Environmental considerations

Environmental and heritage considerations are a key priority for the METRONET Forrestfield-Airport Link, and as such detailed planning occurred before any works began to ensure areas of significant environmental value were identified, managed and reported on.

Environmental Management Plans with appropriate measures and controls have been implemented and were continuously monitored during construction. To find out more about the project's environmental considerations, view the environment and heritage fact sheet.

Dewatering

Dewatering was required along sections of the Forrestfield-Airport Link to allow for the construction of underground structures, such as the station boxes and tunnel portals. The process involved temporarily lowering the water table within the work area to allow soil to be excavated without it refilling with water. Once the soil was removed, a base slab was poured to seal the structures and the dewatering process ceased.

Dewatering was undertaken at High Wycombe and Bayswater as part of the dive structure works, and for the underground stations at Airport Central and Redcliffe. 

To find out more about the dewatering process, view the dewatering fact sheet. 

Fauna and flora

As the rail line is located almost entirely underground, the impact to the environment is minimal. During construction, the impact on vegetation and flora was reduced wherever possible through site layout design and construction methods.

Where clearing was required, the areas were inspected for fauna through ground searches and tree hollow inspections.

Excess fill management

Excess fill refers to the soil generated during tunnelling and station excavation works for the Forrestfield-Airport Link. The project will generate approximately one million cubic metres of excess fill during construction. 

A number of initiatives to beneficially reuse excess fill from the Forrestfield-Airport Link are being investigated.

Transfer of soil from one site to another is routinely undertaken on land development and infrastructure projects in Perth and around Australia. Reuse of excess fill represents a sustainable approach to managing a valuable natural resource.

To date, approximately 25 per cent of the project’s excess fill has been used as engineered backfill on transport projects across Perth, including within the Forrestfield-Airport Link site, within two road interchanges on the NorthLink project and at the Kenwick Rail Freight Facility.

Environmental investigations commissioned by the PTA commenced in 2015 around the Forrestfield-Airport Link project area. The investigations involved testing of soil, sediment, groundwater and surface water. The objective of these environmental investigations was to understand the quality of the soil and water and identify appropriate construction methods.

Soil testing detected a range of natural and man-made compounds in the soil that require consideration prior to reuse, including the identification of minor concentrations of PFAS.

It is important to note that the presence of PFAS in soil has not been caused by the Forrestfield-Airport Link project.

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are manufactured compounds that have been used in certain types of firefighting foams and a range of consumer products, including non-stick cookware, fabric treatments, furniture and carpet stain protection, and food packaging since the 1950s. Environmental contamination by PFAS is an emerging challenge worldwide, and in WA is starting to be reported at various sites.

There are more than 3000 types of PFAS. The best known compounds are perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA) and perfluorohexane sulfonate (PFHxS).

The PFAS levels identified in soil across the project sites, including within the soil that is stockpiled at and transported from the High Wycombe site, are not considered to pose a health risk to neighbouring properties. The soil tested to date meets the strictest health standards in the PFAS National Environmental Management Plan.

Excess fill from the project is retested prior to leaving the construction site. The soil which is being reused meets the strictest health standards in the PFAS National Environmental Management Plan.

The PFAS National Environmental Management Plan provides guidance and a nationally consistent framework for the reuse of soil which contains minor concentrations of PFAS, such as that identified in soil during construction of the Forrestfield-Airport Link.

The soil testing is undertaken in accordance with a suite of project-specific environmental management plans which have been endorsed by a Contaminated Sites Auditor accredited by the Department of Water and Environmental Regulation.