Geological Society of Australia (WA Division)

EXCURSION GUIDEBOOK No. 9

INTERACTION OF LAND USE, WATER SUPPLY AND GEOLOGY ONTHE SWAN COASTAL PLAIN

by

D. P. Commander

Geological Survey of Western Australia, 100 Plain Street, East Perth,Western Australia 6004

Previously published by the Groundwater Branch, Water Authority of Western Australia as anexcursion guide for the International Conference on Groundwater in Large Sedimentary Basins,

Perth 1990.

12th Australian Geological ConventionSeptember 1994

Guidebook for the post-convention excursion E11

12th Australian Geological Convention, Perth, September 1994

Preferred reference for this volume:

Commander, D.P. 1994. Interaction of land use, water supply and geology on the Swan CoastalPlain. Geological Society of Australia (WA Division) Excursion Guidebook, 9, 24p.

© 12th AGC and Geological Society of Australia (WA Division), all rights reserved 1994

ISSN 0819-6613ISBN 0 909869 95 2

Available for purchase from:

Geological Society of Australia (W. A. Division)P O Box 6014East PerthAustralia 6004

Printed by: Optima Press, 32 Kensington Street, East Perth, WA 6004

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CONTENTSPage

PERTH BASIN - NORTH

1. DALKEITH ........................................................................................................................................................ 12. LAKE CLAREMONT ........................................................................................................................................ 13. SUBIACO WASTEWATER TREATMENT PLANT......................................................................................... 14. BROCKWAY TIP ............................................................................................................................................... 25. CSIRO ................................................................................................................................................................ 26. BOLD PARK No2 BORE .................................................................................................................................. 27. BOLDPARK RESERVOIR ................................................................................................................................ 38. COASTLINE ...................................................................................................................................................... 39. HERTHA ROAD ................................................................................................................................................ 310. GWELUP BOREFIELD ..................................................................................................................................... 411. GWELUP TREATMENT PLANT ..................................................................................................................... 412. BEENYUP WASTEWATER TREATMENT PLANT ........................................................................................ 413. PROPOSED NORTH COASTAL GROUNDWATER SCHEME ...................................................................... 414. LAKE JOONDALUP ......................................................................................................................................... 415. WANNEROO GROUNDWATER AREA .......................................................................................................... 516. WANNEROO RESERVOIR............................................................................................................................... 517. LAKE JANDABUP ............................................................................................................................................ 518. WANNEROO BOREFIELD & GROUNDWATER TREATMENT PLANT .................................................... 519. GNANGARA MOUND ...................................................................................................................................... 620. MELALEUCA PARK ......................................................................................................................................... 621. BULLSBROOK TOWN WATER SUPPLY ....................................................................................................... 622. DANDARAGAN PLATEAU ............................................................................................................................. 623. CHITTERING VALLEY AND DARLING SCARP .......................................................................................... 724. SWAN VALLEY ................................................................................................................................................. 7

PERTH BASIN - SOUTH

1. BUCKLAND HILL LOOKOUT 1 ..................................................................................................................... 82. BUCKLAND HILL LOOKOUT 2 ..................................................................................................................... 83. FREMANTLE .................................................................................................................................................... 84. FREMANTLE LANDFILL SITE ....................................................................................................................... 85. COOGEE INDUSTRIES .................................................................................................................................... 96. LAKE YANGEBUP ........................................................................................................................................... 97. URBANISATION ............................................................................................................................................... 98. JANDAKOT MOUND ....................................................................................................................................... 99. JANDAKOT GROUNDWATER TREATMENT PLANT ............................................................................... 1010. THOMPSON LAKE......................................................................................................................................... 1011. LAKE COOGEE ................................................................................................................................................ 012. WOODMAN POINT WASTEWATER TREATMENT ................................................................................... 1013. WOODMAN POINT ARTESIAN BORE ........................................................................................................ 1114. ALUMINA REFINERY RESIDUE AREAS .................................................................................................... 1115. DEEP WELL DISPOSAL ................................................................................................................................ 1116. OIL REFINERY ............................................................................................................................................... 1117. COASTAL LAKES COOLOONGUP/WALYUNGUP .................................................................................... 1118. NICKEL REFINERY RESIDUE AREA .......................................................................................................... 1219. SERPENTINE RIVER FLATS ........................................................................................................................ 1220. DARLING SCARP ........................................................................................................................................... 1221. SWAN VALLEY ............................................................................................................................................... 12

Figure 1 Location diagram of the Swan Plain near Perth showing the excursion route ......................................... 13

APPENDIXSelected figures from Allen (1981) ........................................................................................................................... 14

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PERTH BASIN - NORTH

1. DALKEITH

The site of the Dalkeith (Sunset Home) artesian bore is at the base of the cliff. The bore wasdrilled in 1908 to a depth of 699m, and later flowed out of control for some years forming a poolof warm water. This became a favourite bathing place and passed into local folklore as the ‘hotspring’.

Salt water interface monitoring bores have been drilled around the foreshore. The superficialaquifer is 25-35m thick, and the interface is 10-20m below the water table.

From 1829 to 1890 water was supplied to Perth from springs and shallow wells which becameincreasingly insanitary. In 1891 the Queen Victoria Reservoir in the Darling Range was completed,but there were problems with the water quality from activities in the catchment area. The SunsetHome bore was one of about forty artesian bores drilled in Perth between 1895 and 1905 and thesuccess of these led to the drilling of 21 artesian bores for public supply between 1897and 1932.These provided 60 to 70% of the city’s water supply until the completion of Canning Dam in1940. The names of the geological formations Leederville, Claremont (now Yarragadee), KingsPark, Osborne, and South Perth were defined from intersections in these bores, and two importantaquifers, the Leederville and the Yarragadee Formations, were recognised.

2. LAKE CLAREMONT

Formerly known as Butler’s Swamp, the land was once used for growing vegetables. After thesurrounding area was cleared, the water table rose and formed a permanent lake, drowning theeucalypts. Like many other swamps in Perth, the area around it was used as a rubbish tip, and thisis now concealed by the golf course.

About one in four houses in Perth now has its own bore or well for garden watering During the1977 drought and consequent water restrictions it is estimated that one in ten houses had a boreinstalled. The total quantity of groundwater pumped for public and private supplies from theunconfined aquifer is about 220M m3/a, representing 60% of all water use in Perth. Waterconsumption from the public supply system has only just recovered to pre-1977 levels. Bore licensinghas recently been extended to the Metropolitan area for bores drawing over 1500 m3/a.

3. SUBIACO WASTEWATER TREATMENT PLANT

Subiaco waste water treatment plant is one of two treatment plants discharging secondary effluentto the ocean. Waste water from here is discharged into 10m of water one kilometre offshore.

Solid waste was formerly put in lagoons behind the electricity sub-station, and used as gardenfertilizer. As a result of leakage from the lagoons there is a plume of contaminated groundwaterextending westwards.

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Perth is part sewered and part reliant on septic tanks (mainly houses built between 1950 and1970). Sewage is treated at three main plants, and secondary treated effluent disposed throughocean outfalls from the Subiaco and Beenyup plants. Secondary treatment removes between 35%and 55% of nitrogen, and the effluent contains 10-15 mg/L BOD, 20-25 mg/L suspended solids,30-40 mg/L Nitrogen and 12 mg/L Phosphorus, meeting current EPA standards for ocean disposal.These standards are becoming more stringent and higher quality effluent may be necessary in thefuture.

4. BROCKWAY TIP

Brockway tip is operated by a consortium of local councils but is overdue for closure. It is likelyto be replaced by the Mindarie site 30km to the north. The area in the foreground has beenrehabilitated as open space.

Waste in the Perth area has been disposed of in about 150 former and existing landfill sites, buturban development has encroached around them and in the future waste will go to a limitednumber of large sites on the outer fringes of the metropolitan area, thus increasing the cost.Virtually all sites are on sand, resulting in a plume of contaminated groundwater, and emission ofmethane and other gases. Most sites have been rehabilitated as public open space, and developmentfor building is not allowed. Hydrogeological criteria are important in the selection of new sites.

5. CSIRO

Headquarters of the Commonwealth Scientific and Industrial Research Organisation’s Divisionof Water Resources.

The major areas of research carried out by CSIRO Division of Water Resources (Perth) are in soiland stream salinisation, groundwater contamination, groundwater modelling, and resourcesmanagement.

6. BOLD PARK No2 BORE

Bold Park No2 bore is one of eight ‘artesian’ bores drilled between 1954 and 1973 at reservoirsand treatment plants to cater for peak demand. The bore was drilled in 1973 to 780m. It producesat 5000 m3/d with a salinity of 880 mg/L TDS. Bold Park Nol, 1.3km to the north, also feeds intothe reservoir.

Artesian bores have been drilled close to many of the reservoirs in the Metropolitan area in orderto augment the supply from surface sources at times of peak demand. The water is untreated, andbecause the salinity of some of the artesian bores (especially south of the Swan River) is as highas 1800 mg/L TDS, the water has to be mixed to lower the salinity.

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7. BOLD PARK RESERVOIR

The reservoir is situated on one of the highest points on the Pleistocene dunes (Spearwood DuneSystem) of the Tamala Limestone. It receives water from the Hills reservoirs and in peak periodsfrom the artesian bores. The reservoir is roofed to prevent contamination.

Rottnest Island can be seen on the horizon 20km offshore. It represents the peak of a more westerlyline of submerged Pleistocene dunes.

Rottnest is a popular holiday resort and the water supply is obtained from a thin, fresh water lensin the limestone aquifer on the island. Holiday cottages are supplied with brackish water fortoilets and showers, and fresh water is supplied only to a limited number of taps. An artesian borewas drilled in 1911 and was reported to have encountered saline water in the Leederville Formation.The chances of obtaining fresh water in the underlying Yarragadee Formation have recently beenreassessed on the basis of the potentiometric head, here at the coast (about 20m AHD), andindications from oil exploration wells that fresh water could extend as far as the island. Theproposal to drill a 1500m bore to supply brackish water for desalination is now under consideration.

8. COASTLINE

Groundwater from the unconfined aquifer passes beneath the Pleistocene coastal dunes andischarges along the coast. The bores watering the reserve here are 15m deep and obtain yields of2 000 m3/d from 10m of screen above the seawater interface which is at about 20m below sealevel. To the south towards Fremantle the freshwater layer is substantially thinner.

The fore dunes (Quindalup Dunes) are of Holocene age and in places along the coast are mobileand unvegetated. North of Scarborough the Tamala Limestone crops out in low cliffs

To the north of Floreat Beach, drainage water from Herdsman Lake is discharged on the beachthrough a large diameter pipe.

9. HERTHA ROAD

The route crosses the former Hertha Road landfill site which has been filled to a depth of about5m. The site lies over a peat swamp, and investigations have been carried out to determine themovement of leachate

Here the Mitchell Freeway has been built over a swamp, and loading to consolidate the peat is inprogress. Alteration of the hydraulic characteristics by loading appeared to have caused a rise inwater table, causing flooding of septic tanks at the retirement homes in Hertha Road (to the left).

Other land subdivisions in Perth have suffered from flooding In a recent case removal of a pineplantation caused the water table to rise and form a lake, where previously it was dry. Floodingafter heavy rain has also occurred in a closed depression due to breakdown of an automaticpumping system. These occurrences indicate the pressure for development of unsuitable land,and the need for correct groundwater information.

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10. GWELUP BOREFIELD

The Gwelup borefield (commissioned in 1974) is the only one of the Metropolitan area’s borefieldsin the unconfined aquifer to be entirely within the urban area. There are twelve bores ranging indepth from 32 to 66m. Some water is also drawn from the Leederville Formation. Design yieldsrange up to 7000 m3/d. As a result of urban and agricultural development several of the boreshave nitrate concentrations up to 29 mg/L.

Dissolved iron is a troublesome constituent of much of the groundwater in the Perth Basin, andcan cause unsightly staining in parks and gardens. Treatment is necessary for public water supply.This involves aeration, clarification by the flocculation of iron oxide precipitates (using sodiumalginate) and finally filtration through sand.

11. GWELUP TREATMENT PLANT

The treatment plant treats water from all the Gwelup bores before reticulation to the servicereservoirs.

The borefields in the unconfined superficial formations supply 20% of Perth’s public water supply.Groundwater from the unconfined aquifer requires treatment for dissolved iron and colour causedby colloidal organic matter. All of the Authority’s borefields have strict pollution control regulationsto protect groundwater quality.

12. BEENYUP WASTEWATER TREATMENT PLANT

Waste water is conducted through a 5km tunnel and an outfall 1.65km offshore. This outfall andthe Cape Peron outfall (to the south of Perth) are the longest ocean outfalls in Australia.

13. PROPOSED NORTH COASTAL GROUNDWATER SCHEME

Investigations to define groundwater resources for supply to the fast expanding northwesternsuburbs has been carried out to the north of the urban fringe, about 2km from the coast. Boreshave investigated yields and water quality from the superficial aquifer. Production rates greaterthan 5000 m3/d have been obtained from the Tamala Limestone. It is planned to constructproduction bores screened in the top part of the aquifer which is iron free, and which will thereforenot require treatment

14. LAKE JOONDALUP

Lake Joondalup is the largest of a chain of wetlands lying between two major ridges of the TamalaLimestone. The water table has a steep hydraulic gradient on the west side of the lake. Farthernorth at Yanchep there are extensive karst features in this zone of steep gradient.

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Nutrient input and eutrophication is an important problem due to market gardening and urbanisationupgradient of the lakes.

15. WANNEROO GROUNDWATER AREA

Groundwater use in this area is controlled in order to allocate the groundwater resources equitably,and to ensure maintenance of water levels in the wetlands.

The soils developed on the Tamala Limestone are preferred for market gardening. A wide rangeof vegetables, vines and citrus are grown in the Wanneroo area. Groundwater is readily available,and proximity to markets is an important economic factor. Urban development is, however, pushingagriculture farther out. The groundwater resources in parts of this area are now fully allocated.

16. WANNEROO RESERVOIR

From this vantage point can be seen Lake Jandabup in the foreground, the Gnangara Pine Plantationin the middle distance and the Darling Scarp on the skyline. Lake Jandabup is at the boundarybetween the calcarenite of the Tamala Limestone and the leached quartz sands of the BassendeanSand and Guildford Formation.

Chlorination and fluoridation of the water is carried out in the building near the reservoir entrance.

17. LAKE JANDABUP

The lake is an expression of the water table of the Gnangara groundwater mound. An investigationof the lake showed that a plume of higher salinity groundwater resulting from evapotranspirationextended downgradient from the lake. The need to maintain these wetlands for ecological reasonsis a major constraint on the utilisation of the groundwater resources of the Gnangara Mound.

18. WANNEROO BOREFIELD & GROUNDWATER TREATMENTPLANT

Bores obtain groundwater from the superficial formations, and the shallow Leederville Formationand deep Yarragadee Formation artesian aquifers. The plant has a capacity of 145 ML/d. Thegroundwater contains dissolved gases, turbidity, dissolved iron and colour. These are treated byaeration, iron oxidation, coagulation and flocculation, clarification, and filtration

Wanneroo 257 is the deepest water supply bore in Perth, 1150m deep, and produces water of lessthan 300 mg/L from the Yarragadee formation. The bore has 100m of screen and is pumped at 10000 m3/d. The water is likely to be greater than 40, 000 years old.

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19. GNANGARA MOUND

The mounded water table in the superficial formations in this area is referred to as the GnangaraMound. The aquifer has a saturated thickness of up to 70m and contains water with an averagesalinity of 250 mg/L TDS. The mound is Perth’s major groundwater resource. Fortunately thecorridor plan and the location of State Forests have limited urban and agricultural development.However, there is increasing pressure for urbanisation on the fringes of the mound.

Exploration of the Gnangara Mound was commenced in 1962 by the Geological Survey andresulted in the commissioning of the Mirrabooka borefield in 1970. The shallow and deep artesianaquifers are fed by recharge of fresh water, from the unconfined Gnangara Mound, mixing withhigher salinity water, derived from farther north. The hydrodynamics and age of the groundwaterare discussed in the conference paper by Thorpe and Davidson.

Recharge on the Gnangara Mound has been quantified by the Geological Survey using tritium asa tracer, and by CSIRO using natural chloride and applied bromide tracers, soil moisturemeasurement and modelling These studies indicate that recharge below the natural banksiawoodland is 20-30% of rainfall, whereas under pines recharge is much reduced, and under pasturethe recharge is as high as 50%.

20. MELALEUCA PARK

At a site 2km to the south, the Geological Survey has determined recharge rates using tritium as atracer. The interface between tritiated and non-tritiated groundwater was defined by drilling andsampling bores at various depths below the water table. The position of the interface indicated arecharge rate of 21% through the banksia woodland. Cores were also taken from the unsaturatedzone to investigate seasonal changes, but these results were inconclusive.

21. BULLSBROOK TOWN WATER SUPPLY

This is one of the few non-Water Authority town water supply borefields and is operated by theRAAF. The water is piped to Bullsbrook, which is east of the Darling Fault.

The Water Authority is responsible for the supply of water to most towns in Western Australia.The few exceptions are Bunbury and Busselton, and single company, mining towns, which havelocal water boards, and use artesian water. The Water Authority is progressively assumingresponsibility for the borefields in those mining towns which are undergoing normalisation.

22. DANDARAGAN PLATEAU

The route passes up the Gingin Scarp, a Tertiary shoreline formed in Cretaceous sedimentaryrocks. Cropping out in these quarries are highly weathered siltstones of the late Cretaceous OsborneFormation.

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23. CHITTERING VALLEY AND DARLING SCARP

The route crosses the Darling Fault at a point where there is no surface expression and descendsinto the Chittering Valley. The Brockman River which occupies the valley is an underfit streamdraining into the Swan River. It is likely that the valley was made by a river, now diverted throughthe Moore River, which extended 200km to the north along the line of the Darling Fault .

The route runs back down the Darling Scarp into Bullsbrook and travels south with the DarlingScarp on the left and the Darling Fault to the right, concealed by the coastal plain sediments.

Dams in the Darling Range account for about 60% of Perth’s public water supply. However, damstorage has been only about a third of capacity during the last decade due to years of lower thanaverage rainfall. Predictions of a lower rainfall due to the greenhouse effect give greater importanceto the groundwater resources of the Perth Basin.

24. SWAN VALLEY

The Swan Valley is intensively developed for irrigation of vines with groundwater from theLeederville Formation. Falling potentiometric levels and fears of increasing salinity resulted inproclamation of the area in 1975 as a groundwater area.

A Groundwater Advisory Committee was constituted to advise the Water Authority of WA onallocation, the issue of licences and the conditions that should attach to them. The committeeserves as a useful and effective means of providing public input to the management of an importantgroundwater resource. By 1980, 75% of the estimated renewable resource was being used suchthat only moderate scope for increased abstraction remained. The consequence of over abstractionwould be the lowering of head and upward migration of the underlying brackish water. Commercialirrigation is licensed according to viability, order of application and suitability to existingdevelopment. A low priority is given to pasture and hobby farms.

Groundwater abstraction in Western Australia is controlled by the Rights in Water and IrrigationAct 1914 and amendments, which is administered by the Water Authority. Groundwater resourcesare vested in the Crown, and the government has wide discretionary powers in the administration,allocation and control of groundwater use.

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PERTH BASIN- SOUTH

I & 2. BUCKLAND HILL LOOKOUT

The reservoir is situated on top of the Pleistocene Spearwood Dune System which forms theTamala Limestone. It receives water from the Hills reservoirs and in peak periods from the artesianbores. The reservoir is roofed to prevent contamination.

Artesian bores have been drilled close to many of the reservoirs in the Metropolitan area in orderto augment the supply from the surface sources at times of peak demand. The water is untreated,and because the salinity of some of the artesian bores (especially south of the Swan River) is ashigh as 1800 mg/L TDS, the water has to be mixed to lower the salinity.

Sea water extends beneath the peninsula to the south and the interface is monitored with multiportbores drilled for the Perth Urban Water Balance Study. Industrial activity in North Fremantle hasresulted in a number of groundwater pollution plumes. Rottnest Island can be seen on the horizon20 km offshore. It represents the peak of a more westerly line of submerged Pleistocene dunes.

Rottnest is a popular holiday resort and the water supply is obtained from a thin fresh water lensin the limestone aquifer on the island. Holiday cottages are supplied with brackish water fortoilets and showers, and fresh water is supplied only to a limited number of taps. An artesian borewas drilled in 1911 and was reported to have encountered saline water in the Leederville Formation.The chances of obtaining fresh water in the underlying Yarragadee Formation have recently beenreassessed on the basis of the potentiometric head here at the coast (about 20m AHD) andindications from oil exploration wells that fresh water could extend as far as the island. Theproposal to drill a 1500m bore to supply brack7sh water for desalination is now underconsideration.

3. FREMANTLE

The original water supply for the city was drawn from wells and horizontal shafts excavatedthrough the Tamala Limestone. It was recently discovered that there was a pool of oil floating inthe shafts beneath the Fremantle Prison, suspected to be from a ruptured oil pipeline. Recovery ofthe oil is now underway.

4. FREMANTLE LANDFILL SITE

The landfill was used for the disposal of industrial, liquid and domestic waste, and the groundwateris contaminated as a result. The council controlled caravan village is located over the levelledlandfill area.

Waste in the Perth area has been disposed of in about 150 former and existing landfill sites, buturban development has encroached around them and in the future waste will go to a limitednumber of large sites on the outer fringes of the metropolitan area, thus increasing the cost.

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Virtually all sites are on sand and result in a plume of contaminated groundwater, and emission ofmethane and other gases. Most sites have been rehabilitated as public open space, and developmentfor building is not allowed. Hydrogeological criteria are important in the selection of new sites.

5. COOGEE INDUSTRIES

The Coogee area has a concentration of animal based industries centred on the Robb Jetty abattoir.Thirty-five point sources of groundwater contamination have been identified in the area. Wastesfrom these activities have been disposed of into sinkholes and consequently the groundwater ishighly contaminated and likely to discharge into Cockburn Sound. All these industries are to berelocated.

6. LAKE YANGEBUP

This is a degraded lake affected by clearing which has raised the water level and killed the fringingtrees. Disposal of waste from Jandakot Wool scourers has contaminated the groundwater withhigh nutrient and heavy metal levels which have entered the lake.

7. URBANISATION

Increasing demand for housing land is causing conflict between urban development and protectionof wetlands and water resources in the region. Rezoning of rural land to urban to permit developmentof about 10 000 houses is currently being considered in the South Jandakot area. If the proposalproceeds, a drainage scheme costing in the order of $7 million will be required to ensure adequatedrainage of the area, and to protect wetlands and water resources from contamination.

8. JANDAKOT MOUND

The water table in this area is referred to as the Jandakot Mound. The superficial formations havea saturated thickness of up to 30m and contain water with a salinity less than 200 mg/L TDS. Themound is the major groundwater resource in the southern Perth area

Special rural zoning is allowed in the water supply area with strict controls on lot density, clearingand water use .

The Water Authority is responsible for the supply of water to most towns in Western Australia.The few exceptions are Bunbury and Busselton, and single company mining towns, which havelocal water boards and use artesian water. The Water Authority is progressively assumingresponsibility for the borefields in those mining towns which are undergoing normalisation.

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The borefields in the unconfined superficial formations supply 20% of Perth’s public water supply.Groundwater from the unconfined aquifer requires treatment for dissolved iron and colour causedby colloidal organic matter. All of the Authority’s borefields have strict pollution control regulationsto protect groundwater quality.

9. JANDAKOT GROUNDWATER TREATMENT PLANT

The plant treats groundwater from the Jandakot Mound. The groundwater contains dissolvedgases, turbidity, dissolved iron and colour. These are treated by aeration, iron oxidation, coagulationand flocculation, clarification, and filtration.

Dissolved iron is a troublesome constituent of much of the groundwater in the Perth Basin, andcan cause unsightly staining in parks and gardens. Treatment is necessary for public water supply.This involves aeration, clarification by the flocculation of iron oxide precipitates (using sodiumalginate) and filtration through sand.

10. THOMPSONS LAKE

Thompsons Lake is a relatively pristine lake, with little development nearby, and is an expressionof the water table on the Jandakot Mound. There is a plume of higher salinity groundwaterdowngradient from the lake. The need to maintain these wetlands for ecological reasons is amajor constraint on the utilisation of the groundwater resource; management is also complicatedby their use as compensating basins for drainage.

11. LAKE COOGEE

Bores and shallow wells are used for market gardens in the area. The salinity has risen due toupcoming of the saltwater interface, evaporation and recirculation of salts, including fertilizers.The lake has a salinity range of 8000 to 48 000 mg/L TDS. Multiport bores have been installedaround the lake to monitor the saltwater interface.

The soils developed on the Tamala Limestone are preferred for market gardening. A wide rangeof vegetables, vines and flowers are grown in the area. Groundwater is readily available, andproximity to markets is an important economic factor. Urban development is however pushingagriculture farther out. The groundwater resource in parts of this area are now fully allocated.

12. WOODMAN POINT WASTEWATER TREATMENT PLANT

All sewage from south of the Swan River passes through the Woodman Point Waste WaterTreatment Plant. Unlike the plants to the north of the Swan River, the effluent receives onlyprimary treatment before discharge through an outfall 4km offshore at Cape Peron (the longestocean outfall in Australia). The effluent contains about 150 mg/L BOD, 110 mg/L suspendedsolids, 45 mg/L nitrogen and 12 mg/L phosphorus.

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Perth is part sewered and part reliant on septic tanks (mainly houses built 1950-70). Sewage istreated at three main plants and secondary treated effluent disposed through ocean outfalls fromthe Subiaco and Beenyup plants. Secondary treatment removes between 35% and 55% of nitrogenand the effluent contains 10-15 mg/L BOD, 20-25 mg/L suspended solids, 30-40 mg/L Nitrogenand 12 mg/L Phosphorus, meeting current EPA standards for ocean disposal. These standardsare becoming more stringent and higher quality effluent may be necessary in future.

13. WOODMAN POINT ARTESIAN BORE

Groundwater is obtained from an artesian bore in the Yarragadee Formation at Woodman Point forwashing lime sands dredged from Cockburn Sound, and for piping the slurry inland to the cementworks. Groundwater is also obtained from the Yarragadee Formation offshore on Garden Island.

14. ALUMINA REFINERY RESIDUE AREAS

Red mud residues from alumina refining have been placed in large clay lined ponds. Recovery ofthe caustic soda liquor from within the residues is being carried out with a grid of windpumps.Leaks in the clay seal are identified by a combination of air photography and piezometer grids,and are sealed with an intense network of grout holes. Leakage into the superficial aquifer hasresulted in plumes of a concentration up-to 20 000 mg/L at the base of the aquifer extendingbeneath the refinery site. Recovery of this is recycled within the plant.

15. DEEP WELL DISPOSAL

Small quantities of toxic waste from the agricultural chemical plant is now disposed through adeep bore into the saline formation waters of the Cockleshell Gully Formation at a depth of about1 300-1400m.

The waste was formerly disposed in a soakage pit and the resultant groundwater contamination isthe worst case in the Perth area. The shallow groundwater is contaminated with 2-4-D and 2-4-5T. The plume extends westwards below the adjacent construction site and has caused problemswith excavations and dewatering.

16. OIL REFINERY

Leaks from oil storage tanks have created a large pool of oil floating on the water table. Recoveryis now in progress using various skimming well techniques, and the amount of oil recovered paysthe recovery cost.

17. COASTAL LAKES COOLOONGUP/WALYUNGUP

The lakes are hypersaline and are evaporative sinks. They lie at the boundary of Holocene beachridges with the Pleistocene Tamala Limestone.

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18. NICKEL REFINERY RESIDUE AREA

Ammonium sulphate residues (from the nickel refinery at Kwinana) have leaked from the disposalpond into the groundwater, and possible discharge to Lake Cooloongup is causing concern.Recovery has been underway since 1979, and the distribution and movement of the effluent isbeing monitored. A hydraulic barrier formed by injection of fresh water is under consideration toprevent seepage into the lake.

19. SERPENTINE RIVER FLATS

The clay flats and floodplain of the Serpentine river are a groundwater discharge area, andgroundwater salinity in the superficial formations generally exceeds 1000 mg/L. Drainage is theresponsibility of the Water Authority.

20. DARLING SCARP

The route runs along the foot of the Darling Scarp from Armadale to Midland with the DarlingFault to the west.

Dams in the Darling Range account for about 60% of Perth’s public water supply. However damstorage has been only about a third of capacity during the last decade due to years of lower thanaverage rainfall. Predictions of a lower rainfall due to the greenhouse effect give greater importanceto the groundwater resources of the Perth Basin.

21. SWAN VALLEY

The Swan Valley is intensively developed for irrigation of vines with groundwater from theLeederville Formation. Falling potentiometric levels and fears of increasing salinity resulted inproclamation of the area in 1975 as a groundwater area.

A Groundwater Advisory Committee was constituted to advise the Water Authority of WA onallocation, the issue of licences and the conditions that should attach to them. The committeeserves as a useful and effective means of providing public input to the management of an importantgroundwater resource. By 1980, 75% of the estimated renewable resource was being used suchthat only moderate scope for increased abstraction remained. The consequence of over abstractionwould be the lowering of head and upward migration of the underlying brackish water. Commercialirrigation is licensed according to viability, order of application and suitability to existingdevelopment. A low priority is given to pasture and hobby farms.

Groundwater abstraction in Western Australia is controlled by the Rights in Water and IrrigationAct 1914 and amendments, which is administered by the Water Authority. Groundwater resourcesare vested in the Crown and the government has wide discretionary powers in the administration,allocation and control of groundwater use.

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Figure 1 Location diagram of the Swan Plain near Perth showing the excursion route.

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ACKNOWLEDGEMENT

Published with the permission of the Director, Geological Survey of Western Australia.

APPENDIX

Selected figures taken from:

Allen, A. D. 1981. Groundwater resources of the Swan Coastal Plain, near Perth, Western Australia.In B. R. Whelan (ed.), Proceedings of Symposium on the Groundwater Resources ofthe Swan Coastal Plain. CSIRO Division of Land Resource Management. p29-74.

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Figure 4 Generalized geological map.

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Figure 6 Subcrop map

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Figure 9 Water table contours and relationships to wetlands

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Figure 10 Groundwater salinity (TDS) in superficial formations. (Note the map is verygeneralized

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Figure 11 Leederville Formation water levels, March-April, 1980.

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Figure 13 Lowest salinity (TDS) groundwater in the Leederville Formation as estimatedfrom resistivity logs.

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Figure 14 Yarragadee Formation water levels, March-April, 1980.

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Figure 15 Lowest salinity (TDS) groundwater in the Yaragadee and Cockleshell GullyFormations as estimated from resistivity logs.