INVESTIGATION OF SOIL AND GROUNDWATER ACIDITY, STIRLING
EXECUTIVE SUMMARY AND RECOMMENDATIONS
Identification of Problem and Immediate ResponseConcern about acidic groundwater in Stirling was raised in mid-December 2001 by a concerned resident whose garden was dying. The resident contacted the City of Stirling, and preliminary testing by the City of Stirling indicated that the groundwater was extremely acidic and contained high metal concentrations. The City of Stirling contacted the Swan Regional Office of the Water and Rivers Commission on 20 December 2001, and the Commission provided technical advice to Stirling on 21 December 2001 that the problem was likely to be due to the disturbance of acid sulfate soils.
The City of Stirling invited officers from the Commission to a meeting and site inspection about the issue on 7 January 2002 and this indicated the scale of the problem. On 10 January 2002 the Department of Health (DOH) released a press release about acidity and the City of Stirling delivered letters warning of the issue to householders in an area that could be affected by groundwater acidity. The letter also indicated that the Water and Rivers Commission would undertake groundwater testing to determine the extent of the acidity problem.
Further testing was carried out on the initial affected bore for arsenic on 14 January 2002 as this contaminant was not originally sampled and commonly occurs in groundwater in areas affected by acid sulfate soils. The results of chemical analysis indicating a high arsenic concentration were received by the Commission on 29 January 2002. This was immediately referred to DOH. This agency put out a media release about the detection of arsenic on 1 February 2002.
InvestigationsSince January 2002 a major program of investigation and testing has been undertaken. Preliminary groundwater sampling indicated that arsenic and heavy metal concentrations of possible health concern were only found where groundwater was acidic (less than pH 5.5), and therefore measurement of pH was used a screening tool to select bores that required chemical analysis for arsenic and heavy metals.
A total of 802 domestic bores were screened for pH, and 49 bores were sampled for arsenic and heavy metals. Of these bores, 22 were found to have arsenic concentrations that exceeded the Australian drinking water guideline value (7µg/L).
Between 14 and 22 February, the Commission installed 13 investigation bores to determine possible sources of acidity and arsenic contamination. The drilling indicated that the major sources of contamination were new residential developments on the Roselea and Hamilton Lake estates and excavated wetlands in public open space on Spoonbill Reserve. Drilling and groundwater sampling downgradient of peat stockpiles and excavated lakes indicated that groundwater was acidic to 3-5 metres below the watertable but that pH values returned to background values of 6 to 7 at greater depths.
Vegetable, fruit and soil samples were collected from 11 premises to determine whether crops were accumulating heavy metals and arsenic from soil. None of the plant samples exceeded the Australian food standard for arsenic, but 14 samples exceeded the standard for lead. Lead in food is unlikely to be associated with groundwater acidification but the Department of Health is continuing to investigate this issue.
Of a total of 20 peat samples taken from peat stockpiles on development sites, nine indicated that the material had a moderate to high acid generation potential, suggesting that the peat is the major source of acidity in the area.
Causes of the Acidity and Arsenic in the GroundwaterThere are several factors that have contributed to groundwater acidity in the area. These include:
Extent of Acidity at StirlingInvestigations to date show that groundwater acidity issue is restricted to 49 domestic bores immediately downgradient in the direction of groundwater flow from the Roselea and Stirling Lakes residential estates, and the Spoonbill Reserve.
Public Health and Environmental Implications - Test results discussionArsenic and heavy metal concentrations in groundwater in the area are unlikely to have a significant effect on public health as groundwater in the area is mostly used for irrigation and not for drinking. The Department of Health recommends that water from domestic bores in the metropolitan area is not used for drinking, mainly because of the risk of bacterial contamination.
Although some Water Corporation water supply bores occur in the area, these pump water from deep in the aquifer, and ongoing monitoring indicates that these are unaffected by contamination.
Immediate Corrective ActionThe 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.
History of Regulatory actionsRoselea 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. Monitoring results between December 1999 to April 2001 did not indicate adverse changes in the groundwater condition 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 indicated little variation in pH values between June 2000 and May 2001.
Departmental fax on 11 September 2000 to Welltech (Dewatering Operator) indicated that the 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.
Statutory Approvals for DevelopmentsThe assessment of new urban developments is the joint responsibility of the Department of Environmental Protection (DEP), the Environmental Protection Authority (EPA), the Western Australian Planning Commission (WAPC), and local government. The bulk of land development proposals are informally assessed by the EPA (DEP under delegation) on the basis of competent and responsible developers ensuring developments are environmentally acceptable. The system recognises the degree of management that should be done by the government agencies while not subsidising from the public purse the development industry which reaps the benefits of projects. Currently there are about 965 informal assessments per year out of 1000 proposals referred to the EPA (ie EPA formally assesses 35 proposals a year). The EPA/DEP receives about 160 subdivision referrals per year and 350 rezoning proposals. Currently urban development approvals are not referred to WRC, although this system will change as part of the formation of the Department of Environment, Water and Catchment Protection.
Future Management of Acid Sulfate Soil ExposuresThe significance of acid sulfate soils is widely understood in the literature and is relevant on the eastern seaboard. Historically, however, this issue has not been seen as critical in urban Perth. As noted above, responsibility for environmental management of urban development rests across state and local governments and developers. The Stirling groundwater acidity and arsenic contamination issue highlights the need for state planning and environmental approvals processes and the management actions of developers to better identify and respond to the potential for acid sulfate soils exposure.
Unlike many other states, Western Australia does not have a State Planning Policy that specifically addresses acid sulfate soils, and consequently there is an ongoing risk that sites with acid sulfate soils will be developed inappropriately in WA. The soil characteristics in the Stirling area are not typical of acid sulfate soils found in other states. Further research is required to properly identify the characteristics for acid forming soils in WA. Issues such as the groundwater acidity problem in Stirling could be effectively managed if WA were to develop and adopt an acid sulfate SPP modelled on Queensland and New South Wales policies. This would ensure that acid sulfate soils are considered at a very early stage in a development program before soils are disturbed and acidity problems are created. It is also recommended that Western Australia adopts and implements measures set out in the National Strategy for the Management of Coastal Acid Sulfate Soils (available at web site http://www.affa.gov.au/docs/operating_environment/armcanz/pubsinfo/ass/ass.html ).
The principal objectives of the National Strategy are:
In Western Australia, the first objective is particularly important as there is currently only a very general understanding of the distribution of acid sulfate soils within the State. Queensland and New South Wales have produced detailed acid-sulfate risk maps for coastal areas, and a similar mapping exercise in Western Australia could identify areas where inappropriate development may cause acidity problems.
In February 2002, the Water and Rivers Commission conducted a desktop study of areas with potential for acid sulfate soils (PASS) in the Perth metropolitan area. This indicative study is a first pass only to guide future detailed mapping of PASS and ASS. DEWCP will now write to each metropolitan local government authority advising them of the potential for sulfate soils presence in their areas asking that the issue be taken into consideration for any future residential developments. DEWCP will also write to the WA Planning Commission, Urban Development Institute of Australia (WA) and Association of Consulting Engineers (WA) ensuring they are aware of the issue and that it is considered as part of their deliberations.
Conclusion and RecommendationsThe acidification of groundwater in Stirling presents a considerable management challenge for the State. It is manageable, provided State and local governments and developers act on recommendations contained in this report. Until recently, acid sulfate soils have not been a significant issue in Western Australia but the episode in Stirling provides a serious wake-up call to lift the profile of the issue and our capacity to respond to it.
The following measures are recommended to ameliorate the groundwater acidity and arsenic contamination issue in Stirling:
NOTE: Recommendations 8 through 10 are unfunded and cannot be implemented with current departmental resources.