An initial Phase 1 acid sulfate soil investigation of the Hart Lagoon (12006) wetland during March 2010 showed acid sulfate soils to be a priority concern within this wetland complex. Based on Phase 1 recommendations, a Phase 2 investigation was undertaken for the Hart Lagoon (12006) wetland to determine the nature, severity and the specific risks associated with acid sulfate soil materials. The 24 hour reactive metals tests were undertaken to determine those metals and metalloids extractable with a moderately strong acid i.e. potentially available from binding sites on soil minerals such as iron (Fe), manganese (Mn) and aluminium (Al) oxides. Although comparisons can be made with soil and sediment quality guidelines, these are defined for total concentrations and not partial extractions. The results showed that concentrations were generally below the sediment quality guidelines (SQG) and soil ecological investigation levels (EIL) for those elements where guidelines are available. The exception was manganese which breached the soil ecological investigation level (EIL) in one sample. Although most metals and metalloids did not breach sediment quality guidelines and soil ecological investigation level trigger values, the concentrations of some elements were high enough that they may impact water quality if mobilised, particularly for aluminium (Al), and iron (Fe) and manganese (Mn). The contaminant and metalloid dynamics tests were undertaken to assess the release of metals during a water extraction, and to assess dynamics in response to saturation over time by incubating soil materials for periods of 1, 7, 14 and 35 days. The degree to which metal and metalloid concentrations exceed ANZECC/ARMCANZ guideline values was used to characterise the degree of hazard. For Hart Lagoon (12006), vanadium (V) was assigned a moderate hazard with concentrations exceeding ANZECC/ARMCANZ environmental protection guidelines by more than 10 times. Arsenic (As) and manganese (Mn) were above the guideline values. The Hart Lagoon (12006) wetland has been classified as medium conservation status by the SA Murray-Darling Basin Natural Resources Management Board (Miles et al. 2010). The main hazards considered in this study that may impact on wetland values are acidification, contaminant mobilisation and deoxygenation. The wetland has been allocated a low risk rating due to acidification and a medium contaminant risk rating for soils. For surface waters, the risk is largely dependent on surface and sub-surface hydrology and is thus scenario dependent. Taking into account the range of likely scenarios, from very low flows (highest risk) to very high flows (lowest risk), the risk to surface waters in the wetland has been allocated low risk rating for acidification and medium risk rating for contaminant mobilisation. Acidification is likely to occur only locally in sub-surface soils as there is very high alkalinity within most soils which is likely to neutralise acid flux over a larger scale.The highest risk for metals and metalloids is related to the metalloid oxyanions arsenic (As) and vanadium (V). This risk may increase as Eh was also decreasing, which may lead the reductive dissolution of iron (Fe) and manganese (Mn) oxides/oxyhydroxides and any associated adsorbed metals and metalloids. A monosulfide formation potential test was not undertaken for Hart Lagoon (12006) wetland samples as monosulfides were identified during an earlier Phase 1 survey (Grealish et al. 2010). The risk associated with deoxygenation was determined as medium, due to relatively high levels of acid volatile sulfide. In designing a management strategy for dealing with acid sulfate soils in Hart Lagoon (12006) wetland, other values and uses of the wetland need to be taken into account to ensure that any intervention is compatible with other management plans and objectives for the wetland. The wetland soils studied were largely dry at the time of sampling,
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