ULAN COAL MINES LTD
CONTINUED OPERATIONS – GROUNDWATER ASSESSMENT
July 2009
ULAN COAL – CONTINUED OPERATIONS: GROUNDWATER ASSESSMENT – JULY 2009
ULAN COAL MINES LTD
CONTINUED OPERATIONS - GROUNDWATER ASSESSMENT
JULY 2009
prepared by:
Mackie Environmental Research
193 Plateau Rd., Bilgola
for:
Umwelt (Australia) Pty Limited
Toronto
on behalf of:
Ulan Coal Mines Limited
Ulan
Mackie Environmental Research
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ULAN COAL – CONTINUED OPERATIONS: GROUNDWATER ASSESSMENT – JULY 2009
ABSTRACT
Ulan Coal Mines Limited (UCML) is seeking approval to continue mining operations by extending
the West Pit open cut to the west, continuing the underground No.3 operations northward, and by
commencing another underground mine now identified as Ulan West.
Proposed mining would continue to exploit coal reserves in the Ulan seam and would provide for
the extraction of up to 20 million tonnes per annum of coal over a period of about 21 years. All
open cut and underground mining would continue to be undertaken at depths below the regional
water table which will result in further depressurisation of the coal seam and strata above and
below the seam. Depressurisation above the seam will be accelerated through caving and
subsidence (for underground operations). Such depressurisation will lead to changed groundwater
flow directions within the Permian coal measures and the overlying Triassic and younger strata.
Significant recent studies underpin a reasonably well defined hydrogeologic system that is
extensively monitored. These studies have been assimilated into the current environmental
assessments in order to predict the magnitude and extent of groundwater related impacts likely to
arise from the proposed mining operations. They have included hydrogeological map preparation,
laboratory based hydraulic properties measurements of different strata, groundwater quality
assessments as part of routine monitoring, confirmation-census of existing private bores and wells,
development of a regional groundwater model, and predictive modelling of future mining and post
mining scenarios. Results support the following.
The geological strata of interest are (from top down) Jurassic sandstones and siltstones which are
mostly unsaturated within the proposed mining areas, Triassic sandstones which are variably
saturated, and Permian coal measures comprising sandstones, siltstones, shales and coal seams
which remain saturated within the proposed mining areas but have been largely depressurised in
mined out areas.
Water tables and groundwater pressures in the saturated strata are sustained by rainfall infiltration
to the regolith and to underlying hard rock layers with estimates of recharge to deep hard rock
strata varying from close to zero, to no more than about 2% of annual rainfall. The shallow
regolith-weathered bedrock zone is considered to act as a temporary water store with rainfall
recharge percolating downwards at a reducing rate as increasing confinement in hard rock strata
impedes flow. Shallow vertical flow while not measured, is likely to be influenced by the
connectivity of joints and fractures.
A regional composite water table has been prepared from the available piezometric data for both
pre-mining conditions (taken as prior to 1986) and current conditions in 2009. The pre-mining
water table generally reflects a regime where mounding occurs beneath topographically high areas,
and lower groundwater elevations prevail adjacent to the major drainage systems. The Talbragar
and Goulburn rivers act as regional drainage sinks.
Formation hydraulic properties data for the various strata have been gathered from historical
testing within and around the project area. Core inspections and packer testing have been
undertaken to assess the presence of fractures and joints, and to estimate the hydraulic conductivity
of the Ulan seam and overburden in the Permian, Triassic and Jurassic strata. Findings
demonstrate the Ulan seam exhibits a hydraulic conductivity that is several orders of magnitude
higher than Permian interburden strata and as a result, the seam preferentially depressurises the
system, as observed in historical piezometric monitoring data. Core tests support very low
conductivities for Permian non-coal strata which will not easily drain. The overlying Triassic
sandstones are much more conductive and porous. They are regarded as a significant regional
groundwater store by virtue of their uniformity and favourable properties. The Jurassic rocks are
more variable with generally reduced hydraulic conductivities when compared to the underlying
Triassic strata. Shallow alluvial deposits along the major drainages tend to be mixed assemblages
of clayey silts and sands with occasional coarser gravel layers. They seem to exhibit quite variable
hydraulic properties.
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ULAN COAL – CONTINUED OPERATIONS: GROUNDWATER ASSESSMENT – JULY 2009
Groundwater sampling over a long period of time suggests water qualities are consistent with the
observed mineralogies. Permian strata are characterised by an ionic species distribution where
Na>Mg,Ca and HCO3,Cl >>SO4, an average EC value of 1151 uS/cm and a pH average of about
9.5. Triassic strata are characterised by Na>Mg,Ca and Cl,HCO3 >>SO4, EC values averaging
471 uS/cm and a pH average of about 7.5. A recent bore census has indicated that shallower
groundwaters in the Triassic sandstones may be useful for stock and domestic water supply.
Recent installation of a number of pore pressure monitoring bores in both undisturbed areas and
areas close to or above subsided longwall panels, has provided further insight to the extent of strata
depressurisation attributed to mining operations. Pore pressure data for piezometers in undisturbed
areas supports the conceptual hydraulic conductivity distribution - high conductivity in the Ulan
seam, low conductivity and storage in the Permian and deeper strata, and high conductivity and
storage in Triassic strata. Pore pressures in the subsidence zone above extracted panels, are
observed to reduce rapidly in advance of mining, and following undermining. At two monitoring
sites, pressures have apparently reduced to zero throughout the entire profile while at a third site
they are declining steadily. These pore pressure reductions (in the subsidence zone) are consistent
with connected and drainable cracking from the Ulan seam upwards through the entire succession
of saturated strata, probably to surface. This response is consistent with geotechnical predictions
for subsidence related cracking.
Evaluation of the likely impacts of future mining on regional groundwater systems has been
assessed using computer based modelling techniques. A regional groundwater model comprising
11 layers has been developed using a finite difference based computer code. The model has been
calibrated using extensive groundwater monitoring data and historical groundwater seepage
estimates to underground operations. It has been used to generate a pre-mining estimate of the
regional water table and to determine probable groundwater flow pathlines within the various
strata. Results support a pre-mining flow system that is recharged by rainfall and sustains a
groundwater mounding in subcrop areas to the south and southwest of mining operations. From
here, flow path directions are predicted to be north-easterly before turning easterly down the
Goulburn River catchment. Some flow paths also turn to the northwest down the Talbragar River
catchment. Interestingly, the groundwater divide between easterly and westerly groundwater
flows, lies some 4 to 5 km west of the Great Divide.
Simulation of open cut and underground mining operations from 1986 to 2008 supports the
preferential depressurisation of the Ulan seam and complete dewatering of strata overlying
extracted panels. This dewatering has created a groundwater sink which has attracted flow from
surrounding strata and modified the pre-mining flow path directions. Model predicted
groundwater seepage rates agree with anecdotal estimates for early years of mining, and with
measured estimates for recent years of mining. The model generates an average rate of seepage of
8.5ML/day for early 2008 consistent with calculated estimates from detailed site water balance
studies.
Simulation of future mining to 2029-2030 supports sustained depressurisation of the Ulan seam to
distances of 10 to 20 km beyond the mine panel footprint. Permian interburden is depressurised to
distances of 5 to 15 km while Triassic strata are depressurised to distances of 3 to 5 km as defined
by the 2 m drawdown contours. All strata are predicted to be dewatered within the subsidence
zone.
The total cumulative groundwater seepage to mine workings from all underground operations is
predicted to rise from a current rate of about 9.2 ML/day to approximately 24.0 ML/day in 2018
when operations in Underground No.3 are near their northern extremity and the greatest pressure
heads in the groundwater system, prevail. Thereafter, the seepage rate is predicted to decline to a
rate of about 8 ML/day at the end of mining in 2029-2030 and to decline in an exponential manner
thereafter. Occasional short term ‘nuisance’ flows of possibly up to 1.0 ML/day could be generated
during mining if as yet unidentified water bearing structures like faults, shears or volcanic plugs
and sills are intercepted. Typically, such structures if intercepted in the Permian strata, offer
relatively low storage that would be expected to deplete over a number of months. Longer periods
are likely if the structures occur in the Triassic strata.
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ULAN COAL – CONTINUED OPERATIONS: GROUNDWATER ASSESSMENT – JULY 2009
The reduction in aquifer pressures caused by Underground No.3 and Ulan West operations will
have an impact on groundwater baseflows to the catchments. At the close of mining it is predicted
that losses to the Goulburn River catchment arising from the proposed mining, may be of the order
of 0.11 ML/day while losses to the Talbragar River catchment may be of the order of 0.2 ML/day.
Cumulative impacts arising from proposed underground mining operations at Moolarben Coal
Underground No.4, are likely to dewater Permian and Triassic strata within the subsidence zone if
a cracking and draining regime similar to UCML experience, develops above extracted longwall
panels. This may lead to more widespread depletion of the water table in and adjacent to the
impacted area(s) surrounding the Moolarben project.
There are a number of water supply bores that are likely to be impacted by continued mining.
Most are believed to draw groundwater from the Triassic or younger strata including alluvium
along the Talbragar River. There are 5 privately owned bores (excluding UCML bores) located
within the 5 m drawdown contour in Triassic strata at the end of mining. Of these 5 bores, only
one is in use, the remaining bores are either inoperable (3 bores) or cannot be located (1 bore).
The 5 m head loss contour is considered to be an important contour insofar as bores are likely to
succumb to some loss of yield if drawdowns of this magnitude occur. UCML policy in relation to
bore water supplies supports replacement of loss of yield through new bore construction.
The Drip is recognised as an important natural feature which hosts localised groundwater
dependent ecosystems. It is sustained by surficial and relatively shallow groundwater storage
which is governed mostly by short term rainfall events that surcharge the regolith, weathered rock
and vertical joints in the area. Rainfall recharge and downwards percolation is intercepted at
horizontal bedding planes which then transmit the groundwater to the unconfined rock faces along
the Goulburn River gorge, where it emanates as seeps and drips. During dry periods some seeps
may cease to flow. Seepage that migrates past this shallow perched system, sustains the deeper
water table and from numerical modelling, is calculated to be less than 5 mm/year or less than 1%
of annual average rainfall. Depressurisation of Triassic strata in the area of the Drip has already
occurred as a result of historical mining operations at UCML and no impacts have been observed
to date. No observable impacts are likely as a result of future UCML operations which are moving
northward and westward away from the Drip. There are no other identified groundwater dependent
eco-systems within the area that are likely to be impacted by loss of formation groundwater
pressures.
Simulation of the recovery of groundwater levels indicates more than 200 years will pass before
groundwater levels and pressures within the depressurised strata, substantially rebound.
Groundwater quality within the coal measures both during and post mining, is expected to exhibit
a speciated signature (cations and anions) consistent with the range of water qualities currently
encountered in exploration holes and observation piezometers - a sodium-magnesium bicarbonatechloride water. Triassic strata water quality is unlikely to change with time.
The extended open cut area to the west of the existing open cuts, will be filled with waste rock
(spoils) in a manner consistent with historical operations. Reshaping will be undertaken and there
will be no long term void on completion of mining. Rainfall will recharge the spoils and the water
table within the spoils will recover to an equilibrated level (after more than 200 years) which will
be connected to the existing open cut pits. The water quality is expected to be Na>>Mg>Ca and
HCO3>Cl>>SO4 with total dissolved solids greater than 1000 mg/L and pH between 7.0 and 8.0.
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ULAN COAL – CONTINUED OPERATIONS: GROUNDWATER ASSESSMENT – JULY 2009
Table of Contents
ABSTRACT .............................................................................................................................................2
1.
1.1
2.
2.1
2.2
2.2.1
2.2.2
2.3
2.4
2.5
2.6
3.
INTRODUCTION..........................................................................................................................8
HISTORICAL AND RECENT STUDIES OF RELEVANCE .......................................................................9
REGIONAL SETTING ...............................................................................................................10
CLIMATE .....................................................................................................................................10
DRAINAGE, RUNOFF AND RAINFALL RECHARGE ..........................................................................11
Base flow to the Goulburn and Talbragar Rivers ......................................................................11
River water quality .....................................................................................................................12
GEOLOGY ....................................................................................................................................12
WIRELINE GEOPHYSICAL LOGS....................................................................................................14
BEDDING AND STRUCTURAL FEATURES .......................................................................................15
REGIONAL STRESS FIELD AND JOINTING ......................................................................................15
GROUNDWATER HYDROLOGY............................................................................................16
3.1
3.2
3.2.1
3.3
3.3.1
3.4
3.4.1
3.4.2
3.4.3
3.4.4
EXISTING LICENSED BORES AND WELLS IN THE REGION ..............................................................16
GROUNDWATER OCCURRENCE IN UNCONSOLIDATED SEDIMENTS ...............................................16
Hydraulic properties of alluvium ...............................................................................................17
GROUNDWATER OCCURRENCE IN HARD ROCK STRATA ...............................................................17
Hydraulic properties of hard rock strata ...................................................................................18
GROUNDWATER MONITORING .....................................................................................................19
Piezometric surfaces and groundwater flows.............................................................................20
Groundwater Quality .................................................................................................................20
Goaf Water Quality ....................................................................................................................21
Historical mine water influx.......................................................................................................22
4.0
COMPUTER SIMULATION OF PROPOSED MINING....................................................23
4.1
4.2
4.3
4.4
4.5
4.6
GROUNDWATER MODEL PROPERTIES AND INITIAL CONDITIONS ..................................................24
MODEL CALIBRATION TO FIELD CONDITIONS ..............................................................................24
FUTURE MINING INDUCED DEPRESSURISATION OF ROCK STRATA ................................................25
PREDICTED GROUNDWATER SEEPAGE TO UNDERGROUND OPERATIONS ......................................26
RECOVERY OF AQUIFER PRESSURES POST MINING .......................................................................26
BASEFLOW LOSSES TO REGIONAL RIVERS AND CREEKS ...............................................................27
5.
5.1
5.2
5.3
5.4
POTENTIAL ENVIRONMENTAL IMPACTS........................................................................27
REDUCTION IN REGIONAL HARD ROCK PRESSURES AND BASEFLOW IMPACTS ..............................27
LOSS OF GROUNDWATER YIELD AT EXISTING BORE LOCATIONS ..................................................28
CHANGE IN GROUNDWATER QUALITY .........................................................................................29
IMPACTS ON GROUNDWATER DEPENDENT ECOSYSTEMS ..............................................................29
6.
DWE LICENSING REQUIREMENTS .....................................................................................29
7.
GROUND WATER MONITORING.........................................................................................30
8.
IMPACTS VERIFICATION CRITERIA..................................................................................30
8.1
IMPACT MITIGATION MEASURES ..................................................................................................32
REFERENCES: .....................................................................................................................................32
APPENDIX A:
BASEFLOW ANALYSES ......................................................................................35
APPENDIX B:
DWE REGISTERED BORES AND WELLS .........................................................1
APPENDIX C:
STRATA HYDRAULIC PROPERTIES.................................................................1
C1.
C2.
C3.
PACKER INJECTION TEST ANALYSES ..............................................................................................1
LABORATORY CORE TESTS ............................................................................................................1
ROCK CORE MECHANICAL PROPERTIES..........................................................................................7
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ULAN COAL – CONTINUED OPERATIONS: GROUNDWATER ASSESSMENT – JULY 2009
APPENDIX D:
GROUNDWATER MONITORING........................................................................1
APPENDIX E:
REGIONAL GROUNDWATER MODEL..............................................................1
E1 CONCEPTUALISATION .......................................................................................................................1
E2 NUMERICAL MODEL CODE.................................................................................................................1
E3.
MODEL LAYER GEOMETRY ............................................................................................................2
E4.
MODEL HYDRAULIC PROPERTIES ...................................................................................................2
E5.
MODEL BOUNDARY CONDITIONS ...................................................................................................4
E5.1
Treatment of the subsidence zone.................................................................................................5
E6.
MODEL CALIBRATION – STEADY STATE ........................................................................................6
E7.
MODEL CALIBRATION – TRANSIENT STATE ...................................................................................8
E8.
SIMULATION OF FUTURE MINING ...................................................................................................9
E9.
RECOVERY OF AQUIFER PRESSURES POST MINING .......................................................................11
E10.
SIMULATION OF CUMULATIVE IMPACTS OF MINING (MOOLARBEN UG4) ....................................12
E11.
SENSITIVITY ANALYSIS ...............................................................................................................12
E12.
FACTORS AFFECTING ACCURACY OF NUMERICAL MODEL............................................................12
List of Figures in Main Text
Figure 1:
Figure 2:
Figure 3:
Figure 4:
Figure 5:
Figure 6:
Figure 7:
Figure 8:
Figure 9:
Figure 10:
Figure 11:
Figure 12:
Figure 13:
Figure 14
Figure 15
Figure 16
Figure 17
Figure 18
Figure 19
Figure 20
Figure 21
Figure 22
Figure 23
Figure 24
Regional features and mine plans
Published coalfield geology
Typical stratigraphy – Ulan West
Comparison of natural gamma logs from different locations
Monitoring piezometers and representative wireline logged holes
Ulan seam floor and regional faults
Private bore locations from DWE database and bore census
DDH242 wireline logs and permeability tests
DDH242 Hydraulic conductivity versus natural gamma count
DDH242 effective porosity versus hydraulic conductivity
Triassic sandstone piezometric surface - 2008
Ulan seam piezometric surface - 2008
Trilinear plot of major ionic species
Submergence of Jurassic strata floor
Submergence of Triassic strata floor
Submergence of Ulan seam floor
Predicted piezometric heads and drawdowns in Triassic strata – 2008
Predicted piezometric heads and drawdowns in Ulan seam – 2008
Predicted piezometric heads and drawdowns in Triassic strata – end of 2029
Predicted piezometric heads and drawdowns in Ulan seam – end of 2029
Summary of predicted groundwater seepage rates
Predicted baseflow trends in river catchments
Predicted long term recovered piezometric heads and drawdowns – Triassic
Locations of bores with respect to water table drawdown at the end of mining
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ULAN COAL – CONTINUED OPERATIONS: GROUNDWATER ASSESSMENT – JULY 2009
List of Figures in Appendices
Figure A1:
Figure A2:
Figure B1
Figure C1:
Figure C2:
Figure C3:
Figure D1:
Figure D2:
Figure E1:
Figure E2:
Figure E3:
Figure E4:
Figure E5:
Figure E6:
Figure E7:
Figure E8:
Figure E9:
Figure E10:
Figure E11:
Figure E12:
Figure E13:
Figure E14:
Figure E15:
Figure E16:
Figure E17:
Figure E19:
Figure E20:
Figure E21:
Calculated baseflows from Goulburn River flow records
Flow exceedance probability plots
Locations of registered bores and wells
Hydraulic conductivity test locations
Packer test histograms
Core test histograms
Groundwater monitoring bore locations
Water level monitoring plots
Model layers - perspectives
Groundwater model mesh and drainage network
Recharge areas and steady state calibration control points
Subsidence regime
Calculated versus observed heads – steady state
Steady state pre mining piezometric surface – Triassic aquifer
Steady state pre mining piezometric surface – Ulan seam
Model predicted piezometric surfaces at January 2009
Model predicted piezometric drawdowns at January 2009
Section C100 and Section C166 pore pressures – 1986, 2008
Mine plan and panel identification
Model predicted piezometric surfaces at January 2022
Model predicted piezometric drawdowns at January 2022
Model predicted piezometric surfaces at January 2029
Model predicted piezometric drawdowns at January 2029
Section C166 pore pressures – 2022, 2029
Summary of predicted groundwater seepage rates
Model predicted recovery in Triassic and Ulan seam: 100 and 200 years
Model predicted piezometric surfaces at January 2029 – Moolarben UG4 inc.
Model predicted piezometric drawdowns at January 2029 – Moolarben UG4 inc.
Acknowledgement:
Mackie Environmental Research acknowledges the contributions to this report provided by Coffey
Geotechnics on behalf of Ulan Coal Mines Limited. A considerable volume of information has been
drawn directly from Coffey Geotechnics reports.
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ULAN COAL – CONTINUED OPERATIONS: GROUNDWATER ASSESSMENT – JULY 2009
1.
INTRODUCTION
Ulan Coal Mines Limited (UCML) is seeking approval to extend mining in areas to the north and
west of current operations. The proposal provides for the continued mining of coal at a rate of up
to 20 Million tonnes per annum (Mtpa) over a period of approximately 21 years. Mining will
continue as both open cut and underground longwalls in the Ulan seam at depths ranging from 30
m in the open cut area, to more than 300 m in the underground area. Longwall panels are planned
to be approximately 400 m wide and will be extracted over panel lengths ranging from less than
1.5 km to a maximum length of about 7 km.
Coal extraction will continue to depressurise groundwater contained within the coal seam and in
surrounding Permian strata. In underground areas, subsidence and associated cracking above
caved (goaf) areas will induce depressurisation above the seam which in turn, will induce more
widespread depressurisation extending through undisturbed overburden. Such depressurisation is
likely to induce leakage from groundwater resources in overlying strata including Triassic
sandstones and to a lesser degree alluvial materials associated with the regional river systems.
Mackie Environmental Research Pty. Ltd. (MER) was commissioned by Umwelt Australia Ltd. on
behalf of UCML in 2008 to consolidate existing groundwater studies undertaken by various
consultants, in order to assess the likely impacts of mining on groundwater systems and to provide
advice in respect of future measurement and monitoring of aquifer conditions. The groundwater
assessment was designed to comply with the Department of Planning (DoP) Director-General’s
Requirements for the project, being:
•
a description of the existing environment,
•
an assessment of the potential impacts of all stages of the project including any cumulative
impacts associated with concurrent existing or approved mining activity in the region,
taking into consideration any relevant policies, guidelines, plans and statutory provisions;
•
a description of the measures that would be implemented to avoid, minimise, mitigate
and/or offset the potential impacts, including detailed contingency plans for managing any
significant risk to the environment.
In this context, key areas of study relating to groundwater have been broadly identified as follows:
a description of the different aquifer systems including extent, inter-relationships and
connectivity to surface water systems and any groundwater dependent eco systems;
a description of the interaction between hard rock aquifer systems and surface drainage
systems with a focus on potential loss of baseflows to the Goulburn and Talbragar River
catchments;
an assessment of the regional groundwater systems, flow directions, rates of flow and
hydrochemical signatures of the groundwaters;
details of proposed open cut and underground mining and any water supply works
connected with the mining process that may intercept the aquifer systems;
details of the extent of predicted impacts of mining on identified aquifer systems including
cumulative impacts from other approved mining operations;
assessment of the magnitude of impacts on existing groundwater users likely to be
affected by the proposed (continuing) development;
details of any long term impacts on the groundwater regime.
The contained report provides a summary of information generated and reported in previous
studies. It also includes various computer based simulations undertaken by MER to assess the
likely impacts arising from proposed mining operations.
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ULAN COAL – CONTINUED OPERATIONS: GROUNDWATER ASSESSMENT – JULY 2009
1.1
Historical and recent studies of relevance
Mining of coal at UCML has been conducted since the early 1920’s. The modern open cut and
underground mining operations commenced in 1982 and 1986 respectively and have been ongoing
and continuous ever since. Open Cut mining ceased in 2008 due to approved coal reserves being
exhausted. Historically mined areas, existing operations and proposed mining operations to 2029
together with the approved underground mine plan at the nearby Moolarben Coal Mines situated to
the east and southeast of UCML operations, are indicated on Figure 1.
Significant studies undertaken by UCML relating to groundwater and groundwater-surface water
interactions have mostly been conducted in recent times. With the exception of a study addressing
the Goulburn River diversion, they focus almost exclusively on the underground operations. This
apparent bias is attributed largely to the greater submergence of longwall mining beneath the
regional water table when compared to open cut operations, and the water management issues
arising therefrom.
Significant groundwater assessments have been conducted in five previous studies. Coffey
Geotechnical (Coffey, 2008b) provides a useful summary of those studies which are represented as
follows:
•
In 1991, Coffey Partners International (Coffey, 1991) assessed inflows to the East Pit open
cut, the underground No. 3 longwall operation (current at the time) situated north of the
open cut, and the proposed underground No.4 located to the east of the Goulburn River
and now known as Moolarben underground No. 4. The results of the assessment
suggested groundwater inflows to the underground No. 3 (UG3) workings could be
governed by the presence of a clay layer beneath the Ulan seam which served to isolate the
seam from the underlying Marrangaroo Conglomerate. Groundwater inflows at the time
of the assessment were reported to be around 3 ML/day and the assessment concluded that
future underground mine inflows would increase to 7 ML/day assuming no hydraulic
connection between the Ulan Seam and the conglomerate, or up to 11.5 ML/day if
connection was established.
•
In 1998, the National Centre for Groundwater Management (NCGM, 1998) conducted an
assessment of groundwater inflows to the underground No. 4 operations using computer
based numerical model simulations. The study was in support of an Environmental Impact
Statement for the northern part of the current mine lease, then known as Mining Lease
Application (MLA) 80. The results of that assessment indicated groundwater inflows
increasing from around 4 ML/day in 1998 to about 7 ML/day in 2005, to around 11
ML/day in 2017.
•
In 2005, Coffey Geosciences conducted an assessment of groundwater inflows to the
current underground operations (UG3) using numerical simulation techniques. The results
of that study (Coffey 2005a) were similar to those of NCGM (1998).
•
In 2006 Parsons Brinckerhoff (PB, 2006) conducted an assessment of the impacts of
longwall mining on regional groundwater systems, and future groundwater inflows to UG3
and proposed Ulan West (UW) operations. The regional stratigraphy and aquifer systems
were updated from previous studies based on more recent exploration drill hole data.
Impacts were again assessed using numerical simulation techniques and a maximum
predicted groundwater inflow for all underground operations including UG3 and UW, was
reported as just over 35 ML/day.
•
In 2008, Coffey Geotechnics consolidated a number of studies into a revised groundwater
model (CG, 2008b) in support of a Subsidence Management Plans (SMP) for future
extraction of longwall panels at UG3. The model also included proposed Ulan West
operations and predicted inflow rates of about 18 ML/day at the completion of LW-W3
located on the western side of UG3 (see Figure 1), and a maximum 27 to 30 ML/day at the
completion of mining of both UG3 and Ulan West areas. The model also predicted
depressurisation of shallower strata to distances of 3 to 10 km beyond the mine panel
footprint.
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ULAN COAL – CONTINUED OPERATIONS: GROUNDWATER ASSESSMENT – JULY 2009
Other relevant hydrogeological data has been generated in the course of geotechnical studies
conducted by Strata Control Technologies. Significant data has been generated through the
installation of pore pressure monitoring boreholes designed to provide information on specific
strata depressurisation and groundwater flows in proximity to the subsidence zone above extracted
panels at UG3.
In addition to the above studies there are two other significant regional studies that provide useful
information relating to groundwater:
•
In 2005, Wilpinjong Coal Mine prepared an Environmental Impact Statement in support of
proposed open cut operations (6 pits) located approximately 7 km to the southeast of
UCML operations. Drilling and hydraulic testing of the strata were conducted over a large
area and the Ulan seam and underlying Marrangaroo Sandstone were identified as the
main aquifers. Permian coal measures were noted to contain a large proportion of
mudstones and siltstones exhibiting very low permeabilities. Triassic sandstones were
noted to be elevated and unsaturated in some parts of the area. Impacts of proposed
mining on the aquifers were subsequently assessed using numerical computer based
simulation modelling techniques.
•
In 2006, Moolarben Coal Mines (MCM) prepared an Environmental Impact Statement in
support of proposed open cut and underground operations located to the east and south of
UCML operations. Drilling and hydraulic testing of the Ulan seam and overlying strata
were conducted over a large area and groundwater-aquifer impacts were subsequently
assessed using numerical computer based simulation modelling techniques. Findings from
the study confirmed the relatively permeable nature of the Ulan seam when compared to
overburden strata. Likely impacts on groundwater systems arising from proposed open cut
operations were found to be limited in magnitude and extent since large parts of the open
cut areas were found to be either above the water table or penetrated the water table to
relatively shallow depths. Impacts arising from proposed underground (No. 4) longwall
operations close to UCML, were noted to be largely restricted to Permian age strata with
relatively minor impact predicted on shallower Triassic sandstone strata and the Goulburn
River.
The Moolarben project was subsequently considered by an Independent Hearing and Assessment
Panel (IHAP) in 2007. Panel findings in respect of groundwater noted the open cut operations
were likely to impact in a minor way. In contrast, concerns were raised with respect to the
proposed underground operations and potential impacts on the Goulburn River and adjacent
Triassic sandstone strata. MCM subsequently undertook additional field testing and groundwater
modelling to demonstrate such impacts would be negligible. Approval was subsequently granted
by DoP in 2008.
2.
REGIONAL SETTING
The UCML mine site is located approximately 19 kilometres north-east of Gulgong within the Mid
Western Regional Council Local Government Area (LGA). The area of interest straddles the
Great Dividing Range and drainage catchments associated with the Goulburn River to the east of
the divide, and catchments associated with the Talbragar River to the west of the divide (see Figure
1). Current and proposed mining operations consume a large area - the southern perimeter of the
proposed open cut is located a few kilometres to the north of the village of Ulan.
2.1
Climate
The climate is typical of the western slopes with some similarity to the Upper Hunter region.
Coffey (2008b) report that historical rainfall data for Ulan township indicates annual rainfall
varying between 285 mm and 1157 mm, with an annual average of about 643 mm. The rainfall is
quite evenly distributed with a slight increase during the summer months.
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Evaporation records for Scone weather station (nearest available data) indicate average pan losses
varying between 6 mm/day in summer and 3 mm/day in winter. Annual evaporation ranges
between 1329 and 2093 mm/yr for the 1973 to 2009 period. Since evaporation significantly
exceeds rainfall, a soil water deficit is expected in undisturbed areas for much of the year.
2.2
Drainage, runoff and rainfall recharge
The UG3 and Ulan West panel footprints straddle the Great Dividing Range and include portions
of the upper catchments of Ulan Creek, Bobadeen Creek and several unnamed creeks that drain to
the Goulburn River, and Mona Creek, Cockabutta and other creeks that drain to the Talbragar
River (see Figure 1).
The tributaries of the Goulburn River upstream of the township of Ulan are considered historically
to be intermittent or ephemeral, becoming perennial at some point downstream of the confluence
with Murrumbline Creek. The Talbragar River is probably ephemeral upstream of the confluence
with Turee Creek and intermittent as far downstream as the confluence with Cockabutta Creek
(pers. comm. Umwelt). All other drainages are considered to be naturally ephemeral - the creeks
cease to flow in dry spells.
2.2.1
Base flow to the Goulburn and Talbragar Rivers
Rainfall recharges the shallow and deep groundwater systems throughout the region. In general,
rainfall events are likely to promote limited infiltration in areas of hardrock exposure due to the
relatively impermeable nature of rock exposures unless the presence of jointing and fracturing
provides permeable conduits. Increased recharge is expected in areas where the regolith is well
developed or where alluvial deposits have accumulated.
In areas along the Talbragar River where significant alluvial deposits are reported, or along the
Goulburn River where localised alluvial deposits have been noted, rainfall and stream flow
recharge will replenish these aquifers more readily, and temporarily elevate the water table.
Following these recharge events, the elevated water table will provide a driving head to sustain
localised bank seepage and exfiltration of groundwater back to the drainages in the form of
conventional baseflow. In extended dry and drought periods, baseflow ceases within most
tributaries in the area of interest. The duration and magnitude of these baseflows can be used as a
general indicator of aquifer storage along the river or stream course. In general, sustained
baseflow normally supports the presence of connected transmissive and relatively high storage
aquifers, while a rapid decline in baseflow after significant rainfall events tends to indicate limited
aquifer transmission and storage capacity.
Flow in the Goulburn River has been broadly assessed as part of the current study for the purpose
of considering groundwater-surface water interactions within the shallow alluvial and hard rock
aquifer systems. Flow data for the period 1956 to 1982 for gauging station 210046 at Ulan
township (see Figure 1) has been reviewed and processed to derive estimates of baseflow
contributions using a filtering technique. Results are provided in Appendix A as selected flow
periods (Figure A1) and as a summary flow duration plot (Figure A2). Calculations for a typical
baseflow index of 0.3 suggest flow was mostly sustained during extended dry periods as indicated
on Figure A2.
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The recession trends also suggest the alluvium-colluvium-regolith and weathered bedrock
upstream of the gauging station offers useful storage potential - baseflow exceeds 0.1 ML/day 90%
of the time. These characteristics have been employed in a general way to constrain numerical
modelling of the deeper hardrock baseflow discussed in Section 4. Coffey (2008a) also report
recent estimates of baseflow at Ulan to be generally in the range 1.5 to 2.5 ML/day based on
catchment runoff modelling and other methods.
Baseflow estimations for the Talbragar River have not been conducted since the nearest gauging
station is situated at Elong Elong some 50 km west of the mine lease boundary. Anecdotal
information suggests the river in the vicinity of the project area sustains small flows during dry
periods and ceases to flow during drought periods.
2.2.2
River water quality
Electrical conductivity (EC) of a water sample is an accepted basic water quality parameter that
reflects the total dissolved salts. Baseline monitoring of EC provides a useful indicator of the
stability of a flow system and the occurrence of events that impose change to water quality.
Coffey (2008b) reports that monthly monitoring conducted by UCML in the Goulburn River at
locations upstream and downstream of mining areas over the period 2001 to 2005 inclusive,
indicate an average EC of around 450 μS/cm at the upstream station located near Ulan school.
This average is assumed to be generally unaffected by mining operations. An average EC of
around 1700 μS/cm was recorded at the downstream gauge located at the Ulan Road bridge (see
Figure 1) prior to 2003, and was attributed to UCML mine water discharges from Rowans Dam
into the river via Ulan Creek. Following cessation of discharges, the river water EC fell to an
average of around 750 μS/cm.
Continuous monitoring conducted by UCML at the same stations over the period June 2006 to
October 2007 supports an average EC of around 494 μS/cm at the upstream station and around
1011 μS/cm at the downstream station. The EC at the downstream station over this period was
influenced by discharge into Ulan Creek from a water treatment facility as part of a Reverse
Osmosis (RO) trial, with the water discharged to Ulan Creek from the water treatment facility
having a higher average EC than Goulburn River water. Subsequent to this trial UCML has
incorporated the Bobadeen water treatment facility into its water management system. The
electrical conductivity for water discharged from the water treatment facility has also been
lowered.
The Talbragar River is monitored by Department of Water and Energy (DWE) on a daily basis in
the river channel at Elong Elong about 50km west of the mine lease boundary. While this location
is beyond the area of interest, it does provide a useful indicator of regional water quality. Results
over the period 2000 to 2004 (Pinnenna database, 2004) indicate that EC has an average value of
around 1500 μS/cm but falls significantly (for short periods of time) during intense rainfall events,
and can increase steadily to at least as high as 2500 μS/cm during prolonged dry periods.
2.3
Geology
The mapped geology according to the Western Coalfields Geology Map, Northern Part (NSW
Geological Survey, 1998) is shown in Figure 2 while a stratigraphic column for the Ulan West area
is provided on Figure 3. Sedimentary rock in the area of interest dip at about 1.0o to the northeast
and appear to be contained within structurally disturbed areas around sedimentary-igneous contacts
in the Gulgong area to the southwest, and the Liverpool Ranges to the northeast. The main
lithologies in stratigraphic order (youngest to oldest) are indicated on Figure 2 and include:
•
Recent-Quaternary alluvium
•
Tertiary volcanic intrusives
•
Jurassic Purlewaugh Siltstone
•
Triassic Wollar Sandstone
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•
Permian Coal Measures
•
Carboniferous igneous rocks
•
Silurian to Devonian age basement rocks
Coffey (2008b) provides a summary of the different lithologies which is represented in the
following descriptions.
Recent-Quaternary alluvial sediments of limited extent are associated with some of the creeks in
the project area including Mona Creek, Ulan Creek, Bobadeen Creek, and an unnamed tributary of
Cockabutta Creek. The alluvium tends to be present in relatively discontinuous stringer deposits
along the valley floors and generally consists of fine to coarse grained sands and gravels in a
silt/clay matrix, although some clean sand and gravel deposits are also present. Thicker sequences
are present at the confluence of Ulan Creek and the Goulburn River, as well as to the northwest in
areas adjacent to the Talbragar River. The distribution of Talbragar River alluvium has been
refined for current hydrogeological assessment purposes, to the generally flat lying areas adjacent
to the river defined using regional digital terrain data. These areas are identified on Figure 1 and
are generally supported by borehole information contained in the Department of Water and Energy
(DWE) database of registered bore or well structures. Similarly, alluvium in the vicinity of the
East Pit has been plotted on Figure 1 as the generally flat lying areas adjacent to the Goulburn
River. Coincidentally, this representation agrees with the greater thicknesses of alluvium
associated with the old river course and paleo-channel. The alluvium distributions shown on
Figure 2 generally include thinner occurrences or areas grading to colluvium that may be
unsaturated.
Tertiary volcanics are associated with an area of volcanic activity centred on the Liverpool
Ranges to the northeast. The rocks comprise grey amygdaloidal, and alkaline olivine, basalts and
have intruded strata as plugs and sills.
Jurassic rocks some of which, are present in the northern parts of the project area, are classified
into the following units:
Pilliga Sandstone also known as the Munmurra Sandstone: This unit consists of crossbedded, coarse, quartzose sandstone (commonly ferruginous) with some conglomerate,
minor claystone and shale. It has been reported as a soft, porous quartz sandstone with
occasional conglomeritic beds which is often an excellent aquifer. The basal bed is noted
as being extremely porous. Merriwa town water supply is obtained from this aquifer.
Purlewaugh Siltstone: This unit consists of grey siltstone and mudstone with interbedded
fine to medium grained, grey lithic sandstone in some areas. Observations and
measurements of permeability of core from UCML exploratory drill holes suggest this unit
may act as an aquiclude inhibiting vertical groundwater flow. In the project area it has an
average thickness of around 50 m.
Triassic rocks are represented by a single unit:
Wollar Sandstone: This sandstone is equivalent to the Narrabeen Group further to the
south. In the project area it has an average thickness of around 120 m with minor
variation. Far to the northeast its thickness increases to in excess of 170 m (Coffey 2008b,
Yoo et al, 1983). The sandstone consists of two main facies which are widely identified as
either quartzose or lithic sandstones.
The quartzose facies comprises cross-bedded porous sandstone with well-rounded quartz
pebbles (conglomeritic in parts). McElroy Bryan Geological Services (MBGS) describe
this facies as comprising a cream to yellow coloured, quartz-rich, coarse grained to pebble
sandstone. The average thickness of this unit in the project area is about 85-90 m.
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The lithic facies underlies the quartzose facies and comprises a light grey/green, poorly
sorted sandstone. It contains acid volcanic pebbles (15% to 20%) and grey/green chert
pebbles (20% to 25%) typically to +5mm diameter. A sandstone matrix comprises up to
55% of the remaining rock mass. The average thickness of this unit is about 35 m.
Permian rocks are represented by the Illawarra Coal measures and have an average thickness of
approximately 145 m in the project area. The Triassic/Permian contact is conformable (MBGS,
1996) and occurs at the top of the Middle River and Goulburn coal seams. The sequence has been
intruded by numerous dolerite and basalt plugs and sills which have also penetrated the Ulan
Seam.
Permian Coal Measures (PCM) comprise an interbedded sequence of claystone, siltstone,
sandstone and coal seams. Claystones may be carbonaceous in parts while siltstones and
sandstones vary from fine to coarse grained, commonly well cemented and often with
carbonaceous laminations. Coal seams include the Middle River, Moolarben, Glen Davis,
Irondale and Ulan seams which are all generally dull with minor bright bands and
moderately to weakly cleated (see Figure 3).
The Ulan seam is about 10m thick. The base of the Ulan Seam D working section (the
mined section) is an average of about 90m below the top of the PCM sequence. The Ulan
Seam is commonly underlain by the Marrangaroo Conglomerate.
Marrangaroo Conglomerate: In some areas this conglomerate approaches to within 0.6m
of the Ulan seam. It is a reasonably permeable, weakly cemented, massive rock unit with
granular to pebbly phases. This unit cannot be readily correlated across the project area
and appears to grade to a medium to coarse-grained sandstone in some areas.
Carboniferous rocks occur in the west of the region and form the eastern limit of the Lachlan
Fold Belt which borders the sedimentary sequence of the Gunnedah Basin. They consist mostly of
intrusive igneous bodies and associated volcanics. The main lithologies are (Coffey 2008b):
The Wuuluman Granite to the north which consists of medium to coarse-grained
hornblende-biotite granite.
The Gulgong Granite pluton located to the southwest of the project area. The Gulgong
Granite (and Ulan Granite) is a quartz monzonite, with adamellite, granodiorite, and
diorite. Aeromagnetic mapping suggests the pluton is ovular with a radius of about 10km
or less and an area of approximately 310 km2. The pluton surface dips to the northeast and
probably underlies the Permian rocks. Granite has been intersected below the PCM in
boreholes in the southwest and western part of the project area.
Silurian/Devonian meta-sediments form the basement of the sedimentary basin rocks in the Ulan
area. They are known as the Lue Beds and consist of sandstone, phyllite, slate, limestone, shale,
and greywacke, with additional tuffs, andesitic volcanics, and limestone. These rocks are often
strongly folded and sheared.
2.4
Wireline geophysical logs
Wireline geophysical logging is used routinely by UCML to accurately locate, identify and
correlate strata intersected in exploration drill holes. Typical logs include caliper, resistivity,
natural gamma, density, neutron and sonic. These logs contribute to an understanding and
hydrogeological characterisation of strata.
Figure 4 provides wireline natural gamma logs for several exploration boreholes within the mine
lease (locations shown on Figure 5). The logs essentially record natural gamma radiation emitted
by the rock strata which is in turn, attributed to clay content. In an indirect way, the logs provide a
general indication of both the matrix permeability of the strata and the likelihood of anisotropic
conditions (variable permeability in different directions) within a stratigraphic unit.
The interface between major stratigraphic units is well defined by these logs with the Permian Coal
Measures and Jurassic Purlewaugh Siltstone revealing greater clay content than the Triassic Wollar
Sandstone. The logs are especially useful in discriminating the Triassic quartzose facies from the
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underlying lithic facies within the Wollar Sandstone. The quartzose facies generally identifies
with a relatively low and remarkably constant emission count indicative of more porous,
permeable and weakly anisotropic sandstone, than other strata (see Section 3.3.1 below).
2.5
Bedding and structural features
Drilling and geophysical wireline logging has provided an extensive database which underpins the
interpreted bedding geometry in the project area. Beyond the project area the strata are defined by
exploration activity associated with Moolarben and Wilpinjong coal projects, or with established
geological maps.
Sedimentary rock strata dip to the north-east as indicted by the structure contour mapping for the
Ulan seam floor shown on Figure 6 which has been generated from UCML geological modeling
with regional inference using kriging techniques supported by hand contouring in areas where
there is a low density of exploration bores.
A number of near vertical faults have been identified that displace the strata. A major fault zone
known as the Spring Gully Fault is located in the eastern portion of the mine lease (Figure 6) and
has been observed in the East Pit open cut highwall. The fault is situated along the eastern
boundary of UG3 and is a barrier to mining. It trends north-south and exhibits a displacement of
up to 8m. Test pumping was conducted at several water bore sites in 2005 in order to assess the
hydraulic continuity across the structure (Coffey, 2005b). Results of testing confirmed continuity,
suggesting the fault does not act as a significant barrier to groundwater flow. This continuity is
also evident in regional observation piezometers like PZ04, PZ14, PZ24 and MPZ101 (Figure 5)
which are all situated on the eastern side of the fault and exhibit head losses associated with
mining activity on the western side of the fault.
A number of other major faults are identified on the regional geological map (Figure 2) and are
also indicated on Figure 6. Very little is known about these faults. However for current
hydrogeological assessments they are assumed to be similar to the Spring Gully Fault insofar as
they do not act as a barrier to groundwater flow - depressurisation of strata induced by future
mining operations is assumed to be uncontained.
A number of volcanic plugs have also been identified eg. The Echidna sill. These features may
enhance groundwater storage around their perimeters as a result of alteration, cracking or seam
cindering.
2.6
Regional stress field and jointing
Coffey (2008b) report the in-situ stress field can be a significant control on the permeability of
fractured rock. The report also notes that the orientation of the in-situ horizontal stress over the
Ulan Mine lease was estimated from dilated rock cores from exploration drill holes, together with
palaeomagnetism information by Schmidt (1998). Results appear to indicate that the principal
horizontal stress at Ulan is oriented N-S in the part of the mine lease north of the Echidna Sill
(located underneath the northern reach of Ulan Creek) but is deflected E-W between the Echidna
Sill and the Spring Gully Fault. SCT (2007a) note the direction to be NE-SW from subsidence
bias observations and from over-coring measurements.
Joint controlled drainage lineaments evident from detailed airborne topographic survey and from
the regional 1:25000 topographic surface, support numerous directions including N-S, NNW-SSE
and NE-SW all of which have influenced weathering and erosion to some degree. This is
particularly evident in the course of Ulan Creek and its tributaries, and the Goulburn River in the
vicinity of ‘The Drip’ (see Figure 1).
Joint control tends to be less conspicuous or absent in areas of upper Triassic strata (upper
quartzose sandstone) or Jurassic cover probably as a result of the more friable sandstones in the
quartzose facies or the increased presence of siltstones and claystones in Jurassic strata.
Jointing in Triassic sandstones might be expected to provide increased secondary permeability and
porosity. However, general observations of outcrop and inspections of rock core suggest that
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jointing is often widely spaced and as such, may not significantly enhance groundwater flow
systems at depth due to infrequency and increasing confinement. The Ulan seam may be an
exception where a combination of cleating, bedding shear and jointing provides the dominant
transmission mechanism.
3.
GROUNDWATER HYDROLOGY
Groundwater occurrence within the region has been mapped over many years.
domains have been identified:
•
the unconsolidated alluvial aquifers associated with some drainages;
•
the shallow regolith and weathered rock zone; and
•
the more regional sedimentary rocks.
Three principal
The presence and geometry of these domains has been determined using geological mapping, air
photos, remote sensing, exploration drilling and regional borehole databases.
3.1
Existing licensed bores and wells in the region
Relatively shallow groundwater resources have been exploited by the construction bores and wells
throughout the region. In order to determine the locations of existing bores and wells, a records
search has been conducted on the DWE database. This database contains all registered structures
and includes both pumping bores and wells, and exploration/test wells which may have been
completed as monitoring bores. Measurement of water level and basic water quality parameters
has also been undertaken as part of a regional bore census conducted in 2007 (Coffey, 2008) and
updated in 2009 by UCML. Appendix B provides a summary of known locations of bores and
wells.
Figure 7 identifies 48 private bores located within a zone extending some 8 km or more beyond the
mine panel footprint for UG3 and Ulan West. An overview of bore construction information
indicates most locations appear to draw groundwater from hard rock aquifer zones rather than the
alluvial areas. Yields are variable but generally low, and water qualities vary from fresh to slightly
brackish.
3.2
Groundwater occurrence in unconsolidated sediments
Alluvial sediments can be broadly classified as either Quaternary shallow valley fill sediments that
are substantive along the Talbragar River and relatively minor along other drainages west of the
Great Divide, or the deeper and older Tertiary sediments noted particularly in the Moolarben area
east of the divide. Quaternary (and Recent) alluvium east of the divide is more localised.
Figure 1 provide shows the occurrence and approximate boundaries to the unconsolidated alluvial
materials associated with the Talbragar River based on topographic grade, air photo inspections
and limited borehole information (DWE database). This distribution is less extensive than the
distribution identified in Figure 2. Beyond the perimeter of the alluvium shown on Figure 1, the
unconsolidated materials are expected to grade into colluvial deposits and weathered bedrock (and
regolith), the characteristics of which may be highly variable.
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The alluvium tends to be a mixed sequence of sands, silts and clays as determined from a small
number of bores identified as part of a regional bore census undertaken by UCML. Groundwater
contained within these sediments occurs at depths of 10m or so with estimated saturated
thicknesses of alluvium of the order of 20 to 25m. Minor occurrences in the upper reaches of
Mona Creek and Broken Back Creek, were drilled in late 2008 and piezometers were installed as
part of the UCML regional groundwater monitoring program (see Figure 5 for locations). Results
have shown the alluvium to be thin (less than 5m) and comprised of sandy, silty deposits with
limited saturated thickness. Most test holes were essentially dry.
Shallow alluvial materials associated with the Goulburn River tend to be more localised than the
Talbragar River alluvium. Alluvium (now removed) that was originally located along the river
course as a paleo-channel before the river was diverted around the East Pit, is also shown on
Figure 1 as are alluvial deposits in the vicinity of the confluence of the river with Ulan Creek that
are known as the ‘northern alluvium’. Paleo-channel deposits comprise interbedded clays, sandy
clays, sands and sandy gravels that are strongly cemented in the upper 5m with clay bands up to
5m thickness alternating with more granular beds up to 4m thickness. The northern alluvium
exhibits different characteristics comprising silty sands at the surface, underlain by sands and
clayey sands, with sands and gravels towards the base (Coffey, 2008a). Deposits along Moolarben
Creek appear to be similar in character to sediments identified in the northern alluvium
(Moolarben EA, 2006).
Tertiary paleo-channels identified in the central south part of the Moolarben project area are
reported to host infill sediments up to 48m thick which are comprised of poorly sorted quartzose
sediments partly consolidated within a clayey matrix.
3.2.1
Hydraulic properties of alluvium
Hydraulic properties of the alluvial deposits along the Talbragar River, have not been measured.
Since the materials comprise a mixed assemblage of clays, silts, sands and gravels, the horizontal
hydraulic conductivity range is expected to range from 0.01 to 10 m/day while an effective
porosity range is likely to range from 1% to perhaps 20%. The vertical conductivity range is
expected to be lower.
Measured hydraulic conductivities of alluvium associated with the Goulburn River range from
0.01 to 10 m/day. Measured conductivities of alluvium in the Moolarben project area are reported
to range from 0.05 to 3 m/day (Moolarben EA, 2006).
3.3
Groundwater occurrence in hard rock strata
Groundwater within the Jurassic, Triassic and Permian strata in the project area is held
predominantly as interstitial (pore space) storage. The groundwater is derived from recharge by
rainfall infiltration through the shallow weathered rock zone into the underlying rocks over
geologic time. Recharge in topographically high areas has sustained a moderately elevated water
table that is constrained mostly by surface drainage systems flanking these high areas. That is, the
water table mound beneath the elevated areas is intercepted by local drainages which act to relieve
groundwater pressures by either conveying seeped groundwater as baseflow down slope to the
Goulburn and Talbragar rivers, or by evapotranspirational losses through vegetation along these
same drainages. As a result, the geometry of the water table tends to be a subdued reflection of
topography.
Groundwater flow rates within the hard rock strata while not measured, are likely to vary
significantly. Higher rates of flow are expected within the Triassic sandstones which are porous
and permeable, while much lower rates of flow are expected within Permian sandstones, siltstones
and claystones which are relatively impermeable.
There is potential for groundwater exchange between strata via fractures and micro cracks which
introduce secondary permeability throughout the strata if they form a connected network.
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However it is extremely difficult to establish the occurrence, frequency and extent of these
fractures since they are mostly vertical or sub vertical and consequently are less likely to be
intersected by exploration boreholes than fractures that might occur at shallow angles. Core
inspections and borehole permeability testing undertaken as part of the current study suggest
fracturing in hard rock strata at depth is relatively limited and deeper strata are therefore likely to
exhibit low secondary permeability. Where observed in core, the fractures are often clean and
without alteration, implying negligible movement of groundwater along these features.
The Ulan coal seam is identified as the main aquifer in the Permian strata insofar as it offers
enhanced groundwater storage and transmission characteristics through the presence of cleating.
Historical mining operations at Ulan have depressurised the seam for distances of more than 10 km
beyond mined areas. Seam depressurisation has in turn induced vertical leakage and pressure
losses within overlying and underlying strata.
3.3.1
Hydraulic properties of hard rock strata
Hydraulic testing has been conducted by UCML in the hard rock strata within the project area as
part of regional hydrogeological evaluations over a number of years. Test procedures have
historically comprised conventional packer injection type testing and test pumping. Laboratory
measurements on strata core have been conducted as part of the current study to establish an
expected range in matrix hydraulic conductivities together with bulk and effective porosities.
Other measurements that have contributed to the hydraulic properties knowledge base include
parameters relating to geomechanical properties - sonic velocity, unconfined compressive strength
(UCS) and Youngs modulus. Testing of the Ulan seam and other strata, has also been undertaken
in the Moolarben area (Moolarben, 2006) as part of Environmental Assessment studies. This
information has been used to supplement UCML data.
Recent UCML packer testing has been completed at 8 exploration borehole locations. Testing has
been conducted using either a single packer drill stem assembly (eg. borehole DDH242) or a
straddle packer assembly with test intervals varying from 3 m to 6 m. Test procedure has
comprised measurement of the rate of clean water injection to test intervals over a range of
injection pressures. Test locations and results are provided in Appendix C. However it is noted
that a number of tests may have been conducted at the limit of the equipment. For these tests the
analytical results are regarded as upper limit estimates of hydraulic conductivity.
Laboratory tests have been conducted on selected core from two exploration holes DDH242 in
longwall panel LW24 in the UG3 area, and DDH340 in LW-UW8 in the Ulan West area. These
tests were undertaken in order to provide improved estimates of intergranular matrix conductivity
and to examine the ratio of vertical to horizontal conductivity (anisotropy). Total porosity and
effective porosity were also determined for selected samples. Details are provided in Appendix C
and summarised in Table 1.
Table 1: Summary of core measurements by formation
Strata
Kv (LN)
Effective porosity
m/day
%
Jurassic sandstones
2.15E-03
Triassic quartzose sandstones
5.62E-02
6.1 to 16.9
Triassic lithic sandstones
2.66E-04
1.5 to 12.8
Permian sandstones
8.03E-06
0.3
Permian siltstones
4.13E-07
Permian shales
1.98E-07
Kv=vertical hydraulic conductivity LN = mean for log normal distribution
The hydraulic conductivity distribution for the different strata is usefully summarised on Figure 8
which illustrates selected wireline logs for borehole DDH242 together with the results of packer
and core conductivity tests.
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The plot indicates:
•
a general correlation between packer tests and core tests to the extent that higher core
conductivities tend to correlate with higher packer test conductivities;
•
core conductivities tend to inversely correlate to sonic velocities - high conductivities
equate to low velocities (eg. Triassic quartzose sandstones) and lower conductivities
equate to higher velocities that are generally associated with higher cementation and
increased rock strengths;
•
core conductivities inversely correlate to wireline gamma ray emission counts – high
conductivities equate to low counts (eg. Triassic quartzose sandstones) and lower
conductivities equate to higher counts;
•
The Jurassic (sandstone) samples tend to exhibit an order of magnitude lower
conductivities than the Triassic quartzose samples;
•
Most of the Triassic quartzose samples exhibit relatively high conductivities (above
0.01 m/day) consistent with a porous and sometimes friable sandstone evident in hand
specimen;
•
Triassic lithic sandstones are evidently less permeable than the Triassic quartzose
samples with the upper 10 to 15 m exhibiting very low conductivities;
•
Permian non coal strata are the least permeable rocks being mostly below 1.0E-5 m/day
for sandstone-siltstone core samples (claystone-shales and coal not sampled).
Figure 9 explores the correlation between measured core conductivities and gamma count. This
relationship is considered to be particularly useful in extrapolating the strata matrix conductivities
to locations where core tests have not been conducted ie. at all exploration holes since wireline
gamma and other logs are routinely run. Regionally, the gamma log characteristics show a high
degree of similarity (Figure 4).
Figure 10 explores the relationship between effective porosity and conductivity for selected
sandstone samples. While the data is limited, a useful relationship is clearly apparent – high
effective porosity equates to high conductivity, and low porosity equates to low conductivity as
expected. The relationship implies Triassic quartzose sandstones are the most permeable and
porous strata while Permian non coal strata are the least permeable and least porous strata.
Compressibility and subsequent estimates of storativity (as Ss) have been calculated from
laboratory measurements of Youngs Modulus undertaken by SCT Operations Limited (SCT,
2007) and measurements of total porosity (Appendix C). Specific storage estimates ranging from
1.69E-06 to 5.13E-06 1/m have been calculated for a modulus range from 3.1 to 17.7 GPa.
3.4
Groundwater monitoring
Coffey (2008a) provides a comprehensive summary of the groundwater monitoring networks
installed at UCML.
The main network comprises the North Monitoring Network (NMN) shown on Figure 5 which
supports regional scale monitoring of the impacts of mining on groundwater systems. The NMN
serves the purpose of monitoring groundwater levels at relatively discrete horizons in the Permian
strata and the overlying Triassic and Jurassic strata. The monitoring data collected from the
network facilitates an assessment of the piezometric head distribution in the hardrock groundwater
system. The network currently comprises more than 20 locations where strata piezometric levels
or pore pressures are monitored, usually at numerous depths. Conventional screened piezometers
are monitored manually on a quarterly basis for groundwater levels and on an annual basis for
groundwater quality. This network also includes piezometers associated with geotechnical studies
relating to the subsidence zone. Appendix D lists monitoring piezometer survey and completion
information for the networks, and plotted piezometric responses over time.
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The Bobadeen Monitoring Network (BMN) was installed in 2003 to monitor the impacts of
irrigation of mine water on groundwater levels and groundwater quality of unconsolidated
sediments within the upper catchments of Mona Creek, Ulan Creek, and Spring Gully Creek.
Irrigation water is applied using five pivots in the northwest and central parts of the mine lease.
The BMN consists of 9 piezometers installed to depths of up to 12m in residual soils, regolithic
materials and colluvium. The network does not provide information with respect to the regional
aquifer systems.
The Intermittent Monitoring Network (IMN) consists of 20 locations in hardrock strata or mine
spoil (see Appendix D). The IMN comprises bores or piezometers that either have been installed
for specific purposes, and/or have extensive screens (and so measure a depth-averaged or
composite hydraulic head). The network may be monitored intermittently for groundwater levels
and qualities to provide additional data to complement the NMN monitoring data.
The Goulburn River and Ulan Creek Alluvium Monitoring Network (AMN) consists of 9
locations (see Appendix D) which are generally screened throughout the thickness of alluvium
associated with the Goulburn River or Ulan Creek. They may be monitored intermittently for
groundwater levels and quality to provide additional data for ongoing projects.
The Goulburn River Diversion Baseline Assessment Monitoring Network (GRDBAMN)
network was installed in 2006 as part of an assessment of the Goulburn River Diversion. It
consists of 4 locations in the East Pit and together with piezometers in the AMN, is monitored to
provide groundwater level data for the alluvium, Permian Coal Measures, and East Pit spoil
associated with the Goulburn River.
3.4.1
Piezometric surfaces and groundwater flows
Water level data for the NMN has been compiled since late 2005 for both undisturbed areas, and
areas impacted by mining and is the main database underpinning current hydrogeological studies
for future impacts assessments. This database has been used as the primary source for
interpolating piezometric surfaces in the regional hardrock strata. Data plots for individual
piezometers within this network are provided in Appendix D.
The phreatic surface (water table) which resides in the Triassic quartzose facies of the Wollar
Sandstone, is shown in Figure 11 for measured responses in 2008-9. The piezometric contours in
the project area support a north-easterly groundwater flow direction which tends easterly at the
northern end of UG3 then south-easterly under the influence of the Goulburn River drainage
system. These changing flow directions suggest rainfall recharge to the Triassic strata occurs
where it subcrops and outcrops to the southwest of the proposed Ulan West mine. In this area
there is minimal or no overlying Jurassic Purlewaugh Siltstone present. The Great Divide is
plotted to illustrate an apparently weak influence from the Talbragar River in the area of interest –
the groundwater divide does not align with the topographic divide.
Figure 12 shows the assessed piezometric surface for the Ulan Seam for 2008-9. This surface
differs markedly from the water table shown in Figure 11 and illustrates the significant impact of
mining operations where extracted and dewatered panels have depressurised strata and attracted
flow from all directions as expected – the UG3 operations effectively act as a groundwater sink.
3.4.2
Groundwater Quality
Groundwater sampling data collected over the last 10 years, but particularly over the annual water
quality monitoring rounds from 2002 to 2008, reveal distinctive water types for the Jurassic,
Triassic, Permian strata and the Ulan seam with respect to basic water quality parameters EC and
pH while ionic speciation suggests broader similarities.
Parameters EC and pH for 104 groundwater samples collected between 2002 and 2008, are
summarised in Table 2. Results indicate that overall, the groundwater salinity (as EC) of the
Triassic (Wollar) Sandstone is typically around half the salinity of Permian strata sampling and
less than one fifth the salinity of Jurassic sampling. pH measurements support a weakly basic
signature for Permian groundwaters, a neutral signature for Triassic groundwaters and a weakly
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acidic signature for the Ulan seam. It is also noted that the EC of groundwater of the quartzose
strata of the Wollar Sandstone is comparable to the EC of Goulburn River surface water and is
significantly lower than the average value of EC for surface water of the Talbragar River at Elong
Elong.
Table 2. EC and pH of undisturbed strata
Unit
No. samples
EC (St.Dev) uS/cm
pH (St.Dev)
Jurassic
9
2554 (1148)
7.61 (1.17)
Triassic
59
471 (326)
7.50 (1.64)
Permian
10
1151 (626)
9.53 (1.62)
Ulan seam
26
1310 (1739)
6.47 (0.31)
Representative water sample data for major ions is provided in Appendix D. A number of samples
for the Moolarben project (Moolarben, 2006) have also been included for completeness. This data
set is summarised on the tri-linear speciation plot also known as a Piper diagram – Figure 13. The
plot comprises two triangular fields representing cations and anions, and a central diamond field.
Individual samples are represented as percentage milli-equivalents within the lower triangular
fields where each apex represents 100% of the nominated ion. Plotted positions within the
triangular fields have been projected into the central diamond field, thereby facilitating a
generalised classing of groundwaters and examination of possible mixing trends.
Plotted data is summarised in the following Table 3. The Ulan seam exhibits elevated bicarbonate
(as percentage milli-equivalents) when compared to other strata possibly due to the influence of
carbonates associated with localised volcanic intrusives. The presence of sodium in Permian coal
measures samples (interburden) may be attributed to similar mechanisms observed in the Upper
Hunter coalfield where enhanced levels are associated with cation exchange (Na for Ca) relating to
the presence of smectite in interburden.
Table 3. Ionic species relevance for different stratigraphic units
Unit
3.4.3
Cations
Anions
GR alluvium
Na > Mg > Ca
SO4 > Cl > HCO3
Jurassic
Na > Mg > Ca
Cl > HCO3 >> SO4
Triassic
Na > Mg, Ca
HCO3, Cl >>SO4
Permian
Na > Mg, Ca
HCO3, Cl >>SO4
Ulan seam
Na > Mg, Ca
HCO3 > Cl >>SO4
Goaf Water Quality
Coffey (2008a) report that monthly monitoring of goaf water being extracted by underground
dewatering pumps provides some information on the change in groundwater quality in the
workings with time. The results of an assessment of monitoring of extracted groundwater from
dewatering pumps 12, 20, and 22 over the period November 2006 to August 2007 are shown in
Table 4 and plotted on Figure 5. Each of these pumps controls the groundwater levels in specific
underground compartments. Pump P12 is in the oldest (up dip) goaf compartment (longwalls LW9
to LW12) while pump P22 is in the youngest (down dip) goaf compartment – see Figure 5 for
locations of pumping bores.
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Table 4. Average goaf water EC and pH over the period 2006 to 2007 (from Coffey 2008a)
Pleuger Pump P12
(LW9 to LW12)
Pleuger Pump P20
Pleuger Pump P22
Average
2195
1326
846
Standard Deviation
131
285
32
Average
6.5
6.7
7.2
Standard Deviation
0.2
0.1
0.2
Average
945
302
10*
Standard Deviation
133
160
*
EC (µS/cm)
pH
Sulphate (mg/L)
* Two measurements only (10mg/L each).
A trend of increasing salinity and sulphate concentration, and decreasing pH in a down dip
direction, is suggested and is attributed to pyrite oxidation and dissolution (and limited pH
buffering from interburden) – the longer the timeframe, the greater the effects. It is noted that
significant recirculation of mine water and tailings decant water was occurring during this period
which potentially impacted the pH and EC measurements of the goaf water.
Single water samples collected from each of the dewatering pumps P 6 (longwalls LW1 to LW8),
P10 (longwalls LW9 to LW12), and P12 (longwalls LW9 to LW12) in August 1997 (Kinhill,
1998) further demonstrate the general impact of pyritic material on water quality. Results for basic
water quality parameters are listed in Table 5. Overall, the salinity (expressed as EC) appears to
increase at a rate of around 1000 µS/cm per 10 years however this process is not expected to be
linear.
Table 5: Goaf water quality in August 1997 (from Coffey 2008a)
3.4.4
Pleuger Pump P6
(LW1 to LW8)
Pleuger Pump P10
(LW9 to LW12)
Pleuger Pump P12
(LW9 to LW12)
EC (µS/cm)
1714
1450
984
pH
6.05
6.44
7.36
Sulphate (mg/L)
733
550
210
Historical mine water influx
Underground mine water influx has historically comprised contributions from many sources
including
•
seepage into the old underground No.2 (UG2) operations to the south of UG3;
•
seepage to UG3;
•
seepage to open cut mining in the East and West pits;
•
rainfall and runoff to local catchments and infiltration through pit spoils;
•
and potential river leakage through the East Pit end wall.
The determination of theses various contributions is important for future predictions but
quantification has been complicated by the presence of re-circulated mine waters that have been
sourced via different leakage pathways.
For example, Coffey 2008a report that in August 1996 tailings disposal at Ulan mine was
redirected from the East Pit overburden to the Northwest Pit overburden in order to mitigate the
build-up of mine water in the East Pit ahead of highwall mining. About 2.2 ML/day of tailings
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were being produced in 1995 and reposited in dams within spoils. Much of the supernatant is
believed to have leaked from the dams and reported to the East Pit pond and resulting in an
increase in East Pit water levels in August 1996 (approximately 650 ML of water - HLA, 2001).
This may have driven an increased rate of leakage to UG3 operations which are situated down dip
of the open cut.
The average calculated groundwater inflow to UG3 during 1997 was around 3.5 to 4.0 ML/day.
Short-duration increases in inflow of up to 12 ML/day or more were experienced in mid 1998 and
early 2000. The sharp increase in mid 1998 coincided with commencement of highwall mining in
the West Pit and a 1 in 100-year rainfall event that flooded the access pit to a depth of several
metres. This event also generated a hydraulic head of approximately 15 m of water on the 40 m
barrier between the end of the highwall entries and longwall LW-A (see Appendix E, Figure E11
for panel location). The sharp increase in early 2000 coincided with the introduction of the South
5 Tailings Dam in 1999 and a subsidence event at Ulan Creek associated with highwall mining.
The historical dataset indicates that water within the West Pit, and probably the East Pit,
(comprising runoff, rainfall infiltration, supernatant and some groundwater) was migrating through
the highwall entries and potentially along fractures or cleats, to the underground goaf. HLA
(2001) estimated that a yearly average of about 2.6 ML/day of water acceded to the underground
workings from these sources during very wet conditions.
In 2008 UCML decommissioned the use of South 5 Tailings Dam which was estimated to
contribute up to 10 ML/day water make into Underground No. 3.
UCML currently monitors water levels in the goaves and discharge volumes from underground
dewatering pumps, via an electronic monitoring system. This data and other site data have been
used to generate a water balance for the 2007-2008 period for underground operations. The
balance takes into account the volumes of water pumped into and out of underground operations,
product coal moisture, estimates of re-circulation from surface stored waters, rainfall and runoff to
spoils and numerous other factors which are described in detail in Umwelt, 2009. Results of the
most recent water balance monitoring support a groundwater ingress to operational and subsided
areas (including rainfall influx via surface subsidence related cracks) of about 7.8 ML/day in
January 2007 rising to 9.2 ML/day in December 2008 and averaging about 8.5 ML/day at the
beginning of 2008.
4.0
COMPUTER SIMULATION OF PROPOSED MINING
Proposed mining will continue to extract coal from the Ulan seam in the extended West Pit open
cut area and from longwall panels in the UG3 and Ulan West areas. In underground areas, panel
extractions will continue below the prevailing regional water table and will result in further
depressurisation of the coal seam and overlying strata including Permian coal measures and
Triassic strata. Depressurisation above the seam will continue to be enhanced through caving and
subsidence, and a pressure (loss) wave will propagate further beyond the extracted panels at a rate
governed by the prevailing hydraulic properties of all strata and the drainage characteristics within
the subsidence zone.
Evaluation of the pressure loss regime for seam extraction that includes simultaneous evolution of
a subsidence zone, is extremely difficult and complex and requires analyses in both space and
time. The most appropriate technique to undertake such analyses, is numerical simulation using
computer based modelling techniques.
An updated computer based mathematical model of the region has been developed in order to
understand the likely regional extent of depressurisation and to predict mine water influx. The
model computer code known as Modflow-Surfact (Hydrogeologic, 1996) employs a numerical
finite difference scheme for solving a set of differential equations known to govern groundwater
flow. Importantly, the code is reasonably robust in handling steep hydraulic gradients and variably
saturated zones that commonly evolve above subsided panels.
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The modelling method requires dividing the overall area of interest into a large number of separate
cells defined by a mesh area which incorporates the proposed mine panel geometry and seam
extraction sequence, the spatial variations occurring in strata properties, the prevailing drainage
system, and the expected hydraulic gradients that evolve during the simulation period.
A summary of the constructed model is provided in Appendix E. The model layers adopt a
geometry consistent with the known regional stratigraphy but with additional layers included to
provide improved representation of strata groundwater pressures.
4.1
Groundwater model properties and initial conditions
Properties assigned to the model which govern groundwater flow, include hydraulic conductivity,
elastic storage and specific yield. Hydraulic conductivities assigned to each model layer below
layer 1 were initially informed by core testing (matrix conductivities only) as summarised in
Appendices C and E. These values were then adjusted within a reasonably narrow range as part of
the model calibration process which involved both steady state and transient simulations.
Resulting values suggest the regional flow system at depth is dominated by matrix intergranular
flow rather than fracture flow, except for the coal seams where cleating provides the flow conduits.
Boundary conditions were also assigned throughout the aquifer model. These are numerical
conditions that constrain or bound the model domain. Constant head river conditions have been
imposed along the Goulburn River for the reach downstream of the confluence with Bobadeen
Creek where river flow is assumed to occur at all times. These conditions enforce seepage from
surrounding areas of elevated water table to the river, or seepage from the river to surrounding
strata if the water table in those strata, is lower than the river level(s). River conditions have also
been imposed on the Talbragar River in the western part of the model below the confluence with
Mona Creek. Drain cells have been used to represent all other reaches of the rivers and creeks
which are assumed to be either intermittent or ephemeral. Assigning these conditions allows the
model water table to drain to the creek lines if the elevation of the water table is higher than the
creek bed elevations, or to fall below the creek bed without inducing leakage from the creek ie. the
creek dries up. Drain cells have also been assigned to open cut areas, underground development
headings, gate roads and longwall panels at elevations equivalent to the seam working section
floor. These nodes have been carefully scheduled to attract groundwater seepage in general
accordance with the historical and proposed mine plan.
Distributed flux conditions have been employed to represent regional rainfall recharge. This
recharge has been applied at differing rates across the model domain depending on the shallow and
surficial geology present at particular locations.
Groundwater abstraction by local landholders for domestic, stock and irrigation purposes, has not
been included.
4.2
Model calibration to field conditions
The assembled groundwater model has been calibrated against measured groundwater levels and
historical mining operations. This process has involved both steady state and transient history
matching of model predictions to measured water table and pore pressure data.
Steady state calibration aimed to generate a pre-mining water table nominally at January 1986
before open cut operations had advanced significantly below the water table, and before any UG3
operations were commenced. The procedure involved adjustment of strata hydraulic properties
and regional rainfall recharge rates until a plausible match was achieved between the observed
water levels at a number of regional bore locations, and the predicted levels at those same
locations.
The transient calibration process involved further adjustment of strata hydraulic properties and
other parameters on a trial and error basis until predicted piezometric elevations and groundwater
seepage to UG3 operations plausibly matched observed piezometric elevations and observed water
make. Results of both calibration procedures are provided in Appendix E.
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Figure E6 in Appendix E illustrates the predicted pre-mining water table. This plot establishes a
steady state baseline position and facilitates an understanding of groundwater flow directions and
rates of flow. The piezometric contours shown on Figure E6 reasonably correlate to those shown
on Figure 11. Flow pathlines are also shown on Figure E6. These pathlines describe individual
water particle tracks over a long period of time and are useful in understanding the regional flow
systems. The prescribed pathlines that transgress the project area, define recharge in an area west
and south-west of the proposed Ulan West underground mine. From that area the pathlines
describe a route either to the north and north-west to the Talbragar River catchment, or to the
north-east and east eventually turning south-eastward and exiting the model down the Goulburn
River catchment. The groundwater flow divide defined by these pathlines is located up to 5 km
west of the topographic Great Divide.
Figure 14 gives the predicted pre-mining saturation height (submergence) of Jurassic strata
calculated by subtracting the floor of these strata from the pre-mining water table shown on Figure
E6. This plot clearly shows Jurassic strata are only likely to be saturated in areas to the north-east
of UG3 with increasing submergence further to the north-east.
Figure 15 gives the predicted pre-mining submergence of Triassic strata similarly calculated by
subtracting the floor of the Wollar Sandstone (lithic sandstone base) from the pre-mining water
table. This plot shows the sandstone was saturated over most of the UG3 area prior to mining,
with zero saturation located at the southern extremity of the panel footprint. Increasing
submergence to more than 100 m head of water, is indicated in north-eastern areas above panels
LW-29 to LW-33.
Figure 16 gives the predicted pre-mining submergence of the Ulan seam. This plot shows the
seam was probably saturated over most of the underground and open cut areas prior to mining.
Increasing submergence to more than 190 m (including Triassic strata) is indicated in north-east
areas above panels LW-29 to LW-33.
Transient calibration results for the simulation of mining from 1986 to 2009 are provided in
Figures 17 and 18 as both the predicted piezometric surface and the drawdown for both the
Triassic strata (Wollar Sandstone lithic facies) and the Ulan seam in 2009. Figure 17 indicates
complete dewatering of Triassic and deeper strata above mined panels with measurable
depressurisation extending some 2 to 3 km beyond the panel footprint (defined by the 2 m
drawdown contour) in down-dip directions and further in up-dip directions. The extended
drawdown in a north-west to south-east direction in areas south and south-west of mining
operations, represents loss of saturation in shallow non-Triassic strata which have been assigned to
the same model layer in areas up-dip of mining and have been affected by down-dip drainage. In
reality, parts of these areas are likely to be perched water tables supported by rainfall recharge to
the shallow regolith and weathered bedrock. Figure 18 similarly indicates complete dewatering of
the Ulan seam in mined panel areas with depressurisation in the Ulan seam extending more than 10
km beyond the panel footprint in down-dip directions and further in the Moolarben area.
Appendix E provides a detailed summary of other aspects relating to the calibration procedures.
Vertical section plots of pore pressure distributions are also provided as Figure E10 in Appendix E.
These plots are useful in illustrating the dewatered zone above mined panels.
4.3
Future mining induced depressurisation of rock strata
The calibrated aquifer model has been used to simulate depressurisation of the Ulan seam and
overlying strata based on the future mine plan which provides for extraction of coal over a period
of 21 years to the end of 2029 in both UG3 and Ulan West underground areas, and in extensions to
West Pit open cut.
Underground headings, gate roads, longwall panels and open cut strips have all been carefully
scheduled in the prediction model according to the mining timetable provided in Appendix E,
Table E6.
Figures 19 and 20 provide the extent of predicted depressurisation at the end of mining at Ulan
West in 2029. Figure 19 indicates complete dewatering of Triassic strata above all mined panels
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with depressurisation extending some 4 to 5 km beyond the panel footprint. Figure 20 indicates
complete dewatering of the Ulan seam in mined panel areas with depressurisation in the Ulan seam
extending more than 20 km beyond the panel footprint.
Figures E16 and E17 in Appendix E provide vertical section plots of pore pressures at the
completion of mining. These plots illustrate the extent of the unsaturated zones above mined
panels.
4.4
Predicted groundwater seepage to underground operations
On completion of the 21 years simulation period, specific zone budgets were extracted from the
groundwater model in order to provide estimates of mine water influx. Results are summarised on
Figure 21 for UG3 and UW operations respectively.
Reference to Figure 21a indicates a
predicted water make in UG3 which rises steadily from less than 0.1 ML/day at the
commencement of mining, to about 6 ML/day in 2006-2007. After that time the seepage rate
increases more rapidly due to an increased mining footprint as a result of larger panel widths
(increased rate of coal extraction) and increasing contributions from the Triassic strata due to
increasing submergence. The rate of influx is predicted to peak at about 16 ML/day in 2019 with
the extraction of the last of the longer panels LW-W8, and to decline thereafter as shorter length
panels are extracted.
Figure 21b indicates a water make in Ulan West operations which rises quite rapidly from
commencement of mining in 2012 to about 6 ML/day in 2014 as the first two panels are extracted.
After that time the seepage rate increases at a subdued rate, peaking in 2021 at about 8 ML/day
during the extraction of panel UW6. The rate of influx is predicted to decline thereafter as the
remaining shorter length panels are extracted.
Total mine water seepage rates are summarised on Figure 21c where a peak rate of 24 ML/day is
predicted in 2018. The seepage rate assumes no contributions from localised fracture related
storage (that might be associated with a fault for example) since the extent and hydraulic properties
of this type of storage remain unknown. However it would not be unreasonable to expect up to
0.5 to 1.0 ML/day increase in groundwater seepage over periods of days to weeks if significant and
as yet unidentified fracture network storage is encountered and drained. These types of flows have
been previously encountered in the vicinity of the volcanic plugs and sills.
4.5
Recovery of aquifer pressures post mining
Mining is expected to cease in 2029-2030 following extraction of panel LW-UW11 at Ulan West.
After this time regional aquifer pressures and the water table will begin to rebound. The rate of
rebound will be dependent upon the piezometric head distributions of groundwater held in storage
within the surrounding hard rock strata, the hydraulic properties of goaf and the overlying
fractured zone, and the ongoing gravity drainage of strata above mined panels until piezometric
heads equilibrate.
Recovery of strata pressures has been simulated by adopting the groundwater pressure
distributions at 2030 as initial conditions for a recovery model. The operations are simply left to
recover without further pumping from underground. Adjustments in model hydraulic properties
prior to commencement of recovery, are summarised in Appendix E.
The predicted long term steady state water table is shown on Figure 23. The time taken to achieve
this is predicted to be in excess of 200 years (Appendix E provides plots of the piezometric head
distributions at 100 and 200 years). The difference between the water table shown on Figure 23a
and the pre-mining water table, is provided on Figure 23b (pre-mining minus post mining water
tables). This plot demonstrates:
•
ultimate recovery above mine panels is likely to generate a relatively flat lying water table
within the mine footprint as a result of enhanced hydraulic conductivities from cracking
within the subsidence zone and open storage along headings, roadways and in goaves;
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•
4.6
a relatively flat lying water table may be generated within the extended West Pit open cut
spoils which will be governed ultimately by the water levels in the East Pit and by the
effectiveness of rehabilitation in inhibiting rainfall percolation (to spoils) and the
diversion of runoff around the final landform.
Baseflow losses to regional rivers and creeks
The impact of shallow depressurisation on groundwater baseflows from the deep hardrock strata to
the regional drainage systems, has also been extracted from the simulation model. Figure 22
provides seepage budget results. These plots demonstrate almost complete loss of baseflow
contributions to Ulan Creek and Bobadeen Creek (including Spring Gully) catchments by 2020
from predicted initial (pre-mining) rates of 10 kL/day (0.01 ML/day). Losses to the Goulburn
River tributaries above Ulan township are negligible while losses over the reach from Ulan
township to the confluence with Bobadeen Creek are predicted to be sustained over the entire
mining period. Summation of losses for the Goulburn River catchment indicate a decline over the
mine life (1986-2030) of about 0.2 ML/day for the total drainage system extending to the eastern
extremity of the model. It is noted that these flows represent only part of total baseflows. They do
not include the more commonly recognised seepage contributions from unconsolidated stream
bank (and regolith) systems which are often perched (eg. Mona Creek alluvium) and respond to
rainfall and stream flows which are event based. The localised scale of these processes and their
changes in storage due to rainfall events, precludes their inclusion in the groundwater model.
Table 6 provides a useful summary of losses to the deeper hardrock system.
Mona Creek catchment is the most affected catchment providing baseflow to the Talbragar River
but sustained losses are also noted in Cockabutta Creek catchment. Summation of losses for the
Talbragar River catchment indicate a decline over the mine life of 0.24 ML/day.
Table 6: Estimated baseflow losses attributed to the hardrock system
Period
5.
Goulburn River
(ML/day)
Talbragar River
(ML/day)
1986 to 2009
0.092
0.035
2009 to 2030
0.110
0.205
2030 to 2230 (200 years post mining)
0.521
0.384
POTENTIAL ENVIRONMENTAL IMPACTS
The proposed continuation of mining would induce further change to the local groundwater
environment. Potential impacts arising from the development include:
Sustained reduction in regional hard rock aquifer pressures;
Loss of groundwater yield at some existing bore locations;
Change in groundwater quality in the strata;
Impact on groundwater dependent ecosystems;
5.1
Reduction in regional hard rock pressures and baseflow impacts
Continued mining of the Ulan seam will sustain a pressure loss regime in the regional hardrock
strata. This pressure loss regime has been predicted using aquifer numerical modelling techniques
described in Section 4 above. Strata depressurisation and dewatering is predicted to migrate
upwards from extracted longwall panels, through the subsidence zone to the Triassic (Wollar)
sandstones where near complete drainage is expected (over the panel footprint). Reductions in
piezometric head in these sandstones are also predicted to extend some 3 to 4 km beyond the panel
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footprint except in the Moolarben area where the impact of dewatering and depressurisation due to
MCM open cut and underground mining will extend the regional pressure reductions further to the
east and south-east. Groundwater pressure reductions in the Ulan seam are more widespread than
the shallower Triassic strata in the UCML project area, and are predicted to migrate distances of
more than 20 km beyond the panel footprint in the long term before receding as the system
recovers after cessation of mining.
The net cumulative groundwater seepage to UCML mine workings is predicted to rise from a
current rate of about 9.2 ML/day to approximately 24.0 ML/day in 2018 when operations in UG3
are near their northern extremity. Thereafter, the seepage rate is predicted to decline to a rate of
about 8 ML/day at the end of mining in 2029-2030 and declining exponentially thereafter.
Occasional short term ‘nuisance’ flows of possibly up to 0.5 to 1.0 ML/day could be generated
during mining if as yet unidentified water bearing structures like faults, shears or volcanic plugs
are intercepted. Typically, such structures if intercepted in the Permian strata tend to offer
relatively low storage that would be expected to deplete over a number of months. Longer periods
are likely if the structures occur in the Triassic strata and become connected to the subsidence zone
above extracted longwall panels.
The reduction in aquifer pressures caused by UG3 and Ulan West operations will have an impact
on groundwater baseflows to the catchments. At the close of mining it is predicted that losses to
the Goulburn River catchment arising from the proposed mining, may be of the order of 0.11
ML/day while losses to the Talbragar River catchment may be of the order of 0.2 ML/day. These
losses may increase further until recovery of groundwater pressures is substantially complete.
However it is unlikely that the losses can be physically measured as they represent upwards
seepage from hardrock strata. The losses would also be masked by the more conventional
baseflows related to recharge and discharge of shallow weathered rocks and alluvial-colluvialregolith materials by rainfall events.
The Drip is recognised as a an important natural feature which sustains groundwater dependent
ecosystems. It is sustained by surficial and relatively shallow groundwater storage which is
governed mostly by short term rainfall events that surcharge the shallow strata in the manner
described above. Rainfall recharge and downwards percolation is intercepted at horizontal
bedding planes which then transmit the groundwater to the unconfined rock faces along the
Goulburn River gorge where it emanates as seeps and drips. During dry periods some seeps may
cease to flow. Seepage that migrates past this shallow perched system, sustains the deeper water
table and from numerical modelling, is calculated to be less than 5 mm/year or less than 1% of
annual average rainfall. Depressurisation of Triassic strata in the area of the Drip has already
occurred as a result of historical mining operations at UCML and no impacts have been observed
to date. No impacts are likely as a result of future UCML operations which are moving northward
and westward away from the Drip.
5.2
Loss of groundwater yield at existing bore locations
Loss of pressure induced by mining within the hard rock strata is predicted to affect a relatively
small number of privately owned boreholes that are identified on Figure 24 which shows all bores
identified within about 5 km of the perimeter of the mine panels from DWE database information
and bore census conducted by UCML. These bores are constructed in Triassic or younger strata.
There are 11 privately owned bores identified within the 2 m drawdown contour (UCML owned
bores plotted in green). This contour is judged to be a reasonable lower bound for impact
assessments on the assumption that most water supply structures have sufficient submergence of
the water yielding zone to accommodate loss of 2 m head. Yield in most cases would be only
marginally affected.
Of the 11 privately owned bores, 7 fall within the 2 to 10 m predicted head loss range. These
bores are likely to succumb to some loss of yield. Of these bores, only three are in use and the
remaining bores are either inoperable (3 bores) or cannot be located (1 bore). The remaining 4
privately owned bores, are located within the 10 to 20 m head loss range. This head loss is
considered to be sufficient to either significantly reduce yield or to generate complete loss of yield.
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Vulnerable bores are highlighted in Appendix B, Table B1. UCML policy in relation to bore water
supplies is addressed in the Statement of Commitments which supports replacement of loss of
yield, most likely through new bore construction.
5.3
Change in groundwater quality
It is unlikely that any regional change in groundwater quality will be observed in hard rock strata
as pressures decline above and adjacent to mined panels. Localised change in salinity at depth,
may be observed as groundwaters contained within different stratigraphic horizons mix within
goaves and cracked areas, as is already evident from historical monitoring.
Similarly, it is unlikely that any measurable change in water quality will be observed in the
shallow unconsolidated alluvial aquifer systems since these are either remote from the longwall
panel footprint (eg Talbragar River alluvium), and/or they are actively recharged by rainfall.
Water quality in the underground operations is expected to be consistent with observed qualities.
However, on cessation of mining, significant dilution is expected as Triassic groundwaters
continue to migrate downwards through the subsidence zone to goaves and through to existing
roadways and headings. Mine waters are expected to reflect a TDS range of 1000 to 2000 mg/l
with increasing sulphate presence up dip. Triassic groundwaters typically range from 300 to 600
mg/l and with sustained contributions from these waters, mine waters in underground operations
are expected to progressively dilute with an end water calculated to lie somewhere in the range 700
to 1300 mg/l.
5.4
Impacts on groundwater dependent ecosystems
There are no identified groundwater dependent ecosystems within the project area. However any
as yet unidentified local spring systems that might be present within the mine panel subsidence
footprint, may be affected if cracking of the subsurface occurs in proximity to such features.
6.
DWE LICENSING REQUIREMENTS
Licensing relating to groundwater seepage to mining operations will be required in accordance
with Part 5 of the Water Act. Consideration may also need to be given to offset arrangements for
loss of hardrock baseflow to the Goulburn and Talbragar rivers.
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ULAN COAL – CONTINUED OPERATIONS: GROUNDWATER ASSESSMENT – JULY 2009
7.
GROUND WATER MONITORING
The established groundwater monitoring networks must be maintained and augmented as mining
operations expand to the north and west. Information should be used to validate and verify model
predicted depressurisation of strata and seepage to the underground workings.
Future groundwater monitoring should include:
continued measurement of groundwater levels, pressures and water quality (EC, pH and
major ion speciation) within the existing regional network of monitoring bores and an
expanded network;
improvements in measurement of groundwater seepages and water qualities (EC and pH)
within the mine water systems for UG3 and the proposed Ulan West operations, in order
improve prediction of seepage, contributions from different stratigraphies, and
contributions from rainfall infiltration via the subsidence zone;
compliance monitoring and measurement of any water discharges including quality
monitoring of major ions and specific rare elements;
adoption of data transfer protocols to convey monitoring data from the mine to DWE;
annual reporting as part of licensing conditions.
8.
IMPACTS VERIFICATION CRITERIA
Future impacts assessment criteria should address the pressure regime within the coal measures
and overlying strata. Vertical leakage in areas beyond the subsidence zone, from Triassic strata to
underlying Permian strata can be estimated by interpolation of the pressure/water table hydraulic
gradients and calculation of the leakage flux from measured rock permeabilities. This estimate can
also be reconciled with the volume of mine water pumped from underground operations. In order
to establish both the strata hydraulic gradients and the rock mass permeabilities it may be
necessary to expand the groundwater monitoring network, particularly in the Ulan West area. The
following recommendations are provided.
Depressurisation monitoring should include:
Installation of at least 3 multi level piezometer strings equipped with vibrating wire
transducers (or equivalent) and distributed within the Permian-Triassic strata;
Strata hydraulic conductivity measurement on rock core obtained at the above noted
piezometer locations. Such measurement should comprise testing for intergranular
permeability and effective porosity, and insitu testing for conductivity over selected
intervals;
Daily or more frequent monitoring of pore pressures and piezometric elevations by
installed auto recorders in selected new piezometers in order to discriminate between
oscillatory groundwater movements attributed to rainfall recharge or subsidence related
strata movements, and longer term pressure losses related to mining.
Three monthly or more frequent water level monitoring of the regional monitoring network
(NMN) using automated monitoring apparatus in selected piezometers. The monitoring
interval should be reduced when increasing strata depressurisation is evident from
encroaching mining operations;
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ULAN COAL – CONTINUED OPERATIONS: GROUNDWATER ASSESSMENT – JULY 2009
Mine water seepage monitoring should include:
Measurement of all water pumped underground and all mine water pumped to surface on a
daily basis. Measurement should be undertaken using calibrated flow meters or other
suitable gauging apparatus;
Routine monitoring of coal moisture content delivered from the working face in order to
more accurately determine the underground water balance;
Routine monitoring of ventilation humidity
Routine monitoring of any build in water storage in goaves.
Water quality monitoring should include:
Monthly monitoring of basic water quality parameters pH and EC in pumped mine water.
Such monitoring may provide early indication of mixing of shallow groundwaters with
groundwaters in deeper strata. While this process is expected within the subsidence zone,
it may not be evident within the wider piezometer network at the leakage levels predicted
by groundwater monitoring;
Six monthly monitoring of pH and EC in the regional monitoring network (NMN);
Annual measurement of total dissolved solids (TDS) and speciation of water samples in
selected piezometers to support identification of mixing of groundwater types. Speciation
should include as a minimum - major ions Ca, Mg, Na, K, CO3, HCO3, Cl, SO4 and
elements including Al, As, B, Ba, F, Fe (total), Li, Mn, P, Se, Si, Sr, Zn;
Graphical plotting of basic water quality parameters and identification of trend lines and
statistics including mean and standard deviation calculated quarterly. Comparison of
trends with rainfall and any other identifiable processes that may influence such trends.
The monitoring network and monitoring programme should be reviewed on an annual basis to
determine ongoing suitability and any proposed changes should be discussed in the Annual
Environmental Management Report (AEMR).
Impact verification analyses are already addressed within UCML trigger-response plan (TARP)
contained in the existing groundwater monitoring plans. Actions could also include:
Quarterly assessment of departures from identified monitoring or predicted data trends.
The key data sets in this regard should be the mine water seepage rate calculated from the
underground water balance, and the pressure monitoring data recorded within the NMN..
If the average daily seepage rate exhibits an increase beyond the rate predicted (allowing
for 1.0 ML/day additional transient storage depletion), or if consecutive pressure
monitoring data over a period of 6 months exhibit an increasing divergence in an adverse
impact sense from the previous data or from the established or predicted trend (from
aquifer numerical modelling), then such departures should initiate further actions. These
may include a need to conduct more intensive monitoring (including installation of
additional piezometers) or to invoke impacts re-assessment and/or mitigative measures;
Formal review of depressurisation of coal measures and comparison of responses with
aquifer model predictions annually. Expert review should be undertaken by a suitably
qualified hydrogeologist;
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8.1
Impact mitigation measures
Mitigative measures for any identified negative impacts beyond those predicted, may include
replacement of water supply or relinquishment of groundwater or surface water allocations as an
offset.
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July 2009
REFERENCES:
ANZECC, 2000, Australian water quality guidelines for fresh and marine waters. Aust & New
Zealand Env. Conservation Council.
Coffey Partners International. 1991. Hydrogeological Study No.3 and No.4 Underground Mines.
Report No. Z60/7-AB compiled for UCML. April.1991
Coffey Geosciences. 2005b. Spring Gully Fault Pump Test, Ulan Coal Mine, Ulan, NSW. Report
No. S21754/06-AA. December 2005.
Coffey Geotechnics. 2007c. Subsidence Management Plan Longwall Panels W2 and W3, Ulan
Coal Mine, Ground and Surface Water Assessment. Report No. GEOTLCOV21754AA-AN.
December.
Coffey Geotechnics, 2008a. Goulburn River diversion – baseline assessment.
report. Report compiled for UCML, May, 2008.
Groundwater
Coffey Geotechnics, 2008b. Groundwater modelling study – Ulan Coal Mine. Final report.
Report compiled for UCML, Sep., 2008.
Eckhardt, K, 2005. How to construct recursive digital filters for baseflow separation. Hydrological
Processes, Vol.19, 2005
Forster, I, B. 1995. Impact of underground mining on the hydrogeological regime, Central Coast
NSW. AGS, 1995.
Geotechnical Consulting Services (GCS). 2000. Review of Underground Water Management
with Respect to Road Construction. Report prepared for UCML, August
HLA-Envirosciences Pty Ltd. 2001. Water Management Plan, ML1468 Underground Mine
Expansion, Ulan Coal Mine, Revision 1. April.
Hydrogeologic Inc. 1996. Modflow-Surfact user manual.
Long J.C., J.S. Remer, C.R. Wilson, P.A. Witherspoon, 1982. Porous media equivalents for
networks of discontinuous fractures. Water Resources Research, Vol.18-3
Moolarben, Coal Mines, 2006. Moolarben Coal Project – Environmental Impact Assessment
(Appendix 5). Compiled by Moolarben Coal Mines, 2006
National Centre for Groundwater Management. 1998. Ulan Groundwater Model. Report No.
C97/44007b. February 1998.
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Parsons Brinckerhoff Australia. 2006. Ulan groundwater model - Investigation of mine
development and dewatering from the Ulan Seam. December 2006.
Schmidt PW. 1996. Stress orientation from drill core – does it work ?. Symposium on Geology
in Longwall Mining, 12-13 November, pp 257-267.
SCT, 2007a. Geotechnical testing and analysis of rock samples for Ulan DDH242 and DDH243.
Report compiled for UCML, Jan. 2007.
SCT, 2007b. Subsidence assessment for longwalls W2 and W3 at Ulan Coal Mine. Report
compiled for UCML, June 2007.
SCT, 2007c. Near-goaf hydrogeology project – Hydrogeological measurements at sites A, B and C
to end of longwall 23. Draft report compiled for UCML, October 2007.
Safe Production Solutions (SPS). 2003. Water Balance – Letter Report. Report compiled for
UCML.
Umwelt Australia Ltd., 2009. Ulan Coal Continued Operations. Surface water assessment. Report
prepared for UCML, July 2009.
Wilpinjong Coal Mine, 2005. Wilpinjong Coal Project – Environmental Impact Assessment
(Appendix B). Compiled by Wilpinjong Coal Mine, 2005.
Yoo EK, West P, and Bradley G. 1983. Geology and coal resources of the Coolah-BinnawayMendooran Area (Goulburn River – Binnaway drilling programme - Authorisation 286). NSW
Department of Mineral Resources, Coal Geology Branch. Report No. GS1983/154.
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IMPORTANT INFORMATION ABOUT YOUR HYDROLOGICAL REPORT
Mackie Environmental Research (MER) has applied skills, standards and workmanship
expected of Chartered Professionals in the preparation of this report, the content of which is
governed by the scope of the study and the database utilised in generating outcomes.
In respect of the database underpinning the study, MER notes that historical data is often
obtained from different sources including clients of MER, Government data repositories,
public domain reports and various scientific and engineering journals. While these sources
are generally acknowledged within the report, the overall accuracy of such data can vary.
MER conducts certain checks and balances and employs advanced data processing techniques
to establish broad data integrity where uncertainty is suspected. However the application of
these techniques does not negate the possibility that errors contained in the original data may
be carried through the analytical process. MER does not accept responsibility for such errors.
It is also important to note that in the earth sciences more so than most other sciences,
conclusions are drawn from analyses that are based upon limited sampling and testing which
can include drilling of exploration and test boreholes, flow monitoring, water quality sampling
or many other types of data gathering. While conditions may be established at discrete
locations, there is no guarantee that these conditions prevail over a wider area. Indeed it is
not uncommon for some measured geo-hydrological properties to vary by orders of
magnitude over relatively short distances or depths. In order to utilize discrete data and
render an opinion about the overall surface or subsurface conditions, it is necessary to apply
certain statistical measures and other analytical tools that support scientific inference. Since
these methods often require some simplification of the systems being studied, results should
be viewed accordingly. Importantly, predictions made may exhibit increasing uncertainty with
longer prediction intervals. Verification therefore becomes an important post analytical
procedure and is strongly recommended by MER.
This report, including the data files, graphs and drawings generated by MER, and the findings
and conclusions contained herein remain the intellectual property of MER. A license to use
the report is granted to Ulan Coal Mines Limited for the Ulan Coal Project. The report
should not be used for any other purpose than that which it was intended and should not be
reproduced, except in full. MER also grants Ulan Coal Mines Limited a licence to access, use
and modify the data files supporting the groundwater model described in this report. Ulan
Coal Mines must not permit any third party to use or modify these data files without
obtaining the prior written consent of MER.
Dr. C. Mackie
CP. Env
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