A unique technical insight into the use of an innovative low calorific flare and pin well system to manage landfill gas on the Garden Island Landfill, South Australia, from Aidan Marsh, who oversaw the project.
Landfill gas (LFG) has been used for electrical power production for many years. Historically, organisations have undertaken this with a primary focus on selling the electrical power generated to a state utility company and/or to increase profitability of the project via feed-in tariffs or carbon trading schemes.
However, in harvesting the low hanging fruit, a portion of the LFG is not collected. In common with other extractive industries, there is a law of diminishing returns: as the resource depletes it becomes increasingly expensive to extract.
Eventually, due to the inevitable drop in LFG flow and methane concentration, at some point extraction of LFG will stop. This can happen for several reasons, but most commonly it’s as a result of an operational decision by the site’s management team or technical difficulties associated with combusting methane at low concentration, typically less than 25 per cent by volume.
On landfills that are geographically remote or where there aren’t sufficient LFG generation rates to offset the cost of installing a gas collection system (GCS), it can be left to freely migrate laterally or vent into the atmosphere. Therefore, it is usually when a stakeholder identifies an elevated risk that a chain of events is initiated that may result in the requirement to control the LFG.
Some jurisdictions already have financial and policy drivers in place that indirectly promote the efficient collection of LFG. Regulatory change in Victoria, for example, has been prompted as a result of the migration of LFG from one particular landfill.
LFG can be extracted more efficiently by a combination of different factors, including the type of plant and infrastructure, and how it is managed.
Garden Island Landfill background
The LFG management aspect of the Garden Island Landfill Closure and Rehabilitation Project was a collaborative venture for the Western Region Waste Management Authority (WRWMA) and Renewal SA, involving contractors McMahon Services with David Lane Associates, which is part of the Pacific Environment Group.
Garden Island Landfill (the site) was first used as a waste facility by Port Adelaide Enfield Council, before its operation was transferred to the WRWMA in 1982. EPA South Australia managed the operational licence that included as part of its conditions that the 54-hectare site be rehabilitated after its closure in 2001.
The site is based in a sensitive coastal environment in Port Adelaide. It was unlined and before 2005 was uncapped. The rehabilitation program involved capping the landfill with around 1.4 million tonnes of clay and soil, while also planting hundreds of native grasses, trees and shrubs. It also included management of storm water, groundwater and LFG.
Investigations had shown that LFG was still in an active stage of generation at the site. Given the age and size of the site, this was expected to be produced beyond 2030, but no successful GCS has been installed there.
The project team monitored surface and lateral emissions of LFG. They found that both required managing to control emissions and to mitigate potential risks to human health and the environment. Methane had been recorded above 1,000 parts per million (ppm) venting through the surface at various locations around the site. Methane concentrations at over 50 per cent by volume/volume (v/v) had been consistently reported in two particular boreholes, which were close to buildings used by the general public.
WRWMA and Renewal SA opted to solve these issues through the installation and management of a shallow perimeter GCS to effectively extract and safely combust LFG using appropriate flaring technology.
Engaged by McMahon Services, Pacific Environment implemented an innovative methodology to manage LFG at the site. This included a site-specific approach to design, construction and operation of an effective system, which was designed to control LFG emissions in the areas of concern to the specified performance requirements using pin wells and low calorific flaring.
Installing the pin wells and flares
The design involved the installation of six-metre deep “pin wells” by adapted earthmoving plant. The system has been modified and developed following extensive deployment of the technique in other parts of the world.
The wells were spaced five metres apart over 100 linear metres in the areas where surface emissions were recorded. The impact wells in combination with deeper drilled extraction wells created an effective vacuum “curtain” around the site perimeter.
For the initial stage, two conventional flares that combusted methane from 25 to 40 per cent v/v were used for more than 3,000 hours to test whether the compliance targets could be met. When measured on the surface of the landfill and at the perimeter boreholes, this had been achieved.
The objective was long-term management of the landfill and, as methane concentration was reducing, a low calorific landfill flare was deployed so the system could run autonomously without the risk of repeated shutdown, as is commonplace with conventional flares on old sites. Biogas Systems Australia supplied the low calorific flare equipment.
The team successfully designed, installed and managed a combination of novel GCS, operating protocols and flaring equipment at the site within 18 months from commissioning and within the deadline of the end of August 2015. This resulted not only in the complete reduction of the “fugitive release” of LFG through the site surface in the areas of GCS, but the methane also reduced to zero at the two main compliance boreholes.
One of the main innovations was that the flare deployed could sustainably combust methane at more than 1,000 degrees Celsius and down to 12 per cent v/v methane. Its wide range meant it could extract the hard-to-reach LFG at the site’s perimeter, while its flexibility meant very little intervention was required by the operators, therefore decreasing long-term risk at the site.
The Garden Island Landfill Closure and Rehabilitation project recently won the South Australia Civil Contractors Federation Earth Award for projects between $10 and $30 million.
The flare project is also showcased on the South Australian EPA website.
Aidan Marsh works for David Lane Associates, part of the Pacific Environment Group. Aidan specialises in landfill remediation and LFG, and has been working on LFG-related projects for the past 18 years. He designed and operated the system for use in Australia. Biogas Systems Australia supplied the Lo-Cal low calorific, high temperature flare equipment installed at the Garden Island Landfill.
Aidan Marsh (right) demonstrating the programmable flare control panel to (left) Cr Oanh Nguyen and Mayor Angela Evans, City of Charles Sturt.