Reduction of chlorinated ethenes with iron metal was studied in pilot-plant tests. The test showed a sufficient ability of the iron material to reduce a mixture of tetrachloroethene and trichloroethene. The reactions were well approximated by the first-order kinetics. The rate constants per surface area were 0.22 ± 0.11 and 0.44 ± 0.09 mL m⁻² L⁻¹, respectively. Significant changes of Ca, total Fe, HCO₃⁻, and NO₃⁻ concentrations were found in the reaction zone. Speciation calculations indicated aragonite and siderite as possible precipitating minerals. The change in HCO₃⁻ concentration in the reaction zone was gradual and could be approximated by zeroth-order reaction kinetics with the rate constant value 0.096 mol L⁻¹ h⁻¹. The surface precipitate may influence the operating life of a permeable reactive barrier as a consequence of permeability decrease and coating of iron.