Former Bacchus Marsh Gasworks

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Bacchus Marsh Gasworks.jpg

The Project

BlueSphere was engaged on this project from 2011-2023 undertaking a complex range soil and groundwater investigations through to remedial design and implementation which has seen this former gasworks site rendered suitable for future uses. The site is currently owned by DTF and was subject to a 53X environmental audit (completion pending). The site is located adjacent to sensitive residential receptors and groundwater users.

The project has involved detailed characterisation and delineation of non-aqueous phase liquids (NAPL) and dissolved phase impacts using a variety of technologies, including sonic drilling, Membrane Interface Probe (MIP) and NAPL FLUTe liners. A thorough review of human health risks was also conducted, as well as an assessment of risks to other receptors: extractive bore users and a river. By 2015 a remediation strategy had been developed, which included innovative remedial options (e.g. chemical oxidation, surfactant mobilisation). A pilot chemical oxidation trial was conducted during 2017, and full-scale source zone remedial works using surfactants was conducted during 2019.

A commonality with this gasworks project and catchment-scale assessments is the consideration of nutrients in groundwater and surface water and understanding of interactions between these bodies of water. While gasworks sites are commonly source of gross ammonia pollution to groundwater, there are often other sources of nutrients in groundwater and surface water as a result of regional pollution.

Outcomes

The project team completed development of a robust CSM for the site, including fate and transport of key contaminants suitable for endorsement by the appointed environmental auditor under the provisions of the 53X Audit being conducted for the site.

A Remediation Action Plan was developed that led to a pilot trial of in-situ chemical oxidation (ISCO) in the contamination source zones. Full-scale implementation using Surfactant Enhanced Aquifer Remediation (SEAR) was completed during 2019 and subsequently monitored for effectiveness. The primary benefit of this remedial approach was to use a more sustainable remediation methods that require less chemicals, less pumping and lower cost to meet the remedial objectives. Treated groundwater could also be reinjected into the aquifer. The diffuse ammonia issues were managed through a careful CSM development and strong understanding of the nutrient guidance document nuances, along with post-audit monitoring and institutional controls. A validation report was completed for soil and groundwater remedial works in order to fulfill the requirements of the environmental audit.

Benefits to Client

  • Development of a robust hydrogeological and geochemical conceptual model that facilitated well targeted/value for money investigations.

  • Provision of a pragmatic and relatively cost effective remedial strategy that has been endorsed by the environmental auditor and is on track to achieve auditor and EPA approved CUTEP.

  • Incremental improvements of the site have been realised through the reduction of source zone contaminant mass. The use of an engineered non-ionic surfactant to mobilise recalcitrant chemicals has allowed for a relative short period of operation (6 months) and will be a key in the future divestment of contaminated surplus government land.