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INVESTIGATION OF SOIL AND GROUNDWATER ACIDITY, STIRLING
4.0 SAMPLING METHODOLOGY
4.1 Private Groundwater Bores
Preliminary pH screening was conducted extensively to locate the hotspots within the declared affected areas. Initially, residents registered their addresses with the City of Stirling, the WRC, or the Health Department to have their bores sampled. Officers from the WRC and/or City of Stirling individually visited each property and had the resident run their bore for two minutes. The bore water was then used to rinse the sampling bucket, prior to collecting a sample. The water pH was measured immediately using a calibrated portable pH probe.Bores recording a low pH (less than 5.5) were sampled for toxic metals. These samples were collected in polyethylene bottles provided by the laboratory and delivered to the Chemistry Centre of WA in accordance with the Chain of Custody procedures.
The laboratory analysed the groundwater samples using the methods outlined in Table 1.
| Analyte | Method of analysis |
|---|---|
| Arsenic, As | Vapour generation atomic absorption |
| Lead, Pb; Cadmium, Cd | ICPMS |
| Aluminium,Al; Barium, Ba; Boron, B; Calcium, Ca; Chromium, Cr; Cobalt, Co; Copper,Cu; Iron, Fe; Potassium,K; Magnesium, Mg; Manganese,Mn; Molybdenum, Mo; Sodium, Na; Nickel,Ni; Sulfur expressed as sulfate; Vanadium, V; Zinc, Zn | ICPAES |
| PH | Meter |
| Conductivity | Meter |
| Chloride | Segmented flow auto analyser |
Table 1 : Analytical methods used by the laboratory (water)
As the demand for bore water testing increased, residents were requested to collect their own samples in clean bottles and take them to the City of Stirling for pH screening. The City of Stirling undertook the vast majority of pH measurements within 24 hours of receiving the samples, using a calibrated portable pH probe. Residents unable to take samples to the City of Stirling were visited individually as outlined above.
In total, over 800 local bores were screened for pH during February 2002, and 49 were sampled for chemical analysis.
4.2 Groundwater monitoring - drilling program
Between 14 - 22 February, WRC officers installed thirteen investigation bores to depths between 13 - 15 metres below the ground level replicating the normal domestic bore depths in the affected areas. Figure 1 shows the location of the monitoring bores marked as SLA#1 to SLA#13. Each bore was constructed with a length of 0.4 mm slotted PVC 50mm casing, flushed at ground level, capped and distinctly marked. A centrifugal pump was used to recover the groundwater water samples for analysis. Discrete water samples were retrieved at 3 metre intervals down the soil profile. The retrieved water samples were field tested for pH and salinity using a calibrated WTW meter. Acid washed polyethylene bottles were used to collect the samples for chemical analysis, stored in an esky for up to six hours, and delivered to the Chemistry Centre of WA (CCWA) in accordance with the Change of Custody procedures.The laboratory analysed the groundwater samples using the methods outlined in Table 1.
4.3 Soil from Peat Stockpiles
Thirteen samples were retrieved from the peat stockpile on the Stirling Lakes development and seven peat stockpile samples were collected from the Roselea Gardens development on 21 February. The locations of the peat stockpiles are shown in Figure 1. The samples were collected by officers from the WRC and DEP. The samples were randomly selected, collected in glass jars, and delivered to the CCWA to determine the Net Acid Generation (NAG).At the laboratory the samples were dried to 38 - 40°C and crushed to a normal 75 µm average particle size. Homogenised sub-samples of the powdered samples were subjected to chemical tests. The pH was determined by a pH electrodes on a slurry (1 part of solid to 2 parts water, w/w) that had been allowed to maturate for 24 hours.
4.3.1 Net Acid Generation (NAG) test description
The sample was allowed to react with hydrogen peroxide (H2O2) at pH 4.5, the excess H2O2 was decomposed and the solution was allowed to cool prior to make up and determine of pH and acidity. Hydrogen peroxide has the advantage of being a neutral oxidation reagent. In its pure state H2O2 does not contribute to the alkalinity or acidity of the sample (a vital consideration for acidity titration methods).4.3.2 Gross Acid Production Potential (GAPP)
This is calculated from the total sulfur value and expressed as sulfuric acid. The test may over estimate the acid producing potential of a soil as it assumes all sulfur is present as sulfide. A corrected GAPP makes allowance for sulfur present in the less deleterious form.To determine sulfate sulfur the samples were heated with dilute hydrochloric acid to drive off any sulfur present as sulfide. The residual sulfur present in solution is assumed to be due to sulfates. The sulfur concentration was measured using inductively coupled plasma atomic emission spectroscopy (ICPAES)
4.4 Sediment and water samples from the Spoonbill Lakes
One sediment and two water samples were collected from the Spoonbill Lakes by WRC officers on 15 February 2001. The locations of these samples are shown in Figure 1.The water samples were collected in laboratory acid-washed polyethylene bottles using a sampling pole to reach beyond the shoreline. The sediment sample was collected in a glass jar from the yellow stained layer of the southern lake shoreline. The samples were stored in an esky for approximately two hours, and delivered to the CCWA in accordance with the Chain of Custody procedures.
The water samples were analysed at the laboratory using the methods described in Table 1. The sediment sample was analysed using the methods outlined in Table 2.
| Analyte | Method of analysis |
|---|---|
| Arsenic, As | Aqua Regia digest and vapour generation atomic absorption spectroscopy |
| Aluminium,Al; Barium, Ba; Boron, B; Cadmium, Cd Chromium, Cr; Cobalt, Co; Copper,Cu; Iron, Fe; Mg; Manganese,Mn; Molybdenum, Mo; Lead, Pb; Nickel,Ni; Sulfur expressed as sulfate; Vanadium, V; Zinc, Zn | Aqua Regia digest and ICPAES |
Table 2 : Analytical methods used by the laboratory (sediment)
4.5 Soil samples from Stirling properties
In February and March 2002, the City of Stirling collected six soil samples from commercial vegetable grower's properties, and four soil samples from residential properties found to have bore water with a low pH. The samples were composite samples, approximately 1 kilogram in weight, taken to a depth of 10 centimetres. They were collected in food grade plastic bags and submitted to CCWA within 5 hours of collection.The samples were analysed at the laboratory using the methods outlined in Table 3.
| Analyte | Method of analysis |
|---|---|
| Arsenic, As | Acid digest and vapour generation atomic absorption |
| Lead, Pb | Aqua regia and FAAS |
| Aluminium,Al; Barium, Ba; Boron, B; Cadmium, Cd; Chromium, Cr; Cobalt, Co; Copper,Cu; Iron, Fe; Manganese,Mn; Molybdenum, Mo; Nickel,Ni; Sulfur expressed as sulfate; Vanadium, V; Zinc, Zn | Aqua regia and ICPAES |
Table 3: Analytical methods used by the laboratory (soil)
4.6 Plant samples
In February 2002, the City of Stirling collected various fruit and vegetable samples from 11 premises, mostly commercial growers. Samples included pumpkins, tomatoes, potatoes, strawberries, sweet potatoes, eggplant, grapes, radish, onions, cabbage, zucchini, oranges, plums, lettuces, celeriac, parsley, mint and leek.The plants were initially sampled as whole plants, including roots, and were analysed by the laboratory in both washed and unwashed forms.
Fruit and vegetables were later collected without roots; approximately 2 kilograms if a large fruit, or five samples of the same fruit if small.
Samples were collected in food grade plastic bags or bags/boxes provided by the growers, and submitted to CCWA within 5 hours of collection.
The samples were analysed at the laboratory using the methods outlined in Table 4.
| Analyte | Method of analysis |
|---|---|
| Arsenic, As | Acid digest and vapour generation atomic absorption |
| Lead, Pb; Cadmium, Cd | Nitric acid / peroxide digest and ICPMS |
| Aluminium,Al; Barium, Ba; Boron, B; Chromium, Cr; Cobalt, Co; Copper,Cu; Iron, Fe; Manganese,Mn; Molybdenum, Mo; Nickel,Ni; Sulfur expressed as sulfate; Vanadium, V; Zinc, Zn | Nitric acid / peroxide digest and ICPAES |
Table 4: Analytical methods used by the laboratory (plants)
4.7 Criteria to assess public health and environmental impact
Public health and environmental risk factors are the two key components used in assessing the impact of various contaminants in the environment. The risk assessment process is a determination of the level of risk for human, fauna or flora. The level of risk is associated with specific doses of the pollutants which could result from either or both direct and indirect exposure.Health risk assessment is a process of predicting whether an adult or child is likely to suffer adverse health effects from exposure to levels of contaminants over certain periods. The precise risks cannot be quantified but the aim of the guidelines is to have a conservative approach where information may be limited, allowing for a margin of safety.
4.7.1 Water
All water analysis results were compared with the National Health and Medical Research Council Drinking Water Guidelines (1996). These guidelines apply to human health and are based on a number of factors such as a life-time's consumption of water at those levels. The application of these standards reflects the chronic contamination levels that are not likely to impact on human health, and generally provides a conservative assessment. Domestic bore owners have been advised against using their bore water for drinking purposes.The Australian and New Zealand Environment and Conservation Council Guidelines for Protection of Aquatic Ecosystems (Fresh Water) (1992) were also used to assess the water results due to the potential for the water to enter surface water bodies. The use of these guidelines is to ensure no acute and long-term impact on aquatic fauna.
In addition, the soluble chloride : soluble sulfate (Cl:SO4) ratio was used as an indicator to determine whether sulfidic material was being, or had been, oxidised. Where the analysis indicates that there is an elevated level of sulfate ions relative to the chloride ions, these results may indicate the presence of acid sulfate soils. A Cl:SO4 ratio by mass of less than 4, and certainly a ratio less than 2, is a strong indication of an extra source of sulfate from previous sulfide oxidation.2
2 Queensland Government Department of Natural Resources, 2000 - State Planning Policy 1/00 Planning and Management of Coastal Development involving Acid Sulfate Soils.. 4.7.2 Soil
Soil analysis results were compared against the Australian and New Zealand Guidelines for the Assessment and Management of Contaminated Sites (ANZECC/NHMRC) (1992) Ecological Investigation Levels. These guidelines are based on threshold levels for phytotoxicity and uptake of contaminants which may result in impairment of plant growth or reproduction or unacceptable residue levels. The use of these levels was adopted due to the potential for impact on sensitive receiving waterbodies, including the conservation category Herdsman Lake, and the Gwelup Underground Water Pollution Control Area.4.7.3 Plants
Plant analysis results were compared with the Australian and New Zealand Food Authority Food Standard Code (1998). These guidelines apply to human health and are based on a number of factors such as a life-time's consumption of food at those levels. The application of these standards ensures the food is safe to eat and people are unlikely to become ill.
