Report - Planning

Report

COESR Hydrogeological Baseline Study

Cape Otway Road Australia

26 March 2019

Cape Otway Road Australia | 26 March 2019 COESR Hydrogeological Baseline Study Page 1

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Document Status

Version Doc type Reviewed by Approved by Date issued

1.3 Final ALT SLE 26 March 2019

Project Details

Project Name COESR Hydrogeological Baseline Study

Client Cape Otway Road Australia

Client Project Manager Daryl Pelchen

Water Technology Project Manager Scott Evans

Water Technology Project Director Andrew Telfer

Authors Scott Evans

Document Number SP18143 HglBaseline v1.3 SLE 190326

COPYRIGHT

Water Technology Pty Ltd has produced this document in accordance with instructions from Cape Otway Road Australia

for their use only. The concepts and information contained in this document are the copyright of Water Technology Pty Ltd.

Use or copying of this document in whole or in part without written permission of Water Technology Pty Ltd constitutes an

infringement of copyright.

Water Technology Pty Ltd does not warrant this document is definitive nor free from error and does not accept liability for

any loss caused, or arising from, reliance upon the information provided herein.

1/198 Greenhill Road

Eastwood SA 5063

Telephone (08) 8378 8000

Fax (08) 8357 8988

ACN 093 377 283

ABN 60 093 377 283


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26 March 2019

Daryl Pelchen Director and Co-Founder Cape Otway Road Australia 1300 Cape Otway Road, MODEWARRE VIC 3240 Via email [email protected] Dear Daryl

COESR Hydrogeological Baseline Study

Please find attached Water Technology’s report on the preliminary hydrogeological investigations into the near-

surface groundwater system(s) located beneath the proposed Cape Otway Elite Sports Retreat (COESR)

development.

Yours sincerely

Scott Evans Principal Hydrogeologist

[email protected]

WATER TECHNOLOGY PTY LTD


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CONTENTS

1 INTRODUCTION 4

2 BACKGROUND 5

2.1 Groundwater Receptors 5

Groundwater Dependent Ecosystems 5

Environmental Significant Management Areas 5

Land Subject to Inundation Management Areas 6

Salinity Management Areas 6

Groundwater Users 6

3 METHODOLOGY AND RESULTS 7

3.1 Regional Bore Data Summary 13

4 DISCUSSION 15

4.1 Description of Stratigraphy and Conceptual Hydrogeology 15

5 SUMMARY 17

APPENDICES

Appendix A Proposed Standing groundwater Depth Monitoring Record

LIST OF FIGURES

Figure 1-1 COESR Concept Plan and Monitoing Bore Locations 4

Figure 2-1: Identified Groundwater Receptors. Source: VicMaps 6

Figure 3-1 Drilling of CORA10 7

Figure 3-2 Distribution of Saturated Soil Depth, Standing Groundwater Depth Observations and Contours of Shallow groundwater Potentiometric Surface Depth 10

Figure 3-3 Distribution of Estimated Standing Groundwater Level and Estimated Shallow groundwater Potentiometric Surface Contour Elevation 11

Figure 3-4 Distribution of groundwater Salinity from Bailed Samples 12

Figure 3-5 Regional Bore Data [VVG data] against Surface Geology 13

Figure 3-6 Historical Groundwater Level Hydrographs 14

Figure 4-1 Surface Geology across the COESR Site 15

LIST OF TABLES

Table 3-1 Observation Bore Identification for Works Licence WLE073771 7

Table 3-2 Observation Bore Network Summary Auger Returns Description 9

Table 3-3 Observation Bore Network ‘As-Constructed’ Specifications 9


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1 INTRODUCTION

This project aims to establish a preliminary groundwater monitoring bore network to provide an initial

understanding of the local shallow (water table1) groundwater system(s) across the proposed development

site. This network targets the major southwest-northeast topographic depression that form a modified drainage

line feeding surface run-off north-east towards Lake Modewarre. This area regularly inundates during the

wetter months and is a focus of potential land salinisation under the Salinity Overlay management tool2.

A ten (10) bore drilling program was undertaken, targeting the first intersection of saturated sub-surface

material to a maximum depth of six (6) metres. The current Concept Plan and the location of the monitoring

bore sites is shown in Figure 1-1.

FIGURE 1-1 COESR CONCEPT PLAN AND MONITOING BORE LOCATIONS

1 Water Table is referred to where the piezometric pressure is equal to atmospheric pressure. Below this level all pore spaces within the

subsoil are filled with water (saturated). Where water level rises above the point of saturated subsoil, this groundwater system is considered to be semi-confined and the ‘surface’ at which groundwater level stands is referred to as a ‘potentiometric surface’ which is the potential height groundwater would rise to (in balance with atmospheric pressure) if it was not for ‘confining’ sediments of the subsoil preventing groundwater levels to rise. 2 Dept. of Environment, Land, Water and Planning [http://nvt.dse.vic.gov.au/arcgis/services ]

http://nvt.dse.vic.gov.au/arcgis/services


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2 BACKGROUND

The proposed COESR Concept Masterplan features a multi-faceted array of sports facilities, function centres,

retail precinct, a rural residential subdivision, and a range of accommodation including a hotel and eco-lodges.

The site is situated on the southern fringes of the Lake Modewarre floodplain and proposes to adopt best

practice approaches to ecosystem preservation, floodplain risk management and stormwater treatment and

reuse.

Gaining an understanding of the shallow groundwater processes that currently operate will be necessary for

the considered development of the site and interaction with the environment.

Historic groundwater level data in existing observation bores located up to two kilometres from this site

indicates that the depth to groundwater can be from seven to less than two metres below the land surface and

that groundwater generally flows from west to east.

This limited information indicates that groundwater occurs at shallow depths across the proposed development

site. When groundwater is present at shallow depths, there will need to be an understanding of:

◼ how the groundwater will impact on the construction and operation of new infrastructure, including how

groundwater/surface water interact in excavated surface water bodies, particularly salinity stratification

and anoxic surface water conditions

◼ how the development will change the natural groundwater processes, including;

◼ changes to current natural processes and patterns of rainfall/runoff infiltration to the groundwater and

evapotranspiration from groundwater

◼ changes to interactions between groundwater and surface water in the natural and constructed

environments,

◼ changes to the groundwater systems that may impact groundwater dependant ecosystems,

◼ salinisation of the land surface through evapotranspiration of the groundwater which may result in

high soil and surface salinity issues that may restrict plant growth and development opportunities.

2.1 Groundwater Receptors

Receptors are human or environmental entities that use or interact with groundwater. The likely receptors of groundwater, as presented by the Victorian State Government, are presented below.

Groundwater Dependent Ecosystems

Groundwater dependent ecosystems (GDEs) are flora and fauna relying on a groundwater source to maintain

their ecological function. Interfering with the groundwater system may significantly impact the health of GDEs.

Lake Modewarre is a permanent saline lake wetland with known GDEs from regional studies (shown as yellow

area in Figure 2-1 A). Additional GDEs may also be present in or near the site. Identified wetlands occur

within the study area (shown as hatched blue areas in Figure 2-1 A). It is uncertain if this temporary saline

march/meadow receives groundwater inflow during the wetter months.

Environmental Significant Management Areas

The Environmental Significant Management Area (shown as light green areas in Figure 2-1 B) identifies areas

where the development of land may be affected by environmental constraints. Conditions of development may

require permits to carry out works in these areas.


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Land Subject to Inundation Management Areas

The Land Subject to Inundation Management Area (shown as blue areas in Figure 2-1 C) identifies land in a

flood storage or flood fringe area affected by the 1 in 100-year flood or any other area determined by the

floodplain management authority. Conditions of development may require an understanding of groundwater

quality to protect seasonal surface water quality.

FIGURE 2-1: IDENTIFIED GROUNDWATER RECEPTORS. SOURCE: VICMAPS

Salinity Management Areas

The Salinity Management Areas (shown as brown areas in Figure 2-1 D) identifies areas subject to saline

ground water discharge or high ground water recharge. Conditions of development would likely require an

understanding of areas affected by salinity (such as caused by groundwater discharge to surface) and may

require mitigating activities to reduce/manage salinized areas and possible impacts to infrastructure. These

areas may support halophytic ecosystems.

Groundwater Users

Neighbouring properties may access groundwater and an understanding of the shallow groundwater system

would inform how this proposed development may influence changes in groundwater levels that may affect

neighbouring groundwater users.

A B

C D


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3 METHODOLOGY AND RESULTS

Water Technology sought licences to construct observation bores. Works Licence WLE073771 was granted

on 4 March 2019. The Works ID for each of the observation bores is listed in Table 1 below.

TABLE 3-1 OBSERVATION BORE IDENTIFICATION FOR WORKS LICENCE WLE073771

Site Name Works ID Use Easting Northing Zone Volume Folio

CORA01 WRK112229 Observation 245543 5760406 55 10762 064










Urban Drilling (refer Figure 3-1) was engaged to drill and construct the proposed ten (10) observation bores.

Drill method was solid augers to target depth (or refusal). Bore construction included 50 mm uPVC threaded

casing with the bottom 3m machine slotted with 0.5mm aperture. The annulus was gravity fed gravel pack to

~0.5 m above the screen interval, bentonite pellet seal for ~1 m, filled with cutting to ~0.5 m from ground level,

then Bentonite pellets to surface. Bentonite surface seal was chosen as some drill sites were located in

swelling clays and it was considered that a cement plinth would ‘lift’ and dislodge the casing. The uPVC casing

was extended above ground level and protective guards installed to limit damage by livestock.

FIGURE 3-1 DRILLING OF CORA10


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A brief geological description (refer Table 3-2) was made of the auger returns, observing when saturated

sediments were intersected. Accurate geological logging was difficult to perform as the augering method can

obscure the specific depth intervals from which drill cutting originate from. As a consequence, it is not

recommended that these drill-hole records are utilised to perform geotechnical assessments. Available drill-

hole information and bore construction specifications are provided in Table 3-3.

The bores were constructed as per specifications apart from CORA04 which struck refusal at 4.0 mbGL

(assumed to be either fresh basalt bedrock or a ‘floater’ boulder) and CORA 09 which was drilled to 6.0 m but

completion was delayed and the hole collapsed to ~5.0 mbGL before casing was installed.

Each reference point was located using a hand-held GPS that provided UTM coordinates and an approximate

elevation to metres Australian Height Datum (mAHD). Note, no licensed surveying of reference points has

been undertaken so all reference to elevation is approximate.

After at least 6 hours post bore completion each bore was measured for end of hole (EoH), depth to

groundwater and casing stickup from the top of casing (ToC) and then ‘developed’ (extracting water from the

bore to remove possible sediment and contamination introduced through the drilling process) by hand bailer

either until the bore volume was fully removed or for four casing volumes of water were removed.

The following day all bores were measured for depth to groundwater from the top of casing and bailed for a

field electrical conductivity (EC) reading to provide indicative groundwater salinity at each monitoring point.

Results from this field sampling are listed in Table 3-3. This information is shown spatially on Figure 3-2,

Figure 3-3 and Figure 3-4 below. Sample were collected for future Anion/Cation analyses. These samples

are held by Ken Hole.

Additional in-field observations/anecdotal comments were taken as follows:

◼ A small surface water dam, located ~90 m north of CORA07 contained water of salinity ~990 µS/cm. Given the

observation that CORA07 was dry to 6 mbGL it is postulated that the source of this water is from surface runoff using

the Cape Otway Road and catchment. The observation that this dam still contains water after a notable dry summer

suggests that leakage rates to groundwater are not high and therefore that the subsurface clay material is effectively

confining in nature in this location;

◼ A small farm dam, located ~250 m east north east of CORA01 contained water of salinity of ~5600 µS/cm. This stock

watering point was excavated to greater than 3 m depth (pers. comm. Ken Hole 15/3/19) and now is a permanent

watering point. It is postulated that the deep excavation within this dam has penetrated to the saturated sediments

and has effectively exposed the shallow semi-confined groundwater system to the atmosphere. The brackish salinity

suggests that this dam water may be a mixture of shallow groundwater and surface water runoff;

◼ Discussion with the Farm Manager (pers. comm. Ken Hole 14/3/19) identified that in this region land managers have

exploited ‘springs’ in the landscape for stock water supplies. This landscape appears not to be typical of country with

springs, as it is relatively flat lying with poorly defined drainage lines. Seeking expansion of this concept, typical

description of how these ‘springs’ have been utilised in this country, included the shallow excavation of low-lying areas

to the point where seeping ground would yield water perennially;

◼ The low-lying area within the COESR Development site area has been observed to inundate as a consequence of

Lake Modewarre filling and surface water ‘backing-up’ into this area. Some of the berms were constructed to try to

prevent this inundation to increase the periods this low-lying area could be put to agricultural land use; and

◼ Lake Modewarre appears to not fill as often now, compared to historical observations. This has been related to the

re-direction of surface flow higher in the catchment areas that feed Lake Modewarre. The use of Lake Modewarre for

stock water has been reduced due to water salinity exceeding that palatable for stock. Therefore, it is likely that local

shallow groundwater levels may have a falling groundwater hydrograph trend.


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TABLE 3-2 OBSERVATION BORE NETWORK SUMMARY AUGER RETURNS DESCRIPTION

Site Name Works ID Cuttings Description

CORA01 WRK112229 0-1m CLY dk green grey, stiff, plastic; 1-2m CLY dk olive green, firm, plastic; 2-4.5m CLY grey, soft; 4.5-5.5m CLY sandy, moist, grading to SND clayey; 5.5-6m SND clayey, orange

CORA02 WRK112230 0-2.5m CLY dk grey, stiff plastic; 2.5-6m Basalt, highly weathered top clay, olive grey, stiff to sticky, hard and soft sections, moist from 5m

CORA03 WRK112231 0-1m CLY grey; 1-3m CLY orange grey; 3-5.5m SND clayey, buff, moist, wet from ~5m; 5.5-6m CLY olive green,

CORA04 WRK112232 0-1m CLY dk grey, loamy; 1-3m CLY dk olive green; 3-4m CLY a/a sandy, gritty, moist, 4m refusal on hard rock/stone

CORA05 WRK112233 0-1m CLY sandy, grey brown; 1-3m CLY grey brown, stiff; 3-4m CLY olive grey, stiff; 4-5.5m CLY sandy, lt olive grey, v slightly moist @ 5.5m; 5.5-6m CLY orange green, gritty

CORA06 WRK112234 0-1m SND grey, v fine grained, unconsolidated; 1-2m CLY red brown, stiff; 2-4m CLY orange grey, stiff to plastic; 5-6m CLY silty, lt olive grey, stiff, moist from 5.5m

CORA07 WRK112235 0-4m CLY lt orange grey; 4-6m SND clayey, lt grey, v slightly moist from 5.5m

CORA08 WRK112236 0-1m CLY sandy, lt grey; 1-2m CLY grey brown, stiff, gritty; 2-5m CLY olive green, stiff, minor plastic; 5-6m CLY silty, sandy, red brown, plastic, moist from 5.5m

CORA09 WRK112237 0-1m CLY stiff; 1-2m CLY sandy, grey brown; 2-3m CLY sandy, olive green;3-5m CLY sandy, silty, lt grey, soft, moist from 4m; 5-6m CLY orange grey, plastic

CORA10 WRK112238 0-1m CLY silty, olive grey; 1-2m CLY grey, gritty, friable; 2-3m CLY sandy, it grey to lt red, friable; 3-4m CLY red, firm, plastic; 4-6m CLY lt red, firm, moist from 5.5m

TABLE 3-3 OBSERVATION BORE NETWORK ‘AS-CONSTRUCTED’ SPECIFICATIONS

Site Name

Works ID Elevation of ToC(1)

Depth Drilled(2)

Moisture From(2)

Screen From(2)

Srceen To(2)

Completion Depth(2)

End of Hole(3)

Casing Stick Up(4)

Depth to Groundwater(3)

Field Salinity(5)

Standing Water Depth(2)

Standing Water Level(1)

CORA01 WRK112229 124 6 4.5 2.7 5.7 5.87 6.85 0.98 2.96 8460 1.98 121.04

CORA02 WRK112230 120 6 5 3 6 5.91 6.98 1.07 2.4 10250 1.33 117.6

CORA03 WRK112231 117 6 5 3 6 5.94 6.74 0.8 1.98 17030 1.18 115.02

CORA04 WRK112232 118 4 3 1 4 3.97 5.19 1.22 2.69 16140 1.47 115.31

CORA05 WRK112233 123 6 5.5 3 6 6 7.46 1.46 [email protected] below 6.00 below 115.54

CORA06 WRK112234 121 6 5.5 3 6 6.1 7.26 1.16 6.97 6200 5.81 114.03

CORA07 WRK112235 126 6.2 5.5 3 6 6.16 6.88 0.72 [email protected] below 6.16 below 119.12

CORA08 WRK112236 121 6 5.5 2.8 5.8 5.94 6.08 0.14 4.84 10540 4.7 116.16

CORA09 WRK112237 119 6 4 2 5 5.15 5.99 0.84 3.4 9490 2.56 115.6

CORA10 WRK112238 125 6 5 3 6 6.03 7.25 1.22 5.07 1431 3.85 119.93

(1) Elevation to mAHD is approximate as taken by hand-held Garmin eTrax GPS – would need to be verified by Licensed Surveyor survey.

(2) Measured depth as metres below Ground Level (mbGL)

(3) Measured Depth as metres below Top of Casing (mToC)

(4) Measured height as metres above Ground Level (maGL)

(5) Field Electrical Conductivity (EC) by WTW Cond330i unit, reported in units of µS/cm @25oC – convert to TDS by multiplying by 0.54 for readings ~1500EC and by 0.59 for readings between 8000 and 17000EC

mailto:[email protected]


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FIGURE 3-2 DISTRIBUTION OF SATURATED SOIL DEPTH, STANDING GROUNDWATER DEPTH OBSERVATIONS AND CONTOURS OF SHALLOW GROUNDWATER POTENTIOMETRIC SURFACE DEPTH


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FIGURE 3-3 DISTRIBUTION OF ESTIMATED STANDING GROUNDWATER LEVEL AND ESTIMATED SHALLOW GROUNDWATER POTENTIOMETRIC SURFACE CONTOUR ELEVATION


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FIGURE 3-4 DISTRIBUTION OF GROUNDWATER SALINITY FROM BAILED SAMPLES


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3.1 Regional Bore Data Summary

A review of bore data [Source: Visualising Victoria’s Groundwater (VVG)] within a 5 km radius of the COESR

Development site indicated that, from the limited data available, the salinity of groundwater (from various

depths) in the area west and north of Lake Modewarre are similar to that observed from the recent drilling

program (refer to red text in Figure 3-5).

FIGURE 3-5 REGIONAL BORE DATA [VVG DATA] AGAINST SURFACE GEOLOGY

To the south east of the COESR Development site there is recorded a groundwater salinity of 1522 µS/cm EC,

which is of similar range found in CORA10. This bore [87744] however is completed at a depth of greater than

25 mbGL.

There is present in the region around the COESR Development site a series of observation bores constructed

in the mid-1990s (refer to red dots on Figure 3-5). Of these bores, those that are completed at shallow depth

and close to the COESR Development site were plotted for analyses (refer Figure 3-6). These bores were

monitored semi-regularly until 2000 and the groundwater hydrograph trends show a general decline over that

period. A single monitoring round in 2002 shows a recovered groundwater level trend for two locations south

of the COESR Development site. This may be after a significant rainfall event that occurred between 2000

and 2002.


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This hydrograph plot also shows the elevation of the ground level (as provided by VVG), to provide an

indication of the relative depth to groundwater at each observation bore location. There appears to be a

seasonal rise and fall in groundwater level (in most of the plotted groundwater hydrographs – Bore

WRK956780 is the exception to this), with the depth to standing groundwater often within one or so metres of

ground level during the wetter months. This behaviour indicates that the shallow groundwater system(s) are

influenced by the seasonal rainfall patterns however it is uncertain whether rising groundwater levels are

responding to recharge of incident rainfall or from lateral groundwater flow from recharge remote from the

monitoring site.

There is limited information available on the construction of these bores so no conclusions can be made as to

whether the groundwater system(s) monitored by these observation bores are unconfined or semi-confined in

character.

FIGURE 3-6 HISTORICAL GROUNDWATER LEVEL HYDROGRAPHS


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4 DISCUSSION

4.1 Description of Stratigraphy and Conceptual Hydrogeology

The establishment of a ten (10) observation bore network at the proposed COESR development targeted the

shallow groundwater system in the surficial sediments3 (refer Figure 4-1) has identified the surficial deposits

as:

◼ the Hansen Plain Sand Formation (or Brighton Group), but current nomenclature lists this unit as the

Pliocene to Miocene Sandringham Sandstone Formation, and is described as sandy silt, fine sandstone,

sandy conglomerate to pebbly sandstone, clayey sand, clayey gravel, minor carbonaceous clay and

limonitic pisolites, often lateritic, lag deposit including variable to highly-rounded pebbles; horizontal and

swaley cross-lamination; burrows;

◼ Quaternary Alluvium deposits, described as lagoon and swamp deposits, paludal, sand silt and clay; and

◼ the Newer Volcanic Group basalts which appear to be variable weathered where intersected. This

formation is described as cinder cones/scoria, minor ash and agglutinates; Lava flows - tholeiitic to minor

alkaline and basanitic lavas.

FIGURE 4-1 SURFACE GEOLOGY ACROSS THE COESR SITE

In most of the drill holes, clay-rich sediments were intersected within the soil profiles drilled. At CORA04

refusal at 4 m on hard rock suggests the unweathered basalt was encountered, whereas at CORA01 and

3 Outcrop geology has been adopted from seamless geology layer provided by DPI that is based on many years of Geolgicla mapping

by the (former) Geological Survey of Victoria.


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CORA02 the interpreted basalt formation was able to be penetrated to 6 m depth. At CORA03, although

mapped to be within the Newer Volcanic Basalts, returned sediments more likely to be Quaternary Alluvium

and/or equivalents of the Sandringham Sandstone Formations

Results from the drilling program (refer Table 3-3) indicates that the depth at which saturated soils are

penetrated are generally deeper that the depth at which resting groundwater level stands within the

Observation Bore Network. This suggests that at the COESR Development site the shallow groundwater

system is predominantly semi-confined in nature. This semi-confined characteristic leads to an understanding

that, locally, this first zone of saturation is not likely to receive direct infiltration recharge locally, apart from

isolated zones where the confining subsoil clay material may be ‘weakened’ by fractures or more permeable

sediment profile. That is, the clay sub-soil material that prevents the groundwater from raising to saturate

these sediments to the same depth that the groundwater rises within the observation bores will likely also

prevent infiltrating surface water from draining to the shallow groundwater system locally.

The exceptions to this were at CORA05 and CORA07 where saturated soils were deeper than 6 mbGL or at

CORA06 where standing groundwater depth was measured at depth approximating the observed depth of

saturated sediment. At CORA05 and CORA07, with no observed standing groundwater within the bore, no

conclusions are drawn on the recharge processes that may operate at these sites. At CORA06, with the depth

of standing groundwater being within the zone of recorded saturated sediments suggests that at this location

the shallow groundwater system may be unconfined. The results for these sites suggest that here may be a

‘groundwater divide’ along the alignment between CORA05 and CORA07 with this eastern portion of the

COESR Development site having a shallow groundwater of different hydrogeological character with

groundwater flow direction towards Brown Swamp (outside the study area to the east).

West of the possible groundwater divide (on the alignment between CORA05 and CORA07) the shallow

groundwater system (refer Figure 3-3) appears to be flowing in a north east direction (in parallel with the local

topography) eventually intersecting with the subsurface area beneath Lake Modewarre. In this western portion

of the COESR Development site the general depth at which saturated soils were intersected was deeper than

4 mbGL (apart from CORA04 where saturated sediments were interested at ~3 mbGL).

In this western portion of the COESR Development site the depth at which the shallow groundwater system is

measured at is shown in Figure 3-2. The surface drawn from these depth measurements is referred to as the

potentiometric surface depth. This surface is not the depth at which saturated soils are found, but the depth

the shallow groundwater would potentially rise to if restrictive clay sub-soils were more permeable. An artificial

example of this is the stock water dam where to base of the dam was excavated into the saturated sediments

and the dam appears to be perennial.

The distribution of the shallow groundwater salinity is presented in Figure 3-4. Apart from CORA10 all bores

containing groundwater yielded groundwater salinity in the brackish to saline range (>6,000 µS/cm EC). The

spatial distribution of this shallow groundwater system indicated an increasing salinity trend towards Lake

Modewarre. This increasing trend may reflect the influence the dominant impact that Lake Modewarre has on

the areas immediately adjacent the lake as the lake, being an end-point (or discharge area) for both surface

water and local shallow groundwater system(s). The long-term inundation and evaporative cycles that have

operated over many years is likely to have generated a high salinity zone beneath the lake and the areas

adjacent.

The low groundwater salinity found in CORA10 indicates that local variability in recharge may exist in an area

close to CORA10 the infiltration of surface water may be occurring locally through the above-mentioned zones

of ‘weakness’ in the sub-soil clay material. The proximity of this bore to the Cape Otway Road reserve and

how the surface water run-off from this road reserve may be influencing the local groundwater salinity in this

area.


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5 SUMMARY

The recent drilling program has identified the shallow groundwater system across the proposed COESR

Development site. The salinity of this shallow groundwater system is generally brackish and appears to be

similar to the groundwater found in areas in similar proximity to Lake Modewarre.

The depth at which the shallow groundwater was struck appears to be consistently deeper than the depth at

which groundwater is found within the observation bores indicating that this shallow groundwater system has

a semi-confined characteristic in the low-lying area subject to inundation when Lake Modewarre fills and over-

flows.

The proposed COESR Development intends to revert this low-lying area to natural wetland ecology, which due

to the inferred semi-confined nature of the subsoil, is not likely to exacerbate potential soil salinity processes

that may operate across this area in times of high regional shallow groundwater levels.

To further inform this understanding, it is suggested that this observation bore network is regularly monitored

(at least monthly for the first 12 months) for depth to groundwater level. A suggested table of monitoring record

is provided in Appendix A. It is also suggested that the reference points, used to measure the depth to

groundwater level, are surveyed to Australian Height Datum (AHD) so that more accurate contouring of the

potentiometric surface of the shallow groundwater system can be determined.

Additional sampling of the shallow groundwater system at the beginning and end of the wet season for salinity

may further assist the understanding of how this shallow groundwater system behaves seasonally.

As the COESR Development is constructed, commissioned and operated, the continued monitoring of the

response of the shallow groundwater system to the reinstating of wetland ecological systems would be

desirable.

Cape Otway Road Australia | 26 March 2019 COESR Hydrogeological Baseline Study

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APPENDIX A PROPOSED STANDING GROUNDWATER DEPTH MONITORING RECORD

COESR SHALLOW GROUNDWATER DEPTH MONITORING RECORD (METRES DEPTH BELOW REFERENCE POINT)

Date CORA01 CORA02 CORA03 CORA04 CORA05 CORA06 CORA07 CORA08 CORA09 CORA10

15/3/19 2.96 2.40 1.98 2.685 [email protected] 6.965 [email protected] 4.84 3.40 5.07

D@ : Dry at metres below Reference Point


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Melbourne 15 Business Park Drive Notting Hill VIC 3168 Telephone (03) 8526 0800 Fax (03) 9558 9365

Brisbane Level 3, 43 Peel Street South Brisbane QLD 4101 Telephone (07) 3105 1460 Fax (07) 3846 5144

Adelaide 1/198 Greenhill Road Eastwood SA 5063 Telephone (08) 8378 8000 Fax (08) 8357 8988

Perth Ground Floor 430 Roberts Road Subiaco WA 6008 Telephone 08 6555 0105

Geelong PO Box 436 Geelong VIC 3220 Telephone 0458 015 664

Gippsland 154 Macleod Street Bairnsdale VIC 3875 Telephone (03) 5152 5833

Wangaratta First Floor, 40 Rowan Street Wangaratta VIC 3677 Telephone (03) 5721 2650

Wimmera PO Box 584 Stawell VIC 3380 Telephone 0438 510 240

www.watertech.com.au

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http://www.watertech.com.au/

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Report - Planning