Oral Presentation NCGRT/IAH Australasian Groundwater Conference 2019

Groundwater impacts assessment and minimisation for rail trenches in a sensitive location (17)

Tony Cauchi 1
  1. GHD, Melbourne, VIC, Australia

The objective of this project was to obtain environmental approvals to remove two level crossings via ‘rail under road’ (rail trench) construction methods.  The Edithvale and Bonbeach project area is sensitive owing to a nearby Ramsar listed wetland, numerous beneficial uses of groundwater and its complex urban coastal setting.

In order to meet project timelines, a staged approach to groundwater impact assessment was required to identify and address the requirements of relevant state and commonwealth environmental approvals and relevant stakeholders. This involved:

  • Preliminary conceptual and numerical modelling – which informed an Environmental Effects Statement (EES) and EPBC Act (Environment Protection and Biodiversity Conservation Act 1999) referral to the Victorian and Commonwealth Governments respectively.
  • Site investigations – which informed the development of a regional numerical groundwater model, as well as risk and impacts assessment
  • Modelling the water environment – which focussed on the numerical groundwater model, and included a saltwater intrusion model, wetland water balance model and analytical modelling
  • Impacts assessment – which used the model predictions as a basis for assessing the relevant risks.

Data from the predictive modelling was used to assess potential impacts of the identified risks.  Preliminary modelling indicated the potential for the projects to impact Edithvale Wetlands (Ramsar site), and an EES referral was developed in response to these predictions.

Site investigations progressed in advance of the EES referral outcome, in recognition of project timeframes.  Detailed modelling indicated that based on the initial assessment, groundwater level changes (either groundwater mounding or groundwater drawdown) could occur as a result of the tanked pile walls.  Groundwater levels were predicted to increase on the up gradient (inland) side of the pile wall and decrease on the down gradient (coastal) side of the pile wall, as groundwater throughflow is impeded by the pile walls.

Because of the potential impacts identified in the initial assessment for Edithvale, modifications to the construction design were considered to minimise the impacts. Additional modelling was undertaken to assess the effectiveness of the design changes.

The assessment provided a detailed understanding of the project’s potential hydrogeological impacts.  The staged and collaborative approach adopted by the project team informed and involved relevant stakeholders and peer reviewers at each stage of the assessment. This achieved the benefit of harnessing the collective knowledge of experienced (technical and non-technical) project members, maximising multidisciplinary collaboration and achieving an outcome that informed the development of management measures within a robust Environmental Management

The objective of this project was to obtain environmental approvals to remove two level crossings via ‘rail under road’ (rail trench) construction methods.  The Edithvale and Bonbeach project area is sensitive owing to a nearby Ramsar listed wetland, numerous beneficial uses of groundwater and its complex urban coastal setting.

In order to meet project timelines, a staged approach to groundwater impact assessment was required to identify and address the requirements of relevant state and commonwealth environmental approvals and relevant stakeholders. This involved:

  • Preliminary conceptual and numerical modelling – which informed an Environmental Effects Statement (EES) and EPBC Act (Environment Protection and Biodiversity Conservation Act 1999) referral to the Victorian and Commonwealth Governments respectively.
  • Site investigations – which informed the development of a regional numerical groundwater model, as well as risk and impacts assessment
  • Modelling the water environment – which focussed on the numerical groundwater model, and included a saltwater intrusion model, wetland water balance model and analytical modelling
  • Impacts assessment – which used the model predictions as a basis for assessing the relevant risks.

Data from the predictive modelling was used to assess potential impacts of the identified risks.  Preliminary modelling indicated the potential for the projects to impact Edithvale Wetlands (Ramsar site), and an EES referral was developed in response to these predictions.

Site investigations progressed in advance of the EES referral outcome, in recognition of project timeframes.  Detailed modelling indicated that based on the initial assessment, groundwater level changes (either groundwater mounding or groundwater drawdown) could occur as a result of the tanked pile walls.  Groundwater levels were predicted to increase on the up gradient (inland) side of the pile wall and decrease on the down gradient (coastal) side of the pile wall, as groundwater throughflow is impeded by the pile walls.

Because of the potential impacts identified in the initial assessment for Edithvale, modifications to the construction design were considered to minimise the impacts. Additional modelling was undertaken to assess the effectiveness of the design changes.

The assessment provided a detailed understanding of the project’s potential hydrogeological impacts.  The staged and collaborative approach adopted by the project team informed and involved relevant stakeholders and peer reviewers at each stage of the assessment. This achieved the benefit of harnessing the collective knowledge of experienced (technical and non-technical) project members, maximising multidisciplinary collaboration and achieving an outcome that informed the development of management measures within a robust Environmental Management Framework.