4 The Proposed Landfill Gas Standard

4.1 The proposed standard

The objective of the proposed standard is to develop a national policy that ensures that landfill greenhouse gas emissions are being effectively managed. It aims to lock in existing best practice of capturing and flaring landfill gas at all large landfills, but also aims to provide flexibility to encourage organic waste diversion.

The standard would require landfill gas collection and destruction, with the flaring of gas likely to be the most common option. Beneficial uses of methane such as electricity generation would be permissible provided the landfill owner can demonstrate equivalent or better mitigation of methane gas emissions. The following summarises features of the draft standard. Note that aspects of the standard may be subject to change.

4.1.1 Applies to operational landfills that accept municipal solid waste

The standard would not apply to sites that accept only cleanfill (soil and rubble) or construction and demolition landfill sites, which produce only minor amounts of methane.

4.1.2 Applies to landfills that are designed to accept over 1 million tonnes of refuse throughout their design life

Installing gas collection systems at landfills smaller than this threshold is not likely to be economically viable.

4.1.3 Applies to sites that are currently operating

It would not apply to existing closed landfills. It is expected that existing gas management control systems at closed landfills will continue to operate as per existing consent conditions.

4.1.4 Applies to proposed sites immediately.

Note, however, that in practice gas collection systems are generally not installed until adequate methane generation is occurring. This is dependent on the period of time the refuse has been in place and the total quantity of refuse. This varies, but is usually between 80 and 260 days after refuse placement begins for approximately 200,000 tonnes of refuse.

4.1.5 Applies after a transitional period

The standard will apply to existing operational sites after a transitional period of three years if a site does not currently have a landfill gas collection system. This provides time for the landfill owner to fund, design and install a landfill gas collection system.

4.1.6 Specifies flaring standards based on international best practice

This would include a minimum flare temperature of 750 degrees centigrade for a retention time of 0.5 seconds. Conditions would also address flame arrestors and back-flow protection devices to prevent flash-back and landfill fires, plus a flame detector with an automatic slam-shut valve and blower isolation to prevent unburnt discharges of landfill gas.

4.1.7 Specifies a methane emission limit

Gas collection efficiencies are variable and so measurements are relatively inaccurate and unreliable. It is therefore not possible for the standard to specify a percentage efficiency for a gas collection system. Measuring methane emissions at the landfill surface and at monitoring points around the landfill is currently common practice in resource consent conditions at major landfills, including many recently closed sites. The limit is commonly 1% methane (by volume in air), corresponding to approximately 25% of the lower explosive limit. We recommend that this be adopted as the draft methane emission limit during consultation, but will be guided by submissions.

After consideration of submissions, the Minister for the Environment will inform Cabinet that the surface methane emission limit will be 0.5% methane (5000 ppm).

4.1.8 Flexibility

There may be situations where a landfill exceeds the refuse quantity threshold of 1 million tonnes but through the effective diversion of organic matter, or shallow landfill cells, methane emissions are below the surface methane emission limit.

In this case effective operation of a methane collection and destruction system may not be warranted or feasible. This could occur at sites with waste quantities close to the proposed threshold, sites with a shallow depth of refuse, dry sites, or those where organic waste diversion has resulted in a reduction in methane generation.

After consideration of submissions, the Minister for the Environment will inform Cabinet that landfill sites may apply for an exemption to installing a landfill gas collection system if the site contains less than 5% biodegradable and putrescible matter.

4.2 Implementation

Within three years after the introduction of the standard, regional councils will be required to place consent conditions requiring the installation of a landfill gas collection and destruction system on any resource consent granted for landfills with a projected total capacity of over 1 million tonnes, unless the applicant can demonstrate that they will be able to limit surface methane emissions below the performance limit specified by this standard.

Regional councils will be required to review landfill gas monitoring data to ensure that landfills are complying with the surface methane emission limits.

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