Year

2012

Degree Name

Bachelor of Environmental Science (Honours)

ANZSRC / FoR Code

050205 Environmental Management

Department

School of Earth & Environmental Science

Advisor(s)

Brian Jones

Abstract

Acid Sulfate Soils are a major environmental issue for NSW coastal regions. Many problems have arisen due to the installation of flood mitigation drains in prime agricultural areas, assisting the exposure and oxidation of sulfidic materials. As a result of this, options for management of drains and surrounding areas have become a leading area of research. Focus has been on not only identification and mapping, but remediation of affected areas. Many options such as the use of weirs, floodgates and permeable barriers have been described in the literature, however significantly less research has been invested into treatment of material once it is removed from flood drains or channels during management and routine maintenance activities. In order to aim for consistency across the country there are now a number of guidelines that have been made available by the Acid Sulfate Soils Management Advisory Committee (ASSMAC) that target the management of Acid Sulfate Soils.

The ability to predict the liming requirement for acidic dredge material in project areas of the Shoalhaven River estuary floodplain was investigated to facilitate the treatment and management of sediment removed from flood mitigation drains as a result of maintenance activities. The “Routine maintenance of flood mitigation drainage structures Review of Environmental Factors” document produced by the Shoalhaven City Council in 2011 has provided the basis upon which to conduct this study. Previous work and landholder experiences have come to show that a simplified method for treating acidic dredge material dumped along the sides of drains is required in order to neutralise the material which, left untreated, has significant impacts on the surrounding environment following oxidation and acidification. Three different methods were used to calculate the weight of lime necessary for neutralisation of every unit of material removed from drains in each of the separate project areas of the Shoalhaven River estuary. 65 samples were collected from a range of 17 drains. X-ray diffraction was used to detect levels of pyrite and the subsequent level of acid produced from its oxidation, while X-ray fluorescence was used to detect trace levels of sulfur, and the potential amount of pyrite that could be produced from those amounts. A third method involved testing field pH following hydrogen peroxide initiated oxidation and calculation of lime that would be required based on values provided in a ‘Look-up table’. The maximum lime requirements calculated from each different method were graphed against each other to analyse correlation of values. Values calculated from XRF and XRD data analysis showed the greatest level of correlation when graphed against each other. Drain P2G1 has been identified as the drain with the highest recorded sulfur and pyrite concentrations, as well as zinc concentration, indicative of its ability to produce acid concentrations beyond that of any other drain sampled. The significance of this drain being a naturally formed entity rather than an artificial construction component of the flood mitigation scheme is discussed as well as the characteristics of all project areas that have given rise to differing levels of lime and overall management required. These results give information to those responsible for maintenance of the drains about which areas are of highest concern and the monitoring that needs to be implemented to ensure success of neutralisation efforts.

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