LAKES AND SWAMPS IN THE

DOUGLAS – TOOLONDO

AREA

REPORT TO BASIN MINERALS HOLDINGS N.L.

by

John Smart

Goldfields Revegetation Pty Ltd

August 2001-10-12

Goldfields Revegetation Pty Ltd, 230 Tannery Lane, Mandurang, Victoria 3551 Ph 03 5439 5384, fax 5439 3618, email goldrevg@netcon.net.au

LAKES AND SWAMPS IN THE

DOUGLAS – TOOLONDO AREA

CONTENTS

1. OBJECTIVES 2. SUMMARY 3. INTRODUCTION 4. GENESIS 5. FRESHWATER LAKES & SWAMPS 6. SALINE LAKES & SWAMPS 7. MONITORING PROGRAM 8. IMPACTS OF MINING BIBLIOGRAPHY

FIGURES

Figure 1 - Locality Map Figure 2 – Schematic Geological Cross Section Figure 3 – Connangorach Swamp, photos Figure 4 – Connangorach Swamp, cross section Figure 5 – Lake Kanagulk, photos Figure 6 – Lake Kanagulk, cross section Figure 7 – White Lake, photos Figure 8 – White Lake, photos Figure 9 – White Lake, cross section Figure 10 – Brooksby’s Swamp, photos Figure 11 – Brooksby’s Swamp, cross section Figure 12 - Tea Tree Lake, photos Figure 13 - Tea Tree Lake, cross section Figure 14 - Saline Lake, Harrow-Kanagulk Road

TABLES TABLE 1 Drillhole Locations TABLE 2 Bore Completion Details

APPENDIX Drill logs – BW 4, BW 5, BW 8, BW 9, BW 27.

LAKES AND SWAMPS IN THE

DOUGLAS – TOOLONDO AREA 1. OBJECTIVES The objective of this investigation was to provide an understanding of the hydrogeology of the lakes and swamps in the Douglas – Toolondo area and to establish the means of on-going monitoring of selected lakes and swamps near areas likely to be mined. 2. SUMMARY Lakes and swamps in the Douglas – Toolondo area fall into two distinct categories, each controlled by different geological conditions and hydrological mechanisms:

• Freshwater lakes/swamps, independent of the local watertable • Saline lakes and swamps, discharge sites for saline groundwater

The latter all lie along the Douglas Depression, the major hydrogeological feature of the area. Two saline lakes, a saline swamp and two freshwater swamps, all located near strandlines proposed for mining, were investigated by:

• surveying the cross section of the lake/swamp • augering its base • erecting a gauge pole (or poles) for monitoring water levels • establishing an observation bore on its edge.

Measuring of water levels in both bores and lakes has been instituted on a monthly basis, beginning in April 2001. 3. INTRODUCTION Basin Minerals Holdings NL holds mineral tenements over several significant mineral sands deposits near Douglas, in the Southern Wimmera, southwest of Horsham. Figure 1 shows the area of the Douglas Project and the location of the heavy mineral-bearing strandlines. The company is currently engaged in feasibility studies for the development of commercial mining and is preparing an Environmental Effects Statement for Stage 1 of the Project. Basin Minerals Holdings NL engaged Goldfields Revegetation to investigate the hydrogeology of the area of interest and the initial program was carried out in January 2001; this covered four swamps and lakes. Subsequently, an area southeast of Douglas was selected for the start of mining, the “Stage 1 area”, and Tea Tree Lake immediately west of this was added to the scope.

2 This report covers the preliminary results of investigations into the lakes and swamps near to the Douglas mineral sands deposits, namely Connangorach Swamp, Lake Kanagulk, White Lake, Tea Tree Lake and Brooksby’s Swamp. Observation bores have been established adjacent to each of these lakes/swamps and gauge poles erected in them. The surface profiles between the bores and gauge poles have been surveyed and elevations reduced to the Australian Height Datum (AHD). The abnormally dry conditions of the past four years have rendered most lakes dry and only those employed as water storages or with substantial influx of groundwater were wet at the time of the study (January 2001).

Lakes and swamps are common throughout the Southern Wimmera and, within the project area, the 1:100 000 scale map shows over twenty named lakes and swamps, with at least twice that number not formally named. Many of the larger natural lakes and swamps in the Wimmera have been developed as water storages, for example, Toolondo Reservoir, Pine Lake and Taylor’s Lake, around Horsham, and Lake Wallace at Edenhope. Other lakes and swamps have also been modified significantly, either by draining them, or, alternatively, by using them as sumps for the drainage of the surrounding land, such as Jalumba Swamp, north of Toolondo. In some cases, the changes to the natural conditions have had a significantly adverse impact on the local groundwater regimes. Swamps and seasonal lakes are commonly grouped together and described as wetlands, a term which implies periodic submergence, combined with substantial periods of relative dryness. Although wetlands were formerly regarded as a waste of land, habitat for vermin and mosquitoes, their ecological importance is now widely recognised. Swamps and ephemeral lakes provide the essential habitat for many species of plants and animals, and many lakes are important for migratory birds. The current preparation, by Birds Australia, of a proposal to have the salt lakes near Douglas listed under the RAMSAR convention is an example of the biological importance now attached to these lakes. All the lakes and swamps described in this report are reserves administered by Parks Victoria. 4. GENESIS A schematic geological cross section of the project area is shown in Figure 2 and the typical geological settings of lakes and swamps are indicated. Within the project area, lakes and swamps occur in the swales between the northerly trending ridges, or else within the Douglas Depression. In the latter area, the lakes and swamps are all at similar elevations, well below the land on either side of the Depression. Freshwater lakes and swamps are found at various elevations. Most of the lakes and many of the swamps in the area have developed in association with lunettes, aeolian dunes formed on the leeward side of a lake by the deposition of sediment derived from the erosion of the lake-bed (Hills, 1940). The material in a lunette may be clay, sand or gypsum, but is typically clay in a granular form or sand. In some places, the clay lunettes form good cropping land, such as east of White Lake and Tea Tree Lake south of Douglas (Figure 8).

3 The initial formation of the lake or swamp is not necessarily associated with the formation of the adjacent lunette and both theories for lunette formation assume a pre-existing lake (Hills, 1940 and subsequent authors) or, at least, a hollow in which the watertable is close to the surface (Macumber, 1970). Once initiated, erosion of the lake-bed can proceed to a depth of many meters below the natural ground surface and penetrate through the clay into the underlying sand. Subsequent deposition of clay may effectively seal the bottom of the lake/swamp and render it independent of the local watertable. Lakes and swamps in the area fall into two categories, freshwater and saltwater, with the latter divisible into two sub-categories. Each is controlled by different geological conditions and hydrological mechanisms and surrounded by different types of vegetation. Two freshwater swamps, one saline lake and one saline swamp, all located close to areas proposed for mining, have been selected for more detailed study and for long term monitoring. These are representative of all the lakes and swamps in the overall project area:

• Freshwater swamps, independent of the local watertable (Connangorach Swamp and Lake Kanagulk)

• Saline lakes, discharge sites for saline groundwater (White Lake and Tea Tree Lake)

• Saline swamps, discharge sites for saline groundwater (Brooksby’s) None of these lies within the Stage 1 area; Lake Kanagulk adjoins the northeast corner of the area and is about 750m east of the nearest strandline, while White Lake and Tea Tree Lake are further away (Figure 1). Although the geology of the above features is reasonably well defined, some of the hydrological conclusions may be further refined once the effect of seasonal changes is observed. The past four years have all had below average rainfall and that, combined with an abnormal distribution of rainfall, has meant there has been very little run-off and probably, little if any, recharge to groundwater. 5. FRESHWATER LAKES & SWAMPS For a lake or swamp to remain fresh, there must be drainage away from it, either by an outlet stream or by recharging groundwater. Otherwise, evaporation will increase the concentration of salt by removing water and the water in the lake will eventually become saline. Even with a surface outlet, a lake may be saline because of the upward movement of saline groundwater. As the groundwater in the project area is everywhere saline, a lake can only remain fresh if its base is well above the watertable and is either recharging the underlying aquifer or sealed from it by a low permeability lining of clay. Within the general area, many of the freshwater lakes/swamps have been used as sumps for farm drainage and some swamps have been converted to permanent lakes by this process. Jalumba Lake, north of Toolondo Lake, was cropped in dry years during the 1950s; it is now a permanent lake as a result of farm drainage.

4 Connangorach (10 Mile) Swamp. This swamp (Figures 3 & 4) lies at the southern end of the Echo strandline and is surrounded by mature River Red Gums (Eucalyptus camaldulensis). It was completely dry at the time of survey (January 2001). Although there is no distinct outlet, the swamp and the surrounding swampy land appears to drain northwards, eventually reaching the Wimmera River. This flow is likely to be a relatively rare occurrence, but it is adequate to keep the swamp fresh. The swamp is slightly elliptical, with an orientation just west of north and is about 1.5 km long and 1.2 km wide, covering an area of about 140 ha. The land on the western side, where the observation bore BW 9 is located, lies at about 170m AHD. The depth of the swamp is about 2m below the edge of the surrounding land, giving it a nominal capacity of about 2.5 GL. An auger hole 300m from the edge and 2m deep did not encounter water, but clay at the bottom was soft, so the watertable was probably about 3m or so below the base of the swamp (Figure 4). The standing water level in the adjacent bore (BW 9) was 14.5m in fine - grained clayey sand, confirming that the watertable of the swamp is perched and is independent of the regional watertable. Lake Kanagulk (Scotchman’s Lake). This lake lies about 12 km ESE of Douglas and was completely dry at the time of survey (Figures 5 & 6). According to the adjacent landowner, the lake has been dry for the past five years, but is occasionally full; in 1970 it flooded over the road. Although the 1:100 000 topographic map shows the lake water as salt, it contains freshwater. The lake is surrounded by mature River Red Gums (Eucalyptus camaldulensis) and has an inner fringe of young saplings. The latter would appear to date from the last wet period in 1992-3, as this species only reproduces during exceptionally wet periods, such as 1973-4 and 1992-3, so that stands typically consist of single age trees, or two or three distinct generations. In the centre of the lake, are many large dead trees, all of which appear to have been dead for many years. There is no obvious outlet, but there must be an adequate flushing mechanism to maintain it fresh. The lake appears to receive water from several swamps/intermittent lakes on a drainage line upstream, while several drains bring in water from the area to the south and west, enhancing this natural drainage. The lake is roughly circular, with a slight elongation in the N – S direction, covering an area of about 400 ha; the deepest point is in the southeast, where the base is about half a meter below the general level. At the western side of the lake, where observation bore, BW 8, is located, the elevation is about 179m AHD. As the typical depth is 4 – 5m below the surrounding land, this gives a nominal volume in the order of 18 GL. The lake’s cross section (Figure 6) shows that the lake is fairly deeply eroded (4 – 5m) below the surrounding area and apparently several meters into the Parilla Sand. The base of the lake is lined with heavy clay, washed in from the swamps upstream and this presumably effectively seals the lake from the underlying sand, as the local watertable is about 11m below the lake bottom (observation bore BW 8 on 19-1-01).

5 6. SALINE LAKES AND SWAMPS The saline lakes in the project region all lie along the line of the Douglas Depression. This is a major geological and hydrogeological feature, into which saline groundwater discharges and moves northwards along the Depression, past Mount Arapiles, eventually reaching Lake Hindmarsh (Swane et al., in press). Lakes and swamps along the Depression show seasonal fluctuations in level, but the strong upward flow of groundwater ensures that water is always close to the surface. The main lakes, such as White, Centre and North Lakes, as well as smaller lakes such as Tea Tree Lake, always contain water in the form of brine overlying a thin crust of crystalline salt, which rests on soft mud. In winter, run off from the surrounding land raises the water level. At a slightly higher elevation lie a number of saline swamps, such as Brooksby’s and Green’s. In these, the summer water level may fall below the surface during very dry periods, such as the present. The actual amount of groundwater discharged into such swamps is uncertain. Unless the watertable in the swamp rises above the surface, to expose a free water surface for evaporation, the only loss of water will be by water passing upwards through the soil by capillary action and will be therefore comparatively small. White Lake. White Lake (Figures 7-9) lies about 1.5 km south of Douglas and about 2 km west of the Bondi strandline. It is roughly elliptical, elongate in the NNW direction, being about 3.5 km long by 2 km wide, covering an area of almost 700 ha. It is a typical example of the perennial saline lakes that lie along the Douglas Depression with the salt flats surrounding it supporting a vegetation cover of halophytes. The bottom of the lake beside the gauge pole is at an elevation of 147m AHD about 5m below the level of the surrounding surrounding land, while the water level is similar to that in the adjacent observation bore (BW 5; Figure 8). Tea Tree Lake. Tea Tree Lake (Figures 12 & 13) lies about 8 km SSE of Douglas and less than 2 km west of the Bondi strandline. It is roughly circular, with a slight elongation in the N-S direction, being about 800m by 700m and covers an area of about 45 ha. A lunette is present on the eastern side. The lake is surrounded by River Red Gums (Eucalyptus camaldulensis), with an inner fringe of Tea Tree (Salt Paperbark –Melaleuca halmaturorum), including some large, mature examples. The water in the lake lacks the crust of salt, which is so prominent at White Lake, and the water level in the lake is significantly lower than that in the adjacent bore (BW 27). The ground at the base of the outer gauge pole is about 148m AHD, very similar to that of White Lake. About 3 km WSW of Tea Tree Lake, there is a shallow saline lake on the southern side of the Harrow-Kanagulk Road (Figure 14). This lake is a metre or so higher than Tea Tree Lake, but probably also receives saline groundwater. Brackish water from perennial creeks fed by seepage from fine-grained sand on the hills to the east flows into the lake (see report on watertable investigations- Smart, 2001); its over flow drains into the Glenelg River.

6 Brooksby’s Swamp. Brooksby’s Swamp is adjacent to the Douglas – Clear Lake road, about 4 km NE of Douglas and is typical of the saline swamps in the Douglas Depression (Figures 10 & 11). The Bondi East strandline is about 4 km east. It is elongate in the N – S direction, about 500m long by 300m wide, covering an area of about 12 ha. A thicket of Tea Tree (Salt Paperbark – Melaleuca halmaturorum) surrounds the swamp, while the sandy lunette on the northeast side supports a stand of Yellow Gum (E. leucoxylon). The depth of the swamp is about 3m, with the base elevation about 146m AHD. The hollow appears to have been eroded into the Shepparton Clay, as the lithology in the base of the swamp is similar to that in the adjacent observation bore (BW 4; Figure 11) and its watertable is similar to that in the bore. 7. MONITORING PROGRAM The first stage of this investigation has been described above (Section 6). This has provided an understanding of the geology of the lakes and swamps and the basic hydrogeology. The next stage will be to measure water levels in the lakes/swamps and in the adjacent bores every month, so that seasonal changes can be monitored and the relationship between the water levels in these lakes/swamps and the watertable of the surrounding area. These established data will also provide the background against which the effects of future mineral sands mining can be judged. At present, there is no systematic monitoring of levels in lakes or swamps. The predecessor of DNRE established two lines of bores on Centre Lake, north of Douglas, but these are not currently being monitored. From 1990 to 1992, CRA subsidiary Wimmera Industrial Minerals monitored levels in Jalumba Swamp (north of Toolondo Reservoir) and in adjacent bores (WIM monitoring: NT 296, bore; NT 9999, lake). This former swamp is now a permanent lake, due to its use as a sump for land drainage. The hydrogeology of Jalumba Swamp is similar to Connangorach Swamp and the monitoring by WIM showed the lake and bore water levels were completely unrelated, with a typical difference in level of about 13m. Basin Minerals Holdings NL commenced monthly monitoring of water levels in March 2001 and, when an adequate volume of data has been collected (probably 18 to 24 months), the data will be analysed and the results reported.

7 8. IMPACTS OF MINING Freshwater lakes/swamps are surface phenomena, situated well above, and independent of, the local watertable. They are dependent on periodic inputs of freshwater as well as occasional flushing to prevent the build up of salt by evaporation. Any changes to surface drainage may reduce or increase the input or output from these lakes/swamps, but if this occurs, the effect is likely to be temporary. In principle, this would be no different from the natural changes experienced as a result of variations in rainfall from year to year. Rainfall at Horsham has a long-term average of about 400mm, but has ranged between extremes of 200 and 800mm; in the Stage 1 area, rainfall is much higher, in the order of 600mm annually. Pan evaporation in the region typically exceeds total rainfall by about 1200mm, which is equivalent to about 1000mm from open water. The variation in rainfall combined with the high evaporation, means that lake/swamp levels can change dramatically in a relatively short period due to completely natural effects. It must also be remembered that many lakes and swamps have been permanently affected by the increased inputs from land drainage. The water levels in both Lake Kanagulk and Connangorach Swamp are perched and independent of the local watertable, which, in both cases, is more than 10m below the base of the lake/swamp. The hydrogeology of the freshwater lakes/swamps is quite simple: a hollow on a drainage line, a few meters below the surrounding surface, lined with clay. The latter was derived from the erosion of the Shepparton Formation, a stratigraphic unit present throughout the region. This unit consists dominantly of sandy clay, whose dominant clay mineral is smectite; thus the formation has a very low permeability and it is ideally suited to the sealing of water storages, whether natural or man-made. When the clay dries out, cracks may penetrate a meter or more below the surface, but as soon as water is applied, the clay swells, sealing the cracks and thus rendering the bottom of the lake/swamp essentially impermeable. Mining within a lake/swamp would obviously destroy the impermeable clay layer that maintains its perched watertable; to restore the pre-existing hydrological conditions will require the re-instatement of the clay layer. Alternatively, it may be more appropriate to re-construct the lake/swamp nearby. Either option would be straightforward, requiring little more than careful surveying and a simple earthworks exercise. Restoration of the indigenous vegetation would then occur; this would require careful planning and execution, but evidence elsewhere in the region suggests it is quite feasible. The occurrence of saline lakes and swamps in this area is attributable to the hydrogeological situation in the Douglas Depression, whereby saline groundwater is under pressure and moves upwards to the surface. Evaporation then concentrates the saline water to brines, which gradually move northwards along the Depression, ending up in the Wimmera River. While there is some westerly movement of brackish groundwater into the Depression from the Stage 1 area (Smart, 2001), this appears to be of quite modest volume and the great bulk of the water comes from the aquifer system to the west of the Depression, the Renmark Group and the Duddo Limestone. Any effects on groundwater caused by mining in the Stage 1 area are likely to be slight or negligible and any impact on the saline lakes even less marked.

BIBLIOGRAPHY Hills, E.S., 1940. The lunette, a new landform of aeolian origin. Aust. Geogr., 3(7), pp. 15-21. Macumber, P.G., 1970. Lunette initiation in the Kerang district. Min.Geol. J.Vict.

6(6), pp.16-18. Smart, J., 2001. Watertable investigations in the Douglas – Toolondo area.

Unpublished report to Basin Minerals Limited. Goldfields Revegetation.

Swane, I.P., Weaver, T.R., Lawrence, C.R., & Cartwright, I. in press. Hydrologic

controls on groundwater salinisation, Murray Basin, Australia. Paper submitted to WRIO conference, June 2001.

Brownbill, R.J., 1995. The hydrology and chemistry of shallow groundwater and

associated lake systems in the southern Wimmera area, Victoria. M.Sc thesis submitted to School of Earth Sciences, University of Melbourne, Australia. (unpubl.)

J.Smart 15/2/01

Locality Map Figure 1

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#

#

# #

# #

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#

# #

#

565000

565000

570000

570000

575000

575000

580000

580000

585000

585000

590000

590000

595000

595000

5895

000 5895000

5900

000 5900000

5905

000 5905000

5910

000 5910000

BW7 Observation Bore#

BW5 BW6

BW18

BW19

BW7

BW8

BW4

BW3

BW2

BW1

LAKEKANAGULK

WHITELAKE

Cross Section

Cros

sSe

ctio

n

Cross Section

BROOKSBYSSWAMP

TOOLONDOLAKE

Legend

BW11

BW9

BW10

10 MILESWAMP

CrossSection

0 1 2 3

Kilometers

Tea TreeLake

Cross SectionBW27

HOLE No.

REG No.

1:100 000 SHEET

DATE DEPTH (m)

COLLAR AHD

DATUM AHD

EASTING (SURVEY)

NORTHING(SURVEY)

BW 4 143043 Balmoral 10-1-01

17 151.0 151.0 568761 5904166

BW 5 143044 Balmoral 10-1-01

10 152.0 152.0 566630 5896950

BW 8 143047 Balmoral 10-1-01

17 179.1 179.1 574056 5895373

BW 9 143048 Horsham 10-1-01

30 170.7 170.7 574056 5895373

BW27 Balmoral 8-5-01 15 156.19 156.19 566516 5892873

DRILLHOLE LOCATIONS

Table 1 HOLE

No. DATUM

AHD DEPTH

SCREENED

WATER LEVEL (May 2001)

EC (uS/cm)

pH

BW 4 151.0 3.4 – 8.4 (4.05) 51 000 BW 5 152.0 2.9 - 7.9 (4.72) 27 500 BW 8 179.1 14.5 – 16.5 (15.52) 19 150 BW 9 170.7 24.6 – 29.6 (14.51) 4 020 BW 27 156.2 7.9-12.9 5.02 15 020 6.2

WATER LEVELS

Table 2

Saline lake, south of Harrow – Kanagulk Road. 10/7/01

Saline ditch adjacent to saline lake, Harrow – Kanagulk Road. 10/7/01

Figure 14