Abstract

Analysis of stable and radiogenic isotopes of carbon and hydrogen in methane provides an effective method for identifying landfill gas. Determination of the stable-carbon isotopic composition (¹³C/¹²C) and the stable-hydrogen isotopic composition (²H/¹H) generally makes it possible to distinguish methane formed in landfills from natural gas, coalbed gas, and glacial-drift gas. In cases where stable isotope analysis is not definitive, analysis of the radiogenic isotopes, radiocarbon (¹⁴C), and tritium (³H) generally is definitive. Methane formed from the microbial decomposition of recent organic materials such as wood, paper, yard waste, and food scraps contains elevated ¹⁴C concentrations that reflect the above-normal ¹⁴C concentration of atmospheric carbon dioxide during the past 35 years caused by the above-ground testing of nuclear devices in the 1950s and 1960s. Methane from marshes and swamps that have been in existence for thousands of years typically has lower ¹⁴C concentrations due to radioactive decay. Methane formed along with coal or petroleum contains no ¹⁴C. Tritium analysis of methane provides a potential method for differentiating landfill gas from swamp gas and may also allow distinguishing landfill gas from sewer gas. The methane in landfill gas frequently has elevated tritium concentrations believed to be from tritiated luminous paints used on items disposed in municipal landfills.