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