The distribution of reaction sites on iron particles exposed to water containing carbon tetrachloride hasbeen examined by measuring the locations of reaction products. The uniformity or localization of reactionsites has implications for understanding and modeling the reduction of environmental contaminants byiron in groundwater systems. Granular iron surfaces similar to those being used for environmentalremediation applications were studied using surface analysis techniques to develop an understanding ofthe physical and chemical structure of the surface and oxide films. Scanning Auger microscopy and imagingtime-of-flight secondary ion mass spectroscopy revealed that granular iron exposed to carbon tetrachloridesaturated water exhibits chloride-enriched regions with a high degree of localization. These results indicatethat significant CCl4 reduction occurred at pits rather than on the passive oxide film on the metal.