Gasworks produced ‘town gas’ for heating, lighting and cooking. Most ceased operating in the early- to mid-1900s and the last of the known gasworks was decommissioned in 1985.
Typically, gasworks were located near waterways or train lines for easy delivery of coal (the principal material used to make gas in NSW). They were often also close to the centre of the city, to minimise the size of the network of pipes used for gas distribution.
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The soil and groundwater at these former gasworks sites are invariably contaminated by materials produced during the gas-making process even though operations ceased many years ago. These sites need some level of assessment to ensure that the soil contamination is not posing a threat to human health or the environment.
Major wastes associated with former gasworks sites include tars, oils, hydrocarbon sludges, spent oxide wastes, ash and ammoniacal recovery wastes. Some of the wastes, such as tars, commonly exist in soils and in groundwater in the form of non-aqueous phase liquids (NAPLs), which are a range of contaminants that can either float on a water body or sink to the base of an aquifer. While many of these wastes and by-products were recycled or reused, it was common for some to be buried on or near the gasworks site, for instance in underground tar wells, liquor wells, pipes and purifier beds and were not removed when the gasworks were decommissioned. It is essential that the locations of these plant items are identified in the investigation stage.
Many of the principal wastes can be identified visually or by the odour they emit. For example, tar oils are easily identifiable as a black, odorous ooze and iron cyanide complexes (formed during the removal of hydrogen cyanide) are recognisable by their intense Prussian blue colour.
Provided conditions are suitable, over time, natural degradation processes can reduce concentrations of some of the ‘lighter’ chemicals, for example, phenolic compounds, volatile monocyclic aromatic hydrocarbons and some polycyclic aromatic hydrocarbons. Degradation rates for some ‘heavier’ organic compounds can be slow in many soil and groundwater environments and as a consequence these compounds may persist for many years. Heavy metals and complex cyanides do not break down and will remain in the soil unless they are leached out.
Source: Department of Environment and Conservation NSW
Information for the assessment of former gasworks sites
ISBN 1 74137 386 7 DEC 2005/237 July 2005
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