Identification, transport and treatment of adhered deleterious substances of stormwater in an urban catchment
Ng, Warren Heng Wan
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This thesis develops and presents a practical, rapid and cost effective method of assessing the most efficient strategy to limit sediment and associated contaminants from entering and impacting on Auckland’s waterways. Although sediment removal objectives have been defined by Auckland Regional Council’s stormwater quality guidelines, the deployment of treatment systems based upon current best management practice does not ensure that these objectives will be achieved. Due to the lack of established methods for the collection and analysis of stormwater related contaminants, an elaborate sampling and analytical protocol was established to validate the results obtained. The research has been undertaken as a series of studies with specific sampling methodology described in detail at the beginning of each study. Current issues and practices relating to the local stormwater industry are also reviewed. The accumulation of metal contaminants in estuarine studies is typically considered in terms of the preferential accumulation of heavy metals in the sediment fine fraction and the accumulation of these contaminants in the bulk sediment. For these data to be considered in the context of stormwater treatment, a third factor, looking at the total mass load distribution of these contaminants within the particle ranges of sediment is introduced. This thesis proposes that a substantial amount of coarser particles are making their way into our receiving environment and that attached to them are a significant proportion of the total contaminant load. Although the contaminants on coarse particles may not be bioavailable in their original state, they undergo physical changes while in transport and once deposited the chemical and biological effects on the receiving environment will ultimately be just as detrimental. A contaminant yield assessment method is developed in which the removal efficiency of every stormwater contaminant can be accessed based on a target sediment removal range. From a cost-benefit perspective, the marginal benefit of higher contaminant removal is also discussed. Finally the framework of a contaminant-based stormwater model, incorporating provenance, nature and transport is developed to access the true nature of stormwater contamination discharged to the receiving environment. The model will generate generic particle and contaminant distributions, which may be used by policy makers to predict treatment efficiencies based on target sediment removal objectives.