Portsmith Landfill was one of the largest regional waste disposal facilities in Queensland. Servicing Cairns and the surrounding area between 1985 and 2009, the landfill covers an area of 20 ha and contains 1.7 million m3 of waste material. Subject to tropical monsoon rainfall conditions and located within a protected mangrove wetland adjacent to the Great Barrier Reef Marine Park World Heritage Area, Portsmith Landfill was originally constructed without engineered liners or leachate collection systems. The $15 million Portsmith Landfill Closure Project was project managed by Cairns Regional Council (Council), designed by Golder Associates Pty Ltd (Golder) and constructed by BMD Constructions.
The Portsmith Landfill Closure Project required the innovative adoption of best practice planning, design, construction and project management methods to sustainably upgrade environmental protection measures that included:
- Increasing flood immunity to 1 in 100 year average recurrence interval rainfall events.
- Reducing stormwater seepage into the waste by 99%.
- Reducing sediment discharge into adjacent wetlands by 90%.
- Reducing greenhouse gas emissions by 80%.
Golder worked with Council to manage potentials risks associated with the surrounding environment, high rainfall and other difficult site conditions using GoldSET, Golder’s inhouse sustainability assessment (community, environment and cost) tool. The GoldSET assessment process identified a number of innovative options which included the adoption of a composite clay and geomembrane capping liner, construction of sediment basins within the landfill footprint to facilitate appropriate water treatment, use of readily available materials such as cover soils and pre-grown turf to reduce costs and increase sustainability, a staged and systematic approach to landfill gas management and the design and construction of a 300m long landfill gas barrier wall between closed and active areas of the landfill.
During construction all parties worked closely together to address unexpected site conditions and other challenges such unseasonal rainfall, limited availability of suitable clay material and the construction of the landfill gas barrier wall. The Portsmith Landfill Project was considered by Council to be a significant success, meeting its primary objectives within approved timelines and budget. The project was also recognized by the wider engineering community winning both the Environment and Sustainability Categories at the 2012 Engineers Australia Queensland Engineering Excellence Awards.