The trace volatile organic compounds (VOCs) in landfill gas were examined at seven U.K. waste disposal facilities. Over 140 compounds were identified, of which more than 90 were common to all seven sites. The groups of compounds and concentrations observed were alkanes, 302−1543 mg m-3; aromatic compounds, 94−1906 mg m-3; cycloalkanes, 80−487 mg m-3; terpenes, 35−652 mg m-3; alcohols and ketones, 2−2069 mg m-3; and halogenated compounds, 327−1239 mg m-3. The observed variations in landfill gas composition were largely attributed to differ ences in the waste composition and the stage reached in the decomposition processes at each of the sites. Three sites were found to have total chlorine concentrations, derived from the organochlorine compounds in the gas, of above 250 mg m-3. Chlorine contents of this level were considered to be potentially damaging to landfill gas fueled engines used for electricity generation. Chloroethene (>0.1−87 mg m-3) was identified as the most abundant toxic component. Chloroethene levels in the landfill gases from two of the sites studied were found in excess of the U.K. maximum exposure limit by a factor of 5 and 3. Total VOCs emissions from four of the seven sites studied were estimated to be of the order of 104 kg/yr.

A gas plume emanating from the Foxhall Landfill in Suffolk (U.K.) has been defined within unsaturated ferruginous sands on the basis of elevated concentrations of methane, carbon dioxide and volatile organic compounds (VOCs). The plume is relatively narrow, extends more than 100 m from the landfill boundary, and lies mainly between 2 m bgl (below ground level) and the water table at 9.5 m bgl. With increasing distance along the axis of the plume, the ratio of methane to carbon dioxide gradually decreases, while nitrogen increases. Oxygen appears beyond 80 m from the landfill boundary. Stable carbon and hydrogen isotope ratios in methane become heavier with distance, while carbon dioxide becomes isotopically lighter with respect to stable carbon. This provides strong evidence for microbially mediated methane oxidation. Zones of black reduced sediment near the landfill suggest that ferric iron [Fe(III)] may be acting as an electron acceptor for oxidation. No thermal anomaly was observed, thus suggesting that the rate of oxidation/flux of methane is low.Volatile organic compounds in the plume were trapped using a combination of sorbants (Tenax GR, Haysep Q and Carbosieve S-III), and desorbed thermally into a GC/MS for semi-quantitative analysis. The 79 VOCs identified were similar to those found in other landfills, and their concentrations, both in the landfill and in the soil gas, were broadly related to their volatility. Only two compounds (vinyl chloride and dichlorofluoromethane) approached or exceeded the long-term exposure limit (LTEL, as defined by the U.K. Health and Safety Executive, 1992) outside the landfill. Halogenated compounds (dichlorodifluoromethane, dichlorofluoromethane and trichlorofluoromethane) were found to be most mobile but their concentration profiles suggest that they may have been flushed out of the landfill during its early stages. It is suggested that the association of volatile halogenated compounds with methane is good evidence that they are derived from a landfill.

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