INVESTIGATION OF SOIL AND GROUNDWATER ACIDITY, STIRLING
3.0 RESPONSE TO WATER QUALITY PROBLEMS IN STIRLING
3.1 Initial assessmentThe City of Stirling invited Dr Steve Appleyard from the Land and Water Quality Branch to a meeting and site visit on 7 January 2002 to further discuss the issue. During the site visit, it became apparent that the acidity problem was likely to be widespread in the area, as in addition to the affected bore, there were open excavations in the area containing acidic water. An excavated soil profile in the area showed the typical yellow mottles of the mineral jarosite that indicated acid sulfate soils, and peat stockpiles on new residential development areas also showed evidence of acid generation. The lakes in Spoonbill Reserve with playground facilities were also found to be acidic. City of Stirling officers have since indicated that they had been monitoring the acidity of water in these lakes, and had been aware of low pH problems, since at least 1995.
The Water and Rivers Commission contacted the Department of Health (DOH) immediately after the site inspection in Stirling, and an emergency meeting was convened on the 9 January 2002 with City of Stirling officers, the Mayor, proponents of the Roselea residential development, DOH, DEP and the WRC officers. The purpose of the meeting was to address the potential health threats caused by the acidic water. Prior to the meeting, officers from the WRC and the City of Stirling undertook a rapid pH assessment of surface water bodies and council reticulation bores to determine the extent of the area affected by the acidity. This assessment indicated that surface water acidity occurred on Roselea Estate and in the council lakes at Spoonbill Reserve.
The major outcomes of the meeting were:
Following the 7 January 2002 meeting more domestic bores in various pH ranges were tested for arsenic and heavy metals to determine whether these contaminants were present at significant concentrations, and to determine whether there was a relationship between arsenic concentrations and water pH.
Sampling indicated that arsenic was present in all the sampled bores, but not at concentrations of health significance above a pH of 5.5. A small proportion of groundwater samples with a pH of less than 5.5 contained arsenic at concentrations of health concern. Consequently, measurement pH was used as screening tool to select bores that would require chemical analysis for arsenic and heavy metals. High concentrations of arsenic (800 µg/L ) about 114 times above the NHMRC, 1996 guidelines for drinking water, was detected in a bore located immediately adjacent to Roselea Garden on the 29 January 2002. The DOH was immediately notified, and DOH put out a media release on 1 February 2002 indicating the presence of arsenic in some bores. The issue received extensive coverage on television, on radio, and in the press (see Attachment 4).
3.2 Assessment of private boresInitially, more than 60 domestic and Council bores were tested for pH, but this was increased to about 802 bores following media interest in the discovery of high concentrations of arsenic found in six domestic bores. Testing of pH was carried out both by the WRC and the Stirling City Council. Due to the large demand for pH assessment, residents were referred to the City of Stirling for an initial pH test. Where pH was greater than 5.5, no further sampling was required, but bores with a pH at or less than 5.5 were sampled for metal analysis. Of the 802 domestic bores assessed for pH, 49 were sampled for chemical analysis.
3.3 Assessment of water supply production boresStirling is situated within the Gwelup Underground Water Pollution Control Area (UWPCA), and the Water Corporation pumps water from several production bores for public water supply in the area. Immediately after the detection of acidic conditions in domestic bores, the Water Corporation were warned about the risk of water supplies being contaminated. These bores are routinely monitored for a wide range of chemicals, and the water treatment plant at Gwelup would remove any arsenic present in groundwater. However, the Water Corporation conducted additional testing for arsenic on each of the bores on 9 January. The results of these investigations indicated that two production bores were affected by slightly elevated of arsenic contamination and pH was in the neutral range. The DOH is currently investigating this issue.
3.4 Public Information SessionThe Water and Rivers Commission and the Health Department held a public information session between 3:00pm and 9:00pm at the Tuscani Club, 100 Jones Street, Sterling, on 28 February 2002. All local residents who had contacted the relevant authorities and had had their groundwater bores tested were invited to attend via letter.
The information display included maps of areas of impacted bores, descriptions of acid sulfate soil issues and health information. Copies of a 'Frequently Asked Questions' Information Sheet were also available (see Attachment 5). Representatives from WRC and DOH were available to answer questions. The session was well attended with a steady flow of residents throughout the afternoon and evening.
The main issues arising from the session were as follows;
3.5 Preliminary mapping of Potential Acid Sulfate SoilsIn 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 in the State. Its present form cannot be used as a prescriptive guide for management decisions without considering other factors such as groundwater fluctuations and soils.
However 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 ASS issue and that it is considered as part of their deliberations.
The State should support the National Coastal Mapping project for ASS proposed by the National Coastal Acid Sulfate Soil Committee (NatCASS).
3.6 Other actionsIn addition to the above, the following actions were undertaken:
These actions are detailed in subsequent sections of this report.