Landfill Gas Isotopic Characterisation

Brief Overview Of The Theory

Modern waste tips which contain organic rubbish will carry the ¹⁴C levels appropriate to the time the material was living. If the composition of the rubbish is largely current, 'modern' organic material, e.g. garden waste, then these levels transmit directly to the ¹⁴CH₄ formed by their decomposition.

CH₄ which originates from sources of geological age e.g. coal measures or oil products do not contain ¹⁴C. There is, in this case, a clearly measurable difference between CH₄ originating from decomposition of matter in the waste tip (~100% 'modern') and CH₄ from coal measures or oil products (0% 'modern').

¹⁴C values between 0% and 100% 'modern' levels are more difficult to interpret, these possibly arising from mixtures of ancient and modern sources or, directly from older peat deposits. Often this can be resolved from knowledge of the site and its environs, and, in the case of a nearby peat deposit, a measurement of the peat age may help.

Due to the dumping of objects manufactured with dials originally made using luminous paint containing ³H, certain sites may also still show enhanced ³H levels in the exuding CH₄ and/or leachates.

A measurement of the stable isotopes ¹³C/¹²C (as δ¹³C) is included routinely with the ¹⁴C in methane measurement. Measurement of the tritium in the water content of the landfill gas or of the water formed in the combustion of the methane is offered as a possible option.

What The Measurement Process Involves

Process involves a number of steps:

1. Collection of an adequate quantity of gas in a suitable transportable container.
2. Separation of the relevant gas species, CO₂ or CH₄ (or both) plus ³H as water from CH₄ combustion.
3. Conversion of the methane sample to pure carbon dioxide (CO₂) and water.
4. Determination of the δ¹³C/¹²C ratio of the CO₂ in the relevant CO₂ samples produced.
5. Conversion of the CO₂ samples to C₆H₆ for liquid scintillation counting or dispatch of a purified CO₂ aliquot to an AMS laboratory for ¹⁴C determination.

Points To Consider

How Much Sample Is Required

In whatever form, the collected gas sample should be capable of yielding a minimum of approximately 1g of carbon for the liquid scintillation counting method, or 5mg carbon for the AMS procedure.

How You Will Receive Your Results

• Samples are normally processed between 6 to 8 weeks from the sample being taken or received by us.
• A report will be complied giving results for every batch of samples received, together with notes to help with their interpretation

Confidentiality

No results will be disclosed to a third party unless we are instructed by you to do so.

Further Details

For further details download our landfill document here (PDF Format, 164kb). Please contact us first to discuss your sampling requirements before collecting or submitting samples.