// Landfill

By David Ife

ALTHOUGH there have been major advances in alternative waste treatment across Australia, landfill remains the most utilised form of waste disposal.

In Measures of Australia’ s Progress, 2010( ABS, 2013), in 2007, out of a total of 44 million tonnes of waste generated, 21 million were disposed in landfill, comprising 60 % municipal waste, 44 % commercial and industrial waste, and 42 % construction and demolition waste.

Previously, landfills were not much more than waste dumps, with little engineering and no controls on fugitive emissions of leachate, landfill gas and odour. It is no surprise that former sites now represent significant environmental risks for previous operators, predominantly local government.

New standards for landfill design have been adopted across Australia. In Victoria, the Best Practice Environmental Management Guidelines Siting, Design, Operation and Rehabilitation of Landfills( BPEM) provide standards for new landfill development.

AECOM( formerly URS) was engaged by the Greater Shepparton City Council in March 2015, under management by Attero Projects, to prepare the concept design and supporting documentation for an EPA works approval application for the development of a proposed extension of the existing Cosgrove 2 landfill.

At the start of the project, it was recognised that the design objectives and the operational and management rules as well as the post-closure requirements for the facility must fall under the framework of the BPEM.

The site

The proposed landfill extension was to be located within a former basalt quarry, adjacent to the existing Cosgrove 2 landfill but in a separate

The proposed landfill extension was to be located within a former basalt quarry.( Credit: AECOM)

quarry void with steep sides up to 15 metres high. The project presented many challenges, including a very tight timeframe, mandatory design and siting constraints, and a rapid turnaround for regulatory approval to fit with the looming closure of the adjacent facility.

BPEM Requirements

At the outset, it was recognised that regulatory approval of the works approval was conditional on the proposed design meeting BPEM requirements, and the technical and planning constraints that the site offered. To meet BPEM requirements, the application had to demonstrate that there was a need for the proposed facility and that it was recognised in the regional waste management plan.

The Greater Shepparton City Council currently utilises the existing Cosgrove 2 landfill but with limited airspace available, the development of a new facility in the adjacent quarry void was acknowledged as a priority. Council identified the need to continue to own and operate its own landfill facility in the Cosgrove Landfills Precinct in the early 2000s, well before Cosgrove 2 had reached capacity. This decision was communicated to

The site plan.( Credit: AECOM)

the community through the Council Waste Management Strategy 2005- 2015 and subsequently in the Greater Shepparton Waste and Resource Recovery Management Strategy 2013 – 2023. The total population to be served was 62,000, and allowing for a waste density of 0.8 t / m 3 and cover and capping requirements, the annual airspace consumption was estimated to be 60,000 m 3 / year.

The current quarry walls are steep and geotechnical analysis was necessary to show that side liners could be constructed as stable landforms that would maintain the long-term integrity of the landfill cap and liner system. The site itself is underlain by nonpotable groundwater but analysis of hydrographs was necessary to establish a level for the lowest point of the liner system( the base of the leachate sump) to conform to the criterion of a minimum separation distance of 2m between the waste and the water table. Although the site is more than 100m from Congupna Creek and is not located on flood prone land, a surface water drainage plan was necessary to demonstrate that runoff would be diverted around the quarry void without surcharging the leachate collection system. Preliminary monitoring and management plans were developed for progressive rehabilitation and to manage risks of fugitive emissions of leachate, landfill gas and odour as well as amenity issues of noise and dust.

BPEM is prescriptive in terms of landfill design objectives, and the Works Approval application included conceptual site design to meet the design elements, as listed in Table 1.

The BPEM provides guidance for preparation of technical material to support landfill developments. It encompasses best practice design, operation and management imperatives for Victoria and adherence in the supporting technical documents to BPEM meant that the proposed development was well-received by the community and the relevant authorities and, as a result, the EPA Victoria expeditiously issued the works approval with no objections.

David Ife is the technical practice lead for landfill and waste for AECOM Australia and he and his team have been involved in the siting, design, monitoring, and reporting of landfills around Australia for more than 20 years. Contact: 03 9653 1234 / 0418 172 847 or david. ife @ aecom. com iw

TABLE 1: MEETING THE DESIGN ELEMENTS

Design Element BPEM Design Objective Design Groundwater Minimum separation of waste from water table 2m between base of leachate sump and long term standing water table

Leachate collection system

Side wall stability

• Able to drain leachate sufficiently that the leachate head above the liner is minimised to 0.3m

• Resistant to chemical attack and clogging

• Able to withstand weight of waste and compaction equipment

• Able to be inspected and cleaned when required

Landfill should be constructed in areas where the landform is stable, thereby enabling the long-term integrity of the landfill cap and liner system

Aggregate leachate collection system comprising leachate collection pipes, leachate aggregate, leachate sump and sump risers.

Quarry sidewalls will be regraded to a stable slope for construction, supported by slope modelling.

Weekly news updates at www. BEN-global. com / waste AUGUST 2016 INSIDEWASTE 25