Incorporating perfluoroalkyl acids (PFAA) into a geochemical index for improved delineation of legacy landfill impacts on groundwater.

Historical, or 'legacy' landfills are commonly unlined and can therefore pose risks to human health and the environment via the discharge of leachate to sensitive groundwater and surface waters. Characterising the impacts on groundwater from legacy landfills located within urban re-development precincts is therefore of growing importance worldwide and is difficult using conventional indicators. At Australia's largest urban re-development precinct, Fishermans Bend, seven known legacy landfills exist, as well as numerous other contamination sources (e.g. historical industrial spillages). Conventional landfill leachate indicators (e.g. ammonia-N and bicarbonate) and perfluoroalkyl acids (PFAA) were measured in 36 bores to distinguish leachate-impacted groundwater from non-impacted areas. Whilst eleven bores showed clear leachate impacts based on conventional indicators, others did not show clearly identifiable leachate signals, particularly those installed near landfills thought to have accepted a larger component of non-putrescible waste (e.g. industrial, construction and/or demolition waste). A new index for detection of legacy landfill leachate impact on groundwater was therefore developed, incorporating perfluorooctanoate (PFOA) as a proportion of PFAA (PFOA/∑PFAA) into an existing method based on leachate to native cation ratios, ('L/N ratios'). Significant differences between the means of the leachate-impacted versus non-impacted bores were found using the 'modified L/N ratio' (p = .006), whereas no significant differences were found between the means of the two groups using the standard L/N ratio (p = .063). The modified L/N ratios also showed a statistically significant difference between the means of the bores impacted by municipal waste versus those impacted by non-putrescible waste (p = .003), indicating they are a much more sensitive indicator of both the existence and type of landfill leachate impact on groundwater than previously reported. This new index may prove particularly useful in complex urban areas where multiple potential contamination sources exist, and land use histories are either unknown or complicated. CAPSULE: Conventional methods for leachate detection in groundwater surrounding legacy landfills have been analysed and further developed via the inclusion of perfluoroalkyl acids, to better understand contaminant sources, fate and transport.

A method for separation of heavy metal sources in urban groundwater using multiple lines of evidence.

Determining sources of heavy metals in soils, sediments and groundwater is important for understanding their fate and transport and mitigating human and environmental exposures. Artificially imported fill, natural sediments and groundwater from 240 ha of reclaimed land at Fishermans Bend in Australia, were analysed for heavy metals and other parameters to determine the relative contributions from different possible sources. Fishermans Bend is Australia's largest urban re-development project, however, complicated land-use history, geology, and multiple contamination sources pose challenges to successful re-development. We developed a method for heavy metal source separation in groundwater using statistical categorisation of the data, analysis of soil leaching values and fill/sediment XRF profiling. The method identified two major sources of heavy metals in groundwater: 1. Point sources from local or up-gradient groundwater contaminated by industrial activities and/or legacy landfills; and 2. contaminated fill, where leaching of Cu, Mn, Pb and Zn was observed. Across the precinct, metals were most commonly sourced from a combination of these sources; however, eight locations indicated at least one metal sourced solely from fill leaching, and 23 locations indicated at least one metal sourced solely from impacted groundwater. Concentrations of heavy metals in groundwater ranged from 0.0001 to 0.003 mg/L (Cd), 0.001-0.1 mg/L (Cr), 0.001-0.2 mg/L (Cu), 0.001-0.5 mg/L (Ni), 0.001-0.01 mg/L (Pb), and 0.005-1.2 mg/L (Zn). Our method can determine the likely contribution of different metal sources to groundwater, helping inform more detailed contamination assessments and precinct-wide management and remediation strategies.