The widespread use of chlorofluorocarbons (CFCs) as refrigerants, aerosols and foam insulation gases has led to their ubiquitous presence in modern landfills. Landfill leachates may have concentrations of CFC11, CFC12 and CFC113 thousands of times higher than in uncontaminated surface and groundwaters. Such great disparity offers a means of using CFCs as tracers of environmental contamination by landfill leachate. The threshold at which diluted leachate can be detected is around 0.1–1%, compared with 10–50% for conventional indicators such as COD, Cl− or NH4+. A single, systematic survey may establish the extent and pattern of a leachate plume, whereas conventional indicators must rely on monitoring continued over many years to establish trends rising above background. This paper presents results from just such a survey conducted at a landfill site in Yorkshire, England. There were clear impacts on surface water courses and shallow groundwater, whereas an upward hydraulic gradient protected deeper groundwater beneath the site. Selective degradation of CFC11 was observed in groundwaters.