Summary & Recommendations



Response to Problems









2.1 Geological setting

The city of Perth lies on the Swan Coastal Plain, an alluvial and aeolian plain largely formed of Quaternary sand and sand/limestone dunes that are as much as 100 metres thick. The plain lacks surface drainage due the high permeability of the sediments (that is, surface water soaks in quickly), and the only fresh surface water in the region is in wetlands in interdunal depressions which are surface expressions of the water table of an extensive unconfined aquifer. Groundwater is extremely important for water supply, and provides about 70% of all water used in the region. There are more than 130,000 domestic bores in the metropolitan area that are used for garden watering. On average, 25-30% of houses in Perth have domestic bores, and in some suburbs, such as Stirling, where the water table is very shallow, almost all houses have bores.

The coastline in Perth does not have mangroves or salt marshes typically associated with acid sulfate soils on the eastern seaboard, and most of the sandy soils in the region have little or no acid generation potential except near existing or historical wetlands where pyritic peat deposits up to 6 metres thick may occur. The dewatering and excavation of these soils for urban development near wetlands can cause environmental impacts on wetlands, and there are potential health effects on domestic bore users from elevated arsenic concentrations (up to 800 µg/L) and low pH values (as low as pH 2.4) in these areas. The most significant occurrence of acid sulfate soil impacts in Perth was recorded this year in the suburb of Stirling associated with new urban developments in the area.

2.2 Discovery of the Stirling groundwater acidity issue

Concern about acidic groundwater in Stirling was initially raised in mid-December 2001 by a resident in Jones Street who found that his vegetable crop had progressively been affected by water from his bore. The resident contacted the City of Stirling, and testing carried out by Environmental Health Officers indicated that the groundwater was extremely acidic (pH less than 3) and contained very high metal concentrations (particularly aluminium and iron) and high levels of sulfate. The City of Stirling contacted the Swan regional office of the Water and Rivers Commission (WRC) about the issue on 20 December 2001, and the WRC Land and Water Quality Branch were contacted on 21 December 2001 for technical advice on the cause of the problem. The Land and Water Quality Branch indicated that the likely cause of the problem was the disturbance of acid sulfate soils by new residential developments near the affected bore, and that there was a risk that acidic, metal-rich drainage from the area could affect Herdsman Lake.

2.3 Contributing factors to the acidity issue

Field inspections and preliminary sampling in the area have indicated that there are likely to be several sources of the groundwater acidity caused by the disturbance of acid sulfate soils. These included:

  • Dewatering - The water table in the development areas was lowered by as much as 6 metres to allow the excavation and removal of peat which was unsuitable for housing foundations. Additional dewatering was carried out in the area to construct sewage infrastructure.

  • Peat stockpiles - Peat excavated from the development areas was stockpiled before removal. Some of this material had a high acid generation potential, and visual inspection of the stockpiles indicated the presence of large amounts of jarosite and other sulfate salts.

  • Peat fire - Peat in the area had been slowly burning for approximately three weeks. This is also likely to have caused the rapid oxidation of pyritic material.

  • Artificial Lakes - Lakes in public parks have been created by excavating soils to the water table and stockpiling the spoil in the centre of the lakes to create islands.

  • Climatic factors - Perth has had a long succession of dry winters, and the winter of 2001 was exceptionally dry. The water table during the summer months of 2001/2002 was lower than average, and many shallow bores ran dry due to the combined effects of the dry weather and dewatering. The reduced water table would expose the pyrites to oxygen and produce sulfate.

2.4 Statutory approvals process for new residential developments

The majority of urban developments are informally assessed by the Environmental Protection Authority. It is expected that consultants, acting on behalf of developers, understand the technical issues associated with developing these sites, and raise issues with regulatory authorities as appropriate.

There are two residential developments in Stirling that may have contributed to the groundwater acidity issue. These are the Roselea and the Hamilton Lake developments (Figure 1). The approvals process for these developments is described below.

2.4.1 Roselea

On 7 May 1999, the City of Stirling referred District Planning Scheme No. 2 Amendment No. 358 to rezone the land generally bounded by Jones Street, Grindleford Drive and Karrinyup Road, Stirling from "Low Density Residential R20", "Rural" and "Private Institutions" to "Residential - Jones Street Precinct" for assessment.

Accompanying the Scheme Amendment report was the Roselea Structure Plan (April 99) Technical Appendix, which included an Environmental Assessment and Management Plan (April 1999) prepared by Alan Tingay & Associates acting for the developer WR Carpenter Properties Pty Ltd. The Management Plan referred to the removal of peat from the site and additional clean fill being imported for future development. However, it appears that the Management Plan did not identify the PASS occurring on site. The main issue that was of concern was in relation to potential site contamination due to previous landuse as market gardens.

Consequently, the Department of Environmental Protection (DEP) requested further information, in a letter of 3 June 1999, on the inclusion of scheme provisions relating to the implementation of a Contaminated Soil Management Plan.

The City of Stirling responded to the DEP's request for information in a letter of 14 June 1999 and stated that it would undertake to modify the amending documents to include a section relating to the Contaminated Soil Management Plan, which stated:

The development of the precinct shall be undertaken in a manner which ensures that any contaminated soil is remediated to the requirement of the City of Stirling and the DEP in accordance with a Contaminated Soil Management Plan to be prepared and implemented to the satisfaction of both of these authorities.

In this respect, an adequate soil sampling program is to be finalised to the satisfaction of the DEP prior to any subdivision occurring.

As a result of the above, the Environmental Protection Authority (EPA) set a level of assessment at "Scheme Not Assessed - Advice Given" on 2 July 1999. Under delegation from the EPA, the DEP provided the following advice:

  • Soil contamination - the DEP identified that the subject land had been previously used for market garden activities and that there was the potential for soil and groundwater pollution and that the above provision be included during finalisation of the amendment.

  • Surface water quality - recommended that the proposed management measures for the reconstruction of the Albert Street Link drain into a "living stream" and the development of a water quality monitoring program be referred to the Water and Rivers Commission (WRC) prior to implementation.

The DEP also provided advice relating to noise and dust impacts.

A copy of this letter was forwarded to WRC for their information. As highlighted above, the potential for acid sulfate soils was not identified as an issue on site during the EPA's assessment process.

However, the potential for acid sulfate soils occurring on site was raised by the WRC in a letter to Alan Tingay & Associates, dated 5 November 1999. The DEP's Contaminated Sites Branch and Evaluation Division received an electronic copy of this letter, which commented on a draft Sampling and Analysis Plan, Dewatering Program Jones Street, Stirling (October 1999). The letter referred to being involved in several aspects of this proposal since receiving the DEP's letter of 2 July 1999 to the City of Stirling regarding Amendment 358 and highlighted that dewatering of the site may lead to the generation of a significant volume of acid-sulfate soil.

Subject to conditions, the Western Australian Planning Commission (WAPC) approved subdivision of the Roselea development (WAPC Ref: 112189) in a letter dated 2 March 2000. The WAPC identified the DEP as a nominated authority when advising the WAPC on the clearance of subdivision condition numbers 19, 20 and 21 (WAPC Ref: 112189), which required a Noise Management Plan, Air Quality Management Plan and Contaminated Soil Management Plan respectively.

Since then, the DEP has received the above Environmental Management Plans for Stage 1 of the Roselea development from ATA Environmental. Stage 1 covers the southern section of the land previously rezoned under the City of Stirling's Scheme Amendment 358. The DEP stated in letters dated 8 December 2000 and 21 December 2000 (see Attachment 3) that the Environmental Management Plans for Stage 1 appeared to be adequate. However, the DEP advised ATA Environmental that they should liaise with WRC with regard to groundwater and surface water contamination at the site.

The balance of the land to the north still requires clearance of subdivision conditions before development can proceed and to date the DEP has not received the above Environmental Management Plans for this stage of development.

In a letter dated 2 January 2002, the WAPC referred a proposed residential subdivision (WAPC Ref: 118165) for Lots 42, 201 & 1009 Karrinyup Road, Stirling for comment. The proposed subdivision appears to amend the subdivision for the northern part of the Stage 1 (which has received subdivision approval, WAPC Ref: 112189) and the southern part of Stage 2 (which has not received subdivision approval). In a letter dated 4 February 2002, the DEP received an amended plan of the proposed subdivision (WAPC Ref: 118165) from the WAPC.

In light of the recent events which have taken place regarding the acidic groundwater issue within the Stirling area, the EPA requested the following information before it could finalise its consideration of the proposed subdivision (WAPC Ref: 118165):

  • acid potential of soils and groundwater on site;

  • groundwater pH and heavy metal concentrations;

  • the requirement for a Acid Sulfate Soil Management Plan; and

  • information on the quality of peat material being removed from the site and location for off-site disposal/use of the material.

Since then, the DEP has been advised by the WAPC in a letter dated 5 March 2002 that the subdivision application for Lots 42, 201 & 1009 Karrinyup Road (WAPC Ref: 118165) has been cancelled at the applicant's request.

2.4.2 Hamilton/Stirling Lakes

On 10 March 2000, the City of Stirling requested the DEP's comments on a residential design layout for Stirling Lakes, formerly known as the Stirling Lakes Precinct Area, which is bounded by Karrinyup road, Hamilton Street, Hutton Street, Mitchell Freeway and Telford Crescent, from the City of Stirling. Accompanying the design layout was an Environmental Overview Report (January 2000) prepared by Bowman Bishaw Gorham for Menzies Court Holdings Ltd. The report referred to peat being currently mined from a large proportion of the site, however, the potential for acid sulfate soils occurring on site was not identified.

The DEP provided the City of Stirling with preliminary comments, in a letter dated 12 April 2000, on the environmental issues concerning the Stirling Lakes area. The comments provided were with regard to the creation of the proposed lakes, wetlands, surface water quality, groundwater quality, site contamination, mosquitoes and midges, and surrounding land uses.

In a letter of 17 April 2000, the WAPC referred a proposed residential subdivision (WAPC Ref: 113695) of Lot 53 & Pt Lot 19 Karrinyup Road, Stirling to the DEP for comment. The proposed subdivision covered the northern half of the design layout for Stirling Lakes. The DEP informed the WAPC, in a letter dated 1 May 2000, that preliminary comments had been provided on the residential design layout for the subject area and that further information was still required before the EPA could set a level of assessment.

The DEP provided further comment on 1 June 2000, which was in relation to surface water quality, site remediation and management of mosquitoes and midges. Bowman Bishaw Gorham provided the DEP with the further information requested by the DEP in its previous letters.

As a result, the EPA set a level of assessment for the proposed subdivision of Lot 53 and Pt Lot 19 Karrinyup Road, Stirling (WAPC Ref: 113695) at "Informal Review with Public Advice" on 7 August 2000.

No appeals were received against the level of assessment set for the proposed subdivision and the DEP under delegation from the EPA provided the WAPC with advice, in a letter dated 31 August 2000, on the following issues:

  • Nutrient Export & Budget - recommended the preparation of a Nutrient and Irrigation Management Plan that this be imposed as a subdivision condition.

  • Site Contamination - recommended that a site investigation to determine the extent and severity of contamination be imposed as a subdivision condition, with a Site Remediation and Validation Report to be prepared if the site is found to be contaminated.

  • Management of Mosquitoes and Midges - recommended that a mosquito management program be imposed as a subdivision condition.

The DEP also provided comments relating to industrial noise, traffic noise and rail vibration.

Subject to conditions, the Western Australian Planning Commission (WAPC) approved the subdivision of Lot 53 & Pt Lot 19 Karrinyup Road, Stirling (WAPC Ref: 113695). The DEP was identified as a nominated authority when advising the WAPC on the clearance of subdivision condition numbers 5, 23 and 24, which requires the provision of a Contaminated Soil Management Plan, Nutrient and Irrigation Management Plan and a Mosquito Management Plan respectively.

To date the DEP has received none of the above Management Plans for comment. As highlighted above, the potential for acid sulfate soils was not identified as an issue on site during the EPA's assessment process.

Note: The DEP receives approximately 160 subdivision referrals per year and 350 rezoning proposals per year. The WRC does not receive any subdivision referrals in the City of Stirling due to an arrangement with the WAPC where subdivisions within the metropolitan area are not referred to the WRC.

2.5 History of Regulatory actions - Roselea and Stirling Lakes

The permit and licensing systems for the Roselea and Stirling Lakes developments are managed by the Water and Rivers Commission Swan Region Office.

Roselea development was subject to Water and Rivers Commission groundwater abstraction permit and licence to cover the company's dewatering operations that included the submission of a Sampling and Analysis Plan for approval. The dewatering operation involved 9 abstraction spears which pumped the groundwater into the Water Corporation's main drains along Albert Street and Jones Street. Monitoring results between December 1999 to April 2001 did not show adverse change in the groundwater conditions during the active dewatering periods. Although some metals such as aluminium, zinc and cadmium were occasionally detected in the groundwater, it did not however, impact on the receiving surface waters. Since that time no further monitoring results have been received. Dewatering operations ceased in August 2001. Roselea's groundwater permit expired on 17 December 2001. An application has been received for renewal and is currently being reviewed.

In May 2001 several complaints were received by the Department of Environmental Protection about the peat stockpile fire at the Roselea Estate. Investigation revealed that the peat was smouldering for about three weeks impacting on the local residents with offensive odour and smoke.

Stirling Lakes was granted a groundwater permit on 26 May 2000 with commitment from the developer (MM Development) to maintain water quality standards (ANZECC, 1992) including the removal of peat as soon as practicable following extraction. Monitoring results indicate little variation in pH values between June 2000 and May 2001.

Departmental fax on 11 September 2000 to Welltech (Dewatering Operator) indicated that their monitoring results showed marginal decline in the groundwater pH and slight elevation of zinc and lead contamination. Regular lime dosing was undertaken to overcome the problem.

Following a letter to MM Development about the breach of permit conditions on 16 January 2002, Mr Pollock responded via letter on 30 January 2002 that the peat stockpile was reduced by 50% since September 2001. This could not be substantiated because there was no estimation of the quantity of earlier stockpile on the site.

The stockpiling of peat on the Stirling Lakes estate is in breach of the dewatering conditions for the site, and the proponent has been directed to remove the material. Under Section 73 of the Environmental Protection Act, proponents on the Roselea estate have been served with notices to remove the stockpiled peat from the area. It is proposed that proponents on the Stirling Lakes estate be served with a Section 73 notice shortly.

2.6 Significance of acid sulfate soils

With the media attention on salinity, it is often easy to forget that another significant environmental problem which besets Australia's wetlands and waterways is acid sulfate runoff. The disturbance of acid sulfate soils (ASS) is a significant environmental issue in coastal regions of Australia, particularly in Queensland and New South Wales, and is a major health issue in South and South East Asia.

Acid sulfate soils are soils that naturally contain large amounts of pyrite and other iron sulfide minerals. They have formed naturally over the last 10,000 years in waterlogged areas, and are usually associated with estuaries, mangroves, coastal salt marshes or with wetlands. If these soils are exposed to air by drainage or by excavation, the sulfide minerals react with oxygen in the atmosphere to form sulfuric acid, and leachate from the soil may contain very high concentration of metals. The release of acidic, metal-rich leachate into waterways or the ocean can have severe impact on aquatic life, and large fish kills have occurred in rivers on the eastern seaboard as a result of the drainage of ASS. Without adequate management, the acidity of drainage and groundwater can also corrode concrete and steel infrastructure in urban developments on this soil type.

There are more than two million hectares of acid sulfate soils in Australia, and these mostly occur along the northern and eastern coastlines of the continent. These soils contain a total of about one billion tonnes of pyrite. One tonne of pyrite can generate about 1.5 tonnes of sulfuric acid when oxidised.

The ASS in south-western coastal areas in Western Australia have a very limited distribution, and are mostly restricted to the immediate vicinity of existing and historical wetlands. Further information on the distribution and impacts of ASS in Australia can be found in a publication produced by Environment Australia, which is available as a PDF file at the following web site:

Pyrite in acid sulfate soils commonly contains large amounts of arsenic that is released if the pyrite is oxidised. The arsenic may leach into groundwater, and can be a significant health issue if the groundwater is used as a source of drinking water.

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