Forbes Hill Landfill Sites

Burning and wildlife at the tip

Rubbish had previously been burnt at the Forbes Hill tip to reduce its volume. The 1985 plan states that this practice had stopped following a number of fires and to bring the operation into line with Health Department policy for metropolitan tips.

 

Ending the burning reduced the risk of further fires and smoke pollution. However, it also meant that rubbish occupied more space and left more material available for animals to scavenge.

 

Although rubbish was covered with sand each day, several hours could pass between unloading and covering. During this period, wildlife could feed on the exposed waste.

 

The plan’s appendices describe the tip as unfenced and supporting substantial resident populations of quokkas, feral cats, silver gulls and ravens.

 

Wildlife and disease concerns

The exposed rubbish provided an additional food source for wildlife. The appendices raised concerns that this encouraged unusually large concentrations of animals and allowed quokka and silver gull populations to increase.

 

Bringing different species together around rubbish also created opportunities for infections to pass between them. The report specifically discussed exposure to Salmonella, a group of bacteria that can cause illness in people and animals.

 

However, its findings were not straightforward. Salmonella infection rates monitored in quokkas at the tip had consistently been lower than those recorded in quokkas without access to supplementary food. The report therefore did not establish that feeding at the tip resulted in higher infection rates among quokkas.

 

Regular inspections and control of rodents and feral cats were recommended, together with a review of the tip’s location, security and operating procedures.

 

Options for future waste disposal

Paper and cardboard were estimated to make up seventy per cent of Rottnest Island’s rubbish in 1985, compared with approximately twenty-two to thirty per cent in mainland Perth. The plan attributed part of this difference to the small amount of garden waste generated on the island.

 

With the tip approaching its estimated capacity, the plan considered several alternatives. These included compressing rubbish into bales, mechanically breaking it into smaller pieces, transporting it to the mainland and incineration.

 

One option discussed was a pyrolytic incinerator. This type of equipment uses heat to break down waste under restricted oxygen conditions, with gases subsequently burnt in a secondary chamber. The plan considered it potentially suitable because of the high proportion of paper and cardboard in the island’s rubbish.

 

The proposed benefits included a substantial reduction in waste volume and the possibility of recovering energy. Disadvantages included installation costs and the need to separate materials such as bottles and cans.

 

Landfill cells from 1992

The 2003-2008 Rottnest Island Management Plan records a later arrangement of separate landfill cells at Forbes Hill. A cell is an excavated section of a landfill that is filled with rubbish before being closed and covered.

 

The Authority originally had approval to excavate four cells. The first was cut in 1992 and capped in 1996. Capping involves placing a final covering over the filled cell.

 

The second cell was excavated in 1996 and remained in use when the plan was prepared. By 2002, it was approximately sixty-five per cent full.

 

Neither of these cells had been lined. A landfill liner forms a barrier intended to limit the movement of contaminated liquid into the surrounding ground. The plan states that leachate from the first two cells had instead been absorbed into the island’s underlying ground. Leachate is liquid that drains through rubbish and can carry dissolved substances from the waste.

 

The Department of Environmental Protection required any third cell to be lined. The option of developing a fourth cell had been removed.

 

Waste reduction and environmental monitoring

By the preparation of the 2003-2008 management plan, the Forbes Hill landfill operated under Department of Environmental Protection licence conditions and the island’s Waste Management Plan.

 

The Authority had changed its waste-management practices to extend the life of the second cell and commissioned a consultant to investigate future disposal options.

 

The plan identified limits to how much rubbish could continue to be treated and buried on Rottnest. Available land was restricted, and further disposal had to be considered alongside the island’s environmental values and its use for holidays and recreation. Highly packaged products consumed by visitors added to the waste burden.

 

Recycling, reuse and reducing the amount of rubbish generated were identified as necessary parts of future waste management.

 

Woodland restoration

During 2002-2003, implementation of the Woodland Restoration Strategic Plan linked vegetation corridors around Forbes Hill, with financial support from the Rottnest Island Foundation.

 

The annual report records this as woodland restoration around the hill. It does not specify that the work involved rehabilitating the landfill cells.

 

Sources

• Rottnest Island Management Plan - Volume 1: The Plan, August 1985, waste-disposal sections.

• Rottnest Island Management Plan - Volume 2: Appendices, August 1985, tip-site discussion.

• Rottnest Island Management Plan 2003-2008, section 10.4.2.

• Rottnest Island Authority Annual Report for the Year Ended 30 June 2003.