 3.7).

Hydrographs and contour plans of modelled and measured potentiometric head show

good visual agreement (Annexure D).

The water budget for the transient model with the steady state water balance

components showed good agreement to ensure the stability of the numerical solution

(Table 3.8).

The model-calculated baseflow contributions to the Pages River showed good

agreement with the baseflow estimated from stream gauging data (Section 3.1.2).

Transient calibration performance of the Bickham Model is summarised in Table 3.7.

Table 3-7 Transient Calibration Performance

Calibration Parameters Value

Count n 1593

Sum of Residuals R 3579 m

Sum of Absolute Residuals SR 7460 m

Scaled Mean Sum of Residuals SMSR 2.76 %

Root Mean Square RMS 6.40 m

Scaled RMS SRMS 6.43 %

Root Mean Fraction Square RMFS 1.47 %

Scaled RMFS SRMFS 5.89 %

Coefficient of Determination CD 1.39

3.2.2 Scaled Root Mean Square (SRMS) Performance Indicator

The SRMS is the major quantitative performance indicator, and is calculated as the RMS value

divided by the range of measured heads across the site. It was considered that a 10% SRMS

value on aquifer water levels would be an appropriate target maximum for this project,

consistent with the guideline (MDBC, 2001).

A scatter diagram of measured water levels versus modelled potentiometric heads

(Figure 3.6) shows most of the 1593 calibration target points located close to the line of

45°. Some deviations are observed, viz bores OH72 and OH94 (in Bickham Formation, Layer

2), and OH71B, OH73, OH77 and OH99 (in the E Seam overburden, Layer 3). However,

based on all 1593 target points from the 29 hydrographs, the SRMS value is around 6.4%,

which is well below the target maximum of 10% (MDBC, 2001).



Page 25 March 2009

Annexure B includes a map of the spatial distribution of calibration residuals (ie difference

between observed and modelled heads).

3.2.3 Transient Calibration Water Budget

The global water budget for all model layers at the completion of the transient calibration

period is summarised in Table 3.8.

Table 3-8 Bickham Model Global Water Budget at the End of the Transient

Calibration Period

DescriptionGroundwater Inflow

(ML/d)

Groundwater Outflow

(ML/d)

Recharge 6.16 0.00

ET 0.00 3.96

River 0.30 2.71

GHB 0.33 0.56

Well 0.00 0.01

Storage 1.92 1.45

TOTAL 8.71 8.69

Discrepancy (%) 0.20

Neglecting changes in storage, which are of similar magnitude at 22% of total water inputs

and 17% of total water outputs, Table 3.8 shows that:

The major input to the system is rainfall recharge (71% of total inputs), with smaller

inputs from leakage from the river-stream system (3%) and head dependent inflow at

the model boundary (4%).

The two major outputs from the system are evapotranspiration (46% of total outputs)

and baseflow leakage to the rivers and streams (31%), with a smaller output via head

dependent outflow at the model boundary (6%).

The water balance shows acceptable discrepancy between inputs and outputs of 0.20%.

3.2.4 Model Predicted Baseflows During Bulk Sample Dewatering

The model-predicted baseflows during the transient calibration period showed generally

steady baseflows in most reaches of Pages River throughout the simulation (Figure 3.7). The

exception to this was reach 113, which showed a moderate seasonal recharge and recession

pattern. Reach 113 is located downstream of the Bickham Project area, within low

permeability Werrie Basalt.

SCATTER PLOT FOR BICKHAM TRANSIENT CALIBRATION (BULK SAMPLE DEWATERING) FIGURE 3.6

SCATTERGRAM

340

360

380

400

420

440

460

340 360 380 400 420 440 460

Measured Head (mAHD)

Mo

de

lle

dH

ea

d(m

AH

D)



Page 27 March 2009

During the period of bulk sample dewatering, the model predicted a slight baseflow reduction

in two reaches – Reach 108 and Reach 110 (Figure 3.7). The magnitude of predicted

baseflow reduction has been calculated by comparing the baseflows from the transient

calibration run with those from a second run without dewatering pumping, and is shown in

Figure 3.8, which also shows the combined pumping rate from the two dewatering bores

DW1 and DW2. A baseflow reduction of 6 m3/d was predicted to have occurred in Reach 108,

and 16 m3/d in Reach 110. No discernible baseflow reduction was observed in the other

reaches.

Reaches 108 and 110 are located in the section of Pages River north-east of the proposed

mine where the G Seam subcrops close to or in contact with the river, roughly coinciding with

the northern part of the Long Pool (see Figure 3.2).

In addition to the predicted small baseflow reductions, Figure 3.8 also shows a clear

recovery response in both reaches after pumping ceased.

As well as predicting some baseflow reduction, the model also predicted some drawdown

response in the bores located adjacent to river Reaches 108 and 110 (OH75A and OH75B,

OH78 and OH79). However, monitoring showed no dewatering-induced reduction in river

water levels, nor any drawdown in these bores during the bulk sample dewatering. Hence

the river and groundwater interaction process is accommodated in the model in a

conservative manner, because the model over-predicted both baseflow impacts and

drawdown impacts due to pumping.

Kingdon Ponds baseflows as predicted by the model during the 5-year transient calibration

period January 2001 to February 2006 are shown in Figure 3.9. No significant reductions

were noted in any Kingdon Ponds reach during the bulk sampling dewatering.

PAGES RIVER BASEFLOW HYDROGRAPHS DURING TRANSIENT MODELLING CALIBRATION FIGURE 3.7

MODEL PREDICTED RIVER BASEFLOW CHANGE DUE TO PUMPING FROM DW1 AND DW2

FIGURE 3.8



Page 29 March 2009

Figure 3.9 Kingdon Ponds Baseflow Hydrographs During Transient Calibration

3.3 Sensitivity Analysis

Sensitivity analysis has been carried out to assess the sensitivity of the model calibration to

the assumed input parameters and boundary conditions. The sensitivity analysis was carried

out by first decreasing and then increasing one input parameter or boundary condition at a

time, and evaluating the impacts of the changes on the calibration statistics. Any parameter

change that resulted in a change to the SRMS statistic by a significant amount was identified

as a sensitive parameter in the model. The base SRMS value for these runs was 6.23%.

Sensitivity analysis was carried out on:

Hydraulic conductivity (horizontal and vertical)

Recharge

River-bed conductance

Storage coefficients and specific yield.

Table 3.9 summarises the parameters and the spatial zones that were tested during the

sensitivity analysis. The calibrated model aquifer hydraulic parameter values and zones are

summarised in Table 3.9 and shown diagrammatically in Annexure D.



Page 30 March 2009

Table 3-9 Parameters, Zones and the Multipliers Tested in the Sensitivity

Analysis Process

Parameter Zone Calibrated Value Layer Model Multiplier

1 0.1 m/d 1 Steady-state 0.5, 2

18 1 m/d 1, 2, 6 and 7 Steady-state 0.5, 2


12 0.02 m/d 2, 4 Steady-state 0.5, 2

23 0.004 m/d 2 Steady-state 0.5, 2

3 0.001 m/d 3 Steady-state 0.5, 2

8 0.01 m/d 3, 5, 7 Steady-state 0.5, 2


28 0.003 m/d 5 Steady-state 0.5, 2




26 0.11 m/d 6 Steady-state 0.5, 2

27 30 m/d 6 Steady-state 0.5, 2


32 20 m/d 6 Steady-state 0.5, 2

13 0.005 m/d 7 Steady-state 0.5, 2

11 0.005 m/d 8 Steady-state 0.5, 2

25 0.15 m/d 8 Steady-state 0.5, 2

38 0.01 m/d 8 Steady-state 0.5, 2

7 0.001 m/d 2, 3, 4, 5, 6, 7, 8 Steady-state 0.5, 2

10 0.005 m/d 2, 3, 4, 5, 6, 7, 8 Steady-state 0.5, 2

Horizontal

Hydraulic

Conductivity

16 0.001 m/d 2, 3, 4, 5, 6, 7, 8 Steady-state 0.5, 2

1 0.01 m/d 1 Steady-state 0.1, 10

18 0.1 m/d 1, 2, 6 and 7 Steady-state 0.1, 10

4 0.007 m/d 2 Steady-state 0.1, 10

12 0.01 m/d 2, 4 Steady-state 0.1, 10

23 0.002 m/d 2 Steady-state 0.1, 10

3 0.001 m/d 3 Steady-state 0.1, 10

8 0.001 m/d 3, 5, 7 Steady-state 0.5, 2

2 0.01 m/d 4 Steady-state 0.1, 10

28 0.003 m/d 5 Steady-state 0.1, 10

29 0.001 m/d 6 Steady-state 0.1, 10

6 0.001 m/d 6 Steady-state 0.1, 10

5 0.05 m/d 6 Steady-state 0.1, 10

26 0.01 m/d 6 Steady-state 0.1, 10

27 0.05 m/d 6 Steady-state 0.1, 10

31 0.05 m/d 6 Steady-state 0.1, 10

32 0.01 m/d 6 Steady-state 0.1, 10

13 0.0001 m/d 7 Steady-state 0.1, 10

11 0.0005 m/d 8 Steady-state 0.1, 10

25 0.0005 m/d 8 Steady-state 0.1, 10

38 0.0005 m/d 8 Steady-state 0.1, 10

7 0.01 2, 3, 4, 5, 6, 7, 8 Steady-state 0.1, 10

10 0.005 2, 3, 4, 5, 6, 7, 8 Steady-state 0.1, 10

Vertical HydraulicConductivity

16 0.01 2, 3, 4, 5, 6, 7, 8 Steady-state 0.1, 10

1 3% Applied to the Highest Active Layer Steady-state 0.5, 2

2 2% Applied to the Highest Active Layer Steady-state 0.5, 2

3 2.67% Applied to the Highest Active Layer Steady-state 0.5, 2

4 7% Applied to the Highest Active Layer Steady-state 0.5, 2Recharge

5 1.33% Applied to the Highest Active Layer Steady-state 0.5, 2

River BedConductance

All River Reaches in the Model Steady-state 0.1, 10

4 0.03 4 Transient 0.5, 2Specific Yield 9 0.05 6 Transient 0.5, 2

4 0.0003 4 Transient 0.1, 10StorageCoefficient 9 0.0005 6 Transient 0.1, 10

3.3.1 Hydraulic Conductivity

Hydraulic conductivity zones in the model were tested by applying factors to the horizontal

hydraulic conductivity of 0.5 (decrease) and 2 (increase) to the calibrated model values,

whereas the vertical hydraulic conductivity was changed by factors of 0.1 and 10. The results



Page 31 March 2009

for the horizontal hydraulic conductivity (Kh) and vertical hydraulic conductivity (Kv)

sensitivity analysis are summarised in Table 3.10.

Sensitivity analysis for Kh was completed on 23 zones defined over 8 model layers. The Kh

for Zone 29 in Layer 6 (0.1m/d base case value) gave a 5% to 25% change in SRMS in

sensitivity analysis, and is the most sensitive Kh parameter in the model, so this parameter

was later used for uncertainty analysis of the prediction scenarios. Other zones showed a

slight decrease in the SRMS when they were multiplied by 0.5, but generally the SRMS

increased only slightly if the hydraulic conductivity values were increased by a factor of 2,

showing minimal sensitivity.

Of the 23 zones of Kv tested, Zone 23 in Layer 2 (Bickham Formation) was the most sensitive

Kv parameter in the model, giving a 13% to 24% change in SRMS, and this parameter was

later used for uncertainty analysis of the prediction scenarios. The SRMS for some

parameters increased slightly when the vertical hydraulic conductivity was increased by a

factor of 10, but overall displayed limited sensitivity. The adopted calibration values for the

vertical hydraulic conductivity zones are considered the optimal values.

3.3.2 Recharge

Recharge zones representing the lowest and highest recharge areas were examined by

changing their values by factors of 0.5 and 2. The results of the recharge sensitivity analysis

are presented in Table 3.11.

Five zones representing low and high recharge rates were tested, and the results showed that

the SRMS decreased slightly if the recharge rates were multiplied by factors of 2 for the

recharge Zones 3, 4 and 5. However, reducing the recharge rate for Zone 4 from 7% to

3.5% of rainfall resulted in a 92% change to the SRMS value. It should be noted that

recharge and Kh are correlated as a ratio, and it would be possible for a different combination

of values to achieve model calibration. For example, it is possible that incorporating

additional compartmentalisation (e.g. unmapped low permeability faults) into the model may

enable the relatively high recharge rate in Zone 4 (7%) to be reduced to a value more

consistent with the other parts of the model, and still achieve model calibration.

3.3.3 River Bed Conductance

River-bed conductance values for all reaches in the model were tested by multiplying by 0.1

and 10. Sensitivity was evaluated in relation to groundwater levels via the SRMS statistic,

and also to predicted river baseflow. The SRMS results of sensitivity analysis on river-bed

conductance are shown in Table 3.11, and revealed that the model was insensitive to

multiplying the calibration river bed conductance values by either 0.1 or 10, in all river

reaches.

The sensitivity to river bed conductance parameter values was also evaluated in terms of

effects on the computed baseflow for all river reaches of Pages River and Kingdon Ponds near

the Bickham Coal Project (Table 3.12). Pages River reaches 106, 107 and 109 were found

to be sensitive to a reduction in river bed conductance, but no reaches were sensitive to an

increase in conductance. Kingdon Ponds reaches 153 to 158 were all found to be sensitive to

both increases and decreases in the river bed conductance parameter.



Page 32 March 2009

Table 3-10 Sensitivity Analysis of Horizontal and Vertical Hydraulic Conductivity

Values in the Bickham Model

Horizontal Hydraulic Conductivity (m/d) Vertical Hydraulic Conductivity (m/d)

Zone

Calibrated

Value Layer Multiplier

SRMS

(%) Zone

Calibrated

Value Layer Multiplier

SRMS

(%)

0.5 5.94 0.1 6.371 0.1 1 1 6.23 1 0.01 1 1 6.23

2 6.62 10 5.85

0.5 6.23 0.1 6.2318 1 1, 2, 6, 7 1 6.23 18 0.1 1, 2, 6, 7 1 6.23

2 6.24 10 6.23

0.5 6.19 0.1 6.214 0.01 2 1 6.23 4 0.007 2 1 6.23

2 6.31 10 6.28

0.5 5.91 0.1 7.3512 0.02 2, 4 1 6.23 12 0.01 2, 4 1 6.23

2 6.51 10 6.22

0.5 5.68 0.1 7.7423 0.004 2 1 6.23 23 0.002 2 1 6.23

2 7.59 10 7.03

0.5 6.19 0.1 6.773 0.001 3 1 6.23 3 0.001 3 1 6.23

2 6.31 10 6.79

0.5 6.06 0.1 6.348 0.01 3, 5, 7 1 6.23 8 0.001 3, 5, 7 1 6.23

2 6.47 10 6.41

0.5 5.97 0.1 6.122 0.05 4 1 6.23 2 0.01 4 1 6.23

2 6.88 10 6.24

0.5 6.16 0.1 5.7228 0.003 5 1 6.23 28 0.003 5 1 6.23

2 6.38 10 6.40

0.5 5.89 0.1 5.8729 0.1 6 1 6.23 29 0.001 6 1 6.23

2 7.76 10 6.30

0.5 6.23 0.1 6.216 0.01 6 1 6.23 6 0.001 6 1 6.23

2 6.25 10 6.24

0.5 6.22 0.1 6.235 0.12 6 1 6.23 5 0.05 6 1 6.23

2 6.27 10 6.23

0.5 6.23 0.1 6.2326 0.11 6 1 6.23 26 0.01 6 1 6.23

2 6.23 10 6.23

0.5 6.25 0.1 6.2327 30 6 1 6.23 27 0.05 6 1 6.23

2 6.23 10 6.23

0.5 6.28 0.1 6.2331 0.5 6 1 6.23 31 0.05 6 1 6.23

2 6.22 10 6.23

0.5 6.23 0.1 6.2332 20 6 1 6.23 32 0.01 6 1 6.23

2 6.23 10 6.23

0.5 6.10 0.1 5.6313 0.005 7 1 6.23 13 0.0001 7 1 6.23

2 6.49 10 7.22

0.5 5.53 0.1 5.7911 0.005 8 1 6.23 11 0.0005 8 1 6.23

2 7.22 10 6.40

0.5 6.23 0.1 6.2025 0.15 8 1 6.23 25 0.0005 8 1 6.23

2 6.26 10 6.34

0.5 5.72 0.1 6.3338 0.01 8 1 6.23 38 0.0005 8 1 6.23

2 6.84 10 6.27

0.5 6.32 0.1 6.187 0.001 2, 3, 4, 5, 6, 7, 8 8 1 6.23 7 0.01 2, 3, 4, 5, 6, 7, 8 8 1 6.23

2 6.16 10 6.23

0.5 6.19 0.1 6.2110 0.005 2, 3, 4, 5, 6, 7, 8 1 6.23 10 0.005 2, 3, 4, 5, 6, 7, 8 1 6.23

2 6.30 10 6.30

0.5 5.64 0.1 6.0216 0.001 2, 3, 4, 5, 6, 7, 8 1 6.23 16 0.01 2, 3, 4, 5, 6, 7, 8 1 6.23

2 6.84 10 6.50



Page 33 March 2009

Table 3-11 Sensitivity Analysis of Recharge, River Bed Conductance, Storage

Coefficient and Specific Yield Values in the Bickham Model

Sensitivity to Recharge

Zone Calibrated Value Layer Multiplier SRMS (%)

0.5 9.18

1 3% Applied to Highest Active Layer 1 6.23

2 6.60

0.5 6.24


2 6.23

0.5 7.18

3 2.67% Applied to Highest Active Layer 1 6.23

2 5.55

0.5 11.97


2 6.13

0.5 6.26

5 1.33% Applied to Highest Active Layer 1 6.23

2 6.19

Sensitivity to River Conductance (m2/d)

Reach Calibrated Value Layer Multiplier SRMS (%)

0.1 6.37

All 0.1, 25, 50 All 1 6.23

10 6.25

Sensitivity to Storage Coefficient


0.1 6.44

4, 9 0.0003, 0.0005 4, 6 1 6.43

10 6.36

Sensitivity to Specific Yield


0.5 6.45

4, 9 0.03, 0.05 4, 6 1 6.43

2 6.41

3.3.4 Storage Parameters

Confined storage coefficient for the aquifer units Layer 4 (E Seam) and Layer 6 (G Seam) was

varied by factors of 0.1 and 10. Unconfined specific yield values for Layers 4 and 6 were

changed by factors of 0.5 and 2.

The results, summarised in Table 3.11, showed that the model was not sensitive to either

the confined storage coefficient or unconfined specific yield values in either layer.



Page 34 March 2009

Table 3-12 Sensitivity Analysis of River Bed Conductance on Pages River and

Kingdon Ponds Baseflows in the Bickham Model

Pages River Baseflow (m3/d)

Reach 1.0 x River Bed Conductance (Baseline) 0.1 x River Bed Conductance 10 x River Bed Conductance

101 131.5 129.3 132

102 50.1 52.4 49.7

103 34 39.6 33.2

104 8 10 7

105 6 8 5.

106 3 6 3

107 4 6 3

108 356.9 259.4 372.2

109 3 5. 2

110 58.4 52.8 58.7

111 7 9 7

112 27.5 35.9 25.9

113 137.5 150.3 135.6

Kingdon Ponds Baseflow (m3/d)

Reach 1 x River Bed Conductance (Baseline) 0.1 x River Bed Conductance 10 x River Bed Conductance

153 10 1 59.8

154 6 1 40.2

155 12.7 1 61.8

156 8 1 41.9

157 4 0 24.2

158 2 0 10.1

159 0 0 0

160 0 0 0



Page 35 March 2009

4. PREDICTIVE MODELLING

The overall objective of the groundwater modelling was to assess the potential impacts of the

Bickham Coal Project on the groundwater environment, specifically with regard to:

Predicted mine inflow rates;

Regional changes in groundwater levels, both during mining and after mine closure;

Changes in baseflow contributions to surface watercourses; and

Long-term salinity impacts of the final landform post-mining.

The calibrated Bickham Model has been applied to predicting the mine dewatering

requirements, and the related hydrological impacts of progressive mining and inpit diposal of

overburden, for the proposed 25 year mine life, and for a 100 period of post-mining recovery.

Impacts have been predicted in terms of changes to groundwater levels, and groundwater-

surface water interactions. The predictive modelling using the calibrated set of hydraulic

properties and boundary conditions is referred to as the “Base Case” simulation. Uncertainty

in the predicted outcomes has been assessed by re-running the model after varying the

hydraulic parameters which were found to be the most sensitive during the sensitivity

analysis (as described in Section 3.3).

4.1 Simulation of Mining and In-pit Overburden Disposal

Open-cut mining is represented in the Bickham Model by specifying drain cells wherever

active workings occur (i.e. in the open cut), with drain levels set 1m above the base of the

appropriate model layer for the period of mining and backfilling. The drain discharges from

all in-pit drain cells are summed to determine the total groundwater inflow rate to the mine

at each stage of the mining simulation. The drain cell configuration is progressed in annual

increments, in line with the progressive advancement of the pit in accordance with the mine

plan detailed on Figure 4.1. As parts of the pit are progressively backfilled with waste, the

drain cells are progressively de-activated.

A high drain conductance value of 1000 m2/d was adopted for the mine drain cells. The drain

cell conductance parameter reflects the resistance to flow from the saturated rocks into the

drain cells, and is a critical model parameter which determines the seepage inflow into the

workings simulated by the model. The high value adopted ensured that groundwater would

drain freely to the pit.

The mine plan involves commencement of mining at the north-eastern end of the deposit,

accelerated coal extraction and in-pit backfilling with overburden at this north-eastern end of

the pit, and deferring commencement of mining at the south-western end of the deposit until

Year 6.

The prediction model was configured with annual changes in terms of the area and level of

drainage features to suit the progressive mine plan.

4.2 Model Parameter Changes with Time

In order to simulate the changes in hydraulic properties that occur during open cut mining

(with the material inside the pit area starting with in-situ rock properties, then being

progressively replaced first by a temporary void and finally by waste backfill), it is necessary

to be able to change the hydraulic properties of the in-pit cells with time in accordance with



Page 36 March 2009

the proposed mining/backfilling schedule. This progression from rock to void to waste will

occur progressively cell by cell through the mine life.

MODFLOW-SURFACT does not automatically allow for changing of hydraulic conductivity

parameters with time during a simulation. To ensure that the hydraulic aquifer parameters

were able to be changed with time to represent the progressive removal of rock and

backfilling of the pit with overburden as mining proceeds, the 25 year period of mining at

Bickham was divided into 19 consecutive “time slice” simulations, each representing 1 or 2

years.

Each time slice simulation comprised a separate model run, with the final water level

conditions from each time slice used as the initial conditions for the subsequent time slice,

and the hydraulic properties of relevant cells changed to represent areas mined and backfilled

with overburden. The hydraulic conductivity (Kh and Kv) values of the cells representing the

mined and backfilled open cut areas were increased for the specific portion of the pit

backfilled during each time slice (backfill Kh = 1m/d and Kv = 0.1m/d), with the changes

invoked progressively in accordance with the mining and backfilling plan. The specific yield

(Sy) value was also changed for the mined and backfilled areas (backfill Sy = 0.05), in

parallel with the changes in Kh/Kv values.

For the post-mining recovery model run, aquifer properties of the cells within the open cut

shell were assigned values appropriate to the overburden backfill, or void space in the final

pit void.

Years 1 to 10, 15, 16 and 25 were simulated as 1-year time slices, and the remainder as 2-

year time slices. Each 2-year time slice was divided into two annual stress periods. A stress

period is the timeframe in the model when all hydrological stresses (e.g. recharge, pumping)

are held constant. Post-mining recovery was run as a single 100-year transient model run.

The ATO adaptive time stepping package in MODFLOW-SURFACT was used to ensure the

stability of the numerical solution and to increase the accuracy of the heads and fluxes during

model simulation.

The results at the end of the Bickham mine dewatering prediction (i.e. at the end of Year 25)

were used as the initial condition for the post-mining recovery simulation. The recovery

simulation was run for a period of 100 years post mining. Results indicate that virtually full

recovery had occurred after 75 years (i.e. Mine Year 100).

For the recovery run, aquifer parameters were increased from the in situ rock values, to

represent either pit backfill or the residual water-filled pit void. The backfill material has

been assigned a higher hydraulic conductivity (Kh = 1 m/d and Kv = 0.1 m/d) than the in-

situ rock. The residual open pit void is represented in the model with high permeability values

(Kh = Kv = 1000 m/d) and high unconfined specific yield (Sy = 0.99).

MINE PLAN SHOWING DEWATERING BORE LOCATIONS FIGURE 4.1

PREDICTED MINE DEWATERING RATES (BASECASE PREDICTIVE MODEL RUN) FIGURE 4.2

N

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

2400

0 2 4 6 8 10 12 14 16 18 20 22 24 26

Year

To

tal

De

wa

teri

ng

Ra

te(m

3/d

)

Total Pit Inf low

Dewatering Bore

Total Dewatering



Page 38 March 2009

4.3 Simulation of Mine Dewatering

4.3.1 Dewatering Approach

Dewatering of the Bickham open cut will be achieved by a combination of drainage into the

pit and pumping from external or in-pit dewatering bores. Natural inflow to the pit may

account for the bulk of the dewatering, but it may be supplemented by some pumping from

bores either to assist pit working conditions or for other operational reasons. The

requirement for supplementary bores, and their locations if required, will be determined

during the mine life, based on conditions encountered and the effectiveness of natural inflows

as a dewatering approach.

In the modelling, dewatering has been assumed to occur predominantly by natural inflows to

the pit, apart from one external dewatering bore as described below. An initial predictive

simulation was run for the 25 year mine life, with only pit inflows, to provide an indicative

assessment of potential impacts on baseflows in Pages River and/or Kingdon Ponds.

Groundwater inflow rates were determined via the drain cells used to represent active open

cut areas in the model (as described in Section 4.1 above).

The Bickham Model was then re-run, with an external dewatering bore in operation

throughout the mine life, pumping at a variable rate set at 20% above the indicative Pages

River baseflow reductions, in addition to natural pit inflows via the operation of the drain

cells. This predictive run is referred to as the “Base Case” predictive run.

This external dewatering bore, situated downdip of the central pit area (see location on

Figure 4.1), also provides a supply of water at suitable quality for discharge to Pages River

to offset any baseflow reduction caused by the mining. By intercepting part of the

groundwater inflow prior to entering the pit, an un-contaminated source of water will be

assured. The suitability of the chosen site from both groundwater quality and aquifer

permeability considerations has been confirmed by testing and sampling of the nearby

piezometer (OH72). When constructed, the dewatering bore will be tested to assess its

sustainable yield and if necessary one or more additional bores may be drilled to obtain the

desired flow. However, for the modelling purposes, it has been assumed that the supply will

be obtained from a single bore, pumping from both the G Seam and the E Seam.

Hence, the Base Case predictive modelling took into consideration both natural inflows and

pumping from the external dewatering bore.

Figure 4.1 also shows the location of an in-pit dewatering bore. This is a contingency

provision for advance dewatering in the western pit, as a means of supplementing the water

available from groundwater inflows which may be insufficient to meet the project’s water

supply needs in the early years under some climatic conditions. The model was run for the

first six years to verify that sufficient water could be obtained by pumping this bore, but it

was not part of the Base Case modelling as it will only be used if adverse climatic conditions

occur.

4.3.2 Predicted Dewatering Rates

Pit inflow rates in the Bickham Model were calculated by the weighted average method, in

which the model-calculated inflow rate at the end of each time step is multiplied by the

duration of the time step, summing the average volumes and dividing by the stress period

time (i.e. essentially a step-wise integration of the area under the inflow curve). The

In-Pit Mine Dewatering

External Mine Dewatering



Page 39 March 2009

weighted average method allows the dewatering inflow to be computed separately for each

model layer.

In the Bickham Model, it was not practicable to save the head and flux after every time step

because of file size constraints, so the heads and fluxes were saved every 20 days using the

MODFLOW-SURFACT adaptive time step ATO package. Each 365-day stress period therefore

generated 19 values of head and flux output for each stress period.

Hence, the weighted average pit inflow was calculated as:

n

ii

i

n

ii

W

XW

X

1

1~

where:

X~

: is the weighted average pit inflow (m3/d)

iW : is the corresponding time step size (weight) for each pit inflow

iX : is the pit inflow at the end of each time step at which head and flux are saved

(m3/d)

n : is the total number of readings.

The average pit inflows from each model layer, and the flow from the external dewatering

bore, are presented in Figure 4.2 and Table 4.1.

The predicted average annual dewatering rate ranges from a minimum of 33 kL/d in Year 1 to

a maximum of 2,203 kL/d in Year 17. The average total dewatering rate over the 25 years of

mining is 1,185 kL/d. Production of water from the external dewatering bore ranged from

6 kL/d (Year 1) to 195 kL/d (Year 25), in accordance with the indicative baseflow reductions

discussed in Section 4.4. The average production rate from the external dewatering bore

was 125 kL/d.



Page 40 March 2009

Table 4-1 Base Case Predictive Model Run Predicted Annual Dewatering Rates by

Model Layer

Weighted Average Pit Inflow Rate* (kL/d)

Year

Layer 1 Layer 2 Layer 3Layer 4

E SeamLayer 5

Layer 6

G SeamTotal

External

Dewatering

Bore (kL/d)

Total

Dewatering

Rate**

(kL/d)

1 0 0 0.4 27 0 0 27.4 6 33

2 0 0 4.9 85 0 0 89.9 18 108.

3 0 5.5 6.3 48 33 165 257.8 60 318

4 6.7 21 26 47 45 245 390.7 90 481

5 3.5 59 65 88 14 180 409.5 100 510

6 0 68 22 67 30 356 543 105 648

7 0 72 30 276 16 364 758 112 870.

8 0 107 32 141 70 1005 1355 115 1470

9 0 76 19 101 98 1128 1422 118 1540

10 0 62 22 52 102 1130 1368 120 1488

11 0 191 48 185 66 865 1355 123 1478

12 0 79 36 126 61 935 1237 125 1362

13 5.1 285 26 67 140 1338 1862 130 1992

14 0.6 114 12 33 99 1051 1309.6 135 1445

15 0 210 39 56 67 1270 1642 137 1779

16 0 220 20 72 114 1502 1928 140 2068

17 0 140 32 91 178 1619 2060 143 2203

18 0 66 7.1 52 156 1496 1777.1 145 1922

19 0 94 4.1 5.8 44 511 658.9 150 809

20 0 46 0 0.2 21 444 511.2 152 663

21 0 53 14 45 51 668 831 165 996

22 0 19 9 21 40 589 678 176 854

23 0 337 11 33 75 736 1192 185 1377

24 0 343 5.8 20 62 703 1133.8 190 1324

25 0 542 14 29 98 1022 1705 195 1900

Ave 0.6 128 20 71 67 773 1060 125 1185

Min 0 0 0 0.2 0 0 27 6 33

Max 6.7 542 65 276 178 1619 2060 195 2203

* Weighted average is calculated from instantaneous water balance values reported every 20 days for each layer

** Total dewatering rate is the summation of the total pit inflow and the rate of the dewatering bore



Page 41 March 2009

The predicted pit inflow rates show that most water will be derived from the G Seam (Layer

6), with an average inflow rate over 25 years of 770 kL/d. Next most productive are the

Bickham Formation (Layer 2) with average flow of 130 kL/d, and the E Seam (Layer 4) with

an average inflow rate of 70 kL/d.

Layer 1 (comprising alluvium and regolith) is predicted to produce almost no pit inflow

(average 0.6 kL/d over the mine life).

4.4 Predicted Baseflow Impacts

The impact of mining on groundwater baseflow discharges to Pages River and Kingdon Ponds

has been assessed from the results of the Base Case predictive model run. Baseflows were

examined separately for each of the thirteen Pages River reaches and eight Kingdon Ponds

reaches described in Section 3.1.2 and shown on Figures 3.2 and 3.3, respectively.

Baseflow impacts have been assessed through the 25 year mining period and the subsequent

100 year recovery period.

4.4.1 Pages River

Figure 4.3 shows the predicted baseflows and the magnitude of baseflow reductions, for the

thirteen river reaches along the Pages River, from the commencement of mining (Year 0) to

the end of the recovery model run (Year 125).

Small reductions in groundwater baseflow to Pages River are predicted to start occurring in

Year 1, and to steadily increase as mining proceeds, reaching a maximum of 200 kL/d

(0.2 ML/d) by the completion of mining (Year 25), as shown on Figure 4.3.

Two periods of increasing impact are observed, namely during Years 3 and 4, and then after

Year 20. The increased impact in Year 3 occurs with the start of mining of the G Seam at the

north-eastern end of the pit. The baseflow impact slows from Year 5 after commencement of

overburden backfilling at that end of the pit. The second period of increase in baseflow

impact (after Year 20) occurs when mining resumes in the east pit after a hiatus of several

years.

In the years immediately following the cessation of mining, baseflow continues to reduce,

before starting to recover from Year 35. Baseflows are predicted to have re-stabilised by

Year 100 (i.e. 75 years after completion of mining).

Most of the predicted impact during the early years of mining is in Reaches 108 and 110, and

to a lesser extent in Reaches 102 and 103. Both 108 and 110 are located north-east of the

mine, and 102 and 103 are to the north. In the latter stages of the project, baseflow impacts

are shown to slightly increase in Reach 101 adjacent to the alluvium flats upstream of

Bickham Gorge.

The predicted maximum total baseflow impact during mining is about 220 kL/d, which

represents about 25% reduction in the pre-mining baseflow from these thirteen reaches. The

maximum reduction occurs in Year 34, i.e. 9 years after mining is completed.

At no stage during the 25 year mine life or the post-mining recovery period is there predicted

to be a net flow of water from the river to the groundwater, from any of the 13 reaches

within the mine area. Positive baseflow contribution will continue from all reaches throughout

the mine life and post-mining. The impact of the mining operation will be merely a reduction

in the rate of groundwater discharge into the river, not a reversal of flow.



Page 42 March 2009

It should be noted that the predicted baseflow reduction from the model is believed to

overstate the potential baseflow impacts, as it did during the bulk sample dewatering in the

transient calibration. Hence the model predicted baseflow impacts are considered to be

conservative.

4.4.2 Kingdon Ponds

The impact of mining on groundwater baseflow discharges to Kingdon Ponds has also been

assessed for the reaches defined in Section 3.1.2. The modelling prediction shows no

reduction in baseflow to Kingdon Ponds during the first 7 years of mining (Figure 4.4).

Minor baseflow reduction is predicted from Year 8, which coincides with the commencement

of mining in the west pit, and reaches a maximum of 15 kL/d by Year 35.

Baseflows are predicted to re-stabilise at more than 80% of the pre-mining baseflows by Year

100 (i.e. 75 years after completion of mining).

Kingdon Ponds is an ephemeral stream system with no sustained visible flow during the

baseline monitoring period (2002-2009). Calculated Kingdon Ponds baseflows are small

(total of 41 kL/d from all 8 reaches, although several reaches are dry (i.e. with zero

baseflow). The predicted maximum reduction in Kingdon Ponds baseflow from the project is

only 15 kL/d (Year 35), with the majority of reduction (12 kL/d) predicted to occur in reach

155, which occupies the tributary catchment that will be intersected by the west pit itself.

Predicted impacts in all other Kingdon Ponds reaches are minor, and all recover to near pre-

mining baseflow rates.

The baseflows predicted by the model are consistent with a small volume of flow, partly

above ground and partly in the shallow sub-surface within the alluvium/weathered rock

material. The model is considered to be very conservative in this area, and would tend to

over-estimate the impacts of mine dewatering drawdowns on the Kingdon Ponds catchment.

PAGES RIVER PREDICTED BASEFLOW AND BASEFLOW REDUCTION FIGURE 4.3

Baseflow Impacts (25 Years Mining + 100 Years Recovery)

0

100

200

300

400

500

600

700

800

900

0 10 20 30 40 50 60 70 80 90 100 110 120 130

Year

Pag

es

Riv

er

Basefl

ow

(m3/d

)

Reach 101 Reach 102 Reach 103 Reach 104 Reach 105 Reach 106 Reach 110

Reach 107 Reach 109 Reach 111 Reach 108 Reach 112 Reach 113 Total


-300

-280

-260

-240

-220

-200

-180

-160

-140

-120

-100

-80

-60

-40

-20

0

20

0 10 20 30 40 50 60 70 80 90 100 110 120 130

Year

Pag

es

Riv

er

Basefl

ow

Red

ucti

on

(m3/d

)

Reach 101 Reach 102 Reach 103 Reach 104 Reach 105 Reach 106 Reach 110

Reach 107 Reach 109 Reach 111 Reach 108 Reach 112 Reach 113 Total

KINGDON PONDS PREDICTED BASEFLOWS AND BASEFLOWS REDUCTION FIGURE 4.4


0

100

200

300

400

500

600

700

800

900

0 10 20 30 40 50 60 70 80 90 100 110 120 130

Year

Kin

gd

on

Po

nd

sB

asefl

ow

(m3/d

)

Reach 151 Reach 152 Reach 153 Reach 154 Reach 155 Reach 156

Reach 157 Reach 158 Total


-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

0 10 20 30 40 50 60 70 80 90 100 110 120 130

Year

Kin

gd

on

Po

nd

sB

asefl

ow

Red

ucti

on

(m3/d

)

Reach 151 Reach 152 Reach 153 Reach 154 Reach 155 Reach 156

Reach 157 Reach 158 Total



Page 45 March 2009

4.5 Predicted Water Level Impacts

4.5.1 Mining Period

Figures 4.5 to 4.7 show predicted water level drawdown in Model Layer 1 (Regolith and

Alluvium), Layer 2 (Bickham Formation) and Layer 6 (G-Seam) at the completion of mining

(Year 25).

Regional groundwater level drawdown is predicted to occur in all layers that are intersected

by the proposed mine. These impacts are predicted to extend for varying distance from the

proposed mine, depending on the hydrogeological unit. Predicted impacts in the surficial

groundwater in the regolith layer and/or alluvium (ie the water table) are quite localised and

relatively small in magnitude. Predicted impacts on the potentiometric groundwater levels

within the deeper Permian units are relatively more extensive and larger in magnitude. Note

that the predicted impacts in the Permian units refer to reductions in groundwater pressure,

and not to dewatering, and they are unrelated to the near-surface water table levels in the

weathered zone and alluvium.

Within the Permian (G Seam), water levels are predicted to draw down by up to 200 m within

the pit, 80 m immediately adjacent to the pit, and by up to 20 m just west of the New

England Highway. Drawdowns of 1 m or more are predicted to extend to approximately 3 km

northwest of the pit. However, these are drawdowns of the potentiometric water levels in the

confined coal measures, and the predicted extent of drawdown impact on the water table is

much less.

Within the overlying Bickham Formation (Layer 2), water levels are predicted to be drawn

down by up to 50 m between the pit and New England Highway. Just northwest of the

highway this drawdown has reduced to 10 m. Drawdowns of 1 m or more are predicted to

extend to approximately 3 km northwest of the pit. The Bickham Formation and Upper Coal

Measures are not present to the south-east of the mine.

By the completion of mining, localised drawdown of up to 10m, is predicted within the

regolith and alluvium (Layer 1) from the mine area across to the New England Highway, with

a small extension across to the western side of the highway centred along the ridgeline

marking the catchment boundary between Pages River and Kingdon Ponds. Drawdowns of

no more than 1 m are predicted to be confined to areas within 1.75 km of the proposed pit.

No impacts are predicted for Permian Layers 2 to 6 to the south-east of the pit (ie up-dip

from the pit), as they are not present up-dip from the G Seam outcrop line. Some

depressurisation impacts are predicted for Layer 7 (basal Koogah Formation) and Layer 8

(Werrie Basalt). These impacts do extend to the south-east from the pit, but once again they

are depressurisation impacts, not dewatering. Those units remain saturated.

4.5.2 Post Mining Water Levels

Post-mining water levels do not recover completely to pre-mining levels in some parts of the

mine area, due to the replacement of in situ rock with waste rock backfill within the mined

out pit. The waste rock backfill will be more homogeneous than the in situ rock, and there

will therefore be more uniform hydraulic interconnection along the pit than currently exists

pre-mining.



Page 46 March 2009

For the post-mining recovery simulation, evapotranspiration rates were adjusted to represent

evaporation from the open water surface of the pond in the final pit void. Rates equivalent to

50% of the net pan evaporation rate were used, i.e. 795 mm/yr, or 0.00218 m/d, based on

an annual evaporation rate of 1591 mm/yr (Table 2.2). Recharge rate was also increased

over the area of the pit void to equal 100% of the annual average rainfall (724 mm/yr),

slightly less than the adopted evaporation rate.

Figures 4.8 to 4.10 show predicted water level drawdown in Model Layer 1 (Regolith and

Alluvium) , Layer 2 (Bickham Formation) and Layer 6 (G-Seam) at the end of the recovery

period (Year 125). Hydrographs of predicted water level recovery at key Bickham monitoring

bores are presented in Annexure E.

In summary, the drawdown plots and hydrographs show the following:

Residual drawdowns in the water table (Layer 1) at the end of the recovery period are

predicted to be less than 1 m, except for the area generally between the New England

Highway and the Bickham open cut, where some larger residual drawdowns, of up to

5 m, are predicted. Residual drawdowns of 1 m are predicted to be limited to the

area within 2.25 km of the pit.

Within the Bickham Formation (Layer 2) residual water level drawdowns of up to 20m

are predicted immediately adjacent to the pit. Predicted residual drawdowns of 5 m

are limited to the area within 1.75 km of the pit.

In the area immediately around the pit void potentiometric groundwater levels in the

Permian (Layer 6) are predicted to recover to approximately 40 m below pre-mining

levels.

4.5.3 Post Mining Pit Void Water Level

Figure 4.11 represents the predicted pit void water level during 100 year recovery period.

The post-mining pit void water levels are predicted to stabilise at around

405 mAHD, compared with pre-mining levels that range up to as high as 450+ mAHD at the

Pages River – Kingdon Ponds catchment divide, near the south-western end of the pit area.

Water level recovery is rapid during the initially 10 years following cessation of pit

dewatering. By around 20 years post-mining water levels have recovered by 140 m, taking

pit void water levels to approximately 350 m AHD. Modelled hydrographs show that the

recovering water levels flatten out during later recovery years, with the system predicted to

reach a quasi-equilibrium by Year 100 (75 years after completion of mining).

4.6 Water Quality Impacts

4.6.1 Pit Inflow Salinity During Mining Period

The bulk salinity of groundwater inflows to the mine has been estimated using two methods,

to determine a weighted average salinity.

The first method calculates the salt load on the basis of the groundwater storage reductions

in each layer over the entire model area in each year of mining, without any weighting for

distance from the mine area, and applies to each layer volume the average salinity for

groundwater from that layer derived from baseline monitoring. The calculation using this

method is presented in Table 4.2. In reality, groundwater released from storage at more

distant parts of the model area will never reach the mine, but will merely move towards it.



Page 47 March 2009

The inflow salinity will be more heavily influenced by groundwater closer to the mine, which is

generally of lower salinity. Hence the calculation in Table 4.2 is considered to overstate the

bulk inflow salinity.

Table 4-2 Average Salinity Based on Annual Groundwater Storage Changes for Each

Model Layer (kL/d)

Year Layer 1 Layer 2 Layer 3 Layer 4 Layer 5 Layer 6 Layer 7 Layer 8 Total

Average

TDS (mg/L)1500 1220 760 570 410 470 470 2360

Average

TDS

(mg/L)

1 6.6 6.4 2.0 2.2 2.3 2.5 0.4 0.2 1028

2 11 27 4.8 2.7 10 14 5.3 1.2 935

3 24 64 10 8.4 18 42 20 3.5 902

4 41 111 16 16 20 44 34 5.5 960

5 47 145 13 14 12 38 39 6.0 1021

6 68 190 20 18 4.5 60 45 8.0 1040

7 83 261 23 29 39 87 48 10 1000

8 140 493 35 53 59 121 68 22 1042

9 151 581 37 51 57 111 74 21 1065

10 166 599 33 48 46 80 80 19 1093

11 201 574 0 26 0 67 104 20 1154

12 199 445 9 24 16 68 99 14 1121

13 239 626 0 9.2 0 167 129 22 1106

14 224 453 0 7.0 0 47 118 13 1161

15 219 592 30 34 39 67 113 15 1108

16 224 667 31 36 48 91 119 20 1100

17 251 958 55 63 41 99 131 26 1114

18 251 786 40 43 37 75 118 17 1124

19 235 239 0 0 0 0 98 0 1206

20 213 0 0 0 0 0 79 0 1220

21 206 35 0 0 0 0 79 4.6 1232

22 189 0 0 0 0 0 65 1.1 1242

23 176 207 0 1 0 6 64 5.1 1225

24 163 180 0 0 0 0 56 4.0 1240

25 153 423 42 24 57 34 61 9.0 1096

Total 3880 8664 401 508 507 1321 1846 267 1101

Note: Values above 10 kL/d have been rounded up or down to the nearest whole number.

The second method calculates the salt load from pit inflows from each model layer (obtained

from the model mass balance for each year of mining) and applying average salinity for each

model layer derived from the baseline monitoring data. The calculation using this method is

presented in Table 4.3. This calculation assumes that all groundwater flowing into the mine

is derived from model layers that are directly intersected by the mine, i.e. Layers 1 to 6. It

assumes that water flowing in from a particular layer originated in that layer, and does not

account for groundwater flow between layers en route to the mine. This approach may

understate the salinity, as it does not include the small inflows from the more saline Layer 8

(Werrie Basalt), via Layers 7 and 6, and may also understate the total derived from the more

saline Layers 1 and 2 (alluvium, Bickham Formation and Upper Coal Measures).



Page 48 March 2009

Table 4-3 Average Salinity Based on Weighted Average Annual Pit Inflows from

Each Model Layer (kL/d)

Year Layer 1 Layer 2 Layer 3 Layer 4 Layer 5 Layer 6 Layer 7 Layer 8 Total

Average

TDS (mg/L)1500 1220 760 570 410 470 470 2360

Average

TDS

(mg/L)

1 0 0 0.4 27 0 0 - - 572

2 0 0 4.9 85 0 0 - - 580

3 0 5.5 6.3 48 33 165 - - 504

4 6.7 21 26 47 45 245 - - 551

5 3.5 59 65 88 14 180 - - 651

6 0 68 22 67 30 356 - - 585

7 0 72 30 276 16 364 - - 587

8 0 107 32 141 70 1005 - - 543

9 0 76 19 101 98 1128 - - 517

10 0 62 22 52 102 1130 - - 508

11 0 191 48 185 66 865 - - 596

12 0 79 36 126 61 935 - - 533

13 5.1 285 26 67 140 1338 - - 590

14 0.6 114 12 33 99 1051 - - 536

15 0 210 39 56 67 1270 - - 573

16 0 220 20 72 114 1502 - - 558

17 0 140 32 91 178 1619 - - 524

18 0 66 7.1 52 156 1496 - - 496

19 0 94 4.1 5.8 44 511 - - 575

20 0 46 0 0.2 21 444 - - 534

21 0 53 14 45 51 668 - - 524

22 0 19 9.0 21 40 589 - - 493

23 0 337 11 33 75 736 - - 683

24 0 343 5.8 20 62 703 - - 696

25 0 542 14 29 98 1022 - - 708

Total

Inflow 16 3210 506 1768 1680 19323- - 569

Note: Values above 10 kL/d have been rounded up or down to the nearest whole number.

Each of the two approaches is an approximation, and the actual salinity of mine inflows is

expected to be between the two results. Despite their shortcomings, the alternative

approaches provide a good indication of the likely upper and lower bounds for the salinity of

groundwater inflows to the pit during the mine life. Based on these calculations, the salinity

of groundwater inflows is expected to be within the range 569 and 1101 mg/L TDS, but will

more likely be less than 1000 mg/L.

4.6.2 Post-Mining In-Pit Salinity

At the conclusion of mining a void of 69.6 Mm3 will remain. This void will partially fill up with

water post mining due to rainfall and groundwater inflow, and there is the potential for the

pond water to concentrate salts if evaporation is greater than rainfall. Alternatively, there is

also the potential for the salt concentration to be diluted in the unfilled void water, which



Page 49 March 2009

would tend to be stabilise salinity concentrations in the pit void lake. Dilution would occur if

rainfall exceeds evaporation. There could also be losses via groundwater outflow.

The water body in the void will accumulate over time due to both direct rainfall and

groundwater inflow. Groundwater inflow to the void will come mainly from the overburden

backfill occupying the remainder of the mined out pit. Water from both rainfall recharge and

groundwater inflow from the surrounding rocks will enter the backfill, which will consist of a

mix of overburden lithologies, and its unconsolidated nature will allow rapid mixing of the

inflowing groundwater and rainfall recharge. Rainfall recharge will serve to dilute the salinity

of the groundwater inflow, whilst additional leaching from the crushed rock within the spoil

will tend to increase it. Any rainfall and groundwater inflow water will also mix with the

existing pore water within the spoil heap.

Leachate analysis of spoil bulk samples (Robert Carr & Associates, 2002) indicated that

leaching the spoil material with distilled water under laboratory conditions produced a TDS

increase of only 85 mg/L. This should be compared with the 400 – 1500 mg/L TDS range

obtained from baseline groundwater sampling of the coal measures and overburden aquifers.

The amount of salinity that will leach from the spoil will depend on the particle size of the

spoil and its exact mineralogy. A short term leaching test will typically remove less than half

of the total leachable salt from the spoil (Fityus et al, 2007), hence to take a conservative

approach, for the purposes of this analysis a sensitivity range of between 2 and 3 times the

leach values obtained by Robert Carr (2002) was taken to represent the medium term salinity

increase in the spoil.

It has been assumed that the overburden placed in the pit would be partly saturated, with

the contained water volume equal to 30% of the effective porosity. This water was given a

TDS of 700 mg/L, which is a representative average value for the insitu groundwater quality

within the overburden (coal measures, Bickham Formation and regolith). Average

groundwater quality entering the spoil from the surrounding rock mass was assumed to be

835 mg/L TDS, based on the results of weighted average annual pit inflows, and the storage

change per year within each model layer.

Mass balance calculations were undertaken using the above values for recharge, groundwater

inflow and spoil leaching in order to estimate the average groundwater quality within the in-

pit spoil. Analysis shows that groundwater quality within the spoil material should average

out at between 733 mg/L and 777 mg/L TDS during the 100 year post-mining recovery

period.

4.6.2 Pit Void Salinity

Utilising the above salinity values (for both groundwater inflow from the surrounding rock

mass and the overburden backfill material) as input parameters, a salt balance was

generated for the pit void lake using five year time steps. Complete mixing of the salinity

within the lake was assumed.

The volume of water flowing into and out of the unfilled pit void was quantified from the post

mining recovery model results. Inputs to the salt balance analysis were as follows:

The salt concentration in rainfall would be 30mg/L (source: UNSW Connected

Waters);

Salt in groundwater flowing from the rock mass aquifers to the north and south would

be 835mg/L;



Page 50 March 2009

Salt in groundwater flowing from the east and west spoil areas is calculated as the

average of spoil groundwater salinity (733 - 777mg/L).

The results of the mass balance modelling indicate that the groundwater that enters the pit

void will be quickly diluted by rainfall. Mixing of groundwater and rainfall results in water

within the pond diluting to between 375 mg/L and 395 mg/L TDS within the first 5 years after

completion of mining, as shown in Figure 4.12. Salinity values reach near equilibrium within

30 years post-mining, at concentrations in the range 360–375mg/L TDS, with only minor

fluctuations predicted as the balance between groundwater, evaporation and rainfall varies

with the depth of water in the pit.

Bulk leachate testing of the type undertaken indicates that average leachability within the

spoil area is likely to be low.

4.6.3 Post-Mining Migration of Groundwater from Pit

In order to assess the potential salinity impact of water migrating from the pit (void and

backfill areas) on the water environment, particle tracking and vector mass balances have

been carried out on the pit void and backfill areas.

Results of mass balance analysis show that net groundwater flow within the first 45 years

(post-mining) is towards the pit void lake, and there is no significant outflow of groundwater

water from the pit area during that period. In the following years, i.e. from 45 years post-

mining, the water level within the pit void is high enough to reverse this hydraulic gradient

and start causing small outflow into the surrounding pit spoil. Net drainage only occurs to the

east, where it moves through the spoil around to the north-eastern end of the pit. This flow

then drains, via the coal measures strata, to the nearest point on the Pages River, gradually

re-instating the pre-mining baseflow contribution of groundwater from the pit area.

Particle tracking confirms this mass balance approach. Figure 4.13 shows that groundwater

in the backfill in the western end of the pit flows continually towards the pit void for the 100

year modelled period. Figure 4.14 shows that nearly all particles within the backfill in the

eastern part of the pit initially move towards the pit void, but some then change direction at

around Year 45 to Year 50 and migrate towards the Pages River. This reflects the point at

which rising water levels in the pit causes a reversal in the hydraulic gradient, as discussed

above. Water from the eastern edge of the pit then takes between 15 and 30 years to reach

the river after this hydraulic reversal has occurred.

The water from the pit void itself has a slightly lower salinity than the Pages River (360 mg/L

to 375 mg/L TDS compared with 450 mg/L TDS average for Pages River) and therefore pit

void salinity does not pose a risk to Pages River.

Mass balance analysis shows that most of the movement between the north eastern end of

the pit and the river is mainly through Layers 3 and 5 (with some flow via Layers 4 and 6).

The weighted average TDS of the aquifer water in these layers is lower than the 733 mg/L to

777 mg/L TDS range quoted previously for the groundwater within the spoil rock mass. Based

on the relative flow rates and in-situ salinity concentrations within each aquifer layer that

flows to the river, the non-impacted salinity of the groundwater moving from the pit area to

the river would be around 580 mg/L. Under a worst case scenario, the presence of the pit

void and the mine spoil could therefore increase the salinity of the groundwater flowing from

the pit to the river by a maximum of around 157 - 193mg/L TDS. This is a maximum,

transient peak that in reality would be diluted within the existing groundwater. The impact

on total salinity within the river will be negligible.



Page 51 March 2009

The maximum flow rate from the pit area to the river is less than 100 kL/d during the 100

year modelled period. Based on the average (mean) river flow rate of 108,000 kL/d, and an

average measured river TDS of 450mg/L, the maximum transient impact from the effect

described above would result in a salinity increase within the river of between 0.12 mg/L and

0.16 mg/L (around 0.03%).

Water from the pit void will progressively move through the spoil and reduce salinity between

the pit void and the eastern half of the spoil area. The long-term impact will therefore be to

maintain, or even slightly improve, the water quality of the groundwater between the pit area

and Pages River.

4.6.4 Salinity of Drainage From Out-of-Pit Overburden Dump

Overburden material produced during mining, which is not able to be backfilled in the pit, is

to be stored in out-of-pit overburden dumps. Unsaturated zone modelling has been

undertaken to assess the salinity of drainage likely to arise from water draining through this

overburden material, and to determine potential travel times of any drainage from within the

overburden material to the underlying water table. Particle tracking utilising the transient

Bickham Model during the 100 year post-mining recovery period was then undertaken to

determine estimated travel times from the water table beneath the overburden dumps to the

Pages River. Full details and results of the modelling undertaken are reported in Annexure

F.

Unsaturated zone modelling predicted a maximum drainage water concentration of

approximately 650 mg/L TDS, below the range of the salinity of the local groundwater in the

alluvium. This peak concentration of drainage water is predicted to last for up to 5 years with

any salt present taking between 10 and 15 years to reach the base of the overburden dump.

Salinity within the overburden dump materials are predicted to subsequently dissipate over a

period of 20 to 30 years.

Particle tracking from the Bickham Model (Figure 4.15) indicates minimum travel times from

the base of the overburden dump to the river of 15 to 25 years from the eastern edge of the

northern out-of-pit overburden dump, which is the closest to the Pages River. From the

central sections of the dump, travel times were greater than 60 years.

Combining the travel times indicated from the Bickham Model with the times of drainage

water arrival to the water table (as determined through unsaturated zone modelling)

indicates that the earliest appearance of drainage water in the Pages River is likely to be

approximately 20 to 25 years from the commencement of dump construction. Drainage water

from the thicker sections of the dump would potentially not reach the river within 100 years.

4.7 Bickham Model Mass Balance Evaluation

The discrepancy between the cumulative volumes at the end of each stress period (i.e. the

difference between the inflow and the outflow rates of the reported model mass balance) is a

good indicator for evaluating the stability of the numerical solution.

The Bickham Model runs were carried out with a head closure criterion of 0.05 m to enhance

the stability of the numerical solution and to achieve a good mass balance for the entire

model. The cumulative mass balance discrepancy plot for the Base Case predictive modelling

is presented in Figure 4.16, and shows that the Bickham model performance is consistent

with the modelling guideline criterion of a discrepancy of less than 1%.

PREDICTED PIT VOID WATER LEVEL DURING RECOVERY SIMULATION FIGURE 4.11

POST MINING PIT VOID SALINITY FIGURE 4.12

PARTICLE TRACKING FOR THE EASTERN SIDE OF THE PIT FIGURE 4.14

PARTICLE TRACKING FOR THE WESTERN SIDE OF THE PIT FIGURE 4.13

CUMULATIVE MASS BALANCE DISCREPANCY PLOT FIGURE 4.16

PARTICLE TRACKING PLOT FOR THE OUT-OF-PIT OVERBURDEN DUMP FIGURE 4.15

-0.5

-0.4

-0.3

-0.2

-0.1

0

0 2 4 6 8 10 12 14 16 18 20 22 24 26

Year

Dis

cre

pa

nc

y(%

)



Page 61 March 2009

4.9 Uncertainty Analysis

Uncertainty analysis was carried out using the parameters that were found to cause the

highest model sensitivity (i.e. Kh in the G Seam and Kv in the Bickham Formation). This

involved re-running the predictive model, with each of the high-sensitivity parameters

changed to determine the impact of the change on pit inflows and baseflow impacts.

The uncertainty analysis modelling was undertaken using a single 25-year model run of the

mining period, rather than the 19 consecutive time-slice model used for the Base Case

predictive modelling of mining impacts, as it involved much shorter run times and simpler

data processing procedures. The single 25-year simulation was found to give consistent

results to the 19 time-slice model, and was therefore deemed suitable for use in the

uncertainty analysis.

It was found from sensitivity analysis of the model calibration performance that the model is

most sensitive to a higher horizontal hydraulic conductivity in the G Seam (Layer 6) and a

higher value of the vertical hydraulic conductivity in the Bickham Formation (Layer 2).

Considering that most of the mine dewatering inflow comes from the G Seam (Layer 6) and

the Bickham Formation (Layer 2), the higher sensitivity values of the horizontal and vertical

hydraulic conductivity for these layers were selected for uncertainty analysis.

Table 4.4 summarises the results of impacts on predicted inflow rates from possible

uncertainty in aquifer parameters of Layers 6 and 2. Figure 4.17 illustrates the predicted

dewatering rates with increased horizontal hydraulic conductivity in the G Seam and

decreased vertical hydraulic conductivity in the Bickham Formation.

The uncertainty prediction runs revealed that increasing the horizontal hydraulic conductivity

(Kh) in Layer 6 by 100% (from 0.1 m/d to 0.2 m/d) would increase the yearly average

dewatering rate by 12% (from 0.90 ML/d to 1.01 ML/d). Conversely, decreasing the vertical

hydraulic conductivity (Kv) in Layer 2 by a factor of 10 (from 0.002 m/d to 0.0002 m/d)

would reduce the average dewatering rate by just 3% (from 0.90 ML/d to 0.87 ML/d)).

The results show that prediction uncertainties in regard to the horizontal hydraulic

conductivity value for the G Seam (Layer 6) are more significant in relation to the mine

dewatering rates than changes to the vertical hydraulic conductivity in the Bickham

Formation, but overall do not substantially affect predicted mine inflow rates as shown in

Table 4.5 and Figure 4.17. In simple terms, the range of uncertainty in predicted

dewatering rates is small.

Figure 4.17 also presents a baseflow comparison between the Base Case and the

uncertainty model run predictions. The uncertainty analysis results show that predicted

baseflows are very consistent during the early stages of mining up to mine year 13, but show

some divergence thereafter to the end of mining (Year 25).

The results reveal that increasing the horizontal hydraulic conductivity in Layer 6 by a factor

of 2 (from 0.1 m/d to 0.2 m/d) would increase the total baseflow reduction at the end of

mining year 25 by around 21% (from 115 KL/d to 140 KL/d). Decreasing the vertical

hydraulic conductivity in Layer 2 by a factor of 10 (from 0.002 m/d to 0.0002 m/d) would

lead to a 10% greater total baseflow reduction (from 115 KL/d to 126 KL/d).

These results are consistent with the uncertainty results for impacts on mine dewatering rate

However, the range of uncertainty in predicted baseflows is not significant. At all times there



Page 62 March 2009

is predicted to be a significant net flow from the groundwater to Pages River, in all river

reaches.

Table 4-4 Bickham Model Range of Uncertainty Predictions in Terms of Predicted

Inflow Rates

Uncertainty Analysis: Horizontal Hydraulic Conductivity of the G Seam (Layer 6)

Calibrated Kh High Kh

Layer 6 0.1 m/d 0.2 m/d

SRMS % 6.23% 7.76%

Total DewateringRate

Mine Inflow Rates (ML/d)for Calibrated Kh

Mine Inflow Rates (ML/d)for High Kh

Min 0.03 0.08

Max 1.82 1.91

Ave 0.90 1.01

Uncertainty Analysis: Vertical Hydraulic Conductivity of the Bickham Formation(Layer 2)

Calibrated Kv Low Kv

Layer 2 0.002 m/d 0.0002 m/d

SRMS % 6.23% 7.74%

Total DewateringRate

Mine Inflow Rates (ML/d)for Calibrated Kv

Mine Inflow Rates (ML/d)for Low Kv

Min 0.03 0.02

Max 1.82 1.71

Ave 0.90 0.87

PREDICTED PAGES RIVER BASEFLOW AND MINE DEWATERING RATES (UNCERTAINTY ANALYSIS) FIGURE 4.17

0

100

200

300

400

500

600

700

800

900

0 2 4 6 8 10 12 14 16 18 20 22 24 26

Year

To

tal

Bas

eflo

w (

m3 /d

)

Base Case

2 x Kh G-Seam (Layer 6)

0.1 Kv Bickham Formation (Layer 2)

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 2 4 6 8 10 12 14 16 18 20 22 24 26

Year

To

tal

Dew

atei

ng

Rat

e (m

3 /d)

Base Case

2 x Kh G Seam (Layer 6)

0.1 Kv Bickham Formation (Layer 2)



Page 64 March 2009

4.10 Impact of Old Mine Workings

The presence of old mine workings in the Bickham Project area has been documented (MEGS,

2006). The best estimates of the extent of the old workings based on research of old mine

records, is that they were unlikely to have extended more than 50m from the old mine shaft,

due to ventilation limitations. The Bickham Model has been used to evaluate the potential

influence of the old mine workings on the predicted inflow rates and impacts on river

baseflows.

The shafts accessing the old mine workings are located between the eastern end of the pit

and Pages River Reaches 106 and 110. Since the extent of the old mine workings is

uncertain, two impact assessment scenarios were considered.

An initial model run was carried out, with the old workings conservatively assumed to extend

for a distance of around 200m from the shaft locations (ie about four times further than the

most likely distance). The assumed mine extent is shown as Scenario 1 on Figure 4.18. A

second extremely conservative and improbable scenario was run, with the workings assumed

to extend radially for a distance of 400 m from the old shafts, shown as Scenario 2 on

Figure 4.18.

The old mine workings were simulated in the model as open voids in the G Seam (Layer 6),

with horizontal and vertical hydraulic conductivity of 100 m/d and a specific yield of 0.5

(allowing for remnant pillars, roof and floor coal and partial collapses). All other parameters

in the model were retained at the values used for the Base Case prediction simulations

described in Sections 3 and 4.

The two scenarios were first run for a 5-year period without any mine development, to

establish steady state conditions before starting the simulation of mining impacts. The two

scenarios were then run as sequential yearly time slices for a further five years, simulating

only the first five years of the mine plan described in Section 4.1 (ie until mining has

commenced in the G Seam at the north-eastern end of the proposed Bickham Mine), but with

the assumed old mine workings added.

The impacts on Pages River baseflow and pit inflows from the proposed Bickham mining with

the two old mine workings scenarios were assessed and are summarised, along with Base

Case data for comparison in Table 4.5, and shown diagrammatically in Figure 4.19.

In both scenarios, like the Base Case, there is a positive net flow from the groundwater to the

river at all times and the impacts derived from scenarios which include the old mine workings

are also almost identical with the Base Case prediction.

The results further illustrate that the pre-mining Pages River baseflows are not significantly

different due to the presence of the void space in the G seam coinciding with the old

workings. Hence even in the improbable event that the old mine workings were to extend for

400m, water would not drain from the river to the pit. There would still be a strong net

groundwater flow to the river.

Predicted Bickham pit inflows under the two old mine scenarios (Figure 4.19) are also

virtually identical with the base case prediction.

AS

SU

MED

EX

TEN

TS

OF O

LD

MIN

E W

OR

KIN

GS

FO

R U

NC

ER

TA

INTY

AN

ALY

SIS

FIG

URE 4

.18

Sce

nario

2S

cena

rio 1

PREDICTED PAGES RIVER BASEFLOW AND PIT INFLOWSIMPACT OF OLD MINE WORKINGS COMPARED TO BASE CASE(YRS 1 TO 5) FIGURE 4.19

0

100

200

300

400

500

600

700

800

900

1000

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Year

Bas

eflo

w (

m3/

d)

Total Baseflow (Base Case)

Total Baseflow (Old Mine Workings - Scenario 1)

Total Baseflow (Old Mine Workings - Scenario 2)

0

50

100

150

200

250

300

350

400

450

500

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Year

To

tal

Pit

In

flo

w (

m3 /d

)

Proposed Bickham Mine

Old Mine Workings - Scenario 1

Old Mine Workings - Scenario 2



Page 67 March 2009

Table 4-5 River Baseflow Reduction - Potential Impact of the Old Mine Workings

RiverReach

YearBickham Base Case

(kL/d)Old Mine Workings Scenario 1

(kL/d)Old Mine Workings Scenario

2 (kL/d)

1 0.0 -0.1 0.0

2 -0.3 -0.3 -0.2

101 3 -1.1 -1.2 -0.8

4 -2.3 -2.4 -1.7

5 -3.3 -3.2 -2.4

1 -0.4 -0.4 -0.2

2 -1.3 -1.2 -0.7

102 3 -3.9 -3.8 -2.4

4 -7.1 -6.9 -4.7

5 -8.9 -8.3 -5.9

1 -1.3 -1.2 -0.5

2 -2.9 -2.6 -1.3

103 3 -6.2 -5.6 -3.0

4 -9.8 -8.9 -5.1

5 -12.0 -10.5 -6.3

1 -0.1 -0.1 0.0

2 -0.3 -0.2 -0.1

104 3 -0.7 -0.4 -0.3

4 -1.1 -0.7 -0.5

5 -1.3 -0.8 -0.6

1 -0.1 0.0 0.0

2 -0.1 -0.1 -0.1

105 3 -0.4 -0.2 -0.2

4 -0.7 -0.3 -0.4

5 -0.8 -0.4 -0.5

1 0.0 0.0 0.0

2 -0.1 0.0 0.0

106 3 -0.2 -0.1 -0.1

4 -0.3 -0.1 -0.2

5 -0.3 -0.2 -0.3

1 0.0 0.0 0.0

2 -0.1 0.0 0.0

107 3 -0.2 -0.1 -0.2

4 -0.3 -0.2 -0.3

5 -0.4 -0.3 -0.4

1 -0.9 -0.9 -0.3

2 -4.7 -4.4 -3.0

108 3 -19.9 -19.3 -14.9

4 -33.0 -32.2 -26.2

5 -35.8 -31.8 -26.3

1 0.0 0.0 0.0

2 -0.1 -0.1 -0.1

109 3 -0.3 -0.3 -0.2

4 -0.5 -0.4 -0.4

5 -0.6 -0.5 -0.4

1 -1.2 -1.1 -1.6

2 -3.1 -3.2 -5.4

110 3 -9.6 -9.8 -21.1

4 -14.5 -16.6 -36.9

5 -15.9 -19.6 -43.1

1 -0.2 -0.2 0.0

2 -0.5 -0.5 -0.1

111 3 -1.8 -1.7 -0.3

4 -2.7 -2.5 -0.5

5 -2.9 -2.5 -0.6

1 -0.2 -0.2 -0.1

2 -0.9 -0.8 -0.5

112 3 -3.8 -3.7 -2.8

4 -6.2 -6.1 -4.8

5 -6.8 -6.1 -4.9



Page 68 March 2009

RiverReach

YearBickham Base Case

(kL/d)Old Mine Workings Scenario 1

(kL/d)Old Mine Workings Scenario

2 (kL/d)

1 -0.1 -0.2 -0.2

2 -0.9 -0.9 -0.7

113 3 -3.9 -3.8 -3.2

4 -6.7 -6.6 -5.6

5 -8.1 -7.4 -6.4

4.11 High Conductivity Zone between Mine and Long Pool on Pages River

The hydraulic conductivity zone map for the G Seam (Layer 6) shown on Figure 4.20

includes a high hydraulic conductivity zone (Kh = 30 m/d) adjacent to Pages River Reaches

106 and 110. This high conductivity zone is situated in the region of G Seam close to

outcrop/subcrop, where hydraulic testing revealed higher hydraulic conductivities.

Due to the steep terrain, it was not possible to install any piezometers or conduct hydraulic

testing south of this zone along the western side of the long pool on Pages River. In this

area, a relatively low hydraulic conductivity value was adopted for Layer 6, based on the lack

of reported groundwater intersections in exploration holes OH04 and OH08 (Figure A3.12).

In order to evaluate the potential impact of high conductivity in the G Seam within this area,

the high Kh zone was extended south to the limit of outcrop of the G Seam at river level, as

shown in Figure 4.20, and a further predictive model run carried out. This zone covers

Pages River Reaches 106, 107, 108, 109, 110 and 111 (see Figure 3.2).

The Bickham Model was used to evaluate the impact of this scenario on Pages River

baseflows for all thirteen river reaches (as shown on Figure 3.2). The model was initially

run for a 5-year period without any mine development but with the extended high hydraulic

conductivity zone to establish steady state conditions. After that, the model was run as

sequential yearly time slices to simulate the first five years of the mine plan, when mining is

planned to take place at the north-eastern end of the pit closest to this area.

The predicted impacts on Pages River baseflows from the proposed Bickham mining, with the

extended high hydraulic conductivity zone, are plotted with the Base Case prediction for

comparison on Figure 4.21.

The results show that marginally higher baseflow reductions would result if the high hydraulic

conductivity zone were to extend throughout the entire G Seam outcrop/subcrop region. The

predicted total reduction in Pages River baseflow under this scenario is around 100 kL/d at

the end of mine Year 5 compared with a total reduction of about 97 kL/d from the Base Case

predictive model run.

This confirms that the predicted impact on river baseflows of a more extensive high hydraulic

conductivity zone is not significant.

ASSUMED HIGH CONDUCTIVITY ZONES IN THE G-SEAM LAYER ADJACENT PAGES RIVER FIGURE 4.20

PREDICTED BASEFLOW REDUCTION DURING THE FIRST FIVE YEARS OF MINING HIGH

HYDRAULIC CONDUCTIVITY SCENARIO (COMPARISON WITH BASE CASE) FIGURE 4.21

River Reach 106

High Conductivity Zone

River Reach 106Extended

High Conductivity Zone

River

Reach

110

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

0 1 2 3 4 5Year

To

tal

Ba

se

flo

wR

ed

uc

tio

n(m

3/d

)

Base Case

High Conductivity Scenario

River

Reach

110



Page 70 March 2009

5. MODEL LIMITATIONS

The Bickham groundwater model development has been supported by an extensive program

of acquisition and analysis of groundwater and surface water monitoring data over a 6 year

period. This period included both natural and imposed stresses. The natural system has

been stressed firstly by extended drought conditions between 2003 and 2007, and secondly

by the imposed stress of the 6-month bulk sample dewatering in 2004. These two factors

have greatly assisted the calibration of the groundwater model, and enhanced the reliability

of the model predictions.

Nevertheless, the model is a simplified representation of the actual groundwater and surface

water environment, and therefore has some limitations. The bulk sample dewatering was

also of limited duration and areal extent relative to the proposed mining operation, and the

model predictions will need to be verified on an ongoing basis as the mine proceeds.

Due to uncertainties in some model input parameters, certain limitations apply to the

Bickham Model. These are summarised below:

It is possible that actual mine inflows will be lower than predicted in the Bickham

Model, and the resultant impacts would also be less than those predicted. While it is

known that there are a number of discontinuities in the rock mass, such as

impermeable faults, which will limit the extent of drawdown and baseflow impacts and

groundwater inflows, only those faults revealed during the bulk sample dewatering or

mapped on the published geological maps have been included in the model. Some

short-scale spatial variations in parameters (not necessarily related to faults) have

also been specified in some areas to better match model predictions to the observed

monitoring bore responses to the bulk sample dewatering. However, due to the

fractured nature of the hard rock aquifer system, with a high degree of variability in

the distribution and continuity of permeable flow paths and zones of reduced

permeability, it is expected that other discontinuities will be encountered. Hence

there is some uncertainty with respect to the distribution of hydraulic conductivity, in

the vertical as well as horizontal direction, which will likely tend to reduce the actual

mine inflows below the predicted rates, as well as the resultant impacts on both

groundwater levels and baseflows.

While it is also possible that some zones of higher permeability may be encountered

in the pit, that may lead to short term higher rates of inflow at times, it is expected

that the discontinuities will limit the potential for higher total rates of inflow longer

term.

Recharge is included in the Bickham Model as a constant process based on mean

annual rainfall rates, and climatic variability has not been incorporated in prediction

runs. Recharge values have been applied within a plausible range to obtain a

calibrated model, but site-specific values have not been verified. Model sensitivity

assessment has shown that the model is not sensitive to those large areas in the

model with recharge rates of 4% or less of annual rainfall, and hence there is little

uncertainty in relation to the model recharge configuration across the bulk of the

modelled area. The sensitivity analysis showed, however, that the model results were

sensitive to recharge rates in some small areas (see Section 3.3 for sensitivity

analysis, and Annexure C for recharge zones). It is possible that the model is

affected by non-uniqueness in this area, meaning that an alternative parameterisation



Page 71 March 2009

could potentially achieve model calibration, with lower recharge in these areas, along

with decreased permeability values and/or with additional hydraulic discontinuities).

The current arrangement of higher recharge and permeability is a conservative model

setup, in that it would likely over-estimate baseflow impacts on rivers and streams,

and would likely over-estimate the extent of drawdown effects.

Evapotranspiration is included in the Bickham Model at constant mean annual rates,

and climatic variability has not been incorporated. The maximum possible rate of

evapotranspiration in the Bickham Model is 650mm/yr (except for the pit void area

during post mining recovery), based on the Australian Climatic Atlas.

Evapotranspiration is acting in the Bickham Model in areas of shallow (<3m) water

levels, to represent possible groundwater dependent ecosystems. This configuration

is a best estimate, and is implemented according to best practice approaches, but

could be improved as mining proceeds with benefits of operational experience and

monitoring data.

In conclusion, the Bickham Model is based on a sound data set, but the heterogeneous nature

of the hydraulically discontinuous aquifer system invariably results in some model

uncertainties. The model results can be regarded as a best estimate based on the currently

available data, and the model is considered a suitable predictive tool to simulate the complex

multi-layered Bickham aquifer system.



Page 72 March 2009

6. INDEPENDENT REVIEW

Development and use of the Bickham Model has been independently reviewed by Associate

Professor Noel Merrick. Dr Merrick has been involved at all stages of the model development

including model calibration and prediction simulations.

Dr Merrick’s review report is presented in Annexure G.



Page 73 March 2009

7. REFERENCES

Aquaterra (2006). Groundwater Model Design Report – Bickham Coal Mine Project. Report

to Peter Dundon and Associates, 5th May, 2006.

Beckett, J (1988). The Hunter Coalfield and accompanying 1:100,000 geological map.

Geological Survey Report No GS 1988/051, published by NSW Department of Mineral

Resources.

Bureau of Meteorology (2001). Climatic Atlas of Australia. Evapotranspiration.

Commonwealth of Australia.

Department of Infrastructure, Planning and Natural Resources (2005). Draft Guidelines for

Management of Stream/Aquifer Systems in Coal Mining Developments – Hunter Region.

Draft guideline, dated April, 2005.

Department of Planning (2005). Coal Mining Potential in the Upper Hunter Valley – Strategic

Assessment. Dated December 2005.

ESI (2000-2004). Groundwater Vistas, Version 4 User’s Manual.

URL: www.groundwatermodels.com

Fityus S, Hancock G and Wells T (2007). The Environmental Geotechnics of Coal Mine Spoil.

Centre for Geotechnical and Materials Modelling, University of Newcastle, NSW.

Web publication at http://livesite.newcastle.edu.au

McDonald M G and Harbaugh A W. (1988) A modular three- dimensional finite-difference

ground-water flow model: U.S. Geological Survey Techniques of Water-Resources

Investigations.

MDBC (2001). Groundwater flow modelling guideline. Murray-Darling Basin Commission.

URL: www.mdbc.gov.au/nrm/water_management/groundwater/groundwater_guides

Mining and Exploration Geology (MEGS) Pty Ltd (2006). Bickham Coal EL 5306 & 5888

Outcrop and Near Surface Geological Interpretation. Dated September 2006.

Nathan, R.J. and McMahon, T.A. (1990). Evaluation of automated techniques for baseflow

and recession analysis. Water Resources Research, 26(7), pp.1465-1473.

Peter Dundon and Associates (2003). Proposed Bickham South Bulk Sample – Groundwater

Management. Report to Bickham Coal Company, dated June 2003.

Peter Dundon and Associates (2005a). Bickham South Bulk Sample Dewatering. 6-monthly

Report. Period ending 31 December 2004. Report to Bickham Coal Company, dated January

7th, 2005.

Peter Dundon and Associates (2005b). Submission in Response to: Coal Mining Potential in

the Upper Hunter Valley, Strategic Assessment (March, 2005). Report to Bickham Coal

Company, April 28th, 2005.

Peter Dundon and Associates (2005c). Bickham South Bulk Sample Dewatering. 6-monthly

Report. Period ending 30 June 2005. Report to Bickham Coal Company, July 25th, 2005.

Robert Carr and Associates (2002). Water Chemistry Analysis Bulk Sample Overburden

Bickham Coal. Report to Bickham Coal Company October 15th 2002.

http://www.groundwatermodels.com/

http://livesite.newcastle.edu.au/

http://www.mdbc.gov.au/nrm/water_management/groundwater/groundwater_guides

ANNEXURE A

TRANSIENT CALIBRATION

ANNEXURE A BICKHAM LAYER ELEVATIONS

ANNEXURE B

BICKHAM MODEL STEADY STATE CALIBRATION (LAYER BOUNDARY CONDITIONS AND GROUNDWATER CONTOUR MAPS

AND HEAD RESIDUAL MAP)

ANNEXURE B BICKHAM MODEL STEADY STATE CALIBRATION

Layer 1 Steady State Groundwater Contour Map in mAHD


Hea

d R

esid

ual

Map

fo

r B

ickh

am S

tead

y S

tate

Cal

ibra

tio

n(R

esid

ua

l is th

e a

bsolu

te v

alu

e o

f th

e d

iffe

ren

ce b

etw

ee

n t

he

me

asure

d a

nd

mo

de

lled

he

ad

)

AN

NEX

UR

E B

BIC

KH

AM

MO

DEL S

TEA

DY

STA

TE C

ALIB

RA

TIO

N

299

000

3000

00

3010

00

3020

00

30

30

00

30

400

030

500

030

600

0307

00

0

64

74

000

64

75

000

64

76

000

64

77

000

Resi

dual (

m)

0

to

1

1

to

2

2

to

3

3

to

4

4

to

5

5

to

6

6

to

7

7

to

10

1

0 to

12

1

2 to

14

1

4 to

17

BC

OH

114

BC

OH

115

OH

94

OH

70A

OH

70B

OH

70C

OH

93O

H69

AO

H69

BO

H79

OH

78O

H75

AO

H75

BO

H95

DW

1D

W2

OH

111A

OH

111B

OH

71A

OH

71B

OH

71C

OH

90

OH

56B

OH

38

DD

H99

OH

97

OH

102

OH

100

OH

77

OH

110

OH

105

OH

112

OH

108

OH

106

OH

113A

OH

113B

DD

H85

B

OH

92

OH

87O

H88

OH

91

OH

65

Pages

River

Kin

gdon P

onds

ANNEXURE C

BICKHAM MODEL CALIBRATED PARAMETERS

ANNEXURE C BICKHAM MODEL CALIBRATED PARAMETERS

HORIZONTAL AND VERTICAL HYDRAULIC CONDUCTIVITY OF LAYER 1



CALIBRATED RECHARGE ZONE (APPLIED TO THE HIGHEST ACTIVE LAYER)

CALIBRATED EVAPOTRANSPIRATION ZONE(APPLIED TO THE HIGHEST ACTIVE LAYER)

ANNEXURE D

TRANSIENT CALIBRATION (OBSERVED versus SIMULATED HYDROGRAPHS)

ANNEXURE D BICKHAM MODEL TRANSIENT CALIBRATION

360

370

380

390

400

410

420

430

440

450

460

01-Jan-02 01-Jan-03 01-Jan-04 01-Jan-05 01-Jan-06

Wate

r L

evel

(m A

HD

)OH70C (Layer 2)

Observed Simulated

360

370

380

390

400

410

420

430

440

450

460


Wate

r L

evel

(m A

HD

)

OH72 (Layer 2)

Observed Simulated


360

370

380

390

400

410

420

430

440

450

460


Wate

r L

evel

(m A

HD

)OH87 (Layer 2)

Observed Simulated

360

370

380

390

400

410

420

430

440

450

460


Wate

r L

evel

(m A

HD

)

OH88 (Layer 2)

Observed Simulated


360

370

380

390

400

410

420

430

440

450

460


Wate

r L

evel

(m A

HD

)OH91 (Layer 2)

Observed Simulated

360

370

380

390

400

410

420

430

440

450

460


Wate

r L

evel

(m A

HD

)

OH94 (Layer 2)

Observed Simulated


360

370

380

390

400

410

420

430

440

450

460


Wate

r L

evel

(m A

HD

)OH71B (Layer 3)

Observed Simulated

360

370

380

390

400

410

420

430

440

450

460


Wate

r L

evel

(m A

HD

)

OH73 (Layer 3)

Observed Simulated


360

370

380

390

400

410

420

430

440

450

460


Wate

r L

evel

(m A

HD

)OH77 (Layer 3)

Observed Simulated

360

370

380

390

400

410

420

430

440

450

460


Wate

r L

evel

(m A

HD

)

OH93 (Layer 3)

Observed Simulated


360

370

380

390

400

410

420

430

440

450

460


Wate

r L

evel

(m A

HD

)OH99 (Layer 3)

Observed Simulated

360

370

380

390

400

410

420

430

440

450

460


Wate

r L

evel

(m A

HD

)

OH70B (Layer 4)

Observed Simulated


360

370

380

390

400

410

420

430

440

450

460


Wate

r L

evel

(m A

HD

)OH71C (Layer 4)

Observed Simulated

360

370

380

390

400

410

420

430

440

450

460


Wate

r L

evel

(m A

HD

)

OH56B (Layer 5)

Observed Simulated


360

370

380

390

400

410

420

430

440

450

460


Wate

r L

evel

(m A

HD

)OH57 (Layer 5)

Observed Simulated

360

370

380

390

400

410

420

430

440

450

460


Wate

r L

evel

(m A

HD

)

OH69B (Layer 5)

Observed Simulated


360

370

380

390

400

410

420

430

440

450

460


Wate

r L

evel

(m A

HD

)OH65 (Layer 6)

Observed Simulated

360

370

380

390

400

410

420

430

440

450

460


Wate

r L

evel

(m A

HD

)

OH69A (Layer 6)

Observed Simulated


360

370

380

390

400

410

420

430

440

450

460


Wate

r L

evel

(m A

HD

)OH70A (Layer 6)

Observed Simulated

360

370

380

390

400

410

420

430

440

450

460


Wate

r L

evel

(m A

HD

)

OH71A (Layer 6)

Observed Simulated


360

370

380

390

400

410

420

430

440

450

460


Wate

r L

evel

(m A

HD

)OH75A (Layer 6)

Observed Simulated

360

370

380

390

400

410

420

430

440

450

460


Wate

r L

evel

(m A

HD

)

OH78 (Layer 6)

Observed Simulated


360

370

380

390

400

410

420

430

440

450

460


Wate

r L

evel

(m A

HD

)OH79 (Layer 6)

Observed Simulated

360

370

380

390

400

410

420

430

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ANNEXURE E

BICKHAM MODEL RECOVERY RUN RESULTS

ANNEXURE E BICKHAM MODEL RECOVERY RUN RESULTS

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ANNEXURE F

BICKHAM OUT-OF PIT OVERBURDEN DUMPDRAINAGE MODELLING

1. BACKGROUND AND OBJECTIVES

Overburden resulting from mining activities, consisting predominantly of sandstone, siltstone,conglomerate, mudstone and minor coal, will be placed partly in an overburden dump whichoverlies the edge of an alluvial flat near the Pages River immediately north of the proposedmine. Concerns have been raised regarding potential impacts of possible saline drainage waterfrom the dump into the alluvium and thence to the river. To investigate this problem, a 1Dunsaturated flow and solute transport model has been developed to assess the following:

1. The time frame and amount of drainage from the proposed Overburden Dump to the watertable.

2. The salinity of drainage from the proposed Overburden Dump.

The groundwater model of the Bickham Mine, the “Bickham Model”, was also subsequently usedto assess the travel time from the overburden dump to the river. The footprint of the proposedOverburden Dumps are shown in Figure 1.

2. CONCEPTUAL MODEL

Two aspects of the Overburden Dump were developed into conceptual models, detailed below,from which the unsaturated zone numerical models were developed.

1. A vertical section consisting of 100m of sand (representing the dumped overburdenmaterial) for the thickest section of the dump (Figure 2).

2. A vertical section consisting of 0.75m cap, 15m of sand (representing dumped overburdenmaterial) and 7m of base (representing in situ alluvium to the top of the water table).This represented the toe section of the dump (Figure 3. This model was also run withoutthe 0.75m cap as a sensitivity run.

3. METHODOLOGY

The model was constructed in two stages:

1. To simulate water movement through the soil, this required basic textural and assumedsoil characteristics, thickness of layers and rainfall data.

2. Subsequently, to simulate solute transport, this required information about the verticalspatial salinity and recharge.

In addition, the Bickham Model (Aquaterra, 2009) was used to simulate particle movement fromthe proposed site of the overburden dump to the Pages River.

3.1 MODEL SELECTION

The primary model used to simulate the scenarios was LEACHP. LEACHP is an unsaturated zonemodel capable of modelling one dimensional flow and solute transport. In addition, Neuro Theta,a pedotransfer function program, was used to obtain soil hydraulic parameters based on soiltextural assumptions. HYDRUS, an unsaturated zone model, was also used to predict soilhydraulic parameters for some soils. LEACHP contains built in pedotransfer functions, howeverthey relate to British, South African and USA soils, whereas Neuro Theta was designed in Sydneyfor Australian soils.

Soil hydraulic parameters used in the LEACHP simulations were obtained using percentages ofsand, silt and clay or textural class (in the case of the overburden material) as input for NeuroTheta and the pedotransfer function component of HYDRUS. Given that different hydraulicparameters can cause variations in the output from unsaturated zone models, and thatpedotransfer function programs derived in different countries will give different results for thesame soil textures, a range of the parameters obtained from these programs were used in themodels. From this range, two sets of parameters were selected for use in consultation withPeter Dundon, to represent the expected range of soil hydraulic parameters for this site.

The Bickham Model (using MODPATH) was used in its transient state to simulate particlemovement from the overburden dump to the Pages River. Particle tracking was carried out forthe 100-year post mining recovery period, and hence incorporated the head and groundwaterflow changes arising during throughout the recovery period as the pit backfilled with water. Thefull details of this model can be found in the Bickham Coal Project Groundwater Model Report(Aquaterra, 2009).

3.2 ASSUMPTIONS

The following assumptions were made (for the 1D Model):

▼ Homogeneity within layers

▼ No preferential flow within layers

▼ Darcy’s Law is valid (i.e. flow is laminar and fluid is incompressible)

▼ No change in the compaction of the soil with time

▼ Chemical processes within the soil do not affect the salinity of the soil

▼ Complete mixing of solute

▼ No surface runoff

▼ No slope (model is a vertical 1-D section)

Sand soil hydraulic parameters were assumed for the overburden component of the model,based on representative saturated hydraulic conductivity and geological information. While thisdid not reflect the actual textural class (the waste rock dump will likely be a heterogeneous mixof boulder to clay sized rock fragments, ie poorly-sorted “gravel”), the hydraulic properties forcoarse sand are considered appropriate and conservative.

Simulating a gravel component in the unsaturated zone was not possible as the pedotransferfunction programs used did not exceed “coarse sand (200 - 2000μm)” in the particle sizedefinition. However, the mechanism through which the majority of the flow would occur incoarse gravel is different to sand. Water flowing through a sand travels primarily through thematrix or micropore component of the soil. Water travelling through poorly-sorted gravel travelsprimarily through large void spaces or macropores and is known as preferential flow. Watertravelling by preferential flow (gravels) will not completely mix with any waste rock pore waterpresent and hence will not carry the full concentration of salt from the waste rock. In addition,water travelling via preferential flow (gravels) may drain faster than water travelling through asand matrix. These assumptions mean that the model with a coarse sand assumption couldpotentially overestimate the quantity of salt leached from the waste rock and potentiallyoverestimate the time taken for drainage to occur.

Assumptions were also made in regards to the initial saturation of the soil. The saturationassumptions applied varied from total saturation, graduated saturation (i.e. water contentdecreasing down the profile), a mid range saturation of -100 kPa and completely dry soil. Thesescenarios were investigated to examine the impact of the full range of initial saturation, howeverit was assumed that either the graduated or mid range saturation would be more realistic thaneither a completely dry or saturated soil state.

The transient state of the Bickham Model was considered suitable for estimation of travel time ofparticles from the water table underneath the waste rock overburden dump to the river. Due tothe model being run in transient state changes in hydraulic gradient and flow were incorporatedinto the model run.. Note that particles in the simulation can only travel in saturated cells. Thisresults in particles having different travel times depending on the lateral hydraulic conductivityof the layer. Where cells become dry during modelling no flow can occur.

3.3 MODEL INPUTS

Model inputs for the vertical section consisting of 100m depth section of sand, representing thethickest section of the dump (Model 1) were:

▼ Rainfall and evaporation

▼ Soil water salinity of the overburden (700 mg/L – pers comm. Peter Dundon)

▼ Assumed soil hydraulic properties for sand as determined using Neuro Theta.

Model inputs for the vertical section consisting of 0.75m cap, 15 m of sand (representingdumped overburden material) and 7m of base, representing the toe section of the dump(Model 2) were:

▼ Soil water salinity of the overburden

▼ Rainfall and evaporation

▼ Percentages of clay, silt and fine and coarse sand (taken from Appendix A)

▼ Average salinity of the cap and base (taken from Appendix B)

The percentages of clay, silt, fine sand and coarse sand were used as input into both NeuroTheta and HYDRUS to obtain soil hydraulic parameters for this data. These were then examinedand sets representing the widest realistic range for the site were selected as inputs for theLEACHP model.

3.4 MODEL RUNS

Unsaturated

1. Model 1 (100m vertical sand) was run with varying initial water contents, ranging fromcompletely saturated to completely dry. From these runs, two models were selected torepresent an assumed minimum and maximum water content for the site.

2. Model 2 (toe of overburden) was initially run with different starting saturations, howeverdue to the difference in thickness of the toe compared to the centre, the starting watercontent did not significantly affect these simulations and hence it was discounted forfurther models.

3. Model 2 was then run with and without the cap and for the two selected sets of soilhydraulic parameters used for the cap and the base.

Saturated

1. A subsequent run of the Bickham Model in post-mining transient conditions was alsoundertaken with particles placed both along the eastern edge of the overburden dump,and within the central area of the overburden dump to determine travel times of particlesto the Pages River.

4. RESULTS

Results from Model 1 indicate that vertical drainage from the central section (overburdenthickness of approximately 100m) of the proposed dump, providing the overburden soil was notsaturated, would be in the order of 100 to 150 years (Figure 4). However, the degree of initialsaturation of the dumped materials affects the time taken for drainage to occur as a fullysaturated profile will drain almost immediately. All profiles eventually show a drainage rate ofbetween 0.12 and 0.14 mm/day or approximately 0.05 m per year.

As indicated in Section 2, the toe of the overburden was modelled both with and without a caplayer and for two different soil types, a topsoil containing 51% clay (“Topsoil 1/1” seeAppendix A) and a midlayer soil containing 22 % clay (“Midlayer 3/3” see Appendix A).

The results from Models 2 and 3 indicate that drainage would start after 10 to 15 years, at ratesof between 0.3 and 2 mm per day (Figure 5). Average yearly drainage for the four differentruns ranged from 145 to 224 mm/year (Table 1). Average drainage rates were higher with thecap present and when the midlayer soil was used.

Table 1: Drainage rates from Toe section of dump (Model 2)

Soil Used CapPresent

Average DailyDrainage(mm/day)

Median DailyDrainage(mm/day)

Maximum DailyDrainage(mm/day)

Average YearlyDrainage(mm/yr)

Midlayer 3/3 N 0.6 0.5 1.8 203

Topsoil 1/1 N 0.4 0.4 1.1 145

Midlayer 3/3 Y 0.6 0.6 2.1 224

Topsoil 1/1 Y 0.5 0.5 1.7 183

Figure 6 shows the concentration of salt in the drainage water over time with both the cappresent and absent on the toe of the overburden dump. The model indicates a maximumdrainage water concentration of approximately 650 mg/L. This is below the range of the salinityof the local groundwater in the alluvium underlying the toe of the dump (TDS range850-4300 mg/L and average 1850 mg/L; pers comm. Peter Dundon). This peak concentration ofdrainage water appears to last for up to 5 years, depending on the model scenario. Any saltpresent would take between 10 and 15 years to reach the base of the dump, and the salt storefrom the overburden dump materials would subsequently dissipate over between 20 and 30years. These models (2 and 3) represent a one-dimensional view of the toe of the overburdendump and it should be noted that as the thickness of the dump increases, the time for the salt toreach the base of the overburden dump will increase.

The particle tracking from the Bickham Model (Model 4) indicated minimum travel times to theriver of 15 to 25 years from the eastern edge of the overburden dump closest to the Pages

River. From the central sections of the dump, travel times were greater than 60 years(Aquaterra, 2009).

Combining the travel times indicated from the Bickham Model with the times of drainage waterarrival to the water table (as determined through unsaturated zone modelling) indicates that theearliest appearance of drainage water in the Pages River is likely to be approximately 20 to 25years from the commencement of dump construction. Drainage water from the thicker sectionsof the dump could potentially reach the river in excess of 100 years. It is important to note thatthere would be continuous output from the dump throughout this period, however this outputwould have a maximum predicted concentration of 650 mg/L, which is less than the meangroundwater (in situ) salinity.

5. CONCLUSION

Based on the above assessment, a likely scenario for drainage from the overburden dump couldbe as follows: initial drainage from the toe of the overburden starting from approximately 10years and reaching the Pages River within another 15 to 25 years. Thicker sections of the dumpwould contribute to drainage as time increases, potentially in excess of 150 years with amaximum predicted concentration of 650 mg/L, which is below the salinity range of the localgroundwater (850 to 4300 mg/L; pers comm. Peter Dundon). This flushing time wouldpotentially increase with depth of overburden dump. However, drainage should begin to occuras the dump is being constructed, so there may be some drainage from the start of theconstruction.

These conclusions were based on a conservative modelling approach that examined minimumtravel times and maximum concentrations. Travel times may be increased by changing hydraulicconditions and salinities may be decreased due to preferential flow.

6. REFERENCES

Aquaterra (2009). Bickham Coal Company – Groundwater Modelling Report (Ref: 059a)

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6

SOIL ANALYSIS DATA.PDF

APPENDIX A TO ANNEXURE F - SOIL TEXTURAL INFORMATION

REPRESENTATIVE WATER QUALITY.XLS

APPENDIX B TO ANNEXURE F - SALINITY OF GROUNDWATER

Bore15-Aug-06 18-Sep-06 05-Jun-07 25-Jul-07 15-Aug-06 05-Jun-07

ALS Ecowise ALS ALS ALS ALS ALS ALS

pH Value (Lab) 0.01 0.10 7.39 6.82 6.87 6.75 7.28 6.88pH Value (Field)Conductivity @ 25°C (Lab) μS/cm 1 10 2760 2850 3280 3160 2120 2690Conductivity (Field)Total Dissolved Solids (TDS) mg/L 1 5 1930 4300 1970 2300 1500 1690Total Suspended Solids (TSS) mg/L 2 16100 56 1400 176Turbidity NTU 1 5200 60.1 634 87.6Free CO2 mg/L 1 233 126 179 84

Total CO2 mg/L 1 912 538 622 363

Calcium mg/L 1 1 174 265 181 188 100 122Magnesium mg/L 1 1 114 144 118 123 71 87Sodium mg/L 1 1 340 337 356 357 295 322Potassium mg/L 1 1 4 8 7 10 5 8Hydroxide Alk as CaCO3 mg/L 1 <1 <1 <1 <1 <1 <1Carbonate Alk as CaCO3 mg/L 1 2 <1 <1 <1 <1 <1 <1Bicarbonate Alk as CaCO3 mg/L 1 2 375 771 468 503 263 317Sulphate mg/L 1 2 376 303 370 352 446 478Chloride mg/L 1 2 652 633 709 752 320 405

Silica mg/L 0.1 38.8 35.9 37.1 42.4Silicon mg/L 0.05 18.1Fluoride mg/L 0.1 0.1 0.3 0.2 0.5

Aluminium - Filtered mg/L 0.1/0.01 0.02 0.055 <0.01 315 0.02 0.01 <0.01 0.01Arsenic - Filtered mg/L 0.01/0.001 0.001 0.013 <0.001 0.048 0.005 0.002 <0.001 0.001Cadmium - Filtered mg/L 0.005/0.0001 0.00005 0.0002 <0.0001 0.0021 0.0001 0.0001 <0.0001 <0.0001Chromium - Filtered mg/L 0.01/0.001 0.001 ID <0.001 0.49 <0.005 <0.005 <0.001 <0.005Copper - Filtered mg/L 0.01/0.001 0.002 0.0014 <0.001 0.442 0.002 0.001 <0.001 0.002Lead - Filtered mg/L 0.01/0.001 0.00005 0.0034 <0.001 214 <0.001 <0.001 <0.001 <0.001Manganese - Filtered mg/L 0.01 0.01 1.9 0.002 0.099 4.79 6.51 0.003 2.8Nickel - Filtered mg/L 0.01/0.001 0.001 0.011 0.001 15.4 0.006 0.011 <0.001 0.003Selenium - Filtered mg/L 0.01 0.001 0.005 <0.01 0.0016 <0.01 <0.01 <0.01 <0.01Silver - Filtered mg/L 0.001 0.001 0.00005 <0.001 <0.001 <0.001 <0.001 <0.001Zinc - Filtered mg/L 0.01/0.001 0.005 0.008 0.685 0.782 0.013 0.025 0.109 0.025Boron - Filtered mg/L 0.1/0.01 0.01 0.37 <0.05 0.015 <0.05 <0.05 0.05 0.05Iron - Filtered mg/L 0.1 0.01 ID <0.05 0.001 4.67 3.11 <0.05 4.29Mercury - Filtered mg/L 0.0001 0.0001 0.00006 <0.0001 <0.05 <0.0001 <0.0001 <0.0001 <0.0001

Barium - Filtered mg/L 0.01Beryllium - Filtered mg/L 0.01 IDHexavalent Chromium mg/L 0.002 0.001Cobalt - Filtered mg/L 0.01 IDMolybdenum - Filtered mg/L 0.01 IDPhosphorus - Filtered mg/L 1Silicon - Filtered mg/L 0.1Strontium - Filtered mg/L 0.01Sulphur - Filtered mg/L 1Vanadium - Filtered mg/L 0.01 ID

WAD Cyanide mg/L 0.005 0.007

Ammonia as N mg/L 0.01 0.01 0.9 0.015 0.422 1.36 1.44 <0.01 1.38Nitrite as N mg/L 0.01 <0.01 <0.01 <0.01 0.046 <0.01 <0.01Nitrate as N mg/L 0.01 0.01 0.7 0.136 <0.01 <0.05 0.032 0.586 0.318Total Nitrogen as N mg/L 0.01Total Kjeldahl Nitrogen as N mg/L 0.1 <0.1 28.3 1.6 4.4 <0.1 1.6Total Phosphorus as P mg/L 0.01 0.01 0.19 18.4 0.34 1.6 0.27 0.62Reactive Phosphorus as P mg/L 0.01 0.01 0.19 <0.01 0.014 <0.01 0.26 0.052

Parameter Units

LOR ANZECC (2000)

Guideline Value for

Freshwater Ecosystem

TP02 TP06

Bore

ALS Ecowise

pH Value (Lab) 0.01 0.10pH Value (Field)Conductivity @ 25°C (Lab) μS/cm 1 10Conductivity (Field)Total Dissolved Solids (TDS) mg/L 1 5Total Suspended Solids (TSS) mg/L 2Turbidity NTU 1Free CO2 mg/L 1

Total CO2 mg/L 1

Calcium mg/L 1 1Magnesium mg/L 1 1Sodium mg/L 1 1Potassium mg/L 1 1Hydroxide Alk as CaCO3 mg/L 1Carbonate Alk as CaCO3 mg/L 1 2Bicarbonate Alk as CaCO3 mg/L 1 2Sulphate mg/L 1 2Chloride mg/L 1 2

Silica mg/L 0.1Silicon mg/L 0.05Fluoride mg/L 0.1

Aluminium - Filtered mg/L 0.1/0.01 0.02 0.055Arsenic - Filtered mg/L 0.01/0.001 0.001 0.013Cadmium - Filtered mg/L 0.005/0.0001 0.00005 0.0002Chromium - Filtered mg/L 0.01/0.001 0.001 IDCopper - Filtered mg/L 0.01/0.001 0.002 0.0014Lead - Filtered mg/L 0.01/0.001 0.00005 0.0034Manganese - Filtered mg/L 0.01 0.01 1.9Nickel - Filtered mg/L 0.01/0.001 0.001 0.011Selenium - Filtered mg/L 0.01 0.001 0.005Silver - Filtered mg/L 0.001 0.001 0.00005Zinc - Filtered mg/L 0.01/0.001 0.005 0.008Boron - Filtered mg/L 0.1/0.01 0.01 0.37Iron - Filtered mg/L 0.1 0.01 IDMercury - Filtered mg/L 0.0001 0.0001 0.00006

Barium - Filtered mg/L 0.01Beryllium - Filtered mg/L 0.01 IDHexavalent Chromium mg/L 0.002 0.001Cobalt - Filtered mg/L 0.01 IDMolybdenum - Filtered mg/L 0.01 IDPhosphorus - Filtered mg/L 1Silicon - Filtered mg/L 0.1Strontium - Filtered mg/L 0.01Sulphur - Filtered mg/L 1Vanadium - Filtered mg/L 0.01 ID

WAD Cyanide mg/L 0.005 0.007

Ammonia as N mg/L 0.01 0.01 0.9Nitrite as N mg/L 0.01Nitrate as N mg/L 0.01 0.01 0.7Total Nitrogen as N mg/L 0.01Total Kjeldahl Nitrogen as N mg/L 0.1Total Phosphorus as P mg/L 0.01 0.01Reactive Phosphorus as P mg/L 0.01 0.01

Parameter Units

LOR ANZECC (2000)

Guideline Value for

Freshwater Ecosystem

13-Sep-05 08-Dec-05 06-Apr-06 22-Jun-06 18-Sep-06 15-Dec-06 22-Mar-07 05-Jun-07 06-Jul-07 22-Dec-04 22-Dec-04 04-Mar-05 22-Mar-05 24-Jun-05 21-Sep-05 15-Dec-05 05-Apr-06 22-Jun-06 18-Sep-06

ALS ALS ALS ALS ALS ALS ALS ALS ALS Ecowise ALS ALS ALS ALS ALS ALS ALS ALS ALS

4.64 5.25 5.6 5.89 5.75 5.72 5.9 5.85 5.60 5.99 5.74 5.93 5.5 5.7 6.32 5.46 5.31 5.465 6.3 5.5 5.7 5.3 5.2

7590 8010 3730 3490 3270 3530 3910 3950 160 156 225 218 148 178 197 126 149 1266210 1700 5010 250 200 120

10200 7890 4500 5020 4560 4700 4140 4500 150 101 174 184 140 150 179 123 123 12148 27 26 16 50 9 6 110 66 19 2 <1

63.9 26.2 45.2 70.5 236 32.1 7.7 47 3.3 64.2 14.5 2.3 2.2427 261 294 320 259 302 44 183 180 62 173 264 180

461 307 394 399 319 408 136 209 219 119 195 288 203

493 465 500 478 394 461 422 435 4.7 3 10 9 3 9 12 3 3 3713 606 435 414 359 404 369 386 2.2 2 6 4 2 4 5 2 2 2110 151 156 130 98 125 107 112 12 13 13 15 13 17 21 11 13 1448 28 20 16 12 16 14 14 10 12 13 19 11 12 16 11 13 11<1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1<1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1<1 38 52 114 90 68 120 104 14 23 54 43 29 45 65 25 27 26

4120 5730 3390 3310 2670 2850 2460 2870 3.7 1 7 19 4 14 14 4 4 457 42.6 36.7 41.3 42.9 39.8 41.1 40.7 23 22 21.6 21 23.5 24.2 27.6 21.9 20.1 21.6

21.2 25.4 35.1 31.5 23.7 31.4 35 47.1 47.5 43.2 52 52.39.87 11.8 16.4 14.7 22.2 20.2 24.2 24.4<0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

38.2 0.96 0.08 <0.01 0.02 <0.01 0.02 0.01 0.01 <0.02 0.03 <0.01 0.07 0.03 0.01 0.08 0.03 0.04 <0.010.002 0.001 <0.001 <0.001 0.001 <0.001 0.001 0.001 0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.0010.0014 <0.0001 0.0002 <0.0001 <0.0001 <0.0001 <0.0001 0.0004 <0.0001 0.00008 0.0001 <0.0001 0.0002 <0.0001 <0.0001 <0.0001 0.0011 <0.0001 <0.0001<0.005 0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.005 <0.001 <0.002 <0.001 0.002 <0.001 <0.001 <0.001 <0.001 <0.001 0.001 <0.0010.181 0.002 0.004 0.003 0.001 0.002 0.004 0.005 0.003 0.002 0.001 0.003 0.008 0.001 0.002 0.011 0.003 0.007 <0.0010.096 0.002 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.002 0.002 0.002 0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.00138.4 32.4 15.1 12 6.684 7.06 9.13 5.68 7.55 0.042 0.046 0.007 0.073 0.05 0.106 0.086 0.048 0.052 <0.0012.66 0.916 0.245 0.147 0.151 0.196 0.127 0.15 0.193 0.018 0.02 0.034 0.034 0.019 0.016 0.025 0.018 0.02 <0.001

<0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.010 <0.001 <0.01 <0.01 <0.010 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01<0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001

7.88 2.4 0.052 0.077 0.31 0.358 0.055 0.324 0.393 0.079 0.083 0.092 0.407 0.063 0.039 0.083 0.067 0.179 <0.0050.26 0.24 0.12 0.11 0.08 0.08 0.08 0.08 0.09 0.03 0.03 0.05 <0.05 <0.05 <0.05 <0.05 <0.05 0.09 <0.05672 550 263 196 136 133 161 118 145 0.02 <0.1 <0.05 0.08 <0.05 <0.05 0.06 <0.05 0.08 <0.05

<0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001

5.96 7.33 1.5 5.27 1.51 1.01 3.76 1.03 0.895 <0.01 0.01 0.256 0.058 0.015 0.067 0.015 <0.01 <0.01<0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.010 0.027 <0.01 <0.01 <0.01 <0.01 <0.01 <0.010.652 0.011 <0.01 0.04 0.034 0.023 <0.05 0.019 2.6 2.69 2.26 0.527 1.39 1.94 0.468 0.436 0.391

3.2 0.314.6 10.5 6.1 5 3.7 4 3.9 2.9 3.3 1.2 0.3 0.4 1.3 0.4 0.1 0.30.78 <0.01 0.01 0.79 <0.01 <0.01 0.03 0.07 0.03 0.07 0.06 0.13 0.04 0.09 0.1 0.03 0.8 0.05

0.018 0.01 <0.01 <0.01 <0.01 0.016 <0.01 <0.010 0.02 0.51 0.078 <0.01 0.017 0.09 0.028 0.024 0.03

OH106 OH56B

ANNEXURE G

INDEPENDENT EXPERT REVIEW REPORT

Independent Review Bickham Coal Model_FINAL.doc HC2009/5

i

HERITAGE COMPUTING REPORT

REVIEW OF THE BICKHAM COAL PROJECT GROUNDWATER MODELLING STUDY

FOR

BICKHAM COAL COMPANY PTY

By

Dr N. P. Merrick under contract to

Aquaterra Consulting Pty Ltd 9/1051 Pacific Highway PYMBLE NSW 2073

Report Number: HC2009/5 Date: 31 March 2009


ii

DOCUMENT REGISTER

REVISION DESCRIPTION DATE AUTHOR

A FINAL 31 MARCH 2009 NPM


i

EXECUTIVE SUMMARY

A groundwater model of the proposed Bickham open cut coal mine project near Murrurundi in New South Wales has been developed by Aquaterra Consulting Pty Ltd for Bickham Coal Company Pty Ltd. The purpose of the modelling is to assess potential impacts on local aquifers and surface water bodies, Pages River in particular, and to make a preliminary assessment of mine dewatering requirements. This report provides a peer review of the model according to Australian modelling guidelines (MDBC, 2001). The review is based on a checklist of 36 questions across nine (9) model categories. The review finds that the model has been developed competently, and is suitable for addressing environmental impacts and for estimating indicative dewatering rates. However, the complex geology of the site and the likelihood of compartmentalisation mean that there is a limit to what can reasonably be expected of the Bickham model. This study has the advantage of a substantial data set that consists primarily of more than six (6) years of monitored groundwater levels at a dense network of piezometers spread across the proposed mine site, with a concentration of measurements adjacent to Pages River. Many piezometers are multi-level. Standard stream hydrographic data in association with spot and run-of-river water quality monitoring have provided information on the location and magnitude of groundwater baseflow to Pages River. The aquifer system is stressed only by natural rainfall and stream-aquifer processes. Most groundwater hydrographs show a quiescent response, suggesting a minor role for rainfall infiltration and no groundwater abstraction by bores. The bulk sample dewatering in 2004 provided an artificial stress that enabled an insight into the complex response of the aquifer system. This exercise revealed the presence of compartmentalisation (by faulting) and suggested minimal impact on Pages River for the duration of the dewatering (six months). Model calibration has been performed for both steady-state and transient conditions. Several lines of evidence are provided in support of steady-state calibration, in the form of a scatter plot, a table of performance statistics, a list of residuals at each of 49 targets, and a map of residual errors. The overall performance statistics are good: 6.2 % SRMS and 5.9 m RMS. Similar substantive lines of evidence are provided for transient calibration. The overall performance statistics based on 1593 target water levels are good: 6.4 % SRMS and 6.4 m RMS. In addition, simulated groundwater baseflow magnitudes conform with independent baseflow estimates at Pages River. The steady-state model calibration has better performance in the vicinity of Pages River than near Kingdon Ponds, where it tends to overestimate groundwater levels. The transient calibration replicates 29 hydrographic patterns reasonably well, but there are some large offsets in water level, again close to Kingdon Ponds and over part of the mine site. While predicted heads are close to those observed at lower elevations (such as Pages River), there is a tendency for the model to underestimate groundwater levels at higher elevations (over the mine site). This is probably due to


ii

aquifer compartmentalisation by as yet unidentified faults that constitute barriers to groundwater flow. Model development and mine planning have been iterative processes, with the model informing the mine plan of potential impacts. As a result of this feedback, the mine plan has been modified on a number of occasions in terms of setback distance, mined seams, mining sequence and backfilling rate so that simulated impacts were reduced. The model predicts a reduction in Pages River baseflow of about 0.2 ML/day in a background baseflow of 0.7 ML/day and average river flow in the order of 100 ML/day. The actual baseflow reduction is expected to be less than that predicted by the model, as the model includes a higher degree of connectivity than was demonstrated during the bulk sample dewatering episode. The model predicts a reduction in Kingdon Ponds baseflow of about 0.015 ML/day in a background baseflow of 0.041 ML/day. Most baseflow reduction is due to interception of a tributary by the west pit. A thorough sensitivity analysis has been conducted, and two of the most sensitive parameters have been explored for their influence on model predictions. In most cases there is very little shift from the base run’s performance statistic, with the calibration set of parameters being near optimal for most parameters. Numerical experiments were conducted on the model to assess the effect of posited old mine workings and a posited highly permeable link between the river and the mine. In both cases, the extra baseflow reduction was found to be negligible.


iii

TABLE OF CONTENTS

EXECUTIVE SUMMARY ..........................................................................................i

1.0 INTRODUCTION............................................................................................1

2.0 SCOPE OF WORK..........................................................................................1

3.0 MODELLING GUIDELINES ........................................................................1

4.0 EVIDENTIARY BASIS...................................................................................2

5.0 PEER REVIEW ...............................................................................................3

6.0 DISCUSSION ...................................................................................................3

6.1 THE REPORT ...................................................................................................3 6.2 DATA ANALYSIS .............................................................................................3 6.3 CONCEPTUALISATION .....................................................................................4 6.4 MODEL DESIGN...............................................................................................4 6.5 CALIBRATION..................................................................................................5 6.6 PREDICTION ....................................................................................................6 6.7 SENSITIVITY ANALYSIS...................................................................................7 6.8 UNCERTAINTY ANALYSIS ...............................................................................8

7.0 CONCLUSION ..............................................................................................15

8.0 REFERENCES...............................................................................................15


1

1.0 INTRODUCTION

This report provides a peer review of the groundwater model of the Bickham Coal Mine Project, a proposed open cut mining operation in the Hunter Coalfield of New South Wales (NSW). The mine is to be situated midway between Blandford and Wingen, about 12 km southeast of Murrurundi. The model has been developed by Aquaterra Consulting Pty Ltd, who are undertaking the environmental impact hydrogeological investigations on behalf of Bickham Coal Company Pty Ltd.

The modelling forms a component of the environmental assessment for the project. The purpose of the modelling is to assess potential impacts on local alluvial and hard rock aquifers, as well as interactions with Pages River and Kingdon Ponds, and to make a preliminary assessment of dewatering requirements for the Bickham mine.

2.0 SCOPE OF WORK

This reviewer had an integral role in the overall project, with the following key tasks:

Distil into concise form the key groundwater issues confronting the proposed development;

Outline an appropriate scope of investigations and methods of responding to these issues to provide the highest level of certainty of the outcomes;

Comment on the effectiveness of proposals for additional investigations at the site to address the identified key issues, in particular radon and canoe surveys;

Advise and direct hydrogeological investigations and model development;

Review the groundwater model as documented against the guidelines developed for the Murray Darling Basin Commission;

Provide an independent review in the form of a written report.

Given this integral participation in the project, the model review was conducted progressively. The reviewer has been engaged at all steps of the modelling process from data analysis and conceptualisation, through to calibration, prediction, sensitivity analysis and uncertainty analysis, and iterative model revision. This approach applies frequent review milestones during the modelling process and results in a model of high rigour.

3.0 MODELLING GUIDELINES

The review has been structured according to the checklists in the Australian Flow Modelling Guideline (MDBC, 2001). This guide, sponsored by the Murray-Darling Basin Commission, has become a de facto Australian standard. This reviewer was one of the three authors of the guide, and is the


2

person responsible for creating the peer review checklists. The checklists have been well received nationally, and have been adopted for use in the United Kingdom, California and Germany.

The modelling has been assessed according to the 2-page Model Appraisal checklist in MDBC (2001). This checklist has questions on (1) The Report; (2) Data Analysis; (3) Conceptualisation; (4) Model Design; (5) Calibration; (6) Verification; (7) Prediction; (8) Sensitivity Analysis; and (9) Uncertainty Analysis.

The effort put into a modelling study is very dependent on timing and budgetary constraints that are generally not known to a reviewer. In this case, however, it is acknowledged that considerable time and funds were expended on the many revisions of the model, and in no way was model development constrained.

4.0 EVIDENTIARY BASIS

The primary documentation on which this review is based is:

1. Aquaterra, 2009, Bickham Coal WRA & Draft WMP Appendix 13 - Groundwater Modelling. March 2009. File: “059c Appendix 13 Groundwater Modelling_FINAL.pdf”

At the start of the project, the following document was provided for review:

2. Middlemis, H. and Wallis, I., 2006, Groundwater Model Design Report – Bickham Coal Mine Project. Aquaterra Simulations Memo Report A29/015a [13 April 2006]

A progressive review was conducted on interim modelling outputs from late 2006 to early 2009, and on many draft reports. There has been considerable direct communication with the Aquaterra modelling team in the form of emails, teleconferences and a number of face-to-face meetings.

The objectives of the modelling study are stated in Document #1 as:

“To assist in the overall hydrogeological assessment and the design of the dewatering and water supply systems to support the proposed coal mining operation;

To examine connectivity between the Permian coal measures aquifer system and the Pages River and any associated alluvium in the vicinity of the proposed mine; and;

To predict potential impacts of the proposed mining operation on the groundwater and surface water resources.”

The statement of objectives is supported by a list of seven specific outcomes (see Document #1).


3

5.0 PEER REVIEW

In terms of the modelling guidelines, the Bickham coal model is best categorised as an Impact Assessment Model of medium complexity.

As this review was conducted progressively, the model and model report have been enhanced progressively in response to reviewer recommendations.

The appraisal checklists are presented in Tables 1 and 2 (at the back of this report).

6.0 DISCUSSION

6.1 THE REPORT

The Model Report (Document #1) is a substantial, high quality document of 84 pages total, with 6 Annexures. To an external reader with no prior knowledge of the study area, the report is reasonable as a standalone document. As the modelling study forms one Appendix in a broad Water Resource Assessment (WRA), there is some assumed knowledge that can be found in companion WRA Appendices or the main WRA report.

Coverage of the modelling component of the study is complete, with full disclosure in the Annexures of layer elevations, aquifer parameterisation, boundary conditions, and recovery simulation results. There is reliance on parallel studies in the WRA for full reporting on field investigations and data analysis.

The report has sufficient description of the modelling process and modelling results, and addresses the project objectives satisfactorily. Water balance estimates are reported globally at steady state (Table 3.3) and for the period of transient calibration (Table 3.8). For prediction runs, water balance reporting concentrates on baseflow and pit inflows, the primary outputs of the project.

6.2 DATA ANALYSIS

This study has the advantage of a substantial data set that consists primarily of monitored groundwater levels at a dense network of piezometers spread across the proposed mine site and adjacent areas, with a concentration of measurements adjacent to Pages River. Many piezometers are multi-level, to show the direction of vertical hydraulic gradients. Standard stream hydrographic data in association with spot and run-of-river water quality monitoring have provided information on the location and magnitude of groundwater baseflow to Pages River.

The aquifer system is stressed only by natural processes such as rainfall and stream-aquifer interaction. Most hydrographs show a quiescent response, suggesting a minor role for rainfall infiltration and no groundwater abstraction by bores. The bulk sample dewatering in 2004 provided an


4

artificial stress that enabled an insight into the complex response of the aquifer system. This exercise revealed the presence of compartmentalisation (by faulting) and suggested minimal impact on Pages River for the duration of the dewatering episode (six months).

There will always be uncertainty in chosen hydraulic conductivity and rainfall infiltration factors, which usually are resolvable only as a ratio without supporting information (e.g. flux measurements or estimates). In this case, uncertainty is mitigated by a baseflow analysis for Pages River.

Model extent is necessarily much broader than the monitoring network. As a result, there is minimal control data at the northern, western and southern extremities of the model. There is limited data in the vicinity of Kingdon Ponds.

6.3 CONCEPTUALISATION

The modelling team’s conceptualisation is discussed in detail, and is informed by data analysis findings by others in parallel studies for the WRA. The conceptual model is illustrated very clearly by means of a perspective view (Figure 2.2) and two stratigraphic cross-sections (Figures 2.4 and 2.5).

A conceptual model diagram is a simplified 2D or 3D summary picture (without stratigraphic detail) that conveys the essential features of the hydrological system, denoting all recharge/discharge processes that are likely to be significant. The diagram can serve a dual purpose for displaying the magnitudes of the water budget components derived from data sources or from simulation.

The stratigraphic section is approximated appropriately by eight (8) layers, with separate representation of the E and G coal seams. Lateral compartmentalisation is accommodated wherever there is evidence.

6.4 MODEL DESIGN

There are no existing prior models near the proposed mine site.

The model has been built with Groundwater Vistas software and MODFLOW-SURFACT, an advanced version of standard MODFLOW which is regarded widely as a standard, particularly by government agencies. This version was selected to reduce numerical issues with dry cells (common in open cut mining and dewatering operations). The pseudo-soil option was used, rather than full simulation of variable saturation.

One limitation that all versions of MODFLOW have for coal mining simulations is that they do not permit material properties to vary in time. For open cut mining, there is a need to simulate backfilling with spoil as mining proceeds. This has been accomplished in this study by model stops and starts in annual steps (time-slices).


5

Discretisation in space is appropriate. Model cells are 20 m square across the mine site, with progression to 200 m at model extremities. There are 383 rows and 360 columns. The broad model extent of 15 km by 18 km isolates the boundaries from likely impacts, and reduces the need for accurate representation of boundary conditions. The model is taken out to topographic divides so that “no flow” conditions can be assumed with confidence.

Active mining is represented appropriately by MODFLOW “drain” cells which are deactivated when backfilling commences.

Streams are handled as MODFLOW “river” features. Minor streams are given a coincidence of stream stage and stream base, which means in effect that they operate in the same way as MODFLOW “drain” features.

There is no imposed time variation for river levels. This approach should be justified in the report. It is recognised that the nearest gauging station on Pages River is at Blandford some 3-4 km upstream of the mine site, and field data analysis shows no convincing groundwater responses to high river flow events.

In general, the stress period is one month for calibration and one year for prediction and recovery.

6.5 CALIBRATION

Calibration has been performed for both steady-state and transient conditions.

Several lines of evidence are provided in support of steady-state calibration, in the form of a scatter plot, a table of performance statistics, a list of residuals at each of 49 targets, and a map of residual errors. The residuals map is most informative as it shows that calibration is good close to Pages River but poor in the vicinity of Kingdon Ponds (OH113). However, only the absolute magnitude of the residual is shown. Retention of polarity would have informed the reader of possible bias in the form of systematic over-estimation or under-estimation.

Calibration is generally good across the mine site with a few exceptions. There are seven sites with residuals in excess of 10 m. The overall performance statistics are good: 6.2 % SRMS and 5.9 m RMS.

Similar substantive lines of evidence are provided for transient calibration. In addition, 29 hydrographs of simulated and observed responses are compared. While the hydrographic patterns match well, and there is reasonable replication of the bulk sample dewatering episode, there are some large offsets in water level. The overall performance statistics based on 1593 target water levels are good: 6.4 % SRMS and 6.4 m RMS. In addition, simulated groundwater baseflow magnitudes conform with independent baseflow estimates at Pages River.


6

The scatter plots in Figures 3.1 and 3.6 show no apparent bias in residuals at lower elevations (near streams) except at Kingdon Ponds where levels are overestimated. At higher elevations (across the mine site) there is a tendency for water levels to be underestimated, particularly during transient simulation. The maximum residuals are about 16 m at OH71B (easting 305015) and about 14 m at OH77 (easting 303035).

Calibrated material properties and rain recharge rates are generally plausible. Rain recharge rates range from 1.3% to 7%, with the highest rate over the western mine site. There is full disclosure of calibrated property distributions in the Annexures.

There is no specific comment in the report on whether observed vertical head gradients are preserved in the model.

6.6 PREDICTION

Predictions are based on transient simulation for 25 years of mining followed by 100 years of recovery (to year 125). No natural dynamic stresses from rainfall or river flow are applied during prediction, so that the hydrological effects of mining can be isolated.

The stress period is one year with some variation in years 4, 11 and 12. In the model, pits must be excavated instantly at the start of each period. This will cause a slight overestimation of inflows if the model cells are “mined” in advance of what will occur in reality.

Pit inflows are reported at the end of each year according to a well-documented weighted average method. This approach is more accurate than the common practice of reporting instantaneous flux at the end of a stress period. The weighted average method has the advantage of applicability to separate model layers to isolate the most important sources of water. Over the 25 year mining period, the average pit inflow is estimated to be about 1.1 ML/day with a maximum in year 17 of 2.1 ML/day. Total dewatering rate, including small pumping from external dewatering bores, is predicted to average about 1.2 ML/day, with a maximum of 2.2 ML/day in year 17.

Model development and mine planning have been iterative processes, with the model informing the mine plan of potential impacts. As a result of this feedback, the mine plan has been modified on a number of occasions in terms of setback distance, mined seams, mining sequence and backfilling rate so that simulated impacts were reduced.

The model predicts a reduction in Pages River baseflow of about 0.2 ML/day in a background baseflow of 0.7 ML/day and an average river flow in the order of 100 ML/day. The actual baseflow reduction is expected to be less than that predicted by the model, as the model includes a higher degree of connectivity than was demonstrated during the bulk sample dewatering episode.


7

The model predicts a reduction in Kingdon Ponds baseflow of about 0.015 ML/day in a background baseflow of 0.041 ML/day. Most baseflow reduction is due to interception of a tributary by the west pit.

There are old workings of unknown extent with an adit near the river bank. The model has simulated likely and worst case scenarios, with neither case causing a reversal in groundwater flow direction in the vicinity of Pages River. A numerical experiment for a posited highly permeable link between the river and the mine showed negligible baseflow reduction.

Three additional types of modelling are used to support the assessment:

Particle tracking during transient recovery;

In-pit salinity evolution during transient recovery; and

Unsaturated zone modelling for out-of-pit waste dumps.

While limited information is provided on these approaches, they are acknowledged methods in their own right. It is not clear why LEACHP software was used for the unsaturated zone modelling, when MODFLOW-SURFACT (the 3-D groundwater modelling platform) could have been used just as well, and with more recognition of heterogeneities in the model.

6.7 SENSITIVITY ANALYSIS

A thorough sensitivity analysis has been done for four parameters at steady-state (stream conductance; horizontal hydraulic conductivity; vertical hydraulic conductivity; rainfall infiltration) and for two parameters during transient simulation (specific yield; storage coefficient). In each case, a base run is contrasted with two extreme runs. The sensitivity scenarios are documented in Table 3.9 for steady-state runs, with results in Tables 3.10 and 3.11 in the form of scaled %RMS. In most cases there is very little shift from the base run’s performance statistic, with the calibration set of parameters being near optimal for most parameters.

The best runs give 5.5-5.6% SRMS compared to the base run’s 6.2% SRMS. This occurs for horizontal hydraulic conductivity of the basal layer, the vertical hydraulic conductivity of fault zones, and the rainfall recharge rate for Kingdon Ponds alluvium. The worst runs occur for higher horizontal hydraulic conductivity in the G seam (7.8% SRMS), lower vertical hydraulic conductivity in the Bickham Formation (Layer 2; 7.7% SRMS) and for lower rainfall recharge in the highest infiltrating zone (12% SRMS).

As the performance statistic is a function of groundwater heads only, there was only minor sensitivity to river conductance. Of more importance is the sensitivity of baseflow to this parameter. This is reported in Table 3.12. River conductance cannot be measured directly and has to be inferred in the process of model calibration. The sensitivity analysis shows that, even if the assumed parameter value is not correct, this is not significant in terms of either pit inflows or baseflow impacts.


8

6.8 UNCERTAINTY ANALYSIS

Two of the most sensitive parameters were chosen for checking the uncertainty in predictions: horizontal hydraulic conductivity for Layer 6 (the G Seam), and vertical hydraulic conductivity for Layer 2 (the Bickham Formation). The model was run in an uninterrupted time slice of 25 years and showed only minor changes (3-12% for 100% perturbation) on pit inflows. Corresponding baseflow effects were found to be 10-21% for 100% perturbation.

Numerical experiments were conducted on the model to assess the effect of posited old mine workings and a posited highly permeable link between the river and the mine. In both cases, the extra baseflow reduction was found to be negligible, and was not enough to reverse the direction of groundwater flow towards Pages River.

Model limitations are discussed at length in Section 5 of the report. The main issues are:

Likelihood of more geological discontinuities than can be represented in the model;

Expectation of limited mine inflows due to geological discontinuities;

Uncertainty as to rain recharge rates, especially the higher rate adopted over the central part of the mine site;

Absence of climate variability in prediction runs; Simplified representation of the evapotranspiration process.

In

depe

nden

t Rev

iew

Bic

kham

Coa

l Mod

el_F

INA

L.d

oc

H

C20

09/5

9

Tab

le 1

. MO

DE

L A

PP

RA

ISA

L:

Bic

kham

Co

al

Q.

QU

ES

TIO

N

No

t A

pp

licab

le

or

Un

kno

wn

Sco

re 0

S

core

1

Sco

re 3

S

core

5

Sco

re

Max

. S

core

(0

, 3, 5

)

CO

MM

EN

T

1.0

TH

E R

EP

OR

T

1.1

Is th

ere

a cl

ear

stat

emen

t of p

roje

ct o

bjec

tives

in th

e m

odel

ling

repo

rt?

M

issi

ng

Def

icie

nt

Ade

quat

e V

ery

Goo

d

1.2

Is th

e le

vel o

f mod

el c

ompl

exity

cle

ar o

r ac

kno

wle

dge

d?

M

issi

ng

No

Yes

Infe

rred

, not

sta

ted:

Impa

ct A

sses

smen

t M

odel

, med

ium

com

plex

ity

1.

3 Is

a w

ater

or

mas

s ba

lanc

e re

port

ed?

M

issi

ng

Def

icie

nt

Ade

quat

e V

ery

Goo

d

S

tead

y st

ate

(Ta

ble

3.3)

; tra

nsie

nt (

Tab

le

3.8)

– g

loba

l. D

etai

l for

bas

eflo

w.

1.4

Has

the

mod

ellin

g st

udy

satis

fied

proj

ect o

bjec

tives

?

M

issi

ng

Def

icie

nt

Ade

quat

e V

ery

Goo

d

S

ubje

ct to

sta

ted

limita

tions

.

1.5

Are

the

mod

el r

esu

lts o

f any

pra

ctic

al u

se?

No

Ma

ybe

Yes

S

ome

unce

rtai

nty

due

to g

eolo

gica

l co

mpl

exity

, pa

rtic

ular

ly

com

part

men

talis

atio

n; li

mite

d in

form

atio

n on

reg

iona

l gro

und

wat

er s

yste

m

resp

onse

und

er

stre

ss.

2.

0 D

AT

A A

NA

LY

SIS

2.1

Has

hyd

roge

olog

y da

ta b

een

colle

cted

and

ana

lyse

d?

Mis

sing

D

efic

ient

A

dequ

ate

Ver

y G

ood

Mor

e de

tail

in p

ara

llel E

A s

tudi

es.

2.2

Are

gro

und

wat

er

cont

ours

or

flow

dire

ctio

ns p

rese

nted

?

Mis

sing

D

efic

ient

A

dequ

ate

Ver

y G

ood

Mor

e de

tail

in p

ara

llel E

A s

tudi

es.

2.

3 H

ave

all p

oten

tial r

echa

rge

dat

a b

een

colle

cted

and

an

alys

ed?

(rai

nfa

ll, s

trea

mflo

w, i

rrig

atio

n, fl

oods

, etc

.)

M

issi

ng

Def

icie

nt

Ade

quat

e V

ery

Goo

d

M

ore

deta

il in

pa

ralle

l EA

stu

dies

.

2.4

Hav

e al

l pot

entia

l dis

char

ge d

ata

bee

n co

llect

ed a

nd

anal

ysed

? (a

bstr

actio

n, e

vapo

tran

spira

tion,

dra

inag

e,

sprin

gflo

w, e

tc.)

M

issi

ng

Def

icie

nt

Ade

quat

e V

ery

Goo

d

M

ore

deta

il in

pa

ralle

l EA

stu

dies

.

2.5

Hav

e th

e re

cha

rge

and

disc

harg

e da

tase

ts b

een

anal

ysed

fo

r th

eir

gro

und

wat

er r

espo

nse?

N

/A

Mis

sing

D

efic

ient

A

dequ

ate

Ver

y G

ood

Mor

e de

tail

in p

ara

llel E

A s

tudi

es.

Dis

cuss

ion

of in

divi

dual

hyd

rogr

aph

resp

onse

in A

ppen

dix

10.

2.6

Are

gro

und

wat

er

hyd

rogr

aphs

use

d fo

r ca

libra

tion?

N/A

No

Ma

ybe

Yes

M

any

hyd

rogr

aphs

ove

r 7

yea

rs.

In

depe

nden

t Rev

iew

Bic

kham

Coa

l Mod

el_F

INA

L.d

oc

H

C20

09/5

10

Tab

le 1

. MO

DE

L A

PP

RA

ISA

L:

Bic

kham

Co

al

Q.

QU

ES

TIO

N

No

t A

pp

licab

le

or

Un

kno

wn

Sco

re 0

S

core

1

Sco

re 3

S

core

5

Sco

re

Max

. S

core

(0

, 3, 5

)

CO

MM

EN

T

2.7

Hav

e co

nsis

tent

dat

a un

its a

nd s

tand

ard

geom

etri

cal

datu

ms

been

use

d?

No

Yes

3.0

CO

NC

EP

TU

AL

ISA

TIO

N

3.1

Is th

e co

ncep

tual

mod

el c

onsi

sten

t with

pro

ject

obj

ectiv

es

and

the

requ

ired

mod

el c

ompl

exity

?

U

nkno

wn

No

Ma

ybe

Yes

3.2

Is th

ere

a cl

ear

des

crip

tion

of th

e co

ncep

tual

mod

el?

Mis

sing

D

efic

ient

A

dequ

ate

Ver

y G

ood

3.3

Is th

ere

a gr

aphi

cal r

epre

sent

atio

n of

the

mod

elle

r’s

conc

eptu

alis

atio

n?

M

issi

ng

Def

icie

nt

Ade

quat

e V

ery

Goo

d

E

xcel

lent

per

spe

ctiv

e vi

ew in

Fig

ure

2.2

.

3.4

Is th

e co

ncep

tual

mod

el u

nnec

essa

rily

sim

ple

or

unne

cess

arily

co

mpl

ex?

Yes

N

o

Sen

sibl

e st

ratig

raph

ic d

ivis

ion.

4.0

MO

DE

L D

ES

IGN

4.1

Is th

e sp

atia

l ext

ent o

f the

mod

el a

ppro

pria

te?

No

Ma

ybe

Yes

15

km x

18k

m. B

road

ext

ent i

sola

tes

boun

darie

s fr

om im

pact

s. 2

0-20

0m

cel

l si

ze is

suf

ficie

ntly

fine

. 8 la

yers

, 383

ro

ws,

360

col

umns

.

4.2

Are

the

appl

ied

bou

ndar

y co

nditi

ons

plau

sibl

e an

d un

rest

rictiv

e?

M

issi

ng

Def

icie

nt

Ade

quat

e V

ery

Goo

d

G

ene

rally

nat

ura

l bou

ndar

ies

(top

ogra

phic

div

ides

). G

ener

al h

ead

bo

unda

ry a

t riv

er e

ntry

and

exi

t. R

iver

pa

ckag

e fo

r st

ream

s.

4.3

Is th

e so

ftwa

re a

ppro

pria

te f

or th

e o

bjec

tives

of t

he s

tud

y?

No

Ma

ybe

Yes

G

rou

ndw

ate

r V

ista

s an

d M

OD

FL

OW

-S

UR

FA

CT

. Pse

udo

-Soi

l opt

ion

to r

educ

e nu

mer

ical

effe

cts

of d

ry c

ells

. Can

not

hand

le ti

me

vary

ing

mat

eria

l pro

per

ties

dire

ctly

. LE

AC

HP

for

unsa

tura

ted

zone

mod

ellin

g of

was

te d

umps

. M

OD

PA

TH

for

par

ticle

trac

king

. E

xcel

Spr

eads

heet

for

in-p

it sa

linity

ev

olut

ion

(mas

s ba

lanc

e al

gorit

hm w

ith

com

plet

e m

ixin

g).

In

depe

nden

t Rev

iew

Bic

kham

Coa

l Mod

el_F

INA

L.d

oc

H

C20

09/5

11

Tab

le 2

. MO

DE

L A

PP

RA

ISA

L –

Bic

kham

Co

al

Q.

QU

ES

TIO

N

No

t A

pp

licab

le

or

Un

kno

wn

Sco

re 0

S

core

1

Sco

re 3

S

core

5

Sco

re

Max

. S

core

(0

, 3, 5

)

CO

MM

EN

T

5.0

CA

LIB

RA

TIO

N

5.1

Is th

ere

suff

icie

nt e

vide

nce

prov

ided

for

mod

el c

alib

ratio

n?

M

issi

ng

Def

icie

nt

Ade

quat

e V

ery

Goo

d

S

ever

al li

nes

of e

vide

nce:

sca

tterg

ram

s fo

r st

ead

y st

ate

(Fig

3.1

) an

d tr

ansi

ent (

Fig

3.

6),

stat

istic

s, m

ap o

f ste

ady

stat

e re

sidu

als;

hyd

rog

raph

com

paris

ons.

Li

mite

d da

ta to

the

nort

h an

d w

est.

Poo

r co

ntro

l clo

se to

Kin

gdon

Pon

ds. G

ood

data

ac

ross

min

e si

te a

nd c

lose

to P

ages

Riv

er.

5.

2 Is

the

mod

el s

uffic

ient

ly c

alib

rate

d a

gain

st s

patia

l ob

serv

atio

ns?

M

issi

ng

Def

icie

nt

Ade

quat

e V

ery

Goo

d

6.

2% S

RM

S a

nd

5.9m

RM

S.

Goo

d cl

ose

to

Pag

es R

iver

. Poo

r at

Kin

gdon

Po

nds

and

wes

t en

d of

min

e.

5.

3 Is

the

mod

el s

uffic

ient

ly c

alib

rate

d a

gain

st te

mpo

ral

obse

rvat

ions

?

N/A

M

issi

ng

Def

icie

nt

Ade

quat

e V

ery

Goo

d

6.

4% S

RM

S a

nd

6.4

RM

S. 2

9 h

ydro

grap

hs, 1

593

targ

et w

ater

leve

ls,

orde

r of

mag

nitu

de b

asef

low

che

ck.

Hyd

rogr

aph

ic p

atte

rns

mat

ch w

ell.

Rea

sona

ble

repl

icat

ion

of r

espo

nses

to

bulk

sam

ple

dew

ater

ing.

Som

e la

rge

offs

ets

in w

ate

r le

vel.

5.

4 A

re c

alib

rate

d pa

ram

eter

dis

trib

utio

ns a

nd r

ang

es

plau

sibl

e?

M

issi

ng

No

Ma

ybe

Yes

R

ain

rech

arge

ra

tes

rang

e fr

om 1

.3%

to

7% –

pla

usib

le. P

erm

eabi

lity

valu

es a

re

reas

onab

ly c

onsi

sten

t with

oth

er s

tudi

es.

Lim

ited

cros

s re

fere

nce

to p

ara

llel E

A

stud

ies.

C

ompr

ehen

sive

rep

ortin

g of

pro

pert

y va

lues

and

dis

trib

utio

ns in

Ann

exur

es A

&

C.

5.

5 D

oes

the

calib

ratio

n st

atis

tic s

atis

fy a

gree

d pe

rfor

man

ce

crite

ria?

M

issi

ng

Def

icie

nt

Ade

quat

e V

ery

Goo

d

A

imed

for

5-10

%. A

chie

ved

6-7%

. E

xten

sive

sta

tistic

s in

Tab

les

3.1,

3.7

.

5.6

Are

ther

e go

od r

easo

ns fo

r no

t mee

ting

agre

ed

perf

orm

ance

crit

eria

?

N/A

M

issi

ng

Def

icie

nt

Ade

quat

e V

ery

Goo

d

C

ompl

ex g

eol

ogy,

com

part

men

ts, l

ong

run

times

.

In

depe

nden

t Rev

iew

Bic

kham

Coa

l Mod

el_F

INA

L.d

oc

H

C20

09/5

12

Tab

le 2

. MO

DE

L A

PP

RA

ISA

L –

Bic

kham

Co

al

Q.

QU

ES

TIO

N

No

t A

pp

licab

le

or

Un

kno

wn

Sco

re 0

S

core

1

Sco

re 3

S

core

5

Sco

re

Max

. S

core

(0

, 3, 5

)

CO

MM

EN

T

6.0

VE

RIF

ICA

TIO

N

6.1

Is th

ere

suffi

cien

t evi

denc

e pr

ovid

ed fo

r m

odel

ve

rific

atio

n?

N/A

M

issi

ng

Def

icie

nt

Ade

quat

e V

ery

Goo

d

A

ll da

ta n

eede

d fo

r ca

libra

tion.

Litt

le p

oint

in

usi

ng a

n ex

tra

quie

scen

t dat

a se

t re

spon

ding

onl

y to

nat

ural

str

esse

s.

6.

2 D

oes

the

rese

rve

d da

tase

t inc

lude

str

esse

s co

nsis

tent

w

ith th

e p

redi

ctio

n sc

enar

ios?

N/A

U

nkno

wn

No

Ma

ybe

Yes

6.3

Are

ther

e go

od r

easo

ns fo

r an

un

satis

fact

ory

verif

icat

ion?

N/A

M

issi

ng

Def

icie

nt

Ade

quat

e V

ery

Goo

d

7.0

PR

ED

ICT

ION

7.1

Hav

e m

ultip

le s

cena

rios

been

run

for

clim

ate

varia

bilit

y?

N/A

M

issi

ng

Def

icie

nt

Ade

quat

e V

ery

Goo

d

N

ot d

one,

as

clim

ate

varia

bilit

y is

exp

ecte

d to

hav

e a

min

or e

ffect

on

grou

nd

wat

er

leve

ls c

ompa

red

to o

pen

cut m

inin

g.

7.

2 H

ave

mul

tiple

sce

nario

s be

en r

un fo

r op

era

tiona

l /m

anag

emen

t alte

rnat

ives

?

Mis

sing

D

efic

ient

A

dequ

ate

Ver

y G

ood

Sev

eral

min

e pl

ans

durin

g m

odel

de

velo

pmen

t; a

men

dmen

ts to

min

e pl

ans

to r

educ

e im

pact

s (s

etba

ck d

ista

nce,

min

ed

seam

s, m

inin

g se

quen

ce, r

ate

of

back

fillin

g); o

ld w

orki

ngs;

rec

over

y af

ter

min

e cl

osur

e.

7.

3 Is

the

time

horiz

on fo

r pr

edic

tion

com

para

ble

with

the

le

ngth

of t

he c

alib

ratio

n / v

erifi

catio

n pe

riod?

Mis

sing

N

o M

ayb

e Y

es

25 y

ears

pre

dict

ion

com

pare

d to

6 y

ears

ca

libra

tion.

In

depe

nden

t Rev

iew

Bic

kham

Coa

l Mod

el_F

INA

L.d

oc

H

C20

09/5

13

Tab

le 2

. MO

DE

L A

PP

RA

ISA

L –

Bic

kham

Co

al

Q.

QU

ES

TIO

N

No

t A

pp

licab

le

or

Un

kno

wn

Sco

re 0

S

core

1

Sco

re 3

S

core

5

Sco

re

Max

. S

core

(0

, 3, 5

)

CO

MM

EN

T

7.4

Are

the

mod

el p

redi

ctio

ns p

laus

ible

?

N

o M

ayb

e Y

es

The

re w

ill a

lwa

ys b

e un

cert

aint

y in

pro

pert

y va

lues

that

dic

tate

min

e in

flow

s. E

stim

ates

w

ill im

prov

e on

ly a

fter

min

ing

star

ts.

Bas

eflo

w im

pact

s at

Pag

es R

iver

are

ex

pect

ed to

be

cons

erva

tive,

as

mod

el

give

s ne

ar-r

iver

red

uctio

ns in

gro

und

wat

er

leve

ls w

hen

non

e ar

e ob

serv

ed (

bulk

sa

mpl

e).

Goo

d di

scus

sion

on

perc

enta

ge

impa

cts

on

base

flow

s.

8.

0 S

EN

SIT

IVIT

Y A

NA

LY

SIS

8.1

Is th

e se

nsiti

vity

ana

lysi

s su

ffic

ient

ly in

tens

ive

for

key

para

met

ers

?

M

issi

ng

Def

icie

nt

Ade

quat

e V

ery

Goo

d

S

tead

y st

ate

(Ta

ble

3.9)

don

e fo

r 4

para

met

ers

: CO

ND

, Kx,

Kz,

RC

H.

Tra

nsie

nt d

one

for

2 pa

ram

eter

s: S

y, S

. T

wo

ext

rem

e va

lues

. Mul

tiplie

rs o

f 0.5

& 2

fo

r K

x, R

CH

, Sy.

Mul

tiplie

rs o

f 0.1

& 1

0 fo

r K

z, S

, CO

ND

. Se

nsib

le p

ertu

rbat

ions

.

8.2

Are

sen

sitiv

ity r

esu

lts u

sed

to q

ualif

y th

e re

liabi

lity

of

mod

el c

alib

ratio

n?

M

issi

ng

Def

icie

nt

Ade

quat

e V

ery

Goo

d

S

RM

S r

epor

ted

for

each

ste

ady

stat

e pe

rtur

bed

run

. Bes

t run

giv

es 5

.5%

co

mpa

red

to c

alib

rate

d pa

ram

ete

r ru

n 6.

2%. T

he c

alib

ratio

n se

t is

near

opt

imal

for

mos

t par

amet

ers

.

8.3

Are

sen

sitiv

ity r

esu

lts u

sed

to q

ualif

y th

e ac

cura

cy o

f m

odel

pre

dict

ion?

M

issi

ng

Def

icie

nt

Ade

quat

e V

ery

Goo

d

T

wo

key

para

met

ers

are

used

for

pred

ictio

n un

cert

aint

y an

alys

is: K

x(La

yer

6), K

z(La

yer

2).

9.0

UN

CE

RT

AIN

TY

AN

AL

YS

IS

In

depe

nden

t Rev

iew

Bic

kham

Coa

l Mod

el_F

INA

L.d

oc

H

C20

09/5

14

Tab

le 2

. MO

DE

L A

PP

RA

ISA

L –

Bic

kham

Co

al

Q.

QU

ES

TIO

N

No

t A

pp

licab

le

or

Un

kno

wn

Sco

re 0

S

core

1

Sco

re 3

S

core

5

Sco

re

Max

. S

core

(0

, 3, 5

)

CO

MM

EN

T

9.1

If re

quire

d b

y th

e p

roje

ct b

rief,

is u

ncer

tain

ty q

uan

tifie

d in

an

y w

ay?

Mis

sing

N

o M

ayb

e Y

es

Unc

erta

inty

is e

xplo

red

in p

art b

y se

nsiti

vity

an

alys

is, a

nd is

dis

cuss

ed u

nder

mod

el

limita

tions

. Thr

ee u

ncer

tain

ty s

imu

latio

ns:

1) 2

5 ye

ar r

un fo

r 2

sens

itive

par

amet

ers

– qu

antif

ied

pit i

nflo

w

2) 5

yea

r ru

n fo

r ol

d m

ine

wo

rkin

gs –

qu

antif

ied

base

flow

& p

it in

flow

3)

5 y

ear

run

for

posi

ted

perm

eabl

e lin

k be

twee

n riv

er a

nd

min

e –

quan

tifie

d ba

seflo

w &

pit

inflo

w.

TO

TA

L S

CO

RE

PE

RF

OR

MA

NC

E:


15

7.0 CONCLUSION

The Bickham Coal groundwater model has been developed competently. It is a suitable model for addressing likely environmental impacts from open cut mining, and for estimating indicative dewatering rates.

Pit inflows are likely to be lower than predicted, given that there is evidence of compartmentalisation in the complex geology of the site.

Anticipated baseflow reductions at Pages River are likely to be conservative, in predicting higher reductions than likely to occur. This is due to the model incorporating a higher degree of stream-aquifer connectivity than was demonstrated during the 6-month bulk sample dewatering episode.

Anticipated baseflow reductions at Kingdon Ponds are likely to be negligible except for the one tributary that is intercepted by mining.

8.0 REFERENCES

MDBC (2001). Groundwater flow modelling guideline. Murray-Darling Basin Commission. URL: www.mdbc.gov.au/nrm/water_management/groundwater/groundwater_guides

Appendix 13 Groundwater Modelling - Bickham Coal 2_Appendices1_16/App… · Appendix 13 –...

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