Nanoscale zerovalent iron (NZVI) is a potentially attractive tool for in situ source zone remediation of chlorinated solvents. Microscale zerovalent iron (MZVI) is already widely used as a reactive media within permeable reactive barriers (PRBs) for treating plumes of chlorinated organics (e.g. trichloroethylene) in groundwater. Several types of NZVI and MZVI are commercially available, each made by different processes, having different surface properties, and therefore likely to perform differently as remedial agents. Treatability studies are conducted at sites proposed for treatment to ensure the suitability of a specific type of NZVI for that site's geochemical conditions. This laboratory study determined the rates of trichloroethylene (TCE) degradation, propensity to form chlorinated intermediates, the mass of TCE degraded per mass of ZVI added, and the effect of ZVI addition on the site geochemistry for five commercially available NZVI products and two MZVI products. The groundwater and aquifer materials used in this study were from a former naval air base in a marine location in California where ZVI products are proposed as remedial agents. The TCE dechlorination rates for the NZVI products were all faster than their MZVI counterparts. TCE half-life times ranged from as little as 1.2 hours to as high as 89 hours for NZVI (2 g/L), and ranged from 200 hrs to 2000 hrs using MZVI (2 g/L). The reactive lifetimes of NZVI ranged from 3 days to more than 60 days. Generally, the fastest reacting material had the shortest reactive lifetime. Acetylene, ethene, and ethane were the dominant reaction products, but chlorinated intermediates persisted in reactors where NZVI had fully reacted, accounting for as much as 5 mol% of the TCE degraded in one case, but typically less than 1-2 mol%. The ratios of mass of TCE reduced to mass of iron added at the end of the NZVI particle reactive lifetime ranged from as much as 1:17 to as little as 1:120. The addition of NZVI or MZVI increased the pH from 7.3 to 7.8, but the high alkalinity of the site groundwater limited the pH increase. Differences in the TCE dechlorination rates and reactive life times between NZVI products were attributed to differences in their compositions (catalyzed vs. bare particles) and surface modifiers (polymeric modified vs. bare particles). Unfavorable geochemical conditions (high DO, neutral to acidic pH, and a high nitrate concentration) contributed to the relatively short reactive life times and low TCE dechlorination rates using NZVI products. Two NZVI products and two MZVI products were recommended as the most promising for application at this site.