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Due to the dumping of objects manufactured with dials originally made using luminous paint containing 3H, certain sites may also still show enhanced 3H levels in the exuding CH4 and/or leachates.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


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.