newmont boddington gold 2018 update of ......newmont boddington gold pty ltd (nbg) operates the...

NEWMONT BODDINGTON GOLD

2018 UPDATE OF GROUNDWATER

CONDITIONS AND REGIONAL

GROUNDWATER MANAGEMENT PLAN

Report Status

Revision Date Signature

A (Draft) April 2018

Rev 0 (Final)

April 2018

Big Dog Hydrogeology

Boddington 2018 Regional Review Rev 0 (Final)

EXECUTIVE SUMMARY Newmont Boddington Gold Pty Ltd (NBG) operates the Boddington Gold mine, located 17 km northwest of the town of Boddington, and around 100 km to the southeast of Perth in WA. Open pit mining of an oxide gold resource was undertaken from 1987 to 2001, with stockpiled ore being processed until 2002 when the operation was placed in care and maintenance. Following definition of a gold resource within the deeper bedrock, construction of a large scale open pit mining operation was commenced by Newmont in 2006. The mining and processing operation was commissioned in 2009, and dewatering operations have been undertaken in the open pits throughout the construction and mining period.

NBG have commissioned BDH to prepare an updated groundwater management plan for the Boddington mine, which provides an updated conceptualisation of the groundwater flow system using the results of the works completed since groundwater conditions were last reviewed in 2016. The resulting groundwater management plan is presented in this report.

The updated conceptual hydrogeological model remains generally consistent with that described in previous reviews and identifies the main groundwater units to be:

1. A seasonal shallow groundwater system, which overlies oxide with low hydraulic conductivity, 2. The weathered and fractured upper bedrock groundwater system including the interface at the base

of the oxide, and 3. A deep fractured bedrock groundwater system.

Current influences of the mine facilities on groundwater conditions are:

1. Seepage from the RDAs and impounding of water behind RDA embankments is causing mounding in the underlying groundwater system.

2. Localised groundwater mounding is occurring at the toes of portions of all of the waste rock storage facilities.

3. Seepage is occurring to groundwater from unlined storage structures. 4. Drawdown due to pit dewatering in the deep bedrock potentially extends more than 2 km from the

open pits. Drawdown due to pit dewatering as measured at the interface at the base of oxide in the weathered and fractured upper bedrock is less than in the underlying bedrock and extends around 2 km from the open pits.

5. In 2016, drawdown due to the operation of the Westwood groundwater supply bores measured in the shallow gravels and in the weathered and fractured upper bedrock extended around 1 km from the bores.

6. These individual influences overlap, and in some locations (between the open pits and the RDAs and at the toes of the waste rock storage facilities), groundwater may be subject to both mounding and drawdown.

In higher elevation locations, the groundwater elevation in laterite gravels in the seasonal shallow groundwater system is higher than in the underlying weathered and fractured bedrock. The seasonal shallow groundwater system is present at Round, Boomerang and Pillow Swamps and at Deep VWP02 and IWS07. These swamps now lie within the drawdown associated with pit dewatering, but no dewatering influence has been observed in the seasonal shallow groundwater system. In low elevation locations near 34 Mile Brook and the Hotham River, alluvial and laterite gravels in the shallow groundwater system are permanently saturated and demonstrate hydraulic connection to the underlying groundwater systems.



The upgraded regional monitoring network now includes standpipes and VWP installations monitoring the shallow groundwater system, the oxide, the interface and the deep bedrock. Taking account of the locations of the mine facilities expected to influence the groundwater system, and the potential receptors, the existing monitoring locations and depths are considered appropriate to identify any potential impacts.

The pit dewatering drawdown area in 2018 remains 3 to 4 km distant from the Hotham River. The drawdown area associated with the operation of groundwater supply bores extended to around 1.5 km from the Hotham River in 2016 but has subsequently recovered due to decommissioning of the bores and higher than average precipitation conditions.

Works which have been concluded to be required for the ongoing management of groundwater at the Boddington Gold Mine are summarised as follows:

1. Eventual replacement of MPBR1 with a standpipe screened from 30 to 80 m below surface. 2. Investigations into a potential blockage of MUBR2 and remediation or replacement as necessary. 3. Modification of the stream sensor installed at Pump Station 2.

The frequency of the existing regional groundwater level monitoring is considered appropriate taking account of the objectives of the monitoring. There have been periods of data loss from the VWP installations due to logger or telemetry failures. It is recommended that systems be put in place to poll or test the data collection at monthly intervals and ensure that any failures can be rectified before significant data loss occurs.

Further monitoring data collected through a wet season will be required to confirm that the recently installed VWP sensors are providing accurate data, and to refine the understanding of interactions between the Hotham River and the groundwater system. The conceptual model may then be updated and used as the basis for the construction of a regional numerical groundwater model.



TABLE OF CONTENTS EXECUTIVE SUMMARY .................................................................................................................................................. 2

TABLE OF CONTENTS .................................................................................................................................................... 4

1. Introduction ................................................................................................................................................................ 6

1.1 Background ....................................................................................................................................................... 6

1.2 Objectives .......................................................................................................................................................... 6

1.3 Summary of 2016 regional groundwater management plan ............................................................................. 7

1.4 Scope of work .................................................................................................................................................... 8

2. Completed groundwater works ................................................................................................................................. 9

2.1 Background ....................................................................................................................................................... 9

2.2 Deep VWP installations ..................................................................................................................................... 9

2.3 Shallow standpipe installation ......................................................................................................................... 10

2.4 Hotham River investigations ........................................................................................................................... 10

2.5 LPBR1 replacement ........................................................................................................................................ 10

2.6 Conversion of pilot holes ................................................................................................................................. 10

2.7 Groundwater supply bores .............................................................................................................................. 11

2.8 Pit dewatering and monitoring ......................................................................................................................... 12

3. Updated review of groundwater elevation data ....................................................................................................... 14

3.1 Background and data sources ........................................................................................................................ 14

3.2 DeepVWP01 .................................................................................................................................................... 15

3.3 DeepVWP02 .................................................................................................................................................... 15

3.4 HFVWP01 and HFVWP02 .............................................................................................................................. 15

3.5 HRVWP01 and HRVWP02 ............................................................................................................................. 16

3.6 HFBR10, HFBR11 and HFBR12 ..................................................................................................................... 16

3.7 Converted pilot holes ...................................................................................................................................... 17

3.8 LPBR1-A ......................................................................................................................................................... 17

3.9 Open pit responses ......................................................................................................................................... 18

3.10 Seasonal shallow groundwater system ........................................................................................................... 18

3.11 Weathered and fractured upper bedrock standpipes ...................................................................................... 19

3.11.1 Background trends .................................................................................................................................. 19

3.11.2 Trends near Westwood bores ................................................................................................................. 19

3.11.3 Trends near Hotham River ...................................................................................................................... 19

3.11.4 Regional trends ....................................................................................................................................... 20

3.11.5 Trends in the region of the RDAs ............................................................................................................ 21

3.12 Groundwater elevations and flow directions at the interface in 2018 Q1 ........................................................ 21

3.13 Mine dewatering drawdown extent at the interface in 2018 Q1 ...................................................................... 23

4. Updated conceptualisation of groundwater transmitting units ................................................................................ 24

4.1 Background and data sources ........................................................................................................................ 24



4.2 Seasonal shallow groundwater system ........................................................................................................... 24

4.2.1 Geology ................................................................................................................................................... 24

4.2.2 Hydrogeology .......................................................................................................................................... 25

4.3 Oxide ............................................................................................................................................................... 25

4.3.1 Geology ................................................................................................................................................... 25

4.3.2 Hydrogeology .......................................................................................................................................... 26

4.4 Weathered and fractured upper bedrock ........................................................................................................ 27

4.4.1 Geology ................................................................................................................................................... 27

4.4.2 Hydrogeology .......................................................................................................................................... 27

4.5 Deep fractured bedrock ................................................................................................................................... 28

4.5.1 Geology ................................................................................................................................................... 28

4.5.2 Hydrogeology .......................................................................................................................................... 28

4.6 Interactions with the Hotham River ................................................................................................................. 29

5. Conceptual assessment of groundwater depths ..................................................................................................... 30

5.1 Background and methodology ........................................................................................................................ 30

5.2 Topographic data ............................................................................................................................................ 31

5.3 Estimated groundwater elevations in 2006 ..................................................................................................... 32

5.4 Estimated groundwater depths in 2006 .......................................................................................................... 33

5.5 Estimated groundwater depths in 2016 Q3 ..................................................................................................... 33

5.6 Conceptual groundwater depths at end mining .............................................................................................. 33

5.7 Conceptual groundwater depths at end mining with groundwater supply ...................................................... 34

6. Recommended works to manage regional groundwater ........................................................................................ 35

6.1 Potential mechanisms for mining impacts to occur via groundwater .............................................................. 35

6.2 Review of existing monitoring depths.............................................................................................................. 36

6.3 Review of existing monitoring locations .......................................................................................................... 37

6.3.1 Rationale for monitoring locations ........................................................................................................... 37

6.3.2 Potential sources ..................................................................................................................................... 38

6.3.3 Assessment of monitoring locations ........................................................................................................ 38

6.4 Summary of recommended monitoring works ................................................................................................ 39

6.5 Numerical groundwater model ........................................................................................................................ 39

7. Summary and conclusions ...................................................................................................................................... 40

References ...................................................................................................................................................................... 42

List of Figures .................................................................................................................................................................. 43

Appendix A Bore completion details



1. Introduction

1.1 Background Newmont Boddington Gold Pty Ltd (NBG) operates the Boddington Gold Mine, located 17 km northwest of the town of Boddington, and around 100 km to the southeast of Perth in WA. Open pit mining of an oxide gold resource was undertaken from 1987 to 2001, with stockpiled ore being processed until 2002 when the operation was placed in care and maintenance. Following definition of a gold resource within the deeper bedrock, construction of a large scale open pit mining operation was commenced by Newmont in 2006. The mining and processing operation was commissioned in 2009, and dewatering operations have been undertaken in the open pits throughout the construction and mining period.

The potential for pit dewatering to influence the regional groundwater system was investigated in a large number of studies completed during the permitting and early mining period. These studies provided a wide range of estimates for the total rate of groundwater inflow during mining, and a wide range of predictions for the regional extent of mining related drawdown.

Studies investigating potential regional drawdown which have been calibrated against and matched to the observed groundwater responses during the initial phases of open pit mining include the numerical modelling of regional drawdown undertaken in 2012 (SWS, 2013B), and a groundwater management plan developed in 2013 (BDH, 2013). The 2013 groundwater management plan described additional investigations and monitoring planned to be undertaken to improve the understanding of the regional hydrogeological system and potential interactions between groundwater and the Hotham River. Some of the recommended investigations were completed in 2014 and 2015 and an updated groundwater management plan was developed in 2016 (BDH, 2016). Further investigations which were identified in the 2016 groundwater management plan and have now been completed are:

1. Installation of two deep VWP monitoring points, located between the groundwater supply bores and the Hotham River.

2. Construction of three shallow standpipe monitoring bores near the groundwater supply bores. 3. Replacement of a regional standpipe bore that was close to being dry. 4. Installation of a second shallow VWP monitoring point adjacent to the Hotham River, along with

installation of a stream height monitoring station in the adjacent river. 5. Conversion of regional water supply exploration holes into deep standpipe monitoring bores.

NBG have commissioned BDH to prepare an updated groundwater management plan for the Boddington mine, which provides an updated conceptualisation of the groundwater flow system using the results of the works completed since 2016. The resulting groundwater management plan is presented in this report.

1.2 Objectives In consultation with Newmont, the objectives for the updated groundwater management plan were defined to be:

• To update the conceptualisation of the regional groundwater system using investigations and monitoring data collected from 2016 to 2018.

• To expand the domain of the groundwater management plan to include an assessment of conditions in the environment around the RDAs.



• To identify potential pathways and mechanisms by which mine related drawdowns may be transmitted into the receiving environment, and potential resulting influences, including a more detailed assessment of groundwater interactions with the Hotham River.

• To ensure that the current groundwater monitoring regime is suitably designed to identify the influences of all mine facilities, including mine dewatering and the operation of regional bores for raw water supply.

• To generate conceptual maps of depth to groundwater below topographic surface, for both current and future conditions, for input to prioritising investigations for regional vegetation management.

1.3 Summary of 2016 regional groundwater management plan The conceptualisation of groundwater conditions in the 2016 management plan identified three units which transmitted significant quantities of groundwater and occurred commonly across the Boddington Gold Mine, (see the conceptual section in Figure 1) being:

• A seasonal shallow groundwater system (laterite gravel), • The weathered and fractured upper bedrock groundwater system (saprock) occurring below the

interface at eth base of the oxide and • A deep fractured bedrock groundwater system.

Although the oxide unit illustrated in Figure 1 was saturated in some locations it was concluded not to transmit significant quantities of groundwater. Most of the regional standpipe monitoring bores are screened at the interface between the oxide and the moderately weathered bedrock, which is within the groundwater system defined as the weathered and fractured upper bedrock.

Monitoring data collected during mining confirmed that the seasonal shallow groundwater system supported Pillow Swamp, Boomerang Swamp, and Round Swamp which were located northeast of the open pits. This system was concluded to be driven by rainfall infiltration to shallow gravels, to be separated from the regional groundwater system by a significant thickness of clayey oxide material and was concluded not to be affected by mine dewatering.

The deep bedrock groundwater system comprised discrete zones of fracturing, the occurrence of which were controlled by structural features, sub-vertical dikes, and sub-horizontal dolerites. Drawdown within this unit close to the open pit slopes was well defined from a large number of monitoring points, and was up to 200 m.

The weathered and fractured upper bedrock groundwater system was concluded to be the most regionally extensive unit, and an extensive network of monitoring bores had been constructed in this zone, mostly screened at the interface. Groundwater elevations in this unit were strongly influenced by seasonal precipitation trends, and by long term precipitation trends, including generally declining precipitation over the mining period. Mining related drawdown in the weathered and fractured upper bedrock system was concluded to be limited to within around 2 km of the open pits. Drawdown in the weathered and fractured upper bedrock system near the Westwood groundwater supply bores was noted to extend around 1 km from the borefield.

Potential groundwater receptors for the Boddington Gold Mine were concluded to be:

1. Swamp areas, including Boomerang, Round and Pillow Swamps, but which were concluded not to be in connection with the systems affected by mine dewatering.



2. Any operating groundwater abstraction bores, although no abstraction points were identified within the zone of potential influence of mine dewatering at that time.

3. Surface streams, including the Hotham River, if they should be in hydraulic connection with the underlying groundwater system, and if drawdown in the groundwater system were to reach as far as these streams.

At the time of the 2016 review, the extent of drawdown due to open pit mining remained around 3 to 4 km from the Hotham River, while drawdown from the Westwood groundwater supply bores remained around 1.5 km from the Hotham River.

1.4 Scope of work The scope for generation of the updated groundwater management plan in 2018 was agreed with Newmont to comprise a summary and interpretation of the works completed since 2016, combined with a desktop review of recent monitoring data collected from the site. The 2018 investigation is founded on the interpretation of groundwater transmitting units developed by BDH in 2016 and avoids duplicating or repeating the major components of the 2016 study. Specific tasks completed as part of the current study were:

1. Document the as-built construction details of the regional monitoring installations completed since 2016.

2. Compile all recent monitoring data, provide an updated assessment of hydraulic properties and of the extent of mining or groundwater supply related drawdown, and an updated assessment of potential interactions with the Hotham River.

3. Expand the domain of the review to include groundwater conditions across the entire mine area, including the environment around the RDAs.

4. Define potential pathways for migration of mining related drawdown, or mining related groundwater mounding, and any changes required to the regional monitoring programme to provide early warning of and predict these changes.

5. Use the monitoring data to develop conceptual contour maps of groundwater depth below surface for input to concurrent investigations into regional vegetation management.



2. Completed groundwater works

2.1 Background As described in the 2016 monitoring plan, an extensive regional network of monitoring bores screened in the weathered and fractured upper bedrock groundwater unit has been constructed in stages during the mine development and operating periods. Prior to 2016 these works comprised:

1. The installation of 24 standpipe monitoring bores under the supervision of Golder and Associates in January and February of 2007 (Golder, 2007).

2. The installation of 34 standpipe monitoring bores under the supervision of Golder and Associates in April and May of 2010 (Golder, 2010).

3. The installation of 17 standpipe monitoring bores under the supervision of SWS between January and November of 2012 (SWS, 2013A).

4. Construction of two deep VWP installations in 2015 (DeepVWP01 and DeepVWP02) along strike from the open pits to investigate drawdown trends and vertical hydraulic gradients.

5. Construction of a shallow VWP installation near the Hotham River in 2015 (HRVWP01). 6. Geological mapping and topographic surveys of the Hotham River in April 2015.

The locations of the monitoring bores are presented in Figure 2 and construction details compiled from various reports are re-produced for all standpipes and VWP installations in Appendix A for ease of reference.

The results of the Hotham River survey are presented in Figures 3 to 7. These surveys identified that in some locations, fractured bedrock outcrops in the Hotham River and in these locations, there was no oxide between the river and the underlying groundwater system.

Groundwater works undertaken since compilation of the 2016 groundwater management plan are described in the following sections.

2.2 Deep VWP installations The 2016 groundwater management plan recommended that two deep monitoring bores equipped with grouted Vibrating Wire Piezometer (VWP) sensors be constructed near the Westwood groundwater supply bores. VWP sensors provide an electrical signal which can be converted to the groundwater pressure at the location of the sensor. By sealing the intervals between the sensors with grout, several sensors can be operated in a single bore, providing independent groundwater elevation data for several geological horizons. The objective of installing the deep VWPs was to investigate any differences in groundwater responses between the shallow sediments, the oxide, the interface at the upper bedrock surface, and the deep bedrock, during operation of the Westwood groundwater supply bores.

HFVWP01 and HFVWP02 were constructed in January 2018 between the Westwood groundwater production bores and the Hotham River, as marked in Figure 2. The oxide portion of the hole was drilled using mud rotary techniques and 155 mm PVC slotted casing installed to the base of oxide. The remainder of each hole was drilled using an RC hammer, and slotted 50 mm PVC was installed to the base of the hole. Once all of the planned installations had been cased with 50 mm PVC, a specialist VWP installation and grouting rig was used to install five VWP sensors into the 50 mm casing at each site, and to fully grout the hole to surface (i.e. grouting extends within the 50 mm slotted casing, between the 50 and 155 mm casing, and between the 155 mm slotted casing and the hole wall). Completion diagrams for HFVWP01 and HFVWP02 are provided in Figures 8 and 9.



2.3 Shallow standpipe installation The 2016 groundwater management plan identified that in several locations where paired shallow and deep standpipes had been constructed, the groundwater elevations were very similar between the paired bores. It was noted that this could be due to natural connection, or it could be due to failed seals installed between the bores. In three locations, stand-alone shallow standpipes were therefore installed in 2017, to investigate the responses in the shallow groundwater system in the absence of any potential artificial connection introduced by adjacent bores. These standpipes were labelled HFBR10, HFBR11 and HFBR12 and completion details supplied by NBG are provided in Figures 10 to 12.

2.4 Hotham River investigations A shallow VWP installation was constructed at HRVWP02 in January 2018 as marked in Figure 2, and the immediately adjacent pumping station in the river was equipped with a stream height sensor separately recording the river elevation. HRVWP02 and the stream sensor were accurately surveyed to ensure that the groundwater and surface water levels can be directly compared. HRVWP02 was constructed using the methodology described in Section 2.2 and included sensors in the alluvial gravels and in the bedrock, as illustrated in Figure 13. The Hotham River sensor was installed at Pump Station 2 adjacent to HRVWP02 (Figure 3) and directs a beam on to the river surface at the inlet of Pump Station 2, as illustrated in Figure 14.

2.5 LPBR1 replacement Previous versions of the groundwater management plan have identified that monitoring standpipe LPBR1 is in a key location for monitoring mining drawdown in the regional groundwater system and has been either dry or almost dry. A deeper groundwater monitoring standpipe was therefore installed at this location in 2017 (LPBR1-A) and was constructed as drawn in Figure 15.

2.6 Conversion of pilot holes A number of pilot holes drilled during groundwater supply investigations which were deemed unsuitable for conversion to groundwater supply bores have been converted to monitoring standpipes. In each case the shallow gravels and oxide had been cased off, and the bedrock section of the hole remained open. The pilot holes extended to between 200 and 400 m depth, and therefore provided an opportunity to monitor groundwater elevations in the unweathered bedrock at depth. Where possible, the pilot holes were converted to standpipes, by installing a single length of blank and slotted 65 mm PVC casing suspended from the collar to allow access for a monitoring probe to measure groundwater depths in the open hole through deep bedrock.

The locations of these deep regional standpipes are provided in Figure 2, and construction details provide by NBG are included in Table 1 where available.



Table 1: Deep regional standpipe construction details

2.7 Groundwater supply bores Regional exploration and testing undertaken by NBG has resulted in the construction of 11 regional groundwater supply bores. The bores are intended to be operated as an alternative source of raw water in periods when the raw water demand cannot be met from the combination of 1) decant water recycled from the RDAs, 2) pit dewatering flows and 3) water harvested from the Hotham River during the winter flow period. Construction details for the bores provided by NBG are summarised in Table 2, and the locations of the bores are illustrated in Figure 2. All of the bores included surface casing installed to the base of oxide with a grout seal to ensure groundwater is supplied only from the fractured bedrock at depth.

Figure 16 summarises the groundwater production rates from the regional groundwater supply bores to date. The highest abstraction occurred from the Westwood bores, in the period 2015 to 2016 when the bores operated at an average of around 40 L/s. The largest proportion of the abstraction was provided by Westwood 3 and Westwood 4 in this period. Groundwater abstraction during 2017 has largely been associated with testing the new bores, and all of the groundwater supply bores are currently on standby as there is sufficient raw water from other sources to maintain the NBG processing operations.

Pilot Hole New Name Easting NorthingDrilled depth

(m)

Base of blank 65 mm PVC

casing (m)

Base of slotted 65 mm PVC

casing (m)

Lucif #2 WHBR5D, WHBR5S 442176 6374496 380 NR NR

Lucif #3 WHVWP01 442048 6375368 360 NR NR

Westwood #2 HFBR13 439433 6371315 261 NR NR

Hedam #1a HDBR01 437000 6368715 242 93 105

Hedam #2 HFBR14 437699 6367476 388 12 30

Westwood #9c HFBR15 441636 6370803 350 68 80

Coleman #4 NPBR2 437629 6378122 402 132 150

Lucif #4b WHBR2 442032 6375065 402 88 100

Contact #1- R4 south-east R4BR109 442691 6379404 360 108 120

Lucif #5 (sth of PitD) WD7BR13 441547 6374195 402 66 78



Table 2: Construction details for regional groundwater supply bores

2.8 Pit dewatering and monitoring Dewatering of North pit and South pit is undertaken to provide safe mining conditions and to minimise the influence of groundwater inflows on blasting and mining operations. This is achieved by a combination of passive dewatering (pumping from sumps installed at the lowest elevations in each pit to remove groundwater inflows after mining) and active dewatering (pumping from dewatering bores installed within and surrounding the open pits to achieve dewatering in advance of mining). Total pumping rates since 2013 are plotted in Figure 17. Although the contributions from active and passive dewatering have varied since 2013, including a trial in which only passive dewatering was undertaken in mid-2017, the total pumping rate has consistently averaged around 120 L/s, which has been interpreted to comprise:

• Around 80 L/s groundwater inflow to South pit. • Around 20 L/s groundwater inflow to North pit. • Around 20 L/s contributed from rainfall runoff.

The average total dewatering rate in the current review period (2016 to 2018) was generally consistent with previous periods, however in the middle of 2017 there was no contribution from active dewatering (due to the sumps only trial), and in the first quarter of 2018 there was a significant reduction in the contribution in active dewatering due to changes in infrastructure.

Bore Easting Northing Elevation (mAHD)

Depth (m)

Casing material

Casing ID (mm)

Screened Lithology

Screen Type/Material

Average Yield (L/s)

Coleman 1 436761 6375772 303.3 202.0 PVC 200.0 GraniteSlotted PVC

casing 5.5

Coleman 2 437030 6377984 259.7 203.5 PVC 200.0 DoleriteSlotted PVC

casing 2.7

Coleman 3 436974 6376866 239.2 240.0 PVC 200.0 GraniteSlotted PVC

casing 8

Deewon 2 439317 6380311 325.6 252.0 CS steel 250.0 BasaltSlotted steel

casing 7

Heharo 1 436308 6372942 325.1 281.0 Permaglass 256.0 GraniteStainless steel

screens 17

Roberts 1 443898 6374635 260.7 253.9 Permaglass 256.0 BasaltStainless steel

screens 22

Westwood 1 440626 6370701 205.4 154.0 CS steel 200.0 BasaltSlotted steel

casing 9

Westwood 3 440195 6370403 206.9 206.0 CS steel 250.0 BasaltSlotted steel

casing 16

Westwood 4 439678 6371809 235.8 229.0 CS steel 200.0 GranodioriteStainless steel

screen 18

Westwood 5 441280 6371112 242.7 195.0 PVC 200.0 BasaltSlotted PVC

casing 18

Westwood 8 439087 6371868 253.8 184.0 PVC 200.0 Granite

Slotted PVC casing 6



Monitoring of groundwater elevations in the mine area is achieved by an extensive network of VWP sensors grouted in place within and surrounding the pit slopes and using open pilot holes which have been converted to standpipe piezometers. These data are maintained and interpreted by the NBG mining group, and most recently were reviewed in 2017 (NBG, 2017A, NBG 2017B). Key conclusions from these reviews were:

• All of the deep bedrock around the pits displays drawdown trends in response to open pit mining and dewatering, although the trends are significantly higher in the southern and eastern pit slopes, and drainage rates are lower in the western pit slopes.

• Observations during mining and investigation programs have identified that when exposed to long term large stresses (dewatering of the underlying bedrock), the oxide unit eventually follows the same drainage response, as has occurred in the oxide in North pit and South pit. However, under short term stresses, such as the recent commencement of mining in the S09 pit, the oxide may remain saturated while the underlying bedrock is being drained, which has resulted in elevated pore pressures being present in the oxide slopes in the S09 pit. Figure 18 illustrates that in March 2017, groundwater elevations in the oxide unit were consistently contoured as being around 250 mAHD, while groundwater elevations in the underlying deep bedrock were contoured to be more than 50 m lower, and in the range 100 to 220 mAHD.



3. Updated review of groundwater elevation data

3.1 Background and data sources Groundwater elevations in the deep fractured bedrock and in oxide near the open pits are regularly assessed as part of the dewatering and pit slope depressurisation works and were most recently reviewed by NBG in March 2017 and October 2017 (NBG, 2017A, NBG, 2017B). These data have not been re-presented in any detail in the current document but have been used where relevant to control contoured groundwater elevations near the open pits.

Monitoring data from regional standpipe bores intersecting the seasonal shallow groundwater system and the weathered and fractured upper bedrock system are presented and are briefly discussed in the following sections. Detailed monitoring data collected from automated data loggers in the regional VWP installations are also presented and reviewed. Completion details for all of these standpipes and VWP installations are provided in Appendix A and in Figures 8 to 13 where available.

The current groundwater elevation review has been expanded to include regional monitoring bores in the upper part of the 34 Mile Brook catchment and in the Wattle Hollow and Boggy Brook catchments near the RDAs as illustrated in Figure 2. The bores selected for inclusion were those which are currently being monitored and reported in Annual Environmental Reviews, other bores used for geotechnical or operational purposes are present in this area but have not been investigated. The objective of including the regional bores near the RDAs was to help delineate the boundaries and overlaps between regional groundwater influences associated with 1) open pit mining, 2) groundwater supply bore operation, and 3) RDA operation. Geological logs and construction details were not available for many of these bores, but where paired bores were present the deeper bore was employed in the review, as these are understood to have been typically screened at the base of oxide at the interface with the upper weathered and fractured bedrock. The current review is not intended to investigate the performance of the RDAs, as this is being addressed in separate studies, using detailed data from the RDA water balances, piezometric data collected within the RDAs and using groundwater chemistry as well as groundwater elevations.

All of the available groundwater elevation data have been plotted as grouped hydrographs in Figures 19 to 47. Daily precipitation data are included in all figures to allow correlation between potential recharge events and groundwater elevations. For locations where a groundwater production bore is present in the area, average weekly groundwater production rates are included to investigate any responses to bore operation. Bores in similar areas with similar groundwater elevations have been grouped in the plots, to allow any responses which are regionally present across most of the bores to be identified. There are two gauging stations on the Hotham River (up-gradient of Pump Station 1 and at Pump Station 2), and where relevant the river height data are also presented for comparison. Although a few bores have monitoring data extending back to the 1990s, most of the bores were installed after 2010, and so most of the plots present grouped data from 2010 onwards.

Each of the monitoring installations constructed since compilation of the 2016 groundwater management plan are discussed and interpreted separately in the following sections. However, as the standpipes commenced monitoring in 2017, and HFVWP01, HFVWP02 and HRVWP01 were constructed in January 2018, there are limited data available to compare against the regional seasonal trends, and any conclusions using data from these new installations will need to be revisited and validated when a longer time series of monitoring data covering different seasonal conditions is available.



The brief review of groundwater elevation trends in the following sections has been focussed on identifying any trends that depart from the existing conceptual model of the groundwater system described in Section 1.3. A more detailed review of individual monitoring results was included in the 2016 groundwater management plan (BDH, 2016).

3.2 DeepVWP01 Groundwater elevations measured in the five VWP sensors from the date of installation in February 2015 until the logger failed in July 2017 are plotted in Figure 19. The logger is currently under repair and is planned to be reinstalled. All of the sensors (installed in oxide, at the interface, and in bedrock) display a gradual declining trend attributed to pit dewatering, along with short term and seasonal cycles that can be attributed to precipitation conditions. Responses to precipitation are much less pronounced in the oxide than in bedrock. Comparison with nearby standpipe WD7BR3D illustrates that three-monthly manual dipping of the standpipe captures the broad seasonal trends in groundwater elevations as defined by the detailed data from the VWP sensors.

For most of the monitoring period, there are only small differences in groundwater elevation between the sensors, with groundwater elevations in oxide closely following those in the underlying bedrock. However, the last 2 weeks of data recorded before the logger failed suggest that following a daily precipitation total of 90 mm on 22 June 2017, sensors V5 installed in oxide and V4 installed at the interface potentially measured significantly higher groundwater elevations than in the sensors installed in the underlying bedrock.

3.3 DeepVWP02 At DeepVWP02, a steady drawdown trend due to mining is evident in the bedrock sensors, which matches drawdown trends measured in nearby standpipes WTBR2 and WTBR3 (Figure 20). Sensor V4 installed at the interface also displays a drawdown trend but has a groundwater elevation 15 m higher than in the underlying bedrock. The groundwater elevations measured in sensor V4 are generally consistent with those measured in nearby standpipe WTBR1 which is also screened at the interface. Sensor V5 installed in oxide displays large variations. A shallow gravel unit which is subject to seasonal saturation was encountered at DeepVWP02 during drilling. The groundwater elevation within the oxide ranges from the sensor being dry in mid-2016, to being elevated in response to infiltration from the overlying gravels after large precipitation events. It appears that in this location, the oxide responds slowly to drainage from below, and rapidly to recharge from above, resulting in a perched groundwater system being present in the oxide much of the time. The perched saturation of the oxide may contribute to the groundwater elevations measured at the interface, which remain significantly higher than in the underlying fresh bedrock.

3.4 HFVWP01 and HFVWP02 HFVWP01 and HFVWP02 were installed between the Westwood groundwater supply bores and the Hotham River to identify any drawdown migrating towards the river in the bedrock (which is the source of groundwater produced by the Westwood bores) or in the overlying formations. Although five sensors were installed at each location, some were damaged during installation and have malfunctioned. Currently HFVWP01 has working sensors in shallow gravel, oxide, and at the interface but not in the bedrock (Figure 21). HFVWP02 has working sensors in the oxide and in the deep bedrock but not at the interface (Figure 22). These installations have not been operating long enough to interpret long term trends and were not in operation when the Westwood groundwater production bores were being pumped at full capacity in 2016. The recent groundwater elevations measured by the remaining working sensors appear consistent with the regional conceptual model and with the data from nearby standpipe bores as included on the plots, and future monitoring of the VWP installations should define influences from the Westwood bores if pumping from these bores re-commences.



3.5 HRVWP01 and HRVWP02 Figures 23 and 24 present data from the VWP installations adjacent to the Hotham River. Elevations at HRVWP01 are compared against gauging data from the Hotham River 200 m up-stream (see Figures 3 and 7 for locations), while HRVWP02 is compared against Hotham River gauging data collected immediately adjacent at Pump Station 2, although HRVWP02 has not been operating long enough to capture a full flow season. The deepest sensor (V1) in HRVWP02 was damaged during installation and has malfunctioned. Currently it appears that the remaining four sensors are functioning and recording groundwater elevations similar to but higher than the Hotham River, however a longer period of data will be required to confirm they are functioning correctly.

Both VWP installations identify that groundwater elevations are generally similar in the oxide, at the interface, and in the underlying bedrock. However, the sensors in oxide and at the interface tend to follow a common trend, being more responsive to recharge events, while the sensors in deep bedrock tend to display slightly lower groundwater elevations and less response to recharge events. Groundwater elevations are similar to and slightly higher than the stream elevation in the adjacent river and confirm that groundwater discharge to the Hotham River is likely to be occurring in the dry season. Figure 23 confirms that manual monitoring of standpipe monitoring bores accurately reflects the seasonal trends but may not capture short term events such as the peak groundwater elevations that occurred in the oxide and interface sensors in HRVWP01 in September 2017.

3.6 HFBR10, HFBR11 and HFBR12 Shallow standpipes HFBR10 and HFBR12 were constructed to investigate whether the shallow gravel unit was responding to the operation of the Westwood groundwater supply bores, as had been suggested after standpipe HFBR5D went dry (BDH, 2016). Figure 24 illustrates that the new bores were installed after the main operating period for the Westwood bores and that groundwater recovery was occurring when monitoring commenced. However, the initial data from the new shallow bores suggest that dewatering of the shallow gravels had occurred in 2015 and 2016 but recovered rapidly in 2017. This suggests that the response at HRBR5S (going dry) was not due to a failed seal during bore construction, but reflected natural hydraulic connection, with pumping from the bedrock at depth causing dewatering of the shallow gravels in the area of the Westwood bores. HFBR5S subsequently resaturated in August 2007 due to the combination of above average precipitation conditions and terminating pumping from the Westwood bores. Ongoing monitoring at these locations during any future operation of the Westwood bores will help to refine the understanding of shallow groundwater conditions.

HFBR11 was installed to investigate whether HFBR8S accurately reflects shallow groundwater conditions, or whether it may be affected by a failed seal between this bore and HFBR8D. The limited data collected to date from HFBR11 appear consistent with data from HFBR8S, suggesting the seal is intact, but ongoing monitoring will be required to confirm the interpretation.



3.7 Converted pilot holes In most cases, the limited groundwater elevation data collected to date from the deep bedrock standpipes converted from pilot holes appear consistent with groundwater data from standpipes screened at the interface. However, in three locations close to the open pits, differences are identified as follows:

• Standpipe NPBR2 is installed in a pilot hole that was drilled 402 m into bedrock close to North pit. It is close to standpipes NPBR1 and WD9BR2 screened at the interface between oxide and weathered bedrock. Figure 26 identifies that the few measurements available from NPBR2 indicate the groundwater elevation in the deep bedrock is at around 145 mAHD, and is strongly affected by mine dewatering, while the groundwater elevations measured close to the interface in the other standpipes demonstrate long term responses to mine dewatering, but groundwater elevations are at least 50 m higher.

• Standpipe WHBR2 is installed in a pilot hole that was drilled 402 m into bedrock close to South pit. It is close to standpipe WHBR1 which was screened at the interface at the bedrock surface. Figure 27 compares WHBR2 against the other standpipes in the area and indicates that the initial data from this bore suggest the groundwater elevation in deep bedrock is around 40 m lower than in nearby WHBR1.

• Standpipe WHVWP01 is installed in a pilot hole that was drilled 360 m into bedrock close to South pit and north of WHBR2. A single groundwater elevation measurement included in Figure 27 suggests that the groundwater elevation is 30 m lower than measured at the interface in WHBR1.

While these responses could indicate the bedrock is highly compartmentalised with variable responses to mine dewatering over short distances, the initial data from the deep standpipes are more consistent with there being a significant drawdown response to mine dewatering in the deep bedrock close to the open pits, which is not fully reflected in the overlying oxide and interface zones, which are being very gradually under-drained but maintain significantly higher groundwater elevations. This interpretation is consistent with the responses described for DeepVWP01 and DeepVWP02 in Sections 3.2 and 3.3.

3.8 LPBR1-A Monitoring data from the deeper LPBR1-A are compared against the adjacent shallow LPBR1 and regional standpipes in Figure 28. The base of the screen in LPBR1 is at 302 mAHD and was logged as being installed immediately above fresh rock. LPBR1 responded strongly to mine dewatering up to 2012, and then demonstrated a much lower rate of drawdown, which appears to reflect true conditions at the base of the oxide as the bore retained 2 m of saturated screen at that time, and the trends are consistent with MPBR1 screened in the same zone. Subsequently the bore went dry, but re-saturated after the large precipitation event in January 2018. LPBR1-A was drilled on the same pad as LPBR1 and was screened around 40 m into fresh bedrock. Groundwater elevations in LPBR1-A are around 15 m lower than in LPBR1 and appear to reflect the same drawdown trend that was observed prior to 2012. These observations suggest that the deep bedrock has responded strongly to pit dewatering in this location, but that the oxide and interface zones have responded in a more subdued and delayed manner, resulting in groundwater elevations being higher than in the underlying deep bedrock.



3.9 Open pit responses The deep fractured bedrock groundwater system near the open pits responds to the combination of sump pumping and dewatering bore operation, and on average demonstrates increasing depressurisation responses throughout the mining period. The rate of depressurisation varies, controlled by the influence of structural features which act to connect or compartmentalise the bedrock groundwater system. Typical responses near South pit are illustrated in Figure 29, with depressurisation in response to mining, recovery after precipitation events, and recovery when dewatering bores terminate pumping evident in the plots. In particular, it is noted that groundwater elevations in deep bedrock near South pit were lowest in Q3 2016, recovered during the sumps only trial in mid-2017, and have been declining since the dewatering bores were recommissioned, but have not yet returned to the elevations in 2016 Q3.

3.10 Seasonal shallow groundwater system A total of 29 regional standpipe monitoring bores have been installed into lateritic or alluvial gravels associated with the seasonal shallow groundwater system. Routine monitoring of depth to water in each bore is undertaken, and note is made on whether the bore is dry at the time. These monitoring data indicate that:

• Bores which have been almost always dry since installation and do not appear to become saturated for significant periods are:

HGPZ31B screened to 3 m in gravelly clay, WD7BR1S screened to 12 m in clayey gravels, WD7BR2S screened to 6 m in vuggy cemented laterite, WD7BR3S screened to 8 m in gravelly clays, WD7BR5S screened to 9 m in gravelly clays, HFBR6S screened to 4 m in lateritic gravelly clays, SPBR1S screened to 9.5 m in cemented laterite hardcap, and ESBR1S screened to 5 m in lateritic gravelly clays.

• Bore BMSWPZ1B, screened to 5 m in lateritic gravel clays has always contained water and the seasonal shallow groundwater system may be permanently saturated at this location in Boomerang Swamp.

• In the low elevation areas near 34 Mile Brook and the Hotham River, HFBR5S, HFBR8S, HRBR1S screened in shallow laterite gravels or alluvial gravels have been permanently saturated, and the groundwater elevation trends are consistent with those in the adjacent deeper bores. In these locations the shallow groundwater system behaves differently to the high elevation locations near the mine facilities, where the shallow groundwater system is perched.

• At the remaining shallow bores intersecting lateritic gravels in high elevation locations, the bores are typically dry for some of the summer period and saturated for part of the winter period.

Figure 24 and Figures 30 to 36 plot groundwater elevations in the shallow monitoring bores, compared against data from the adjacent deeper bores intersecting the weathered and fractured upper bedrock. These plots include the monitoring bores at Round Swamp (Figure 30), Pillow Swamp (Figure 31), and Boomerang Swamp (Figure 32). The groundwater elevation responses plotted for the seasonal shallow groundwater system in high elevation areas near the mine facilities confirm that:

• In higher elevation locations the groundwater elevation in the shallow system is typically 5 to 20 m higher than the groundwater elevation in the underlying weathered and fractured upper bedrock system.



• In several locations, (Round Swamp in Figure 30, Pillow Swamp in Figure 31, Q pit in Figure 33, K pit in Figure 34), the long-term data now clearly define depressurisation in the underlying weathered and fractured upper bedrock associated with mine dewatering, while the bores completed in the overlying seasonal shallow groundwater system show no drawdown response. In these locations, the oxide appears to be acting as a seal and preventing under-drainage of the shallow groundwater system associated with the surface swamps.

• In some cases, seasonal trends are present in groundwater elevation in the shallow system, but there are no long-term drawdown trends present that would indicate any connection to the mine dewatering.

3.11 Weathered and fractured upper bedrock standpipes

3.11.1 Background trends

Figure 37 updates and re-presents the available long-term monitoring data dating from 1990 for the weathered and fractured upper bedrock groundwater system, along with four-year average precipitation data. As noted in previous reviews, a long term regional drawdown trend of around 0.4 m per year is present in the data collected prior to the current mining operations, and generally correlates with the measured long term declining precipitation trends. The updated plot suggests that in addition to the long-term background trends, an additional small component of drawdown has been present in bores WHBR1, 34BR8 and N4921-1A since 2010. This timing would be consistent with the onset of the influence of dewatering activities at the open pits. The more recent data identify that the regional background groundwater elevations were stable or rising in 2017 and 2018, due to above average precipitation conditions in this period, consistent with a rise in the four year moving precipitation average in Figure 37.

3.11.2 Trends near Westwood bores

Figure 38 compares groundwater monitoring data in regional standpipe monitoring bores located near the Westwood groundwater supply bores with individual and combined pumping rates from the bores. The monitoring data clearly define a response at HFBR5D to the groundwater supply bores commencing immediately after commissioning the bores in 2015, and it also appears that some drawdown in response to borefield operation was occurring at HFBR1D, HFBR4D and HFBR6D in 2016. By 2018 almost full recovery had occurred due to the termination of pumping from the Westwood bores in combination with higher than average precipitation in 2017 and 2018. As discussed in Section 3.6 and illustrated in Figure 25, comparable responses occurred in the shallow gravels in this area, and the shallow gravel groundwater system is indicated to be in hydraulic contact with and affected by Westwood bore operation.

3.11.3 Trends near Hotham River

Responses at regional standpipe monitoring bores installed close to the Hotham River (HRBR1, HRBR2, HRBR8, HFBR8 and HFBR11) are plotted in Figure 39. Where available, the elevation of the base of the Hotham River streambed surveyed at that location is included for reference. Hotham River stream height data recorded at the gauging station and at Pump Station 2 adjacent to HFBR8 (located as identified in Figures 3 and 7) are also plotted for reference. The plotted data identify that:

• The weathered and fractured bedrock near the river displays similar responses to the rest of the region, with seasonal responses to precipitation of around 2 m and no long-term drawdown trends.

• Monitoring bore HRBR1S, screened within sandy alluvial sediments in a shallow groundwater system, displays identical trends in groundwater elevations to HRBR1D, which is screened in weathered and fractured upper bedrock. This suggests there is a strong degree of hydraulic connection between the two groundwater systems at this location, as has been confirmed by the data from the adjacent HRVWP01 as discussed in Section 3.5.



• At HFBR8, the shallow bore (HFBR8S) completed to 17 m in laterite gravel, and the deep bore completed to 57 m in weathered diorite have similar but not identical groundwater elevations. HFBR11 completed in this area to a depth of 18 m appears to measure similar groundwater elevations to HFBR8S.

• The Hotham River gauging stations identify that groundwater elevations near the river are slightly higher than the river and follow similar trends.

In combination the Hotham River survey data and the updated monitoring data suggest that hydraulic connection is present between the Hotham River and the underlying groundwater systems, including the shallow alluvial gravels, the shallow laterite gravels, and the interface at the upper surface of the weathered and fractured bedrock. While this was considered unlikely during mine development studies due to the assumed presence of an oxide layer between the river and the groundwater system, the Hotham River mapping identified that the oxide is absent and bedrock outcrops in the river in several locations, and the monitoring data near the river indicate that when it is present, the oxide may not act as a seal.

3.11.4 Regional trends

Figures 40 to 47 plot the available time series groundwater elevation data for regional bores completed in the weathered and fractured upper bedrock. Responses identified in these regional standpipe bores include:

• Most of the bores display a response to seasonal precipitation trends, with the changes in groundwater elevation between summer and winter ranging from 0.5 to 3 m.

• Most bores display an unusually large rise in 2017 and 2018, due to the above average precipitation conditions in this period and the individual large events that occurred in February 2017, June 2017 and January 2018. In some cases, such as RNSWPZ23A (Figure 30) and LPBR1 (Figure 41), bores which had become dry resaturated in 2017/2018 as a result of the precipitation conditions.

• Some bores display an unusually flat response, and in some cases the measured water depths may reflect a small amount of water perched in the base of the casing after the local groundwater elevation has fallen below the base of the casing. These responses are discussed further in Section 6.

• Bores located southeast of South pit demonstrate drawdown trends greater than the background rate and confirm mining related drawdown is occurring in this area at the interface.

• Bores located north and west of North pit confirm that mining related drawdown is occurring at the interface.

• Other regional monitoring bores confirm that mining related drawdown at the interface at the top of the weathered and fractured upper bedrock is generally restricted to the area close to the open pits and is not occurring in the bores located between the pits and the Hotham River.

• The monitoring bore installed in 2012 below the medium grade stockpile to define groundwater conditions near the Impacted Water Sump (IWS07, Figure 45) displays strong responses to precipitation events, rising by up to 9 m in winter and declining again in summer and does not respond to pit dewatering despite being close to the pits (Figure 2). Recharge responses at IWS07 are much larger than observed in the other regional standpipe monitoring bores and suggest an additional source of recharge is present. This recharge source most likely represents a combination of seepage from the medium grade stockpile, and leakage from the South Clear Water Pond, both of which if present would be subsequently captured by the Impacted Water Sump.



• Some of the monitoring bores display seasonal changes in groundwater elevation which are larger than expected, combined with long term rising trends, and these most likely reflect enhanced recharge during the mining period. The largest changes (long term rises of 7 to 10 m) occur at WD9BR2 located between North pit and 34 Mile Brook, and at WD8BR7 located near the North Clear Water Pond. In down-gradient locations the enhanced recharge most likely reflects the influence of seepage from the up-gradient waste rock storage facility. In up-gradient locations the enhanced recharge may result from mine facilities impeding natural runoff channels or the influence of adjacent water storage ponds.

3.11.5 Trends in the region of the RDAs

Groundwater elevations measured in regional standpipe bores in the northern part of the 34 Mile Brook, House Brook and Boggy Brook catchments where the RDAs have been constructed are plotted in Figure 48 and 49. Seasonal responses are present in most bores, and in some locations such as R4BR89 are larger than for other regional bores and reflect seepage rates from adjacent facilities. Bores distant from the facilities demonstrate stable groundwater elevations on average, while bores close to the facilities indicate long term rising trends. The largest rises observed during the current operating periods for the RDAs are up to 20 m at F1BR41D and 25 m at F1BR23D (Figure 48). Groundwater elevations have stabilised in these two bores since 2016, due to groundwater discharge occurring to surface, either from the bore itself, or in adjacent low elevation areas.

3.12 Groundwater elevations and flow directions at the interface in 2018 Q1 The reviews of groundwater elevation data above have identified that in some locations, and in particular near the open pits, there may be significant differences between the groundwater elevations in the oxide, in the interface that occurs within the weathered and fractured upper bedrock, and within the fresh bedrock at depth. In these locations, VWP sensors and standpipes in the oxide and at the interface tend to respond in a similar manner, while VWP sensors and standpipes in the fresh bedrock at depth display larger dewatering influences from mining. The regional groundwater monitoring network has been designed to primarily measure groundwater elevations near the interface, as it is the weathered and fractured upper bedrock which is most likely to interact with potential receptors, including the Hotham River and regional vegetation. Groundwater elevations measured near the interface have therefore been contoured in Figure 50 as follows:

• Near South pit and North pit, where the oxide and the interface are known from observations during mining to have been drained, groundwater elevations from the uppermost VWP sensor in the deep bedrock have been used for contouring, along with groundwater elevations measured in deep standpipes and in dewatering bores (measured while the dewatering bores were not operating).

• For the dewatering investigation pilot holes which have been converted to regional deep standpipe monitoring bores, only those bores which have comparable groundwater elevations to the adjacent more shallow standpipe bores have been included.

• For the VWP installations, the groundwater elevations measured in VWP sensors installed in oxide or at the interface have been used.

• Shallow bores completed in surface gravels have not been included in the contouring. • Groundwater flow directions have been automatically calculated from the contoured groundwater

elevations and gradients.

Features of the groundwater elevations contoured in Figure 50 include:

• A lowest groundwater elevation at -60 mAHD coinciding with the deepest part of South Pit in 2018 Q1.



• An area of mining related depressurisation and groundwater capture centred on the open pits and extending preferentially to the northwest and northeast. Close to the open pits all groundwater flow is towards the pits.

• Steep hydraulic gradients at the margin of the depressurisation centred on the pits, being steeper on the southwestern slopes than the northeastern slopes, consistent with mining observations (NBG, 2017A).

• Outside the pit area, on a regional basis groundwater flow is generally to the southeast, consistent with surface water drainage directions defined in 34 Mile Brook. However locally the contours define:

► A groundwater mound near the RDAs, causing groundwater flow to be radially away from the facilities.

► Naturally higher groundwater elevations at WD7BR12 which is located on the northern flank of a local hill, and these groundwater elevations potentially act as a hydraulic barrier preventing direct groundwater flow from the pits to the Hotham River.

► In the area south of the pits, groundwater flow towards and then along the topographic lows defined by 34 Mile Brook and its tributaries, suggesting that groundwater flow paths generally follow the streams.

► In the area southeast of the RDAs, groundwater flow towards and then along the topographic lows associated with House Brook and Boggy Brook.

• Groundwater elevations are close to the river water level or the base of the streambed near the Hotham River.

Figure 50 also includes spot groundwater elevations available for the deep fractured bedrock near the open pits for comparison against the interpolated groundwater surface at the interface, where these data indicate a greater dewatering influence is present in the bedrock compared to the overlying interface. These locations include:

• Deewon 2, a groundwater production bore which is not available for monitoring but where a groundwater elevation was measured prior to it being equipped, which was around 20 m below the contoured surface.

• DeepVWP02 where the deeper bedrock sensors have a groundwater elevation 15 m lower than the sensor at the interface.

• NPBR2 near North pit, which has a groundwater elevation 50 m below the inferred surface as discussed in Section 3.7.

• Hovea 1, a groundwater supply pilot hole close to South pit where a groundwater elevation was measured prior to the site being abandoned and was around 90 m below the contoured elevations at the interface.

• LPBR1-A, where the deeper replacement bore has a groundwater elevation 15 m lower than the original bore as discussed in Section 3.8.

• WHVWP01, where the groundwater elevation is around 30 m lower than contoured for the interface as noted in Section 3.7.

• WBA08580-001 which is a deep dewatering investigation site where the groundwater level was reported as 50 m lower than the interpolated surface.

• WHBR2 where the groundwater elevation is around 40 m lower than the interpolated surface as discussed in Section 3.7.



3.13 Mine dewatering drawdown extent at the interface in 2018 Q1 The time series groundwater elevation plots in Figures 19 to 49 have been reviewed to estimate the total drawdown since mining commenced associated with mine dewatering and associated with groundwater supply bore operation. Only bores and VWP sensors monitoring the interface in the weathered and fractured upper bedrock system have been used. Figure 51 illustrates the locations of the bores at which drawdown has been identified, and provides an interpolated contour defining the approximate extent where mining related drawdown at the interface exceeds 2 m. A value of 2 m has been applied as it is difficult to discern drawdowns smaller than this magnitude from the background and seasonal trends. Observations from the contours and posted values are:

• The extent of pit dewatering drawdown remains consistent with and almost identical to the extent identified in 2016.

• The magnitude of pit dewatering drawdown at the interface (which is inferred to be between 2 and 11 m in the standpipe monitoring bores) is relatively small, compared to the drawdown measured in the deep bedrock within the pits (up to 285 m), and compared to the drawdown indicated from deep bedrock standpipes near the pits as discussed above.

• Regional pit dewatering drawdown at the interface appears to extend preferentially to the northwest along the direction of geological strike, consistent with the anisotropy assumed in the conceptual hydrogeological model. The drawdown extent to the southeast is less than was predicted in the feasibility studies, and there is less drawdown propagating towards the Hotham River than expected. The extent of drawdown to the northeast of the pits is larger than was expected and may relate to the influence of a sub horizontal dolerite which extends from the pits towards this area. Pit dewatering drawdown is now occurring below Boomerang, Pillow and Round Swamps, but is not affecting the shallow swamps.

• The pit dewatering drawdown area in 2018 remains 3 to 4 km distant from the Hotham River at the interface.



4. Updated conceptualisation of groundwater transmitting units

4.1 Background and data sources Details on the hydrogeological formations across the Boddington Gold Mine are available from:

1. The installation of 24 regional monitoring standpipe bores under the supervision of Golder and Associates in January and February of 2007 (Golder, 2007).

2. The installation of 34 regional standpipe monitoring bores under the supervision of Golder and Associates in April and May of 2010 (Golder, 2010).

3. The installation of 17 regional standpipe monitoring bores under the supervision of SWS between January and November of 2012 (SWS, 2013A).

4. The installation of two deep regional VWP monitoring points and one shallow VWP monitoring point near the Hotham River under the supervision of BDH in 2015.

5. The exploration program undertaken by NBG to develop groundwater supply bores within the 34 Mile Brook catchment in 2015 and 2016.

6. The installation of additional VWP monitoring points and standpipe monitoring bores in 2016 and 2017 under the supervision of NBG.

Updated data from these programmes which have been reviewed to refine the understanding of the groundwater transmitting units include logging of drillcore, notes of groundwater occurrence during drilling, notes of flows generated during airlift development, and observations of water level recovery following development. The review has been augmented with information collected during the mining operations.

The locations of the monitoring bores used in the assessment are provided in Figure 2. The resulting locations provide good coverage of hydrogeological conditions within a few km of the open pits, in the area between the open pits and the residue disposal areas (RDAs) where the swamps occur, and in the area between the open pits and the Hotham River.

4.2 Seasonal shallow groundwater system

4.2.1 Geology

Of the 70 locations investigated during the regional monitoring bore programmes, the seasonal shallow groundwater system was intersected in 28 locations. In each case the shallow groundwater system was logged to range from clays with some laterite gravel, to laterite gravels, cemented laterite hardcap, cemented hardcap containing solution cavities, or in low elevation locations near 34 Mile Brook and the Hotham River as alluvial gravels and sands. Where encountered, the shallow unit was typically 3 to 5 m thick, but more extensive deposits were identified as follows:

• 11 m of laterite hardcap at HFBR1, between South pit and the Hotham River. • 17 m of cemented laterite hardcap at HFBR8, close to the Hotham River. • 9.5 m of cemented laterite hardcap at SPBR1, immediately northeast of South pit. • 14 m of lateritic gravel and clay at WD7BR12, located between South pit and the Hotham River. • 11 m of lateritic gravel and clay at WTBR3, located to the north of North pit. • HRVWP02 at the Hotham River adjacent to HFBR8 encountered alluvial gravels from 8 to 30 m

depth. • HFVWP01 located near 34 Mile Brook intersected laterite and alluvial gravel from surface to 54 m

depth.



These observations confirm that the seasonal shallow groundwater system occurs as discrete, isolated lenses and is not regionally continuous. Large changes in thickness may occur between adjacent bores as was observed at HFBR8 and HRVWP02 in the low elevation area adjacent to the Hotham River. Although the laterite system has been identified more often in the areas southeast and northeast of the open pits, it may occur anywhere in the regional system.

In the higher elevation areas near the open pits, the seasonal shallow groundwater system occurs at the Round, Boomerang and Pillow Swamps, where it has been extensively monitored. Shallow gravels also occur in other locations near the pits such as 1) Deep VWP02 where 9 m of clayey gravel is present and remains saturated due to natural recharge; 2) SPBR1 where 9.5 m of cemented laterite hardcap is present but has remained dry throughout the monitoring period, and 3) IWS07 which intersected 13 m of waste rock and laterite and has been saturated during monitoring, most likely due to seepage from the upgradient stockpiles.

4.2.2 Hydrogeology

The seasonal shallow groundwater system over most of the mine area comprises isolated deposits of laterite gravels and hardcap, but in low elevation areas near 34 Mile Brook and the Hotham River may comprise thick sequences of alluvial gravel. The sequences of alluvial gravel in low elevation areas are permanently saturated and appear to be in hydraulic contact with the underlying groundwater units. Operation of the Westwood groundwater supply bores abstracting groundwater from the deep bedrock caused the shallow gravels in this area to go dry at HFBR5S, indicating that the oxide unit does not prevent underdrainage of the shallow system occurring in this area.

In the laterite gravels and hardcap occurring in high elevation areas of the Boddington Gold Mine, infiltration from significant precipitation events potentially saturates this zone in some locations and becomes perched above the underlying oxide clays. Perched groundwater moving through the lateritic gravel material potentially discharges downslope, is removed via evapotranspiration, or infiltrates and saturates the underlying oxide as has been observed at DeepVWP02. Many of the monitoring bores screened in this formation are dry in summer and contain water for some portions of the winter months. In nearly all monitoring locations in the higher elevation areas near the pits, the groundwater elevation in the laterite gravels is higher than in the underlying weathered and fractured bedrock.

The laterite gravel shallow groundwater system is present at Round, Boomerang and Pillow Swamps. The presence of the groundwater system in these swamp locations does not appear to be simply a result of the presence of the gravels but appears to be more controlled by the local topography and geology which act to collect local runoff and trap groundwater above the underlying oxide. These swamps now lie within the drawdown associated with pit dewatering, but no dewatering influence has been observed in the shallow groundwater system in these locations.

4.3 Oxide

4.3.1 Geology

The oxide unit comprises highly weathered bedrock material which occurs in the zone beneath the seasonal shallow groundwater system and above the interface with the weathered and fractured upper bedrock groundwater system (Figure 1). Although the oxide is not interpreted to act as a regional groundwater transmitting unit, it is interpreted to store groundwater, and has been thought to act as a control on the vertical movement of recharge and groundwater within the regional system.



Based on the logging data available from the drilling programmes:

• The oxide unit is present across nearly all of the site and was encountered in all drillholes except at HRVWP02 adjacent to the Hotham River, where the oxide is absent, and alluvial gravels overlie fresh basalt bedrock. The oxide was also unusually thin (around 6 m thick) at HFVWP01 where the oxide also contained significant gravel.

• Depth to the top of the oxide ranged from 0 to 54 m, depending on the presence of the seasonal shallow groundwater system. No consistent regional correlation is evident in the depth to the top of the oxide.

• Depth to the base of the oxide layer ranged from 13 m to 111 m and averaged 45 m in all of the holes drilled to date. The depth to the base of oxide (depth of weathering) demonstrates some regional trends, for example being generally deeper in the north south zone from WD7BR1 to HFBR12, but no clear correlation is evident between elevation and depth of weathering.

• The thickness of the oxide layer ranged from 0 m at HRVWP02 and 6 m at HFVWP01, to 100 m at WD7BR3, and averaged 32 m over all drillholes. Some regional trends of increased oxide thickness are present, including the north south zone from WD7BR1 to HFBR12, and the area around WTBR3, but no clear correlation is evident between thickness of oxide and elevation. Over most of the Boddington region the oxide is more than 20 m thick, other than in the bores close to the Hotham River.

• Logging descriptions for the oxide indicate it to have a massive clay nature, with variable amounts of relict structural features or chips of less weathered material.

4.3.2 Hydrogeology

The oxide zone is present in nearly all locations across the Boddington site and was at least partially saturated prior to mining. Based on data collected during the early stages of mining it has been dewatered in the South pit slopes and North pit slopes where it has been exposed to underdrainage for a long period. In locations distant from the main pits, including in the slopes of the S09 pit, the oxide remains saturated, and has been indicated to receive recharge from the overlying shallow seasonal groundwater system. In high elevation locations near the open pits, the oxide appears to mostly act as a barrier to significant rates of groundwater movement, resulting in the shallow groundwater systems at Round, Boomerang and Pillow Swamps being perched. These responses are consistent with observations in similar deep weathering environments in southwest WA and in the Eastern Goldfields of WA.

However, on a regional basis across the Boddington site, some hydraulic connection through the oxide appears to be present, given that the underlying groundwater systems demonstrate responses to precipitation, and that at HFBR5 (where the oxide is 65 m thick) operating the Westwood bores from bedrock below the oxide caused dewatering of the shallow gravels above the oxide.



4.4 Weathered and fractured upper bedrock

4.4.1 Geology

The weathered and fractured upper bedrock has been identified as the major regional groundwater system at Boddington (due to it being regionally extensive), and it occurs at the interface at the base of the oxide material, where the weathered zone retains sufficient structure to allow some groundwater transmission (Figure 1). Logging data from the drilling programmes indicate that:

• Typically, the transition from weathered bedrock to fresh bedrock is relatively rapid with depth at Boddington. The logged thickness of this weathered interval ranges from 0 m at HRVWP01, to 24 m at WD9BR1.

• The average thickness of the weathered interval across all of the drilling locations was 7 m. • The depth to the top of the weathered and fractured bedrock is highly variable, ranging 13 m to 100

m, but is typically more than 25 m in most locations. • Depth to fresh unweathered bedrock at the base of this unit ranges from 18 m at MUBR3 to 111 m at

WD7BR3. • Logging descriptions confirm that the weathered and fractured upper bedrock comprises highly to

slightly weathered bedrock, including varying degrees of fracturing, veining, mineralisation and alteration.

4.4.2 Hydrogeology

Most of the regional standpipe monitoring bores installed at Boddington have targeted the weathered and fractured upper bedrock unit. As these bores were predominantly drilled using diamond coring with mud circulation, there are no observations of groundwater inflow during drilling. In all cases records were maintained of airlift flows during development of the completed bores. Airlift flow rates typically ranged from nil to less than 0.5 L/s, consistent with a moderate to low hydraulic conductivity for this system. Higher airlift flows were noted at WD7BR12 (0.6 L/s), HFBR7 (0.7 L/s) and at HFBR8 (1.2 L/s).

During the 2012 monitoring bore installation program, recovery of groundwater levels in each bore following airlifting was monitored using a pressure sensor and logger (SWS, 2013A). Interpretation of these responses indicated that for the 2012 bores, the range of hydraulic conductivities for the weathered and fractured upper bedrock was from 0.0003 to 0.04 m/day, with an average of 0.003 m/day, confirming a relatively low hydraulic conductivity, and on a local basis a lesser ability to transmit groundwater compared to the isolated fracture zones in the deep fractured bedrock. RC drilling for the installation of DeepVWP01, DeepVWP02 and HRVWP01 identified damp samples but no airlift flows when drilling through the weathered and fractured upper bedrock.

The weathered and fractured upper bedrock is the groundwater unit which has the greatest extent across the Boddington site. Although on a regional basis it has been observed to act and respond as a relatively continuous and connected hydraulic system, on a localised basis the groundwater transmitting properties are highly variable. The primary storage and transmission of groundwater has been inferred to occur in the saprolite zone at the interface with the upper bedrock surface.



Groundwater flow occurs downslope in response to the prevailing hydraulic gradients, and also as vertical leakage into the underlying deep fractured bedrock system (the vertical gradients defined by the VWP sensors generally act downwards). In many locations the monitoring data define a source of seasonal recharge to this unit, with these locations including areas close to the pits, and areas distant from the pits. In some locations seepage from the waste dumps at surface is indicated to reach the unit. While these observations confirm connection from the surface, through the oxide, to the weathered and fractured bedrock is present, the migration pathway is not clear, and may be a combination of drillholes and natural pathways within the oxide. Near the open pits, the removal of oxide from the pits and the extensive resource drilling program may be a significant contribution to the observed hydraulic connection through the oxide. Distant from the main exploration areas the hydraulic connection may result from remnant structural features within the oxide associated with dikes or less weathered bedrock.

The weathered and fractured bedrock groundwater system displays regional responses to both open pit dewatering and the operation of groundwater supply bores, with groundwater flow directions being towards the pits or the bores in these locations. The magnitude and regional extent of drawdown in this unit around the open pits is relatively small, considering that dewatering of the pits has been undertaken on a continuous basis since 2010.

4.5 Deep fractured bedrock

4.5.1 Geology

In the area of the open pits, the deep bedrock forms part of the regional greenstone unit striking to the north-northwest. Lithologies encountered in the open pits primarily comprise andesite, diorite and dolerite. The dolerite units occur as a large number of sub vertical dikes, generally following the regional strike direction, and as two major sub horizontal dolerites (one north dipping and one south dipping). Basalt and ultramafic units are encountered regionally in the greenstone unit.

Outside of the greenstone boundary (as marked in Figure 2) the regional geology comprises granitoids, with dolerite dike intrusions. These dolerite dykes overprint and are continuous across the greenstone granitoid boundaries. Fracture zones have been identified in the deep basement along some structural features, and also associated with the sub horizontal dolerites.

4.5.2 Hydrogeology

Locally, groundwater transmission and storage in the deep bedrock is controlled by the intensity and openness of the fracture zones present in the unweathered bedrock. Regionally, groundwater transmission is controlled more by the degree of regional connection of these fracture zones, and the presence of any compartmentalising structures. On a regional basis, the deep fractured bedrock system acts as a continuous unit.

Interpretation of 60 packer tests undertaken in diamond drillholes into deep fractured bedrock within North pit and South pit in 2012 indicated that:

• 30 of the test zones had very low hydraulic conductivity, too low to measure (less than 0.00004 m/day).

• 2 of the test zones had a hydraulic conductivity which was too high to quantify by packer testing (more than 0.3 m/day).

• 18 of the test zones had a hydraulic conductivity in the range 0.00004 to 0.3 m/day.



Close to the open pits, the major groundwater transmission zones have been identified to be fracturing associated with the sub horizontal dolerites, and most dewatering bores constructed to date have targeted these features. The orientation of the sub horizontal dolerites has been interpreted to cause the strong hydraulic connection between North pit and South pit, and between the pits and the Jarrah Decline, and also to cause the preferential drawdown to the northeast of the pits.

The limited drawdown observed in the deep fractured bedrock to the southwest of the pits is most likely controlled by the presence of the Western Sediments in this area, which limit regional drawdown to the southwest.

Responses to seasonal recharge occur in the deep fractured bedrock, in some cases with very rapid responses to daily precipitation events, the sources of which have not been defined but may be related to drillholes and sumps in the mine area.

Previously the hydrogeological model suggested that significant groundwater transmitting fracture zones were present only in the greenstone, with limited fracturing expected in the surrounding granitoids. Numerical models used to predict regional drawdown influences from pit dewatering incorporated large reductions in permeability at this geological contact. However, the recent groundwater supply investigations have identified that regionally connected fracture zones suitable for exploitation for water supply are present in the granitoids, and that drawdown associated with pit dewatering is likely to extend across strike beyond the limits of the greenstone unit.

Injection testing of groundwater supply pilot holes targeted at known fracture zones in deep (up to 400 m depth) granite and greenstone units in the greater region of the Boddington Gold Mine indicated that the average hydraulic conductivity of the fractured bedrock ranged from 0.01 to 0.99 m/day and averaged 0.4 m/day. These values are higher than those derived from the packer testing of fracture zones within North pit and South pit described above and confirm that the regional bedrock has a higher potential for the transmission of groundwater than assumed in the previous modelling studies.

Distant from the open pits, on a regional basis, vertical hydraulic gradients in the deep fractured bedrock are indicated to be small, and groundwater elevations in the deep fractured bedrock are interpreted to be similar to the weathered and fractured bedrock. However, in the zone within 2 to 3 km of the open pits, spot measurements of groundwater elevations measured in deep fractured bedrock identify significantly lower values than in the overlying weathered zone. Drawdown associated with mine dewatering is interpreted to have a much larger magnitude and extent in deep bedrock, compared to the extent contoured in Figure 51 for the overlying interface.

4.6 Interactions with the Hotham River Although the groundwater elevation data available from HRVWP02 do not include responses during a wet season, comparing the available data with the measured river height in the Hotham River indicates groundwater is flowing from the groundwater system into the Hotham River. This matches the geology which identifies the river sits in gravels that overlie bedrock with no oxide present in this location. This interpreted flow regime is consistent with that identified at HRVWP01, and with the oxide being absent below the Hotham River in some locations as identified during stream mapping. The potential for groundwater gradients to be reversed, and for the Hotham River to recharge the groundwater system in high flow periods will be investigated during ongoing seasonal monitoring at HRVWP02.



5. Conceptual assessment of groundwater depths

5.1 Background and methodology NBG plan to use the updated hydrogeological conceptual model described in Section 4 to develop a numerical model to simulate regional groundwater conditions at the Boddington mine. The model will be designed to provide updated regional predictions of mine related drawdown, and to investigate the potential influences on groundwater receptors, which include the Hotham River and any potential phreatophytic vegetation in the region.

In the interim, NBG require a conceptual assessment of potential groundwater depths across the mine area, which is intended to be used to prioritise investigations into vegetation health. The assessment is intended to provide a conceptual indication of areas where groundwater is at depths which may result in vegetation being dependent on groundwater in the saturated zone, and to provide an indication of any potential future changes in those groundwater depths. This conceptual assessment will subsequently be superseded by the model predictions.

Depth to groundwater below surface has therefore been estimated and contoured using the following methodology:

1. Contouring utilises observations from VWP sensors and standpipes installed at the interface in the weathered and fractured upper bedrock system. This is the groundwater system which has the most available data, tends to most closely follow groundwater elevations in the oxide, and reflects the geological formations where vegetation roots may potentially penetrate (i.e. the oxide and the interface). Although these geological formations are likely to be penetrated by vegetation roots, whether vegetation is dependent on groundwater in the formations will depend on the extent and nature of the architecture of the root system.

2. Groundwater elevations in the shallow seasonal groundwater system have not been contoured. However, it is noted that:

a. In the high elevation locations near the mine facilities, the laterite gravels are not expected to be influenced by mine dewatering and groundwater depths are assumed to remain consistent with background conditions over the remaining life of mine. This assumption is supported by the observed responses at Round Swamp, Boomerang Swamp, Pillow Swamp, IWS07 and Deep VWP02.

b. In the low elevation area close to 34 Mile Brook and the Hotham River, the alluvial gravels and laterite gravels have been assumed to have the same heads as the weathered and fractured upper bedrock groundwater system. This assumption is consistent with observations at HFBR5 and HFBR8, where depth to groundwater measured in a bore screened only in shallow gravels is the same as depth to groundwater measured in an adjacent bore screened only in weathered bedrock at depth, despite the two screens being separated by 23 to 65 m of oxide. In other locations where a deeper groundwater level is present in the weathered and fractured bedrock, this may result in the shallow gravels being assumed to be dry, consistent with observations at HFBR1S, HFBR2S, HFBR3S and HFBR6S.



3. The contoured groundwater elevations have then been subtracted from the ground surface elevation as defined in a Digital Topographic Models (DTM) supplied by NBG to generate contours of depth to groundwater below surface. All depths have been calculated using the 2006 DTM, as this effectively describes the ground surface prior to the current mining period. It should be noted that the groundwater depths are therefore referenced to the surface present in 2006 following the oxide mining period including any pits and rehabilitated waste rock facilities present and are not referenced to the natural topographic surface prior to any mining disturbance. It should also be noted that in the locations of the current waste rock storage facilities, depth to groundwater below the current surface will be greater than contoured using the 2006 surface. However, for the undisturbed areas which host the natural vegetation which is the target of the regional studies, groundwater depths calculated from the 2006 surface will be the same as depths from the current surface.

4. Depths have been contoured for 2006 to provide an indication of background conditions prior to the modern mining.

5. Depths have been contoured for 2016 Q3, which corresponds to the greatest changes in groundwater depths observed to date, when pit dewatering include a significant component of active dewatering, and when the Westwood groundwater supply bores were in operation. Current groundwater elevations (2018 Q1) are similar to or higher than those measured in 2016 Q3, and in particular near the Westwood bores groundwater elevations were around 10 m higher in 2018 Q1 compared to 2016 Q3.

6. A conceptual indication of potential depths at end of life of mine has been generated, by interpolating and projecting the responses observed to date. This conceptual indication is intended only to assist with designing the vegetation management program and will be replaced by the model predictions once the groundwater model becomes available.

5.2 Topographic data NBG provided a regional DTM for the ground surface over the Boddington Gold Mine area for 2006 (to reflect conditions prior to land disturbance during modern mining), and the land surface defined by this dataset is presented in Figure 52 along with the current groundwater monitoring locations. Key features of the topography include low elevation areas along 34 Mile Brook, Boggy Brook, House Brook and their tributaries, a high elevation ridge between WD7BR4 and the Hotham River, and a prominent north-northwest oriented ridge along the margin of the RDA areas.

Prior to using the DTM to generate groundwater depth contours, the potential reliability and accuracy of the dataset was investigated. 98 groundwater monitoring bores for which accurate surveys of location and elevation are available were selected for comparison. The selected bores were distributed across all of the Boddington Gold Mine, and were located outside of the facility footprints, so that the DTM elevations in these locations would be expected to be the same over the mining period. For each bore, the elevation at that location in the DTM was extracted and compared against the surveyed value. A review of the calculated differences identified that for the 2006 DTM:

• The average offset over all the bores was 0.2 m which confirms there is no datum shift between the datasets.

• The DTM elevation was within 4 m of the surveyed elevation in 99% of bores. • The DTM elevation was within 2 m of the surveyed elevation in 82% of bores. • The DTM elevation was within 1 m of the surveyed elevation in 56% of bores. • The largest difference of 7.9 m was measured at F1BR16D which is at the margin of the RDAs and

has potentially been affected by earthworks occurring between capturing the 2006 DTM and installing and surveying the bore.



Overall, the DTM is indicated to be accurate to within a few metres, which is a small error compared to the uncertainty associated with interpolating the groundwater elevations in areas where there are few monitoring bores, and the DTM accuracy is appropriate for contouring conceptual groundwater depths.

5.3 Estimated groundwater elevations in 2006 In 2006, at the end of the care and maintenance period that followed the oxide mining operations, groundwater elevations had largely recovered from dewatering associated with open pit mining and mining in the Jarrah Decline. Groundwater depths in 2006 therefore provide an indication of background conditions in the absence of mining influences.

Records describing groundwater elevations in background conditions are available from:

• A baseline groundwater report produced in 1999 included a table of 98 regional groundwater bores and measured pre-mining groundwater elevations (Aquaterra, 1999). The groundwater measurements were made in the early to late 1980s, and so reflect background conditions, given that oxide mining started in 1987. These elevations are expected to be comparable with conditions at the end of the care and maintenance period in 2006 and all 98 records were initially included in the contouring dataset.

• Some currently active monitoring bores have a record extending prior to 2006, and groundwater elevations in 2006 were accurately known in these locations and added to the dataset.

• The elevations of the lakes in North pit and South pit were measured in 2006 and have been used to control groundwater elevations near the pits.

• For the large number of monitoring bores installed during the current mining period, for any bores or VWP sensors monitoring the interface, which have been concluded not to be affected by the current mine facilities, the average measured groundwater elevation has been included in the dataset.

Inclusion of all these sources provides the most detailed understanding of baseline groundwater elevations prior to mining and provides the most relevant comparison to conditions during mining, as the number of datapoints is comparable between the background and mining datasets. However due to the large range in actual monitoring dates (early 1980s to 2018), the surface may be accurate to around 5 m, due to the combination of the long-term background declining groundwater elevation trends, and the annual seasonal trends. The potential error introduced by this approach is relatively small compared to the range of groundwater elevations measured across the Boddington Gold Mine.

The resulting dataset was contoured several times, with apparently anomalous or conflicting points progressively removed to achieve groundwater elevations and flow directions which are consistent with the updated conceptual model. The resulting interpreted groundwater elevation surface in 2006 is presented in Figure 53. In areas distant from the mine facilities, the elevations are consistent with the contours for 2018 in Figure 50, demonstrating groundwater flow towards and along 34 Mile Brook, Boggy Brook and Wattle Hollow Brook. However, in 2006 groundwater flow was to the south following 34 Mile Brook in the footprint of the RDAs and locally near the pits groundwater flow was towards the pit lakes that were present in 2006.



5.4 Estimated groundwater depths in 2006 Figure 54 presents contours of the estimated depth to groundwater for pre-mining conditions in 2006, calculated by subtracting the groundwater surface in Figure 53 from the topographic surface in Figure 52. The contours indicate that groundwater was naturally close to or above surface in portions of 34 Mile Brook, including where it is below the current RDAs, at Boomerang Swamp, and below the current location of WRD8. Groundwater is indicated to have been around 200 m deep below the prominent topographic ridge to the west of the RDAs. This depth is likely to be an overestimate, as there are no bores available to define the groundwater elevation below the ridge, but confirms groundwater is deep in this area. Groundwater is indicated to have been more than 100 m deep below the hill between WD&BR12 and the Hotham River, although again there are no monitoring bores to confirm this interpretation. In the remaining areas, groundwater in 2006 was 5 to 20 m below surface near the topographic lows defined by the surface drainages, and up to 60 m below surface in the more elevated areas.

5.5 Estimated groundwater depths in 2016 Q3 Estimated depth to groundwater in 2016 Q3 has been contoured in Figure 55, following the same methodology described in Section 5.4. The most significant changes in groundwater depths for the interface in 2016 Q3 compared to the pre-mining conditions in Figure 53 are:

• Groundwater depth had increased by around 200 m within the pits due to mine dewatering and had increased by up to 10 m within around 2 km of the open pits.

• Groundwater depth had reduced significantly, and groundwater was close to or above the 2006 topographic surface around the margins of the RDAs.

• Groundwater depth had increased by around 10 m within the area of the Westwood groundwater supply bores due to groundwater abstraction.

5.6 Conceptual groundwater depths at end mining Under the current mine plan, mining in the open pits will terminate in 2029, by which time the North pit will have reached an elevation around 130 m deeper than the current pit, and South pit will have reached an elevation around 250 m deeper than the current pit. Dewatering is intended to continue to use a combination of passive and active approaches over life of mine. The total dewatering rate is anticipated to be similar to the current average total rate of 120 L/s in the near future (of which 100 L/s reflects groundwater) but may reduce to around 40 L/s in the long term if a reduced degree of fracturing is encountered in the deeper bedrock.

In the long term, groundwater elevations at the interface around the open pits will continue to decline, with the magnitude of the change controlled by the nature and regional geometry of the fracture zones within the deep bedrock, and by the degree of connection between the bedrock and the overlying interface and oxide. These aspects of the hydrogeological regime will be refined during ongoing monitoring as the pit is deepened, using geological data collected from any regional exploration programs, and using the results of the planned numerical modelling.

In the interim, for input to designing vegetation studies, a conceptual indication of the expected groundwater depths by the end of mining in 2029 has been generated by:

1. Assuming that total dewatering rates continue to be at 120 L/s of which 100 L/s represents groundwater inflow over the remaining life of mine.

2. Assuming that the relatively uniform rates of drawdown observed in bores completed at the interface during dewatering operations from 2012 to 2018 continue for the rest of the mining period;



3. Assuming that drawdown at the interface continues to be at reduced rates compared to dewatering influences in the underlying bedrock; and

4. Assuming that the cone of drawdown expands in all directions, but preferentially to the northeast and northwest, as has occurred to date.

Conceptual groundwater depths estimated for 2029 following this empirical approach are presented in Figure 56. Conceptual groundwater depths around the open pit are increased compared to the current depths along geological strike, are increased under Pillow, Boomerang and Round Swamps, but remain similar to the current depths across the rest of the Boddington Gold Mine.

5.7 Conceptual groundwater depths at end mining with groundwater supply The regional groundwater supply bores described in Section 2.7 are expected to have a total combined capacity of 129 L/s, although some of the bores have not undergone long term operation to confirm these estimates. Currently all of the bores are decommissioned as there is sufficient raw water available from other sources, but the bores will be recommissioned in periods when precipitation conditions reduce the amount of raw water available from other sources. As the total pumping rate available from the groundwater supply bores is greater than the total groundwater inflow to the open pits, the potential operation of the groundwater supply bores is likely to be a significant influence on regional groundwater depths, which will be explored using the planned numerical model.

In the interim, for input to designing vegetation studies, a conceptual indication of the expected groundwater depths by the end of mining in 2029 including the influence of the groundwater production bores has been generated by:

1. Assuming that total dewatering rates from the open pits continue to be at 120 L/s of which 100 L/s reflects groundwater over the remaining life of mine.

2. Assuming that as a result of seasonal conditions, all of the groundwater supply bores are operated at maximum capacity continuously for 2 years at the end of mining.

3. Estimating the magnitude and regional extent of drawdown around the bores by comparison to the observed influence during operation of the Westwood bores in 2015 and 2016,

4. Assuming that the drawdown in deep bedrock due to abstracting groundwater from depths greater than 100 m is reflected in groundwater elevations measured at the overlying interface, which is a conservative approach.

Conceptual groundwater depths estimated for 2029 following this empirical approach are presented in Figure 57. Conceptual groundwater depths are increased compared to Figure 56 close to the operating bores and remain similar across the remainder of the Boddington Gold Mine.



6. Recommended works to manage regional groundwater

6.1 Potential mechanisms for mining impacts to occur via groundwater Based on the updated review of monitoring data collected across the Boddington Gold Mine described in the previous sections, influences of the NBG mining operations on regional groundwater conditions are identified to be:



3. Seepage is occurring to groundwater from water storage structures. 4. Drawdown due to pit dewatering in the deep bedrock potentially extends more than 2 km from the




There are no groundwater users (other than NBG) in the areas being influenced by the mining operations. Potential environmental receptors for groundwater are:

• Round, Boomerang and Pillow Swamps. • Vegetation potentially drawing groundwater from the saturated zone within the oxide, within the

seasonal shallow groundwater system or within the weathered and fractured upper bedrock groundwater system.

• Surface water features which have connection to the underlying groundwater systems, including the Hotham River.

Potential mechanisms by which impacts could occur as a result of the mining influences on the groundwater systems are identified to be:

• Stress to vegetation resulting from changes in groundwater quality or from permanent saturation of the root zone in seepage and mounding areas.

• Reduced saturation in the alluvial gravels, in oxide or in the weathered and fractured upper bedrock due to underdrainage in locations where drawdown is occurring, and vegetation relies on the saturated zone.

• Reduced pooling in the Hotham River in summer if drawdown should reach the underlying groundwater system, and cause the pools to discharge to groundwater, rather than being recharged from groundwater.

The potential sources and pathways for each of these mechanisms to cause impacts are well defined from the conceptual groundwater conditions described in Section 4 and have been employed in the following sections to ensure that adequate monitoring is being undertaken along each of the identified pathways to provide early warning of any potential impacts.



6.2 Review of existing monitoring depths The sources which potentially cause drawdown are the groundwater supply bores and open pit dewatering. Both of these sources are in the deep fractured bedrock groundwater system, while any potential impacts would be manifested in the weathered and fractured upper bedrock groundwater system at the interface and in the overlying oxide.

Most of the existing regional network of standpipe bores are completed at the interface, while the VWP monitoring installations constructed since 2015 include sensors in oxide above the interface, at the interface and in the deep bedrock. The regional network was augmented in 2017 with regional standpipe monitoring bores open in the deep bedrock. In combination the data from these bores confirm that the regional standpipes completed at the interface are appropriate for investigating mining influences, despite groundwater elevations being lower in the deep bedrock in some locations near the open pits. This is because they most closely reflect the groundwater elevations in the oxide and in the weathered and fractured upper bedrock, where impacts to surface water streams and vegetation may occur.

In locations where fresh bedrock is relatively shallow, or where large drawdown occurs, the construction approach for standpipes completed at the interface may result in the local groundwater elevation being close to the base of the screen, and there is potential for these bores to become dry. In order to investigate the potential for this to occur, every monitoring bore at Boddington was plumbed with a weight during 2013, to measure the actual depth to the base of the casing installed in the bore. This measurement has been compared against recent depths to groundwater in Table 3, along with reference to the figure where monitoring data are plotted in each case. The potential requirement to replace these monitoring bores in the next few years has been assessed as follows:

• Although 34BR8 was nearly dry, significant resaturation occurred in the last two years and it is currently providing accurate data.

• GMRBR1 is currently providing good data and has 2 m of saturated screen at the base of the bore. Although it may need replacing eventually, that is not expected to be required in the next few years.

• HBBR1 is currently providing good data, and the plumbed depth confirms it has 1 m of saturated screen at the base of the bore. Although it may need replacing eventually, that is not expected to be required in the next few years.

• MPBR1 has gone dry. It is located at the current margin of drawdown associated with pit dewatering and should be replaced. MPBR1 was screened from 29 to 41 m in weathered igneous rock (Appendix A). It should be replaced with a bore screened from 30 to 80 m below surface.

• MUBR2 currently has 8 m of water above the base of casing as plumbed in 2012. However, the bore is being reported as dry during monitoring. This bore should be investigated and remediated to remove any obstruction at the base of the casing or replaced, as it defines the current margin of mining related drawdown.

• N5005-1A has been dry since 2010. Deeper bores are available in this area, including MUBR4 and WD9BR5, and replacement is not required.

• Q2PZ1A has demonstrated a flat response since 2010, despite the water level being above the base of the casing, and it is likely the base of the screen is blocked, and the bore is effectively dry. There are other monitoring bores in the adjacent areas, including PISWPZ3A which has 12 m of saturated screen, so replacement of this bore is not currently recommended.

• WD7BR2D has demonstrated a flat response since 2012, despite the groundwater level being above the base of the casing, and it is possible the base of the screen is blocked, and the bore is effectively dry. Replacement of the bore is not recommended due to the availability of data from the adjacent bore WD7BR3D.



• WD7BR5D has demonstrated a flat response since 2014, and the current water level is close to the plumbed depth and the bore is effectively dry. However, this bore potentially lies with a future waste rock facility expansion footprint and replacement is not recommended.

• WD9BR2 was close to becoming dry in 2015, but recently groundwater elevations have responded strongly to waste rock storage facility seepage and the screen has resaturated.

• WD9BR4 was drawing down rapidly until 2014 and has demonstrated a flat response since 2015. It appears likely the bore is dry, despite the water level being indicated to be 2 m above the base of the casing, potentially due to blockage of the base of the screen. Deeper monitoring bores are available in the area (WD9BR5, HGPZ31A), and replacement is not required.

Table 3: Bores with potential to become dry

Note: mBGL metres below ground level mBTOC Metres below top of casing

Overall, most of the regional standpipe monitoring bores have been identified to be screened at an appropriate depth for the monitoring objectives. One bore which has gone dry (MPBR1) requires replacing with a deeper bore and one bore which is being reported as dry (MUBR2) should be investigated to see if the casing is blocked.

6.3 Review of existing monitoring locations

6.3.1 Rationale for monitoring locations

Many of the monitoring locations illustrated in Figure 2 were selected during the feasibility studies for the current mining operations and were based on the mine plan at that time and the understanding of likely pit dewatering drawdown impacts at that time (Golder, 2005). As part of the current review, these locations have been reassessed, taking account of the updated mine plan and associated areas of potential future disturbance. These reviews have been based on the potential sources that influence groundwater, and the migration pathways in the groundwater system described in Section 4. The reviews also take account that actual rates of groundwater inflow to the open pits during mining have been much lower than were modelled during the feasibility studies when extensive regional influences were predicted.

Bore Cased Plumbed 2018 Length of Data plotted

depth depth water depth saturated screen in

(mBGL) (mBTOC) (mBTOC) (m)

34BR8 14.53 9.3 5.23 Figure 37

GMRBR1 30.4 31.1 29.2 1.9 Figure 42

HBBR1 41 41.57 40.5 1.07 Figure 40

MPBR1 30 30.44 29.9 0.54 Figure 41

MUBR2 42.1 42.76 34.8 7.96 Figure 42

N5005-1A 12.15 11.4 0.75 Figure 32

Q2PZ1A 39 39.63 38 1.63 Figure 33

WD7BR2D 64.4 64.33 63.3 1.03 Figure 42

WD7BR5D 51.4 51.5 51.7 -0.2 Figure 45

WD9BR2 37.4 37.4 30.9 6.5 Figure 46

WD9BR4 41 41.1 38.9 2.2 Figure 46



6.3.2 Potential sources

At Boddington Gold Mine potential sources acting on the groundwater systems include seepage from the waste rock storage facilities, seepage from mine water ponds, drawdown due to pit dewatering, and drawdown due to any future operation of the 12 regional groundwater supply bores.

The groundwater supply bores result in a significant change to the groundwater regime compared to that assumed when the monitoring network was originally designed (Golder, 2005). The original monitoring regime was based on the largest risk being associated with drawdown from pit dewatering reaching the Hotham River. Under the current mine plan, the open pits are located more than 6 km from the Hotham River, and produce around 100 L/s of groundwater, which may potentially reduce to around 40 L/s as the pits are deepened. The Westwood groundwater supply bores are located around 2 km from the Hotham River, and may be operated at a total rate of 67 L/s, while Roberts 1 is located 4 km from the Hotham River and may be operated at 22 L/s. Monitoring of groundwater conditions between these groundwater supply bores and the Hotham River is therefore now as important or more important than the existing monitoring between the open pits and the Hotham River.

6.3.3 Assessment of monitoring locations

Taking account of the monitoring locations in Figure 2, the completion depths described in Appendix A, the discussion of monitoring data in Section 3, and the assessment of sources above, it is identified that:

1. The geotechnical and dewatering investigations at the open pits are providing sufficient definition of groundwater conditions in the mine area.

2. The existing bores completed at the interface provide sufficient data to detect any potential underdrainage of Round, Pillow and Boomerang Swamps.

3. The converted groundwater exploration pilot holes provide sufficient data on the mining related drawdown occurring in the deep bedrock.

4. There are sufficient monitoring points around the open pits to define the influence of mine dewatering at different depths (including DeepVWP01 and DeepVWP02 which have five VWP sensors at each site).

5. There are sufficient monitoring points around the groundwater supply bores to measure the influence of groundwater abstraction, including HFVWP01 and HFVWP02 installed between the Westwood groundwater supply bores and the Hotham River. However, two VWP sensors in each of HFVWP01 and HFVWP02 were damaged during construction and subsequently failed. Further monitoring will be required to ensure the remaining sensors are providing accurate data, and if additional sensors fail it may become necessary to replace these installations.

6. There are sufficient data defining groundwater and surface water conditions near the Hotham River, including HRVWP01, HRVWP02 and the two stream gauging stations, however it is noted that:

a. The stream gauging station installed on the Hotham River at Pump Station 2 has a limited range and does not record the peak river elevations, and the installation should be modified to increase the measuring range.

b. One sensor at HRVWP02 was damaged during installation and subsequently failed. Further monitoring will be required to ensure the remaining sensors are providing accurate data, and if additional sensors fail it may become necessary to replace this installation.

7. Expansion of the waste rock storage facilities is planned which will result in the decommissioning of monitoring bores, and replacements may be required once the final configuration of the facilities is determined.



6.4 Summary of recommended monitoring works Works which have been concluded to be required for the ongoing management of groundwater at the Boddington Gold Mine are summarised as follows:


The frequency of the existing regional groundwater level monitoring is considered appropriate taking account of the objectives of the monitoring.

There have been periods of data loss from the VWP installations due to logger or telemetry failures. It is recommended that systems be put in place to poll or test the data collection at monthly intervals and ensure that any failures can be rectified before significant data loss occurs.

6.5 Numerical groundwater model The 2013 groundwater management plan described a potential approach to construction of a regional numerical groundwater model. The approach described at that time treated drawdown from open pit dewatering separately from the influences of other facilities, and the model construction plan was structured accordingly.

The current review of monitoring data has identified that the mine facilities are acting as multiple influences on the groundwater system, and that these individual influences are starting to overlap. In order to provide meaningful predictions, any numerical model will now need to address the influences of all of the mine facilities in combination, not just the influences of open pit dewatering, and will need to extend over the full catchment of 34 Mile Brook, and into adjacent catchments.

Facilities and hydrologic processes which will need to be explicitly included in the model simulations, including changes in these processes during operation and closure, will include:

• Dewatering of the open pits by both passive and active approaches. • Seepage from the RDAs. • Seepage from the waste dumps. • Drawdown due to operation of groundwater supply bores. • Seepage from any large water supply reservoirs including potential future structures such as D5 and

D6.



7. Summary and conclusions A review of regional hydrogeological conditions across the Boddington Gold Mine has been completed and makes use of all investigations and monitoring data collected since the previous review of hydrogeological conditions was undertaken in 2016 (BDH, 2016). The resulting updated conceptual hydrogeological model remains generally consistent with that described in previous reviews and identifies the main groundwater units to be:

1. A seasonal shallow groundwater system, which overlies oxide with low hydraulic conductivity, 2. The weathered and fractured upper bedrock groundwater system including the interface at the base

of the oxide, and 3. A deep fractured bedrock groundwater system.

Current influences of the mine facilities on groundwater conditions are:



3. Seepage is occurring to groundwater from unlined storage structures. 4. Drawdown due to pit dewatering in the deep bedrock potentially extends more than 2 km from the




In higher elevation locations, the groundwater elevation in laterite gravels in the seasonal shallow groundwater system is higher than in the underlying weathered and fractured bedrock. The seasonal shallow groundwater system is present at Round, Boomerang and Pillow Swamps and at Deep VWP02 and IWS07. These swamps now lie within the drawdown associated with pit dewatering, but no dewatering influence has been observed in the seasonal shallow groundwater system. In low elevation locations near 34 Mile Brook and the Hotham River, alluvial and laterite gravels in the shallow groundwater system are permanently saturated and demonstrate hydraulic connection to the underlying groundwater systems.

The upgraded regional monitoring network now includes standpipes and VWP installations monitoring the shallow groundwater system, the oxide, the interface and the deep bedrock. Taking account of the locations of the mine facilities expected to influence the groundwater system, and the potential receptors, the existing monitoring locations and depths are considered appropriate to identify any potential impacts.

The pit dewatering drawdown area in 2018 remains 3 to 4 km distant from the Hotham River. The drawdown area associated with the operation of groundwater supply bores extended to around 1.5 km from the Hotham River in 2016 but has subsequently recovered due to decommissioning of the bores and higher than average precipitation conditions.



Works which have been concluded to be required for the ongoing management of groundwater at the Boddington Gold Mine are summarised as follows:


The frequency of the existing regional groundwater level monitoring is considered appropriate taking account of the objectives of the monitoring. There have been periods of data loss from the VWP installations due to logger or telemetry failures. It is recommended that systems be put in place to poll or test the data collection at monthly intervals and ensure that any failures can be rectified before significant data loss occurs.

Further monitoring data collected through a wet season will be required to confirm that the recently installed VWP sensors are providing accurate data, and to refine the understanding of interactions between the Hotham River and the groundwater system. The conceptual model may then be updated and used as the basis for the construction of a regional numerical groundwater model.



References Aquaterra 1999, Boddington Gold Mine, Baseline Hydrological Report, Aquaterra Consulting Pty Ltd.

BDH 2013, Newmont Boddington Gold, Updated Groundwater Conditions and Regional Groundwater Management Plan, Big Dog Hydrogeology Pty Ltd.

BDH 2016, Newmont Boddington Gold, 2016 Update of Groundwater Conditions and Regional Groundwater Management Plan, Big Dog Hydrogeology Pty Ltd.

Golder 2005, Design of Groundwater Monitoring Network, Boddington Gold Mine, Stage 3 Feasibility Study, Boddington WA, Golder and Associates.

Golder 2007, Shallow Monitoring Bore Installation, Boddington Gold Mine Expansion, Report 06641337-R02, Golder and Associates.

Golder 2010, Summary of Boddington Groundwater Drilling Programme, 22 April to 28 May 2010, Letter report to Mr Graeme Reynolds of Newmont from Greg Hookey of Golder, Golder and Associates.

NBG 2017A, Q3 2017 NBG Pits Hydrogeology, Memo from Mr Junji Ohashi, Newmont Boddington Gold.

NBG 2017B, SO9 Hydrogeological Review for Geotechnical Assessment, Memo from Mr Scott Vujcich, Newmont Boddington Gold.

SWS 2013A, Regional Monitoring Drilling Programme Summary, 9th January to 30th November 2012, Technical memorandum to Mr Ben Walley of Newmont, from Jorge Rodriguez of SWS, Schlumberger Water Services.

SWS 2013B, Newmont Boddington Gold. Updated Assessment of Potential Regional Influences of Mine Dewatering, Report 51964/R3, Schlumberger Water Services.



List of Figures 1. Schematic hydrogeological cross section 2. Regional monitoring locations 3. Hotham River mapping locations 4. Subcrop in stream bank at Outcrop A 5. Fractured bedrock outcrop in riverbed at Outcrop B 6. Fractured bedrock in stream bank at Outcrop B 7. Hotham River elevation profile 8. Completion details HFVWP01 9. Completion details HFVWP02 10. Completion details HFBR10 11. Completion details HFBR11 12. Completion details HFBR12 13. Completion details HRVWP02 14. Hotham River water level monitoring 15. Completion details LPBR1-A 16. Groundwater supply pumping rates 17. Total pit dewatering rates 18. Groundwater elevations at S09 pit 19. Groundwater elevations at DeepVWP01 20. Groundwater elevations at DeepVWP02 21. Groundwater elevations at HFVWP01 22. Groundwater elevations at HFVWP02 23. Groundwater elevations at HRVWP01 24. Groundwater elevations at HRVWP02 25. Groundwater responses near HFBR5 26. Groundwater responses near NPBR2 27. Groundwater responses near WHBR2 28. Groundwater responses near LPBR1-A 29. Deep bedrock responses near South pit 30. Groundwater elevations - Round Swamp 31. Groundwater elevations - Pillow Swamp 32. Groundwater elevations - Boomerang Swamp 33. Groundwater elevations - Q Pit 34. Groundwater elevations - K Pit 35. Groundwater elevations - HFBR1 36. Groundwater elevations - HFBR2 37. Groundwater elevations - regional background bores 38. Groundwater elevations - Westwood area 39. Groundwater elevations - Hotham River 40. Groundwater elevations - regional bores 1 41. Groundwater elevations - regional bores 2 42. Groundwater elevations - regional bores 3 43. Groundwater elevations - regional bores 4 44. Groundwater elevations - regional bores 5 45. Groundwater elevations - regional bores 6 46. Groundwater elevations - regional bores 7 47. Groundwater elevations - regional bores 8 48. Groundwater elevations - RDA area 1 49. Groundwater elevations - RDA area 2 50. Regional groundwater elevations at the interface in 2018 Q1 51. Interpreted drawdown at the interface in 2018 Q1



52. Topographic surface in 2006 53. Groundwater elevations in 2006 54. Estimated groundwater depths in 2006 55. Estimated groundwater depths in 2016 Q3 56. Conceptual groundwater depths in 2029 57. Conceptual groundwater depths in 2029 with water supply operation



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Figure 1

Report:

Boddington 2018Regional Review

Date:April 2018

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Figure 2

Report:

2018 RegionalGroundwater Management Plan

Date:May 2018

Legend

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newmont boddington gold 2018 update of ......newmont boddington gold pty ltd (nbg) operates the...

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