Sydney Gateway Permanent Leachate Treatment Plant

The Sydney Gateway project will provide a high-capacity link from the airport precinct, Port Botany, and the surrounding road network to the newly opened St Peters Interchange. John Holland Seymour Whyte (JHSW) engaged SciDev to undertake the design and construction of the permanent leachate treatment plant (LTP) designed to accept and treat leachate generated and extracted from the closed Tempe Landfill both during, and post construction of the Sydney Gateway Project.

The former Tempe Tip site was used for municipal waste landfill between 1910 and 1990. Reported contaminants of concern include landfill gases, heavy metals, nutrients, petroleum hydrocarbons, polycyclic aromatic hydrocarbons (PAH), phenols, pesticides, volatile organic compounds VOCs, ammonia, polychlorinated biphenyls (PCBs) and asbestos. The site was declared a remediation site in July 2000 due to heavy leachate run-off into the Alexandria canal. In 1990, an LPG fuel tank explosion occurred at the former Boral gas plant adjacent to the airport site resulting in highly elevated concentrations of PAH and heavy fraction petroleum hydrocarbons. High Concentrations of PFAS were detected at the site where PFAS firefighting foams had been used.

A major design consideration for the leachate treatment plant construction was to alleviate the potential for plant downtime in the event of required servicing and maintenance. Duplication of critical equipment in a duty/ standby formation and redundancy controls were implemented to ensure that treatment objectives are maintained across the operational life of the plant.

Summary

• The LTP has a nominal treatment capacity of 200 KL per day and 350 KL with hydraulic blending. The LTP can manage ammonia loading concentrations with an upper limit of 450 mg/l.
• In periods of heavy rainfall, the plant can autonomously increase its treatment capacity to the maximum design capacity. This is achieved using an advanced blending function.
• All treated leachate is discharged to trade waste under a valid Trade Waste Agreement from Sydney Water.
• Commission the LTP, including hydraulic and communications connection to the existing Tempe Leachate Collection System.
• Use of metrics and leachate riser level reporting and analysis to ensure targeted dewatering objectives are met before extensive earthworks commence.
• Upgrade and integrate the existing leachate riser system to meet increased extraction and conveyance demand during the project’s construction phase.