proposed short-term dewatering discharge mt henry€¦ · evident in winter months following...

Proposed Short-term Dewatering Discharge

Mt Henry

This report was prepared for:

Higginsville Gold Operations, Metals X Ltd

July 2016 Mark Coleman and Bindy Datson

actis Environmental Services

PO Box 176

Darlington

WA 6070

08 92521050

Contents

1 Executive Summary ................................................................................................ 4 2 Introduction ............................................................................................................. 6 3 Regional Information .............................................................................................. 8

3.1 Regional Conservation Values – Great Western Woodlands ....................................... 8 3.2 Salt Lakes – an introduction ............................................................................................ 8 3.3 Geography ......................................................................................................................... 9 3.4 Lake Dundas ...................................................................................................................... 9 3.5 Chemical aspects of salt lakes .......................................................................................... 9 3.1 Meteorological Data ........................................................................................................ 10

4 Brief Description of Lake Dundas at Proposed Discharge Site ..........................11 4.1 Overview of Proposed Discharge Site, Lake Dundas................................................... 11 4.2 Hydrological Description ............................................................................................... 11

4.2.1 Aquatic Invertebrate Fauna .................................................................................... 12 4.2.2 Vegetation ............................................................................................................... 12 4.2.3 Fringing Vegetation in vicinity of Proposed Discharge Site .................................. 13

5 Description of Discharge .......................................................................................21 5.1 Discharge Quantity ......................................................................................................... 21 5.2 Composition ..................................................................................................................... 21

6 Impact of the Proposed Discharge .......................................................................23 6.1 Hydroperiod .................................................................................................................... 23 6.2 Surface Salt Load ............................................................................................................ 24 6.3 Characteristics of the Discharge Plume ........................................................................ 25 6.4 Shoreline Vegetation ....................................................................................................... 26 6.5 Aquatic Invertebrate Fauna .......................................................................................... 26

7 References..............................................................................................................27 8 Appendix ................................................................................................................28

8.1 Sample Points .................................................................................................................. 28

Table of Figures

Figure 1 - Location of Mine and Discharge Site ............................................................................ 6 Figure 2 - Mean and Median rainfall data ................................................................................... 10 Figure 3 - Discharge and Mine site ............................................................................................... 11 Figure 4 - WP448 Causeway, sample of algal mat ...................................................................... 14 Figure 5 - Upwelling seen on playa ............................................................................................... 15 Figure 6 - Which was a loose drill hole cap .................................................................................. 15 Figure 7 - WP453, terrestrial vegetation ...................................................................................... 16 Figure 8 - WP 453, Tecticornia doleiformis .................................................................................. 16 Figure 9 - WP455, Discharge Site, samphires, west .................................................................... 17 Figure 10 - WP455, Tecticornia halocnemoides ........................................................................... 17 Figure 11 - WP455, Discharge Site, samphires, east ................................................................... 18 Figure 12 - WP455, Discharge Site, samphires close-up ............................................................. 18 Figure 13 - WP456, Disturbance Site, east ................................................................................... 19 Figure 14 - WP456, Hemichroa driandra ...................................................................................... 19 Figure 15 - WP456, Disturbance Site, west .................................................................................. 20 Figure 16 - WP456, Disturbance Site playa, north ...................................................................... 20 Figure 17 - Ionic Composition of the Discharge .......................................................................... 22 Figure 18 - Salt Load Core Sampler ............................................................................................. 24 Figure 19 - Boxplot of salt load samples in top 5cm (kg/m2) ...................................................... 25 Figure 20 - Site visit locations ........................................................................................................ 29

Table of Tables

Table 1 - Aquatic Invertebrate Fauna found in Lake Dundas ................................................... 12 Table 2 - Samphire species ............................................................................................................ 13 Table 3 - Discharge Statistics (extreme discharge TDS) ............................................................. 21 Table 4 - Discharge Ionic Concentration ..................................................................................... 22 Table 5 - Coverage from discharge ............................................................................................... 23 Table 6- Salt load in top 5cm statistics (kg/m2) ........................................................................... 24 Table 7 - Sample point location and elevation (WGS84) ............................................................ 28

Copyright

No part of this document may be reproduced without acknowledgment of actis Environmental Services and stated client.

Disclaimer

The information contained in this report is based on sources believed to be reliable. While every care

has been taken in the preparation of this report, actis Environmental Services gives no warranty

that the said base sources are correct and accepts no responsibility for any resultant errors contained

herein and any damage or loss, howsoever caused, suffered by any individual or corporation.

actis Environmental Services

4

Short term discharge Mt Henry

25 July 2016

1 Executive Summary

Higginsville Gold Operations (HGO) is located in the Eastern Goldfields approximately 60km

north of Norseman and 110km south-south-east of Kalgoorlie. Avoca Pty Ltd acquired the

Higginsville project in June 2004, commencing gold production in July 2008. Avoca was

subsequently amalgamated with Anatolia Minerals to form Alacer Gold Pty Ltd in 2011. In

October 2013 Mineral X Limited acquired Higginsville Gold Operations amongst other assets

as part of its purchase of Alacer Gold Pty Ltd.

Higginsville Gold Operations (HGO) plan to develop the Mt Henry Open Pits Project which is

located on mining lease M63/515 and M63/516 in the Dundas Mineral field south of Norseman (23km).

The mining operation will be managed by the Higginsville Mine located north of Norseman

(55km) and the ore will be transported to that site for further processing.

The pits are located adjacent to Lake Dundas and are expected to be mined to below the

groundwater. The groundwater and any runoff from rainfall events will be used in th e mining

process and transport of the ore (dust control). Any water surplus to need will be discharged to

Lake Dundas - the exact amount to be recovered, used or discharged is not known and the

approach to the discharge impact was to use the worst case scenarios.

actis Environmental Services was asked to review documents and reports pertaining to the

Mt Henry Project and make comments on the potential impact. A site visit to Mt Henry was

carried out on the 16 th May 2016, the results of which are contained in this report.

In compiling this report the worst case scenario proposed/described was used, though in reality

it appears that the likelihood of any extended discharge to the Lake is small due to the shallow

nature of the bores, the location of the mine pits and the short life of the mine. Having said

that, the pit/s will eventually be below the palaeo water table of Lake Dundas, though set away

from the Lake and not directly connecting to the Lake.

Reports on Lake Dundas describe the flora and aquatic fauna of the Lake and appear adequate.

Aquatic fauna was described and though the species list is not long it contains species to be

expected in the Lake. Flora studies mention two priority samphires potentially at Lake Dundas.

These were not seen during the actis site visit. T. flabelliformis is unlikely to be present in

the area of interest as the habitat is not suitable – they grow in flat, damp areas; the gradient

of the sandy lake ‘beach’ in the area of interest is too steep for this species.

Composition of Discharge - The composition of the groundwater is roughly seawater in makeup

and similar to the receiving water (groundwater in the Lake).

Hydroperiod – extreme case scenario. It is estimated that the total area of Lake Dundas

impacted by hydroperiod will be between 15 and 65ha before the discharge will dry to salt. The

salt scald may be larger than this area and only indicates the wet area.

Salt Load – extreme case scenario (volume). The proposed discharge would have a total salt

discharge between 4,000 tonnes for the 10g/L scenario and 48,500 tonnes for each year of

operation (ten years under the current licence GWL181866).

The average of the drawdown test bores gives an elevated salt load (100% of baseload) over

360 ha. Over the entire area of 38,000ha the increase in salt load if the discharge was to remain

at 400,000m3 per year would be 4.4t/ha (0.438kg/m2) or about ten percent of the existing

baseload of salt.

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25 July 2016

The conclusion is that the discharge is unlikely to have any effect on the vegetation. The

analysis suggests that discharging 166,000 tonnes (average salinity and maximum volume) over

ten years is also unlikely to have any effect on the aquatic invertebrates except in isolated

pockets near the discharge. The discharge at maximum salinit y and maximum volume could

possibly have an impact on the recruitment/hatching of aquatic invertebrates.

These numbers do not include any recharge into the Lake sediments, which is likely and will

be increased if the discharge extends over any artificial drawdown caused by the pumping. This

would reduce the mass of salt on the lake playa.

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25 July 2016

2 Introduction

Higginsville Gold Operations (HGO) plan to develop the Mt Henry Open Pits Project which is

located on mining lease M63/515 and M63/516 in the Dundas Mineral field south of Norseman (23km).

The mining operation will be managed by the Higginsville Mine located north of Norseman

(55km) and the ore will be transported to that site for further processing.

The pits are located adjacent to Lake Dundas and are expected to be mined to below the

groundwater. The groundwater and any runoff from rainfall events will be used in the mining

process and transport of the ore (dust control). Any water surplus to need will be discharged to

Lake Dundas.

Figure 1 - Location of Mine and Discharge Site

Recently HGO acquired Mt Henry mine site and propose to develop it. The mine will need dewatering as

it is expected that the pit level will below the water table. The water table(s) are superficial low salinity

waterbodies and one of higher salinity (Lake influences). Runoff from rainfall is also likely to make up the

water discharged from the pit.

Waste water will be used in the mine and haul road for supressing dust leaving the residual to be discharged.

The exact amount to be recovered, used or discharged is not known and the approach to the discharge

impact was to use the worst case scenarios.

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25 July 2016

This report looks at the potential impact based on experience and an inspection of the site. A number of

reports such as the hydrological study (Groundwater Development Services (GDS) Pty Ltd 2015),

Invertebrates (WRM (2013) Lake Dundas Sediment Rehydration) have been used to support the impact

analysis.

Sediment samples from the lake were taken and lake vegetation species were identified to characterise the

chemistry and flora of the lake.

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25 July 2016

3 Regional Information

3.1 Regional Conservation Values – Great Western Woodlands

The Great Western Woodlands are little known locally, but are internationally recognised as one of the

most biologically significant and intact regions left on Earth and the largest remaining temperate woodland

on Earth. At twice the size of Tasmania, it is considered by many as 'Australia's Serengeti' because of the

diversity of life that occur within its boundaries (The Wilderness Society Website www.wilderness.org.au).

The Great Western Woodlands (GWW) is delineated on its western edge by the Vermin Proof Fence where

the Wheatbelt ends. To the north there is a natural (rainfall driven) boundary spanning Menzies to the

north-west, Kalgoorlie to the north and Balladonia out onto the Nullarbor to the south east. The GWW is

an interzone (Coolgardie Interzone) between the Eremean Botanic Province to the north and the South-

west Botanic Province to the south (Watson, Judd et al. 2008).

As an indication of the biological richness of the region the WA Herbarium has records of over 3000

species of flowering plants collected from the Great Western Woodlands. New species are still being found

– as an example, two undescribed species of aquatic invertebrate were found during the baseline

environmental study for the Chalice Pit dewatering discharge (described in this report).

3.2 Salt Lakes – an introduction

The arid and semi-arid interior of Western Australia contains some of the largest regions of salt lakes on

the Australian continent (Geddes, De Deckker et al. 1981). These range from being small periodically

filled basins to lakes which are over 100km in length. Contrary to popular belief, these lakes are not

wastelands, but unique and ancient natural systems, which support a range of plant and animal species in

their surrounds and within (Williams 1993).

Salt lakes are remnant external river systems (now called palaeodrainage systems) which flowed during

the Tertiary era. The progression to a more arid climate and lengthy periods of tectonic stability has led to

the drying of these rivers and formation of the present lakes (Geddes, De Deckker et al. 1981).

Salt lakes generally consist of numerous flat areas, which contain many smaller salt lakes, gullies, clay

pans and samphire flats. The lakes are predominantly dry with hyper-saline surface waters generally

evident in winter months following rainfall events and more permanent waters in years of exceptionally

high rainfall.

Salt lakes are not only of ecological importance, but also have economic, aesthetic, scientific, educational

and Aboriginal mythological values. Furthermore, 0.006% of global water is contained in salt lakes

compared with 0.007% contained in inland freshwater systems, illustrating the major contribution of salt

lakes to the global hydrological cycle (Williams 1998).

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25 July 2016

3.3 Geography

The playa lakes in the Goldfields are important if only because they form a significant part of the landscape.

They act as important reservoirs during episodic flood events for both salt and water flowing out of the

catchment and onto the playas. Present calculations suggest that the playas act as a sink for salt with the

bulk of the water evaporating to the atmosphere. There is little evidence of significant water and salt

flowing out of the lakes over land. During drier periods, evaporation is the dominant mechanism, reducing

the local groundwater levels and causing a ground water depression and an upward salinity gradient in the

local area of the lake. The lunettes provide both well-drained and saturated areas that may have a high or

relatively low salinity.

3.4 Lake Dundas

Dundas is the name of an abandoned town in the Goldfields-Esperance Region of Western Australia. The

town is located about 2 kilometres east of the Esperance Branch Railway. The lake, Lake Dundas, takes

its name from the abandoned town that lies on the western shore of Lake Dundas.

Dundas was the location of an early gold find in the region in 1894. The town was gazetted on 22 May

1895 and derives its name from the Dundas Hills which, in turn, were named after Captain Dundas of the

Royal Navy ship HMS Tagus in 18481.

Lake Dundas, when full, covers an area of around 35,000-40,000hectares. The northern extremity is just

south of the town of Norseman. Lake Dundas’s playa starts about 10-15km south of the town; the exact

measurement is difficult to determine because of the narrowing of the playa to a small creek line. The

southern part of Lake Dundas extends to the agricultural area about 70km to the south. Again the

measurement is difficult to define because of the fragmented nature of the lake in the area. Lake Dundas

changes to a series of small lakes that may or may not act as contiguous zones after heavy rainfall. There

are a number of islands in the Lake which would reduce the overall area of playa.

Overall, very little is known about Lake Dundas but it could be assumed that the catchment is in the region

of 10 times the surface area of the playa as this has been found to be true for other lakes in the area, and

seems to be a recurring factor. This common factor is most likely determined by stable hydrogeological

conditions in the Yilgarn Craton of Western Australia.

3.5 Chemical aspects of salt lakes

The salinity of inland saline waters ranges from 3g/L (arbitrary lower limit defined by (Williams 1998)) to

saturation of halite, depending on the type of system. Ephemeral lakes are subject to wider salinity

fluctuations than those that are permanent.

The pattern of ionic dominance in Western Australia salt lakes is nearly always Na+>Mg+>Ca+>K+ for the

cations, and Cl->SO42->HCO3

2- for anions (pers. ob.). The cation pattern differs in some systems, usually

those of low to moderate salinity, where Ca+ replaces Mg+.

The lakes are NaCl dominated with Na+ values varying from 75% to 90% of cation equivalence and Cl-

accounting for 87% to 97% of anion equivalence (results from a study of 54 Western Australian salt lakes;

Geddes et al. 1981).

Deviation from the normal pattern of ionic dominance occurs as a result of weathering of particular rock

strata, or evaporative concentration or precipitation of particular salts (De Deckker 1983).

1 https://en.wikipedia.org/wiki/Dundas,_Western_Australia

https://en.wikipedia.org/wiki/Goldfields-Esperance

https://en.wikipedia.org/wiki/Western_Australia

https://en.wikipedia.org/wiki/Esperance_Branch_Railway

https://en.wikipedia.org/w/index.php?title=Lake_Dundas,_Western_Australia&action=edit&redlink=1

https://en.wikipedia.org/w/index.php?title=HMS_Tagus&action=edit&redlink=1

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25 July 2016

The similarity in ionic ratios of salt lakes and seawater suggests lake salts are of marine origin, however

there is uncertainty as to whether they are derived from transported marine aerosols (cyclic salts) or relict

marine deposits (connate salts) (De Deckker 1983).

3.1 Meteorological Data

The rainfall data is shown in Figure 2 for Norseman. The climatic classification according to the BOM is

warm to hot, persistently dry.

The annual mean rainfall is 288mm pa and the median is 276mm pa. This indicates a more regular rainfall

than received further north with only a slight tendency for an episodic rainfall pattern. The episodic rainfall

is more pronounced in the summer months.

Figure 2 - Mean and Median rainfall data

The Class ‘A’ pan evaporation is approximately 2,000–2,200mm per year. This does not mean that the

potential evaporation from the lake is 2,200mm per year. The potential evaporation is somewhat less than

half this figure when salinity of brine and extensive water bodies are considered.

Evaporation is complex and must take into consideration surface type, salinity, depth and extent of water

body. Class “A” pan evaporation as measured by the BOM is measured in a small steel container elevated

above the ground. It is freshwater/deionised water which has a much larger water vapour envelope than

water with dissolved salt. Evaporation in a saline water body has a much lower evaporation due to the

modified area effect and the salinity of the brine that the water is being evaporated from. In addition, the

energy of the sun is reflected where the water body is less than 20 cm over a salt floor. The simplest

estimate of net evaporation is therefore the evaporation for a Class ‘A’ pan multiplied by an area factor

multiplied by a salinity factor multiplied by a depth factor minus the recorded rainfall. Complex water

vapour pressure calculations may be a more academically correct representation of evaporation but in

reality estimates of evaporation have to be reduced to simple proportional estimates from pan evaporation.

The Norseman BOM site does not read evaporation and the closest is Salmon Gums (1,534 mm pa) but

the author has some doubt about the veracity of the data given that the reading is so much different from

Esperance and Kalgoorlie. The vegetation near the Salmon Gums station indicates that the evaporation

would be higher than that recorded officially.

Notwithstanding the questions of data validity there is a nett evaporation of water from a saline body in

Lake Dundas.

0

5

10

15

20

25

30

35

Ra

in (m

m)

Mean rainfall (mm) Decile 5 (median) monthly rainfall (mm) for years 1897 to 2007

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25 July 2016

4 Brief Description of Lake Dundas at Proposed Discharge Site

4.1 Overview of Proposed Discharge Site, Lake Dundas

Lake Dundas is a large play salt lake south of Norsemen Western Australia. The area of the lake is

approximately 38,000 hectares of playa. The playa is characterised by many peninsulas and cut off bays.

Figure 3 - Discharge and Mine site

4.2 Hydrological Description

Palaeorivers are erosion features from the Palaeocene and early Eocene. Sediment infilling of the

palaeoriver occurred post late Eocene and has continued, in phases, to the present day. Palaeochannel basal

gravel occurs at depths ranging from 18 metres to 30 metres BGL. All basal gravel sections are of relatively

low hydraulic conductive properties due to poor sorting, silt and clay content.

A desktop assessment by Groundwater Development Services (GDS) Pty Ltd October 2015. Their

description was as follows: Groundwater salinities typically range from about 1,000 to 200,000

mg/L Total Dissolved Solids (TDS). Low salinity groundwater, ranging from 1,000 to 5,000 mg/L

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25 July 2016

TDS occurs in areas most affected by direct rainfall recharge, e.g. near catchment divides and

within shallow alluvium and calcrete units. The highest salinity groundwater occurs low down in

the catchments within palaeochannel sands and deeper fractured rock aquifers.

Small supplies of groundwater can be found throughout the area. Large, fresh groundwater

supplies are rare, but large, reliable supplies of saline to hypersaline groundwater are obtainable

from the palaeochannel sand and site specific shear zones and deeply oxidized zones in the

fractured rocks.

It is anticipated that the Mt Henry pit at 195m AHD will be below the palaeo water table of Lake Dundas

at about 245m AHD. The higher salinity water at 121,000mg/L TDS was associated with the lower water

tables and may be assumed to be connected with the paleo water and Lake Dundas.

4.2.1 Aquatic Invertebrate Fauna

The species below are listed by WRM (2013) as being present in Lake Dundas.

Table 1 - Aquatic Invertebrate Fauna found in Lake Dundas

Class Order Family Species

CRUSTACEA

OSTRACODA Cyprididae Australocypris bennetti

Diacypris sp.

COPEPODA Meridiecyclops baylyi

ANOSTRACA Parartemiidae Parartemia serventyi

Parartemia veronicae

INSECTA Parartemia sp.

COLEOPTERA Hydrophilidae Berosus sp.

DIPTERA Ceratopogonidae Ceratopogoninae spp.

Dolichopodidae Ceratopogonidae spp.

Chironomidae Dolichopodidae spp.

Chironomidae Procladius paladicola

Tanytarsus barbitarsis

4.2.2 Vegetation

The vegetation of interest at the sampling sites is the lake fringing flora – mainly succulent samphires.

These species are the ones in the zone most likely to be affected by any changes in the hydro-period and

salinity of the lake. The two samphire species mentioned in the GHD Biological Report (Wills, January

2015) as having the potential to be present, Tecticornia flabelliformis (listed as vulnerable) and T. mellaria

were not present at any of the sites visited by actis. T. flabelliformis is unlikely to be present in the area

of interest as the habitat is not suitable – they grow in flat, damp areas; the gradient of the sandy lake

‘beach’ in the area of interest is too steep for this species.

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25 July 2016

4.2.3 Fringing Vegetation in vicinity of Proposed Discharge Site

The proposed discharge area was visited on the 15th and 16th May 2016 and 5 sites were photographed

and vegetation in the zone with the potential to be influenced by the potential discharge was identified and

described.

Table 2 - Samphire species

Samphire Species WP 453 WP455 WP456

Tecticornia doleiformis x x

T. halocnemoides x

T. leiostachya x x x

T. pergranulata x x x

T. peltata x x

T. tenuis x x

T. undulata x x

The above samphire species are all commonly found at Lake Dundas and elsewhere. None have Priority

status.

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25 July 2016

4.2.3.1 Site descriptions

WP 448 Causeway

This site was at the causeway crossing an arm of Lake Dundas. A surface water sample was taken which

had a density of 1081. Brine Shrimp were found at this site which appeared to be Parartemia bicorna. A

small sample was taken of algal mat from the playa. It consisted of the filamentous cyanobacteria

Oscillatoria sp. and Phormidium sp. and the diatoms Cymbella sp. and Ulna sp.

Figure 4 - WP448 Causeway, sample of algal mat

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25 July 2016

WP454 ‘Artesian’ Sample

This site was chosen as it had some surface water. On closer inspection it was found that there was an

upwelling of groundwater which was spreading across the lake in a limited area. The upwelling was coming

from a drill hole that had a loose cap – water was coming from depth to the surface. The drill hole cover

was replaced and covered with mud. A groundwater sample was taken.

Figure 5 - Upwelling seen on playa

Figure 6 - Which was a loose drill hole cap

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25 July 2016

WP 453 Dundas Site

This site was quite diverse with Mallees over mixed shrubbery – Eremophila sp., Quondong, Cratystylis

sp. and Scaevola spinescens. Samphires next to the Lake playa were diverse and healthy. A groundwater

sample was taken from a hole dug into the layered playa sediments – 20cm of clay over hard pan then

gypsum.

Figure 7 - WP453, terrestrial vegetation

Figure 8 - WP 453, Tecticornia doleiformis

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25 July 2016

WP455 Discharge Site

This site is the potential dewatering discharge site for the Mt Henry mine. The terrestrial vegetation is

Mallee over mixed shrubbery - some of which extends close to the playa. The vegetation is at some

elevation from the playa however and would be unlikely to be affected by a dewatering discharge.

Samphires, Maireana glomerifolia, Atriplex nana and Frankenia sps were all healthy.

A groundwater sample was taken from a hole dug in the playa.

Figure 9 - WP455, Discharge Site, samphires, west

Figure 10 - WP455, Tecticornia halocnemoides

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25 July 2016

Figure 11 - WP455, Discharge Site, samphires, east

Figure 12 - WP455, Discharge Site, samphires close-up

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25 July 2016

WP456 Disturbance Site

This is an old disturbance site – there had been a small mine dug into the hillside. A groundwater sample

was taken from a hole dug into the playa.

The terrestrial vegetation was Eucalyptus sps over Cratystylis sp., Dodonea sp. and Eremophila sp.

Samphires, Maireana glomerifolia, Hemichroa driandra and Disphyma crassifolium were all healthy.

Figure 13 - WP456, Disturbance Site, east

Figure 14 - WP456, Hemichroa driandra

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25 July 2016

Figure 15 - WP456, Disturbance Site, west

Figure 16 - WP456, Disturbance Site playa, north

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5 Description of Discharge

The Western Australian Department of Water has granted Higginsville Operations (Avoca Mining Pty Ltd)

a licence GWL181866(1) to operate six wells and extract 400,000 Kl pa of groundwater for mine dewatering

and dust suppression. It is likely that the water extracted will be significantly less than this and a substantial

part will be freshwater runoff into the mine.

5.1 Discharge Quantity

It has been estimated that the discharge quality may be as much as 400,000 m3 per annum, although it is

thought unlikely that it would reach this amount.

5.2 Composition

Groundwater salinity of the Mt Henry pit ranges from 10,000 mg/L (MTHWE02) in the north to 121,000

mg/L TDS (MTHWE07) in the south. Seawater is considered to be on average about 35g/L. Therefore,

the discharge is roughly one third to four times the salinity of seawater.

The composition of the groundwater is roughly seawater in makeup. It can be seen in Figure 17 that most

of the major ions are similar in concentration with the discharge chloride concentration being slightly

higher than the seawater equivalent. It could be expected that the brine would behave in much the same

way as evaporated seawater.

Table 3 - Discharge Statistics (extreme discharge TDS)

Discharge Volume M3 Discharge TDS (g/L) TDS discharge (t)

400,000 10 4,000

400,000 42 16,600

400,000 121 48,400

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Table 4 - Discharge Ionic Concentration2

Analyte Unit MTHWE02 MTHWE03 MTHWE04 MTHWE07

pH 7.3 7.5 7.7 7.1

Total Dissolved Solids mg/L 10,000 17,400 18,200 121,000

Electrical Conductivity mS/cm 16,000 20,000 27,000 140,000

Bicarbonate alkalinity as HCO3 mg/L 240 320 460 170

Carbonate alkalinity as CO3 mg/L <1 <1 <1 <1

Hydroxide alkalinity as OH mg/L <5 <5 <5 <5

Total alkalinity as CaCO3 mg/L 190 260 380 140

Chloride mg/L 4,100 5,700 6,900 63,000

Sulphate mg/L 2,200 5,100 5,000 9,200

Nitrate, NO3 mg/L <0.05 <0.05 0.06 <0.05

Aluminium, Al mg/L <0.02 <0.02 <0.1 <1

Arsenic, As mg/L <0.02 <0.02 <0.1 <1.0

Calcium, Ca mg/L 290 370 490 450

Cobalt, Co mg/L 0.01 0.02 <0.05 <0.05

Copper, Cu mg/L <0.005 <0.005 <0.025 <0.25

Iron, Fe mg/L 6.5 <0.02 <0.1 <1

Magnesium, Mg mg/L 550 800 1,000 5,700 Manganese, Mn mg/L 2.5 2.6 1.7 4.1

Nickel, Ni mg/L 0.024 0.099 0.062 0.39

Potassium, K mg/L 64 84 100 370

Silica, soluble mg/L 52 49 52 17

Silicon, Si mg/L 24 23 24 7.8

Sodium, Na mg/L 2,600 5,000 5,500 40,000

Zinc, Zn mg/L 0.03 0.09 <0.05 <0.05

Total hardness by calc CaCO3/L CaCO3//L 3,000 4,200 5,400 24,000

Figure 17 - Ionic Composition of the Discharge

2 Groundwater Development Services (GDS) 2015

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

Na K Mg Ca Cl SO4

Ion

Co

nc.

(m

g/L)

MTHWE07 Seawater

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25 July 2016

6 Impact of the Proposed Discharge

6.1 Hydroperiod

Specific modelling has not been completed as Lake Dundas is an extensive lake with an unknown number

of discharges both historical and current. Instead the comparisons below use extreme case scenarios in an

attempt to give some perspective of the size and impact of the discharge.

The proposed discharge would have minimal impact on Lake Dundas’ hydroperiod. On a rainless day the

effective evaporation of a saturated brine in the area varies between 1.5 and 6mm per day depending on

the time of the year. The brine is not saturated when it is discharged so the effective evaporation may be

20% more depending on a number of factors including the salinity of the receiving water body.

Given the variability of the discharge environment including the number of other discharges and the extent

of Lake Dundas it is only possible to complete rough estimates of the hydroperiod impact. Table 5 shows

that the maximum coverage of the discharge for a low evaporation day may be as much as 62 ha while on

a higher evaporation day the coverage may be as low 16 ha. This coverage would be a salt scald with inter-

crystal brine saturation. No recharge is included in the calculation.

Table 5 - Coverage from discharge

Discharge Scenario m3 per annum Discharge per day m3 Low Evap. Day (ha) High Evap. Day (ha)

400,000 1,096 61.8 15.5

It is estimated that the total area impacted by hydroperiod will be between 15 and 65ha before the discharge

will dry to salt. The salt scald may be extended by rainfall.

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6.2 Surface Salt Load

The existing salt load to a depth of 5cm was estimated using a corer. Basically a measured sample of the

playa was extracted and the salt content measured. This sample result was extrapolated to the larger area.

Figure 18 - Salt Load Core Sampler

Table 6- Salt load in top 5cm statistics (kg/m2)

N Mean SE Mean StDev Minimum Q1 Median Q3 Maximum

9 4.68 0.211 0.634 3.75 4.212 4.622 4.95 5.99

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Figure 19 - Boxplot of salt load samples in top 5cm (kg/m2)

The salt load on the surface to a depth of 5cm was found to be between 3.75kg/m2 and 6.0kg/m2with an

average of 4.6kg/m2.

The proposed discharge would have a total salt discharge between 4,000 tonnes for the 10g/L scenario and

48,500 tonnes for each year of operation (ten years under the current licence GWL181866). This is

equivalent to increasing the salt load of somewhere between 85 and 1,000 hectares on Lake Dundas by

100% per year. The average of the drawdown test bores gives an elevated salt load (100% of baseload)

over 356ha.

Another way to look at the issue is that after ten years of discharge at the average salinity the total amount

of salt added to the Lake would be 166,600 tonnes. Over the entire area of 38,000ha the increase in salt

load would be 4.4t/ha (0.438kg/m2) or about ten percent of the existing baseload of salt.

6.3 Characteristics of the Discharge Plume

Without more detailed modelling and a better estimate of the discharge quantity and quality, it is hard to

be definitive about the final discharge plume. The form will always be a zone of unsaturated (NaCl) brine

feathering into an area of heavier salt layer, which in turn will gradually decompose into a thinner layer of

salt. We can estimate the maximum area based on one year’s discharge will be at maximum 1,000ha in

size but more likely to be less than equal to 350h in size. Given that the above assumes no recharge,

whereas there undoubtedly will be some, especially if the drawdown extends to the playa, it may be

assumed that the ongoing discharge impact zone would look much the same except that the salt scald will

extend further from the discharge zone.

If the drawdown does extend to the discharge site, the recharge under these circumstance is relatively fast

and the salt load in the important biological zone much reduced.

6.0

5.5

5.0

4.5

4.0

Sa

lt lo

ad

Boxplot of Salt load

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6.4 Shoreline Vegetation

All of the sites visited had samphire species common at Lake Dundas and elsewhere. The relatively steep

gradient of the sandy lake ‘beach’ makes it unlikely that samphires present will be affected by dewatering

discharge. Experience at other large playa lakes in the Goldfields has shown that shoreline vegetation is

more likely to be affected by the dewatering cone of depression, especially where a palaeochannel is being

dewatered. As the Mt Henry Project has a short life it is unlikely that there will be any long-terms effects

from the dewatering.

6.5 Aquatic Invertebrate Fauna

The aquatic invertebrate fauna in ephemeral lakes have adapted to survive long periods of desiccation and

periods of high salinity by laying eggs or cysts with tough shells that stay dormant in the lake sediments

until conditions are appropriate for hatching.

The success of aquatic and semi-aquatic invertebrate populations generally relies on the presence and

quality of available waters. Many of the aquatic invertebrates at Lake Lefroy are able to survive the

(naturally) hostile conditions of inundation and desiccation by going through ‘boom and bust’ life cycles.

Their life cycles are relatively short – only a few weeks at best – and they lay salt and desiccation-resistant

cysts which are able to survive in the lake sediments for sometimes years. The dormancy of the cysts is

broken when their surroundings are conducive to another life cycle – the fresh water from rain. The adult

animals are able to cope with the gradual salinisation of their environment by evaporation and if conditions

remain suitable will produce more than one generation. Aquatic invertebrates such as midge and sandfly

larvae colonise suitable water bodies by flying in from other areas.

A list of aquatic invertebrate fauna is contained in the WRM (2013) report3.

3 WRM (2013) Lake Dundas Sediment Rehydration, Water Quality & Aquatic Fauna Surveys. December 2012 & February

2013. Unpublished final report by Wetland Research & Management to Panoramic Resources Limited. December 2013.

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7 References

Aquaterra January 2010 Hydrogeology and Hydrology Desk Study: Chalice and Challenge Gold Mines,

1158B/B1/012a, Prepared for Alacer Gold Ltd

Aquaterra, April 2010, Hydrogeology and Hydrology Desk Study: Chalice Pit Dewatering – Stage 1

Aphrodites Pits Discharge, 1158B/B2/030a, Prepared for Alacer Gold Ltd

Aquaterra July 2010, Chalice Pit Dewatering – Stage 1 Chalice West Lake Discharge, 1158B/B3/032a,

Prepared for Alacer Gold Ltd

Clarke, J.D.A. (1994). Lake Lefroy, a Palaeodrainage Playa in Western Australia. Australian Journal of

Earth Science 41, pp 417-427

De Deckker, P. (1983). "Australian salt lakes: their history, chemistry, and biota — a review."

Hydrobiologia 105(1): 13.

Geddes, M. C., P. De Deckker, W. D. Williams, D. W. Morton and M. Topping (1981). "On the chemistry

and biota of some saline lakes in Western Australia." Hydrobiologia 82: 201-222.

Mann, A. W. (1982). "Hydrogeochemistry and weathering on the Yilgarn Block, Western Australia—

ferrolysis and heavy metals in continental brines " Geochima et Cosmochimica Acta 47(2): 9.

Mann, A. W. and R. L. Deutscher (1978). "Genesis principles for the precipitation of carnotite in calcrete

drainages in Western Australia." Economic Geology 73(8): 1724-1737.

Morgan, K. H. (1993). "Development, sedimentation and economic potential of palaeoriver systems of the

Yilgarn Craton of Western Australia." Sedimentary Geology 85(1-4): 637-656.

Watson, A., S. Judd, J. Watson, A. Lam and D. Mackenzie. (2008). "The Extraordinary Nature of The

Great Western Woodlands." from www.gww.net.au.

Williams, W. D. (1993). "The Conservation Of Salt Lakes: Important Aquatic Habitats Of Semi Arid

Regions." Aquatic Conservation: Marine and Freshwater Ecosystems Vol 3.

Williams, W. D. (1998). Guidelines of Lake Management. Kusatsu, Shiga 525-0001, Japan, International

Lake Environment Committee Foundation & UN Environment Programme.

http://www.gww.net.au/

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8 Appendix

8.1 Sample Points

Table 7 - Sample point location and elevation (WGS84)

ID latitude longitude Elevation (m) Waypoint number

1 -32.3546 121.7596 257.9 447

2 -32.3481 121.8204 241.93 448

3 -32.3511 121.7878 290.0 449

4 -32.381 121.7907 247.0 450

5 -32.3812 121.7866 258.2 451

6 -32.4129 121.783 246.3 452

7 -32.4377 121.821 247.4 453

8 -32.3583 121.8211 250.3 454

9 -32.3809 121.7906 248.5 455

10 -32.4125 121.7831 249.1 456

11 -32.3965 121.7747 260.4 457

12 -32.3735 121.7860 285 MTHWE02

13 -32.3746 121.7865 292 MTHWE03

14 -32.3751 121.7860 284.5 MTHWE04

15 -32.3765 121.785 285.5 MTHWE05

16 -32.3769 121.7873 295.5 MTHWE06

17 -32.3793 121.7854 264 MTHWE07

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Figure 20 - Site visit locations

proposed short-term dewatering discharge mt henry€¦ · evident in winter months following...

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