Environmental and heritage considerations are a key priority for the Forrestfield-Airport Link.
Studies undertaken by specialist consultants during the planning phase of the project have identified the following factors that require consideration:
- Limiting the removal of native vegetation
- Limiting any loss of fauna habitat
- Managing disturbance of acid sulphate soils
- Dewatering and groundwater quality
- Managing existing soil and groundwater contamination
- Managing noise and vibration
- Preserving Aboriginal heritage
- Managing waste.
The need to avoid areas of environmental and heritage value was incorporated into the concept design. Ongoing planning will seek to further reduce impacts to such areas.
The trains will travel under the Swan River in twin-bored tunnels. Construction of the tunnels did not impact the river because the tunnelling process did not disturb the bed of the river or alter flows within the river. The PTA continues to consult with the Department of Parks and Wildlife (Swan River Trust) and will manage any potential impacts from non-tunnelled sections under the Swan and Canning River Management Act 2006.
Noise and Vibration
During construction, which started in 2016, the PTA will manage work in accordance with a project-specific Construction Noise and Vibration Management Plan and the Environmental Protection (Noise) Regulations 199.
Once the rail link is operational in late 2021, it is expected that there will be minimal impact from noise or vibration on surrounding areas due to the railway running primarily in tunnels. Design features, such as the use of noise barriers near surface rail, will be incorporated into the design to minimise potential impacts. A monitoring and complaints procedure will also be implemented once the rail line is operational.
Acid Sulphate Soils
Most of the material excavated to construct the tunnels is likely to be acid sulphate soil. Acid sulphate soils are naturally occurring soils that are benign in an undisturbed state. If not managed appropriately, though, disturbance of acid sulphate soils can result in the release of sulphuric acid and heavy metals, which have the potential to pollute groundwater, watercourses and wetlands.
A site investigation was undertaken to allow the PTA to assess risks associated with construction and operation of the rail line and to develop appropriate management and mitigation measures to protect the community and the environment.
All work is undertaken in accordance with the Department of Environment Regulation (DER) Contaminated Sites guidelines. Further, a DER approved contaminated sites auditor has been appointed by the PTA to independently audit the investigations. Consultation has been, and will continue to be, undertaken with the DER’s Contaminated Sites Branch and the Department of Health.
Temporary lowering of the groundwater table was required to construct the underground structures. Dewatering activities have the potential to mobilise existing groundwater contamination and cause a decline in vegetation and wetland health and function. Importantly, no dewatering was required to construct the tunnels.
A Dewatering Management Plan was prepared to ensure no adverse impacts to the surrounding environment resulted from the dewatering activities. An extensive groundwater-monitoring program was implemented prior to, during and following completion of construction.
Construction of the Forrestfield-Airport Link will require clearing of small patches of native vegetation. Clearing of these areas was managed in accordance with the requirements of the Environment Protection and Biodiversity Conservation Act 1999 and the Environmental Protection Act 1986. Where significant impacts were predicted, environmental offsets were provided by the PTA.